Comparative tests on the efficiency of three methods of methylmercury extraction in environmental samples

Abstract

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.

Determination of methylmercury by solid-phase microextraction inductively coupled plasma mass spectrometry: a new sample introduction method for volatile metal species

“…11 Accurate determination of methylmercury in real samples often requires an extraction step coupled with a further separation prior to detection. Uria and Sanz-Medel 12 have recently reviewed some of the most popular extraction/ derivatization and separation/detection methods for mercury speciation in environmental samples including: liquid±liquid, 13 acid 14,15 and base 16 leaching, distillation 17 and chemical vaporization, employing hydride-, 18 ethyl- 18 and phenyl- 19 derivatization. Although quite simple, these techniques are often non-selective such that methylmercury is extracted with other alkylated forms.…”

Simultaneous radioassays of bacterial production and mercury methylation in the periphyton of a tropical and a temperate wetland

“…Many studies have reported very high methylmercury formation (up to 44% conversion of Hg 2+ to MeHg in 24 h) in the periphyton associated with roots of tropical floating macrophytes, using radiotracers (Guimara˜es et al, 1998(Guimara˜es et al, , 2000aMauro et al, 2001) enriched stable isotopes (Mauro et al, 2002) or other techniques (Brito and Guimara˜es, 1999). When normalized to sample dry weight, the Hg net methylation potentials in the periphyton and epilithon of boreal lakes found by Planas et al (2004) were comparable to the ones found in the periphyton of tropical macrophytes, which are on the average one order of magnitude higher than in the underlying surface sediments (Guimara˜es et al, 2000b).…”

Mercury methylation in sediments of a Brazilian mangrove under different vegetation covers and salinities

“…Results are expressed as the percentage of total added 203 Hg that was converted into MM 203 Hg. The validity of the assumption that all activity in the final extract is MM 203 Hg was confirmed by backextraction in Na 2 S and then in benzene, followed by separation by thin-layer chromatography and quantification by liquid scintillation (Brito and Guimarães, 1999). As mentioned before, it is important to note that this methodology cannot separate methylation and demethylation rates, thus yielding only an estimate of potential net methylation rates.…”