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Pathways Into The Environment...
Before 1977, PCBs entered the air, water, and soil during their manufacture and usage. Wastes generated at the time that contained PCBs were often placed in landfills where due to leakage and spills entered the environment. Even today, PCBs can be released from poorly maintained hazardous waste sites, illegal or improper dumping, or leaks from faulty transformers that contain PCBs.[1]
In the air PCBs can be carried long distances and have been found in snow and sea water in areas far way from where they were released. As a consequence, PCBs are found all over the world, and are present as solid particles or as a vapor in the atmosphere. They will eventually return to land and water by settling as dust or in rain. PCBs stick strongly to soil and may stay in soil for months or years, being carried deep into the ground with rainwater. Generally, the more chlorine that the PCBs contain, the slower they break down.[2]
PCBs are taken up into the bodies of small organisms and fish in water. PCBs especially accumulate in fish and marine mammals (such as seals and whales) reaching levels that may be many thousands of times higher than the concentration in the surrounding water due to PCBs lipophilic nature.[1]
Wildlife Health Effects...
The EPA ruling to strictly limit the manufacture, processing, and distribution of PCBs in 1977 was due to the environmental impact that PCBs had on both humans and wildlife.[2] Health effects in wildlife that supported the banning of PCB use was the mortality in birds; reproductive impairment in monkeys, minks, birds, marine animals; and the endocrine and neurobehavioral effects in birds.
Since then, monitoring has shown that PCBs are highly persistent in the environment and therefore continue to present a potential hazard to humans and wildlife. A variety of other health effects have been evaluated in wildlife, some of which are relevant to human health. Adverse biological effects such as increased mortality, decreased respiratory capacity, and increased cardiovascular disease.[1] There were other effects to mammalian and fish reproduction rates, as well as the thinning of bird egg shells.
Bioaccumulation...
More highly chlorinated PCBs tend to bioaccumulate most readily, and thus are biomagnified in the food chain. Relatively high, toxic concentrations occur at higher trophic levels, such as predator birds and mammals. Once PCBs are in the body, some may be changed by the body into other related chemicals called metabolites. Some of the metabolites may leave the body in the feces within a few days, but others may remain in the body fat for months. Unchanged PCBs also remain in the body and stored for years mainly in the liver and fat deposits, but smaller amounts can be found in other organs as well. PCBs also collect in milk fat and can be transmitted to infants through breast-feeding.[1]
Sources:
[1] "Toxicology Profile for Polychlorinated Biphenyls" Agency for Toxic Substances and Disease Registry (2000): http://www.atsdr.cdc.gov/toxicprofiles/tp17.html
[2] http://www.epa.gov/opptintr/pcb/
