A series of peer-reviewed publications in Regulatory Toxicology and Pharmacology add further compelling evidence that the siloxane D5 does not present a risk to human health.

These recently published assessments are consistent with other peer-reviewed publications that demonstrate the safety of D5, and are also consistent with the independent assessment of D5 conducted by the Government of Canada which concluded that the use of D5 does not pose a danger to human health. These publications provide further support that the use of D5 in consumer products does not warrant any marketplace restrictions, which would unnecessarily hinder trade and limit consumer choice without any corresponding human health benefit.

Toxicology of decamethylcyclopentasiloxane (D5),”By: Dekant and Klaunig

In a toxicology review of D5, Dekant and Klaunig summarize studies on the toxicology (genotoxicity, acute and repeated dose and reproductive/developmental) and mechanistically-based studies (metabolism, toxicokinetics and receptor interactions) of D5. The authors explain that D5 rapidly evaporates following contact with skin with very little D5 entering the body and that any D5 that is inhaled is either quickly exhaled or is metabolized by the body and excreted in urine. The paper explains that the body’s ability to quickly metabolize and eliminate D5 means that the potential for bioaccumulation of D5 is considered unlikely in mammals resulting only in potential effects that are considered mild or adaptive responses to high concentrations of a chemical.

“Biological relevance of decamethylcyclopentasiloxane (D5) induced rat uterine endometrial adenocarcinoma tumorigenesis: Mode of action and relevance to humans,” by: Klaunig et al. and Jean et al.

The scientific manuscripts of Jean et al. and Klaunig et al. conclude that tumors observed for D5 are not relevant for human health.

Jean et al. provides a review of the outcome of the 24-month chronic toxicity and carcinogenicity study of D5. Klaunig et al. question the biological relevance of the tumors. Klaunig et al.’s review questions if the study finding was related to D5 exposure in the rats and discusses the uncertainty of any likely relevance to humans. The in-depth analysis questioned whether the tumors themselves were related to D5 exposure since the type of tumors found spontaneously develop at high rates in the type of rat used in the study.

Further, the publication concluded that if the rat tumors were related to D5 exposure, they were likely formed through a physiological pathway that is unique to rats and that the mode of action (or way the tumors are developed in rats) is not relevant to humans. This conclusion, coupled with the fact that the tumors were only seen at the highest tested dose, provides additional support that these effects are not relevant in humans.

Statistical Considerations for a Chronic Bioassay Study: Exposure to Decamethylcyclopentasiloxane (D5) and Incidence of Uterine Endometrial Adenocarcinomas,” by: Young and Morfeld

The Young and Morfeld publication provides a statistical analysis of the study described in Jean et al. Their analysis shows that the small incidence of tumors in rats is statistically similar to the number of cases normally seen in the overall population of rats of this type. Only at the highest dosage level there is a tendency for an increased incidence of tumors. The result of this analysis could be a chance finding and a threshold effect can be assumed.

"Development of a Multi-Compound and Multi-Dose Route PBPK Model for Volatile Methyl Siloxanes D4 and D5,” by: McMullin .

McMullin et al. developed a single pharmacokinetic (PBPK) model that incorporates key components of the seven previously published PBPK models to derive dose metrics for the siloxanes D4 and D5. Previous models were insufficient for various risk assessment applications when they needed to be used for determining an optimal dose metric. This model is robust enough to derive relevant dose metrics following individual or combined skin and inhalation exposures of workers, consumers or the general population to D4 and D5. This PBPK model provides a means for route-to-route, interspecies and high-to-low dose extrapolation, and can be used for developing high-quality risk assessments such as those demonstrated by Vanlandingham and Gentry, as described below.

Global Human Health Risk Assessment for Decamethylcyclopentaasiloxane,” by: Franzena et al.

Through a global review of the existing publications, study reports and articles on D5, Vanlandingham and Gentry provide a global human health risk assessment of D5 that summarizes the findings of the numerous toxicology and mechanistic studies and then analyzing them in the context of risk, which takes into consideration both hazard and exposure. Their analysis shows that the weight of evidence demonstrates that D5 does not pose a risk to human health at typical exposure levels for consumers or workers.

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