Mercury levels assessment in hair of riverside inhabitants of the Tapajós River, Pará State, Amazon, Brazil: Fish consumption as a possible route of exposure

The study present evaluated the levels of mercury (Hg) and methylmercury (MeHg) in hair samples of people from Barreiras community, riverside inhabitants of the Tapajós River (Pará, Brazil), an area impacted by clandestine gold mining, as well as we analyzed the levels of Hg and Se (selenium) in nine fish species (carnivores and non-carnivorous) from the Tapajós River, which stand out as the main species consumed by riverside inhabitants, to evaluate a relationship between frequency of fish consumption and Hg concentration, and also to evaluate possible mechanisms of fish protection (or non-protection) to Hg exposure by Se. Furthermore we analyze the water quality to evaluate the environmental trophic state, fact responsible by creating conditions that can potentiate the effects of toxic mercury. Concentrations of Hg and MeHg were analyzed in hair samples of 141 volunteers in different age band. Of those, 84.40% of samples present values above the threshold for biological tolerance, which is 6.00 μg g−1 of total Hg in hair. Total Hg, in men there was a variation of 2.07–24.93 μg g−1, while for women the variation was 4.84–27.02 μg g−1. Consequently, the level of MeHg in men presented a variation of 1.49–19.57 μg g−1, with an average of 11.68 μg g−1, while with women the variation was from 3.73 to 22.35 μg g−1, with an average of 10.38 μg g−1. In fish species, Hg concentrations in carnivorous species had an average of 0.66 μg g−1, higher than that permitted by current legislation, ranging from 0.30 to 0.98 μg g−1, while the non-carnivorous species have values below the recommended by the legislation averaging 0.09 μg g−1, ranging between 0.02 and 0.44 μg g−1. For Se in fish, show that among carnivores, the contents of Se ranged between 0.18 and 0.54 μg g−1 with a mean of 0.34 μg g−1, while for non-carnivores these values were of the order of 0.16–0.56 μg g−1, with an average of 0.32 μg g−1. In surface water quality variables at the sampling points all showed values in accordance with the range established by current legislation. In this regard, the results provided by this study, while not conclusive, are strong indicators that despite not having been shown the relationship between the concentration of mercury in hair and feeding habits along the Tapajós River basin communities showed that a plausible correlation exists between levels of mercury and selenium in fish. This fact may serve as a subsidy to research human health, because in the Amazon, there is still a lot to examine with regards to the full understanding of the Se cycle.