Ozone acts alone and synergistically with ionizing radiation to induce in vitro neoplastic transformation

Ozone, a major chemical oxidant in the atmosphere, is an environmental air pollutant whose ability to act as a direct carcinogen is unclear Using in vitro transformation, a technique which permits the study of oncogenesis in the absence of host specific effects, we report for the first time that ozone (5 p.p.m. for 5 min) induces neoplastic transformation in vitro in both primary hamster embryo cells and mouse fibroblast cultures (C3H/10-1/2). Exposure of the hamster and mouse cells to ozone also results in enhanced levels of free radical-mediated lipid peroxidation products. We also report for the first time on the carcinogenic interaction between ozone and ionizing radiation. Exposure of the cells to 3 or 4 Gy of gamma-rays, 2 h prior to O3 treatment, results in markedly enhanced rates of transformation, statistically consistent with a synergistic interaction between the agents. The results demonstrate that O3 acts as a direct carcinogen and co-carcinogen on susceptible cells, therefore having important consequences for public health.