Mercury is used in gold mining in the Brazilian Amazon and released in significant amounts to the environment as Hg0. 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 203Hg2+. Method A is based on acid leaching and extraction of Me203Hg in toluene. Method B uses alkaline digestion, extraction in dithizone–benzene and separation of organic and inorganic 203Hg dithizonates by thin‐layer chromatography (TLC). Method C consists in separating the Me203Hg from the sample matrix by distillation. Total 203Hg and Me203Hg were detected by gamma spectrometry or liquid scintillation.
For both matrices, Me203Hg 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 Me203Hg extraction efficiencies: 7–13, 5–14 and 4–17% of total added 203Hg 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 203Hg present as Me203Hg) 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 Me203Hg extracts by gamma spectrometry only. In the specific conditions we used, extraction via distillation required re‐extraction of Me203Hg in the distillate, due to the presence of traces of inorganic 203Hg in the latter. Copyright © 1999 John Wiley & Sons, Ltd.