Systematic review of the human health hazards of propylene dichloride

• Published in: Regulatory toxicology and pharmacology 2023-10, Vol.144, p.105468-105468, Article 105468
• Main Authors: Lynch, Heather N., Kozal, Jordan S., Vincent, Melissa J., Freid, Rachel D., Beckett, Evan M., Brown, Sarah, Mathis, Claire, Schoeny, Rita S., Maier, Andrew
• Format: Article
• Language: English
• Subjects: 1,2-Dichloropropane; Cancer; Mode of action; Propylene dichloride; Systematic review; TSCA
• ISSN: 0273-2300; 1096-0295
• DOI: 10.1016/j.yrtph.2023.105468

Propylene dichloride (PDC) is a chlorinated substance used primarily as an intermediate in basic organic chemical manufacturing. The United States Environmental Protection Agency (EPA) is currently evaluating PDC as a high-priority substance under the Toxic Substances Control Act (TSCA). We conducted a systematic review of the non-cancer and cancer hazards of PDC using the EPA TSCA and Integrated Risk Information System (IRIS) frameworks. We identified 12 epidemiological, 16 toxicokinetic, 34 experimental animal, and 49 mechanistic studies. Point-of-contact respiratory effects are the most sensitive non-cancer effects after inhalation exposure, and PDC is neither a reproductive nor a developmental toxicant. PDC is not mutagenic in vivo, and while in vitro evidence is mixed, DNA strand breaks consistently occur. Nasal tumors in rats and lung tumors in mice occurred after lifetime high-level inhalation exposure. Cholangiocarcinoma (CCA) was observed in Japanese print workers exposed to high concentrations of PDC. However, co-exposures, as well as liver parasites, hepatitis, and other risk factors, may also have contributed. The cancer mode of action (MOA) analysis revealed that PDC may act through multiple biological pathways occurring sequentially and/or simultaneously, although chronic tissue damage and inflammation likely dominate. Critically, health benchmarks protective of non-cancer effects are expected to protect against cancer in humans. •Nasal and respiratory lesions most sensitive endpoints in rodents.•Animal respiratory tumors likely resulted from point-of-contact PDC tissue metabolism.•Co-exposures and other risk factors likely involved in human cholangiocarcinoma.•Cancer MOA involves saturation of detoxification and chronic inflammation.•Protecting against non-cancer lesions expected to protect against cancer.