The U.S. Environmental Protection Agency (EPA) has finalised its risk evaluation for diisodecyl phthalate (DIDP), concluding that the chemical poses significant health risks under certain workplace conditions. Specifically, unprotected female workers of reproductive age face developmental toxicity risks from exposure to DIDP in six industrial and commercial uses, according to the Toxic Substances Control Act (TSCA) evaluation completed in January 2025.
What is DIDP and Where Is It Used?
DIDP is a phthalate chemical primarily used as a plasticiser to enhance the flexibility of polyvinyl chloride (PVC). Common applications include building and construction materials, automotive products, adhesives, sealants, paints, and coatings. However, its usage is limited in consumer goods like toys, thanks to regulatory measures that prohibit concentrations exceeding 0.1%.
The EPA's risk evaluation, conducted at the request of DIDP manufacturers, focused exclusively on TSCA-regulated uses, excluding areas like cosmetics, medical devices, and food contact materials.
Why DIDP Poses a Risk
The most concerning health effect associated with DIDP exposure is developmental toxicity. The EPA determined that when unprotected female workers of reproductive age are exposed to airborne mists during spray applications of adhesives, sealants, paints, and coatings, they face significant risks. The agency also flagged potential liver toxicity, although it stated these findings were secondary to developmental concerns.
Notably, DIDP does not contribute to cancer risk or male reproductive issues such as "phthalate syndrome," a condition associated with other chemicals in the phthalate family.
Key Conditions of Use Linked to Risk
The EPA identified six conditions of use (COUs) that significantly contribute to unreasonable health risks:
- Industrial and commercial use of adhesives and sealants
- Industrial and commercial use of paints and coatings
- Commercial use of lacquers, stains, varnishes, and floor finishes
- Commercial use of penetrants and inspection fluids
These high-risk applications represent only 1% of the DIDP production volume, yet they pose acute risks to exposed workers.
What DIDP’s Evaluation Didn’t Cover
The EPA explicitly excluded non-TSCA uses, such as food additives, from its evaluation. Past research, including assessments by the U.S. Consumer Product Safety Commission (CPSC), indicated that dietary exposure remains a significant route for DIDP exposure in women and children.
What Happens Next?
The EPA will now proceed to mitigate the identified risks by initiating regulatory measures under TSCA Section 6. A proposed rule is expected to address workplace exposures and safeguard vulnerable populations from the developmental toxicity risks posed by DIDP.
While DIDP does not present significant risks to consumers or the general population, its impact on workplace health is critical. The EPA's action underscores the need for stringent safety measures in industrial and commercial applications, particularly for vulnerable worker subgroups.
