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The Quality of Our Nation's Waters
Pesticides in the Nation's Streams and Ground Water, 1992-2001

Appendix 2 - Properties affecting the transport and fate of selected pesticide compounds.

[Pesticide compounds selected are those detected most frequently in NAWQA samples (see figs. 4-2 and 4-4), as well as several that were detected infrequently, despite extensive use. All values measured at (or estimated for) 25°C, except for those shown in italics. Unless noted otherwise, (1) values for octanol-water partition coefficient (Kow, dimensionless), soil organic carbon-water partition coefficient (Koc), water solubility (Sw) and Henry's law constant (KH) are from Mackay and others (1997); (2) transformation half-lives in soil and water were measured in the laboratory (rather than in the field) at neutral pH in the dark, and obtained from the U.S. Department of Agriculture (2005); and (3) all are recommended values selected by the compilation authors when more than one value was available from the literature. Compounds are listed in the same order as in figures 4-2 and 4-4. Numbers of significant figures are identical to those given in original sources. kJ/mol, kilojoule per mole; mg/L, milligram per liter; mL/g, milliliter per gram; NA, data not available from any of the references consulted; Pa•m3/mol, pascal-cubic meter per mole; >, greater than.]

Compound

log Kow

log Koc

(Koc in mL/g)

Sw

(mg/L)

log KH

(KH in Pa•m3/mol)

Half-life for transformation
(days)

In aerobic soil

In water

Agricultural herbicides and degradates detected most frequently in water

Atrazine

2.75

2.00

30

-3.54

146

1742

Deethylatrazine (DEA)

21.3

31.90

42700

5-4.12

6170

NA

Metolachlor

3.13

2.26

430

-2.63

26

7410

Cyanazine

2.22

2.3

171

-6.52

817

9>200

Alachlor

2.8

2.23

240

-2.7

1020.4

11640

Acetochlor

123.0

132.38

12,14223

12,15-2.15

13,1514

162300

Metribuzin

14,171.60

1.72

14,171,000

17,18-5.31

172

9>200

Bentazon

192.80

201.54

14,17500

21-3.7

2235

23>200

EPTC

3.2

2.3

370

0.00988

247

9>200

Trifluralin

5.34

4.14

250.5

1.00

169

26>32

Molinate

3.21

1.92

970

-0.839

2721

9>200

Norflurazon

172.45

172.55

1734

17-4.46

130

9>200

Urban herbicides detected most frequently in water

Simazine

2.18

2.11

5

-3.46

891

28>32

Prometon

2.99

2.54

750

-4.05

932

9>200

Tebuthiuron

81.79

172.1

292400

17-4.88

1050

30>2700

2,4-D

2.81

171.68

890

-3.61

312.3

7732

Diuron

2.78

2.6

40

-3.17

372

>500

Dacthal (DCPA)

324.28

173.75

170.5

17-0.66

3316

9>200

Bromacil

2.11

1.86

815

-4.89

275

34>30

Insecticides detected most frequently in water

Diazinon

3.3

2.76

60

-1.39

39

140

Chlorpyrifos

4.92

3.78

0.73

0.0374

30.5

29

Carbofuran

2.32

2.02

351

-4.30

11

35289

Carbaryl

2.36

2.36

120

-4.35

17

11

Malathion

2.8

3.26

145

-2.64

<1

366.3

Dieldrin37

5.20

4.08

0.17

0.0492

NA

3830

Organochlorine pesticide compounds detected most frequently in bed sediment and fish tissue

p,p'-DDE

5.7

5.0

0.04

0.900

NA

38>44,000

p,p'-DDD

5.5

5.0

0.05

-0.194

NA

3910,000

p,p'-DDT

6.19

5.4

0.0055

0.37

NA

405000

o,p'-DDE

5.8

85.58

0.1

0.405

NA

NA

o,p'-DDD

6.0

85.36

250.10

41-2.7

NA

39NA

o,p'-DDT

42NA

42NA

0.026

-0.460

NA

NA

cis-Chlordane

6.0

5.5

0.056

-0.466

NA

43>7.2x107

trans-Chlordane

6.0

5.5

0.056

-0.582

NA

44>10,000

Nonachlor

455.66

454.86

450.06

45-1.69

NA

NA

Oxychlordane

462.6

462.48

46200

46-1.52

NA

NA

Dieldrin37

5.20

4.08

0.17

0.0492

NA

3830

Heptachlor epoxide

5.0

4.0

0.35

460.51

NA

NA

Pentachloroanisole

465.66

464.62

460.2

462.91

NA

NA

Hexachlorobenzene

325.31

174.7

320.0062

471.69

NA

48>26,000

Chlorothalonil

2.64

3.2

0.6

1.77

NA

9>200

Dicamba

2.21

171.11

4500

-3.66

4928

9>200

Parathion-methyl (Methyl parathion)

3.0

3.7

25

-1.68

503.3

41

Pendimethalin

175.2

174.13

170.275

170.0899

1300

9>200

Terbufos

4.48

2.70

5

0.39

5

1.9

1Measured by Khan (1978) in a solution containing 0.5 g/L fulvic acid.

2Computed from Koc value using Kow-vs.-Koc regression for "triazines" from Sabljić and others (1995).

3Koc value measured on a clay loam soil (1.3% organic carbon) by Seybold and Mersie (1996), the study—among those having measured Koc for both DEA and atrazine—reporting the Koc value for atrazine (140 mL/g) that was closest to the value selected for atrazine (100 mL/g) by Mackay and others (1997).

4Value from Ciba-Geigy, Ltd., cited by Bayless (2001)

5Estimated by (1) computing estimates of KH for both DEA and atrazine (KH,est[DEA] and KH,est[atr], respectively) using the bond-contribution method of Meylan and Howard (1991); and (2) scaling from the value measured for atrazine (KH,meas[atr]) using the following equation:

formula

6Measured by Kruger and others (1997) in the aerobic soil (sandy clay loam, 0.6% organic carbon) for which the half-life for atrazine reported by the authors and adjusted to 25°C (191 d) was most similar to the value selected by the U.S. Department of Agriculture (2005) for atrazine at 25°C (146 d). Half-lives for both atrazine and DEA in soil were adjusted to 25°C from 24°C using an activation energy of 48.4 kJ/mol, measured by Baer and Calvet (1999) for atrazine disappearance in an aerobic silt loam (1.1% organic carbon).

7Rate extrapolated to 25°C using data reported by Cavalier and others (1991) for disappearance of the pesticide in ground-water samples (pH = 7.4-7.6) at 15 and 22°C, based on the experiment with the highest initial pesticide concentration (and thus maximum analytical sensitivity).

8Sole value reported by the U.S. Department of Agriculture (2005) database authors, but not "selected."

9Classified as "stable" with respect to hydrolysis (U.S. Department of Agriculture, 2005), meaning that the compound exhibits "less than 10% reaction after 30 days at 25°C" (Cheryl Sutton, U.S. Environmental Protection Agency Office of Pesticide Programs, Environmental Fate and Effects Division, personal communication, 1/4/05).

10Half-life interpolated to 25°C from rates of alachlor disappearance from a sandy loam soil (0.7% organic carbon) at 10, 20 and 30°C reported by Zimdahl and Clark (1982).

11Rate extrapolated to 25°C from data reported by Cavalier and others (1991) for alachlor disappearance in ground water (pH = 7.4-7.6) at 15 and 22°C, based on the experiment with the highest initial alachlor concentration (and thus maximum analytical sensitivity). Value consistent with half-life estimate of ">100 d" at 20°C in deionized water reported by Gan and others (2002).

12Source: U.S. Environmental Protection Agency (1994).

13Median value among those reported by U.S. Environmental Protection Agency (1994).

14Measured at 20°C.

15Temperature of measurement not given.

16Source: Zheng and Ye (2001), cited by Carlson (2003). Consistent with half-life of ">100 d" at 20°C in deionized water reported by Gan and others (2002).

17Source: U.S. Department of Agriculture (2005).

18Adjusted from value measured at 20°C to 25°C using equation provided by Mackay and others (2000), and an enthalpy of vaporization (ΔHv) of 46.8 kJ/mol, based on KH data from 197 compounds (Staudinger and Roberts, 2001).

19Source: Sabljić and others (1995). Form of molecule (salt vs. benzothiadiazine) not given.

20Measured using the sodium salt of bentazon, rather than the benzothiadiazine form (U.S. Department of Agriculture, 2005).

21Computed from dimensionless value given by Tiktak (1999). Temperature of measurement not given, but similarity of value to that computed from vapor pressure and solubility (both obtained from EXTOXNET) suggests that it may have been 20°C.

22Median value among 19 measurements of bentazon disappearance rates in a variety of soils (pH= 6.1-7.7) over a temperature range of 20-23°C (Huber and Otto, 1994; Thorstensen and Lode, 2001), after adjusting all values to 25°C using an activation energy of 90 kJ/mol for bentazon disappearance, measured for a sandy soil with 4.90% organic carbon (Tiktak, 1999).

23Statement by Huber and Otto (1994) that "hydrolytically, bentazon is nearly stable...at pH...7" presumed to be equivalent to U.S. Environmental Protection Agency's definition of "stable" (see footnote 9), although temperature of measurement not given.

24"[H]alf-life in moist loam soil at 21 to 27°C is approximately one week" (Mackay and others, 1997).

25According to Mackay and others (1997), "the reported values for this quantity vary considerably [0.05 - 40 mg/L for trifluralin; 0.10 - 0.24 mg/L for o,p'-DDD]; whereas this selected value represents the best judgement of the authors...it may be subject to large error."

26Computed from rate constant (maximum value) provided by U.S. Department of Agriculture (2005).

27According to Mackay and others (1997), "half-life is approximately 3 weeks in moist loam soils at 21-27°C."

28For biodegradation in pond water. Source: Tucker and Boyd (1981), cited by Mackay and others (1997).

29Arithmetic mean of the two values reported by U.S. Department of Agriculture (2005), neither of which was "selected."

30Estimated from assumption that "no hydrolysis in 64 days" at 51°C and pH 3, 6 and 9 (U.S. Department of Agriculture, 2005) implies less than 5% reaction. Extrapolated to 25°C using the minimum activation energy (Ea) for the transformation in soil of methabenzthiazuron (35.6 kJ/mol), the urea herbicide most similar in structure to tebuthiuron among those for which Ea values appear to be available (FOCUS, 1997). (No Ea values appear to be available for the disappearance of either methabenzthiazuron or tebuthiuron in water.)

31Average of values computed for two soils, based on data reported by Veeh and others (1996).

32Source: Syracuse Research Corporation CHEMFATE Database.

33Source: Wettasinghe and Tinsley (1993).

34Transformation rate given for pH 5 and 9 only (U.S. Department of Agriculture, 2005).

35Transformation rate measured at pH 6.2 (U.S. Department of Agriculture, 2005).

36Value measured at pH 7, rather than the pH (5) at which the value recommended by the U.S. Department of Agriculture (2005) was measured.

37Dieldrin is both an insecticide and a product of aldrin transformation (Nowell and others, 1999), and was one of the pesticide compounds detected most frequently in bed sediments, as well as in water.

38Reaction rate measured in 5% acetonitrile solution, extrapolated to 27°C from higher temperatures, and interpolated to pH 5 by Wolfe and others (1977).

39No distinction made between o,p' and p,p' isomers for this parameter by the U.S. Department of Agriculture (2005), but reported half-life was identical to that provided by Ellington and others (1987a) for p,p'-DDD, suggesting that the U.S. Department of Agriculture (2005) value was for the p,p' isomer only.

40Reaction rate measured in 5% acetonitrile solution, extrapolated to 27°C from higher temperatures, and interpolated to pH 7 by Wolfe and others (1977).

41Source: Suntio and others (1988).

42Available estimation methods appear inadequate for distinguishing between ortho and para isomers.

43Source: Ellington and others (1987a).

44Estimated from assumption that "zero degradation...during five days" at 85°C and pH 7 (Ellington and others, 1987b) implies less than 10% reaction (Ellington and others, 1988). Extrapolated to 25°C using the activation energy for the transformation of γ-HCH in borate buffer at pH 9 (84.6 kJ/mol), reported by Ngabe and others (1993).

45Source: Nowell and others (1999). No distinction made between cis and trans isomers.

46Source: Nowell and others (1999).

47Computed for 25°C using regression equation from Staudinger and Roberts (2001).

48Estimated from assumption that "zero hydrolysis observed after 13 days at 85°C and pH 7 (Ellington and others, 1987b) implies less than 10% reaction (Ellington and others, 1988). Extrapolated to 25°C using the activation energy for the transformation of γ-HCH in borate buffer at pH 9 (84.6 kJ/mol), reported by Ngabe and others (1993).

49Interpolated to 25°C from data for a clay soil (1.5% organic matter) by Comfort and others (1992).

50Extrapolated to 25°C from value measured at 30°C in a silt loam soil (organic carbon content not given) by Lichtenstein and Schulz (1964) after 12 days of reaction (the longest reaction period examined by the authors), using the activation energy (Ea) measured by Lartiges and Garrigues (1995) for methyl parathion disappearance in unfiltered river water at pH 7.3 (26 kJ/mol). (No Ea values appear to be available for methyl parathion disappearance from aerobic soil.)

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