Hyderabad: Mercury in fish due to hotter seas

  • Hyderabad: Mercury in fish due to hotter seas

Hyderabad: Mercury in fish due to hotter seas

A joint research by the Indian Institute of Technology, Hyderabad (IIT-H), Harvard University, and Fisheries and Oceans Canada, a Canadian government agency, has found that though there has been a decrease in the levels of mercury pollution, the amount of mercury found in fish have been different in different species - some types of fish have less mercury than before, and some, alarmingly more.

"This research is a major advance in understanding how and why ocean predators, such as tuna and swordfish, are accumulating mercury", said Elsie Sunderland, senior author of the paper. Working in this direction, the researchers focused on whether these and other environmental measures alleviated or exacerbated the problem of increased mercury levels in fish. This means that larger, more predatory organisms that sit at the top of the food chain will have higher levels of methylmercury than the organisms that they eat, which scientists have known for a long time.

According to researchers, this increase was caused by shifts in diets due to over-fishing. These fish that burn a lot more calories are exposed to more methylmercury because they're consuming so much more food without having extra body mass to dilute the harmful toxin. The research notes its important role in determining mercury accumulation in the fish.

The model also forecast an estimated 56% increase in the mercury concentrations in Atlantic bluefin tuna due to increases in sea-water temperature between a low point in 1969 and recent peak levels.

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.

Around four-fifths of the mercury put into the atmosphere from natural and human causes, such as burning coal, ends up in the ocean where some is converted by tiny organisms to a particularly risky form known as methylmercury.

Fish are the main source of human exposure to methylmercury, with 82 percent of population-wide exposure coming from the consumption of marine seafood, and nearly 40 percent from fresh and canned tuna alone. About 80 percent of those inorganic mercury emissions end up getting deposited in the ocean, where microorganisms convert some of it to methylmercury.

The study showed that despite a decrease in global mercury emissions since late 1990s, MeHg concentration in fishes like Atlantic cod, Atlantic bluefin tuna, which are widely consumed by humans, has actually increased.

Pregnant women have always been advised to avoid swordfish and shark due to high mercury levels, but cod is one fish variety that the USA government recommends as a nutrient and protein-rich food that can help children's development. "We can all agree less methylmercury in these fish in the future would be a good thing".