Department of Natural Resources scientists measured the amount of PCBs - short for polychlorinated biphenyls - in chinook and coho salmon from Lake Michigan. They found that PCB levels went down 4 percent per year in chinook salmon and 2.6 percent per year in coho salmon from the mid-1980s to 2010. Those numbers compare to a yearly decline of 16.7 percent per year in chinook salmon and 23.9 percent per year in coho salmon from 1975 to the mid-1980s.
Manufacturers used PCBs in the process of making carbonless copy paper, electrical transformers, cutting oils and hydrolic fluids. The PCBs were dumped into waterways, but they are slow to break down in the environment. Eating fish contaminated with PCBs has been linked to developmental disorders and reduced birth weights, increased cancer risk, diabetes and thyroid problems.
PCBs were banned in the United States in 1979.
"Although the rate of decline has slowed from the early days of the ban, the continuing improvement is significant," Candy Schrank, an environmental toxicologist and fisheries expert with DNR, said in a news release. "PCBs remain the contaminant of greatest concern for the health of people who eat fish from Lake Michigan and these findings will help us evaluate ongoing efforts to reduce the amount of chemical contamination entering the lake and to learn about how PCBs move in the environment."
The DNR does not expect the reduction of PCB levels found in fish to lead to an immediate change in recommendations of how much salmon people should eat from Lake Michigan. Right now, the DNR warns people not to eat more than one meal per month of chinook and coho salmon.