Climate change ‘increasing the level of toxic mercury in fish’

New research suggests increasing sea temperatures can increase human exposure to toxic chemicals, through consumption of seafood such as cod, tuna and swordfish

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Climate change is increasing the level of toxic chemicals in fish.

That’s according to research led by the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Harvard T. H. Chan School of Public Health (HSPH), which suggests this is likely to increase human exposure to methylmercury through the consumption of seafood such as cod, tuna and swordfish.

Methylmercury is a type of organic mercury that accumulates in food chains, with organisms at the top generally having higher levels of methylmercury in their bodies than creatures at the bottom.

The research found despite mercury emissions having been successfully reduced in recent years, methylmercury levels in fish are being driven up as changing water temperatures affect natural habitats and behaviours, forcing certain fish to change their prey to larger organisms containing more methylmercury, such as shifting from herrings to squid.

It notes higher water temperatures also result in more calories being burned, especially among high-speed hunters and migratory fish – this means they eat more and as a result accumulate more mercury in their bodies.

Researchers predict that each increase of 1°C in seawater temperature, relative to the year 2000, would lead to a 32% increase in methylmercury levels in cod and a 70% increase in spiny dogfish.

Senior Author Elsie Sunderland said: “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.

“It is important also to remember that fish are a very healthy food overall and when people switch away from fish in their diet they generally pick less healthy alternatives. We can all agree less methylmercury in these fish in the future would be a good thing.”

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