Decamethylcyclopentasiloxane (D5).

Decamethylcyclopentasiloxane (D5; CAS No. 541-02-6) is a precursor in the production of siloxane polymers for industry and medicine and is a carrier ingredient in many toiletries and cosmetics. D5 has a relatively low order of toxicity following acute administration via the oral, dermal, and inhalation routes of exposure. It is not considered to be a dermal or eye irritant or a dermal sensitizer. There is no appreciable dermal absorption of D5 based on results from in vivo and in vitro studies. It has not been shown to be genotoxic/mutagenic when tested in a number of short-term in vitro and in vivo assays and did not cause reproductive or developmental toxicity in rats. Inhalation exposure of rats to 160 ppm D5 for up to 24 months produced adverse effects in the liver (weight changes and hepatocellular hypertrophy) and uterus (increased incidence of endometrial adenocarcinoma, endometrial adenoma, and adenomatous polyps in several animals); however, the results of recent mode-of-action studies are consistent with a uterine tumorigenesis mechanism that is not relevant for humans. Based on the results of the chronic inhalation study, 160 ppm was determined to be the no-observed-adverse-effect level (NOAEL) and was selected as the point of departure for the derivation of the workplace environmental exposure level (WEEL®) value. This NOAEL was adjusted to account for interindividual variability and residual uncertainty regarding upper respiratory tract changes still occurring at 160 ppm. The resulting 8-h time-weighted average WEEL value of 10 ppm is expected to provide a significant margin of safety against any potential adverse health effects in workers exposed to airborne D5.