Mercury is used in gold mining in the Brazilian Amazon and released in significant amounts to the environment as Hg 0 . After its oxidation it may be methylated, mainly in bottom sediments and in the rhizosphere of floating aquatic macrophytes. Methylmercury (MeHg) is highly bioavailable and subject to biomagnification.
The objective of this work was to evaluate the efficiency of three methylmercury extraction techniques, applied to replicates of environmental samples (stream sediments from Floresta da Tijuca, Rio de Janeiro; and roots of the floating macrophyte Eichhornia crassipes from Lagoinha, Rio de Janeiro) previously incubated with 203 Hg 2 . Method A is based on acid leaching and extraction of Me 203 Hg in toluene. Method B uses alkaline digestion, extraction in dithizone-benzene and separation of organic and inorganic 203 Hg dithizonates by thin-layer chromatography (TLC). Method C consists in separating the Me 203 Hg from the sample matrix by distillation. Total 203 Hg and Me 203 Hg were detected by gamma spectrometry or liquid scintillation. For both matrices, Me 203 Hg extraction efficiency was better for smaller samples (range: 0.08-0.5 g for sediment, 0.1-0.5 g for E. crassipes roots). For the sediment samples, the three selected methods presented similar Me 203 Hg extraction efficiencies: 7-13, 5-14 and 4-17% of total added 203 Hg was found as MeHg for procedures A, B and C, respectively. For E. crassipes roots, on the other hand, a lower extraction efficiency was obtained for the procedure C (11-28% of total 203 Hg present as Me 203 Hg) than for methods B (22-36%) and A (20-44%). In all the root samples prepared with procedure B, a strong and durable chemiluminescence effect was observed, which required measuring the final Me 203 Hg extracts by gamma spectrometry only. In the specific conditions we used, extraction via distillation required reextraction of Me 203 Hg in the distillate, due to the presence of traces of inorganic 203 Hg in the latter.