The mutagenicity of ambient air particles from local traffic and distant sources during episodes with moderate photochemical air pollution.

The mutagenicity of ambient air particles in the Ames test was investigated during episodes with moderate photochemical air pollution. The particles were sampled on 11 occasions, each consisting of at least four sampling periods of 3 h during the day and one period of not more than 12 h during the following night. During the last 4 days, sampling was carried out at three locations, which allowed observation of the contribution from local sources (traffic in a town and on a motorway) to the mutagenicity. The local sources caused an increase in the indirect (S9-dependent) mutagenicity; the direct mutagenicity was not significantly affected. The particles sampled upwind dominated the mutagenicity in the area; in contrast to the locally emitted particles, their effects decreased in the presence of S9 fraction. This difference may indicate a qualitative change in the mutagenicity during the residence of the particles in the air. The direct mutagenicity depended very much on bacterial nitro reduction, as was demonstrated by using strain TA98NR; the effect in this strain was substantially increased in the presence of S9 fraction. This increase shows that, in the presence of S9 fraction, the effect in the TA98 strain is to a great extent the result of indirect mutagens and not only the result of partially deactivated direct mutagens. No typical quantitative or qualitative diurnal variation could be demonstrated. This is most probably due to the overwhelming influence of long-range transported mutagens which had already undergone maximum conversion during their residence in the air. Multivariate analysis of the effects and concentrations of gaseous pollutants indicated a rather strong link between mutagenicity and SO2, which confirms the important contribution of long-range transported mutagenicity.