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A recently developed hanging dropair exposure system for toxicitystudies of volatile chemicals was applied to evaluate the cell viabilityof lung carcinoma A549 cells after 1 and 24 h of exposure to benzene,toluene, ethylbenzene, and xylenes (BTEX) as individual compoundsand as mixtures of four or six components. The cellular chemical concentrationscausing 50% reduction of cell viability (EC50) were calculatedusing a mass balance model and came to 17, 12, 11, 9, 4, and 4 mmol/kgcell dry weight for benzene, toluene, ethylbenzene, m-xylene, o-xylene, and p-xylene,respectively, after 1 h of exposure. The EC50decreasedby a factor of 4 after 24 h of exposure. All mixture effects werebest described by the mixture toxicity model of concentration addition,which is valid for chemicals with the same mode of action. Good agreementwith the model predictions was found for benzene, toluene, ethylbenzene,and m-xylene at four different representative fixedconcentration ratios after 1 h of exposure, but lower agreement withmixture prediction was obtained after 24 h of exposure. A recreatedcar exhaust mixture, which involved the contribution of the more toxic p-xylene and o-xylene, yielded an acceptable,but lower quality, prediction as well. [ABSTRACT FROM AUTHOR]