Toxic mercury is once again increasing in some Great Lakes fish and birds after decades of consistent, promising reductions.
Scientists are still trying to figure out what’s going on, but one of the suspected culprits in reversing decades of mercury reductions in wildlife is a climate change-induced increase in water temperatures.
Mercury is a known toxic — in wildlife it impairs reproduction, growth, behavior, or just flat-out kills them. The reports of increases are a surprise as there’s been steady progress on mercury since the 1970s. Fewer domestic coal plants, accountable for about half of U.S. mercury emissions, helped decrease pollution.
From the 1970s to the early 2000s, Great Lakes wildlife saw regular, consistent reductions in mercury loads.
But mercury travels the globe, and as coal has taken off in places such as Asia over the past 20 years so, too, has the atmospheric export of toxic mercury. Those additions have offset coal reductions in the U.S. and Europe. In addition, climate change is altering how legacy chemicals are stored, transformed and transported in land, water and air.
Warmer water more quickly converts mercury to its more toxic form — methyl mercury. This form also more quickly accumulates in fish and birds, with each step of the food chain more contaminated than the previous.
Warmer water also does not dissolve oxygen as well as cold water, so fish have to pump more water across their gills, which can lead to more contact with toxics in the water.
Also more rainfall — total annual precipitation has increased 11 percent in the Great Lakes since 1900 — means more flooding. "Flooding takes a lot of earth off the surface, this erosion of soils and sediments carries mercury and methylmercury," said Agnes Richards, a researcher at Environment and Climate Change Canada
It’s another ecological problem born of the complex interplay of toxics, global warming, our food, and, ultimately, our health.
Read more at Toxic Mercury Levels on the Rise in Great Lakes Wildlife