Toxic chemicals known as P-C-B’s haven’t been used in the U.S. for morethan two decades. But dangerous levels of P-C-B’s remain in the naturalenvironment and pose a threat to human health. To address this problem,scientists are trying to understand how these chemicals get into thefood chain. Now, a scientist at Northwestern University has found alikely answer. The Great Lakes Radio Consortium’s Steve Frenkelreports: