Pesticide Prioritization by Potential Biological Effects in Tributaries of the Laurentian Great Lakes.

This article focuses on assessing the potential biological impacts of pesticides and their transformation products on aquatic life in 16 tributaries of the Laurentian Great Lakes Basin (USA/Canada). Using a combination of organismal-level aquatic life benchmarks (ALBs) and high-throughput screening (HTS) assay data from the US Environmental Protection Agency's ToxCast program, the study identified widespread pesticide contamination year-round, with exceedances of toxicity thresholds at 15 of 16 sites. The Maumee River watershed, characterized by extensive agricultural land use, exhibited the highest potential biological impact, detecting 72 pesticide-related compounds with 47 exceeding benchmarks. Fifteen parent pesticides—including eight herbicides (e.g., atrazine, metolachlor), three fungicides (e.g., chlorothalonil), and four insecticides (e.g., imidacloprid, fipronil)—were prioritized as compounds of concern due to their frequency, concentration, and potential toxicity. The study highlights the importance of considering both parent compounds and transformation products, as well as pesticide mixtures, in evaluating ecological risks and suggests that further targeted toxicological research is needed to better understand the effects of frequently detected but understudied transformation products.