Determination of low methylmercury concentrations in peat soil samples by isotope dilution GC-ICP-MS using distillation and solvent extraction methods

Heidi Pietilä; Paavo Perämäki; Juha Piispanen; Mike Starr; Tiina Nieminen; Marjatta Kantola; Liisa Ukonmaanaho

doi:10.1016/j.chemosphere.2014.11.001

Determination of low methylmercury concentrations in peat soil samples by isotope dilution GC-ICP-MS using distillation and solvent extraction methods

Chemosphere. 2015 Apr:124:47-53. doi: 10.1016/j.chemosphere.2014.11.001. Epub 2014 Nov 28.

Authors

Heidi Pietilä¹, Paavo Perämäki², Juha Piispanen³, Mike Starr⁴, Tiina Nieminen⁵, Marjatta Kantola⁵, Liisa Ukonmaanaho⁵

Affiliations

¹ Finnish Forest Research Institute, Oulu Research Unit, P.O. Box 413, FI-90014 University of Oulu, Finland; University of Oulu, Department of Physics and Chemistry, P.O. Box 3000, FI-90014 University of Oulu, Finland.
² University of Oulu, Department of Physics and Chemistry, P.O. Box 3000, FI-90014 University of Oulu, Finland. Electronic address: paavo.peramaki@oulu.fi.
³ Finnish Forest Research Institute, Oulu Research Unit, P.O. Box 413, FI-90014 University of Oulu, Finland.
⁴ University of Helsinki, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland.
⁵ Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland.

PMID: 25434268
DOI: 10.1016/j.chemosphere.2014.11.001

Abstract

Most often, only total mercury concentrations in soil samples are determined in environmental studies. However, the determination of extremely toxic methylmercury (MeHg) in addition to the total mercury is critical to understand the biogeochemistry of mercury in the environment. In this study, N2-assisted distillation and acidic KBr/CuSO4 solvent extraction methods were applied to isolate MeHg from wet peat soil samples collected from boreal forest catchments. Determination of MeHg was performed using a purge and trap GC-ICP-MS technique with a species-specific isotope dilution quantification. Distillation is known to be more prone to artificial MeHg formation compared to solvent extraction which may result in the erroneous MeHg results, especially with samples containing high amounts of inorganic mercury. However, methylation of inorganic mercury during the distillation step had no effect on the reliability of the final MeHg results when natural peat soil samples were distilled. MeHg concentrations determined in peat soil samples after distillation were compared to those determined after the solvent extraction method. MeHg concentrations in peat soil samples varied from 0.8 to 18 μg kg(-1) (dry weight) and the results obtained with the two different methods did not differ significantly (p=0.05). The distillation method with an isotope dilution GC-ICP-MS was shown to be a reliable method for the determination of low MeHg concentrations in unpolluted soil samples. Furthermore, the distillation method is solvent-free and less time-consuming and labor-intensive when compared to the solvent extraction method.

Keywords: Distillation; GC-ICP-MS; Methylmercury; Peat soil sample; Solvent extraction; Species-specific isotope dilution.

Publication types

Comparative Study
Research Support, Non-U.S. Gov't

MeSH terms

Bromides / chemistry
Copper Sulfate / chemistry
Distillation*
Environmental Monitoring / methods*
Gas Chromatography-Mass Spectrometry*
Liquid-Liquid Extraction*
Methylmercury Compounds / analysis*
Nitrogen / chemistry
Potassium Compounds / chemistry
Soil / chemistry*
Soil Pollutants / analysis*
Solvents / chemistry

Substances

Bromides
Methylmercury Compounds
Potassium Compounds
Soil
Soil Pollutants
Solvents
Copper Sulfate
Nitrogen
potassium bromide