Polychlorinated Biphenyls (PCBs)

Reference Dose for Oral Exposure (RfD) (PDF) (22 pp, 150 K) Last Updated: 06/01/1994

Information reviewed but value not estimated.

Note: See the assessments under Related Links for information on the effects of oral exposure to specific PCB mixtures, including RfDs for Aroclor 1016 and Aroclor 1254.

Reference Concentration for Inhalation Exposure (RfC) (PDF) (22 pp, 150 K)

Not assessed under the IRIS Program.

Weight of Evidence for Cancer (PDF) (22 pp, 150 K) Last Updated: 10/01/1996

• A 1996 study found liver tumors in female rats exposed to Aroclors 1260, 1254, 1242, and 1016, and in male rats exposed to 1260. These mixtures contain overlapping groups of congeners that, together, span the range of congeners most often found in environmental mixtures. Earlier studies found high, statistically significant incidences of liver tumors in rats ingesting Aroclor 1260 or Clophen A 60 (Kimbrough et al., 1975 Norback and Weltman, 1985 Schaeffer et al., 1984). Mechanistic studies are beginning to identify several congeners that have dioxin-like activity and may promote tumors by different modes of action. PCBs are absorbed through ingestion, inhalation, and dermal exposure, after which they are transported similarly through the circulation. This provides a reasonable basis for expecting similar internal effects from different routes of environmental exposure. Information on relative absorption rates suggests that differences in toxicity across exposure routes are small. The human studies are being updated currently available evidence is inadequate, but suggestive.
• This may be a synopsis of the full weight-of-evidence narrative.

Quantitative Estimate of Carcinogenic Risk from Oral Exposure (PDF) (22 pp, 150 K)

Inhalation Unit Risk: 1 x 10^-4 per µg/m³ (Applies to inhalation of evaporated congeners)
Extrapolation Method: Linear extrapolation below LED10; route-to-route extrapolation from the oral slope factor
Tumor site(s): Hepatic
Tumor type(s): Liver hepatocellular adenomas, carcinomas, cholangiomas, or cholangiocarcinomas (Brunner et al., 1996; Norback and Weltman, 1985)
Note: For inhalation of an aerosol or dust contaminated with PCBs, see the IRIS Summary for information on the appropriate inhalation unit risk.