New research has found methylmercury -- a potent neurotoxin -- in sea ice in the Southern Ocean. Published today in the journal Nature Microbiology, the results are the first to show that sea-ice bacteria can change mercury into methylmercury, a more toxic form that can contaminate the marine environment, including fish and birds.

If ingested, methylmercury can travel to the brain, causing developmental and physical problems in foetuses, infants and children.

The findings were made by an international team of researchers led by Ms Caitlin Gionfriddo and Dr John Moreau from the University of Melbourne, and also included scientists from the Centre for Systems Genomics at the University of Melbourne, the US Geological Survey and Lawrence Livermore National Lab.

Methylmercury builds up in the food web through a process called 'biomagnification', said Ms Gionfriddo, PhD candidate from the School of Earth Sciences, University of Melbourne.

"Larger fish eat smaller contaminated fish, and continuously accumulate methylmercury at harmful levels for human consumption," Ms Gionfriddo said.

The team wanted to understand more about how the most toxic form of mercury enters the marine environment, and the food we eat. 

Ms Gionfriddo spent two months aboard the icebreaker Aurora Australis to collect samples of Antarctic sea ice during an expedition mounted by the Australian Antarctic Division. 

The ice was analysed for different forms of mercury, including methylmercury, at the US Geological Survey in Wisconsin (USA). The DNA and proteins from sea ice microorganisms were studied at the University of Melbourne (AUS) and Lawrence Livermore National Lab (USA).