High levels of methylmercury are known to accumulate in the fatty tissues of large ocean-going fish such as tuna, swordfish and marlins. Though most people do not eat enough of these types of fish to result in mercury poisoning, pregnant women are advised to restrict their intake because of the risk to the fetus.
Now it looks like climate change may make the consumption risk even greater.
Biologists observed higher accumulation of methylmercury in killifish, a small fish, as temperatures increased both in the wilderness of Maine and in laboratories.
The contamination levels in the fish may increase with temperature because the metabolism of the tiny fish speeds up in warmer water, according to the recent research published in PLOS ONE. The cold-blooded fish eat more and thereby pick up more methylmercury from the environment.
Coal-burning power plants produce most of the mercury pollution in the atmosphere. When the mercury falls back to Earth's surface it lands either in the ocean or on land where it can be washed into lakes, streams, and eventually the ocean. Certain bacteria transform the mercury into methylmercury, a more toxic form. After this bacterial conversion, the methylmercury enters the food chain, accumulating in fatty tissues. When people worry about mercury in their fish and other seafood, it is actually this bacterially-altered form of methylmercury.