A comparative review and computational assessment of acetochlor toxicity in fish: A novel endocrine disruptor?

Acetochlor is a chloroacetamide herbicide applied to various crops worldwide and is one of the top selling herbicides on the global market. Due to rain events and run-off, the potential for acetochlor-induced toxicity is a concern for aquatic species. Here we review the current state of knowledge regarding the concentrations of acetochlor in aquatic ecosystems globally and synthesize the biological impacts of acetochlor exposure to fish. We compile toxicity effects of acetochlor, outlining evidence for morphological defects, developmental toxicity, endocrine and immune system disruption, cardiotoxicity, oxidative stress, and altered behavior. To identify mechanisms of toxicity, we utilized computational toxicology and molecular docking approaches to uncover putative toxicity pathways. Using the comparative toxicogenomics database (CTD), transcripts responsive to acetochlor were captured and graphically depicted using String-DB. Gene-ontology analysis revealed that acetochlor may disrupt protein synthesis, blood coagulation, signaling pathways, and receptor activity in zebrafish. Further pathway analysis revealed potential novel targets for acetochlor disruption at the molecular level (e.g., TNF alpha, heat shock proteins), highlighting cancer, reproduction, and the immune system as biological processes associated with exposure. Highly interacting proteins in these gene networks (e.g., nuclear receptors) were selected to model binding potential of acetochlor using SWISS-MODEL. The models were used in molecular docking to strengthen evidence for the hypothesis that acetochlor acts as an endocrine disruptor, and results suggest estrogen receptor alpha and thyroid hormone receptor beta may be preferential targets for disruption. Lastly, this comprehensive review reveals that, unlike other herbicides, immunotoxicity nor behavioral toxicity have been fully investigated as sub-lethal endpoints for acetochlor, and such mechanisms of toxicity should be emphasized in future research investigating biological responses of fish to the herbicide.