Source: 9News

Albatrosses in the Southern Ocean have led scientists to flag a possible future problem with high levels of toxic mercury in tuna and other fish caught for human consumption.

Southern Ocean mercury levels are being studied by scientists aboard the Australian Antarctic Division icebreaker Aurora Australis.

While high levels have not been found in Southern Ocean fish yet, CSIRO oceanographer Steve Rintoul tells AAP an early clue that something unusual is happening with mercury in the Southern Ocean comes from albatrosses and petrels with high concentrations of the toxic methyl mercury in their liver.

In some cases the levels are so high they would be fatal to other types of birds.

“They’ve somehow evolved to handle this large exposure to mercury,” Dr. Rintoul said.

He said scientists have found that levels of the toxic form of mercury are higher in the Southern Ocean than elsewhere.

Dr. Rintoul said mercury is converted to its toxic form by bacteria and much of that happens deep in the ocean.

Deep water rises to the surface in the Southern Ocean, unlike elsewhere, and that is one reason levels of the toxic form of mercury are higher in that ocean.

Another source of toxic mercury in the Southern Ocean has been found to originate from the burning of fossil fuels.

Mercury pumped into the atmosphere is combining with bacteria in waters around Antarctica, Dr. Rintoul said.

“We now understand that the natural system concentrates mercury in the Southern Ocean. But part of it is the levels have got even higher in the industrial period because we are releasing much more mercury into the ocean. Once it’s in the ocean it starts getting into the food chain.”

Dr. Rintoul said when the toxic form of mercury is ingested by larger animals such as fish and seals, it stays in their system.

He said there is evidence of high mercury levels in seabirds and some evidence of it in seals.

“We don’t know yet if there's a mercury problem with animals or fish that humans are eating.”

But Dr. Rintoul said rising mercury levels in the oceans, boosted by fossil fuel burning, could have a potential future impact on fish caught for human consumption.