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PROVISIONAL DATA--SUBJECT TO REVISION

Quality of Pesticide Data for Environmental Water Samples Collected for the National Water-Quality Assessment Program, 1992-96 and Examples of the Use of Quality-Control Information in Water-Quality Assessments

Jeffrey D. Martin
jdmartin@usgs.gov

October 27, 1999


INTRODUCTION
Acknowledgments
Disclaimer
FIELD AND LABORATORY QUALITY-CONTROL DATA
CONTAMINATION
Contamination and the Frequency of Detection
Contamination and the Magnitude of Concentrations
FALSE NEGATIVE DETECTIONS
BIAS AND VARIABILITY IN CONCENTRATIONS
SUMMARY
REFERENCES
FIGURES
Figure 1. Histogram of recovery of azinphos-methyl in 304 field matrix spikes
Figure 2. Histogram of recovery of azinphos-methyl in 998 laboratory control spikes
TABLES
Table 1. Contamination in field blanks
Table 2. False negative detections of pesticides
Table 3. Bias and variability of recovery of pesticides
Table 4. Uncertainty in selected measures of bias and variability of recovery of pesticides


INTRODUCTION

Water-quality assessments for pesticides are complicated by a variety of sources of uncertainty. These include identification and quantitation of pesticides, nondetections, the type of reporting limit, the numerical value of the reporting limit, changes in the reporting limit, bias and variability of the analytical methods, and additional bias and variability contributed (potentially) by sample collection, processing, and transport in the field. Capel and others (1996) explain these sources of uncertainty and how to consider them in data analysis and interpretation. Childress and others (1999) explain reporting limits and how to consider them in data analysis and interpretation.

The National Water-Quality Assessment (NAWQA) Program and the National Water Quality Laboratory (NWQL) dedicated considerable resources to the collection and analysis of quality- control (QC) samples to ensure and document the quality of the pesticide data collected for the NAWQA Program. The purpose of this paper is to describe the quality of the NAWQA pesticide data for environmental water samples and to provide examples that show how quality-control information can be used in analysis and interpretation of environmental data.

Information on initial method performance (termed "proveout" data by NWQL) is published in the documentation for the pesticide analytical methods. Bias and variability of recovery are reported for six to seven spikes in a blank water matrix, a surface-water matrix, and a ground- water matrix at concentrations of 0.1 µg/L and 1 µg/L and for six to seven spikes at concentrations less than 0.1 µg/L in a blank-water matrix (Zaugg and others, 1995, tables 3-9; Werner and others, 1996, tables 4-9, 12). Although method performance data is published in the method documentation, the performance data provided in this paper should be used to describe the quality of the NAWQA pesticide data because: (1) the proveout data were collected over a limited period of time (weeks) at the beginning of the NAWQA program by a limited number of analysts and analytical instruments whereas the NAWQA environmental and QC data sets were collected over a much longer and more similar period of time (years) using a variety of analysts and instruments, (2) only one surface-water matrix and one ground-water matrix were used for the proveout data whereas hundreds of natural water matrixes were used for field matrix spikes, and (3) many more field matrix spikes have been analyzed than those for proveout spikes and will provide more precise estimates of data quality.

Acknowledgments

Jonathon C. Scott, U.S. Geological Survey, calculated the recovery of pesticides in field matrix spikes. Bruce R. Darnel, Ronald W. Brenton, and Chris E. Lindley, U.S. Geological Survey, provided data of the recovery of pesticides in laboratory control spikes and assisted in review of the laboratory data. David K. Mueller, U.S. Geological Survey, provided the inspiration for the calculation of confidence limits for percentiles.

Disclaimer

The field matrix-spike data have not been reviewed thoroughly, are provisional, and are subject to change. Further review of the field-spike data is expected to identify spikes that have extremely high or low recoveries because the spikes either were improperly collected or incorrectly documented in the NAWQA QC data base. The expected result of further review is a data set of field matrix spikes with fewer extreme values than the provisional data set described in this paper; consequently, the provisional data set provides a conservative estimate of the quality of the NAWQA pesticide data. Interpretations of field matrix spike data in this paper are not expected to change greatly as a result of further review of the data, however, the statistics and confidence limits reported in the text and tables will change on further review (especially for pesticides with low numbers of field spikes [less than 50]).

FIELD AND LABORATORY QUALITY-CONTROL DATA

Data compiled for this paper include field blanks, laboratory control spikes, and field matrix spikes collected by the 1991 NAWQA Study Unit teams or the NWQL during 1992-96. This period of record was selected to correspond to the period of record for the NAWQA pesticide data sets available at URL http://wwwdwatcm.wr.usgs.gov/ccpt/pns_data/data.html. The environmental data summarized in this paper were accessed May 4, 1998.

Environmental water samples and blank and spiked QC samples were analyzed for pesticides by gas chromatography/mass spectrometry (GCMS) using the method of Zaugg and others (1995) or by high-performance liquid chomatography (HPLC) using the method of Werner and others (1996) at the U.S. Geological Survey National Water Quality Laboratory. Field QC samples were collected periodically during 1992-96 using guidelines similar those published in Koterba and others (1995) and in Mueller and others (1997).

Field blanks were collected at the field site with pesticide-grade blank water and are exposed to the field and laboratory environments and equipment similarly to environmental samples. Field blanks measure the frequency and magnitude of contamination (one type of positive bias) in environmental water samples from sources in the field and/or laboratory. Contamination is the main cause of false-positive detections (detecting a pesticide in a sample when, in truth, it is absent).

Spikes are QC samples where known amounts (mass) of pesticides are added to water and then analyzed for pesticides. The amount of a pesticide measured (recovered) in a spiked sample is expressed as a percentage (the percent recovery) of the known amount of pesticide added to the sample. Recovery (rather than concentration) is used to assess the quality of spiked samples because recovery allows comparisons among samples that were spiked with different amounts of pesticides or among samples that have different volumes of water. Recovery is a primary measure of the performance of the analytical method. Pesticides added to pesticide-grade blank water in the laboratory are laboratory control spikes. Pesticides added to environmental water samples at the field site are field matrix spikes. Spikes measure bias and variability in the measurements of pesticides. Spikes also measure the frequency of false-negative detections (the failure to detect a pesticide in a spiked sample when, in truth, it is present at the concentration spiked).

Laboratory control spikes measure the bias and variability of the analytical method at a particular concentration. One laboratory control spike is measured in each analytical set of environmental samples. The laboratory control spike has the target pesticides spiked into pesticide-grade blank water at the laboratory and extracted, processed, and analyzed like environmental samples. Laboratory control spikes analyzed by GCMS were spiked at 0.1 µg/L, whereas those analyzed by HPLC were spiked at 0.5 µg/L.

Field matrix spikes measure the bias and variability of the analytical method PLUS any potential effects caused by (1) degradation of pesticides during shipment to the laboratory, (2) inferences in the determination of pesticides from unusual characteristics of the environmental water sample ("matrix effects"), and (3) other chemical processes that cause bias or variability in the measurements of pesticides in environmental water samples. Field matrix spikes analyzed by GCMS were spiked at 0.1 µg/L, whereas those analyzed by HPLC were spiked at 1.0 µg/L.

Field matrix spikes probably are more representative of the quality of the NAWQA pesticide data than laboratory control spikes because field matrix spikes measure additional possible sources of bias and variability that could affect environmental water samples. Laboratory control spikes, however, are more representative for selected pesticides if those pesticides have degraded in spike solutions used for field spiking. Differences in recovery between field matrix spikes and laboratory control spikes have not yet been assessed and the appropriate type of spike to use to describe data quality has not yet been determined for each pesticide. Although field matrix spikes probably are most representative of the quality of the NAWQA pesticide data, data for laboratory control spikes also are presented because they (1) document method performance in a "clean" water matrix, (2) provide a basis for comparisons of data quality for NAWQA with other data-collection programs that lack field matrix spikes, (3) provide a basis for comparing data quality reported in the published method documentation with data quality achieved in practice, and (4) allow assessment of the potential importance of pesticide degradation, environmental matrix effects, or other chemical processes in the measurement of pesticides in environmental water samples.

CONTAMINATION

Contamination of environmental water samples collected by the NAWQA Program was examined by Martin and others (1999) using field blanks collected from 1992-95. The need to consider contamination in data analysis and interpretation depended upon the type of water-quality assessments to be made and differed for assessments such as detection frequency, median concentrations detected, concentrations near a water-quality criterion, or maximum concentrations measured. Two criteria were used to evaluate the need to consider contamination by pesticides for two types of water-quality assessments: (1) a ratio of the frequency of pesticide detection in environmental water samples to the frequency of detection in field blanks of 5.0 or less was used to evaluate the need to consider contamination in assessing the frequency of detection, and (2) a ratio of the median concentration detected in environmental water samples to the maximum concentration detected in field blanks of 2.0 or less was used to evaluate the need to consider contamination in assessing median concentration detected.

Application of these criteria indicate that, for the majority of the pesticide data collected for the NAWQA Program, contamination probably does not need to be considered in the analysis and interpretation of the data. Contamination needs to be considered in assessing the frequency of detection of cis-permethrin, pronamide, p,p'-DDE, pebulate, propargite, ethalfluralin, and triallate in surface-water samples and fenuron, benfluralin, pronamide, cis-permethrin, triallate, chlorpyrifos, trifluralin, propanil, p,p'-DDE, bromacil, dacthal, diazinon, and diuron in ground-water samples. Contamination needs to be considered in assessing the median concentrations detected for pronamide, p,p'-DDE, propargite, napropamide, and triallate in surface-water samples and benfluralin, cis-permethrin, triallate, chlorpyrifos, trifluralin, p,p'-DDE, dacthal, and diazinon in ground-water samples (Martin and others, 1999, p. 24, 29, 38).

Three approaches and examples for considering contamination in various types of assessments were presented: (1) adjust detection frequencies in environmental samples by subtracting detection frequencies in field blanks, (2) recalculate detection frequencies in environmental samples after censoring all detections in environmental samples at a concentration equal to that of some high, infrequently occurring percentile of contamination in field blanks (the 95th or 99th percentiles for example), and (3) adjust concentrations in environmental samples after subtracting a concentration equal to that of some high, infrequently occurring percentile of contamination in field blanks (Martin and others, 1999, p. 39-40). These approaches will be discussed in the following sections.

Contamination and the Frequency of Detection

Uncertainty in the frequency of contamination in environmental water samples was not assessed in Martin and others (1999). Confidence limits for the percentage of nonconforming units (Hahn and Meeker, 1991, p. 104-105) are calculated herein and used to estimate the uncertainty in the measured frequency of contamination in environmental water samples (table 1). The percentage of nonconforming units in the context of contamination is the percentage of field blanks with pesticide detections. An example interpretation of the upper confidence bound for the percentage of field blanks with pesticide detections follows.

Atrazine (parameter code 39632) was detected in 2.8 percent (4 of 145) of ground-water field blanks (table 1). The number of field blanks and the number of field blanks with detections constitute a "sample" of the unknown, true frequency of atrazine contamination in NAWQA environmental ground-water samples. Confidence limits were calculated to describe the uncertainty in the measured frequency of contamination for the "sample" of field blanks, for a selected degree of confidence. One-sided upper confidence limits (one-sided confidence limits are called confidence "bounds") were calculated because, for some types of assessments, data analysts may desire a "pessimistic" estimate of contamination in NAWQA samples ("How bad might contamination really be?"). A 95-percent confidence level was selected for calculation of the upper confidence bound. Other confidence levels could be selected (which would change the "length" of the confidence interval).

On the basis of the 95-percent upper confidence bound, data analysts are 95-percent confident that 6.2 percent or less of NAWQA ground-water samples are contaminated by atrazine. Alternately, data analysts are 95-percent confident that 93.8 percent or more of NAWQA ground-water samples are free from contamination by atrazine. Data analysts have a high degree of confidence that the vast majority of NAWQA environmental ground-water samples are not contaminated by atrazine.

Data analysts can use this estimate of uncertainty in the frequency of contamination to qualify or adjust their estimates of the frequency of detection of atrazine in environmental ground-water samples. For example, atrazine was detected in 32.5 percent (968 of 2,976) of NAWQA environmental ground-water samples. Data analysts could estimate a best case/worst case effect of contamination on detections of atrazine in ground water in the following manner. If contamination affected only environmental ground-water samples that, otherwise, were free of atrazine (the worst case), then the detection frequency in the NAWQA data set is at least 26.3 percent (32.5 percent minus 6.2 percent). If, however, contamination affected only environmental ground-water samples that, otherwise, contained atrazine anyway (the best case), then contamination had no effect on the detection of atrazine and the detection frequency in the NAWQA data set is 32.5 percent. Therefore, data analysts are 95-percent confident that the detection frequency, adjusted for the frequency of contamination, of atrazine in ground-water samples in the data set is between 26.3 percent and 32.5 percent.

Contamination and the Magnitude of Concentrations

Uncertainty in the magnitude of contamination (the concentration of the contamination) also can be estimated. Upper confidence bounds for the 95th-percentile concentration of pesticide contamination in NAWQA environmental water samples was presented in Martin and others (1991, p. 38-39). The frequency of contamination for most pesticides, however, is less than 5 percent and the upper confidence bound for the 95th percentile is nearly always a nondetection (and, therefore, not very useful for adjusting concentrations). Sample size (the number of field blanks) was insufficient to calculate uncertainty for the 99th-percentile concentration (at a reasonable degree of confidence). Consequently, efforts to adjust for the magnitude of contamination in this paper are based only on the measured magnitude of contamination in field blanks and statements about uncertainty cannot be made. Aggregation of additional field blanks collected by other Study Unit teams in the future will increase sample size and allow assessment of uncertainty in extreme percentiles of contamination.

The 99th-percentile of atrazine concentrations in ground-water field blanks was 0.004 µg/L (Martin and others, 1999, p. 16), and represents a magnitude of contamination that is infrequently exceeded in environmental ground-water samples. Data analysts could use the 99th-percentile of the magnitude of contamination in two different ways to adjust concentrations of atrazine in environmental ground-water samples for a magnitude of contamination that is exceeded only in about 1 percent of the samples.

For example, environmental ground-water samples having concentrations of atrazine of 0.004 µg/L or less could be censored (set to nondetections) in an effort to account for contamination bias in low-concentration environmental samples where contamination could, potentially, account for all of the atrazine present. An alternate approach would be to subtract 0.004 µg/L from the measured concentrations of atrazine in all environmental ground-water samples in an effort to account for contamination bias that might occur in any sample. Adjusted concentrations that are less than the method reporting limit (or, alternately, less than zero) would be considered nondetections (a different method of censoring detections).

The detection frequency of atrazine in NAWQA environmental ground-water samples is 32.5 percent (968 of 2,976) and the median concentration of atrazine detections is 0.022 µg/L. Recalculation of these statistics using data censored at 0.004 µg/L gives a detection frequency of 27.7 percent (825 of 2,976) and the median concentration of detections of 0.036 µg/L. Recalculation using data reduced by 0.004 µg/L and censored at a method reporting limit of 0.001 µg/L gives a detection frequency of 27.7 percent (825 of 2,976) and the median concentration of detections of 0.032 µg/L. [The same rate of detection for both methods of adjustment is a fortuitous consequence of the least significant digit in the data set being equal to the method reporting limit (0.001 µg/L). For example, if the method reporting limit for atrazine was 0.002 µg/L instead of 0.001 µg/L, more samples would be adjusted to nondetections and the recalculated rate of detection would be 26.5 percent (789 of 2,976) and the median concentration of detections would be 0.035 µg/L].

Censoring detections to the 99th-percentile or subtracting the 99th-percentile from detections undoubtedly censors an unknown number of true environmental detections (environmental samples not effected by contamination). The adjustments for contamination are conservative in the sense that they provide a pessimistic estimate of data quality and an optimistic estimate of environmental quality. An optimistic estimate of data quality and a pessimistic estimate of environmental quality can be obtained by not considering contamination in water-quality assessments. On the basis of optimistic/pessimistic estimates of data quality in the example above, data analysts would conclude that the median concentration of detections of atrazine is between 0.022 µg/L and 0.036 µg/L. Data analysts must determine the need to consider contamination bias and the practical or hydrologic significance of the adjusted estimate for particular types of assessment questions. Contamination bias of 0.004 µg/L is clearly insignificant in assessments relating to a health criterion of 3 µg/L. If, however, a health criterion for atrazine was 0.03 or less, contamination bias would need to be considered.

The validity of adjusting concentrations for contamination should be evaluated in view of (1) typical magnitudes of contamination in field blanks, (2) the frequency of censored environmental detections compared to the estimated frequency of contamination, and (3) the ability of the adjusted data to address particular types of assessment questions. In the case for atrazine in ground water, the 99th-percentile concentration (0.004 µg/L) appears to be a reasonable choice for adjustment in that (1) 0.004 µg/L is not an unusually high concentration of atrazine when atrazine is detected in field blanks (Martin and others, 1991, p. 57, 80) and (2) the frequency of censoring (4.8 percent, 143 of 2,976) is less than the 95-percent upper confidence bound for the frequency of atrazine contamination in ground-water samples (6.2 percent) and, therefore, does not appear to be an excessive degree of censoring.

FALSE NEGATIVE DETECTIONS

A false-negative detection (termed a "false negative") is a failure to detect a pesticide when, in truth, it is present. The frequency of false negatives is a function of pesticide concentration (the frequency of false negatives is much greater at low concentrations than at high concentrations). The frequency of false negative detections of pesticides in environmental water samples was estimated by calculation of the frequency of false negatives in laboratory control spikes and field matrix spikes.

The performance of analytical method is thought to be the main factor affecting the frequency of false negatives in laboratory control spikes. Laboratory control spikes measure the performance (the bias and variability of pesticide measurements) for each pesticide in the method. For a fixed amount of variability, pesticides that have a negative measurement bias (biased low) have a greater frequency of false negatives than pesticides that have a positive measurement bias (biased high). For a fixed amount of bias, pesticides that have high measurement variability will have a greater frequency of false negatives than pesticides that have low measurement variability.

The performance of analytical method also is thought to be the main factor affecting the frequency of false negatives in field matrix spikes. In addition, however, potential sources of bias and variability from sample collection and processing, water matrix effects, and pesticide degradation also affect (potentially) the frequency of false negatives in field matrix spikes.

The use of QC information in assessing the frequency of false negatives is illustrated in an example for azinphos-methyl (parameter code 82686). Azinphos-methyl is one of the most poorly performing pesticides in the NAWQA data set. On the basis of recovery in laboratory control spikes, measurements of azinphos-methyl were the tenth most biased (median recovery 53.9 percent) and the third most variable (interquartile range of recovery 62.0 percent).

Azinphos-methyl was not detected in 5 of 998 (0.5 percent) laboratory control spikes and was not detected in 3 of 304 (1.0 percent) field matrix spikes (table 2). As with field blanks, false negatives in spikes can be considered a "sample" of the unknown, true frequency of false negatives for azinphos-methyl in environmental water samples. One-sided, "pessimistic" confidence bounds can be calculated to estimate the uncertainty in the measured frequency of false negatives ("When azinphos-methyl is present in water at 0.1 µg/L, how high might the frequency of false negatives truly be?").

On the basis of laboratory control spikes, data analysts are 95-percent confident that in 1.1 percent or less of environmental samples where azinphos-methyl was present at 0.1 µg/L it would NOT be detected (table 2). Because field matrix spikes include additional sources of bias and variability, estimates of the frequency of false negatives from field spikes probably are more representative than those based on laboratory control spikes. On the basis of field matrix spikes, data analysts are 95-percent confident that in 2.5 percent or less of environmental samples where azinphos-methyl was present at 0.1 µg/L it would NOT be detected. Alternately, analysts are 95-percent confident that in 97.5 percent or more of samples where azinphos-methyl was present at 0.1 µg/L it WOULD be detected. Although azinphos-methyl is a relatively poorly performing pesticide (Zaugg and others, 1995, p. 35) data analysts have a high degree of confidence that when azinphos-methyl is in water at 0.1 µg/L it will be detected.

BIAS AND VARIABILITY IN CONCENTRATIONS

Bias and variability can be described by several measures of location and spread. The mean and standard deviation are common measures of location and spread, respectively, but are strongly influenced by extreme values. The median and interquartile range are common measures of location and spread, respectively, that are resistant to the influence of extreme values (Helsel and Hirsch, 1992, p. 3-9). Measures of location and spread that are resistant to the influences of extreme values are the most useful for describing the bias and variability of pesticide measurements because (1) information on typical data quality is needed for most assessment questions and (2) information on extreme values of data quality can be obtained from more direct measures (percentages for false positives or false negatives, percentiles for extreme values of concentration). Distributions of recovery for many pesticides are approximately normally distributed (distributions are symmetrical and lack extreme values). Distributions of recovery for other pesticides clearly are nonnormal (distributions are uniform, bimodal, highly skewed, or contain many extreme values). Data analysts should use measures of location and spread that are resistant to the influences of outliers for comparing bias and variability among a large number of pesticides, or when an approximately normal distribution of recovery is in doubt.

Median recovery of pesticides in laboratory control spikes ranged from 6.0 percent for chlorothalonil to 102.9 percent for metolachlor (table 3). Median recovery for 70 pesticides ranged from 70.0 to 102.9 percent and median recovery for 7 pesticides was less than 50.0 percent. Median recovery of pesticides in field matrix spikes ranged from 15.6 percent for oxamyl to 132.4 percent for propham. Median recovery for 61pesticides ranged from 70.0 to 105.7 percent and median recovery for 7 pesticides was less than 50.0 percent. No field matrix spikes were available for acetochlor.

Interquartile range of recovery of pesticides in laboratory control spikes ranged from 10.3 percent for butylate to 101.4 percent for carbaryl analyzed by GCMS (table 3). Interquartile range of recovery for 46 pesticides was less than or equal to 25.0 percent and interquartile range of recovery for 15 pesticides was greater than or equal to 40.0 percent. Interquartile range of recovery of pesticides in field matrix spikes ranged from 9.0 percent for oryzalin to 92.3 percent for propham. Interquartile range of recovery for 49 pesticides was less than or equal to 25.0 percent and interquartile range of recovery for 13 pesticides was greater than or equal to 40.0 percent.

The use of QC information in assessing the bias and variability of pesticide concentrations is illustrated in an example for azinphos-methyl. On the basis of the histograms of recovery for laboratory and field spikes (figs 1, 2), it is apparent that the normal distribution is a poor model for recovery of azinphos-methyl. The mean and standard deviation are inflated by several extreme values (very high recoveries), and measures of uncertainty (confidence limits) based upon a normal distribution are inappropriate. Measures of uncertainty based upon the binomial distribution for percentiles of pesticide recovery are presented for azinphos-methyl but are applicable for estimating uncertainty for percentiles of pesticide recovery for any pesticide. Calculation, use, and interpretation of two-sided confidence limits or one-sided confidence bounds for percentiles is described in Hahn and Meeker (1991, p. 82-90) and Helsel and Hirsch (1992, p. 70-72, 83-84).

Confidence limits for the median may be used to estimate uncertainty in the bias of recovery. The median recovery of azinphos-methyl spiked at 0.1 µg/L in 998 laboratory control spikes was 53.9 percent (table 4). Based on laboratory control spikes, data analysts are 90-percent confident that the true median recovery of azinphos-methyl in environmental water samples is between 51.2 and 57.0 percent (table 4). The median recovery of azinphos-methyl spiked at 0.1 µg/L in 304 field matrix spikes was 81.5 percent. Based on field matrix spikes, data analysts are 90-percent confident that the true median recovery of azinphos-methyl in environmental water samples is between 73.9 and 89.6 percent. Because the 90-percent confidence limits for the median (2-sided estimates of uncertainty) are the same as the 95-percent confidence bounds for the median (1-sided estimates of uncertainty), analysts also are 95-percent confident that the true median recovery of azinphos-methyl is not less than 73.9 percent. The reason for the reduced bias in field matrix spikes compared to laboratory control spikes is not known but might be caused by reduced extraction of azinphos-methyl from low ionic-strength blank water used for control spikes. As stated previously, estimates of bias and variability from field matrix spikes probably are more representative of the quality of the NAWQA environmental data than estimates from laboratory control spikes.

Confidence bounds for selected extreme percentiles may be used to estimate uncertainty in the variability of recovery. For many assessment questions, data analysts are interested in a pessimistic estimate of variability (How high might variability truly be?"). For low percentiles of recovery, analysts are interested in a lower confidence bound whereas for high percentiles, analysts are interested in an upper confidence bound. The 10th and 90th percentiles of recovery of azinphosmethyl in laboratory control spikes was 15.3 percent and 129.8 percent, respectively (table 4). Based on laboratory control spikes, data analysts are 95-percent confident that no more than 10 percent of NAWQA environmental samples have recovery of azinphos-methyl greater than 137.0 percent or less than 12.9 percent. The 10th and 90th percentiles of recovery of azinphos-methyl in field matrix spikes was 30.8 percent and 171.0 percent, respectively. Based on field matrix spikes, data analysts are 95-percent confident that no more than 10 percent of NAWQA environmental samples have recovery of azinphos-methyl greater than 214.0 percent or less than 25.6 percent.

In addition to describing and documenting bias and variability of concentrations of pesticides in NAWQA environmental water samples, QC information can be used to (1) make adjustments to data for analysis and (2) qualify interpretations of environmental data. Appropriate qualifications and adjustments depend on the SPECIFIC assessment questions that need to be answered.

Suppose, for example, that an assessment question is "how frequently does azinphos-methyl exceed 0.5 µg/L?" One approach is to adjust the NAWQA environmental data for bias. The median recovery of azinphos-methyl in field matrix spikes was 81.5 percent and is the best estimate of the true bias in the NAWQA environmental data. Data analysts could use the median recovery to adjust concentrations of azinphos-methyl (multiply all environmental detections by 100/81.5=1.23) to adjust for the bias in method performance, matrix effects, and degradation. Only 3 of 164 detections in 5,133 surface-water samples analyzed for azinphosmethyl in the NAWQA pesticide data set exceeded 0.5 µg/L. After adjustment for the median bias, 5 of 164 detections could have exceeded 0.5 µg/L.

For some types of assessment questions analysts may desire a pessimistic estimate of the frequency of exceeding 0.5 µg/L (they wish to err on the side of declaring that a measurement is greater than 0.5 when in fact it is less than 0.5 rather than to err on the side of declaring that a measurement is less than 0.5 when in fact it is more than 0.5). The main data-quality concern for this assessment question is the frequency and magnitude of "low" recoveries and some additional approaches for adjusting data and qualifying interpretations might be used.

Pessimistic estimates of environmental concentrations are obtained by adjusting environmental concentrations by pessimistic estimates of data quality. If analysts desire a pessimistic estimate of concentration, they could use the lower confidence limit for the median recovery (73.9 percent) to adjust the concentrations of azinphos-methyl (multiply all environmental detections by 100/73.9=1.35) to adjust for bias. Adjustments to concentrations of azinphos-methyl using this pessimistic estimate of median bias indicate that 6 of 164 detections could have exceeded 0.5 µg/L. Data analysts are 95-percent confident that no more than 50 percent of the adjusted concentrations for azinphos-methyl are biased low (less than 100 percent recovery).

If analysts wanted to account for variability as well as bias in concentrations, they could select an extreme percentile of recovery (a small one in this case) to adjust the NAWQA environmental data. Previously, it was noted (on the basis of the lower confidence bound for the 10th percentile of recovery for azinphos-methyl in field spikes) that analysts are 95-percent confident that no more than 10 percent of NAWQA environmental samples have recovery of azinphos-methyl less than 25.6 percent. A very pessimistic estimate of environmental concentrations that accounts for bias and variability in recovery could be obtained by adjusting all detections of azinphos-methyl by the pessimistic estimate of the 10th percentile of recovery (100/25.6=3.91). Adjustments to concentrations of azinphos-methyl using this pessimistic estimate of variability and bias indicate that 22 of 164 detections could have exceeded 0.5 µg/L. Data analysts are 95-percent confident that no more than 10 percent of the adjusted concentrations for azinphos-methyl are biased low (less than 100 percent recovery). (Many samples are biased high, but in this case, analysts are interested in a pessimistic estimate of concentration).

SUMMARY

This paper describes the quality of the NAWQA pesticide data collected from 1992-96 for the 1991 Study Units and provides examples that show how quality-control information on bias and variability can be used in analysis and interpretation of environmental data. Questions regarding the quality of the NAWQA pesticide data or requests for custom statistical compilations to address specific water-quality assessment questions should be directed to the author (jdmartin@usgs.gov).

REFERENCES

Capel, P.D., Gilliom, R.J., and Larson, S.J., 1996, Interpretation of data on low-level concentrations of pesticides in water: accessed October 1, 1999 at URL http://ca.water.usgs.gov/pnsp/rep/interpret/

Hahn, G.J., and Meeker, W.Q., 1991, Statistical intervals-A guide for practitioners: New York, John Wiley & Sons, 392 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in water resources: Amsterdam, Elsevier Science Publishers, 522 p.

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, Ground-water data-collection protocols and procedures for the National Water-Quality Assessment Program-Collection and documentation of water-quality samples and related data: U.S. Geological Survey Open-File Report 95-399, 113 p. Available at URL http://wwwrvares.er.usgs.gov/nawqa/protocols/doc_list.html

Martin, J.D., Gilliom, R.J., and Schertz, T.J., 1999, Summary and evaluation of pesticides in field blanks collected for the National Water-Quality Assessment Program: 1992-95: U.S. Geological Survey Open-File Report 98-412, 102 p. Available at URL http://water.usgs.gov/nawqa/pnsp/pubs/files/ofr98412.pdf

Mueller, D.K., Martin, J.D., and Lopes, T.J., 1997, Quality-control design for surface-water sampling in the National Water-Quality Assessment Program: U.S. Geological Survey Open-File Report 97-223, 17 p. Available at URL http://wwwrvares.er.usgs.gov/nawqa/protocols/doc_list.html

Oblinger Childress, C.J., Foreman, W.T., Connor, B.F., and Maloney, T.J., 1999, New reporting procedures based on long-term method detection levels and some considerations for interpretations of water-quality data provided by the U.S. Geological Survey National Water Quality Laboratory: U.S. Geological Survey Open-File Report 99-193, 19 p. Available at URL http://water.usgs.gov/owq/pubs.html

Werner, S.L., Burkhardt, M.R., and DeRusseau, S.N., 1996, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of pesticides in water by Carbopak-B solid-phase extraction and high-performance liquid chromatography: U.S. Geological Survey Open-File Report 96-216, 42 p.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, K.M., 1995, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of pesticides in water by C-18 solid-phase extraction and capillary-column gas chromatography/mass spectrometry with selected-ion monitoring: U.S. Geological Survey Open-File Report 95-181, 49 p. Available at URL http://wwwnwql.cr.usgs.gov/Public/pubs/OFR95-181/OFR_95-181.html


FIGURES

 Percentage

| ** 10 + ** | ** | ** ** | ** ** 9 + ** ** ** | ** ** ** | ** ** ** | ** ** ** ** 8 + ** ** ** ** ** | ** ** ** ** ** | ** ** ** ** ** | ** ** ** ** ** ** 7 + ** ** ** ** ** ** ** | ** ** ** ** ** ** ** | ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** 6 + ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** 5 + ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** 4 + ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** 3 + ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** 2 + ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** 1 + ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** -------------------------------------------------------------- 1 1 1 1 1 1 1 1 1 1 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

Spike recovery, in percent Figure 1. Histogram of recovery of azinphos-methyl in 304 field matrix spikes, 1992-96. Recoveries less than 0 percent or greater than 500 percent were deleted from the data set. Recoveries greater than 200 percent were set to 200 percent for the histograms.

 Percentage

          |             **                                                      
       12 +             **                                                      
          |             **                                                      
          |             **                                                      
          |             **                                                      
       10 +    ** **    **                                                      
          |    ** **    **                                                      
          |    ** ** ** **                                                      
          |    ** ** ** **                                                      
        8 +    ** ** ** ** **       **                                          
          |    ** ** ** ** **       **                                          
          |    ** ** ** ** ** **    **                                          
          |    ** ** ** ** ** **    **                                          
        6 +    ** ** ** ** ** **    **                                          
          |    ** ** ** ** ** **    **    **                                    
          | ** ** ** ** ** ** ** ** **    **                                    
          | ** ** ** ** ** ** ** ** ** ** **                                    
        4 + ** ** ** ** ** ** ** ** ** ** **                                    
          | ** ** ** ** ** ** ** ** ** ** **                         **         
          | ** ** ** ** ** ** ** ** ** ** ** ** **                   **         
          | ** ** ** ** ** ** ** ** ** ** ** ** **                   **         
        2 + ** ** ** ** ** ** ** ** ** ** ** ** ** **                **         
          | ** ** ** ** ** ** ** ** ** ** ** ** ** **                **         
          | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **       **         
          | ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **         
          --------------------------------------------------------------
                                           1  1  1  1  1  1  1  1  1  1
                1  2  3  4  5  6  7  8  9  0  1  2  3  4  5  6  7  8  9
             5  5  5  5  5  5  5  5  5  5  5  5  5  5  5  5  5  5  5  5

                            Spike recovery, in percent

Figure 2. Histogram of recovery of azinphos-methyl in 998 laboratory control spikes,
          1992-96. Recoveries less than 0 percent or greater than 500 percent 
          were deleted from the data set. Recoveries greater than 200 percent
          were set to 200 percent for the histograms.


TABLES




Table 1. Contamination in field blanks of the NAWQA Program, 1992-95. 
         Pesticides sorted by analytical method, water type, and parameter code.

 [Parm, NWIS/STORET parameter code; MRL, Method reporting limit; µg/L, microgram per liter; 
 GCMS, gas chromatography/mass spectrometry; HPLC, high-performance liquid chromatography;
 GW, ground-water field blanks; SW, surface-water field blanks; nd, pesticide not detected]
----------------------------------------------------------------------------------------------------
                                                                                 95-percent
                                                                                   upper 
                                                                                 confidence 
                                                        Number   Number           bound for Maximum
                                                        of       of       Percent percent   concen-
                               Analytical  MRL   Water  field    detec-   detec-   detec-   tration
Parm  Pesticide                  method  (µg/L)  type   blanks   tions    tions    tions    (µg/L)
----------------------------------------------------------------------------------------------------

04024 Propachlor                  GCMS    0.007    GW    145       0        0.0     2.0      nd  
04028 Butylate                    GCMS     .002    GW    145       0         .0     2.0      nd  
04035 Simazine                    GCMS     .005    GW    145       2        1.4     4.3     0.001
04037 Prometon                    GCMS     .018    GW    145       1         .7     3.2      .013
04040 Desethylatrazine            GCMS     .002    GW    145       1         .7     3.2      .005

04041 Cyanazine                   GCMS     .004    GW    145       0         .0     2.0      nd  
04095 Fonofos                     GCMS     .003    GW    145       0         .0     2.0      nd  
34253 alpha-HCH                   GCMS     .002    GW    145       0         .0     2.0      nd  
34653 p,p'-DDE                    GCMS     .006    GW    145       6        4.1     8.0      .002
38933 Chlorpyrifos                GCMS     .004    GW    145       2        1.4     4.3      .013

39341 gamma-HCH                   GCMS     .004    GW    145       0         .0     2.0      nd  
39381 Dieldrin                    GCMS     .001    GW    145       0         .0     2.0      nd  
39415 Metolachlor                 GCMS     .002    GW    145       2        1.4     4.3      .006
39532 Malathion                   GCMS     .005    GW    145       0         .0     2.0      nd  
39542 Parathion                   GCMS     .004    GW    145       0         .0     2.0      nd  

39572 Diazinon                    GCMS     .002    GW    145       1         .7     3.2      .011
39632 Atrazine                    GCMS     .001    GW    145       4        2.8     6.2      .012
46342 Alachlor                    GCMS     .002    GW    145       0         .0     2.0      nd  
49260 Acetochlor                  GCMS     .002    GW     15       0         .0    18.1      nd  
82630 Metribuzin                  GCMS     .004    GW    145       0         .0     2.0      nd  

82660 2,6-Diethylaniline          GCMS     .003    GW    145       0         .0     2.0      nd  
82661 Trifluralin                 GCMS     .002    GW    145       1         .7     3.2      .002
82663 Ethalfluralin               GCMS     .004    GW    145       0         .0     2.0      nd  
82664 Phorate                     GCMS     .002    GW    145       0         .0     2.0      nd  
82665 Terbacil                    GCMS     .007    GW    144       0         .0     2.1      nd  

82666 Linuron                     GCMS     .002    GW    145       0         .0     2.0      nd  
82667 Methyl parathion            GCMS     .006    GW    145       0         .0     2.0      nd  
82668 EPTC                        GCMS     .002    GW    145       0         .0     2.0      nd  
82669 Pebulate                    GCMS     .004    GW    145       0         .0     2.0      nd  
82670 Tebuthiuron                 GCMS     .010    GW    145       0         .0     2.0      nd  

82671 Molinate                    GCMS     .004    GW    145       0         .0     2.0      nd  
82672 Ethoprop                    GCMS     .003    GW    145       0         .0     2.0      nd  
82673 Benfluralin                 GCMS     .002    GW    145       2        1.4     4.3      .003
82674 Carbofuran                  GCMS     .003    GW    145       0         .0     2.0      nd  
82675 Terbufos                    GCMS     .013    GW    145       0         .0     2.0      nd  

82676 Pronamide                   GCMS     .003    GW    145       1         .7     3.2      .002
82677 Disulfoton                  GCMS     .017    GW    145       0         .0     2.0      nd  
82678 Triallate                   GCMS     .001    GW    145       2        1.4     4.3      .001
82679 Propanil                    GCMS     .004    GW    145       1         .7     3.2      .002
82680 Carbaryl                    GCMS     .003    GW    145       0         .0     2.0      nd  

82681 Thiobencarb                 GCMS     .002    GW    145       0         .0     2.0      nd  
82682 Dacthal                     GCMS     .002    GW    145       1         .7     3.2      .001
82683 Pendimethalin               GCMS     .004    GW    145       0         .0     2.0      nd  
82684 Napropamide                 GCMS     .003    GW    145       0         .0     2.0      nd  
82685 Propargite                  GCMS     .013    GW    145       0         .0     2.0      nd  

82686 Azinphos-methyl             GCMS     .001    GW    144       0         .0     2.1      nd  
82687 cis-Permethrin              GCMS     .005    GW    145       1         .7     3.2      .003
04024 Propachlor                  GCMS     .007    SW    175       0         .0     1.7      nd  
04028 Butylate                    GCMS     .002    SW    175       0         .0     1.7      nd  
04035 Simazine                    GCMS     .005    SW    175      16        9.1    13.6      .007

04037 Prometon                    GCMS     .018    SW    175       3        1.7     4.4      .004
04040 Desethylatrazine            GCMS     .002    SW    175       1         .6     2.7      .004
04041 Cyanazine                   GCMS     .004    SW    175       0         .0     1.7      nd  
04095 Fonofos                     GCMS     .003    SW    175       0         .0     1.7      nd  
34253 alpha-HCH                   GCMS     .002    SW    175       0         .0     1.7      nd  

34653 p,p'-DDE                    GCMS     .006    SW    175       4        2.3     5.2      .010
38933 Chlorpyrifos                GCMS     .004    SW    175       1         .6     2.7      .006
39341 gamma-HCH                   GCMS     .004    SW    175       0         .0     1.7      nd  
39381 Dieldrin                    GCMS     .001    SW    175       0         .0     1.7      nd  
39415 Metolachlor                 GCMS     .002    SW    175       8        4.6     8.1      .020

39532 Malathion                   GCMS     .005    SW    175       3        1.7     4.4      .015
39542 Parathion                   GCMS     .004    SW    175       0         .0     1.7      nd  
39572 Diazinon                    GCMS     .002    SW    175       4        2.3     5.2      .038
39632 Atrazine                    GCMS     .001    SW    175      19       10.9    15.5      .009
46342 Alachlor                    GCMS     .002    SW    175       3        1.7     4.4      .005

49260 Acetochlor                  GCMS     .002    SW     17       0         .0    16.2      nd  
82630 Metribuzin                  GCMS     .004    SW    175       1         .6     2.7      .007
82660 2,6-Diethylaniline          GCMS     .003    SW    171       0         .0     1.7      nd  
82661 Trifluralin                 GCMS     .002    SW    171       1         .6     2.7      .006
82663 Ethalfluralin               GCMS     .004    SW    171       1         .6     2.7      .006

82664 Phorate                     GCMS     .002    SW    171       0         .0     1.7      nd  
82665 Terbacil                    GCMS     .007    SW    164       0         .0     1.8      nd  
82666 Linuron                     GCMS     .002    SW    171       0         .0     1.7      nd  
82667 Methyl parathion            GCMS     .006    SW    171       0         .0     1.7      nd  
82668 EPTC                        GCMS     .002    SW    171       3        1.8     4.5      .086

82669 Pebulate                    GCMS     .004    SW    171       1         .6     2.7      .005
82670 Tebuthiuron                 GCMS     .010    SW    171       1         .6     2.7      .053
82671 Molinate                    GCMS     .004    SW    171       0         .0     1.7      nd  
82672 Ethoprop                    GCMS     .003    SW    171       0         .0     1.7      nd  
82673 Benfluralin                 GCMS     .002    SW    171       0         .0     1.7      nd  

82674 Carbofuran                  GCMS     .003    SW    171       0         .0     1.7      nd  
82675 Terbufos                    GCMS     .013    SW    171       0         .0     1.7      nd  
82676 Pronamide                   GCMS     .003    SW    171       2        1.2     3.6      .120
82677 Disulfoton                  GCMS     .017    SW    171       0         .0     1.7      nd  
82678 Triallate                   GCMS     .001    SW    171       2        1.2     3.6      .004

82679 Propanil                    GCMS     .004    SW    171       0         .0     1.7      nd  
82680 Carbaryl                    GCMS     .003    SW    171       2        1.2     3.6      .012
82681 Thiobencarb                 GCMS     .002    SW    171       0         .0     1.7      nd  
82682 Dacthal                     GCMS     .002    SW    171       1         .6     2.7      .003
82683 Pendimethalin               GCMS     .004    SW    171       0         .0     1.7      nd  

82684 Napropamide                 GCMS     .003    SW    171       2        1.2     3.6      .100
82685 Propargite                  GCMS     .013    SW    171       2        1.2     3.6      .074
82686 Azinphos-methyl             GCMS     .001    SW    164       0         .0     1.8      nd  
82687 cis-Permethrin              GCMS     .005    SW    171       1         .6     2.7      .003
04029 Bromacil                    HPLC     .035    GW    104       1        1.0     4.5      .010

38442 Dicamba                     HPLC     .035    GW     97       0         .0     3.0      nd  
38478 Linuron                     HPLC     .018    GW     98       0         .0     3.0      nd  
38482 MCPA                        HPLC     .170    GW     97       0         .0     3.0      nd  
38487 MCPB                        HPLC     .140    GW     97       0         .0     3.0      nd  
38501 Methiocarb                  HPLC     .026    GW     98       0         .0     3.0      nd  

38538 Propoxur                    HPLC     .035    GW     96       0         .0     3.1      nd  
38711 Bentazon                    HPLC     .014    GW     97       0         .0     3.0      nd  
38746 2,4-DB                      HPLC     .240    GW     97       0         .0     3.0      nd  
38811 Fluometuron                 HPLC     .035    GW     98       0         .0     3.0      nd  
38866 Oxamyl                      HPLC     .018    GW     98       0         .0     3.0      nd  

39732 2,4-D                       HPLC     .150    GW    103       0         .0     2.9      nd  
39742 2,4,5-T                     HPLC     .035    GW    103       0         .0     2.9      nd  
39762 Silvex                      HPLC     .021    GW    103       0         .0     2.9      nd  
49235 Triclopyr                   HPLC     .250    GW     97       0         .0     3.0      nd  
49236 Propham                     HPLC     .035    GW     98       0         .0     3.0      nd  

49291 Picloram                    HPLC     .050    GW     97       0         .0     3.0      nd  
49292 Oryzalin                    HPLC     .310    GW     98       0         .0     3.0      nd  
49293 Norflurazon                 HPLC     .024    GW     98       0         .0     3.0      nd  
49294 Neburon                     HPLC     .015    GW     98       0         .0     3.0      nd  
49296 Methomyl                    HPLC     .017    GW     98       0         .0     3.0      nd  

49297 Fenuron                     HPLC     .013    GW     98       1        1.0     4.7      .010
49299 DNOC                        HPLC     .420    GW     97       0         .0     3.0      nd  
49300 Diuron                      HPLC     .020    GW     98       1        1.0     4.7      .020
49301 Dinoseb                     HPLC     .035    GW     97       0         .0     3.0      nd  
49302 Dichlorprop                 HPLC     .032    GW     97       0         .0     3.0      nd  

49303 Dichlobenil                 HPLC    1.200    GW     98       0         .0     3.0      nd  
49304 Dacthal monoacid            HPLC     .017    GW     97       0         .0     3.0      nd  
49305 Clopyralid                  HPLC     .230    GW     97       0         .0     3.0      nd  
49306 Chlorothalonil              HPLC     .480    GW     96       0         .0     3.1      nd  
49307 Chloramben                  HPLC     .420    GW     98       0         .0     3.0      nd  

49308 3-Hydroxycarbofuran         HPLC     .014    GW     98       0         .0     3.0      nd  
49309 Carbofuran                  HPLC     .120    GW     98       0         .0     3.0      nd  
49310 Carbaryl                    HPLC     .008    GW     98       0         .0     3.0      nd  
49311 Bromoxynil                  HPLC     .035    GW     97       0         .0     3.0      nd  
49312 Aldicarb                    HPLC     .550    GW     98       0         .0     3.0      nd  

49313 Aldicarb sulfone            HPLC     .100    GW     98       0         .0     3.0      nd  
49314 Aldicarb sulfoxide          HPLC     .021    GW     98       0         .0     3.0      nd  
49315 Acifluorfen                 HPLC     .035    GW     97       0         .0     3.0      nd  
04029 Bromacil                    HPLC     .035    SW    109       0         .0     2.7      nd  
38442 Dicamba                     HPLC     .035    SW     96       0         .0     3.1      nd  

38478 Linuron                     HPLC     .018    SW     97       0         .0     3.0      nd  
38482 MCPA                        HPLC     .170    SW     96       0         .0     3.1      nd  
38487 MCPB                        HPLC     .140    SW     96       0         .0     3.1      nd  
38501 Methiocarb                  HPLC     .026    SW     97       0         .0     3.0      nd  
38538 Propoxur                    HPLC     .035    SW     93       0         .0     3.2      nd  

38711 Bentazon                    HPLC     .014    SW     96       0         .0     3.1      nd  
38746 2,4-DB                      HPLC     .240    SW     96       0         .0     3.1      nd  
38811 Fluometuron                 HPLC     .035    SW     97       0         .0     3.0      nd  
38866 Oxamyl                      HPLC     .018    SW     97       0         .0     3.0      nd  
39732 2,4-D                       HPLC     .150    SW    108       1         .9     4.3      .230

39742 2,4,5-T                     HPLC     .035    SW    108       0         .0     2.7      nd  
39762 Silvex                      HPLC     .021    SW    108       0         .0     2.7      nd  
49235 Triclopyr                   HPLC     .250    SW     91       0         .0     3.2      nd  
49236 Propham                     HPLC     .035    SW     92       0         .0     3.2      nd  
49291 Picloram                    HPLC     .050    SW     91       0         .0     3.2      nd  

49292 Oryzalin                    HPLC     .310    SW     92       0         .0     3.2      nd  
49293 Norflurazon                 HPLC     .024    SW     92       0         .0     3.2      nd  
49294 Neburon                     HPLC     .015    SW     92       0         .0     3.2      nd  
49296 Methomyl                    HPLC     .017    SW     92       0         .0     3.2      nd  
49297 Fenuron                     HPLC     .013    SW     92       0         .0     3.2      nd  

49299 DNOC                        HPLC     .420    SW     91       0         .0     3.2      nd  
49300 Diuron                      HPLC     .020    SW     92       1        1.1     5.1      .010
49301 Dinoseb                     HPLC     .035    SW     91       0         .0     3.2      nd  
49302 Dichlorprop                 HPLC     .032    SW     91       0         .0     3.2      nd  
49303 Dichlobenil                 HPLC    1.200    SW     92       0         .0     3.2      nd  

49304 Dacthal monoacid            HPLC     .017    SW     91       0         .0     3.2      nd  
49305 Clopyralid                  HPLC     .230    SW     91       0         .0     3.2      nd  
49306 Chlorothalonil              HPLC     .480    SW     91       0         .0     3.2      nd  
49307 Chloramben                  HPLC     .420    SW     92       0         .0     3.2      nd  
49308 3-Hydroxycarbofuran         HPLC     .014    SW     92       0         .0     3.2      nd  

49309 Carbofuran                  HPLC     .120    SW     92       0         .0     3.2      nd  
49310 Carbaryl                    HPLC     .008    SW     92       0         .0     3.2      nd  
49311 Bromoxynil                  HPLC     .035    SW     91       0         .0     3.2      nd  
49312 Aldicarb                    HPLC     .550    SW     92       0         .0     3.2      nd  
49313 Aldicarb sulfone            HPLC     .100    SW     92       0         .0     3.2      nd  

49314 Aldicarb sulfoxide          HPLC     .021    SW     92       0         .0     3.2      nd  
49315 Acifluorfen                 HPLC     .035    SW     91       0         .0     3.2      nd  
----------------------------------------------------------------------------------------------------


Table 2. False negative detections of pesticides in NAWQA field matrix spikes and NWQL 
         laboratory control spikes, 1992-96. Pesticides sorted by analytical method, 
         parameter code, and spike type. GCMS spikes at 0.1 µg/L, HPLC field matrix spikes 
         at 1.0 µg/L, HPLC laboratory control spikes at 0.5 µg/L. Recoveries greater than 
         500 percent were deleted. Recoveries less than 0 percent in field matrix spikes
         were deleted.

   NOTE: Data for field matrix spikes have not been reviewed thoroughly, are provisional, 
         and are subject to revision.

 [Parm, NWIS/STORET parameter code; GCMS, gas chromatography/mass spectrometry; HPLC, 
 high-performance liquid chromatography; FLD, field matrix spikes; LAB, laboratory control 
 spikes; nc, not calculated; *, pesticide identified as poorly performing in method 
 documentation or NWQL memoranda]
---------------------------------------------------------------------------------------------
                                                                                  95-percent
                                                                                    upper 
                                                                                  confidence 
                                                             Number               bound for 
                                                    Number     of      Percent     percent     
                               Analytical  Spike      of     false      false       false     
Parm  Pesticide                  method    type     spikes  negatives  negatives  negatives 
---------------------------------------------------------------------------------------------

04024 Propachlor                  GCMS     FLD       304       0         0.0         1.0
04024 Propachlor                  GCMS     LAB       999       0          .0          .3
04028 Butylate                    GCMS     FLD       308       0          .0         1.0
04028 Butylate                    GCMS     LAB      1002       0          .0          .3
04035 Simazine                    GCMS     FLD       308       0          .0         1.0
04035 Simazine                    GCMS     LAB      1001       0          .0          .3

04037 Prometon                    GCMS     FLD       301       0          .0         1.0
04037 Prometon                    GCMS     LAB      1002      11         1.1         1.8
04040 Deethylatrazine *           GCMS     FLD       308       0          .0         1.0
04040 Deethylatrazine *           GCMS     LAB      1002       0          .0          .3
04041 Cyanazine                   GCMS     FLD       304       0          .0         1.0
04041 Cyanazine                   GCMS     LAB      1002       0          .0          .3

04095 Fonofos                     GCMS     FLD       304       1          .3         1.6
04095 Fonofos                     GCMS     LAB       999       0          .0          .3
34253 alpha-HCH                   GCMS     FLD       304       0          .0         1.0
34253 alpha-HCH                   GCMS     LAB      1002       0          .0          .3
34653 p,p-DDE                     GCMS     FLD       304       0          .0         1.0
34653 p,p-DDE                     GCMS     LAB      1001       0          .0          .3

38933 Chlorpyrifos                GCMS     FLD       304       1          .3         1.6
38933 Chlorpyrifos                GCMS     LAB      1002       0          .0          .3
39341 Lindane                     GCMS     FLD       304       1          .3         1.6
39341 Lindane                     GCMS     LAB      1002       0          .0          .3
39381 Dieldrin                    GCMS     FLD       303       0          .0         1.0
39381 Dieldrin                    GCMS     LAB      1001       0          .0          .3

39415 Metolachlor                 GCMS     FLD       306       4         1.3         3.0
39415 Metolachlor                 GCMS     LAB      1002       0          .0          .3
39532 Malathion                   GCMS     FLD       308       0          .0         1.0
39532 Malathion                   GCMS     LAB      1002       0          .0          .3
39542 Parathion                   GCMS     FLD       304       1          .3         1.6
39542 Parathion                   GCMS     LAB      1002       0          .0          .3

39572 Diazinon                    GCMS     FLD       308       1          .3         1.5
39572 Diazinon                    GCMS     LAB      1002       0          .0          .3
39632 Atrazine                    GCMS     FLD       305       0          .0         1.0
39632 Atrazine                    GCMS     LAB      1002       0          .0          .3
46342 Alachlor                    GCMS     FLD       308       1          .3         1.5
46342 Alachlor                    GCMS     LAB      1001       0          .0          .3

49260 Acetochlor                  GCMS     FLD         0       0          nc          nc
49260 Acetochlor                  GCMS     LAB       646       3          .5         1.2
82630 Metribuzin                  GCMS     FLD       308       0          .0         1.0
82630 Metribuzin                  GCMS     LAB      1002       0          .0          .3
82660 2,6-Diethylaniline          GCMS     FLD       304       2          .7         2.1
82660 2,6-Diethylaniline          GCMS     LAB      1002       0          .0          .3

82661 Trifluralin                 GCMS     FLD       304       0          .0         1.0
82661 Trifluralin                 GCMS     LAB      1002       0          .0          .3
82663 Ethalfluralin               GCMS     FLD       304       0          .0         1.0
82663 Ethalfluralin               GCMS     LAB      1002       0          .0          .3
82664 Phorate                     GCMS     FLD       304       1          .3         1.6
82664 Phorate                     GCMS     LAB      1002       0          .0          .3

82665 Terbacil *                  GCMS     FLD       302       3         1.0         2.5
82665 Terbacil *                  GCMS     LAB      1000       0          .0          .3
82666 Linuron                     GCMS     FLD       303       0          .0         1.0
82666 Linuron                     GCMS     LAB      1001       0          .0          .3
82667 Parathion-methyl            GCMS     FLD       304       1          .3         1.6
82667 Parathion-methyl            GCMS     LAB      1002       0          .0          .3

82668 EPTC                        GCMS     FLD       304       0          .0         1.0
82668 EPTC                        GCMS     LAB      1002       0          .0          .3
82669 Pebulate                    GCMS     FLD       303       0          .0         1.0
82669 Pebulate                    GCMS     LAB      1001       0          .0          .3
82670 Tebuthiuron                 GCMS     FLD       302       1          .3         1.6
82670 Tebuthiuron                 GCMS     LAB      1000       0          .0          .3

82671 Molinate                    GCMS     FLD       303       0          .0         1.0
82671 Molinate                    GCMS     LAB       999       0          .0          .3
82672 Ethoprophos                 GCMS     FLD       304       0          .0         1.0
82672 Ethoprophos                 GCMS     LAB      1002       0          .0          .3
82673 Benfluralin                 GCMS     FLD       304       0          .0         1.0
82673 Benfluralin                 GCMS     LAB      1002       0          .0          .3

82674 Carbofuran *                GCMS     FLD       301       0          .0         1.0
82674 Carbofuran *                GCMS     LAB      1002       0          .0          .3
82675 Terbufos                    GCMS     FLD       304       0          .0         1.0
82675 Terbufos                    GCMS     LAB      1002       0          .0          .3
82676 Propyzamide                 GCMS     FLD       304       1          .3         1.6
82676 Propyzamide                 GCMS     LAB       999       0          .0          .3

82677 Disulfoton                  GCMS     FLD       304       1          .3         1.6
82677 Disulfoton                  GCMS     LAB      1002       4          .4          .9
82678 Tri-allate                  GCMS     FLD       304       0          .0         1.0
82678 Tri-allate                  GCMS     LAB      1002       0          .0          .3
82679 Propanil                    GCMS     FLD       304       0          .0         1.0
82679 Propanil                    GCMS     LAB      1002       0          .0          .3

82680 Carbaryl *                  GCMS     FLD       306       0          .0         1.0
82680 Carbaryl *                  GCMS     LAB      1000       0          .0          .3
82681 Thiobencarb                 GCMS     FLD       304       0          .0         1.0
82681 Thiobencarb                 GCMS     LAB      1002       0          .0          .3
82682 Dacthal                     GCMS     FLD       298       0          .0         1.0
82682 Dacthal                     GCMS     LAB      1002       0          .0          .3

82683 Pendimethalin               GCMS     FLD       304       0          .0         1.0
82683 Pendimethalin               GCMS     LAB      1002       0          .0          .3
82684 Napropamide                 GCMS     FLD       304       0          .0         1.0
82684 Napropamide                 GCMS     LAB      1002       0          .0          .3
82685 Propargite                  GCMS     FLD       304       0          .0         1.0
82685 Propargite                  GCMS     LAB      1001       0          .0          .3

82686 Azinphos-methyl *           GCMS     FLD       304       3         1.0         2.5
82686 Azinphos-methyl *           GCMS     LAB       998       5          .5         1.1
82687 cis-Permethrin              GCMS     FLD       303       2          .7         2.1
82687 cis-Permethrin              GCMS     LAB      1002       0          .0          .3
04029 Bromacil                    HPLC     FLD        81       0          .0         3.6
04029 Bromacil                    HPLC     LAB       694       5          .7         1.5

38442 Dicamba                     HPLC     FLD        73       4         5.5        12.1
38442 Dicamba                     HPLC     LAB       703      17         2.4         3.6
38478 Linuron                     HPLC     FLD        72       1         1.4         6.4
38478 Linuron                     HPLC     LAB       573       4          .7         1.6
38482 MCPA                        HPLC     FLD        76       0          .0         3.9
38482 MCPA                        HPLC     LAB       709      21         3.0         4.2

38487 MCPB                        HPLC     FLD        21       0          .0        13.3
38487 MCPB                        HPLC     LAB       709      83        11.7        13.9
38501 Methiocarb                  HPLC     FLD        67       6         9.0        16.9
38501 Methiocarb                  HPLC     LAB       559       8         1.4         2.6
38538 Propoxur                    HPLC     FLD        79       0          .0         3.7
38538 Propoxur                    HPLC     LAB       610       7         1.1         2.1

38711 Bentazon                    HPLC     FLD        75       0          .0         3.9
38711 Bentazon                    HPLC     LAB       700      13         1.9         2.9
38746 2,4-DB                      HPLC     FLD        79       0          .0         3.7
38746 2,4-DB                      HPLC     LAB       700      43         6.1         7.9
38811 Fluometuron                 HPLC     FLD        79       0          .0         3.7
38811 Fluometuron                 HPLC     LAB       621       5          .8         1.7

38866 Oxamyl                      HPLC     FLD        70       9        12.9        21.4
38866 Oxamyl                      HPLC     LAB       684      17         2.5         3.7
39732 2,4-D                       HPLC     FLD        77       0          .0         3.8
39732 2,4-D                       HPLC     LAB       702      16         2.3         3.4
39742 2,4,5-T                     HPLC     FLD        72       1         1.4         6.4
39742 2,4,5-T                     HPLC     LAB       662      20         3.0         4.4

39762 Silvex                      HPLC     FLD        80       0          .0         3.7
39762 Silvex                      HPLC     LAB       707      13         1.8         2.9
49235 Triclopyr                   HPLC     FLD        21       0          .0        13.3
49235 Triclopyr                   HPLC     LAB       700      17         2.4         3.6
49236 Propham                     HPLC     FLD        57       1         1.8         8.1
49236 Propham                     HPLC     LAB       444       9         2.0         3.5

49291 Picloram                    HPLC     FLD        58       2         3.4        10.5
49291 Picloram                    HPLC     LAB       668      31         4.6         6.2
49292 Oryzalin                    HPLC     FLD        21       0          .0        13.3
49292 Oryzalin                    HPLC     LAB       707       5          .7         1.5
49293 Norflurazon                 HPLC     FLD        21       0          .0        13.3
49293 Norflurazon                 HPLC     LAB       700       3          .4         1.1

49294 Neburon                     HPLC     FLD        81       0          .0         3.6
49294 Neburon                     HPLC     LAB       719       4          .6         1.3
49296 Methomyl                    HPLC     FLD        72       1         1.4         6.4
49296 Methomyl                    HPLC     LAB       675      16         2.4         3.6
49297 Fenuron                     HPLC     FLD        76       0          .0         3.9
49297 Fenuron                     HPLC     LAB       663       4          .6         1.4

49299 DNOC *                      HPLC     FLD        72       1         1.4         6.4
49299 DNOC *                      HPLC     LAB       632      56         8.9        10.9
49300 Diuron                      HPLC     FLD        82       0          .0         3.6
49300 Diuron                      HPLC     LAB       696       5          .7         1.5
49301 Dinoseb                     HPLC     FLD        80       0          .0         3.7
49301 Dinoseb                     HPLC     LAB       707      20         2.8         4.1

49302 Dichlorprop                 HPLC     FLD        80       0          .0         3.7
49302 Dichlorprop                 HPLC     LAB       707      15         2.1         3.2
49303 Dichlobenil *               HPLC     FLD        21       0          .0        13.3
49303 Dichlobenil *               HPLC     LAB       691     114        16.5        19.0
49304 Dacthal monoacid            HPLC     FLD        20       0          .0        13.9
49304 Dacthal monoacid            HPLC     LAB       674      13         1.9         3.0

49305 Clopyralid                  HPLC     FLD        14       4        28.6        54.0
49305 Clopyralid                  HPLC     LAB       660      60         9.1        11.1
49306 Chlorothalonil *            HPLC     FLD        24       1         4.2        18.3
49306 Chlorothalonil *            HPLC     LAB       693     229        33.0        36.1
49307 Chloramben                  HPLC     FLD         8       0          .0        31.2
49307 Chloramben                  HPLC     LAB       496       3          .6         1.6

49308 3-Hydroxycarbofuran         HPLC     FLD        18       0          .0        15.3
49308 3-Hydroxycarbofuran         HPLC     LAB       678      14         2.1         3.2
49309 Carbofuran                  HPLC     FLD        78       0          .0         3.8
49309 Carbofuran                  HPLC     LAB       668       5          .7         1.6
49310 Carbaryl                    HPLC     FLD        81       4         4.9        10.9
49310 Carbaryl                    HPLC     LAB       710       6          .8         1.7

49311 Bromoxynil                  HPLC     FLD        72       0          .0         4.1
49311 Bromoxynil                  HPLC     LAB       657      14         2.1         3.3
49312 Aldicarb *                  HPLC     FLD        66       4         6.1        13.3
49312 Aldicarb *                  HPLC     LAB       702      32         4.6         6.1
49313 Aldicarb sulfone *          HPLC     FLD        70      15        21.4        31.1
49313 Aldicarb sulfone *          HPLC     LAB       655      57         8.7        10.7

49314 Aldicarb sulfoxide *        HPLC     FLD        70       7        10.0        18.0
49314 Aldicarb sulfoxide *        HPLC     LAB       660      35         5.3         7.0
49315 Acifluorfen                 HPLC     FLD        21       0          .0        13.3
49315 Acifluorfen                 HPLC     LAB       704      13         1.8         2.9
---------------------------------------------------------------------------------------------


Table 3. Bias and variability of recovery of pesticides in NAWQA field matrix spikes and NWQL laboratory control spikes, 1992-96. 
         Pesticides sorted by analytical method and parameter code. GCMS spikes at 0.1 µg/L, HPLC field matrix spikes at 
         1.0 µg/L, HPLC laboratory control spikes at 0.5 µg/L. Recoveries greater than 500 percent were deleted. Recoveries less 
         than 0 percent in field matrix spikes were deleted.

     NOTE: Data for field matrix spikes have not been reviewed thoroughly, are provisional, and are subject to revision.

 [Parm, NWIS/STORET parameter code; N, number of spikes; pct, percent; IQR, interquartile range; Min, minimum; Max, maximum; SD, 
 standard deviation; GCMS, gas chromatography/mass spectrometry; HPLC, high-performance liquid chromatography; FLD, field matrix 
 spikes; LAB, laboratory control spikes; nc, not calculated; *, pesticide identified as poorly performing in method documentation 
 or NWQL memoranda]
-----------------------------------------------------------------------------------------------------------------------------------
                                                                            Percentiles of recovery          
                                                           Relative      -----------------------------                    Relative    
                        Analytical Spike       Median  IQR   IQR    Min    10    25    50    75    90   Max   Mean    SD     SD
Parm  Pesticide            method  type    N   (pct)  (pct) (pct)  (pct) (pct) (pct) (pct) (pct) (pct) (pct) (pct)  (pct)  (pct)  
-----------------------------------------------------------------------------------------------------------------------------------

04024 Propachlor            GCMS    FLD   304   94.9  19.8   20.9     6    78    86    95   106   117   211   97.0   19.1   19.7
04024 Propachlor            GCMS    LAB   999   96.8  20.3   21.0     7    74    87    97   107   117   324   96.5   21.9   22.6
04028 Butylate              GCMS    FLD   308   91.6  13.3   14.5    32    80    85    92    99   107   250   93.5   16.6   17.7
04028 Butylate              GCMS    LAB  1002   90.6  10.3   11.4     7    79    85    91    95    99   420   90.5   20.2   22.3
04035 Simazine              GCMS    FLD   308   90.9  25.7   28.2    18    68    77    91   103   111   245   91.2   22.2   24.4
04035 Simazine              GCMS    LAB  1001   93.7  19.0   20.2     5    72    84    94   103   109   254   92.1   18.5   20.1

04037 Prometon              GCMS    FLD   301   93.2  21.5   23.1    20    71    84    93   105   114   167   92.7   19.3   20.8
04037 Prometon              GCMS    LAB  1002   71.8  36.8   51.2     0    22    50    72    87    99   182   66.6   28.4   42.6
04040 Deethylatrazine *     GCMS    FLD   308   31.5  21.8   69.2     3    15    22    31    44    56   127   34.8   19.4   55.8
04040 Deethylatrazine *     GCMS    LAB  1002   38.7  14.8   38.2     2    23    30    39    45    56   110   39.3   14.1   36.0
04041 Cyanazine             GCMS    FLD   304   96.5  31.4   32.5    22    70    83    96   114   136   194   99.5   27.9   28.1
04041 Cyanazine             GCMS    LAB  1002   97.6  29.6   30.4     7    64    82    98   112   123   250   96.2   26.8   27.8

04095 Fonofos               GCMS    FLD   304   86.8  16.8   19.4     0    70    78    87    95   107   184   88.1   17.6   19.9
04095 Fonofos               GCMS    LAB   999   88.4  16.2   18.4     7    70    80    88    96   103   322   87.6   18.5   21.2
34253 alpha-HCH             GCMS    FLD   304   88.9  21.2   23.9    51    73    79    89   101   109   194   90.5   16.7   18.4
34253 alpha-HCH             GCMS    LAB  1002   89.3  18.8   21.1     6    68    79    89    98   109   228   88.8   19.0   21.4
34653 p,p-DDE               GCMS    FLD   304   66.3  18.8   28.3     5    52    58    66    77    86   175   67.9   16.5   24.3
34653 p,p-DDE               GCMS    LAB  1001   59.7  15.1   25.3     5    46    52    60    67    75   158   60.0   13.7   22.9

38933 Chlorpyrifos          GCMS    FLD   304   88.8  24.7   27.8     0    69    78    89   103   116   230   91.0   23.2   25.6
38933 Chlorpyrifos          GCMS    LAB  1002   89.9  20.1   22.4     5    67    79    90    99   111   230   89.0   21.8   24.5
39341 Lindane               GCMS    FLD   304   89.8  18.2   20.2     0    74    82    90   100   114   183   93.0   20.4   21.9
39341 Lindane               GCMS    LAB  1002   89.0  19.0   21.3     9    70    80    89    99   109   219   89.3   19.1   21.4
39381 Dieldrin              GCMS    FLD   303   89.2  21.1   23.6    49    73    80    89   101   113   183   91.0   17.3   19.0
39381 Dieldrin              GCMS    LAB  1001   82.4  17.2   20.9     7    64    74    82    91   103   208   83.0   18.3   22.1

39415 Metolachlor           GCMS    FLD   306  105.7  16.9   16.0     0    89    97   106   114   126   455  107.5   30.1   28.0
39415 Metolachlor           GCMS    LAB  1002  102.9  19.9   19.3     8    85    94   103   114   122   265  103.3   20.7   20.1
39532 Malathion             GCMS    FLD   308   88.6  26.8   30.3    10    59    76    89   103   113   184   88.4   22.6   25.6
39532 Malathion             GCMS    LAB  1002   93.8  25.2   26.9     5    62    79    94   104   112   204   90.0   22.4   24.9
39542 Parathion             GCMS    FLD   304   94.6  27.5   29.0     0    65    80    95   108   124   287   97.7   31.3   32.0
39542 Parathion             GCMS    LAB  1002   92.2  25.0   27.1     9    63    79    92   103   118   229   91.0   23.4   25.8

39572 Diazinon              GCMS    FLD   308   87.9  16.4   18.7     0    70    79    88    96   105   146   87.9   16.3   18.6
39572 Diazinon              GCMS    LAB  1002   86.4  16.8   19.5     7    69    78    86    94   106   278   86.6   19.9   23.0
39632 Atrazine              GCMS    FLD   305   94.9  18.8   19.9     8    76    85    95   104   113   184   94.5   19.3   20.4
39632 Atrazine              GCMS    LAB  1002   94.1  17.6   18.7     6    75    85    94   102   110   258   93.4   18.7   20.0
46342 Alachlor              GCMS    FLD   308  102.0  17.1   16.8     0    87    93   102   110   121   204  101.7   18.6   18.3
46342 Alachlor              GCMS    LAB  1001   99.5  17.7   17.8     8    79    90   100   107   114   224   97.6   18.2   18.7

49260 Acetochlor            GCMS    FLD     0     nc    nc     nc    nc    nc    nc    nc    nc    nc    nc     nc     nc     nc
49260 Acetochlor            GCMS    LAB   646   97.1  12.1   12.5     0    86    91    97   103   112   228   98.1   16.2   16.5
82630 Metribuzin            GCMS    FLD   308   74.3  23.7   31.9    24    47    62    74    86    95   175   73.6   20.3   27.6
82630 Metribuzin            GCMS    LAB  1002   73.9  18.9   25.6     7    54    64    74    83    94   252   73.8   18.5   25.1
82660 2,6-Diethylaniline    GCMS    FLD   304   89.1  12.0   13.4     0    76    82    89    94   100   232   88.9   17.7   19.9
82660 2,6-Diethylaniline    GCMS    LAB  1002   87.8  10.6   12.1     1    77    83    88    93    99   223   87.5   15.2   17.4

82661 Trifluralin           GCMS    FLD   304   77.3  24.1   31.2    27    56    64    77    88    99   204   78.5   21.9   27.9
82661 Trifluralin           GCMS    LAB  1002   71.7  22.6   31.4     7    48    59    72    81    94   201   71.2   20.3   28.6
82663 Ethalfluralin         GCMS    FLD   304   87.3  23.1   26.4    29    61    76    87    99   116   241   89.6   25.8   28.8
82663 Ethalfluralin         GCMS    LAB  1002   81.0  24.8   30.7     8    54    68    81    93   107   218   80.8   22.9   28.3
82664 Phorate               GCMS    FLD   304   76.7  28.6   37.2     0    52    63    77    92   103   184   77.0   22.7   29.4
82664 Phorate               GCMS    LAB  1002   82.3  23.8   29.0     4    50    69    82    93   105   204   80.4   23.3   29.0

82665 Terbacil *            GCMS    FLD   302   86.8  51.6   59.5     0    39    61    87   113   183   426  100.4   66.3   66.1
82665 Terbacil *            GCMS    LAB  1000   74.2  36.5   49.2     4    37    55    74    92   109   261   75.6   33.1   43.8
82666 Linuron               GCMS    FLD   303   87.7  40.7   46.4    13    47    68    88   109   140   403   94.0   49.3   52.4
82666 Linuron               GCMS    LAB  1001   91.5  36.0   39.4     7    55    72    91   108   125   395   95.3   44.9   47.1
82667 Parathion-methyl      GCMS    FLD   304   84.7  28.2   33.3     0    61    72    85   100   120   330   89.6   32.8   36.7
82667 Parathion-methyl      GCMS    LAB  1002   85.2  31.1   36.5     7    50    69    85   100   111   232   84.6   27.1   32.0

82668 EPTC                  GCMS    FLD   304   91.6  15.3   16.7     2    76    84    92   100   107   204   91.9   17.4   19.0
82668 EPTC                  GCMS    LAB  1002   91.8  10.6   11.6     1    81    87    92    97   103   226   91.5   16.0   17.4
82669 Pebulate              GCMS    FLD   303   93.4  18.5   19.8    30    77    84    93   102   107   204   93.2   16.1   17.3
82669 Pebulate              GCMS    LAB  1001   91.0  10.9   12.0     7    80    86    91    97   103   445   91.2   22.2   24.3
82670 Tebuthiuron           GCMS    FLD   302   84.4  32.0   38.0     0    57    71    84   103   120   430   90.2   42.1   46.6
82670 Tebuthiuron           GCMS    LAB  1000   99.7  42.7   42.8     7    63    79   100   121   140   353  101.2   32.8   32.4

82671 Molinate              GCMS    FLD   303   94.6  18.8   19.8    29    76    86    95   104   113   192   95.1   16.5   17.4
82671 Molinate              GCMS    LAB   999   93.7  10.4   11.1     6    82    89    94    99   104   357   93.3   18.0   19.3
82672 Ethoprophos           GCMS    FLD   304   93.7  20.4   21.8    47    74    84    94   104   114   202   94.8   17.7   18.6
82672 Ethoprophos           GCMS    LAB  1002   92.3  18.5   20.0     6    72    83    92   101   109   215   91.2   19.5   21.3
82673 Benfluralin           GCMS    FLD   304   77.8  26.8   34.5    33    53    60    78    87   104   204   77.7   22.8   29.4
82673 Benfluralin           GCMS    LAB  1002   70.4  22.2   31.6     6    45    58    70    80    91   201   69.7   21.0   30.1

82674 Carbofuran *          GCMS    FLD   301  105.6  50.8   48.1     8    58    83   106   134   189   466  114.4   55.9   48.8
82674 Carbofuran *          GCMS    LAB  1002   96.7  66.8   69.0     1    32    59    97   126   159   395   95.8   48.4   50.5
82675 Terbufos              GCMS    FLD   304   89.7  25.0   27.9    30    63    75    90   100   113   194   89.3   22.1   24.7
82675 Terbufos              GCMS    LAB  1002   86.0  27.2   31.6     8    56    72    86    99   112   244   85.6   24.5   28.6
82676 Propyzamide           GCMS    FLD   304   83.7  20.9   25.0     0    67    74    84    95   109   177   86.6   20.2   23.3
82676 Propyzamide           GCMS    LAB   999   84.4  20.5   24.2     6    62    73    84    94   103   374   83.4   20.7   24.8

82677 Disulfoton            GCMS    FLD   304   86.3  55.2   64.0     0    54    65    86   120   143   290   94.1   40.5   43.1
82677 Disulfoton            GCMS    LAB  1002   85.4  52.8   61.9     0    30    61    85   114   159   305   91.1   51.4   56.3
82678 Tri-allate            GCMS    FLD   304   90.0  13.2   14.7     4    76    84    90    97   105   165   90.7   14.5   16.0
82678 Tri-allate            GCMS    LAB  1002   89.2  15.6   17.5     7    73    81    89    97   103   242   88.3   16.8   19.1
82679 Propanil              GCMS    FLD   304   94.2  23.7   25.2    37    77    83    94   107   118   204   96.8   20.1   20.8
82679 Propanil              GCMS    LAB  1002  101.3  26.0   25.6     5    74    87   101   113   122   276   99.3   22.8   22.9

82680 Carbaryl *            GCMS    FLD   306   98.5  75.4   76.5    13    40    67    99   142   200   456  115.0   72.6   63.1
82680 Carbaryl *            GCMS    LAB  1000   98.4 101.4  103.1     1    20    44    98   145   185   329   99.6   62.0   62.2
82681 Thiobencarb           GCMS    FLD   304   98.4  19.4   19.7    54    83    88    98   107   120   187  100.1   18.7   18.7
82681 Thiobencarb           GCMS    LAB  1002   98.3  18.9   19.2     7    77    88    98   107   114   272   96.9   19.4   20.0
82682 Dacthal               GCMS    FLD   298  105.1  24.2   23.1    66    87    94   105   118   143   223  109.8   23.4   21.3
82682 Dacthal               GCMS    LAB  1002  100.7  18.8   18.7     4    82    91   101   110   121   250  100.9   20.9   20.7

82683 Pendimethalin         GCMS    FLD   304   76.6  29.8   38.9    35    52    62    77    91   103   213   79.5   28.6   36.0
82683 Pendimethalin         GCMS    LAB  1002   70.2  26.0   37.0     7    47    58    70    84    98   218   72.1   23.2   32.2
82684 Napropamide           GCMS    FLD   304  100.9  18.6   18.4    47    83    91   101   109   117   218  101.2   17.8   17.6
82684 Napropamide           GCMS    LAB  1002   97.0  16.8   17.4     9    80    88    97   105   115   260   97.0   18.4   19.0
82685 Propargite            GCMS    FLD   304   86.6  40.1   46.3    11    59    70    87   110   155   330   97.7   44.2   45.3
82685 Propargite            GCMS    LAB  1001   73.4  27.9   38.1     5    50    61    73    89   110   315   78.4   30.9   39.4

82686 Azinphos-methyl *     GCMS    FLD   304   81.5  64.8   79.6     0    31    51    81   116   171   473   96.7   72.8   75.3
82686 Azinphos-methyl *     GCMS    LAB   998   53.9  62.0  115.1     0    15    30    54    92   130   453   67.6   53.1   78.6
82687 cis-Permethrin        GCMS    FLD   303   58.3  73.8  126.6     0    38    47    58   121   258   390   96.6   83.5   86.4
82687 cis-Permethrin        GCMS    LAB  1002   37.5  41.9  111.8     2    10    13    37    55    80   177   39.7   32.3   81.2
04029 Bromacil              HPLC    FLD    81   77.0  19.2   25.0    11    63    68    77    88   105   173   80.9   22.0   27.2
04029 Bromacil              HPLC    LAB   694   81.0  21.0   25.9     0    58    71    81    92   105   154   80.9   20.5   25.3

38442 Dicamba               HPLC    FLD    73   65.8  30.2   45.9     0     8    45    66    75    82   213   60.4   35.0   57.9
38442 Dicamba               HPLC    LAB   703   73.0  31.0   42.5     0    26    53    73    84    93   128   66.2   25.8   38.9
38478 Linuron               HPLC    FLD    72  116.0  45.8   39.5     0    84    91   116   137   157   195  116.1   33.4   28.7
38478 Linuron               HPLC    LAB   573   81.0  24.0   29.6     0    51    68    81    92   105   173   79.1   22.9   28.9
38482 MCPA                  HPLC    FLD    76   60.2  16.2   26.9    19    46    53    60    69    77    95   61.2   12.9   21.1
38482 MCPA                  HPLC    LAB   709   73.0  33.0   45.2     0    24    52    73    85    95   141   66.3   27.2   41.0

38487 MCPB                  HPLC    FLD    21   73.7  20.9   28.4    59    66    67    74    88    90   107   77.6   12.3   15.8
38487 MCPB                  HPLC    LAB   709   42.0  62.0  147.6     0     0    12    42    74    85   128   43.3   32.9   75.9
38501 Methiocarb            HPLC    FLD    67   45.1  66.5  147.3     0     2    16    45    82    89   150   48.7   36.0   73.8
38501 Methiocarb            HPLC    LAB   559   77.0  37.0   48.1     0    25    54    77    91   103   178   71.7   30.2   42.0
38538 Propoxur              HPLC    FLD    79   62.2  26.0   41.8    24    42    50    62    76    96   138   64.9   21.3   32.8
38538 Propoxur              HPLC    LAB   610   75.0  25.0   33.3     0    47    63    75    88   100   149   74.2   21.7   29.2

38711 Bentazon              HPLC    FLD    75   72.0  19.5   27.0    16    49    61    72    80    92   119   69.8   19.9   28.5
38711 Bentazon              HPLC    LAB   700   80.0  26.0   32.5     0    40    65    80    91   101   154   75.2   25.2   33.5
38746 2,4-DB                HPLC    FLD    79   51.6  39.8   77.1    13    31    37    52    77    90    97   55.4   22.0   39.6
38746 2,4-DB                HPLC    LAB   700   47.0  60.0  127.7     0     3    18    47    78    91   129   48.2   32.7   67.8
38811 Fluometuron           HPLC    FLD    79   77.0  20.9   27.2    21    59    68    77    89   101   131   79.0   18.2   23.1
38811 Fluometuron           HPLC    LAB   621   84.0  27.0   32.1     0    53    71    84    98   111   162   83.2   24.1   29.0

38866 Oxamyl                HPLC    FLD    70   15.6  33.4  213.9     0     0     7    16    40    68   102   26.3   25.8   97.8
38866 Oxamyl                HPLC    LAB   684   64.0  44.3   69.1     0    14    35    64    79    91   146   57.8   28.9   50.0
39732 2,4-D                 HPLC    FLD    77   70.0  20.7   29.6    42    53    61    70    81    87   114   70.6   13.9   19.6
39732 2,4-D                 HPLC    LAB   702   75.0  29.0   38.7     0    36    57    75    86    97   143   70.2   25.0   35.6
39742 2,4,5-T               HPLC    FLD    72   75.5  20.9   27.6     0    53    68    76    88   106   166   78.9   25.8   32.7
39742 2,4,5-T               HPLC    LAB   662   75.0  23.0   30.7     0    41    62    75    85    98   193   72.9   26.2   35.9

39762 Silvex                HPLC    FLD    80   76.1  17.9   23.5    44    60    66    76    84    91   116   75.8   13.4   17.7
39762 Silvex                HPLC    LAB   707   80.0  25.0   31.3     0    46    64    80    89   100   139   75.1   23.5   31.2
49235 Triclopyr             HPLC    FLD    21   49.3   9.5   19.3    31    36    44    49    53    65    91   51.2   14.6   28.5
49235 Triclopyr             HPLC    LAB   700   73.0  35.0   47.9     0    28    50    73    85    95   120   66.8   25.7   38.5
49236 Propham               HPLC    FLD    57  132.4  92.3   69.7     0    55    77   132   169   191   199  122.7   51.5   42.0
49236 Propham               HPLC    LAB   444   62.0  34.0   54.8     0    30    46    62    80    91   134   61.8   24.4   39.5

49291 Picloram              HPLC    FLD    58   61.7  31.0   50.3     0    38    48    62    79    89   103   61.9   23.0   37.2
49291 Picloram              HPLC    LAB   668   63.0  40.5   64.3     0    20    40    63    81    89   167   59.0   27.7   46.9
49292 Oryzalin              HPLC    FLD    21   77.8   9.0   11.6    33    44    72    78    81    92   111   73.8   20.4   27.7
49292 Oryzalin              HPLC    LAB   707   70.0  28.0   40.0     0    43    58    70    86    98   202   70.9   22.7   32.0
49293 Norflurazon           HPLC    FLD    21   83.5  11.0   13.1    60    75    79    84    90    98   110   84.8   11.9   14.0
49293 Norflurazon           HPLC    LAB   700   83.0  24.0   28.9     0    56    72    83    96   107   159   82.4   21.6   26.2

49294 Neburon               HPLC    FLD    81   66.7  29.6   44.3    31    47    51    67    81    89   106   67.0   17.4   26.0
49294 Neburon               HPLC    LAB   719   76.0  27.0   35.5     0    45    62    76    89   102   148   74.9   23.0   30.7
49296 Methomyl              HPLC    FLD    72   71.3  21.2   29.7     0    56    64    71    85    97   113   72.8   20.3   27.9
49296 Methomyl              HPLC    LAB   675   80.0  25.0   31.3     0    46    68    80    93   106   164   78.3   26.4   33.6
49297 Fenuron               HPLC    FLD    76   78.4  31.6   40.3    27    58    68    78   100   140   212   90.6   35.7   39.4
49297 Fenuron               HPLC    LAB   663   80.0  41.0   51.3     0    37    53    80    94   104   212   75.5   27.9   37.0

49299 DNOC *                HPLC    FLD    72   63.8  24.3   38.1     0    37    49    64    73    82   128   61.1   20.4   33.5
49299 DNOC *                HPLC    LAB   632   36.0  27.0   75.0     0     4    21    36    48    61    96   35.1   20.6   58.5
49300 Diuron                HPLC    FLD    82   55.8  36.7   65.7     2    33    40    56    77    89   102   59.0   21.8   37.0
49300 Diuron                HPLC    LAB   696   71.0  34.0   47.9     0    36    52    71    86    96   178   68.1   24.3   35.6
49301 Dinoseb               HPLC    FLD    80   70.3  25.4   36.1    39    50    57    70    83    91   120   70.5   16.9   24.0
49301 Dinoseb               HPLC    LAB   707   76.0  25.0   32.9     0    36    61    76    86    94   146   70.5   24.2   34.4

49302 Dichlorprop           HPLC    FLD    80   74.6  19.2   25.7    23    57    64    75    83    93   112   74.3   14.8   20.0
49302 Dichlorprop           HPLC    LAB   707   78.0  26.0   33.3     0    34    62    78    88    98   138   72.3   25.7   35.5
49303 Dichlobenil *         HPLC    FLD    21   61.7  12.7   20.6    32    44    56    62    68    70    81   60.4   11.4   18.9
49303 Dichlobenil *         HPLC    LAB   691   29.0  49.0  169.0     0     0     6    29    55    70   117   32.6   27.6   84.5
49304 Dacthal monoacid      HPLC    FLD    20   74.2  23.3   31.4     6    28    59    74    82    87    93   66.1   23.1   34.9
49304 Dacthal monoacid      HPLC    LAB   674   79.0  22.0   27.8     0    46    66    79    88    96   131   74.7   21.6   29.0

49305 Clopyralid            HPLC    FLD    14   48.8  59.5  121.9     0     0     0    49    60    87    87   39.7   32.8   82.6
49305 Clopyralid            HPLC    LAB   660   66.0  40.5   61.4     0     2    41    66    81    94   155   59.3   31.1   52.4
49306 Chlorothalonil *      HPLC    FLD    24   49.9  36.9   74.0     0     7    24    50    61    70    93   43.5   24.7   56.9
49306 Chlorothalonil *      HPLC    LAB   693    6.0  36.0  600.0     0     0     0     6    36    54   129   18.7   24.2  129.7
49307 Chloramben            HPLC    FLD     8   62.3  12.8   20.5    55    55    59    62    71    76    76   64.4    7.8   12.2
49307 Chloramben            HPLC    LAB   496   61.0  24.5   40.2     0    34    50    61    74    84   128   61.0   19.1   31.3

49308 3-Hydroxycarbofuran   HPLC    FLD    18   79.6  29.3   36.8    14    55    66    80    96   111   115   79.7   24.5   30.7
49308 3-Hydroxycarbofuran   HPLC    LAB   678   70.0  33.0   47.1     0    26    49    70    82    95   184   65.6   26.7   40.7
49309 Carbofuran            HPLC    FLD    78   66.0  29.2   44.2    23    34    53    66    82   110   173   69.4   27.8   40.0
49309 Carbofuran            HPLC    LAB   668   79.0  27.0   34.2     0    50    66    79    93   110   449   80.8   32.0   39.6
49310 Carbaryl              HPLC    FLD    81   32.5  61.0  187.7     0     6    13    32    74    84   103   41.9   31.4   75.0
49310 Carbaryl              HPLC    LAB   710   77.0  40.0   51.9     0    23    50    77    90   100   201   69.3   29.0   41.8

49311 Bromoxynil            HPLC    FLD    72   76.6  19.8   25.9    51    61    67    77    87    92   115   78.0   13.8   17.7
49311 Bromoxynil            HPLC    LAB   657   81.0  25.0   30.9     0    42    66    81    91   101   145   75.4   24.9   33.0
49312 Aldicarb *            HPLC    FLD    66   50.5  37.3   73.7     0     9    31    51    69    92   117   51.5   28.5   55.4
49312 Aldicarb *            HPLC    LAB   702   50.0  35.0   70.0     0    14    32    50    67    84   150   50.3   27.0   53.7
49313 Aldicarb sulfone *    HPLC    FLD    70   18.2  24.0  131.7     0     0     7    18    31    40    65   20.0   15.7   78.4
49313 Aldicarb sulfone *    HPLC    LAB   655   50.0  33.0   66.0     0    15    34    50    67    83   150   50.3   26.7   53.1

49314 Aldicarb sulfoxide *  HPLC    FLD    70   61.0  37.4   61.4     0     2    41    61    79   103   122   58.7   31.8   54.2
49314 Aldicarb sulfoxide *  HPLC    LAB   660   88.0  41.5   47.2     0    39    70    88   111   134   204   87.7   38.6   44.1
49315 Acifluorfen           HPLC    FLD    21   81.4  12.2   14.9    35    74    78    81    90    97   103   81.6   13.6   16.7
49315 Acifluorfen           HPLC    LAB   704   84.0  25.0   29.8     0    49    69    84    94   108   200   80.5   26.3   32.7
-----------------------------------------------------------------------------------------------------------------------------------


Table 4. Uncertainty in selected measures of bias and variability of recovery of pesticides in NAWQA field matrix spikes and NWQL 
         laboratory control spikes, 1992-96. Pesticides sorted by analytical method and parameter code. GCMS spikes at 0.1 µg/L, 
         HPLC field matrix spikes at 1.0 µg/L, HPLC laboratory control spikes at 0.5 µg/L. Recoveries greater than 500 percent were 
         deleted. Recoveries less than 0 percent in field matrix spikes were deleted.

    NOTE: Data for field matrix spikes have not been reviewed thoroughly, are provisional, and are subject to revision.

 [Parm, NWIS/STORET parameter code; N, number of spikes; pct, percent; IQR, interquartile range; Min, minimum; Max, maximum; SD, 
 standard deviation; GCMS, gas chromatography/mass spectrometry; HPLC, high-performance liquid chromatography; FLD, field matrix 
 spikes; LAB, laboratory control spikes; nc, not calculated; *, pesticide identified as poorly performing in method documentation 
 or NWQL memoranda; iss, insufficient sample size to calculate a 95-percent confidence bound]
--------------------------------------------------------------------------------------------------------------------------------------
                                                                               95-percent            95-percent 
                                                                                  lower                 upper
                                                                               confidence            confidence 
                                                         95-percent              bound or              bound or            95-percent
                                                            lower              90-percent            90-percent               upper
                                                         confidence               lower                 upper              confidence
                                                          bound for            confidence            confidence             bound for
                                                            10th       10th     limit for             limit for    90th       90th  
                                                         percentile percentile   median     Median     median   percentile percentile
                               Analytical Spike           recovery   recovery   recovery   recovery   recovery   recovery   recovery
Parm  Pesticide                  method    type     N       (pct)      (pct)      (pct)      (pct)      (pct)      (pct)      (pct)
--------------------------------------------------------------------------------------------------------------------------------------

04024 Propachlor                  GCMS     FLD     304       75.5       78.3       93.5       94.9       96.0      116.9      121.0
04024 Propachlor                  GCMS     LAB     999       72.6       74.4       95.7       96.8       98.2      116.7      118.6
04028 Butylate                    GCMS     FLD     308       77.4       79.5       90.9       91.6       92.6      107.0      110.0
04028 Butylate                    GCMS     LAB    1002       78.0       79.4       90.1       90.6       91.0       99.4      100.3
04035 Simazine                    GCMS     FLD     308       65.0       68.0       89.1       90.9       92.7      111.0      116.8
04035 Simazine                    GCMS     LAB    1001       69.6       72.0       92.7       93.7       94.6      108.9      110.0

04037 Prometon                    GCMS     FLD     301       66.3       71.0       91.1       93.2       95.2      114.0      115.9
04037 Prometon                    GCMS     LAB    1002       17.0       21.8       70.5       71.8       73.3       98.8      100.2
04040 Deethylatrazine *           GCMS     FLD     308       12.1       14.9       29.6       31.5       33.9       55.7       59.8
04040 Deethylatrazine *           GCMS     LAB    1002       22.6       23.4       37.9       38.7       39.4       55.7       58.5
04041 Cyanazine                   GCMS     FLD     304       64.8       69.8       93.9       96.5       99.0      135.9      142.7
04041 Cyanazine                   GCMS     LAB    1002       60.5       63.9       96.2       97.6       98.9      123.4      125.1

04095 Fonofos                     GCMS     FLD     304       69.1       70.4       85.0       86.8       87.9      107.4      112.3
04095 Fonofos                     GCMS     LAB     999       68.2       70.3       87.6       88.4       89.0      102.8      104.0
34253 alpha-HCH                   GCMS     FLD     304       71.3       73.3       86.7       88.9       90.7      108.7      112.1
34253 alpha-HCH                   GCMS     LAB    1002       66.3       68.3       88.4       89.3       90.1      109.5      111.4
34653 p,p-DDE                     GCMS     FLD     304       48.3       51.9       64.4       66.3       68.6       85.8       87.3
34653 p,p-DDE                     GCMS     LAB    1001       43.9       46.1       59.1       59.7       60.5       75.3       76.5

38933 Chlorpyrifos                GCMS     FLD     304       64.8       68.7       87.3       88.8       90.9      115.8      119.6
38933 Chlorpyrifos                GCMS     LAB    1002       64.5       67.1       88.6       89.9       90.7      110.5      112.9
39341 Lindane                     GCMS     FLD     304       71.6       74.3       88.4       89.8       91.5      114.2      124.4
39341 Lindane                     GCMS     LAB    1002       68.3       69.5       87.8       89.0       90.0      109.4      110.7
39381 Dieldrin                    GCMS     FLD     303       69.6       72.7       87.3       89.2       90.9      113.2      115.3
39381 Dieldrin                    GCMS     LAB    1001       62.7       64.1       81.0       82.4       83.2      103.3      105.5

39415 Metolachlor                 GCMS     FLD     306       86.4       88.5      104.7      105.7      106.9      126.5      130.8
39415 Metolachlor                 GCMS     LAB    1002       83.0       85.3      101.9      102.9      104.0      121.8      122.8
39532 Malathion                   GCMS     FLD     308       54.7       59.0       87.3       88.6       89.7      113.0      114.9
39532 Malathion                   GCMS     LAB    1002       59.7       62.2       92.6       93.8       94.5      112.1      113.6
39542 Parathion                   GCMS     FLD     304       63.2       65.3       92.0       94.6       97.2      123.8      134.3
39542 Parathion                   GCMS     LAB    1002       60.0       62.9       91.0       92.2       93.5      117.6      120.5

39572 Diazinon                    GCMS     FLD     308       67.7       69.8       86.6       87.9       89.3      105.5      109.2
39572 Diazinon                    GCMS     LAB    1002       66.4       68.7       85.5       86.4       87.1      105.8      107.7
39632 Atrazine                    GCMS     FLD     305       72.9       75.6       92.9       94.9       96.1      112.6      116.8
39632 Atrazine                    GCMS     LAB    1002       73.7       75.2       93.5       94.1       94.8      109.5      110.7
46342 Alachlor                    GCMS     FLD     308       84.1       87.0      100.0      102.0      103.5      120.8      122.3
46342 Alachlor                    GCMS     LAB    1001       76.9       79.4       98.6       99.5      100.4      113.9      115.4

49260 Acetochlor                  GCMS     FLD       0         nc         nc         nc         nc         nc         nc         nc
49260 Acetochlor                  GCMS     LAB     646       84.5       85.6       96.3       97.1       97.8      111.5      114.2
82630 Metribuzin                  GCMS     FLD     308       40.8       46.8       72.2       74.3       76.3       95.0       99.4
82630 Metribuzin                  GCMS     LAB    1002       52.1       53.6       72.8       73.9       74.7       93.8       95.4
82660 2,6-Diethylaniline          GCMS     FLD     304       72.5       76.2       88.0       89.1       89.7      100.0      104.7
82660 2,6-Diethylaniline          GCMS     LAB    1002       75.1       76.5       87.2       87.8       88.4       99.0       99.9

82661 Trifluralin                 GCMS     FLD     304       54.0       56.2       74.5       77.3       78.7       99.1      106.5
82661 Trifluralin                 GCMS     LAB    1002       46.1       47.6       70.5       71.7       72.7       93.5       95.7
82663 Ethalfluralin               GCMS     FLD     304       56.4       61.3       84.9       87.3       89.3      115.6      128.4
82663 Ethalfluralin               GCMS     LAB    1002       51.0       54.0       79.7       81.0       82.0      107.1      109.4
82664 Phorate                     GCMS     FLD     304       46.3       51.7       75.1       76.7       79.3      102.7      105.8
82664 Phorate                     GCMS     LAB    1002       48.2       49.9       81.3       82.3       83.5      105.1      109.3

82665 Terbacil *                  GCMS     FLD     302       35.3       38.9       81.5       86.8       89.7      182.8      202.8
82665 Terbacil *                  GCMS     LAB    1000       34.3       37.1       72.9       74.2       75.4      109.1      112.5
82666 Linuron                     GCMS     FLD     303       37.0       47.0       85.3       87.7       91.6      140.3      146.7
82666 Linuron                     GCMS     LAB    1001       51.7       54.9       89.8       91.5       93.4      124.8      130.5
82667 Parathion-methyl            GCMS     FLD     304       58.2       60.9       83.3       84.7       87.0      120.3      132.5
82667 Parathion-methyl            GCMS     LAB    1002       47.8       50.0       84.0       85.2       86.6      111.4      114.9

82668 EPTC                        GCMS     FLD     304       71.6       76.3       90.2       91.6       92.7      107.2      112.6
82668 EPTC                        GCMS     LAB    1002       80.2       81.1       91.3       91.8       92.3      103.0      103.6
82669 Pebulate                    GCMS     FLD     303       74.7       77.3       91.6       93.4       94.5      107.3      108.8
82669 Pebulate                    GCMS     LAB    1001       78.1       79.5       90.5       91.0       91.7      102.7      103.6
82670 Tebuthiuron                 GCMS     FLD     302       50.5       57.3       81.5       84.4       87.9      119.6      133.1
82670 Tebuthiuron                 GCMS     LAB    1000       60.8       62.8       97.6       99.7      102.0      139.6      142.3

82671 Molinate                    GCMS     FLD     303       72.0       75.9       93.2       94.6       95.9      113.2      114.2
82671 Molinate                    GCMS     LAB     999       80.9       81.7       93.1       93.7       94.3      103.9      105.0
82672 Ethoprophos                 GCMS     FLD     304       71.5       74.2       91.7       93.7       94.9      114.2      118.2
82672 Ethoprophos                 GCMS     LAB    1002       69.6       71.8       91.4       92.3       93.2      108.8      110.3
82673 Benfluralin                 GCMS     FLD     304       51.2       53.0       75.1       77.8       80.0      103.5      108.7
82673 Benfluralin                 GCMS     LAB    1002       43.8       45.1       69.4       70.4       71.3       91.3       93.2

82674 Carbofuran *                GCMS     FLD     301       53.2       57.6      101.8      105.6      109.8      188.8      200.0
82674 Carbofuran *                GCMS     LAB    1002       27.5       31.6       93.6       96.7       99.6      158.7      163.1
82675 Terbufos                    GCMS     FLD     304       60.9       63.0       86.3       89.7       91.5      113.2      118.2
82675 Terbufos                    GCMS     LAB    1002       54.6       56.5       85.0       86.0       87.2      112.0      114.6
82676 Propyzamide                 GCMS     FLD     304       65.2       67.2       82.1       83.7       85.7      108.9      112.9
82676 Propyzamide                 GCMS     LAB     999       60.6       62.2       83.5       84.4       85.3      102.8      104.3

82677 Disulfoton                  GCMS     FLD     304       48.7       53.7       79.9       86.3       92.0      142.8      149.4
82677 Disulfoton                  GCMS     LAB    1002       22.7       30.0       82.7       85.4       88.2      158.7      165.9
82678 Tri-allate                  GCMS     FLD     304       74.0       76.1       88.8       90.0       90.9      104.7      110.5
82678 Tri-allate                  GCMS     LAB    1002       70.6       72.9       88.5       89.2       89.8      103.3      104.8
82679 Propanil                    GCMS     FLD     304       74.5       76.6       92.2       94.2       96.5      117.6      122.8
82679 Propanil                    GCMS     LAB    1002       71.6       73.7      100.0      101.3      102.4      122.4      123.7

82680 Carbaryl *                  GCMS     FLD     306       33.9       40.2       94.4       98.5      103.7      199.9      225.5
82680 Carbaryl *                  GCMS     LAB    1000       18.6       19.9       93.0       98.4      101.6      185.1      190.4
82681 Thiobencarb                 GCMS     FLD     304       78.6       82.5       96.5       98.4      100.0      120.0      124.2
82681 Thiobencarb                 GCMS     LAB    1002       74.6       77.0       97.5       98.3       99.3      114.0      115.2
82682 Dacthal                     GCMS     FLD     298       84.1       87.5      104.1      105.1      107.0      142.6      145.4
82682 Dacthal                     GCMS     LAB    1002       79.5       81.7       99.8      100.7      101.4      121.1      123.0

82683 Pendimethalin               GCMS     FLD     304       47.1       51.7       73.3       76.6       79.3      102.8      111.2
82683 Pendimethalin               GCMS     LAB    1002       44.5       47.2       69.0       70.2       71.7       97.8       99.9
82684 Napropamide                 GCMS     FLD     304       80.4       83.1       99.4      100.9      103.0      116.8      120.8
82684 Napropamide                 GCMS     LAB    1002       79.6       80.3       96.2       97.0       97.5      114.6      116.7
82685 Propargite                  GCMS     FLD     304       53.0       59.2       82.4       86.6       90.0      155.3      182.6
82685 Propargite                  GCMS     LAB    1001       47.8       49.7       72.7       73.4       74.5      110.4      116.3

82686 Azinphos-methyl *           GCMS     FLD     304       25.6       30.8       73.9       81.5       89.6      171.0      214.0
82686 Azinphos-methyl *           GCMS     LAB     998       12.9       15.3       51.2       53.9       57.0      129.8      137.0
82687 cis-Permethrin              GCMS     FLD     303       34.3       38.0       56.7       58.3       62.2      257.8      273.3
82687 cis-Permethrin              GCMS     LAB    1002        9.8       10.1       32.0       37.5       40.4       80.2       85.0
04029 Bromacil                    HPLC     FLD      81       52.1       63.0       74.3       77.0       81.4      105.2      127.1
04029 Bromacil                    HPLC     LAB     694       55.0       58.0       79.0       81.0       82.0      105.0      108.0

38442 Dicamba                     HPLC     FLD      73         .0        7.7       56.8       65.8       71.2       81.7       90.2
38442 Dicamba                     HPLC     LAB     703       17.0       26.0       71.0       73.0       74.0       93.0       95.0
38478 Linuron                     HPLC     FLD      72       69.0       83.7      101.3      116.0      131.3      156.9      190.3
38478 Linuron                     HPLC     LAB     573       45.0       51.0       79.0       81.0       83.0      105.0      106.0
38482 MCPA                        HPLC     FLD      76       40.8       46.5       57.6       60.2       64.8       77.4       81.6
38482 MCPA                        HPLC     LAB     709       18.0       24.0       70.0       73.0       75.0       95.0       97.0

38487 MCPB                        HPLC     FLD      21        iss       65.7       68.1       73.7       85.7       90.4        iss
38487 MCPB                        HPLC     LAB     709         .0         .0       34.0       42.0       49.0       85.0       87.0
38501 Methiocarb                  HPLC     FLD      67         .0        1.8       30.9       45.1       69.1       89.3       92.0
38501 Methiocarb                  HPLC     LAB     559       17.0       25.0       75.0       77.0       80.0      103.0      106.0
38538 Propoxur                    HPLC     FLD      79       28.5       41.8       58.0       62.2       65.4       95.6      104.5
38538 Propoxur                    HPLC     LAB     610       44.0       46.5       73.0       75.0       76.0      100.0      101.0

38711 Bentazon                    HPLC     FLD      75       18.9       48.6       68.0       72.0       74.8       92.0      103.4
38711 Bentazon                    HPLC     LAB     700       34.0       40.0       79.0       80.0       82.0      101.0      102.0
38746 2,4-DB                      HPLC     FLD      79       26.2       31.3       43.3       51.6       57.0       89.6       93.1
38746 2,4-DB                      HPLC     LAB     700        2.0        3.0       42.0       47.0       51.0       91.0       93.0
38811 Fluometuron                 HPLC     FLD      79       52.8       59.0       74.4       77.0       80.5      100.7      119.7
38811 Fluometuron                 HPLC     LAB     621       48.0       53.0       82.0       84.0       85.0      111.0      114.0

38866 Oxamyl                      HPLC     FLD      70         .0         .0       11.1       15.6       26.6       68.5       75.8
38866 Oxamyl                      HPLC     LAB     684       11.0       14.0       62.0       64.0       66.0       91.0       94.0
39732 2,4-D                       HPLC     FLD      77       47.0       53.2       66.0       70.0       72.6       86.8       97.5
39732 2,4-D                       HPLC     LAB     702       32.0       36.0       74.0       75.0       77.0       97.0       99.0
39742 2,4,5-T                     HPLC     FLD      72       37.4       53.5       71.3       75.5       78.8      105.6      142.0
39742 2,4,5-T                     HPLC     LAB     662       37.0       41.0       74.0       75.0       76.0       98.0      103.0

39762 Silvex                      HPLC     FLD      80       55.9       59.5       72.2       76.1       78.5       91.2      101.2
39762 Silvex                      HPLC     LAB     707       42.0       46.0       78.0       80.0       81.0      100.0      101.0
49235 Triclopyr                   HPLC     FLD      21        iss       36.4       43.9       49.3       52.9       65.3        iss
49235 Triclopyr                   HPLC     LAB     700       26.0       28.0       72.0       73.0       75.0       95.0       97.0
49236 Propham                     HPLC     FLD      57       15.6       55.3       96.5      132.4      147.3      190.9      197.7
49236 Propham                     HPLC     LAB     444       25.0       30.0       60.0       62.0       65.0       91.0       95.0

49291 Picloram                    HPLC     FLD      58         .0       38.4       56.6       61.7       70.9       88.8      100.7
49291 Picloram                    HPLC     LAB     668       14.0       20.0       61.0       63.0       64.0       89.0       92.0
49292 Oryzalin                    HPLC     FLD      21        iss       43.9       72.9       77.8       80.8       92.2        iss
49292 Oryzalin                    HPLC     LAB     707       40.0       43.0       69.0       70.0       72.0       98.0      100.0
49293 Norflurazon                 HPLC     FLD      21        iss       74.8       79.4       83.5       90.2       97.7        iss
49293 Norflurazon                 HPLC     LAB     700       51.0       56.0       82.0       83.0       85.0      107.0      109.0

49294 Neburon                     HPLC     FLD      81       38.6       46.7       60.9       66.7       71.0       89.2       98.2
49294 Neburon                     HPLC     LAB     719       41.0       45.0       75.0       76.0       78.0      102.0      105.0
49296 Methomyl                    HPLC     FLD      72       18.0       55.9       68.3       71.3       78.1       97.0      104.0
49296 Methomyl                    HPLC     LAB     675       41.0       46.0       79.0       80.0       82.0      106.0      109.0
49297 Fenuron                     HPLC     FLD      76       54.8       57.7       75.4       78.4       84.2      140.0      155.5
49297 Fenuron                     HPLC     LAB     663       35.0       37.0       78.0       80.0       83.0      104.0      107.0

49299 DNOC *                      HPLC     FLD      72       18.3       37.0       58.6       63.8       67.1       81.7       97.9
49299 DNOC *                      HPLC     LAB     632         .0        4.0       34.0       36.0       38.0       61.0       64.0
49300 Diuron                      HPLC     FLD      82       30.7       33.4       50.7       55.8       61.5       89.0       94.3
49300 Diuron                      HPLC     LAB     696       33.0       36.0       68.0       71.0       74.0       96.0       97.0
49301 Dinoseb                     HPLC     FLD      80       45.0       50.2       65.4       70.3       75.5       91.4       96.8
49301 Dinoseb                     HPLC     LAB     707       29.0       36.0       75.0       76.0       77.0       94.0       95.0

49302 Dichlorprop                 HPLC     FLD      80       53.4       57.1       70.7       74.6       77.0       92.8       99.2
49302 Dichlorprop                 HPLC     LAB     707       28.0       34.0       77.0       78.0       80.0       98.0      101.0
49303 Dichlobenil *               HPLC     FLD      21        iss       44.2       58.3       61.7       67.5       70.1        iss
49303 Dichlobenil *               HPLC     LAB     691         .0         .0       27.0       29.0       33.0       70.0       73.0
49304 Dacthal monoacid            HPLC     FLD      20        iss       28.4       62.0       74.2       80.3       87.0        iss
49304 Dacthal monoacid            HPLC     LAB     674       44.0       46.0       78.0       79.0       80.0       96.0       97.0

49305 Clopyralid                  HPLC     FLD      14        iss         .0         .0       48.8       59.5       87.0        iss
49305 Clopyralid                  HPLC     LAB     660         .0        2.0       64.0       66.0       68.0       94.0       96.0
49306 Chlorothalonil *            HPLC     FLD      24        iss        6.8       33.7       49.9       59.0       70.0        iss
49306 Chlorothalonil *            HPLC     LAB     693         .0         .0        5.0        6.0        7.0       54.0       60.0
49307 Chloramben                  HPLC     FLD       8        iss       54.7       57.2       62.3       74.6       75.8        iss
49307 Chloramben                  HPLC     LAB     496       32.0       34.0       60.0       61.0       63.0       84.0       86.0

49308 3-Hydroxycarbofuran         HPLC     FLD      18        iss       54.8       71.9       79.6       89.8      110.9        iss
49308 3-Hydroxycarbofuran         HPLC     LAB     678       24.0       26.0       68.0       70.0       71.0       95.0       97.0
49309 Carbofuran                  HPLC     FLD      78       25.7       34.4       62.0       66.0       71.5      110.0      115.1
49309 Carbofuran                  HPLC     LAB     668       46.0       50.0       78.0       79.0       81.0      110.0      113.0
49310 Carbaryl                    HPLC     FLD      81         .0        6.5       21.8       32.5       54.9       84.3       90.3
49310 Carbaryl                    HPLC     LAB     710       20.0       23.0       74.0       77.0       78.0      100.0      102.0

49311 Bromoxynil                  HPLC     FLD      72       57.5       61.3       74.6       76.6       80.8       91.9      109.4
49311 Bromoxynil                  HPLC     LAB     657       35.0       42.0       80.0       81.0       82.0      101.0      102.0
49312 Aldicarb *                  HPLC     FLD      66         .0        9.1       42.9       50.5       60.7       92.0       99.0
49312 Aldicarb *                  HPLC     LAB     702       11.0       14.0       48.0       50.0       52.0       84.0       89.0
49313 Aldicarb sulfone *          HPLC     FLD      70         .0         .0       14.8       18.2       22.7       40.5       49.1
49313 Aldicarb sulfone *          HPLC     LAB     655         .0       15.0       48.0       50.0       53.0       83.0       88.0

49314 Aldicarb sulfoxide *        HPLC     FLD      70         .0        2.1       56.0       61.0       65.2      103.1      116.0
49314 Aldicarb sulfoxide *        HPLC     LAB     660       24.0       39.0       86.0       88.0       91.0      133.5      138.0
49315 Acifluorfen                 HPLC     FLD      21        iss       73.8       78.7       81.4       87.0       97.0        iss
49315 Acifluorfen                 HPLC     LAB     704       44.0       49.0       83.0       84.0       85.0      108.0      110.0
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