Assessing the risk of pesticides to small streams in Southwestern Ontario using high frequency water sampling

Abstract

Pesticides can enter the aquatic stream systems in many ways; however, there is a paucity of field data on the quantity of pesticides in streams during flow events, and therefore, the temporal dynamics of the concentration of pesticides in Southwestern Ontario remain poorly characterized. To increase our understanding on how pesticide exposure changes during flow events, high frequency water sampling was performed over two years. Deterministic risk assessments using water quality guidelines and probabilistic risk assessments using species sensitivity distributions were performed, from which de minimis risk was concluded, except for clothianidin, for which a low risk was determined. To assess the pesticide toxicity, toxicity tests with six herbicides and two insecticides were conducted on Lemna minor and Neocloeon triangulifer. It was found that L. minor was most sensitive to metolachlor, followed by metribuzin, 2,4-D, MCPA, MCPP, and dicamba. The 96-h LC50s for cyantraniliprole and chlorantraniliprole for N. triangulifer were also determined.