On September 17, 2025, the U.S. Environmental Protection Agency (EPA) has released a draft risk evaluation for Octamethylcyclotetrasiloxane (D4) under the Toxic Substances Control Act (TSCA). The agency’s initial findings indicate that D4 may pose unreasonable risks to human health and the environment under certain conditions of use.
Key Findings: Risks to Human Health
EPA identified 23 conditions of use (COUs) where workers face potential risks, particularly during the manufacture of D4 and in processing activities involving adhesives, sealants, paints, and coatings. In addition, one consumer COU involving D4 in paints and coatings was flagged for unreasonable risk.
The draft evaluation clarifies that these determinations do not assume the use of personal protective equipment (PPE). While PPE may reduce exposure, EPA emphasizes that risk exists without its consistent use. Importantly, no unreasonable risks were identified for the general population.
Key Findings: Environmental Risks
EPA’s draft evaluation also highlights seven COUs where D4 could pose risk to the environment. For another 18 environmental COUs and two human health COUs, the agency has not yet reached preliminary conclusions.
The draft incorporates recent studies on bioaccumulation and biomagnification of D4. Studies show D4 can accumulate in aquatic organisms but has a low likelihood of biomagnifying through the food chain, as fish are able to metabolize ingested D4. These findings suggest that while exposure occurs, accumulation across trophic levels may be limited.
Public Comment and Review
- Preparatory meeting – November 18, 2025
- Peer review meeting – December 2–5, 2025, led by the Science Advisory Committee on Chemicals (SACC)
Participants may submit written feedback or request to present oral comments by the deadlines listed on the SACC website.
Following the comment period and peer review, EPA will finalize the risk evaluation. If unreasonable risks are confirmed, the agency may propose risk management actions to reduce exposure to D4 in workplaces, consumer settings, and the environment.
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