Long-Term Trends of Particulate Mutagenic Activity in the Atmosphere of Sapporo. 1. Determination of Mutagenic Activity by the Conventional Tester Strains TA98 and TA100 during an 18-Year Period (1974−1992)

The Ames Salmonella mutagenicity bioassay using strains TA98 and TA100 of airborne particulates from Sapporo, Japan, was studied over an 18-year period starting in 1974. Measurements of mutagenicity and benzo[a]pyrene (BaP), as well as other polycyclic aromatic hydrocarbones (PAHs), were performed on organic extracts which were prepared from seasonal particulate composites of high-volume filter samples for each year. The average contribution of BaP to total indirect-acting mutagenic activity was 1.8% for strain TA98 and 3.5% for strain TA100. During the measurement period, BaP concentrations showed a large decline (to 25−20% their initial values), while indirect-acting mutagenic activity showed a moderate decline (to 66−50% their initial values) and direct-acting mutagenic activity did not show any clear increase or decrease. This clearly indicates that there was almost no change in the amount of exposure to mutagenic substances as a whole. A qualitative change was clearly seen in mutagens, being indicated by the continuous increase in the ratio of direct-acting to indirect-acting mutagenic activity (−S9/+S9 ratio) during the sampling period. Furthermore, these results suggest that, in the long term, BaP may not always be an appropriate indicator of the effect of air pollution on human health.