In vitro relative toxicity screening of combined particulate and semivolatile organic fractions of gasoline and diesel engine emissions.

Engine technology modifications designed to reduce engine emissions are likely to alter the physicochemical characteristics of the emissions. These changes may alter the biological effects of the emissions, but these effects cannot currently be predicted from the physical and chemical properties. Rapid in vitro toxicity screening techniques to compare the biological effects of emission samples would be useful as preliminary guides to assess the relative health impact of modified technology. Here, we demonstrate that selected responses of cultured human lung epithelial cells and rat alveolar macrophages can discriminate among combined particulate matter (PM) and semivolatile organic compound (SVOO fractions of emissions collected from normal- and high-emitter, in-use gasoline and diesel vehicles. Macrophages were more susceptible to cytotoxicity than epithelial cells. Samples from gasoline vehicles (except a vehicle that produced visible white smoke) generally caused greater effects than the diesel engine samples. However, low concentrations of diesel emission samples were more potent stimulators of peroxide production than gasoline emission samples. The same rank order of potency applied to suppression of this response at high concentrations. A diesel PM fraction was much less toxic to both types of cells than the combined PM +SVOC fractions, consistent with a role for the SVOC fraction in cytotoxicity. However, the rank order of potency from the in vitro assays in general did not correspond with the previous rankings from in vivo comparisons of the same samples. Thus, while the in vitro assays may provide mechanistic information, revealing cell type-specific responses, they did not accurately reflect in vivo comparative toxicity in their current form.