Styrene monomer does not induce unscheduled DNA synthesis in the mouse liver following inhalation exposure

Styrene monomer is a commercially important chemical used extensively in the production of plastics. It has been shown to induce lung tumours in the mouse via the inhalation route. Styrene monomer has shown a low reactivity with DNA and also a lack of genotoxic response in the mouse lung in vivo. Together with the fact that the mouse lung tumours were late occurring and mostly benign, which suggest a promotional effect rather than initiation, these factors have led to a suggestion that the tumours may not be of genotoxic origin. The studies examining the genotoxicity of styrene monomer in vivo have to date been predominantly cytogenetic assessments, although low levels of DNA adducts have been reported in the mouse liver and lung. In order to extend this evaluation, a mouse liver unscheduled DNA synthesis study has been performed to assess the ability of styrene monomer to induce DNA damage/repair. The negative response observed in this assay is consistent with the theory that tumours observed in mouse oncogenicity studies are non-genotoxic in origin.