Assessment of Mercury Levels in Amazonian Fishes of the Nanay River, Loreto, Peru: Implications for Human Consumption

Mercury exposure associated with fish consumption remains a significant public-health concern in the Amazon Basin. Here, we quantified total mercury (T-Hg) in muscle of five fish species from the Alto Nanay River (Loreto, Peru) across wet and dry seasons to characterize contamination patterns and implications for human consumers. Across all species, T-Hg ranged from 0.16 to 3.79 mg kg−1. The highest mean burdens occurred in piscivores: Pseudoplatystoma punctifer (2.63 ± 1.03 mg kg−1, 1.60–3.66; n = 6) and Cichla monoculus (2.43 ± 0.26 mg kg−1, 2.17–2.69; n = 6), exceeding a widely used food-safety guideline (0.5 mg kg−1). Mean concentrations were higher in the wet season (1.68 ± 0.94 mg kg−1; n = 15) than in the dry season (1.31 ± 0.54 mg kg−1; n = 15), with a difference of 0.37 mg kg−1 (≈28% increase). Linear regression analyses indicated low–moderate size-dependence of T-Hg (standard length R2 = 0.19; total length R2 = 0.20; total weight R2 = 0.12; all p < 0.05). These findings show that two piscivorous species from the Alto Nanay frequently exceed recommended limits for safe human consumption and highlight the need for continuous monitoring and species- and size-specific fish-consumption advisories to protect Amazonian riverine communities.