1,3-Butadiene is a known male mouse germ-cell mutagen, to which humans may either be occupationally or environmentally exposed. Prolonged exposure to moderate or high doses in male mice can cause dominant lethal mutations and one report has indicated that 10 week inhalation administration of low doses can result in the production of malformed foetuses. The present study had dual purposes: (a) to attempt to clarify the suspected ability of sub-chronic (6 h/day, 5 days/wk, 10 weeks) low-dose exposure to 1,3-butadiene to induce heritable mutations in mouse male germ cells: (b) investigation of the relationships between testicular DNA damage, testicular DNA repair and foetal outcome. Adult male mice were exposed to low or moderate doses of 1,3-butadiene by inhalation sub-chronically or for a single 6 h period and either used for mating (sub-chronic exposure only) or for studies of DNA damage and repair. Litter size, dominant lethality and numbers of abnormal foetuses were determined the day preceding the normal day of parturition. Testicular DNA damage and repair were assessed by the Comet assay (for DNA damage) and the unscheduled DNA synthesis assay (for DNA repair). 1,3-Butadiene caused a statistically significant increase in dominant lethality at 125 ppm but not 12.5 ppm. No significant increase in DNA repair was found with either dose level or exposure period while only 6 h exposure to 125 ppm caused a small but significant increase in DNA damage as detected by the Comet assay. These effects demonstrate the reproductive genotoxicity of (125 ppm) 1,3-butadiene but do not confirm its ability to cause abnormalities in the offspring via the sperm. It is suggested that the relationship between 1,3-butadiene-induced DNA damage, DNA repair and heritable defects in the offspring may depend on the pattern of metabolites produced.

1,3-Butadiene is produced in large quantities for use in the manufacture of synthetic rubber. It is also an environmental pollutant. There is concern about exposure to 1,3-butadiene as it has been shown to produce tumours in rats, mice and an increased risk of leukaemia in humans. It has also been shown to produce germ cell effects in mice. Differences in responses to 1,3-butadiene have been reported in rats and mice, possibly due to different metabolic capabilities. The present study thus investigated somatic and germ cell effects of 1,3-butadiene in mice and its metabolites in both rats and mice to help determine species differences using different endpoints for genotoxic effects. These included DNA strand breakage as measured in the single cell gel electrophoresis (Comet assay) in bone marrow and testicular cells, and micronuclei in bone marrow cells using both the acridine orange and Giemsa staining methods. Unscheduled DNA synthesis (UDS) was also measured in the testes of mice. CD-1 mice were exposed to 1,3-butadiene by inhalation for 6 h/day for 4 weeks, and CD-1 mice and Sprague-Dawley rats to the metabolites after i.p. injection. 1,3-Butadiene did not affect liver, bone marrow and testicular cells in mice as measured in the Comet assay. After treatment with 1,2-epoxybutene in the Comet assay, there was a response in the testes in mice but not in rats and there was little or no effect in the bone marrow assay in mice but there was in rats. After treatment with 1,2,3,4-diepoxybutane in the Comet assay in mice, there was a response in the bone marrow cells but not in the testicular cells, and in rats there was also a response only in bone marrow cells. There was an increase in micronuclei in both rats and mice with both metabolites, but clastogenicity was stronger with 1,2,3,4-diepoxybutane, occurring at lower doses, than with 1,2-epoxybutene. In the UDS assay in the testes of mice, there was an increase in response with 1,2,3,4-diepoxybutane treatment but not with 1,2-epoxybutene. These studies would appear to confirm a species difference of CD-1 mice and Sprague-Dawley rats, where mice were sensitive at lower doses than rats.