Mercury and DDT exposure risk to fish-eating human populations in Amazon

In order to investigate the potential risk of mercury and DDTs exposure to fish-eating human populations in Samuel Reservoir, not affected directly by gold-mining activities, the axial muscle of Cichla monoculus was analyzed. Twenty-nine and thirty adults individuals were collected respectively on February (rainy season) and August (dry season) 2007. The specimens were sacrificed by spinal section before sex identification, body weight and total length determination. For total mercury, DDT and DDE quantifications and cholinesterase activity samples of the axial muscle were frozen at -20°C, and for histopathological studies gill and liver were fixed in ALFAC solution for 16 h. A value of 48.2% and 33% of the individuals, respectively from rainy and dry seasons, presented mercury concentrations higher than the maximum established for safe human consumption (0.5 μg g⁻¹) by World Health Organization. A positive correlation between body weight and Hg concentration was observed only in individuals from the rainy season, but no correlation was observed to DDT and DDE from both seasons. Differently from that observed to mercury, DDT levels presented a significant difference between both studied seasons, but no correlation was observed for both mercury and DDTs and sex. The levels of DDTs in muscle of C. monoculus are under the maximum established by FAO-Alimentarius CODEX and Swedish Food Regulation for human consumption. The histopathological and neurotoxic findings showed that the wild population of fish is affected by chronic exposure to mercury, meaning risk also to fish-eating populations. Finally, the results showed that C. monoculus is an important vehicle for human exposure to mercury and DDTs in Samuel Reservoir and that it is necessary a continuous biomonitoring of the levels of both pollutants in order to manage the risk of exposure to human populations.