Ames test: mutagenic activity of airborne particles collected on airconditioner filters during the fire at a Sandoz storehouse in Schweizerhalle on November 1, 1986. 
The mutagenic activity of methanol extracts from airconditioner filters was tested using the standard plate-incorporation procedure for the Ames test and the strains Salmonella typhimurium TA97, TA98 and TA100 as test organisms.  In a first set of experiments filters from 4 buildings were investigated.  For each building the mutagenic activity of a filter which was in use during the fire (fire-exposed) was compared with the mutagenic activity of a filter which was exposed for a similar time span to normal urban air (non-exposed).  While for 1 pair of filters the non-exposed extract was more mutagenic than the fire-exposed material, the opposite was found for 2 other filter pairs, and in 1 case there was hardly any difference in the mutagenic activities of the fire-exposed and the non-exposed filter extracts.  Overall differences by factors up to 100 were observed in the mutants/m3 air values of the most and the least mutagenic filter extracts.  The second group of experiments was performed to investigate the variations in mutagenic activity of filter extracts occurring due to changes in the weather conditions.  Airborne particles were collected for 3 consecutive periods of 10-11 days at the 2 buildings where the extracts of the fire-exposed filters had been found to be more mutagenic than the corresponding control materials.  The differences between the strongest and the weakest mutagenic filter extracts of these series were similar to the differences observed previously between the fire-exposed filters and the non-exposed filter materials.  The highest mutagenic activities found in the second group of experiments was similar, at both sites, to the mutagenic activities measured in the fire-exposed extracts from these 2 buildings.  Since the differences in the mutagenic activities of filters exposed to urban air during the different meteorological conditions were similar to the differences observed between fire-exposed and non-exposed materials, it is not possible to state whether the fire led to the distribution of mutagenic chemicals, although it is theoretically possible.  However, based on the observation that the maximal mutagenic activities of the fire-exposed and the non-exposed extracts were similar, the present study allows the conclusion that the mutagenic burden for the population of the area of Basel was not significantly increased by the fire in Schweizerhalle on November 1, 1986.