Re‐evaluation of distillation and comparison with HNO₃ leaching/solvent extraction for isolation of methylmercury compounds from sediment/soil samples

Abstract

Distillation was re-evaluated for the formation of artifacts arising from increasing naturally occurring mercury(II) concentrations, as opposed to previous identification of artifacts by spiking standard mercury(II) into samples. Naturally occurring mercury(II) concentrations lower than 2 µg g −1 were found not to affect methylmercury (MeHg) results. However, when the natural concentrations of mercury(II) were greater than 2 µg g −1 , in contrast to standard mercury(II) spiked in samples, the MeHg concentrations measured were found to decrease (not increase) with increasing naturally occurring mercury(II) concentrations. This indicated that standard mercury(II) spiked in samples behaved differently from naturally occurring mercury(II) in the formation of MeHg artifacts during distillation. As a result, spiking standard mercury(II) into samples to identify the formation of MeHg artifacts is not adequate. It is difficult to explain why high naturally occurring mercury(II) suppresses MeHg measurements during distillation. In comparison with HNO 3 leaching/solvent extraction (and other existing techniques), distillation was found to generate results comparable for samples containing less than 2 µg g −1 mercury(II). The HNO 3 leaching/solvent extraction showed significant advantages over other procedures, as this technique generated the highest recoveries with good precision for all samples analyzed, and the results were found to be independent of mercury(II) concentrations for both naturally occurring and spiked standard mercury(II). Thus, except for samples from high mercury-contaminated fields, distillation is still a good choice. Both the positive bias (possibly caused by artifact formation of MeHg) and the negative bias (due to incomplete leaching, back-adsorption, and/or decomposition of MeHg) were investigated. Geologically, physically, and chemically different samples were used for the investigation.

Linkage between community diversity of sulfate-reducing microorganisms and methylmercury concentration in paddy soil

“…For Hg analysis, soil samples were first digested with HNO 3 + HCl (10 ml, 1:1 v/v) in a teflon tube at 100°C for 2 h. Total Hg concentration was then determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Soil samples were prepared for MeHg analysis using CuSO 4 -methanol/solvent extraction according to the method outlined by (Liang et al 2004), following which MeHg contents were determined using HPLC-ICP-MS.…”

Methylmercury Accumulation in Rice Grain (Oryza sativaL.): Environment and Genotype Controls

“…Three rice paddies were selected in Guizhou province, southwestern China, including the background site (located at the Guizhou Rice Research Institute) and the moderately-and highly-contaminated sites (both located (Liang et al, 1996(Liang et al, , 2004, then MeHg was quantified using the same methods described for pore water MeHg concentrations following EPA Method 1630.…”

Simplified sample preparation procedure for measuring isotope‐enriched methylmercury by gas chromatography and inductively coupled plasma mass spectrometry

“…The procedure of Hintelmann et al [5,11] was used for sample preparation (distillation), followed by aqueous-phase ethylation (derivatization) and detection (GC-ICP-MS), according to the P1 procedure shown in Figure 1 (steps 3-5). During MeHg analysis, special attention was paid to sample aliquots to be distilled to maintain the original species distribution and avoid species transformation (formation of MeHg artifacts [10,17,19]); aliquots containing 1 to 2 g sediment (MeHg fraction 0.28%) were taken for distillation. The results were used as a method of comparison for isotopically enriched MeHg quantification, as well as for total methylmercury (SMeHg-all isotopes) values.…”

“…Using an acid extracting procedure (HNO 3 leaching), Liang et al [17] observed no artifact formation, and noted that the measured MeHg was independent of the naturally occurring Hg(II) content in the aliquots of the analyzed sediment samples. In our tests, the stable isotope spike ( 200 Hg 2þ ) and the internal standard (Me 201 Hg) were added just before the acid KBr-CuSO 4 mixture, and no additional MeHg formation was noticed (Table 3) for all samples, except F4 for which a small increase was measured.…”

“…Recently, new extraction approaches [16,17] have been developed for MeHg isotope analysis to replace the distillation step. They employ solvent extraction and back extraction in water prior to derivatization and detection.…”