Dow Chemical recently reported a preliminary result of over 1.6 million parts per trillion (ppt) from a single sediment sample in the Saginaw River. Until now, the highest level found in the Saginaw River was 32,000 ppt. Under June 2007 EPA orders, Dow has been removing three dioxin hotspots from the Tittabawasse River which had concentrations of up to 87,000 ppt. The new Saginaw River sample came from a location a half-mile below the confluence of the Tittabawassee and Shiawassee Rivers, near Wickes Park in Saginaw.
"The sediment concentration recently reported by Dow is probably the highest level ever found in the Great Lakes," said Dr. Milton Clark, EPA Region 5's senior health and science advisor. "While not exactly comparable, the concentration is more than 1,000 times higher than EPA's action level of 1,000 parts per trillion that triggers cleanup of dioxin-contaminated soils at residences. It is more than10,000 times higher than the State of Michigan's residential cleanup criterion of 90 parts per trillion."
"Under most circumstances, EPA is more concerned by high levels of dioxin in sediments because they contaminate the aquatic food chain. EPA national dioxin guidance and risk assessment approaches indicate that dioxin levels found in sediments may need to be lower than those in soils to fully protect public health," Dr. Clark added.
Fish consumption is one of the primary exposure pathways in the Saginaw River system. Adverse human health effects associated with exposure to dioxin include impacts to the reproductive, immune and endocrine systems. Dioxin is also a carcinogen.
Since 1978, the state of Michigan has issued fish consumption advisories for the Saginaw River Watershed. A recent University of Michigan study revealed that people consuming fish from the Saginaw River system have higher than average levels of dioxins in their blood.