Inorganic and methylmercury: do they transfer along a tropical coastal food web?

Methylmercury (MeHg) and inorganic mercury (Hg(inorg)) were evaluated in the water of a Brazilian estuary, with two size classes of plankton and seven fish species of different feeding habits. Water partition coefficients (PCs) in microplankton were fourfold higher for MeHg than for Hg(inorg); and water PCs in mesoplankton were 26 times higher for MeHg than Hg(inorg). Difference between microplankton and mesoplankton MeHg bioaccumulation factor (BAF) was higher (0.60 log units) than Hg(inorg) BAF (0.24 log units), indicating that trophic transfer of MeHg between planktonic organisms is more efficient than Hg(inorg) transference. MeHg concentrations, proportion of mercury as MeHg and its biotransference factors (BTFs) in the microplankton, mesoplankton and fish increased with increasing trophic level while biotic concentrations of Hg(inorg) and proportion of mercury as Hg(inorg) decreased thus indicating that MeHg was indeed the biomagnified species of mercury. MeHg reflected the vertical trophic guilds distribution, due to the fact that the top predator fish presented the highest concentration (0.77 μg g(-1)d.w.), followed by the less voracious species (0.43 μg g(-1)d.w.); while planktivorous fish presented the lowest concentrations (0.044 μg g(-1)d.w.). Hg(inorg) did not present the same behavior. Results suggest that feeding habits and trophic guild are important parameters, influencing biotransference and biomagnification processes.