Mercury is one of the most toxic substances on earth. When inhaled or ingested by humans, mercury can cause severe neurological damage, cardiovascular harm, endocrine disruption, kidney damage and muscle coordination issues. When pregnant women are exposed, their babies can suffer IQ and motor skills impairments that will last their lifetime.
Through rain, snow or dry deposition, mercury can deposit either directly into waterbodies or indirectly into waterbodies via groundwater seepage through plants and soil. Mercury is emitted by sources around the world; some of it travels long distances around the globe, while other sources deposit relatively close to where it has been emitted. Once in water, mercury chemically transforms into methylmercury, which is readily taken up first by plant and then by animal life and moves up the food chain to ultimately be consumed by people. People are primarily exposed to mercury through the consumption of freshwater or marine fish, either self-caught or, more commonly, purchased at the grocery store or a restaurant.
There have been mercury poisoning events of devastating proportion, including in Minamata, Japan where in 1956 a chemical plant released massive amounts of wastes containing mercury into Minamata Bay, ultimately killing 900 people and injuring more than two thousand. Later, in 1971, seed grain treated with a methylmercury fungicide was mistakenly consumed by people in rural Iraq. Hundreds, perhaps thousands, of people died or were seriously sickened as a result. These were extreme events, but they highlight the point that a very small amount of mercury can cause significant contamination. According to the Minnesota Pollution Control Agency, “approximately one gram of mercury enters a 20-acre lake each year. Over time, just this small amount can contaminate the fish in that lake, making them unfit to eat on a regular basis.”