Mercury in the Great Lakes

Photo: WikiMedia, Knepp, Timothy - U.S. Fish and Wildlife Service

Mercury (Hg) contamination of aquatic ecosystems is an international issue that affects literally every region of the planet. Some ecosystems, such as the Great Lakes basin, are seemingly especially prone to the problem and potentially unsafe levels of Hg are found with regularity in consumable game and commercial fish.

Mercury is a toxic substance that, through human and natural activities, cycles through the atmosphere, hydrosphere, and ecosphere where it can affect the health of both humans and wildlife. It enters the environment naturally through erosion, fire, and volcanic processes, and it is also released both directly from and as a biproduct of human industrial practices. Human activities, such as combustion, smelting, and mining, have elevated global mercury levels to approximately three times those found before industrialization.

Mercury emissions arising from human activity in both the United States and Canada dropped substantially between 1990 and 1999. In the United States, significant mercury reductions came principally from emission controls on municipal and medical waste incinerators, as well as improved screening and removal from the waste stream of commercial products such as batteries and paint. While there have been intensive efforts by many government and international bodies to reduce the use and emission of mercury to the environment, the lack of regulations in developing nations means that mercury releases continue unabated in many countries. Mercury’s capacity for long-range atmospheric transport demonstrates a need for global scale reductions efforts. Although Canada, the United States and Western Europe have reduced the use and emission of mercury, their boundaries are subject to mercury flowing from external regions.

Despite the achievements in addressing mercury, mercury’s presence in Great Lakes eco-region continues, partly due to continued deposition to the region from sources outside the basin. This has caused broad scale impacts to wildlife, fisheries, and even human health. The mercury in the Great Lakes ecosystem becomes harmful when it turns into methylmercury, a highly toxic compound that accumulates in the food web. Over time, the contamination magnifies in the food web to concentrations several million times higher than in water. People are exposed primarily when they eat contaminated fish. As a result, all states and provinces in the Great Lakes region have fish consumption advisories related to mercury contamination.

Previous studies have suggested that about 300,000 to 400,000 children born each year are exposed by their mothers to mercury concentrations high enough to cause neurological damage. The scope and intensity of mercury pollution in the Great Lakes region is much greater than previously reported, but additional mercury controls should bring needed improvement, according to a new summary of scientific research on the subject.

Where does the mercury come from that is depositing
into any given waterbody or watershed?

Adapted from slides prepared by USEPA and NOAA.

Despite general declines in mercury levels in the Great Lakes region over the past four decades, mercury concentrations still exceed human and ecological risk thresholds, especially in inland lakes and rivers, according to the report Great Lakes Mercury Connections: The Extent and Effects of Mercury Pollution in the Great Lakes Region, published in Springer's journal Ecotoxicology.

Also, new research indicates that for some species of fish and wildlife in particular areas, mercury concentrations may again be on the rise. The report finds that atmospheric emissions are the primary source of mercury deposition in the Great Lakes basin and it projects that further controls on those emissions will lower mercury concentrations in the food chain.

Credit: www.michigan.gov

Resources:

The MDCH ESF Guide can be used to help you choose fish that are lower in chemicals, so that you can avoid fish higher in chemicals and protect your health.