Mercury on the Move

Photo by Tyson Dudley

Mercury on the Move

Despite a decline in active mercury pollution, lingering environmental mercury is still a human health concern. Scientists working to track the movement of global mercury have discovered a new route – mercury moves through the stocking of lakes for recreational fishing. Because of fish stocking, the toxic heavy metal is moving from oceans to mountain lakes at an estimated global rate of one ton per year. This finding calls for fisheries managers to pay closer attention to the health of their recreational stock before releasing into lakes.

Hansson, S.V., Sonke, J, Galop, D., Bareille, G., Jean, S., Le Roux, G. (2017). Transfer of marine mercury to mountain lakes. Scientific Reports 7:12719. DOI: 10.1038/s41598-017-13001-2. Retreived at: www.nature.com/articles/s41598-017-13001-2.

Mercury pollution remains a persistent problem for human health. Mercury is emitted from coal-fired power plants, municipal waste combustors, and chlorine producers. When mercury enters the environment, it binds to other molecules and is readily taken up by living organisms. The heavy metal can cause a host of neurological, cardiovascular, and developmental problems.

Mercury is now a heavily regulated substance because of the danger it poses to humans and our environment. But here’s the problem: it takes a long time for mercury to leave the environment. Mercury lingers in sediment and is taken up by fish. Fish are the most common way mercury enters our food supply. Fish naturally transport mercury during their migrations, but also when humans move fish to stock lakes and ponds for commercial farming and recreational fishing.

Scientists Sophia Hansson and her colleagues studied the movement of mercury by fish. In a new study published in October 2017 in Nature Scientific Reports, they looked at how mercury ends up in pristine mountain lakes. Their leading hypothesis was that the mercury came from the atmosphere. Using isotopic mercury signatures, they discovered that the mercury in these lakes actually originated in the ocean. This means that mercury is entering alpine lakes through fish stocking.

Mountain lakes are stocked with farmed fish for recreation. These farmed fish are reared on marine-based protein foods which contain trace amounts of mercury and thus accumulate in farmed trout. Their research found stocking lakes has the potential to transport an estimated one ton of mercury per year from marine to terrestrial environments around the globe. One ton of mercury per year could have devastating impacts on larger predators who consume the fish – including humans.

The rate of fish introductions to lakes has more than doubled in the past decade, meaning more mercury will enter alpine lakes. Managers who stock lakes for recreation should pay close attention to where their fish originate because introducing mercury to a lake can have unintended consequences on the land and the people who use it.

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