Add another item to the ever-growing list of the unsafe impacts of climate change: Warming oceans are leading to an increase of the harmful neurotoxicant methylmercury in popular seafood, including cod, Atlantic bluefin tuna and swordfish, according to research led by researchers at Harvard University.
Concentrations of the toxin in cod increased by up to 23 per cent between the 1970s and 2000s as a result of dietary shifts initiated by overfishing and then a recovery of herring populations, they suggested.
The research was led from India by Asif Qureshi, associate professor, Department of Civil Engineering, IIT-H, and co-authored by Amina Schartup, Colin Thackray, Clifton Dassuncao, Kyle Gillespie, Alex Hanke and Elsie Sunderland.
Regulations on mercury emissions have been shown to successfully reduce methylmercury levels in fish, which is why it has always been confounding to scientists that methylmercury levels in some fish were increasing. They modelled the changes in mercury levels in tissues of the Atlantic cod and spiny dogfish that would result from the three factors - overfishing, increase in sea temperature and reductions in mercury emissions.
The researchers chose the Gulf of ME, a marginal sea in the Atlantic Ocean, for their study. The research notes its important role in determining mercury accumulation in the fish.
"This study brings together different kinds of data with models in a way that will have a direct impact on how we manage fisheries", says Hedy Edmonds, a program director in NSF's Division of Ocean Sciences, which funded the research.
For example, the team found that for Atlantic cod, although an increase of 1°C in seawater temperature would lead to an increase in mercury concentrations, dietary disturbances due to overfishing, and reductions in mercury pollution could compensate. Qureshi said that more mercury in the body can cause neurological, cardiovascular and endocrinal disorders in humans.
Overfishing of small herring and sardines has also changed the diet of Atlantic cod, forcing them to consume larger herring and lobster, which have higher levels of methylmercury, the paper said. However, continued warming in the Gulf of ME would cause a reversal and the amount of mercury in ABFT could increase to nearly 30% by 2030. It occurs in sea, ocean and river water after mercury emitted from various polluting sources, mainly thermal power plants, enters the water and gets converted to methylmercury, after which it enters the fishes.
'Climate change is going to exacerbate human exposure to methylmercury through seafood, so to protect ecosystems and human health we need to regulate both mercury emissions and greenhouse gases'. To this effect he is leading his group towards more present and future studies combining modeling with field observations to assess mercury levels in humans, fish and the general environment.