 Polychlorinated biphenyls were produced from 1929 to 1979, when they were banned by the Toxic Substances Control Act.Polychlorinated biphenyls are human carcinogens, and can also have a negative effect on the human immune, reproductive, and endocrine systems.PCBs in the Kalamazoo River adhere to the fatty tissue of fish, and over time a process of bioaccumulation takes place, meaning that the PCBs appear in increasing concentrations in organisms higher up on the food chain, including humans.