Formation of Artifact Methylmercury during Extraction from a Sediment Reference Material

Abstract

We examined monomethylmercury (MMHg) in sediment reference material IAEA-405 and sediments from Long Island Sound. MMHg was extracted by both aqueous distillation and leaching with dilute solutions of nitric acid. MMHg was formed from both ambient and added inorganic mercury in extracts of IAEA-405 by either technique. Artifact MMHg in IAEA-405 was related linearly with ambient reactive mercury (HgR) in leachates having > 1.2 M acid, but little or no artifact was measured in less acidic extracts. Addition of potassium chloride enhanced extraction of HgR from LAEA-405 but had no effect on artifact MMHg for each leachate molarity tested. Mercury methylation occurred in solution and was a function of both the availability of HgR and a methylation potential, being limited by HgR in less acidic solutions (0.5-1.2 M) and by the methylation potential in more acidic ones (> 1.2 M). Formation of artifact MMHg in Long Island Sound sediments was inconclusive, but additions of inorganic mercury demonstrated that a potential exists. A potential for abiotic mercury methylation seems always present in sediment, and the availability of HgR appears to control MMHg production under environmental conditions. Abiotic methylation of mercury may occur in environs where the reactivity of inorganic mercury is enhanced, such as river-seawater mixing zones.

Organic and total mercury determination in sediments by cold vapor atomic absorption spectrometry: methodology validation and uncertainty measurements

“…This alteration was done in order to avoid the accidental formation of organomercurial compounds that can occur in higher concentrations of HCl in samples characterized by high organic matter and high inorganic Hg contents. 12,14,15 In the present study the preliminary results using BCR CRM 580 and IAEA 405 reference materials, the organic concentrations found were much higher than the certified values using 5 mL of HCl 6.0 M. IAEA 405 showed a variation of 9 to 12 µg kg -1 when compared to the 5.5 µg kg -1 certified value. For BCR CRM 580 the values fell between 97 and 115 µg kg -1 , the certified reference value being 75 µg kg -1 .…”

“…Several authors [11][12][13][14][15][21][22][23][24] cite the accidental MeHg formation as one of the main problems in determining this analite and consequently in the organic Hg determination. According to these authors, the % of Hg +2 methylated is low (up to 0.5%, but normally between 0.01 to 0.05% in relation to Hg +2 ).…”

“…This occurs in some polluted sediments and residual waters, depending on the quantity of Hg +2 and methylation potential of the sample, which also depends mainly on organic matter content. 12,14,15,22,23 Then the methylation contribution was not considered in this study once is too low. Table 7 presents the results obtained in the reference material analyses for total Hg using the experimental procedure according to the US EPA 3051A.…”

Mercury and monomethylmercury in fluids from Sea Cliff submarine hydrothermal field, Gorda Ridge

“…If the presence of high percentages of MMHg in very hot hydrothermal vent fluids are the result of abiological methylation of Hg somewhere within the system, this would be the first observation of hydrothermal organometallic chemistry. Abiotic methylation of Hg has been observed under different conditions [Bloom et al, 1997;Hammerschmidt and Fitzgerald, 2001;Gardfeldt et al, 2003] and appears to require relatively high concentrations of a methyl donor. Such conditions may be found in hydrothermal fluids, though more likely on heavily sedimented systems unlike Sea Cliff [Cruse and Seewald, 2001].…”

Methylmercury cycling in sediments on the continental shelf of southern New England

“…Total Hg in the solid phase was quantified with a Milestone DMA-80 pyrolytic Hg analyzer. MMHg was extracted from sediment and pore water by aqueous distillation (Hammerschmidt and Fitzgerald, 2001) and measured with flow-injection gas chromatographic CVAFS (Bloom, 1989;Tseng et al, 2004).…”