An international team of scientists led by the ESRF has found that emperor penguins detoxify mercury with both sulphur and selenium, a new pathway for a marine predator. This new detoxification pathway for mercury has been unveiled in a study published in the Journal of Hazardous Materials.
Mercury is considered by WHO as one of the top ten chemicals of major public health concern. Mercury bioaccumulates in organisms along time and biomagnifies in aquatic and terrestrial food webs as the neurotoxic form of methylmercury. Understanding the internal detoxification processes of methylmercury in animals is essential for protecting wildlife and designing treatments against mercury poisoning.
Alain Manceau, ESRF scientist and researcher emeritus at the CNRS, together with his collaborators from the University of La Rochelle and the CNRS (LIENSs and CEBC), the United States Geological Survey, and the University of California Davis, has been studying how animals detoxify mercury for years.
Back in 2021, they unveiled that apex predators, such as seabirds like giant petrels, and marine mammals like pilot whales, detoxify methylmercury through a sequence of reactions involving reduced selenium in the form of a prominent selenoprotein. Since mercury is ultimately detoxified as nontoxic mercury selenide, it has diminished toxicological consequences as long as there is sufficient selenium, because mercury selenide is chemically inert.
“We knew the mechanism that animals that are exposed to large quantities of mercury use; now we wanted to find out what happens with animals that are lower in the food chain, such as penguins”, Manceau explains. Emperor penguins feed mostly on Antarctic silver fish and squid, which contain methylmercury, albeit not in large quantities. Because of this, penguins are less contaminated with mercury than toothed whales, giant petrels, and other predators higher in the food web.
The scientists, who used X-ray absorption spectroscopy, identified, for the first time, a second demethylation pathway of toxic methylmercury. In Emperor penguins, the toxic mercury is partially detoxified using the same chemical pathway as giant petrels, but theses penguins have also developed a second mechanism whereby their body forms a Hg-dithiolate complex. This complex binds to cysteine amino acids in enzymes, altering their function. This demethylation pathway had never been observed before in animals, only in bacteria.
Read more on ESRF website
Image: A baby penguin.
Credit: Yves Cherel.