Atrazine is a highly used and studied pesticide in the United States, and its effects to non-target species have been controversial at times. Several mixture bioassays have used atrazine, but there are no published studies on mixture toxicity of atrazine and sulfentrazone, a herbicide approved for use on soybeans. The agricultural field studied had a corn/soybean yearly rotation with the usage of atrazine and sulfentrazone, respectively. The objective of this research was to track the fate and transport of the herbicides in soil and water on an agricultural field to access the environmental risk to non-target species. Data from 2013 showed peaks in atrazine concentrations after application with an average soil concentration of 175.8 ng/g dry weight (dw) and runoff water average concentration of 4719 ng/L. Sulfentrazone residues from the 2012 application were also present, with an average soil concentration of 18.76 ng/g dw, and an average runoff water concentration of 154.3 ng/L. The half-life (t1/2) of sulfentrazone was 116 days (2012) and was 45 days (2013) for atrazine. This data indicates that the herbicides do co-exist in the field, validating the need for mixture bioassays. Atrazine and sulfentrazone were not acutely toxic individually or as a mixture to Daphnia magna and Pimephales promelas at concentrations up to one part per million (mg/L). Atrazine is a photosystem II inhibitor and sulfentrazone inhibits protoporphyrinogen oxidase (PPO), both affecting photosynthetic processes. Literature EC50 values for duckweed (Lemna sp.) and green algae (Selenastrum capricornutum) for the individual compounds fall near peak field concentrations, implying there could be potential risk associated with applying these herbicides. Individual and mixture bioassays are being conducted on both species to determine the potential risk to non-target plant species at environmentally relevant concentrations.

Relating herbicide fate and transport to laboratory toxicity data

248th National Meeting (2014)

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