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Climate change and overfishing are increasing toxic mercury levels in fish

(14.08.2019)


Background:
Mercury is a metal that is released into the environment from both natural sources and as a result of human activity. Mainly through the activity of microbes, inorganic mercury is transformed to methylmercury (MeHg). Once transformed, MeHg bioaccumulates and bioamagnifies in marine food webs. In predatory fish, environmental MeHg concentrations are amplified by a million times or more. MeHg is a strong neurotoxin and its presence in food items therefore undesirable. In the United States, 82% of population-wide exposure to MeHg is from the consumption of marine seafood and almost 40% is from fresh
and canned tuna alone.  Many countries have maximum tolerable concentration rules for fish in the range of 0.5-1.0 ppm Hg. While the mercury concentration in seawater was not increasing in general during the last decades, levels in popular fish such as tuna, salmon and swordfish are on the rise. Experts have been trying to find out why this is happening, but now Harvard University researchers might have an answer.

The new study:
Harvard University scientists believe the main cause of this phenomenon is global climate change. According to their research results published in the Journal Nature, some fish species are changing their diets to consume species more contaminated. To reach these results, the researchers evaluated 30 years worth of data accumulated on the Gulf of Maine in the Atlantic Ocean. 

The researchers developed a model incorporating the different factors driving the mercury uptake. The developed model is able to explain the MeHg content for different fish species under different scenarios:


According to the data evaluated, the exploitation of fish resources in the northwestern Atlantic Ocean for the last 30 years has led to large reduction of heering, lobster and cod stocks, which has altered the avaliability of prey for predatory fish.

But the change of prey as a result of overfishing is not the only driving force to increase the mercury uptake. Climate change is another factor. The rising water temperature as a result of climate change is enhancing the energy consumption of more active fish, calling for more food. Consuming more contaminated prey is leading to higher mercury uptake.

The authors conclude that "climate change is likely to exacerbate human exposure to MeHg through marine fish, suggesting that stronger rather than weaker regulations are needed to protect ecosystem and human health".





The original publication:

Amina t. Schartup, Colin P. thackray, Asif Qureshi, Clifton Dassuncao, Kyle Gillespie, Alex Hanke, Elsie M. Sunderland, Climate change and overfishing increase neurotoxicant in marine predators, Nature, (2019). DOI: 10.1038/s41586-019-1468-9



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D. Streets, H.M. Horowitz, Z.F. Lu, L. Levin, C.P. Thackray, E.M. Sunderland, Global and regional trends in mercury emissions and concentrations. Atmos. Environ., 201 (2019) 417–427. DOI: 10.1016/j.atmosenv.2018.12.031

A.T. Schartup, A. Qureshi, C. Dassuncao, C.P. Thackray, G. Harding, E.M. Sunderland, A model for methylmercury uptake and trophic transfer by marine plankton. Environ. Sci. Technol., 52/2 (2018) 654–662. DOI: 10.1021/acs.est.7zb03821

E.M. Sunderland, M. Li, K. Bullard, Decadal changes in the edible supply of seafood and methylmercury exposure in the United States. Environ. Health Perspect., 126 (2018) 017006. DOI: 10.1289/EHP2644

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G. Harding, J. Dalziel, P. Vass, Bioaccumulation of methylmercury within the marine food web of the outer Bay of Fundy, Gulf of Maine. PLoS ONE, 13/7 (2018) e0197220. DOI: 10.1371/journal.pone.0197220

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last time modified: August 16, 2019



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