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Environmental Analysis - Focus on Mercury


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Screening for Mercury at Suspected Contaminated Land Sites


Contaminated land. Land contaminated by previous industrial activities, past military uses and mining operations continue to be a source of concern to communities looking to redevelop brownfield sites, as local authorities struggle to evaluate the risk to health posed from these sites and formulate appropriate remediation plans. In addition to a long list of organic contaminates, such as chlorinated solvents, polyaromatic hydrocarbons (PAHs) and oil residues, soil at many former manufacturing sites have high levels of metals such as arsenic, lead, antimony, chromium, nickel and mercury, which impact drinking water quality.


In summary, a range of sampling and analytical methods can be used to assess mercury contamination at former industrial and mining sites.


Other routes by which these contaminants can affect the health of local residents may be less apparent, such as consumption of vegetables grown in contaminated soil, inhalation of airborne particles and hunting, so risk assessment has to take account not only of all the potential pathways for contaminants, but also the age and sex of likely receptors. Consequently, most regulatory agencies issue guidelines to assist investigators in evaluating contaminated land, such as the Department for Environment, Food and Rural Affairs (DEFRA) in England and Wales (Cole & Jeffries, 2009) or the Scottish Environmental Protection Agency (SEPA) in Scotland.


Mercury was used extensively in many industries, especially in chlor- alkali production, where it was used as an electrode in the production of


Cl2 and NaOH from brine. It was used in the gas industry for manometer and pressure measurements, in switches and thermostats, as well as thermometers. It is still widely used by artisanal miners to extract gold from ore. Mercury compounds are known to be highly toxic and were responsible for one of the most notorious environmental disasters at Minimata, Japan in the 1950’s, where 2,265 victims suffered from often fatal neurological symptoms that were directly linked to the consumption of mercury tainted fish and shell food, later termed Minimata Disease. The source of Hg pollution was directly linked to water discharges from a factory operated by the Chisso Corporation, which manufactured acetaldehyde using mercury sulphate as a catalyst; mercury was discharged into Minimata Bay as a by-product. Mercury use in many industries has been greatly reduced through international agreements, with better control on sources and releases, although the single largest source of Hg0


emissions is from coal-burning power stations.


Mercury is present in the environment in three main forms; elemental mercury (Hg0


) in the atmosphere, inorganic compounds such as the Author Details:


Keith Torrance and Helen Keenan University of Strathclyde, Glasgow, United Kingdom. University of Strathclyde Dept of Civil and


Environmental Engineering 107 Rottenrow, Glasgow, G4 ONG, United Kingdom


Email: keith.torrance@strath.ac.uk Tel: +1 614 264 4506


Web: www.strath.ac.uk/civeng


mineral cinnabar (HgS) in rocks and soils, and a range of organomercury compounds which are present in aquatic sediments and organisms. The toxicity of organic mercury compounds, such as methyl mercury (MeHg), is almost 100 times greater than their inorganic counterparts, so the form of Hg is crucial in assessing potential hazards. Low levels of inorganic mercury in soils and sediments can be converted into potentially more toxic levels through microbiological activity, if conditions are suitable. A further concern is that MeHg bioaccumulates in fish and through predation biomagnifies up the food chain, with methyl mercury accumulating in the tissue of many piscivore species to toxic levels. Mercury levels in some fish species can be 106 greater than Hg levels in river water (Leopold et al., 2010), with no obvious signs of ill effect. This creates a potential pollution linkage to communities downstream of contaminated sites that are dependent on fish as a major component of their diet. Many regions issue warnings advising pregnant women to limit consumption of certain fish such a because of the neurotoxicological effects of Hg on foetal development.


Sampling plans


Site investigation to determine the presence of toxic metals at a site involves the collection of soil samples from trenches, sediments from streams and water samples from boreholes and surface water and modelling the data to assess risk to potential receptors. Historical maps and aerial photographs are invaluable tools for identifying likely spots at the site where waste might have been dumped or chemical leaked, so a desk study of available published material is undertaken to formulate a detailed sampling plan. Analysis of aqueous samples by inductively coupled plasma-mass spectrometry (ICP-MS) is the most widely used method to simultaneously determine the concentrations of trace metals, with detection limits below 1 µg L-1


for most metals. However, as


background Hg levels in surface water are typically in the range of 1 – 80 ng L-1


the most heavily contaminated environmental samples, although detection can be improved by using cold vapour generation prior to introduction into the instrument.


Other analytical techniques allow much lower detection levels for mercury analysis. The USEPA has approved Method 245.1 (USEPA, 1994) for the determination of mercury in water by cold vapour atomic fluorescence spectrometry (CVAFS), which has detection levels down to 0.5 ng L-1


under ideal conditions. Samples for CVAFS analysis should be


collected in amber glass bottles, acidified and sealed with a Teflon® cap to minimise volatile Hg0


loss and kept at 4o C until analysis. , ICP-MS is usually not sensitive enough to measure Hg in all but


Figure 1: Atomic fluorescence spectrometer (PS Analytical Ltd.)


Sequential chemical extractions (SCE) (Bacon & Davidson, 2008), using five or six steps of chemicals is often used to extract Hg from sediments as different inorganic species will be released by successively stronger extractants. Organic mercury compounds are removed by the potassium hydroxide extraction step, as shown in Table 1, and the results be used to estimate bioavailability based on the fractions that are likely to be dissolved in the digestive system.


/iET November / December 2012 www.envirotech-online.com


Article first published in Asian Environmental Technology October/November


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