The Hindu Business Line
How climate change is raising mercury levels in fish
Stringent regulations are needed to protect humans from exposure to this toxin, say researchers
Climate change and over-fishing that is leading to a shift in dietary patterns are pushing up the amount of toxic mercury in certain fish population.
This is the finding of a study by an international consortia of the Indian Institute of Technology-Hyderabad (IIT-H), Harvard University, and Fisheries and Oceans, Canada.
The team used modelling studies and data of three decades from the Gulf of Maine in the Atlantic Ocean to access the impact of climate change and other factors on mercury accumulation in fish. The work was published in the August issue of Nature.
The researchers showed that “As a result of a change in the diet due to overfishing, there was an increase in methyl mercury concentration in Atlantic cod fish while there was a decrease in the case of Spiny dogfish during the past three decades.”
According to the model, a combination of three factors — 20 per cent reduction in methyl mercury concentration in seawater, one degree Celsius increase in ocean temperature and changes in diet — can either increase or decrease the amount of methyl mercury present in fish.
The finding is important in view of the fact that global efforts to reduce mercury levels in fish and other marine animals through various environmental regulations have led to a drop in the overall level of mercury pollution.
The Minamata Convention of Mercury that was enforced in 2017 includes a ban on new mercury mines, phase-out of existing ones and strict control measures on atmospheric emission.
The researchers, who focussed on these measures, observed that the amounts of mercury found in fish have been different in different species — some have less than before, while others have alarmingly more.
The consortia consisted of Asif Qureshi, Civil Engineering, IIT-H; and co-authored by Amina Schartup, Colin Thackray, Clifton Dassuncao, Kyle Gillespie, Alex Hanke and Elsie Sunderland.
Qureshi explained: “There are three factors that affect mercury accumulation in fish — overfishing, which leads to dietary changes among marine animals; variations in the seawater temperature, which leads to changes in fish metabolism that emphasises survival rather than growth; and changes in the amount of mercury found in seawater as a result of pollution.”
Although this study was carried out in the Atlantic Ocean, mercury levels in fish in other seas and oceans are likely to have a similar relationship with the sea temperature, fishing practices and mercury pollution levels, the researchers said.
Regulatory efforts must not only control the release of mercury into the atmosphere, but also significantly reduce greenhouse gas emissions that lead to seawater warming. Only by tackling both mercury emissions and global warming can the levels of toxins be reduced.
The researchers warn that human exposure to the toxins through fish consumption is bound to increase as a result of climate change. Therefore, stronger regulations to protect the ecosystem and human health are needed