Pesticides and metal contaminants in Lake Chapala, Mexico: Differences in bioaccumulation and associated health risks.

Lake Chapala, Mexico's largest freshwater lake and primary drinking water source for approximately 5 million people, lacks comprehensive pesticide and metal contamination assessment across compartments. Unlike previous single-matrix or single-class studies, this is the first seasonal multi-matrix assessment of 17 pesticides and 8 heavy metals in water, sediment, and fish across eight stations over four hydroclimatic periods (2024-2025). The study targets the Poncitlán CKD hotspot and compares bioaccumulation patterns between native (Ictalurus dugesii) and invasive (Oreochromis aureus, Cyprinus carpio, Micropterus salmoides) fish species. Pesticide concentrations peaked at rainy season onset, with diuron (2824 ng/L), atrazine (1649 ng/L), and DDT/DDD detected at all sites. Glyphosate peaked during rain cessation (234,358.62 ng/L), suggesting erosion-dependent transport. These first multi-matrix seasonal patterns show that rainfall timing drives chemical mobilization and risk. Cadmium and lead exceeded Mexican regulatory limits in interstitial water at the Santiago-Zula confluence. Benthic-feeding fish accumulated significantly higher zinc (26.6 mg/kg) than pelagic species, irrespective of invasion status. A statistical correlation was observed between glyphosate and zinc in fish tissue, suggesting a possible co-occurrence pattern warranting further mechanistic validation. Ecological risk (ΣRQ) peaked during the rainy season (ΣRQ = 935.9), driven by DDD and diuron, with persistent year-round risk (ΣRQ 3.2-10.2). Although fish consumption hazard quotients were <1, multi-pathway community burden requires future study. These findings provide the first integrated baseline for this CKD-affected region and underscore the need for seasonal, multi-matrix surveillance that includes invasive species and co-contaminant interactions.