National Water-Quality Assessment (NAWQA) Project
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Average Chemical Use (in 1,000 kg/year of active Compound ingredient) 1982-86 1987-91 1992-95 ----------------------------------------------------- Nitrogen-fertilizer¹ 876,300 836,700 834,200 Alachlor² 6,260 3,740 2,350 Atrazine² 3,710 3,380 3,264 Cyanazine² 4,282 2,654 3,170 Metolachlor² 3,059 4,949 4,709 ---------------------------------------------------- Average Intensity of Use (kg/hectare) 1982-86 1987-91 1992-95 ----------------------------------------------------- Nitrogen-fertilizer¹ 155 145 132 Alachlor² 2.26 2.52 2.54 Atrazine² 1.64 1.08 0.98 Cyanazine² 2.31 2.38 2.53 Metolachlor² 2.69 2.30 2.30 ----- ¹ Vroomen, 1989; U.S. Department of Agriculture, 1995 ² Hartzler and Wintersteen, 1991; U.S. Department of Agriculture, 1995
[N, number of samples; HA, health advisory level; MCL, maximum contaminant level; mg/L, milligram per liter; µg/L, microgram per liter; HA, health advisory level]
Frequency of Reporting detection Compound N limit (%) ----------------------------------------------------------- Nitrate 1929 0.10 mg/L 57.1 Alachlor 1485 0.10 µg/L 3.0 Atrazine 1485 0.10 µg/L 19.5 Cyanazine 1314 0.10 µg/L 3.6 Metolachlor 1309 0.10 µg/L 5.7 ------------------------------------------------------------ Frequency of exceedence, Maximum MCL or MCL, or HA concentration HA¹ (%) ------------------------------------------------------------ Nitrate 53.0 mg/L 10 mg/L 7.2 Alachlor 14.0 µg/L 2.0 µg/L 0.4 Atrazine 21.0 µg/L 3.0 µg/L 0.8 Cyanazine 4.5 µg/L 1.0 µg/L¹ 0.3 Metolachlor 200 µg/L 100 µg/L¹ <0.1 ------- ¹Health advisory from U.S. Environmental Protection Agency (1996)
Table 3. Temporal patterns in frequency of
detection for selected agricultural chemicals in Iowa groundwater
(1,019 wells). A P value ± 0.05 is not considered statistically
significant.
Table 4. Temporal patterns in frequency of
detection for selected agricultural chemicals in Iowa groundwater
(1,019 wells) by well depth group. A P value >/=
0.05 is not considered statistically significant.
Median Frequency of Detection (%) Results of
--------------------------------- Kruskal-Wallis
Compound 1982-86 1987-91 1992-95 test (P value)
----------------------------------------------------------------
Nitrate 48.1 61.5 55.4 0.229
Alachlor 0.0 2.2 3.3 0.541
Atrazine 15.4 19.3 13.2 0.152
Cyanazine 0.0 3.3 4.1 0.096
Metolachlor 0.0 4.8 14.1 0.009
Median Frequency of Detection (%)
---------------------------------
Results of Kruskal-
Compound 1982-86 1987-91 1992-95 Wallis test (P value)
----------------------------------------------------------------
Shallow Wells ( 15 m) (need less than/equal to symbol)
Nitrate 77.1 81.1 76.1 0.292
Alachlor 0.0 1.4 4.0 0.248
Atrazine 20.0 29.7 16.4 0.027
Cyanazine 0.0 5.8 4.1 0.163
Metolachlor 0.0 6.2 6.8 0.480
Intermediate Wells (16-30 m)
Nitrate 72.0 81.2 76.0 0.120
Alachlor 0.0 3.9 1.4 0.390
Atrazine 19.4 25.0 22.2 0.431
Cyanazine 0.0 6.4 8.8 0.108
Metolachlor 0.0 7.1 28.6 0.006
Deep Wells (>30 m)
Nitrate 36.8 40.7 27.8 0.254
Alachlor 0.0 2.4 1.9 0.344
Atrazine 6.9 10.6 7.6 0.361
Cyanazine 0.0 1.2 0.0 0.056
Metolachlor 0.0 1.3 3.4 0.130
Table 5. Temporal patterns in frequency of detection for
selected agricultural chemicals in Iowa groundwater (1,019 wells) by
aquifer type. A P value 0.05 >/= is not considered
statistically significant.
Median Frequency of Detection (%)
---------------------------------
Results of Kruskal-
Compound 1982-86 1987-91 1992-95 Wallis test (P
value)
----------------------------------------------------------------
Alluvial Aquifers
Nitrate 73.8 79.0 74.2 0.309
Alachlor 0.0 1.7 3.1 0.797
Atrazine 19.2 28.3 21.0 0.150
Cyanazine 0.0 4.2 6.5 0.165
Metolachlor 0.0 7.4 16.5 0.023
Glacial-Drift Aquifers
Nitrate 46.9 57.5 34.8 0.214
Alachlor 0.0 3.4 0.0 0.470
Atrazine 6.7 17.2 0.0 0.094
Cyanazine 0.0 3.4 0.0 0.062
Metolachlor 0.0 0.0 0.0 0.927
Bedrock
Nitrate 39.7 47.7 46.3 0.505
Alachlor 0.0 2.5 2.2 0.176
Atrazine 20.0 14.3 14.6 0.823
Cyanazine 0.0 1.8 0.0 0.023
Metolachlor 0.0 1.8 4.7 0.130
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