Trends in contaminants in the Great Lakes

Trends in contaminants in the Great Lakes Legacy contaminants and mercury are generally decreasing in the Great Lakes in response to clean-up of contaminated sites and improved pollution control.4, 13 However, the large volumes of water and sediment in the system act as a storehouse – contaminants continue to be released from sediments and to recycle through the water, sediment, and food webs.19, 20 Contaminants also continue to be deposited into the lakes through long-range atmospheric transport21 and, in the case of mercury, from industrial emissions in the Great Lakes Basin.4 The net result is that rates of decline of some legacy contaminants and mercury have slowed in areas of the Great Lakes, leaving some contaminants at levels that are of concern and likely to remain so for some time to come.13, 20

Brominated flame retardants (PBDEs) increased rapidly in fish and birds starting in the early 1980s,22-24 but levels have now stabilized or are declining in response to action taken to curtail the use and release of these substances.24, 25 Many other emerging contaminants have been detected more recently in environmental samples, often in trace amounts, but little is known about the risk to ecosystems from most of them.26 Chemicals of concern include PFOS, originating in water-repellent coatings and fire-suppression foam, detected in fish samples throughout the Great Lakes, and known to build up in food webs.27 Emerging contaminants also include endocrine disrupting substances, which come from a range of sources, including pharmaceuticals. Potential effects include abnormal gonad development in fish.28 Many emerging contaminants do not originate in industrial emissions, but rather from use and disposal of health and personal-care products and consumer goods, leading to a need for new risk management approaches for contaminants in the Great Lakes.26

PCBs in Great Lakes fish

Total PCB concentrations in lake trout (walleye in Lake Erie) Parts per million (logarithmic scale), 1972 to 2002
Graph: PCBs in Great Lakes fish. Click for graphic description (new window).
Source: adapted from Carlson et al., 2010.13

PCBs in fish declined rapidly until the mid-1980s, halving in concentration every three to six years. Since then, PCBs in fish show either slow declines or no significant trend.13