There are over 42 chemicals in the Duwamish above State environmental and health standards. Industrial carcinogens in airport runoff and from WWII bomber construction, heavy metals in ship paint, arsenic in cement material, oil in stormwater from city streets, and raw industrial and domestic waste from overflowing sewage pipes have all played a role in long-lasting toxic pollution of the river. The most common chemicals include PCBs (polychlorinated biphenyls); mercury, lead and other metals; dioxins; and arsenic.
Many of these pollutants have the potential to pose serious health risks by building up in the tissues of fish and shellfish, and passing through the food chain to eagles, seals, orcas, and people. People who regularly eat fish and crab from the river are at the greatest risk through their diet. Concentrated toxins also occur in some Duwamish river-bottom mud; in these areas, people should avoid daily contact.