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Occurrence and Fate of Pesticides in Four Contrasting Agricultural Settings in the United States

^a U.S. Geological Survey, 5231 South 19th St., Lincoln, NE 68512
^b U.S. Geological Survey, 2130 SW 5th Ave., Portland, OR 97201
^c U.S. Geological Survey, Box 25046 Denver Federal Center, Lakewood, CO 80225
^d U.S. Geological Survey, 122 Civil Engineering Building, 500 Pillsbury Drive, SE, Minneapolis, MN 55455
^e U.S. Geological Survey, 934 Broadway, Suite 300, Tacoma, WA 98402

View larger version (37K): [in this window] [in a new window]   Fig. 1. Cross-section views of flow systems showing well-nest locations at the study sites in (A) Maryland, (B) Nebraska, (C) California, and (D) Washington.

View larger version (26K): [in this window] [in a new window]   Fig. 2. Occurrence of the subset of parent pesticides used in each of the watersheds as a function of chemical properties (A) Maryland, (B) Nebraska, (C) California, and (D) Washington.

View larger version (19K): [in this window] [in a new window]   Fig. 3. Bivariate plots of corrected deethylatrazine relative to (A) corrected atrazine, (B) age of ground water, and (C) depth of screened interval (atrazine and deethylatrazine corrected for recovery). The laboratory reporting level divided by 10 (3.2 x 10–3 nmol L–1) was substituted for a nondetected value so the data point would plot on the log-log plot (A); this value indicates no atrazine was present in the sample while deethylatrazine was present.

View larger version (20K): [in this window] [in a new window]   Fig. 4. Bivariate plots of metolachlor ethanesulfonic acid (ESA) as a function of (A) metolachlor oxanilic acid (OXA), (B) age of ground water, and (C) depth of screened interval. "0" indicates no metolachlor ESA is present while other related compounds (either metolachlor and/or metolachlor OXA) are present.

View larger version (26K): [in this window] [in a new window]   Fig. 5. Graphs showing use of (A) herbicides in agricultural settings and (B) nitrogen fertilizer in the conterminous USA. Interpolations before 1982 in (A) are based on use data for all pesticides; interpolations from 1982–2001 use data for all herbicides.

View larger version (21K): [in this window] [in a new window]   Fig. 6. Site groupings relative to dissolved oxygen and excess nitrogen gas for (A) total pesticide concentration, (B) metolachlor ethanesulfonic acid (ESA), and (C) metolachlor oxanilic acid (OXA).

View larger version (25K): [in this window] [in a new window]   Fig. 7. Ternary plot of metolachlor and metolachlor ethanesulfonic acid (ESA) and oxanilic acid (OXA) degradates in the deepest unsaturated zone and in ground water samples from (A) Maryland, (B) Nebraska, and (C) California study sites.

View larger version (21K): [in this window] [in a new window]   Fig. 8. Root-zone water-quality model predictions of pesticide movement to ground water at Maryland study site.