Toxicokinetics - trdoer40216

reversible after termination of exposure, but the concentration of stored PCB in

adipose tissue will dictate the rapidity with which this will take place.

There is evidence in both animals and humans that PCBs might be fetotoxic,

resulting in decreases in birth weight, head circumference, and gestational age of

the newborn. In addition, behavioral deficiencies have been observed in

newborns exposed to PCBs in breastmilk.

Most genotoxicity and mutagenicity assays of PCBs have been negative. The

carcinogenic effects of PCBs have been studied in rats and mice. The USEPA

carcinogenic slope factor is based upon a data obtained from a chronic feeding

study of PCBs to rats in which trabecular carcinomas and adenocarcinomas were

observed. Based on the positive evidence for carcinogenicity of Aroclors 1254,

1260, Kanclor 500 and Clophen A-30 and A-60 in animals, along with adequate

evidence in humans, the USEPA has categorized these PCBs as B2, or probable

human carcinogens (IRIS 1993).

Toxicokinetics

Following oral exposure to PCBs, gastrointestinal absorption of these

compounds is efficient, estimated to be close to 100 percent. Absorption via

dermal and inhalation routes is not as efficient. The PCBs are poorly

metabolized to more polar compounds, contributing to their long biological half

lives. Distribution of PCBs follows a biphasic pattern: initially to muscle and

liver, followed by redistribution to organs with high fat content, such as fat and

skin. Excretion occurs primarily in the feces.

Ecological effects

Due to the former extensive use and stability of the PCBs, there is widespread

occurrence of these compounds in soils and water. In general, the higher the

degree of chlorination, the more resistant to biodegradation and the more

persistent in the environment are the PCBs. Bioconcentration factors in aquatic

species range from 26,000 to 60,000. Analyses of whole fish samples collected

nationwide revealed PCB residues in 94 percent of all fish surveyed, at a mean

concentration of 0.53 ppm.

It is well documented that PCBs interfere with reproduction in wildlife and in

experimental animals.

References

Agency for Toxic Substances and Disease Registry. (1991). "Toxicological

profile for selected PCBs," U.S. Department of Health and Human Services,

Washington, DC.

Integrated Risk Information System (IRIS). (1993). On-line database, accessed

8/20/97.

D64

Appendix D Toxicological Profiles