The 2012 Great Lakes Water Quality Agreement states that “the Waters of the Great Lakes should be free from pollutants in quantities or concentrations that could be harmful to human health, wildlife, or aquatic organisms through direct exposure or indirect exposure through the food chain.”
Assessment highlights
The Toxic Chemicals indicator shows that concentrations of most toxic chemicals in the Great Lakes have decreased over the long term in water, air, sediment, fish and Herring Gull eggs. Overall, the status of Toxic Chemicals is Fair and the trend is Unchanging to Improving.
Many chemicals, including mercury and PCBs, have decreased significantly since the 1970s. Even with these long-term reductions, there are some instances of chemicals of mutual concern (CMCs), including polychlorinated biphenyls (PCBs), perfluorooctane sulfonate (PFOS), and polybrominated diphenyl ethers (PBDEs) exceeding ecosystem-based objectives in water, sediment, fish and Herring Gull eggs. Concentrations of other chemicals, including polycyclic aromatic hydrocarbons (PAHs), are higher in the waters of lakes Erie and Ontario than in the other lakes.
The 10-year trend for most of the Toxic Chemical sub-indicators show Unchanging or Improving conditions. However, atmospheric deposition remains a significant pathway for mercury, PCBs, PBDEs, and other contaminants into the Great Lakes. In addition, localized areas of highly contaminated sediment in or adjacent to urban areas and in Areas of Concern (AOCs) continue to act as sources of contaminants to the lakes.
The Toxic Chemicals sub-indicators help track progress on reducing inputs of chemicals into the Great Lakes. Status and trends of binationally designated CMCs (hexabromocyclododcane (HBCD), long-chain perfluorinated carboxylic acids (LC-PFCAs), mercury, perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), short-chain chlorinated paraffins (SCCPs) as well as other toxic chemicals (e.g., PAHs, dioxins) are assessed in Great Lakes water, sediment, fish, air and precipitation, and Herring Gull eggs. Herring Gull eggs are a standard medium for monitoring contaminant levels in wildlife in the Great Lakes; adult gulls feed on prey fish in surface waters and exposure to contaminants can be measured in their eggs.
Sub-indicator supporting the Toxic Chemicals assessment
Sub-Indicator | Lake Superior | Lake Michigan | Lake Huron | Lake Erie | Lake Ontario |
Good and Unchanging | Fair and Unchanging | Good and Unchanging | Fair and Improving | Fair and Improving | |
Fair and Improving | Fair and Undetermined | Good and Unchanging | Fair and Unchanging | Fair and Unchanging | |
Fair and Unchanging | Fair and Unchanging | Fair and Unchanging | Fair and Unchanging | Fair and Unchanging | |
Good and Improving | Good and Improving | Good and Improving | Good and Unchanging | Good and Improving | |
Fair and Improving (No lake-by-lake assessments were determined) | |||||
Status
