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Antarctic Mercury Threatens Fish and Birds

Bacteria in Antarctic sea-ice can change mercury into a more toxic form that can contaminate the marine environment, including fish and birds, according to a study published in Nature Microbiology.

Mercury can be released into the environment through volcanic eruptions and re-released from vegetation during bushfires, as well as through human activities such as gold smelting and fossil fuel combustion.

Caitlin Gionfriddo, a PhD candidate at The University of Melbourne who spent 2 months aboard the icebreaker Aurora Australis to collect samples of Antarctic sea-ice during an expedition mounted by the Australian Antarctic Division, says that methylmercury is an even more toxic form that accumulates in the food web.

“Larger fish eat smaller contaminated fish and continuously accumulate methylmercury at harmful levels for human consumption,” Gionfriddo said. Methylmercury ingested by people can travel to the brain, causing developmental and physical problems in foetuses, infants and children.

The sea-ice was analysed for different forms of mercury, including methylmercury, as well as the DNA and proteins from sea-ice microorganisms. Team leader Dr John Moreau said that the results confirmed the presence of sea-ice bacteria that could convert mercury into the more toxic methylmercury form.

The findings highlight the importance of eliminating mercury pollution from the environment, and of following current recommendations by Food Standards Australia and New Zealand to limit the consumption of certain types of fish.

“These results are the first to identify a particular genus of bacteria, Nitrospina, as capable of producing methylmercury in Antarctic ice,” Moreau said. “The presence of these potential mercury-methylating bacteria raises an interesting question: could they also play a role in forming the methylmercury observed in the oceans worldwide?”

“Mercury has a long lifecycle in the atmosphere, up to a year,” said co-author Dr Robyn Schofield. “This means that mercury released through fossil fuel burning from countries over 3000 km away goes up in the atmosphere and ends up in Antarctica.”

“The deposition of mercury into the sea occurs all year long but increases during the Antarctic spring, when the sunlight returning causes reactions that boost the amount of mercury that falls onto sea-ice and the ocean,” Gionfriddo added.

Moreau added that more needed to be understood about marine mercury pollution, “particularly in a warming climate and when depleted fish stocks means more seafood companies are looking south”.