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 in water, air, sediment, whole fish, and Herring Gull eggs have decreased over the long term. Overall, the status of Toxic Chemicals is Fair and the 10-year trend is Unchanging to Improving.
Across the Great Lakes, concentrations of many legacy chemicals, including mercury and PCBs, show longterm declines in most monitored media. However, Lake Ontario and Lake Erie have the highest concentrations of hexabromocyclododecane (HBCD), perfluorooctane sulphonate (PFOS), perfluorooctanoic acid (PFOA), and Polycyclic Aromatic Hydrocarbons (PAHs) in sediment, water, and whole fish compared to the other Great Lakes. The presence of large urban centers and industrial areas in the lower lake basins is associated with elevated chemical concentrations in multiple media typically due to increased emissions from sources such as industry, or releases from wastewater.
The status of sub-indicators in the Toxic Chemicals indicator range from Fair to Good. Over the past 10 years, trends range from Unchanging to Improving to No Trend. Some lake assessments are reported as No Trend due to high temporal variability in the data or differing trend directions for contaminants within a monitored media.
Decreasing trends in PFOS and PFOA concentrations in many monitored media are likely due to phase-outs in both the U.S. and Canada, as well as restrictions in the U.S. and regulatory action in Canada. PFOS and PFOA concentrations are generally higher in locations closer to urban and industrial areas when compared to less developed watersheds.
In whole fish, long-term concentrations of PFOS have significantly declined in lakes Ontario and Huron, but levels still exceed guidelines or targets. Among the contaminants monitored in Herring Gull eggs, the PFAS class of chemicals has shown the most notable short-term decline. PFOS and PFOA concentrations in precipitation are declining at most monitored sites.
The Toxic Chemicals sub-indicator assessments include several binationally designated Chemicals of Mutual Concern (CMCs) and help track progress on reducing the release of these substances into the Great Lakes. Among the CMCs are PFOS, PFOA and long-chain perfluorocarboxylic acids (LC-PFCAs), which are part of a large complex group of chemicals known as Per- and Polyfluoroalkyl Substances (PFAS). PFAS have a wide variety of applications due to their water-, grease- and heat- resistant properties and are often referred to as “forever chemicals” because of their extreme persistence in the environment.
Sub-indicators supporting the Toxic Chemicals assessment
Sub-Indicator | Lake Superior | Lake Michigan | Lake Huron | Lake Erie | Lake Ontario |
Toxic Chemicals in Sediment | Good & Unchanging | Fair & Unchanging | Good & Unchanging | Fair & Improving | Fair & Improving |
Toxic Chemicals in Water | Good & Undetermined | Undetermined & Undetermined | Fair & Improving | Fair & No Trend | Fair & No Trend |
Toxic Chemicals in Whole Fish | Fair & No Trend | Fair & No Trend | Fair & No Trend | Good & Improving | Fair & No Trend |
Toxic Chemicals in Herring Gull Eggs | Good & Unchanging | Good & Unchanging | Good & Unchanging | Good & Unchanging | Good & Unchanging |
Toxic Chemicals in the Atmosphere | Great Lakes Basin Assessment is Fair & Improving | ||||
Status
