Páez-Osuna et al. 2024 — Tilapia metal biomonitoring across eleven mining-watershed dams in NW Mexico
Blue tilapia (Oreochromis aureus, n=320) collected from eleven dams in Sinaloa, Mexico, were analyzed for Cd, Cu, Pb, and Zn in muscle, liver, gills, and gut to assess metal accumulation patterns and human health risk from fish consumption. Dams 1, 2, 5, and 9 showed the highest metal concentrations, consistent with the greater number of mining sites (55, 55, 19, and 16, respectively) in their sub-basins. The liver consistently accumulated higher metal loads than muscle, and non-carcinogenic risk calculations indicated elevated Pb risk for consumers ingesting 231.5 g per week or more of tilapia muscle from the most contaminated dams.
Key numbers
Metals measured by atomic absorption spectrophotometry (Cd, Pb, Cu by graphite furnace; Zn by flame); concentrations expressed as µg/g wet weight (ww). Reference material DORM-4 recoveries: Cd 101.7%, Pb 93.1%, Cu 85.3%, Zn 103.0%.
- Highest metal accumulation consistently in liver tissue across dams 1 and 2 (55 mining sites each); liver Zn exceeded 220 µg/g ww in multiple dams, surpassing previously recorded maxima.
- Muscle Pb concentrations were the key driver of non-carcinogenic risk: THQ values exceeded 1.0 at consumption rates ≥231.5 g/week for the most contaminated dam populations.
- Dams 5, 7, and 9 (19, 20, and 16 mining sites respectively in sub-basins) showed intermediate metal loads relative to dams 1–2 vs. lower-mining-density dams (5–8 sites).
- Seasonal differences were observed, with rainy-season samples showing elevated metal levels in some tissues, attributed to runoff-mediated mobilization of mining tailings.
Methods (brief)
Lyophilized tissues (~300 mg dry) digested with concentrated HNO₃ (Instra-analyzed J.T. Baker) in Teflon Savillex vials at 125 °C for 3 hours; livers additionally used H₂O₂. ICP or AAS quantification with DORM-4 certified reference material. Total metals only; no speciation. Wet weight basis throughout.
Implications
Certification: Tilapia is a commercially important freshwater fish species; this study documents regionally elevated Pb and Cd in muscle tissue from mining-influenced watersheds, relevant to HMT&C fish category sourcing guidance.
Courses: Illustrates tissue-partitioning principle (liver > muscle > gills) and mining-watershed sourcing risk for freshwater fish procurement.
App: Tilapia from known mining-watershed regions warrants elevated Pb/Cd flags in the ingredient-risk estimator.