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Speciated Mercury

DETS was one of the first laboratories to set up for speciated mercury, and continues to be a leading laboratory in this analysis.

Mercury and its compounds are highly toxic and present significant risks to human health, but different forms of mercury present different risks.  Therefore  the determination of speciated mercury can help in assessing that risk on brownfield sites.  
In 2009, the Environment Agency published a Science Report SCO 50021, entitled Soil Guideline Values for Mercury in Soil.  This document details the background, uses and toxicology of mercury, and states that analysis should be performed to provide values for three forms of mercury -  elemental, organic, and inorganic, and soil guideline values (SGVs) are provided for all three:
Land use SGV mg/kg dry weight SGV mg/kg dry weight SGV mg/kg dry weight
  Elemental Hg Inorganic Hg Methyl (organic) Hg
Residential 1 170 11
Allotment 26 80 8
Commercial 26 3600 410
The soil matrix is assumed to be a sandy loam with a TOC value of 6%
Elemental mercury is a volatile silvery liquid at room temperature, inorganic mercury (Hg2+) is measured as mercuric compounds, and organic mercury is measured as monomethylmercury with the general formula CH3HgX.  Elemental and organic are considered to be the most toxic due to inhalation risks.
Analysis of Elemental Mercury
Samples are tested on an as-received basis, as sample drying is likely to lead to loss of elemental mercury. Samples are purged with argon, the elemental mercury is collected on a silica-gold vapour trap and the collected elemental mercury analysed by atomic fluorescence spectroscopy. Quantification is performed by comparison to a generated calibration curve. 
Analysis of Inorganic Mercury and Methyl Mercury
Extraction of samples follows the USEPA Method 3200 guidelines for “Mercury species fractionation and quantification by microwave assisted extraction”.
Samples are homogenised and taken through a two-step microwave extraction procedure to take both the extractable and non-extractable mercury (semi and non-mobile) compounds into solution. The extracted species are separated by HPLC, oxidised to break down the organic complexes followed by treatment with a reducing agent and analysis by atomic fluorescence spectroscopy. All stages are performed on a continuous ‘on-line’ setup directly linked to an atomic fluorescence detector.
Quantification is performed by comparison to a generated calibration curve.
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