Ethylene oxide was listed as known to the state to cause cancer in Proposition 65 list on July 1, 1987. An NSRL for ethylene oxide was adopted as 2 µg/day on July 1, 1988. Since this level was adopted, there has been no change in the NSRL.

Recently, the Office of Environmental Health Hazard Assessment (OEHHA) is proposing to update the No Significant Risk Level (NSRL) for ethylene oxide by amending Title 27, California Code of Regulations, Section 25705(b).

The updated proposal for the daily limit for ethylene oxide is 0.058 micrograms.

Reason for updating the ethylene oxide NSRL

In 2016, the US EPA did an extensive review and analysis of ETO, which provided scientific information on the carcinogenicity of ethylene oxide and the calculation of cancer potency value (i.e., unit risk) based on the NIOSH human epidemiology study.

NIOSH (National Institute for Occupational Safety and Health)

The US EPA evaluation comprised a cancer unit risk (cancer potency value) estimation of 6.1 per ppm (3.3 10-3 per g/m3), which resulted in the OEHHA's analysis of the most recent scientific data and the recommendation of a modification to the ethylene oxide NSRL (no significant risk level).

FYI, please find the information on the US EPA's ethylene oxide risk assessment.

1. Carcinogenic to humans by inhalation
2. Lymphohematopoietic cancers and breast cancers (ETO-exposed workers)
3. Lymphohematopoietic cancers in rats and mice and mammary carcinomas in mice
4. Chromosome damage in humans

Overall, the US EPA concluded that the hazard characterization of ETO as ‘carcinogenic to humans is high.

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