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Sweden: Climate Change Global Warming May Increase Poisonous Methylmercury in Zooplankton

| Editor: Alexander Stark

Research performed in Sweden is now indicating a sevenfold increase in poisonous methylmercury in zooplankton as a consequence of climate change. This increase is due to an altered structure of the aquatic food web. The study has been published in the journal Science Advances.

Erik Björn, associate professor at Umeå University and leader of the research project.
Erik Björn, associate professor at Umeå University and leader of the research project.
(Source: Umeå Marine Sciences Centre)

Umeå/Sweden — Mercury is regarded as one of the top ten chemicals of public health concern according to the World Health Organization, WHO. The problems with mercury are mostly caused by methylmercury, an organometallic mercury compound that acts as a strong neurotoxin and that can be accumulated in the food webs of seas and lakes. The content of methylmercury in fish and other living organisms is controlled both by the total content of mercury in the ecosystems and by complex chemical and ecological processes in the environment. Climate changes and land use are expected to affect these processes in several ways, for instance by input of organic matter, humic substances, from land through watercourses out to lakes and seas.

As an effect of global warming, scientists expect an increased runoff and input of organic matter to aquatic ecosystems in large regions of the Northern hemisphere including the Baltic Sea.

Humic substances affect the aquatic environment in several ways — for instance by reducing the reach of sunlight into the water. That can lead to reductions in the production of phytoplankton via photosynthesis and instead favour growth of bacteria which can make use of humic substances for their growth. In turn, this can cause a trophic shift in the food web where it goes from being dominated by phytoplankton production (autotrophic) to being dominated by bacterial production (heterotrophic). “The study has revealed a phenomenon that has not been described before. The results are critical in the prediction of how global climate changes can affect the exposure of methylmercury to ecosystems, and humans,” says Erik Björn, associate professor at Umeå University and leader of the research project.

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