IIT study throws light on fish contamination

Rodiano Bonacci
Agosto 11, 2019

Climate change and overfishing are increasing levels of toxic mercury in cod and tuna, which can cause neurological disorders in children and babies whose mothers eat fish while pregnant, a study by Harvard scientists said on Wednesday. These variations have been a result of changes in sea temperature in recent years and the changes in dietary pattern due to overfishing.

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.

There have been global efforts to reduce the amount of mercury entering the ocean to reduce the mercury accumulation in fishes and other marine animals.

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.

Using data collected over the last 30 years and ecosystem modelling, the team of researchers from Harvard University and IIT Hyderabad studied the trend of methylmercury presence in two predatory fishes from the Gulf of ME in the Atlantic Ocean which are widely consumed by people - Atlantic Cod and Atlantic Bluefin Tuna.

The researchers included all three factors in their modelling studies.

Based on the new model, the researchers predict that an increase of 1 degree Celsius 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. While worldwide mercury emissions have decreased, warmer ocean waters and unbalanced ecosystems due to overfishing is altering mercury buildup in fish and shellfish.

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.

"Our results help to explain why the variations in mercury concentrations have been mixed across different types of fish, despite overall reductions in mercury release into the sea since the 1970s", Dr. Qureshi said. There was a decrease in tissue mercury levels in the ABFT between 1990 and 2012, and this was driven by a fall in sea temperature during that period. This highlights the importance of sea temperature on mercury accumulation in the marine food chain. The researchers found that, while the regulation of mercury emissions has successfully reduced methylmercury levels in fish, spiking temperatures are driving those levels back up and will play a major role in the methylmercury levels of marine life in the future.

"We need to reduce human emissions (of mercury) and the largest source in the United States presently, accounting for about 40% of emissions, is coal-fired utilities", Sunderland told the Thomson Reuters Foundation.

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