Date of Award
Master of Science
The risk associated with the application and co-occurrence of atrazine and sulfentrazone, two herbicides applied to a corn and soybean rotational field, was evaluated in the current study. Peak field concentrations were found in the soil matrix, with atrazine and sulfentrazone values of 144 ng/g dry weight (dw), and 318 ng/g dw, respectively; however, due to the physicochemical properties of the compounds, the two herbicides were also transported to field water matrices. The highest mean runoff water concentrations for atrazine and sulfentrazone were 4.72 µg/L and 10.3 µg/L, respectively. A direct spray event of atrazine to the runoff water sampler caused concentrations as high as 1.6 mg/L, effectively becoming a worst case scenario concentration. Individual and mixture laboratory bioassays were also conducted to determine the effects of atrazine and sulfentrazone on the survival of D. magna, and P. promelas. Sub-lethal effects including germination of L. sativa, and growth of P. promelas, S. capricornutum and L. minor were also evaluated. Results showed that S. capricornutum and L. minor were the most susceptible non-target species tested, and synergistic effects were observed for both species when equipotent mixtures were tested. Margin of safety of 10% (MOS10) values were calculated for each species using field concentrations and bioassay benchmark concentrations. Atrazine MOS10 values, calculated with environmental concentrations not including the direct spray event, were 0.83 and 0.10 for S. capricornutum and L. minor, respectively. The MOS10 value for sulfentrazone effects on S. capricornutum was 0.31, and effects on L. minor was 1.39. There was a slight risk to S. capricornutum and L. minor growth associated with exposure to atrazine and sulfentrazone in an agricultural field. Although the co-occurrence of atrazine and sulfentrazone was observed, and synergistic effects were observed in the equipotent binary mixture bioassays for S. capricornutum and L. minor, it is believed that there is minimal increase in risk potential due to the co-occurrence, because field concentrations do not proportionally mimic the concentrations that produced synergism in the plant species.
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