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Cytotoxicity of benzene, toluene, ethylbenzene and xylenes (BTEX) to human lung cells was explored using three different exposure methods: Method 1 – in normal 96-well plates using DMSO as a carrier vehicle, we exposed (a) human lung carcinoma A549 cells, (b) A549 cells over-expressed with cytochrome P450 2E1 cells, and (c) normal lung fibroblast LL-24 cells to benzene, toluene, ethylbenzene and xylene individually and in a mixture which models car exhaust gases for between 1–88 h. We found that the order of the BTEX potency is benzene < toluene < ethylbenzene = m- xylene with acute BTEX toxicity to A549 ≈ LL-24 > CYP2E1 over-expressed A549 cells. A significant difference was found between inter-assay responses for all 24 h exposures ( P < 0.005) suggesting a poor assay repeatability. No sign of potency increase was found from 6 to 72 h exposures. Method 2 – Using sealed vials to expose A549 cells to benzene, toluene and ethylbenzene, we observed a twenty-fold increase in their cytotoxicity, but also with no time-course effect. Method 3 – Using air exposed hanging-drop cell culture, we were able to see both an increase of demonstration of toxicity and a time-course effect from 1 to 12 h exposure. We conclude that exposing cells in sealed and unsealed media using DMSO as a carrier vehicle was not suitable for BTEX exposure studies. Hanging-drop air exposure has more potential. It should be noted that if there are any changes in their exposure matrixes, its exposure mass distribution in cells could differ. [ABSTRACT FROM AUTHOR]

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]