Mapping the Invisible Landscape of Pesticides and Adjuvants in Peri-Urban Agricultural Waterways of the Megacity Shanghai

Peri-urban agriculture is expanding rapidly in megacities, yet its contribution to aquatic chemical pollution remains poorly characterized. Here, we present an integrated assessment of agrochemical contamination in peri-urban agricultural surface waters of Shanghai, combining nontargeted screening, in silico hazard prioritization, and in vivo toxicity testing. Across 193 sampling sites, exceptionally high chemical diversity and mixture complexity were observed, with 91 pesticides and 263 formulation adjuvants widely detected. Adjuvants occurred with detection frequencies (DFs) and response intensities comparable to those of pesticides, indicating they constitute a major yet underappreciated component of agrochemical pollution. Besides, correlation network analysis demonstrated extensive co-occurrence between pesticides and adjuvants, suggesting shared transport pathways and exposure dynamics. Hazard screening based on persistence, bioaccumulation, mobility, and toxicity (PBMT) further demonstrated that adjuvants constituted a substantial fraction of prioritized high-risk substances. Moreover, in vivo zebrafish embryo assays showed that representative pesticides and adjuvants, such as bentazone, imidacloprid, and triethyl phosphate, induced adverse developmental effects at environmentally relevant concentrations measured in surface waters, typically in the hundreds of ng/L range. Collectively, these findings identify peri-urban agriculture as a critical source of complex agrochemicals and highlight the need to explicitly incorporate the formulation adjuvants into environmental monitoring and risk assessment.