Sangareddy: A joint research by Indian Institute of Technology-Hyderabad (IIT-H), Harvard University, and Fisheries and Oceans Canada — a Canadian government agency, has been researching how climate change impacts mercury accumulation in fish. The seminal work was published in the August 2019 issues of the prestigious international peer-review journal ‘Nature’.
Studies by the international team of scientists found that although there has been a decrease in levels of mercury pollution due to various environmental regulations, the amounts of mercury found in fish have been different in different species – some types of fish have less mercury than before, and some, alarmingly more. These variations have been a result of changes in sea temperature in recent years and the changes in the dietary pattern due to overfishing.
The research was led by Asif Qureshi, Associate Professor, Department of Civil Engineering, IIT-H, and co-authored by Dr Amina Schartup, Dr Colin Thackray, Dr Clifton Dassuncao, Dr Kyle Gillespie, Dr Alex Hanke and Dr Elsie Sunderland.
There have been global efforts to reduce the amount of mercury entering the ocean to reduce the amount of mercury found in fish and other marine animals. 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 focused on whether have these and other environmental measures alleviated or overall exacerbated the problem of elevated mercury levels in fish. They chose the Gulf of Maine, a well-studied but also exploited, marginal sea in the Atlantic Ocean, to study the trends in mercury accumulation in fish. The researchers used three decades of data on ecosystem and mercury concentrations and developed a model for mercury bioaccumulation.
Dr Qureshi, who wrote the first versions of the model code said, “There are three factors that affect mercury accumulation in fish – overfishing, which leads to dietary changes among marine animals, variations in the temperature of the seawater, which leads to changes in fish metabolism that gears towards survival rather than growth, and changes in the amounts of mercury found in seawater as a result of pollution.”
The researchers included all three factors in their modeling studies. They modeled the changes in mercury levels in tissues of the Atlantic cod and spiny dogfish that would result from the three factors – overfishing, increase in sea temperature and reductions in mercury emissions.
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. Modeling showed a 10 percent decrease in tissue mercury concentrations for this type of fish.
The situation was reversed for dogfish. A 70 per cent increase in tissue mercury concentrations was given the same conditions as for the Atlantic cod.
Talking about their observations Qureshi 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.”
The researchers also modeled the mercury levels found in Atlantic Blue Fin Tuna (ABFT). 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. However, continued warming in the Gulf of Maine caused a reversal and the amount of mercury in ABFT could increase to almost 30 per cent by 2030. This highlights the importance of sea temperature on mercury accumulation in the marine food chain.
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.
He further said that 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 we reduce levels of mercury in marine animals and our exposure to mercury in seafood.
To this effect, he is leading his group towards more present and future studies combining modeling with field observations to assess mercury levels in humans, fish and the general environment.