You may not have heard of octamethylcyclotetrasiloxane (known as D4), but we can guarantee you have probably come into contact with it. Used in products from adhesives and automotive care products to cosmetics, hair treatments, and deodorants, regulators in Canada, the European Union, and the United Kingdom have determined that D4 can pose reproductive and developmental risks to human health. Yet, EPA’s recently released D4 Draft Risk Evaluation underestimates these risks, once again failing to protect people’s health as required under the Toxic Substances Control Act (TSCA).
A Manufacturer-Requested Evaluation with Major Data Gaps Leaving the Public at Risk
The D4 TSCA risk evaluation was requested by the American Chemistry Council in January 2020. EPA approved this request later that year and has had over five years to obtain or generate “reasonably available information” needed for a complete assessment. Yet EPA admits it lacks sufficient information to make unreasonable risk determinations regarding environmental risk for 18 uses of D4, and similarly lacks the information needed to make determinations regarding human health risk for two uses. In other words, EPA failed to use its legal authority to obtain necessary data in a timely manner and is now abdicating its responsibility to adequately assess the risks of D4, leaving the public and environment to bear the burden of its own poor implementation of TSCA.
EPA cannot make final risk determinations for D4 without this missing data. And if EPA obtains new information and updates its findings for these uses, those revisions must undergo independent scientific peer review—which the Agency has not committed to doing.
EPA’s Scientific Approach Falls Short of TSCA’s “Best Available Science” Requirement
For the fraction of uses EPA did assess, the Agency concluded that D4 does not pose unreasonable risk for nearly all consumer uses, all general population exposures (such as through air and drinking water or by inhaling household dust), and several occupational uses. These conclusions rely on a series of scientifically flawed assumptions:
1. Outdated and incomplete review of the scientific evidence
The EPA employed a flawed systematic review process and an outdated literature search, which failed to systematically identify studies published after 2019. This lack of appropriate scientific procedures occurred despite clear recommendations from the National Academies and other scientific bodies to adopt rigorous, transparent, and unbiased methods. This violates TSCA’s mandate that EPA must use the “best available science” when conducting chemical risk evaluations.
2. Misclassification of D4’s environmental hazards
EPA downplayed strong, internationally accepted evidence that D4 is persistent, bioaccumulative, and, in many assessments, very persistent and bioaccumulative. These omissions matter because persistent and bioaccumulative chemicals, like PFAS, increase health risks for communities already facing disproportionate chemical burdens, and once released, cannot be easily cleaned up from the environment.
3. Missing Exposures Pathways
EPA also failed to quantify risks from multiple real-world D4 exposure sources, including:
- D4 in human breast milk, a critical route of exposure for infants and toddlers.
- Down-the-drain releases, which occur when D4-containing products are washed into wastewater systems.
- Landfill leachate, an important environmental source of persistent chemicals like D4.
- Background exposures from non-TSCA uses, such as through personal care product and cosmetic use.
EPA further failed to aggregate exposure routes and pathways across different uses and did not account for all potentially exposed or susceptible subpopulations (PESS)—including individuals experiencing liver disease, poverty, discrimination, or other non-chemical stressors that increase susceptibility to harm from D4. These omissions violate core TSCA requirements.
4. Flawed Risk Quantification
EPA continued to rely on a flawed approach to quantifying risk that assumes a threshold below which risk does not occur and fails to account for risks to susceptible subgroups, like infants, children, and people with underlying disease. We applied methods developed by the WHO that account for risks along the full range of exposures to EPA’s own data and found that the Agency’s approach would accept exposures corresponding to a 1-in-333 risk level for reproductive harm—a risk level 3,000 times higher than the level EPA typically applies for carcinogens.
5. Risk Estimates That Don’t Match the Conclusions
Where EPA did quantify health risks, major issues emerged. First, EPA ignored the risks faced by the half of workers with exposures above the median. For many uses, EPA’s own high-end estimates showed clear evidence of unreasonable risk, but EPA dismissed them without scientific justification. Second, for several consumer and general population scenarios, EPA ignored its own findings of unreasonable risk and repeatedly “refined” its exposure assessments until the risks dropped below levels of concern. These refinements are scientifically indefensible, obscure real-world exposures and risks, and will result in lack of actions to protect health.
What EPA Must Do Before Finalizing the D4 Evaluation
If left uncorrected, EPA’s final risk evaluation could leave workers, consumers, and susceptible populations at continued and unnecessary risk from D4.
We recommend EPA correct its D4 Risk Evaluation before finalizing, including to:
- Obtain all necessary data to make risk determinations for all uses and submitting new analyses to independent panel peer review.
- Conduct an updated, comprehensive literature search and systematic review consistent with best practices.
- Adopt improved methods for determining persistence/bioaccumulation that align with best available science and international standards.
- Revise risk characterization to incorporate quantitative non-cancer risk estimates.
- Use high-end exposure estimates for all worker and consumer uses and exposure scenarios.
- Eliminate scientifically unsupported assumptions that inappropriately minimize or dismiss risk.
EPA has an obligation under TSCA to protect health and the environment using the best available science. The public deserves a D4 risk evaluation that meets this standard, and communities across the country are counting on EPA to get it right.
About the author
Rashmi Joglekar, PhD leads the Science, Policy & Engagement team at PRHE. She comes with a wealth of knowledge and understanding of how toxic chemicals impact susceptible populations and communities and is skilled in addressing these issues with decision-makers in Washington, DC. She completed her PhD in the Integrated Toxicology and Environmental Health Program at Duke University, specializing in neurodevelopmental toxicology.
