Mutagenicity of diesel exhaust particle extracts: influence of car type

Mutagenicity of extracts of particles collected from the exhaust of six different European and American diesel cars was evaluated in Salmonella strains TA 1535, TA 100, TA 1537, TA 1538 and TA 98. The extracts demonstrated direct, dose-related mutagenicity in all strains except TA 1535, with the potencies varying from 6-17 revertants/micrograms in TA 100, the most sensitive strain. Addition of Aroclor 1254 induced rat liver homogenate fractions decreased the direct response in TA 100 and increased the response in four of the six extracts in TA 98. Differences in the extractable organic fraction of the particles and the particulate emission rates for the six cars had a greater influence on the amount of mutagenicity emitted (revertants per mile) than the actual mutagenic potency of the organics. The ranking of the cars by revertants/mile was different than ranking by revertants/micrograms extractable organics. The response of two of the six extracts in a nitroreductase deficient strain of Salmonella (TA 100 FR1) were significantly lower than the response in TA 100, suggesting that reduction of nitroaromatics by bacterial enzymes may be influential in the direct response. Results of testing triplicate samples collected in three different cars demonstrated good repeatability in sampling and bioassay procedures.