Title: Removal of inorganic mercury by selective extraction and coprecipitation for determination of methylmercury in mercury-contaminated soils by chemical vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS)

Abstract

A procedure is developed for selective extraction of methylmercury (CH₃Hg⁺) from heavily Hg-contaminated soils and sediments for determination by chemical vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS). Soils artificially contaminated with 40 μg g^–1 inorganic mercury (Hg²⁺) or methylmercury chloride (CH₃HgCl) were agitated by shaking or exposing to ultrasounds in dilute hydrochloric acid (HCl) or nitric acid (HNO₃) solutions at room temperature. Extractions in HCl (5 or 10% v/v) resulted in substantial leaching of Hg²⁺ from soils, whereas 5% (v/v) HNO₃ provided selectivity for quantitative extraction of CH₃Hg⁺ with minimum Hg²⁺ leaching. Agitation with ultrasounds in 5% (v/v) HNO₃ for about 3 min was sufficient for extraction of all CH₃Hg⁺ from soils. Coprecipitations with Fe(OH)₃, Bi(OH)₃ and HgS were investigated for removal of residual Hg²⁺ in soil extracts. Hydroxide precipitations were not effective. Thiourea or l-cysteine added to soil extracts prior to hydroxide precipitation improved precipitation of Hg²⁺, but also resulted in removal of CH₃Hg⁺. HgS precipitation was made with dilute ammonium sulfide solution, (NH₄)₂S. Adding 30 μL of 0.35 mol L^–1 (NH₄)₂S to soil extracts in 5% (v/v) HNO₃ resulted in removal of all residual Hg²⁺ without impacting CH₃Hg⁺ levels. Vapor generation was carried out by reacting Hg²⁺-freemore » soil extracts with 1% (m/v) NaBH₄. No significant interferences were observed from (NH₄)₂S on the vapor generation from CH₃Hg⁺. The slopes of the calibration curves for CH₃HgCl standard solutions in 5% (v/v) HNO₃ with and without (NH₄)₂S were similar. Limits of detection (LOD, 3s method) were around 0.08 μg L^–1 for 5% (v/v) HNO₃ blanks (n = 10) and 0.10 μg L^–1 for 5% (v/v) HNO₃ + 0.005 mol L^–1 (NH₄)₂S blanks (n = 10). Percent relative standard deviation (%RSD) for five replicate measurements varied between 3.1% and 6.4% at 1.0 CH₃HgCl level. The method is validated by analysis of two certified reference materials (CRM); purely Methylmercury sediment (SQC1238, 10.00 ± 0.291 ng g^–1 CH₃Hg⁺) and Hg-contaminated Estuarine sediment (ERM – CC580, 75 ± 4 ng g–1 CH₃Hg⁺ and 132 ± 3 μg g^–1 total Hg). CH₃Hg⁺ values for SQC1238 were between 13.0 and 13.2 ng g^–1, and 79 and 81 ng g^–1 for ERM – CC580. Hg-contaminated soils (57–96 μg g^–1 total Hg) collected from the floodplains of Oak Ridge, TN were analyzed for CH₃Hg⁺ using the procedure by CVG-ICPMS. CH₃Hg⁺ levels ranged from 30 to 51 ng g^–1 and did not correlate with total Hg levels (R² = 0.01).« less

Authors:

Denmark, Iris S. ^[1]; Begu, Ermira ^[1]; Arslan, Zikri ^[1]; Han, Fengxiang X. ^[1]; Seiter-Moser, Jennifer M. ^[2]; Pierce, Eric M.  ^[3]

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+ Show Author Affiliations

1. Jackson State Univ., Jackson, MS (United States)
2. Engineer Research and Development Center (ERDC), Vicksburg, MS (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:

Tue Aug 28 00:00:00 EDT 2018

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); USDOE Office of Environmental Management (EM)

OSTI Identifier:

1495997

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Analytica Chimica Acta

Additional Journal Information:

Journal Volume: 1041; Journal Issue: C; Journal ID: ISSN 0003-2670

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Methylmercury; Extraction; Coprecipitation; Soil/sediment; Chemical vapor generation; ICP-MS