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PROPYLENE OXIDE<br />

CAS No: 75-56-9<br />

I. PHYSICAL AND CHEMICAL PROPERTIES (From HSDB, 1994)<br />

Molecular weight 58.08<br />

Boiling point<br />

34.2°C<br />

Melting point<br />

-112°C<br />

Vapor pressure 543 mm Hg @ 25°C<br />

Air concentration conversion 1 ppm = 2.37 mg/m 3<br />

II.<br />

HEALTH ASSESSMENT VALUES<br />

Unit Risk Factor: 3.7 E-6 (µg/m 3 ) -1<br />

[Calculated by US EPA (1995) from male rat nasal cavity hemangioma/hemangio-sarcoma data<br />

(NTP,1985) using a linearized multistage procedure, extra risk.]<br />

Oral Cancer Potency Factor: 2.4 E-1 (mg/kg/day) -1<br />

[Calculated by US EPA (1995) from female Sprague-Dawley rat forestomach squamous cell<br />

carcinoma tumor data (Dunkelberg, 1981), using a linearized multistage procedure, extra risk.]<br />

III.<br />

CARCINOGENIC EFFECTS<br />

Human Studies<br />

Theiss et al. (1981) conducted a retrospective cohort study of 602 active and former employees who<br />

had worked for 6 months or more in one of 8 German alkylene oxide production plants. The workers<br />

had been exposed to alkylene oxides (propylene oxide and ethylene oxide) as well as to other chemicals<br />

such as dichloropropane and epichlorohydrin. No ambient propylene oxide concentrations were<br />

reported and the study included workers employed as early as 1928; propylene oxide production did<br />

not begin until 1959. No significant difference was observed between the observed and expected<br />

numbers of cancer deaths.<br />

Animal Studies<br />

Exposure to propylene oxide by gavage at dose levels of 0, 15 or 60 mg/kg twice weekly for 150<br />

weeks has been shown to induce forestomach tumors (primarily squamous cell carcinomas) in female<br />

Sprague-Dawley rats (Dunkelberg, 1982). Female NMRI mice treated with 0.1, 0.3, 1.0 or 2.5 mg<br />

propylene oxide once a week for 95 weeks via subcutaneous injection demonstrated a dose-dependent<br />

increase in injection site tumors (mostly fibrosarcomas) (Dunkelberg, 1984). Subcutaneous injection of<br />

a total dose of 1500 mg/kg propylene oxide over 325 days in rats (sex and strain not specified) resulted<br />

504

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