Mercury, fish and climate change: a new link discovered
Climate change could be driving up levels of methylmercury in a manner not previously recognised. Rising temperatures could boost its levels in fish by up to seven times, according to new research just published. Extra rainfall drives up the amount of organic material flowing into the seas. This encourages the growth of bacteria at the expense of phytoplankton and in turn the proliferation of a new type of predators that feed on the bacteria. Scientist Dr Erik Bjorn told BBC News that "You basically get one extra step in the food chain and methylmercury is enriched by about a factor of ten in each such step in the food web."
Globally, an overall increase of up to 15-20% in organic matter run-off has been predicted before the end of the century by the IPCC. The levels of methylmercury in zooplankton, the bottom link in the food chain, would grow most in coastal waters in the northern hemisphere. Regions such as the Mediterranean may be less impacted due to potentially milder effects of runoff and soil loss. On the other hand, recent research has highlighted the difficulty of predicting future soil loss in this region, which has very high inter-annual climate variability. An increase in extreme events and rainfall intensity may in the future produce significant increases in soil loss.
Mercury is one of the world's most toxic metals, and according to the World Health Organization one of the top ten chemicals threatening public health. There have been concerns over the levels of mercury in fish for many years. The most common form of exposure to mercury is by eating fish, for the heavy metal is known to bioaccumulate in seafood and carry over into human populations. Levels of mercury in the world's ecosystems have increased by between 200 and 500%, since the industrial revolution, driven by the use of fossil fuels such as coal. In humans high levels of mercury have been linked to damage to the nervous system, paralysis and mental impairment in children. International efforts to limit the amount of mercury entering the environment, are enshrined in the Minamata Convention, signed by 136 countries since 2013.
World Maritime Organisation flyer on mercury