Differences in methylmercury and inorganic mercury biomagnification in a tropical marine food web.

Methylmercury (MeHg), inorganic mercury (Hginorg) and their biomagnification factors (BMF) were evaluated along a non-degraded Brazilian bay food web. Highly significant differences (p < 0.0001) were found between MeHg and Hginorg concentrations among all organisms (microplankton, shrimp, fish and dolphin). MeHg increased with increasing trophic position while Hginorg did not present the same pattern. BMF values for MeHg were higher than 1 for all trophic interactions from source to consumer, indicating that MeHg was transferred more efficiently and biomagnified over the entire web. Only one BMF exceeding one was observed for Hginorg (27) between microplankton and their consumer, planktivorous fish. BMF values for Hginorg were significantly different than those found for MeHg (20) at the base of the food web.