Mercury pollution in the atmosphere comes mainly from coal-fired power stations and chemical plants. Mercury is naturally present in coal and is emitted when it is burned as fuel. If deposited in soil or water, mercury can eventually reach toxic concentrations which may pose a health risk to humans through accumulation in food chains.
The dangers of mercury pollution prompted the EU to launch a mercury strategy in 2005, which aims to protect against exposure1. The United Nations is considering what further action should be taken to reduce global emissions.
New research suggests that the source of atmospheric mercury could be traced by analysing mercury 'isotopes', which are already used to study other forms of chemical pollution, such as nitrate pollution. Elements, such as mercury, have a number of variants which differ according to atomic composition, for example, the number of neutrons may differ. Each one of these variants is an 'isotope'.
Environmental factors, such as specific atmospheric and river conditions at the prehistoric point in time when the coal was originally formed, will have influenced the concentrations of specific mercury isotopes. This variation means that isotopes can be used as chemical signatures or 'fingerprints' for the various sources. Isotopes can be detected by analysing samples containing the pollutants in question.
Emissions from power stations are distributed globally and are difficult to attribute to their original source. The research explains how isotopes could be used as tracers for atmospheric mercury pollution. By burning 30 coal samples from across the United States, China and Russia-Kazakhstan, the researchers produced emissions which could then be analysed to identify the mercury fingerprint.
The researchers found that the mercury fingerprint for coal from each of the three regions is different. Even coal deposits in the same country can differ quite considerably and may even be globally unique. This means it could be possible to distinguish between emissions from different sources within a relatively small region.
This method could help us understand the global mercury budget as well as help scientists learn more about how mercury behaves in the environment. Many different processes, such as exposure to light or bacteria, can affect the way mercury is cycled and stored. A better understanding of these processes could lead to new ways of reducing mercury's impact on the environment and human health.