Evaluating total mercury and methylmercury biomagnification using stable isotopes of carbon and nitrogen in fish from the Madeira River basin, Brazilian Amazon

The isotopic signatures of carbon in primary consumer fish species in the Madeira River basin (Western Amazon) follow a pattern, with basal species feeding mainly on C-3 (e.g., vascular plants and phytoplankton). In this study with 196 specimens of 19 fish species and six trophic guilds, significant differences were found between the two main groups of primary consumers (herbivores and detritivores) in the Madeira River basin. The mercury and delta N-15 data indicated that the fish specimens collected in Puruzinho and Cunia Lakes provided greater trophic magnification factors (TMFs) for this metal than those found in the corresponding rivers. In relation to total mercury (0.09-2.07 mu g g(-1)) and methylmercury (0.05-1.91 mu g g(-1)) concentrations, the piscivorous/carnivorous species exceeded the values recommended by the World Health Organization, with a [MeHg:THg] ratio of about 80%. Preventive and educational practices should be adopted to reduce the possible toxic effects of Hg in the riverside population, for whom fish constitutes the main protein source. Also, biomonitoring of the fish species in the Madeira River should be conducted on an ongoing basis to detect possible alterations in mercury concentrations.

Automated summary

The isotopic signatures of carbon in primary consumer fish species in the Madeira River basin show a distinct pattern. This study revealed significant differences between the two main groups of primary consumers in the basin. The mercury and delta N-15 data indicated higher trophic magnification factors in fish specimens collected from lakes compared to those from rivers. Piscivorous/carnivorous species exceeded recommended values for total mercury and methylmercury concentrations. Preventive measures and ongoing biomonitoring of fish species are necessary to reduce potential toxic effects and detect alterations in mercury concentrations.