Every day, as a result of human activity, a wide variety of chemicals make their way into the Great Lakes by air and water. While some of these compounds are naturally-occurring and pose little threat to the health of the lake ecosystem, others can harm or kill plant and animals throughout the food chain, including humans.
Contaminants are highly varied in chemical composition and behavior.
These materials are derived mostly from coal or petroleum and many have valuable applications in industry, transportation, energy production, and commerce. However, when carried into the Great Lakes ecosystem, organic contaminants may pose serious hazards. While environmental regulations over the past 25 years have helped stem the spread of these materials, the contaminants still reach Great Lakes waters via storm-drain runoff, leaking landfills, rivers and streams, accidental spills, or by fallout from polluted air. Inorganic contaminants include heavy metal compounds such as mercury and lead. Sources of contaminants within the Great Lakes ecosystem.