FIGURE 10.19 Mean (and standard deviations) of the mutagenicities of ambient particles (rev m~3; TA98 +S9, TA98 — S9, and TA98NR) sampled for 3-h periods winter and summer at eight streets with different widths and traffic volumes in Padova, Italy, June 1990-February 1991.The decrease on strain TA98NR indicates the presence of nitroarenes (adapted from Nardini and Clonfero, 1992).

highest levels of direct-acting mutagenicity in Barcelona, Spain, were in the fall and spring, whereas the promutagenicity was highest in the summer.

Of course, short-term meteorological variables such as atmospheric stability, height and strength of inversion layers (e.g., strong wintertime, low-radiation inversions), wind speeds, ambient temperature, and precipitation can have major impacts on gas- and particle-phase ambient mutagenicity levels. In terms of air pollution parameters, lead in fine ambient particles sampled from major urban airsheds correlates strongly with mutagenicity and motor vehicle traffic. A number of investigators have also explored possible correlations of ambient levels of PAHs and PACs as well as 03, S02, NOx, and VOCs in a number of locations [e.g., Scandinavian cities (M0ller et al., 1982); downtown Los Angeles and two downwind sites (Pitts et al., 1982b); Detroit, Michigan (Wolff et al., 1986); four San Francisco Bay Area cities (Kado et al., 1986); Wageningen (rural) and Terschelling (background), The Netherlands (van Houdt et al., 1987); two cities and a rural area in Finland (Tuominen et al., 1988); seven sites throughout California (Atkinson et al., f 988a); Athens, Greece (Viras et al., 1990); 17 Italian towns (Barale et al., 1994); Copenhagen, Denmark (Nielsen, 1996; Nielsen et al., 1999a, 1999b)].

2. Sources, Ambient Levels, Transport, and Transformation: Some Case Studies a. Bacterial Mutagenicity

Let us now consider some case studies of PAHs and PACs in ambient air. A number of studies of bacterial mutagenicity of fine ambient aerosols (primary and secondary) have been conducted using different tests for genotoxicity, particularly the Ames Salmonella ty-phimurium reversion bacterial assay and the Salmonella TM677 forward mutation bacterial assay. Human cell assays are discussed in the following section.

Possible health effects on the general public of mutagenic/carcinogenic PAHs and PACs in polluted ambient air are generally viewed as being related to long-term exposures to these agents. In an important contribution to the area, Matsumoto and co-workers (1998) reported the results from an 18-year study (1974-1992) in Sapporo, Japan, of the impacts of seasons and sources on the mutagenicities of seasonal composites of ambient particulate matter and concurrent concentrations of BaP (and eight other PAHs) and its gaseous copollutants NOz and S02. Sapporo (population 1.7 million in 1992) has a great deal of commercial, but relatively little industrial, activity. Outdoor temperatures ranged from —fO°C in the winter to over 30°C in the summer. The two major sources of air pollution were combustion of fossil fuels for heating homes and offices (mainly coal) and exhaust gases and particles from gasoline- and diesel-fueled motor vehicles. The composites were assayed on strain TA98 (and

TA100; see article) without S9 mix (-S9, direct activity) and with added S9 (+ S9, indirect activity, promutagens) using a "preincubation procedure" (Yahagi et al., 1977) of the Ames Salmonella typhimurium reversion assay (Ames et al., f 975; Maron and Ames, f 983).

As seen in Figs. 10.20a and 10.20b with strain TA98, both the direct (-S9) and indirect ( + S9) activities of the ambient particles showed pronounced seasonal variations, being highest in winter and lowest in summer. Furthermore, over the 18-year period, indirect activities for each season (Fig. 10.20b), and for the corresponding annual averages (not shown), declined to ~ 60-50% of their initial values. However, the direct activities of the seasonal and annual aerosol samples did not change significantly. This is reflected in the 3-year moving-average ratios of direct to indirect activity ( —S9/+S9), which rose almost linearly from ~0.6 in 1976 to ~1.2 in 1990. Concurrently, the concentrations of BaP, Fig. 10.20c, showed matching seasonal influences, but the composites and annual averages dropped dramatically, e.g., from ~4.8 ng m~3 in 1975-f976 to -0.7 ng m"3 in 1989-1991. Similar results were found for the sums of the eight other PAHs.

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