Indoor air, a variableoomplex mixture: Strategy for selection of (combinations of) chemicals with high health hazard potential

A system for the selection of indoor air chemicals with high health hazard potential and a strategy for further toxicological research of (combinations of) selected chemicals are considered essential to arrive at healthy indoor environments. A scoring system for priority setting similar to but less extensive than the WMS‐scoring system developed by Kfinemann and Visser [1] for “existing”; chemicals is suggested for indoor air compounds. A classification system for selecting hazardous (combinations of) chemicals occurring in a complex mixture of (indoor air) chemicals should be based on similar or identical biotransformation pathways (kinetic phase), similar or identical receptors for the toxicants (dynamic phase), and structural similarities pointing to hazardous interactions in either the kinetic or dynamic phase. Examples are given to explain and underline the classification system, which in essence is based on both knowledge and expert opinion. Finally, in order to narrow down the indoor environments of real health concern in a rather opportunistic way, toxicity studies are suggested of a combination of the (10) major constituents of a given indoor air mixture using exposure concentrations of a factor 3 to 10 higher than those occurring in the mixture concerned. Four‐week inhalation studies in rats could serve for testing general toxicity, and a mammalian and a non‐mammalian test could be used for testing genotoxic potential. A number of indoor air mixtures is mentioned that might be candidates for this type of testing.