Scientists have said that the possible source of the toxic methylmercury – a more potent neurotoxin – in sea ice in the Southern Ocean are sea-ice bacteria.

Published in journal Nature Microbiology, the new study by researchers at University of Melbourne suggests that the sea-ice bacteria are the possible source of methylmercury and it is this neurotoxin that is finding its way into the food cycle through fish and birds. If ingested, methylmercury can travel to the brain, causing developmental and physical problems in foetuses, infants and children.

The neurotoxin continues to reside within the fish and birds that have ingested them and continues to build up as it moves up the food web through a process called ‘biomagnification’. Methymercury travels up the food web as larger fish consume the smaller contaminated fish and by the time it reaches humans or other larger animals, the build up of the neurotoxin would have reached levels that are harmful.

One of the aim behind the study was to understand how the most toxic form of mercury enters the marine environment, and the food we eat. Researchers spent a couple of months aboard the icebreaker Aurora Australis to collect samples of Antarctic sea ice during an expedition mounted by the Australian Antarctic Division.

Analysis of the ice revealed that there is confirmed presence of bacteria in the sea ice with the genetic ability to convert mercury into the more toxic form.

Mercury enters the environment through volcanic eruptions and is re-released from vegetation during bushfires. It is also created through human activity, such as gold smelting and burning fossil fuels. Mercury has a long lifecycle in the atmosphere – up to a year – and this means that the mercury that is released through various sources could travel for thousands of kilometers and end up in the Antarctic. This is where it comes in contact with the bacteria and is then converted to a more toxic form.

These findings highlight the importance of eliminating mercury pollution from the environment, and following current recommendations to limit consumption of certain types of fish, say the researchers.

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