Human exposure to toxins on the rise due to overfishing

Climate change and shift in dietary patterns due to overfishing by humans are pushing up the amount of toxic mercury in certain fish population in the world.

This significant finding is the result of a study done by an international consortia consisting of the Indian Institute of Technology, Hyderabad (IITH), Harvard University and Fisheries and Oceans,Canada.

The consortia 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 a increase in methylmercury concentration in Atlantic cod fish while there was a decrease in the case of Spiny dogfish during the past three decades”.

Methylmercury concentration

The model predicts that a combination of three factors — 20 per cent reduction in methylmercury concentration in seawater, one degree Celsius increase in ocean temperature and changes in diet — can either increase or decrease the amount of methylmercury 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 seen a decrease in the overall levels 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 emissions to air

The researchers who focused 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, alarmingly more.

The consortia consisted of Asif Qureshi, Civil Engineering, IITH; 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 sea water temperature, which leads to changes in fish metabolism that gears towards survival rather than growth, and changes in the amounts of mercury found in sea water 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 sea temperature, fishing practices and mercury pollution levels, the researchers say.

Regulatory efforts must not only control the release of mercury into the atmosphere, but also significantly reduce greenhouse gas emissions that lead to sea water warming. Only by tackling both mercury emissions and global warming, can we reduce levels of toxins.

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 ecosystem and human health are a necessity.

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