Pesticide occurrence, transformation, and transport from wastewater treatment plants into stream networks with diverse land uses.

Neonicotinoid insecticides and strobilurin fungicides are detected in many environmental compartments and have been associated with negative environmental and human health implications. Wastewater treatment plants (WWTPs) are often hotspots for introducing such contaminants into the environment. Therefore, the occurrence of strobilurin fungicides, neonicotinoids, and their metabolites at two WWTPs with varying land uses and population sizes was investigated. Polar organic chemical integrative samplers were deployed in WWTP influent and effluent and placed upstream and downstream of the effluent mixing zone for 2 weeks in April and July 2022. Biosolids were also collected at each time point. Neonicotinoids were detected with the highest frequency (68%), followed by strobilurin fungicides (49%) and neonicotinoid metabolites (31%). Time-weighted average concentrations for influent/effluent ranged from 85.2 ± 87.8 to 409.4 ± 74.5 ng/L. Pesticide concentrations, specifically the metabolites, typically increased from influent to effluent, resulting in effluent having higher pesticide loads than influent. Pesticide concentrations varied between the upstream and downstream monitoring locations by analyte, with WWTP samples in the highly developed region having significantly higher concentrations of pesticides and less variation by monitoring period. Chronic ecotoxicity benchmarks for freshwater invertebrates for imidacloprid were surpassed in treated effluent at both WWTPs in July and in the downstream monitoring location in the heavily developed area. Findings support the need for further exploration of pesticide contributions from WWTPs to river systems, specifically related to metabolite contributions to downstream streams and their effects on aquatic environments.