Risk Evaluation for Octamethylcyclotetrasiloxane (D4)

In September 2025, EPA released the draft risk evaluation for octamethylcyclotetrasiloxane (D4) under the Toxic Substances Control Act (TSCA) for public comment and independent peer review. EPA granted the manufacturer request for the risk evaluation for D4 in October 2020.

Learn more about manufacturer-requested risk evaluations.

Find information about other chemicals undergoing risk evaluations under TSCA.

On this page:

Draft Risk Evaluation Findings
Background on D4
Uses of D4
Recent Activities and Opportunities for Public Comment
Draft Risk Evaluation and Supporting Materials

Draft Risk Evaluation Findings

EPA is preliminarily determining that D4 presents unreasonable risk of injury to human health driven by risk to workers from 23 conditions of use (COUs) and risk to consumers from one COU. Workers who manufacture D4, use D4 in the processing of products including adhesives and sealants, or use paints and coatings containing D4 in industrial and commercial applications, and consumers who use certain paints and coatings containing D4 are at a higher risk of exposure. The agency is also preliminarily determining that D4 presents an unreasonable risk to the environment from seven COUs. EPA did not preliminarily identify a risk of injury to human health or the environment from the other 37 COUs for D4. For COUs with unreasonable risk to workers, these preliminary risk determinations do not reflect the use of personal protective equipment (PPE); however, as the draft risk evaluation shows, the use of PPE may reduce exposures and mitigate risk. EPA did not preliminarily identify unreasonable risk of injury to human health for the general population from any COU. EPA is not yet making preliminary determinations regarding the contribution to the unreasonable risk to the environment from 18 COUs and to human health from two COUs. EPA is seeking comment on all aspects of the draft risk evaluation, including for the COUs where EPA is not making a preliminary determination.

EPA has integrated recently published information on bioaccumulation and biomagnification metrics into this draft risk evaluation as this field is an area of active research with D4. Although these values indicated that D4 is bioaccumulative, laboratory and field studies suggest that D4 has low potential for biomagnification, meaning it is more likely for D4 concentrations to decrease as it moves up the food chain through dietary exposure. Furthermore, recent research on D4 uptake in fishes has found that while uptake of D4 will occur via both dietary and environmental exposure routes, D4 that is ingested can be metabolized thus limiting uptake and reducing significant accumulation from dietary sources.

Background on D4

D4 is a common chemical name for octamethylcyclotetrasiloxane. The primary use for D4 is to make other silicone chemicals and as an ingredient in some personal care products. Information from the 2016 Chemical Data Reporting (CDR) for D4 indicates the reported production volume is between 750 million and 1 billion pounds per year (domestic manufacture including import). In the 2020 CDR, the national aggregate production volume reported for D4 was 250,000,000 to 500,000,000 pounds per year. D4 was identified in the 2014 Update to the TSCA Work Plan. Also, in 2014 EPA issued an enforceable consent agreement requiring environmental testing data to help the agency better understand the amount of D4 released into the environment and the quantity of D4 in water, sediment and aquatic organisms.

Uses of D4

In the draft scope of the D4 risk evaluation, EPA preliminarily identified COUs associated with the manufacture and importing; processing; distribution in commerce; industrial, commercial and consumer uses; and disposal of D4, including:

In the production of other silicone chemicals;
In paints and coatings;
In cleaning, laundry, and dishwashing products; and
In other commercial and consumer products, including adhesives and sealants, automotive care products, and other plastic and rubber products.

The above listed COUs are ways that a person or the environment could be potentially exposed to this chemical. However, when conducting a risk evaluation, EPA also considers the hazards (i.e., health effects or environmental impacts) that could occur from coming in contact with a chemical.

Recent Activities and Opportunities for Public Comment

In September 2025, EPA released the draft risk evaluation for public comment and peer review by the agency’s Science Advisory Committee on Chemicals (SACC). EPA will accept public comments for 60 days via docket EPA-HQ-OPPT-2018-0443 on regulations.gov. EPA will hold a virtual public meeting to be held on December 2-5, 2025, for the SACC to discuss the draft risk evaluation and technical support documents for D4. EPA will also hold a preparatory virtual public meeting on November 18, 2025, for the SACC and the public to consider and ask questions regarding the scope and clarity of the draft charge questions. Registration instructions for the virtual preparatory and peer review meetings will be announced on the SACC website approximately one month prior to each meeting. View the SACC website for information about how to register and how and submit written and oral comments.

In March 2022, EPA published the final scope document outlining the hazards, exposures, conditions of use, and the potentially exposed or susceptible subpopulations that the agency expects to consider in its risk evaluation. EPA published and took public comment on the draft scope document in September 2021.

As EPA continues to move through the risk evaluation process there will be additional opportunities for public comment. In addition to public comment periods, the agency will continue to engage with stakeholders as it develops the risk evaluation. Stakeholders should reach out to EPA via the staff contact to engage with the agency.

Draft Risk Evaluation and Supporting Materials

Read the Federal Register Notice.

View the supporting documents in EPA-HQ-OPPT-2018-0443.