Environmental contamination by current-use pesticides (CUPs) has become a global concern due to their widespread use. However, very few studies have examined the spatiotemporal dynamics and multiclass occurrence of CUPs in marine environments. This study aimed to comprehensively evaluate the spatiotemporal dynamics, contamination sources, and ecotoxicological risks of multi-class CUPs in marine ecosystems. Water samples were collected along the Korean coast to assess the occurrence and distribution of 169 CUPs. CUPs were widely detected in coastal waters, indicating ubiquitous contamination of marine environments. Pronounced summer peaks were observed, mainly driven by the monsoon "flushing effect" via riverine runoff. Nationwide, the West Coast had the highest contamination, indicating a hotspot characterized by the widespread prevalence of the insecticide ethofenprox. Contamination profiles were highly source-dependent; an agriculture-dominated bay was severely affected by rice paddy herbicides (e.g., metazosulfuron, up to 6008 ng/L), whereas an industry-dominated bay exhibited persistent year-round dominance of the antifouling biocide diuron (up to 986 ng/L). While the general coastline remained within safe baseline levels, ecological risk assessments indicated that summer monsoon events transformed the semi-enclosed bays into ecotoxicological hotspots. Notably, localized elevated concentrations of diuron and oxadiazon pose potential risks. These findings carry important implications for coastal management, demonstrating that climate-driven runoff significantly exacerbates pesticide pollution, thereby necessitating intensive seasonal monitoring and targeted regulatory strategies to protect vulnerable marine ecosystems.
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