NOTE: Although the toxicity values presented in these toxicity profiles were correct at the time they were produced, these values are subject to change. Users should always refer to the Toxicity Value Database for the current toxicity values.
Prepared by C. B. Bast, Ph.D., D.A.B.T., Chemical Hazard Evaluation Group, Biomedical and Environmental Information Analysis Section, Health Sciences Research Division, *.
Prepared for OAK RIDGE RESERVATION ENVIRONMENTAL RESTORATION PROGRAM
*Managed by Martin Marietta Energy Systems, Inc., for the U.S. Department of Energy under Contract No. DE-AC05-84OR21400
Aroclor® 1260 is a polychlorinated biphenyl (PCB) mixture containing approximately 38% C12H4Cl6, 41% C12H3Cl7, 8% C12H2Cl8, and 12% C12H5Cl5 with an average chlorine content of 60% (USAF 1989). PCBs are inert, thermally and physically stable, and have dielectric properties. In the environment, the behavior of PCB mixtures is directly correlated to the degree of chlorination. Aroclor® is strongly sorbed to soil and remains immobile when leached with water; however, the mixture is highly mobile in the presence of organic solvents (USAF 1989). PCBs are resistant to chemical degradation by oxidation or hydrolysis. However, biodegradation, especially of lower chlorinated PCBs, can occur (USAF 1989). PCBs have high bioconcentration factors, and due to lipophilicity, especially of highly chlorinated congeners, tend to accumulate in the fat of fish, birds, mammals, and humans (ATSDR 1995). The use of PCBs in the United States was limited to closed systems in 1974, and in February, 1977, the U.S. Environmental Protection Agency (EPA) issued final regulations prohibiting PCB discharge into waterways (EPA 1977).
PCBs are absorbed after oral, inhalation, or dermal exposure and are stored in adipose tissue. The location of the chlorine atoms on the phenyl rings is an important factor in PCB metabolism and excretion. The major route of PCB excretion is in the urine and feces; however, of more importance is elimination in human milk. Metabolites are predominately found in urine and bile, while small amounts of parent compound are found in the feces. Biliary excretion appears to be the source of fecal excretion (ATSDR 1995).
Accidental human poisonings and data from occupational exposure to PCBs suggest initial dermal and mucosal disturbances followed by systemic effects that may manifest themselves several years post-exposure. Initial effects are enlargement and hypersecretion of the Meibomian gland of the eye, swelling of the eyelids, pigmentation of the fingernails and mucous membranes, fatigue, and nausea. These effects were followed by hyperkeratosis, darkening of the skin, acneform eruptions, edema of the arms and legs, neurological symptoms, such as headache and limb numbness, and liver disturbance (USAF 1989).
Hepatotoxicity is a prominent effect of PCBs, including Aroclor® 1260, that has been well characterized (EPA 1996a). Effects include hepatic microsomal enzyme induction, increased serum levels of liver-related enzymes (indicative of hepatocellular damage), liver enlargement, lipid deposition, fibrosis, and necrosis. Chloracne and Immune function disorders have been observed in humans and several animal species after PCB exposure. Reproductive and developmental effects, including low-birth weight, and decreased gestational time, and decreased reproductive capacity, have been observed in human and animal species. No reference dose (RfD) or reference concentrations (RfC) have been verified for Aroclor® 1260.
Data are suggestive but not conclusive concerning the carcinogenicity of PCBs in humans. The EPA has not determined a weight-of-evidence classification or slope factor for Aroclor® 1260 specifically. However, hepatocellular carcinomas in three strains of rats and two strains of mice have led the EPA (1996b) to classify PCBs as group B2, probable human carcinogen. The carcinogenicity slope factor (q1*) for oral exposure to PCBs is
7.7 (mg/kg/day)-1 based on an increase of hepatocellular tumors in female Sprague-Dawley rats treated with Aroclor® 1260. A drinking water unit risk of 2.2E-4 (µg/L)-1 for PCBs was calculated based on the q1* (EPA 1996b). Retrieve Toxicity Profiles Formal Version
Last Updated 10/07/97