Environ Sci Pollut Res Int. 2026 Aug 10. doi: 10.1007/s11356-026-38124-w. Online ahead of print.
ABSTRACT
The transfer of pesticides to Aiguillon Bay, a major coastal ecosystem on the Atlantic coast of France, was investigated in relation to watershed characteristics, agricultural pressure, and hydrological dynamics. The bay receives inputs from three main rivers (Sèvre Niortaise, Lay, and Curé) as well as from the Vieux channel, a downstream branch of the Lay watershed characterized by distinct land-use and drainage features. This study combined spatial land-use analysis with contamination indicators to clarify pesticide transfer pathways and associated ecological risks in intensively cultivated sub-basins. Monthly surface water samples were analyzed using LC-MS/MS and GC-MS/MS. A Proximity Indicator was developed to identify high-pressure agricultural zones adjacent to watercourses. Individual Risk Quotients (RQs) were also calculated by comparing measured environmental concentrations with Predicted No-Effect Concentrations (PNECs) to evaluate the ecological risk associated with selected pesticide compounds, and the Cumulative Toxic Pressure Index (CTPI) was applied to assess mixture toxicity. CTPI analysis revealed recurrent exceedances of the toxicity threshold (CTPI > 1) across all monitored systems, with strong seasonal variability linked to hydrological conditions. The Sèvre Niortaise and Vieux channel exhibited sustained mixture pressure, whereas the Lay showed pronounced event-driven peaks associated with rainfall episodes. Despite its smaller size, the Curé watershed displayed disproportionately high toxic pressure, reflecting strong hydrological connectivity and cereal-dominated land use. Herbicides and their metabolites were the primary contributors to mixture toxicity, including the persistent metabolite chlorothalonil R471811, frequently detected despite its regulatory ban in 2020, suggesting legacy contamination and progressive remobilization. Although individual Risk Quotients indicated negligible ecological risk for the selected compounds, CTPI revealed repeated mixture toxicity exceedances, demonstrating that cumulative effects represent the primary ecological pressure within the watershed. By integrating land-use characterization, hydrological analysis, statistical comparison, mixture toxicity assessment, and ecological risk evaluation, this study provides a comprehensive framework for understanding pesticide transfer to protected coastal ecosystems and supports the development of more effective watershed management and monitoring strategies.
PMID:42573961 | DOI:10.1007/s11356-026-38124-w
