Occupational exposure limits and mixed exposures

摘要

In general, occupational exposure limits (OELs) are set for single chemicals and for more or less defined complex chemical mixtures such as, for instance, wood dust and welding fumes. To properly assess the potential health risks of chemical mixtures, it is essential to understand the basic concepts similar joint action, dissimilar joint action (with positive or negative correlation of susceptibility) and interaction of combinations of chemicals. It is equally important to distinguish between simple, defined mixtures at the one hand, and complex mixtures at the other hand. In some countries, it has been recognised that in occupational standard setting consideration should be given to combined effects of simple, defined mixtures of two or more chemicals, using the appropriate formulas for assessing whether or not exposure to such mixtures at a given workplace is of health concern. Recently, a scheme has been developed for the safety evaluation of complex mixtures. Two conspicuous elements of this scheme are the dichotomy of complex mixtures into mixtures that are virtually unavailable and mixtures that are readily available for testing in their entirety, and the identification of the n (say, ten) most risky chemicals or most risky classes of chemicals in the mixture. A workplace atmosphere is an excellent example of a complex mixture virtually unavailable for testing in its entirety. Once the (limited number of) most risky chemicals or classes of chemicals have been identified, a safety evaluation of the mixture of these selected chemicals (or pseudo chemicals each of which represents an identified class of chemicals) can be performed, using procedures suitable for hazard identification and risk assessment of simple, defined mixtures. In brief, the safety evaluation of a (complex) workplace atmosphere can be tackled by evaluating the safety of the defined mixture of its major (most risky) constituents.