The US EPA’s draft risk evaluation of octamethylcyclotetrasiloxane (D4) identifies widespread risks to workers and aquatic environments, prompting regulatory scrutiny across the chemicals and manufacturing sectors.
The US Environmental Protection Agency (EPA) has released its September 2025 draft risk evaluation for octamethylcyclotetrasiloxane (D4)—a high-production-volume chemical widely used in adhesives, paints, automotive products, and silicone-based polymers. The draft report finds that D4 poses an “unreasonable risk of injury to human health and the environment” across multiple conditions of use (COUs), especially in industrial manufacturing and aquatic ecosystems.
The evaluation, conducted under the Toxic Substances Control Act (TSCA), applies to D4's use in manufacturing, processing, industrial, commercial, and consumer contexts. The EPA identified 24 COUs with risk to human health—primarily for workers and occupational non-users (ONUs)—and seven COUs with risk to the environment, particularly due to D4 releases into surface water and subsequent sediment accumulation.
Widespread Industrial Exposure Identified
D4 is used to manufacture a range of silicone-based products, including polydimethylsiloxane (PDMS), and appears in downstream products like paints, lubricants, cleaning agents, and sealants. The EPA flagged 21 COUs where workers face significant risk via inhalation and dermal exposure, with two additional COUs posing dermal-only risks.
Key sectors impacted include:
- Domestic and imported manufacturing
- Paint and coating formulation
- Rubber and plastics processing
- Aircraft maintenance using D4-based solvents
The report underscores that use of personal protective equipment (PPE), especially gloves and respirators, can mitigate risks, but current data suggests such measures are inconsistently applied or insufficient across facilities.
Environmental Risk Driven by Surface Water Releases
On the environmental front, the EPA pinpointed acute and chronic toxicity to aquatic organisms as a critical concern. D4’s persistence in sediment, coupled with high bioaccumulation in fish, drives elevated risk in seven COUs, particularly those involving large-scale releases into surface water.
Despite being bioaccumulative, D4 shows low potential for trophic magnification, meaning it does not significantly increase in concentration as it moves up the food chain. However, sediment-dwelling organisms and early-stage aquatic life remain highly vulnerable.
Implications for Regulatory and Industry Action
The EPA’s preliminary determination sets the stage for potential risk management actions, which could range from stricter use restrictions to bans on specific COUs. While consumer uses of D4 (e.g. in sealants or laundry products) generally showed lower levels of concern, industrial applications will likely face increased regulatory scrutiny and reporting obligations.
Notably, this evaluation excludes uses regulated under other statutes, such as D4 in cosmetics or medical devices, which fall outside TSCA's scope.
