Mercury in Fish from Guanabara Bay, Southeast Brazil: Tissue-Specific Accumulation and Human Health Risks

Guanabara Bay is Brazil’s second-largest bay and has a long history of intense industrial and domestic pollution. Some local communities rely on fish as a primary protein source, justifying an assessment of mercury (Hg) contamination. This study determined total mercury (THg) concentrations in nine fish species and evaluated the toxicological risks associated with human consumption. One hundred specimens were analyzed, and samples of muscle, liver, and gills were collected. THg analyses were performed using atomic absorption spectrometry following thermal decomposition, employing a DMA80 ® analyzer. The liver showed the highest mean THg concentrations, followed by muscle and gills, reflecting its role in metal biotransformation. Predatory species exhibited higher levels, particularly Centropomus parallelus and Alosa fallax . One A. fallax individual exceeded the maximum permissible limit established by the Brazilian Health Regulatory Agency (ANVISA) (1.0 mg·kg⁻¹). Correlation analysis showed a significant positive association between liver and gill THg concentrations (ρ = 0.531; p < 0.0001), suggesting shared physiological mechanisms in Hg accumulation. A weak negative correlation was observed between body weight and muscle THg concentrations (ρ = − 0.242; *p* = 0.0153), whereas no significant association was found with fish length. These results suggest that body size alone did not explain the variability in muscle THg concentrations. Dietary habits and other ecological and physiological factors can also influence this. Risk assessment based on fish consumption data from 126 residents showed HQ < 1 across all scenarios, indicating low risk. However, the occurrence of a specimen exceeding the legal limit demonstrates the need for continued Hg monitoring in Guanabara Bay.