Propylene oxide is used extensively in the chemical and food manufacturing industries, but relatively little is known of its ability to interact with genetic material. Studies were undertaken to investigate its ability to induce gene mutations and primary DNA damage in bacteria and chromosomal damage in mammalian cells. The induction of base-substitution mutations was demonstrated in spot tests with strains of Salmonella typhimurium and Escherichia coli at 700 micrograms/plate of propylene oxide; inclusion of a preparation of rat-liver microsomes and cofactors (S9 mix) was without significant effect on this response. A linear dose--response relationship was recorded in plate tests with S. typhimurium strains TA100 and TA1535 over the range 100--750 micrograms/plate. After addition to dividing lymphocytes in cultures established from human peripheral blood, propylene oxide caused dose-related chromosomal damage, detected at 1.85 and 9.25 micrograms/ml. Oral administration of propylene oxide at 2 x 100, 2 x 250 or 2 x 500 mg/kg to male mice produced no detectable increases in the incidence of micronucleated, polychromatic erythrocytes in bone marrow. A male mouse dominant lethal test employing oral doses of 50 or 250 mg/kg/day for 14 days gave no evidence of mutagenic action on sperm. Intraperitoneal injections of propylene oxide at 2 x 300 mg/kg induced increased numbers of micronucleated erythrocytes in mice, but lower doses given by this route had no such effect. Possible reasons for the contrasting findings in vitro and in vivo are discussed.
