Selenium and Mercury (Total and Organic) in Tissues of a Coastal Small Cetacean, Pontoporia blainvillei

Cetaceans present a high capacity to accumulate trace elements and have been considered a good bioindicator of contamination. The study assesses the concentration of selenium (Se) and mercury (Hg), as organic mercury (HgOrg) in the liver and kidney of a dolphin incidentally caught in fishing nets along two Brazilian areas (southeast and south). No significant differences were observed in the concentrations for both sexes. The liver showed the highest concentrations of mercury and organic mercury. Hepatic organic and total mercury in individuals from the South coast were about four times as high as those from the Southeast coast. Body length influenced the accumulation of these contaminants in both organs, and hepatic concentrations increased with this parameter, according to the sampling area. Hepatic organic and total mercury concentrations increased with body length in individuals from the Southeastern coast, although no significant correlations were observed between body length from each area. A significant positive linear relationship was observed between molar concentrations of Hg and Se in the liver of all individuals from both areas, presenting a Se:Hg ratio of 4. Differences found among the concentrations in dolphins from both areas were probably due to the preferred prey, bioavailability of elements in each marine environment, and environment variables (water temperature, net primary production). As a consequence, concentrations of trace elements in the tissues of this species can be considered to be a result of the surrounding environment.