Temporal Patterns of Bacterial Mutagenicity on Ambient Aerosols in Southeastern Michigan

Abstract

The temporal and diurnal patterns of particulate-bound mutagens in the atmosphere were examined for a twomonth period in the summer of 1985. Daily PM-10 samples were collected at 0900-2100 and 2100-0900 along with other air quality measurements from a suburban site in southeast Michigan. The paired samples were collected daily in order to examine day /night variations. Each particulate sample was extracted and separated into 16 different fractions based on polarity before Ames tests were conducted on each fraction to determine the bacterial mutagenic activities in TA98 and TA98/DNP6. Other air quality parameters measured included fine particle mass (diameter less than 2.5 pm), sulfate, sulfur dioxide, nitrogen oxides, nitric acid, ozone, carbonaceous aerosols, some trace elements, and pertinent meteorological data. The results show that the four most polar fractions accounted for at least 70% of the mutagenicity.The highest levels of mutagenic activity occurred during two different types of meteorological conditions. The first type was associated with the long-range transport of coal combustion emissions from south of Michigan's border, whereas the second type was associated with stagnant atmospheric conditions and an accumulation of locally-emitted combustion products. Although nighttime mutagenic activity was slightly higher than daytime activity on some days, rigorous statistical tests indicated that the differences were not significant at the 95% confidence level. However, the mutagenicity profiles of individual paired day /night samples suggest that, under appropriate meteorological conditions, the polar mutagenic species can be formed via nighttime chemical reactions and/or degraded to less mutagenic form via photochemical reactions during the day.