Direct and nitrate-mediated hydroxy radical photoprocesses were examined with respect to atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) transformation. Irradiation (λ > 290 nm) of aqueous solutions of atrazine in the presence of nitrate, which generates • OH, yielded 20% of 6-amino-2-chloro-4-isopropylamino-s-triazine (CIAT), 10% of 6-amino-2-chloro-4-ethylamino-s-triazine (CEAT), 6% of 4-acetamide-2-chloro-6-isopropylamino-striazine (CDIT), 3% of 4-acetamide-2-chloro-6-ethylaminos-triazine (CDET), 16% of chlorodiamino-s-triazine (CAAT), and 3% of hydroxy atrazine (OIET, 4-ethylamino-6-isopropylamino-2-hydroxy-s-triazine) at 87% atrazine conversion. Direct photolysis of atrazine was much slower and at 23% atrazine conversion gave rise to 14% OIET and ca. 9% of chloroalkyloxidized or chlorodealkylated compounds with the ratio of the reaction rate constants equal to 0.14 (k direct / k indirect ). Results also suggest that OIET was not the product of a hydroxy radical process. The efficiency of the hydroxy radical process decreased more than 85%, with increasing DOC obtained from the surface layer of the Chesapeake Bay. However, only a slight decrease (<15%) in efficiency was observed for direct photolysis, suggesting that in the presence of surface layer DOC direct photolysis may become more important relative to the • OH processes.

Keywords: α- and β-endosulfan; conformation; X-ray crystallography; intramolecular conversion; NMR spectroscopy

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The Choptank River is an estuary, tributary of the Chesapeake Bay, and an ecosystem in decline due partly to excessive nutrient and sediment loads from agriculture. The Conservation Effects Assessment Project for the Choptank River watershed was established to evaluate the effectiveness of conservation practices on water quality within this watershed. Several measurement frameworks are being used to assess conservation practices. Nutrients (nitrogen and phosphorus) and herbicides (atrazine and metolachlor) are monitored within 15 small, agricultural subwatersheds and periodically in the lower portions of the river estuary. Initial results indicate that land use within these subwatersheds is a major determinant of nutrient concentration in streams. In addition, the 18 O isotope signature of nitrate was used to provide a landscape assessment of denitrification processes in the presence of the variable land use. Herbicide concentrations were not correlated to land use, suggesting that herbicide delivery to the streams is influenced by other factors and/or processes. Remote sensing technologies have been used to scale point measurements of best management practice effectiveness from field to subwatershed and watershed scales. Optical satellite (SPOT-5) data and ground-level measurements have been shown to be effective for monitoring nutrient uptake by winter cover crops in fields with a wide range of management practices. Synthetic Aperture Radar (RADARSAT-1) data have been shown to detect and to characterize accurately the hydrology (hydroperiod) of forested wetlands at landscape and watershed scales. These multiple approaches are providing actual data for assessment of conservation practices and to help producers, natural resource managers, and policy makers maintain agricultural production while protecting this unique estuary.

Previous studies have provided unequivocal evidence for the symmetry of beta-endosulfan and the corresponding asymmetry of alpha-endosulfan; the conversion of beta-endosulfan to alpha-endosulfan was identified. In this study, evidence from differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) experiments combined with computational chemistry calculations was used to propose a molecular mechanism for the corresponding conformational changes that occur in this process. DSC and NMR data of mixtures indicated that both isomers can influence the conformer populations in the solid, solution, and vapor phase. Computational chemistry demonstrated that the relative S==O configuration between alpha- and beta-isomers can be the intermediate state through which the conformations of alpha- and beta-isomers affect each other. Furthermore, calculations for mixtures indicated that the asymmetrical conformation of the sulfite in alpha-endosulfan can induce asymmetry in beta-endosulfan, and conversion to alpha-endosulfan occurs from this transition state.

Current vegetable production systems use polyethylene (plastic) mulch and require multiple applications of agrochemicals. During rain events, runoff from vegetable production is enhanced because 50 to 75% of the field is covered with an impervious surface. This study was conducted to quantify off-site movement of soil and pesticides with runoff from tomato (Lycopersicon esculentum Mill.) plots containing polyethylene mulch and a vegetative mulch, hairy vetch (Vicia villosa Roth). Side-by-side field plots were instrumented with automated flow meters and samplers to measure and collect runoff, which was filtered, extracted, and analyzed to determine soil and pesticide loss. Seasonal losses of two to four times more water and at least three times as much sediment were observed from plots with polyethvlene mulch (55.4 to 146 L m(-2) and 247 to 535 g m(-2), respectively) versus plots with hairy vetch residue (13.7 to 75.7 L m(-2) and 32.8 to 118 g m(-2), respectively). Geometric means (+/-standard deviation) of total pesticide loads for chlorothalonil (tetrachloroisophthalonitrile) and alpha-and beta-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro6,9-methano-2,4,3-benzodioxathiepin 3-oxide) for a runoff event were 19, 6, and 9 times greater from polyethylene (800+/-4.6, 17.6+/-3.9, and 39.1+/-4.9 microg m(-2), respectively) than from hairy vetch mulch plots (42+/-6.0, 2.8+/-5.0, and 4.3+/-4.6 microg m(-2), respectively) due to greater concentrations and larger runoff volumes. The increased runoff volume, soil loss, and off-site loading of pesticides measured in runoff from the polyethylene mulch suggests that this management practice is less sustainable and may have a harmful effect on the environment.

Climate and soil conditions in South Florida along with an extensive canal system facilitate movement of agricultural pesticides into surface waters. In a two-year study (2002)(2003)(2004) of the currently used pesticides in South Florida, atrazine, endosulfan, metolachlor, chlorpyrifos, and chlorothalonil were the most frequently detected in the canals and in Biscayne Bay, with average concentrations of 16, 11, 9.0, 2.6, and 6.0 ng/L, respectively. Concentrations of atrazine and chlorpyrifos were highest near corn production. Chlorothalonil and endosulfan concentrations were highest near vegetable production, with no clear trend for metolachlor, which is used on multiple crops. Concentration data were used to calculate an aquatic life hazard potential for the planting period (November) versus the harvest period (March). This analysis indicated that a higher hazard potential occurs during harvest, primarily from the use of endosulfan. These data will also serve to document canal conditions prior to implementation of the Comprehensive Everglades Restoration Plan (CERP).

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