Considerations of the chemical complexity of ETS with regard to inhalation studies

Any inhalation study that investigates environmental tobacco smoke, ETS, is considering a very complex entity. ETS contains numerous chemicals that are continuously changing both in their absolute concentration, in the ratio of concentration between one and another, and even in their particulate to vapour phase distribution. Moreover, when considering ETS in real-life situations, many of the chemical components of ETS will be present as a result of sources other than tobacco smoking. This paper emphasises that the chemical and physical nature of ETS must be considered in the design and interpretation of any inhalation study on ETS, and illustrates the difficulty in defining precisely what constitutes ETS in such studies.