Evaluation of In Vivo Mutagenicity of Low-Dose Methylene Chloride in Mice

Methylene chloride, a widely used industrial solvent, has been shown to be mutagenic by in vitro tests. The aim of this study was to determine in vivo mutagenicity. Groups of 20 Swiss-Webster (S/W) male mice were injected subcutaneously three times/week with 5 ml/kg of 5% vol/vol or 10% vol/vol solution of methylene chloride in corn oil for 4 weeks, followed by 1 week of no treatment. Other groups of 20 S/W male mice were exposed to airflow of 10 L/min carrying 100, 150, or 200 ppm of methylene chloride daily for 2 hr/day, 5 days/week for 6 weeks. Each study contained appropriate negative controls. Mating was started 1 week later for the injection group and 2 days later for the inhalation group. Each male mouse was mated with a S/W virgin adult female. The mating was allowed to continue for 2 weeks. Presence of a vaginal plug was taken as a sign of successful mating and was designated as day 0 of gestation. On day 17, the females were killed, and the fetuses were removed and processed. Male mice were killed, and the testes were removed, preserved in 10% formalin, and processed. No significant difference in any of the mutagenicity parameters was found between control and treated groups. No microscopic lesions were found in testes of the treated males.