Great Lakes Environmental Assessment and Mapping Project

Toxic Chemicals

Contaminated sediments are a significant environmental health issue in the Great Lakes basin. While there has been remarkable progress in the past 20 years reducing active discharges of toxic chemicals to the Great Lakes, many chemicals continue to persist in lake sediments, sometimes in high concentrations. Contaminants in buried sediments, present from decades of industrial, municipal, and non-point source pollution, can be resuspended by storms, ship propellers, and bottom-dwelling organisms. They then re-enter food webs and can cause serious human and ecological health concerns.

Multiple lines of evidence point to the impact of chemicals on the Great Lakes.

  • Widespread fish consumption advisories for pregnant women and at risk populations
  • Sediment contamination leading to beneficial use impairments
  • Fish and wildlife effects
  • Concerns for the safety of drinking water

We identified five categories of chemicals that often exceed ambient water quality and sediment guidelines and then selected a representative substance as a surrogate from which to map the spatial distribution in the Great Lakes. The representative chemicals were chosen based on their common identification as a chemical of concern (COC) in risk assessments or because they may serve as a surrogate for other contaminants that have similar properties and sources.

  • Biomagnifying toxic metals: Mercury
  • Non-biomagnifying toxic metals: Copper 
  • Biomagnifying toxic organics: PCBs
  • Non-biomagnifying toxic organics: PAHs
  • Agricultural pesticides: Atrazine

The non-biomagnifying toxic organics and agricultural pesticides categories could not be mapped due to insufficient data at the basin scale.

This category of stressors also includes Great Lakes Areas of Concern.