Speciated Mercury

Mercury is a naturally occurring element that is found in air, water and soil. The symbol for mercury is Hg and it comes from its Greek name, hydrargyrum, which means “liquid silver”.

Mercury Speciation in Environmental Samples

Occurrence and toxicity
Mercury has been used by man since ancient times and was known to the Egyptians as early as 1500BC. In China and Tibet, mercury use was thought to prolong life, heal fractures, and maintain generally good health. Contrary to this, it has been known for some time now that mercury and most of its compounds are extremely toxic and has been responsible for several environmental ‘disasters’. A renowned industrial disaster was the dumping of mercury compounds into Minamata Bay, Japan between 1932 and 1968. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease. Methyl-mercury is the most toxic form; it affect the immune system, alters enzyme and genetic systems and damages the central nervous system, including coordination and the senses of touch, taste and sight (link: WHO Mercury and health).

Mercury in the environment
Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). Cinnabar is highly toxic by ingestion or inhalation of the dust. Mercury poisoning can also result from exposure to water-soluble forms of mercury (such as mercuric chloride or methyl-mercury), inhalation of mercury vapor or from eating seafood contaminated with mercury. Mercury is most commonly encountered in the environment in either:

  • its elemental form
  • as inorganic mercuric compounds
  • or as mono-methyl mercury

The toxicity, biochemical behaviour and transportation of mercury in the environment is highly dependant on its physio-chemical form. It has been shown that organo-mercury compounds (primarily methyl-mercury) may be up to one thousand times more toxic than inorganic mercury. Inorganic mercury can be methylated by abiotic and microbial processes in soil and aquatic systems and is the primary source of methyl-mercury compounds in soils and waters. Methyl-mercury may bioaccumulate in fish and shellfish; bioaccumulation describes a process whereby an organism contains a higher concentration of a substance than do the surroundings (link: Mercury in the environment).

Soil Guideline Values
In 2009, the Environment Agency released a technical note describing Soil Guideline Values (SGVs) for mercury in Soil (Science Report SC050021 / Mercury SGV). SGVs are an example of generic assessment criteria and can be used in the preliminary evaluation of the risk to human health from long-term exposure to chemicals in soil. Specifically this note provides SGVs for elemental, inorganic and methylated forms of mercury in soil. As a consequence of this, laboratories are now required to offer not only ‘total’ mercury analysis but also speciated analysis in order to separate and quantify elemental, inorganic and methyl-mercury compounds.

Analysis and Speciation

The preferred method for mercury speciation is to use reverse phase HPLC coupled to vapour generation atomic fluorescence spectrometry (HPLC-AFS) incorporating post-column oxidation, reduction and detection. As with all instrumental methods used for speciation, it is important that the technique offers good separation and sensitivity in order to quantify the individual species with both accuracy and precision.

Although organo-mercury found in fish and in waters is almost always methyl-mercury, recent publications have reported ethyl-mercury in some sediments and soil samples taken in the USA. HPLC-ACF can speciate methyl- and ethyl-mercury so that results for both are reported.Whereas water samples may be analysed directly without any pre-treatment, mercury from soil samples must first be extracted with a suitable solvent. Extraction can either be carried out using microwave assisted extraction with 4M nitric acid or by ultra-sound assisted digestion with an ethanol / hydrochloric acid mixed solvent. From one injection of extractant into the HPLC-AFC system, results are obtained for methyl-, ethyl- and inorganic mercury.

Elemental mercury is analysed separately also using atomic fluorescence spectrometry. The pre-treatment involves volatilisation of the elemental mercury from the soil and collection on a gold trap. The mercury is then thermally desorbed in a stream of argon and analysed by atomic fluorescence spectrometry.

Limits of detection achieved for all of the mercury species are well below the Soil Guideline Values recommended by the Environment Agency in their Technical Note.

Contact us to find out more about our speciated mercury tests.

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A number of different publications and standards cite sulphate methods. BR279 (1995) has largely been superseded by analytical procedures as detailed in TRL 447 and BRE Special Digest:1 2005 3rd Edition. In addition further reference may be made to BS EN 144-1:2009 + A1:2012 for the testing of aggregates and BS 1377:2018 for soils for civil engineering purposes.

Testing to meet the requirements of UKWIR Report Ref. No. 10/WM/03/21 Guidance for the selection of water supply pipes to be used in brownfield sites.

Testing & reporting is undertaken in accordance with BS 3882:2015 Specification for topsoil and BS 8601:2013 Specification for subsoil and requirements for use

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