People and ecosystems increasingly exposed to mercury pollution

The emissions of some reactive halogens – such as chlorine, bromine or iodine – are causing greater deposition of mercury in the places closest to these emissions, and people and ecosystems, including the most pristine ones, are increasingly exposed in those regions to that powerful neurotoxin.

This has been verified by an international team of scientists, led by the Spanish Higher Scientific Research Council (CSIC), which has verified how these emissions increase the oxidation of atmospheric mercury and how this results in greater deposition on the Earth’s surface.

The researchers, who have published the results of their work in the journal PNAS, have corroborated that exposure to pollution occurs when mercury deposited in the food chain enters, for example, reaching rice, fish, shellfish, and ultimately, through consumption, to human beings.

The conclusions, obtained with a global model of atmospheric chemistry, also reveal that the greatest increases in human exposure to mercury pollution are located in China and India, which are the main emitters of mercury and anthropogenic halogens, the latter coming from the burning of coal and waste.

The work indicates that this impact, until now unknown, must be considered in environmental policies aimed at reducing the risks that exposure to mercury entails on the health of human beings and ecosystems.

“The oxidation chemistry of mercury in the atmosphere is decisive for the deposition of atmospheric mercury to the Earth’s surface, since it produces oxidized mercury compounds that are soluble and are deposited, mainly, by precipitation in the form of rain,” explained Alfonso Saiz-López, researcher at the Blas Cabrera Institute of Physical Chemistry (IQF-CSIC) in Madrid and coordinator of the study.

The scientist pointed out, in a CSIC note released today, that oceanic emissions of halogens, powerful oxidants of mercury, are key to the global oxidation and deposition of mercury, particularly in oceanic and polar regions.

In this work, in addition to natural halogen emissions, the researchers included a new source of halogens from the burning of coal and waste, and the results have shown that anthropogenic halogens considerably accelerate oxidation, and subsequent deposition of mercury in areas continental.

This new mercury oxidation mechanism increases the deposition of this toxin in regions close to the emission points and, thereby, reduces the transport of mercury from the emitting areas to pristine regions of the planet, such as the polar areas.

These results therefore show the need to reevaluate the relative contribution of mercury emissions from polluting regions, such as Asia, to the amount of mercury distributed around the planet.

“There is still ample uncertainty about the true extent of this new process, but our results point to the possible importance of a previously unconsidered mechanism that results in greater oxidation, and deposition, of mercury in inhabited areas.”said the researcher.

He therefore stressed the importance of beginning to include anthropogenic emissions of reactive halogens, and their consequent chemistry with mercury, in evaluations of the global cycle of this metal and its health risks in populated and contaminated areas.

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