IN VIVO AND IN VITRO STUDIES

Laboratory studies can contribute to a better understanding of the factors and mechanisms involved in the induction of disease by environmental agents. There have been numerous bioassays conducted on MS. In examining the effects of MS, many research workers have used condensates of the smoke painted on the shaved skin of mice. This contrasts with the human exposure that is mainly in the respiratory tract. Nonetheless, these skin-painting studies have been useful in examining the carcinogenicity of different tobacco constituents and thus advancing knowledge of the actions of MS on a gross exposure level. Similar work with skin painting has not been done with ETS and would be of value for assessing the differential toxicity of ETS and MS.

In constrast to MS exposure, ETS exposure involves proportionately more exposure to gas phase than to particulate phase constituents. There have not, however, been studies of the effects of exposure to aged ETS. The relative in vivo toxicity of MS, SS, and ETS needs to be assessed.

Some studies have attempted to evaluate the gas phase of MS, SS, and ETS in short-term, in vitro assays. A solution of the gas phase of MS has been shown to induce dose-dependent increases in sister-chromatid exchanges in cultured human lymphocytes. Mutagenic activity has been found in the particulate matter of SS and in condensates of ETS. However, the work done to date is too sparse to permit any estimates of the mutagenicity of ETS per se, even though most of ETS consists of SS. Further in vitro assays of ETS are needed.

HEALTH EFFECTS

This report reviews both chronic and acute health effects associated with ETS exposure in nonsmokers. Most epidemiologic studies of chronic health effects have been conducted on persons who have had long-term exposures to ETS from household members. The studies do not directly address chronic health effects in individuals who are exposed at work or have occasional exposures in the home or elsewhere.

Because the physicochemical nature of ETS, MS, and SS differ, the extrapolation of health effects from studies of MS or of



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