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Diurnal variations in the mutagenicity of airborne particulate organic matter in California's south coast air basin
Mutation Research, 104 (1982)35-41
35
Elsevier BiomedicalPress
Diurnal variations in the mutagenicity of airborne particulate organic matter in California's south coast air basin J a m e s N. Pitts J r . * , William H a r g e r , David M. L o k e n s g a r d , Dennis R. Fitz, G i n a M. Scorziell a n d Victoria M e j i a Statewide Air Pollution Research Center, University of California, Riverside, CA 92521 (U.S.A.)
(Accepted 11 November 1981) Extracts of airborne particulate organic matter (POM) collected in urban areas throughout the world have been known for several decades to be carcinogenic in experimental animals (Leiter et al., 1942; National Academy of Sciences, 1972, 1981; Santodonato et al., 1979). Moreover, they have recently been shown to display direct mutagenicity (not requiring $9 activation) with frameshift detecting strains TA1538 and TA98 in the Ames Salmonella assay (Pitts et al., 1977a, b; Talcott and Wei, 1977; Tokiwa et al., 1977; Alfheim and MOiler, 1981; Chrisp and Fisher, 1980). Finally, this activity predominates in respirable sub-micron particles (Pitts et al., 1978a, b; Pitts, 1979; L0froth, 1981; Talcott and Harger, 1980). Thus, it is important to determine the sources of this activity, as well as the ambient levels to which urban and suburban populations may be exposed. Most studies to date have determined the mutagenicity for sampling periods of 24 h or more. Unfortunately, a collection period of this length averages any mutagenicity peaks which might have occurred. Furthermore, such data may not have sufficient time-resolution to permit assessments of the nature of the mutagen sources (i.e., mobile vs. stationary emissions or primary vs. secondary pollutants). Therefore, investigations were conducted on diurnal variations in the mutagenicity of ambient particles collected simultaneously near downtown Los Angeles (DTLA) and at two downwind sites. These collections were made every 3 h for a 24-h period, on two late summer days in 1980 and an early spring day in 1981. Major results and conclusions follow.
Materials and methods
Ambient particles were collected 30 m above ground level on the campus of California State University at Los Angeles, just east of D T L A and near the inter*Author to whom correspondenceshould be addressed. 0165-7992/82/0000-0000/$02.75
© Elsevier Biomedical Press
36 section of two major freeways. Simultaneously, collections were made at two predominantly downwind sites in California's South Coast Air Basin (SCAB): 15 m above ground at Harvey Mudd College in Claremont ( - 50 km east of DTLA), and 5 m above ground at the University of California, Riverside ( - 100 km east of DTLA). Sampling was conducted from 0 to 2400 h on September 12 and 17, 1980 and from 1200 to 1200 h on March 11-12, 1981. At each sampling site, 5 standard hi-vol samplers (Sierra Instruments Model 305-2000) operating at 40 SCFM ran 3 h between filter changes; a sixth sampler at each site operated for the entire 24 h without filter replacement. Pre-cleaned PaUflex T60A20 Teflon-coated filters were employed and were weighed before and after collection to determine particulate loading. Air quality data for CO, 03, NO, NO2, PAN and ~scat were measured at the sites or obtained from the nearest South Coast Air Quality Management District (SCAQMD) station. To prevent photochemical degradation of the sample, dark room conditions were employed during the sample preparation and bioassay. Each particulate sample (one 24-h filter or three 3-h filters) was extracted twice by ultrasonication with 200 ml of a 1 : 1 : 1 mixture of methanol, toluene and dichloromethane, and filtered (0.5-#m pore size). The extracts were reduced in volume under vacuum, evaporated to constant (_+ 1070) weight under a stream of dry nitrogen at 35°C, and taken up in DMSO for the Ames assay. One set of unextracted filters from the DTLA September 17, 1980 collection was analyzed for lead by X-ray fluorescence. All samples were tested on Ames Salmonella strain TA98 (Ames et al., 1975; Belser et al., 1981) with and without 2°7o $9 (v/v, 0.70 mg protein per plate) at 10, 20, 40, 60, 80, 100, 200, 400 and 600 #g of sample per plate. 3 replicates were tested at each concentration and the mean of the 3 responses was used to determine the dose-response curve. The DTLA September 12, 1980 sample set was also tested using nitroreductase-deficient strain TA98NR (Rosenkranz and Speck, 1975, 1976; Rosenkranz and Poirier, 1979). Stationary phase (16-h) cultures were used. Positive controls were: 2-nitrofluorene, 420 rev/~g TA98 ( - $ 9 ) ; 59 rev/#g TA98NR ( - $9), and benzo[a]pyrene, 410 rev/#g TA98 (+ 207o $9). Results are presented as mutagen densities (rev/m 3 of sampled air). The meteorological conditions in the SCAB on September 17, 1980 were typical for mid-September; stable in the early morning hours with low winds and moderate inversions. In the afternoon, the inversion heights lifted and the westerly winds increased substantially at each site. Ozone maxima were 0.078 ppm (1100-1200 h), 0.29 ppm (1400-1500 h) and 0.26 ppm (1500-1600 h) at DTLA, Claremont and Riverside, respectively; the peaks and their times of occurrence were typical of moderate photochemical air pollution in this air basin. Results and discussion
At DTLA and the two downwind sites, and for two seasons (late summer and
37
early spring), the relation between mutagen densities and hour of the day was remarkably similar even though absolute values differed; the highest peak values in each case were recorded at DTLA. For example, on September 17, 1980 the 0600-0900 h peak densities of activatable mutagens (+ $9) were 170, 100 and 96 rev/m 3, on March 12, 1981, they were 49, 28 and 19 rev/m 3, at DTLA, Claremont and Riverside, respectively. The 3-h mutagen densities (tested with and without $9) determined on September 17, 1980 at DTLA, and concurrently - 100 km east at Riverside, are plotted in Fig. la as a function of the time of day; corresponding ambient concentrations of CO, NO2 and particulate lead at DTLA are shown in Fig. 1b. At these widely separated sites, the mutagen densities displayed pronounced maxima during the morning (0600-0900 h) periods of high traffic densities and smaller, but distinct, local maxima during the evening 'rush' hours. During the midday (1200-1500 h), there were definite minima in the 24-h profiles followed by gradual increases toward nighttime. The degree of $9 enhancement of the samples' mutagenicity was low at most times of the day, but increased substantially during the rush hours (see Fig. la and Table 1). 2 0 0 --
LOS A N G E L E S
•
+ $9
Zx - $ 9 15C
e..
IOC
~-~0
Z
E
50
.
~ I
5-
40
41 z 3o ~20
I0
I
L
I "t'"
l
I
I
AMBIENT CONCENTRATIONS OF CO-POLLUTANTS
9 8 7
C
63
Pb
i43
3
6
9
13
12
15
18
21
24
PST 9 / 1 7 / 8 0
Fig. 1 (a). Diurnal variations in mutagen densities of ambient POM collected in Los Angeles and Riverside and (b) ambient concentrations of co-pollutants, at Los Angeles collection site on September 17, 1980.
38
TABLE 1 COMPARISON OF MORNING 'RUSH HOURS' (0600-0900 h) MUTAGEN DENSITIESa WITH 'CALCULATED' AND OBSERVED 24-h MUTAGEN DENSITIES FOR SEPTEMBER 17, 1980
DTLA Riverside
0600-0900-h values
24-h values
Maximaa
Average of 3-h samplesb
24-h continuous samplesc $9
- $9
+ $9
- $9
+ $9
- $9
+
100 73
170 96
67 30
100 35
63 35
71 38
Net rev/m3 of ambient air sampled. bThis 24-h average was calculated from the sum of the experimental 3-h values. cExperimental values for the 24-h continuous samples. a
As seen in Table 1, the peak values of both direct and activatable mutagenicity were much higher (nearly double) than those found for the corresponding P O M sample taken for a continuous 24-h period. This is relevant to health risk assessment calculations, Thus, for example, one should consider peak doses as well as 24-h or longer average doses in considering the mutagenic impact of ambient particulate matter. In general, there was little evidence for an effect of filter artifacts on sample mutagenicity [e.g., polycyclic aromatic hydrocarbons (PAH), in the P O M reacting with ambient NO2 or 03 (Pitts et al., 1978a, b, c, 1980; Lee et al., 1980)]. At all 3 sites, and on all 3 sampling days, the average 24-h mutagen densities calculated from the 3-h samples were in reasonable agreement with those determined directly f r o m the P O M samples collected continuously for the same 24-h period. This suggests that artifact formation from possible chemical transformations occurring on the sampling filters is not large during the sampling time period from 3 to 24 h. However, if such reactions on the filter occurred on a time scale much faster than 3 h or longer than 24 h, they would not be observed in this experiment. Also, possible reactions in the atmosphere cannot be ruled out. Indeed, the fact that the ratio of activatable to direct activity, while significant during the morning (0600-0900 h), decreases in the afternoon and evening (Fig. la) suggests that some of the activatable mutagens (e.g., benzo[a]pyrene) may be photo-oxidized or may react with gaseous co-pollutants such as 03, NO2 and peroxyacetyl nitrate (Pitts et al., 1978c). The diurnal variations of mutagen density in D T L A are similar to those of several co-pollutants (see Fig. 1). O f particular interest are CO and lead, because in the SCAB these are often used as 'tracers' to differentiate automobile emissions from stationary sources. Indeed, the linear correlation coefficients between mutagen density and air quality data show significant positive correlations (confidence level
39 > 95%) for CO, NO, NO2 and total NOx as well as for lead. Additionally, a less significant negative correlation was seen between mutagenicity and ambient 03 levels. All of this evidence suggests that mobile source primary emissions are important contributors to the mutagenicity, both direct and activatable, of ambient POM in the SCAB. For each of the eight 3-h samples, as well as for the 24-h sample in DTLA collected on September 12, 1980, the mutagenic activity toward TA98NR was about 50-60% lower than toward TA98, and showed similar diurnal variations. This evidence for the presence of nitroarenes (Rosenkranz and Poirier, 1979; Mermelstein et al., 1981; Rosenkranz et al., 1981) is similar to that reported previously in POM collected from urban air in Wayne County, Michigan (Wang et al., 1980), in Stockholm, Sweden (L6froth, 1981) and in diesel POM (Pitts et al., 1982). In summary, these 3-h time-resolved mutagenicity studies of ambient airborne particles at 3 sites across the SCAB and at 2 different times of the year have yielded the following observations for this region: (1) Ambient particulate mutagenicity displays to a significant degree the characteristics of a primary pollutant, responding both to vehicular emission rates and to atmospheric mixing ratios as shown by its high correlation with CO, NOx and lead levels. (2) Short-term peak mutagen densities can be much higher than the 24-h average values commonly reported in the literature. (3) Nitroarenes may contribute substantially to the mutagenicity of ambient particulate organic matter in the SCAB. (4) The good agreement between analyses of the 24-h collection and the average of the 3-h samples suggests that chemical transformations of mutagenic material collected on the filters are either very fast or very slow relative to the time scale used in these experiments. (5) The increased contribution of promutagenic activity to the mutagenicity of the particles during periods of high emission rates, and its subsequent return to lower levels relative to the direct activity, suggest that some promutagenic materials present in freshly emitted POM are subject to rapid destruction in the atmosphere.
Acknowledgments We thank Professors Bruce N. Ames for the Salmonella strain TA98 and Herbert S. Rosenkranz for Salmonella strain TA98NR, as well as Dr. Robert Giauque at the Lawrence Berkeley Laboratory for the lead analyses. Air quality data were graciously provided by the South Coast Air Quality Management District. We thank Mrs. Minn Poe of our technical staff for the statistical analyses of the data, as well as Ms. Margaret C. Dodd, Ms. Susan E. Brown, Mr. William R. Hoffman and Mrs.
40 D i a n e G i l e s f o r t h e i r v a l u a b l e t e c h n i c a l a s s i s t a n c e . T h i s w o r k was s u p p o r t e d by t h e C a l i f o r n i a A i r R e s o u r c e s B o a r d , D r . J o h n R. H o l m e s , C h i e f , R e s e a r c h D i v i s i o n , a n d D r . J a c k K. S u d e r , P r o j e c t M o n i t o r , t h r o u g h A g r e e m e n t A 9 - 0 7 7 - 3 1 .
References Alfheim, I., and M. Mealier (1981) Mutagenicity of airborne particulate matter in relation to traffic and meteorological conditions, in: M.D. Waters, S.S. Sandhu, J.L, Huisingh, L. Claxton and S. Nesnow (Eds.), Application of Short-Term Bioassays in the Analysis of Complex Environmental Mixtures 11, Environmental Science Research, Vol. 22, Plenum, New York, NY, pp. 85-89. Ames, B.N., J. McCann and E. Yamasaki (1975) Methods for detecting carcinogens and mutagens with the Salmonella/mammalian-microsome mutagenicity test, Mutation Res., 31,347-364. Belser Jr., W.L., S.D. Shaffer, R.D. Bliss, P.M. Hynds, L. Yamamoto, J.N. Pitts Jr. and J.A. Winer (1981) A standardized procedure for quantification of the Ames Samonella/mammalian-microsome mutagenicity test, Environ. Mutagen., 3, 123-139. Chrisp, C.E., and G.L. Fisher (1980) Mutagenicity of airborne particles, Mutation Res., 76, 143-164. Lee, F.S.-C., W.R. Pierson and J. Ezike (1980) The problem of PAH degradation during filter collection of airborne particulates - an evaluation of several commonly used filter media, in: Polynuclear Aromatic Hydrocarbons: Fourth International Symposium on Analysis, Chemistry and Biology, Battelle Press, Columbus, OH, pp. 543-563. Leiter, J., M.B. Shimkin and M.J. Shear (1942) Production of subcutaneous sarcomas in mice with tars extracted from atmospheric dusts, J. Natl. Cancer Inst., 3, 155-165. LOfroth, G. (1981) Comparison of the mutagenic activity in carbon particulate matter and in diesel and gasoline engine exhaust, in: M.D. Waters, S.S. Sandhu, J.L. Huisingh, L. Claxton and S. Nesnow (Eds.), Application of Short-Term Bioassays in the Analysis of Complex Environmental Mixtures, II, Environmental Science Research, Vol. 22, Plenum, New York, NY, pp. 319-336. Mermelstein, R., D.K. Kiriazides, M. Butler, E.C. McCoy and H.S. Rosenkranz (1981) The extraordinary mutagenicity of nitropyrenes in bacteria, Mutation Res., 89, 187-196. National Academy of Sciences (1972) Particulate polycyclic organic matter, National Academy Press, Washington, DC. National Academy of Sciences (1981) Health effects of exposure to diesel exhaust, National Academy Press, Washington, DC. Pitts Jr.~ J.N. (1979) Photochemical and biological implications of the atmospheric reactions of amines and benzo[a]pyrene, Phil. Trans. R. Soc. (Londonj A, 290, 551-576. Pitts Jr., J.N., D. Grosjean, T.M. Mischke, V.F. Simmon and D. Poole (1977a) Mutagenic activity of airborne particulate organic pollutants, presented at the 174th American Chemical Society Meeting, Chicago, IL, August 28-31, in: S.D. Lee (Ed.), Biological Effects of-'Environm~ental Pollutants, Ann Arbor Science Publishers, Ann Arbor, MI, c 1979, pp. 77-93. Pitts Jr., J.N., D. Grosjean, T.M. Mischke, V.F. Simmon and D. Poole (1977b) Mutagenic activity of airborne particulate organic pollutants, Toxicol. Lett., 1, 65-70. Pitts Jr., J.N., K.A. Van Cauwenberghe, D. Grosjean, J.P. Schmid, D.R. Fitz, W.L. Belser Jr., G.B. Knudson and P.M. Hynds (1978a) Chemical and biological aspects of organic particulates in real and simulated atmospheres, in: Proceedings, Carbonaceous Particles in the Atmosphere, March 20-22, University of California, Berkeley, Lawrence Berkeley Laboratory Publication LBL-9037, CONF7803101, UC-11.
41 Pitts Jr., J.N., K.A. Van Cauwenberghe, D. Grosjean, J.P. Schmid, D.R. Fitz, W.L. Belser Jr., G.B. Knudson and P.M. Hynds (1978b) Chemical and microbiological studies of mutagenic pollutants in real and simulated atmospheres, in: M.D. Waters, S. Nesnow, J.L. Huisingh, S.S. Sandhu and L. Claxton (Eds.), Application of Short-Term Bioassays in the Fractionation and Analysis of Complex Environmental Mutagens, Plenum, New York, NY, pp. 353-379. Pitts Jr., J.N., K.A. Van Cauwenberghe, D. Grosjean, J.P. Schmid, D.R. Fitz, W.L. Belser Jr., G.B. Knudson and P.M. Hynds (1978c) Atmospheric reactions of polycyclic aromatic hydrocarbons: facile formation of mutagenic nitro derivatives, Science, 202, 515-519. Pitts Jr., J.N., D.M. Lokensgard, P.S. Ripley, K.A. Van Cauwenberghe, L. Van Vaek, S. Shaffer, A.J. Thill and W.L. Belser Jr. (1980) 'Atmospheric' epoxidation of benzo[a]pyrene by ozone: formation of the metabolite benzo[a]pyrene-4,5-oxide, Science, 210, 1347-1349. Pitts Jr., J.N., D.M. Lokensgard, W. Harger, T.S. Fisher, V. Mejia, J.J. Schuler, G.M. Scorziell and Y.A. Katzenstein (1982) Mutagens in diesel exhaust particulate, identification and direct activities of 6-nitro-benzo[a]pyrene, 9-nitroanthracene, l-nitropyrene and 5H-phenanthro[4,5-bcd]pyran-5-one, Mutation Res., 103, 241 249. Rosenkranz, H.S., and W.T. Poirier (1979) Evaluation of the mutagenicity and DNA-modifying activity of carcinogens and noncarcinogens in microbial systems, J. Natl. Cancer Inst., 62, 873-891. Rosenkranz, H.S., and W.T. Speck (1975) Mutagenicity of metronidazole: activation by mammalian liver microsomes, Biochem. Biophys. Res. Commun., 66, 520-525. Roseukranz, H.S., and W.T. Speck (1976) Activation of nitrofurantoin to a nmtagen by rat liver nitroreductase, Biochem. Pharmacol., 25, 1555-1556. Rosenkranz, H.S., E.C. McCoy, R. Mermelstein and W.T. Speck (1981) A cautionary note on the use of nitroreductase-deficient strains of Salmonella typhimurium for the detection of nitroarenes as mutagens in complex mixtures including diesel exhausts, Mutation Res., 91, 102-105. Santodonato, J., P. Howard, D. Basu, S. Lande, J.K. Selkirk and P. Sheehe (1979) Health Assessment Document for Polycyclic Organic Matter (Preprint), U.S. Environmental Protection Agency, EPA-600/9-79-008, December 1979. Talcott, R., and W. Harger (1980) Airborne mutagens extracted from particles of respirable size, Mutation Res., 79, 177-180. Talcott, R., and E. Wei (1977) Airborne mutagens bioassayed in Sahnonella typhimurium, J. Natl. Cancer Inst., 58,449-451. Tokiwa, H., K. Morita, H. Takeyoshi, K. Takahashi and Y. Ohnishi (1977) Detection of mutagenic activity in particulate air pollutants, Mutation Res., 48, 237--248. Wang, C.Y., M.-S. Lee, C.M. King and P.O. Warner (1980) Evidence for nitroaromatics as directacting mutagens of airborne particulates, Chemosphere, 9.83-87.
35
Elsevier BiomedicalPress
Diurnal variations in the mutagenicity of airborne particulate organic matter in California's south coast air basin J a m e s N. Pitts J r . * , William H a r g e r , David M. L o k e n s g a r d , Dennis R. Fitz, G i n a M. Scorziell a n d Victoria M e j i a Statewide Air Pollution Research Center, University of California, Riverside, CA 92521 (U.S.A.)
(Accepted 11 November 1981) Extracts of airborne particulate organic matter (POM) collected in urban areas throughout the world have been known for several decades to be carcinogenic in experimental animals (Leiter et al., 1942; National Academy of Sciences, 1972, 1981; Santodonato et al., 1979). Moreover, they have recently been shown to display direct mutagenicity (not requiring $9 activation) with frameshift detecting strains TA1538 and TA98 in the Ames Salmonella assay (Pitts et al., 1977a, b; Talcott and Wei, 1977; Tokiwa et al., 1977; Alfheim and MOiler, 1981; Chrisp and Fisher, 1980). Finally, this activity predominates in respirable sub-micron particles (Pitts et al., 1978a, b; Pitts, 1979; L0froth, 1981; Talcott and Harger, 1980). Thus, it is important to determine the sources of this activity, as well as the ambient levels to which urban and suburban populations may be exposed. Most studies to date have determined the mutagenicity for sampling periods of 24 h or more. Unfortunately, a collection period of this length averages any mutagenicity peaks which might have occurred. Furthermore, such data may not have sufficient time-resolution to permit assessments of the nature of the mutagen sources (i.e., mobile vs. stationary emissions or primary vs. secondary pollutants). Therefore, investigations were conducted on diurnal variations in the mutagenicity of ambient particles collected simultaneously near downtown Los Angeles (DTLA) and at two downwind sites. These collections were made every 3 h for a 24-h period, on two late summer days in 1980 and an early spring day in 1981. Major results and conclusions follow.
Materials and methods
Ambient particles were collected 30 m above ground level on the campus of California State University at Los Angeles, just east of D T L A and near the inter*Author to whom correspondenceshould be addressed. 0165-7992/82/0000-0000/$02.75
© Elsevier Biomedical Press
36 section of two major freeways. Simultaneously, collections were made at two predominantly downwind sites in California's South Coast Air Basin (SCAB): 15 m above ground at Harvey Mudd College in Claremont ( - 50 km east of DTLA), and 5 m above ground at the University of California, Riverside ( - 100 km east of DTLA). Sampling was conducted from 0 to 2400 h on September 12 and 17, 1980 and from 1200 to 1200 h on March 11-12, 1981. At each sampling site, 5 standard hi-vol samplers (Sierra Instruments Model 305-2000) operating at 40 SCFM ran 3 h between filter changes; a sixth sampler at each site operated for the entire 24 h without filter replacement. Pre-cleaned PaUflex T60A20 Teflon-coated filters were employed and were weighed before and after collection to determine particulate loading. Air quality data for CO, 03, NO, NO2, PAN and ~scat were measured at the sites or obtained from the nearest South Coast Air Quality Management District (SCAQMD) station. To prevent photochemical degradation of the sample, dark room conditions were employed during the sample preparation and bioassay. Each particulate sample (one 24-h filter or three 3-h filters) was extracted twice by ultrasonication with 200 ml of a 1 : 1 : 1 mixture of methanol, toluene and dichloromethane, and filtered (0.5-#m pore size). The extracts were reduced in volume under vacuum, evaporated to constant (_+ 1070) weight under a stream of dry nitrogen at 35°C, and taken up in DMSO for the Ames assay. One set of unextracted filters from the DTLA September 17, 1980 collection was analyzed for lead by X-ray fluorescence. All samples were tested on Ames Salmonella strain TA98 (Ames et al., 1975; Belser et al., 1981) with and without 2°7o $9 (v/v, 0.70 mg protein per plate) at 10, 20, 40, 60, 80, 100, 200, 400 and 600 #g of sample per plate. 3 replicates were tested at each concentration and the mean of the 3 responses was used to determine the dose-response curve. The DTLA September 12, 1980 sample set was also tested using nitroreductase-deficient strain TA98NR (Rosenkranz and Speck, 1975, 1976; Rosenkranz and Poirier, 1979). Stationary phase (16-h) cultures were used. Positive controls were: 2-nitrofluorene, 420 rev/~g TA98 ( - $ 9 ) ; 59 rev/#g TA98NR ( - $9), and benzo[a]pyrene, 410 rev/#g TA98 (+ 207o $9). Results are presented as mutagen densities (rev/m 3 of sampled air). The meteorological conditions in the SCAB on September 17, 1980 were typical for mid-September; stable in the early morning hours with low winds and moderate inversions. In the afternoon, the inversion heights lifted and the westerly winds increased substantially at each site. Ozone maxima were 0.078 ppm (1100-1200 h), 0.29 ppm (1400-1500 h) and 0.26 ppm (1500-1600 h) at DTLA, Claremont and Riverside, respectively; the peaks and their times of occurrence were typical of moderate photochemical air pollution in this air basin. Results and discussion
At DTLA and the two downwind sites, and for two seasons (late summer and
37
early spring), the relation between mutagen densities and hour of the day was remarkably similar even though absolute values differed; the highest peak values in each case were recorded at DTLA. For example, on September 17, 1980 the 0600-0900 h peak densities of activatable mutagens (+ $9) were 170, 100 and 96 rev/m 3, on March 12, 1981, they were 49, 28 and 19 rev/m 3, at DTLA, Claremont and Riverside, respectively. The 3-h mutagen densities (tested with and without $9) determined on September 17, 1980 at DTLA, and concurrently - 100 km east at Riverside, are plotted in Fig. la as a function of the time of day; corresponding ambient concentrations of CO, NO2 and particulate lead at DTLA are shown in Fig. 1b. At these widely separated sites, the mutagen densities displayed pronounced maxima during the morning (0600-0900 h) periods of high traffic densities and smaller, but distinct, local maxima during the evening 'rush' hours. During the midday (1200-1500 h), there were definite minima in the 24-h profiles followed by gradual increases toward nighttime. The degree of $9 enhancement of the samples' mutagenicity was low at most times of the day, but increased substantially during the rush hours (see Fig. la and Table 1). 2 0 0 --
LOS A N G E L E S
•
+ $9
Zx - $ 9 15C
e..
IOC
~-~0
Z
E
50
.
~ I
5-
40
41 z 3o ~20
I0
I
L
I "t'"
l
I
I
AMBIENT CONCENTRATIONS OF CO-POLLUTANTS
9 8 7
C
63
Pb
i43
3
6
9
13
12
15
18
21
24
PST 9 / 1 7 / 8 0
Fig. 1 (a). Diurnal variations in mutagen densities of ambient POM collected in Los Angeles and Riverside and (b) ambient concentrations of co-pollutants, at Los Angeles collection site on September 17, 1980.
38
TABLE 1 COMPARISON OF MORNING 'RUSH HOURS' (0600-0900 h) MUTAGEN DENSITIESa WITH 'CALCULATED' AND OBSERVED 24-h MUTAGEN DENSITIES FOR SEPTEMBER 17, 1980
DTLA Riverside
0600-0900-h values
24-h values
Maximaa
Average of 3-h samplesb
24-h continuous samplesc $9
- $9
+ $9
- $9
+ $9
- $9
+
100 73
170 96
67 30
100 35
63 35
71 38
Net rev/m3 of ambient air sampled. bThis 24-h average was calculated from the sum of the experimental 3-h values. cExperimental values for the 24-h continuous samples. a
As seen in Table 1, the peak values of both direct and activatable mutagenicity were much higher (nearly double) than those found for the corresponding P O M sample taken for a continuous 24-h period. This is relevant to health risk assessment calculations, Thus, for example, one should consider peak doses as well as 24-h or longer average doses in considering the mutagenic impact of ambient particulate matter. In general, there was little evidence for an effect of filter artifacts on sample mutagenicity [e.g., polycyclic aromatic hydrocarbons (PAH), in the P O M reacting with ambient NO2 or 03 (Pitts et al., 1978a, b, c, 1980; Lee et al., 1980)]. At all 3 sites, and on all 3 sampling days, the average 24-h mutagen densities calculated from the 3-h samples were in reasonable agreement with those determined directly f r o m the P O M samples collected continuously for the same 24-h period. This suggests that artifact formation from possible chemical transformations occurring on the sampling filters is not large during the sampling time period from 3 to 24 h. However, if such reactions on the filter occurred on a time scale much faster than 3 h or longer than 24 h, they would not be observed in this experiment. Also, possible reactions in the atmosphere cannot be ruled out. Indeed, the fact that the ratio of activatable to direct activity, while significant during the morning (0600-0900 h), decreases in the afternoon and evening (Fig. la) suggests that some of the activatable mutagens (e.g., benzo[a]pyrene) may be photo-oxidized or may react with gaseous co-pollutants such as 03, NO2 and peroxyacetyl nitrate (Pitts et al., 1978c). The diurnal variations of mutagen density in D T L A are similar to those of several co-pollutants (see Fig. 1). O f particular interest are CO and lead, because in the SCAB these are often used as 'tracers' to differentiate automobile emissions from stationary sources. Indeed, the linear correlation coefficients between mutagen density and air quality data show significant positive correlations (confidence level
39 > 95%) for CO, NO, NO2 and total NOx as well as for lead. Additionally, a less significant negative correlation was seen between mutagenicity and ambient 03 levels. All of this evidence suggests that mobile source primary emissions are important contributors to the mutagenicity, both direct and activatable, of ambient POM in the SCAB. For each of the eight 3-h samples, as well as for the 24-h sample in DTLA collected on September 12, 1980, the mutagenic activity toward TA98NR was about 50-60% lower than toward TA98, and showed similar diurnal variations. This evidence for the presence of nitroarenes (Rosenkranz and Poirier, 1979; Mermelstein et al., 1981; Rosenkranz et al., 1981) is similar to that reported previously in POM collected from urban air in Wayne County, Michigan (Wang et al., 1980), in Stockholm, Sweden (L6froth, 1981) and in diesel POM (Pitts et al., 1982). In summary, these 3-h time-resolved mutagenicity studies of ambient airborne particles at 3 sites across the SCAB and at 2 different times of the year have yielded the following observations for this region: (1) Ambient particulate mutagenicity displays to a significant degree the characteristics of a primary pollutant, responding both to vehicular emission rates and to atmospheric mixing ratios as shown by its high correlation with CO, NOx and lead levels. (2) Short-term peak mutagen densities can be much higher than the 24-h average values commonly reported in the literature. (3) Nitroarenes may contribute substantially to the mutagenicity of ambient particulate organic matter in the SCAB. (4) The good agreement between analyses of the 24-h collection and the average of the 3-h samples suggests that chemical transformations of mutagenic material collected on the filters are either very fast or very slow relative to the time scale used in these experiments. (5) The increased contribution of promutagenic activity to the mutagenicity of the particles during periods of high emission rates, and its subsequent return to lower levels relative to the direct activity, suggest that some promutagenic materials present in freshly emitted POM are subject to rapid destruction in the atmosphere.
Acknowledgments We thank Professors Bruce N. Ames for the Salmonella strain TA98 and Herbert S. Rosenkranz for Salmonella strain TA98NR, as well as Dr. Robert Giauque at the Lawrence Berkeley Laboratory for the lead analyses. Air quality data were graciously provided by the South Coast Air Quality Management District. We thank Mrs. Minn Poe of our technical staff for the statistical analyses of the data, as well as Ms. Margaret C. Dodd, Ms. Susan E. Brown, Mr. William R. Hoffman and Mrs.
40 D i a n e G i l e s f o r t h e i r v a l u a b l e t e c h n i c a l a s s i s t a n c e . T h i s w o r k was s u p p o r t e d by t h e C a l i f o r n i a A i r R e s o u r c e s B o a r d , D r . J o h n R. H o l m e s , C h i e f , R e s e a r c h D i v i s i o n , a n d D r . J a c k K. S u d e r , P r o j e c t M o n i t o r , t h r o u g h A g r e e m e n t A 9 - 0 7 7 - 3 1 .
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