Occupational exposure limits for chemicals in the European Union.

Accepted 1 August 1996 Exposure limits for dangerous substances in working environments have played a major part in the control of occupational disease. Exposure limits are quantitative health standards expressed as mean concentrations over a given period which an environmental pollutant must not exceed if the exposed workers' health is not to be affected. This is true provided the term limit is not accompanied by adjectives such as acceptable or tolerable, which imply the general social acceptability of a particular risk or general biological tolerance of an exposure. It is obvious that acceptable cannot be applied on the basis of a decision taken by scientists alone; it implies evaluation both of the health effect and any other socioeconomic or political factor implied in a decision of this nature. The term tolerable makes no biological sense in that each subject tends to respond to an exogenous nuisance in a personal way, as a function of numerous individual factors. Thus, a certain level of exposure may well be tolerated (the internal environment remains in equilibrium) by one subject and not by another. For these reasons the current scientific trend is to exclude these two adjectives in the context of exposure limits; in 1977 the International Labour Organisation (ILO) defined an exposure limit as: ". .. the concentration in air of a harmful substance which, if the standards are respected, does not generally have harmful effects-including long-term effects on posterity-on the health of workers exposed for 8 to 10 hours a day, 40 hours a week; this exposure is considered acceptable by the competent authority which determines the limits, but it is possible that it may not completely guarantee the protection of the health of all the workers; accordingly, the exposure limit does not constitute an absolute dividing line between harmless and harmful concentrations, but is intended solely as a guide to prevention". In fact, verification that a specific chemical or physical agent does not exceed the exposure limits laid down for working environments (a fundamental and often decisive aspect in the prevention of occupational diseases) is today only one factor in assessing good practice in industrial hygiene, and does not signify biological compatibility for all exposed people. Thus when the results of environmental monitoring have to be compared with reference values, it is essential also to take account of other factors which influence exposure and of different biological conditions if we are not to lose sight of the ultimate objective of prevention.