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