It does not react with other chemicals. The danger is that it has a love affinity for human body fats. There is a build up through the food chains to planktons in the sea to fish and finally to mammals. PCB harmfully effects the hormone systems, results in decreased immunity, arrest of sexual development, is implicated in various cancers, and results in damage to the liver, kidney and central nervous system. It interferes with genetic function.
Dioxins are strong human carcinogens, especially brain cancers.
Eating fish from waters with high levels of PCB also have been implicated in causing anemias, edema, and infectious diseases. The seals all had high levels of PCB, organochlorines and impaired immune systems. The question arose as to where this virus came from. It was found that there was an abundant amount of red algae in the sea. Algae is a well nourished consumer of oxygen in the water, leaving little for other living things.