March 2021 ESRFnews6

NEWS

PA C O B U S TA M A N TE

The results of these two studies shed light on how fauna manage to naturally get rid of the toxicity of mercury

Mercury detoxification in animals consumes more selenium than previously thought, according to research performed at the ESRF s ID26 beamline. The research which also presents a new, possibly universal biomineralisation mechanism suggests that terrestrial animals may be at risk from mercury poisoning, even if there are relatively high levels of selenium in the environment. Mercury is a global pollutant that

is generated both by natural sources, such as volcanoes and forest fires, and human activities, such as gold mining and coal combustion. In aquatic and terrestrial food chains it accumulates as methylmercury, which can affect the function of animals brains and reproductive systems. Chemically reduced forms of selenium, such as selenide, have long been known to detoxify mercury, but the biochemical mechanism was unknown. A team led by environmental

scientist Alain Manceau at Grenoble Alpes University and the CNRS in

Mercury detoxification laid bare France have unveiled the mechanism by studying tissue samples of two bird species those of giant petrels found in the Kerguelen Islands in Antarctica, and the Clark s grebe, a waterbird found in the lakes and wetlands of coastal California in the US via X-ray absorption spectroscopy at ID26. Thanks to years spent perfecting a stable, high energy- resolution and high-sensitivity set-up at ID26, the researchers were able to detect a selenium-containing mercury species, Hg(Sec)4 ( Sec meaning a selenocysteine amino acid), first in the liver of the Clark s grebe, and then in the liver, kidneys, muscles and brain of the giant petrels. They believe that the chemical species, which forms a complex with a protein known as selenoprotein P, is the main missing intermediate in the reaction that helps animals survive high levels of mercury by biomineralising methylmercury into non-toxic mercury selenide (Environ. Sci. Technol. 55 1527). The new chemical species has

unwelcome implications. Because the molar ratio of selenium to mercury in Hg(Sec)4 is 4:1, four selenium atoms are required to detoxify just a single mercury atom. The ESRF data allowed Manceau and colleagues to quantify the levels of selenium that were present in their tissue samples as either the new chemical species or mercury selenide, and found that the new chemical species was most present in muscle tissue. That suggests that on land where, unlike in seawater, selenium is not naturally abundant terrestrial animals could suffer from mercury toxicity more easily than previously thought, starting with their muscles (Environ. Sci. Technol. 55 1515). The results of these two studies

shed light on how fauna manage to naturally get rid of the toxicity of mercury, says Manceau, whose team has since identified the same biomineralisation reaction in other species of bird and a mammal, the long-finned pilot whale. This reaction is clearly universal.

ESRFMar21_News_v9.indd 6 26/02/2021 09:59