Seasonal and Spatial Variations in Human Cell Mutagenicity of

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Environ. Sci. Technol. 1999, 33, 4407-4415

Seasonal and Spatial Variations in Human Cell Mutagenicity of Respirable Airborne Particles in the Northeastern United States DANIEL U. PEDERSEN,† JOHN L. DURANT,‡ BRUCE W. PENMAN,§ CHARLES L. CRESPI,§ H A R O L D F . H E M O N D , * ,† ARTHUR L. LAFLEUR,| AND GLEN R. CASS⊥ Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Department of Civil and Environmental Engineering, Tufts University, Medford, Massachusetts 02155, Gentest Corporation, 6 Henshaw Street, Woburn, Massachusetts 01801, Center for Environmental Health Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Environmental Engineering Science Department, California Institute of Technology, Pasadena, California 91125

Samples of respirable airborne particles (similar in size to PM2.5) were collected at five sites in the northeastern United States every sixth day during 1995 and tested in a mutagenicity assay based on human cells. Three sites were located in Massachusetts: in downtown Boston, in a suburban area 20 km to the north, and in a rural area 100 km west of Boston. The other two sites were located in downtown Rochester in upstate New York and in a rural area 35 km to the west. Bimonthly composite samples (10-11 sampling days per composite) were extracted in organic solvents and tested for mutagenicity at the thymidine kinase locus in h1A1v2 cells, a line of human B-lymphoblasts that constitutively expresses P450 CYP1A1 cDNA. Mutagenicity levels were significantly higher in winter than in summer at all sites, both per microgram of airborne particulate organic carbon (OC) and per cubic meter of air. Mutagenicity per microgram of OC was significantly inversely correlated with air temperature (r ) -0.95 in NY, r ) -0.40 in MA) and ambient concentrations of OC (r ) -0.4). Annual averages of mutagenicity per microgram of OC in upstate New York were roughly 2-fold higher than in Massachusetts; however, no clear intrastate spatial variations were evident. Mutagenicity per cubic meter of air showed an increase of roughly 1.5-2-fold from rural areas to urban centers within each state. This increase was influenced by higher OC concentrations in the urban locations (up to 2-fold) but not by higher mutagenicity per microgram of OC. These results indicate that cold weather is significantly correlated with the human cell mutagenicity of respirable particles in the northeastern United States and further show that populations of urban centers in this region are exposed to higher levels of airborne human cell mutagens than in nearby rural areas.

Introduction Particulate air pollution has long been considered to be harmful to human health. Many epidemiological studies have 10.1021/es9905997 CCC: $18.00 Published on Web 11/06/1999

 1999 American Chemical Society

linked ambient concentrations of airborne particles to respiratory disease (1) and to lung cancer (2, 3). Although smoking is a dominant cause of lung cancer, the smokingcorrected risk of lung cancer in urban areas was found to be up to ∼1.5 times higher than in nearby rural areas (the “urban effect”) (2, 3). Barbone et al. (4) found that lung cancer risk in Trieste, Italy, was highly correlated with total suspended particulate (TSP) pollution and that the risk increased significantly on a gradient from rural to suburban/residential and then to industrial/urban center areas. Epidemiological studies such as these are not sufficient to prove causation but have led to the hypothesis that chemicals present in airborne particles contribute to the risk of lung cancer. One way of testing this hypothesis is to explore the chemical content and biological activity of airborne particles and personal exposures to them. These particles are typically composed of complex mixtures of chemicals, including many known mutagens and carcinogens (5), e.g., polycyclic aromatic hydrocarbons (PAHs) and their transformation products, such as nitro-PAH and oxy-PAH, collectively known as polycyclic aromatic compounds (PACs) (6, 7). Recently, a National Ambient Air Quality Standard was proposed for respirable airborne particles with an aerodynamic diameter of less than 2.5 µm (PM2.5). Respirable particles penetrate deeply into the lung, appear to be most strongly associated with detrimental health effects (1, 8), and are the size fraction most associated with mutagens such as PACs (9, 10). One approach to testing complex mixtures is the use of in vitro mutation assays. Such assays can determine whether extracts of respirable particles are capable of causing mutations, which are necessary initiating events for some forms of cancer. Numerous studies have shown that organic extracts of airborne particles from background, rural, and urban sites are mutagenic in short-term assays using bacterial or mammalian cells (e.g., refs 11-20). It has also been shown that bacterial mutagenicity can vary significantly both with season (e.g., refs 11, 13-18, and 20) and location (e.g., refs 12-14, 18, and 19) and is related to concentrations of mutagens such as PACs (e.g., refs 15 and 17). The bacterial mutagenicity of the particles and the PAC concentrations are often highest during the colder months. They are also highest in urban centers, consistent with the urban effect found for lung cancer risk. Such temporal and spatial variations in the chemical content and biological activity of airborne particles may help identify the sources, transport patterns, and chemical transformations of these pollutants and suggest ways of controlling them. The mutagenicity of ambient particles has been evaluated in the past mostly by bacterial assays. Since bacteria respond differently than human cells to many chemicals (21-23), new assays based on metabolically competent human cells may better represent the human response to mutagens (2429). Human cell assays have recently been used to evaluate the mutagenicity of individual chemical compounds (21, 22, 30-33) and environmental samples such as diesel soot (34), other combustion generated soots (35), contaminated sedi* Corresponding author phone: (617)253-4111; fax: (617)258-8850; e-mail: [email protected]. † Department of Civil & Environmental Engineering, Massachusetts Institute of Technology. ‡ Tufts University. § Gentest Corporation. | Center for Environmental Health Sciences, Massachusetts Institute of Technology. ⊥ California Institute of Technology. VOL. 33, NO. 24, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 1. Location of sampling sites in the northeastern United States. Bars represent the annual average concentrations of organic carbon and elemental carbon (µg m-3) measured in respirable airborne particles during 1995 (47). ments (36, 37), and urban dust standard reference material SRM-1649 (38). Only one previous study, conducted in the relatively mild climate of Los Angeles, has examined seasonal and spatial variations in the human cell mutagenicity of respirable particles collected at a network of air monitoring sites (23). The mutagenicity per unit mass of organic carbon from respirable particles was not found to vary significantly among seasons or locations in the Los Angeles area. The human cell mutagenicity of airborne particles in the northeastern United States has not been previously evaluated. To our knowledge, seasonal variations in human cell mutagenicity of airborne particles in locations with relatively severe winters have yet to be reported. In this study, we used a human cell assay to evaluate the mutagenicity of ambient respirable particles from five sites in two separate regions of the northeastern United States during the entire year of 1995. The seasonal and spatial variations of bimonthly composites are explored as are the differences among urban, suburban, and rural locations across upstate New York and Massachusetts. The resulting trends are compared to population density, location, temperature, humidity, precipitation, and particle phase co-pollutants.

Experimental Section Sampling Locations. Samples of airborne particles were collected at five sites on a transect from Lake Ontario to the Atlantic Ocean representing a wide range of urbanization and development from two major urban centers to an isolated state park (Figure 1). The two sites in eastern Massachusetts were at Kenmore Square in downtown Boston and at Reading. The third site was established in central Massachusetts at Quabbin State Park, and the two sites in northern New York State were located at Rochester and Brockport. The Kenmore Square station was located in Boston (population density 5000/km2), the largest coastal urban center in New England. Important local combustion sources appear to be dense vehicular traffic, heating, and cooking emissions. The Reading station was located on a largely residential street with some commercial activity near the town center (population density 1000/km2), 20 km north-northeast of Boston and appears to be a typical suburban location in coastal New England. Local sources include moderate transportation, home heating, and cooking emissions. The Quabbin station was located 4408

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100 km west of Boston within a protected watershed (no inhabitants in 90 km2) in one of the most rural regions of Massachusetts. Few vehicles are allowed in the immediate vicinity, but there is a backup diesel generator 200 m away that operates on rare occasions. This site was chosen to represent background conditions in central Massachusetts and is probably affected mainly by long-range transport and by area sources outside the park. Rochester (population density of 2500/km2) lies near the southern shore of Lake Ontario, 650 km west of Boston, and represents an inland urban center. This station was located downtown where local sources include vehicular traffic and industrial emissions. Brockport (population density of 200/km2) represents an inland rural site and is located in an agricultural area 35 km west of Rochester, which is probably affected mainly by longrange transport and by area sources. Sampling Methods. Respirable particles from all five sites were collected simultaneously for 24 h every sixth day for the entire calendar year of 1995, following procedures described elsewhere (23). These samples were collected using a highvolume (hi-vol, ∼300 L/min) dichotomous virtual impactor (19, 39) capable of collecting large amounts of size-separated organic aerosol with a cutoff at ∼3 µm. After being separated, the particles of each size class (respirable and coarse) were captured on quartz fiber filters for human cell assays and analyses of organic compounds. Concurrent samples of airborne particles were also collected with a low-volume (lowvol) sampler (19, 40). Particles larger than ∼2 µm were removed with a cyclone separator (41), while the remaining respirable particles were captured (flow 0.8), but sites in different states are not correlated with each other. In general, the annual averages of ambient OC and EC concentrations increase with increasing population density, which can serve as an indicator of urbanization (Figure 4a). The higher concentrations of particulate OC in the cities lead to elevated mutagen density in the urban centers as compared to nearby, less urban areas despite similar mutagenic potencies (Figure 6b). In Massachusetts, for example, the annual average mutagen density increased from Quabbin (0.22 IMF × 106 m-3) to Reading (0.33 IMF ×106 m-3) and Kenmore Square (0.42 IMF ×106 m-3) along with the increase in population density. Significant spatial differences in mutagen density were found among bimonthly composites (Figure 5f-k). The sensitivity analysis identified one outlier, which, if excluded, decreased the mutagenic potency slightly but did not change the results (Figure 2). The response for two composites (March-April and May-June at Reading) failed the linearity test. The mutagenic potency of the MarchApril composite was especially sensitive to the exclusion of the highest dose (0.28 IMF × 106/µg of EOC) and increased the annual averages of mutagenic potency and mutagen density at Reading to 0.14 and 0.53 IMF × 106 m-3, respectively. Note also the elevated concentrations of OC for this composite (Figure 4), which also had the highest respirable particle mass concentration of all 30 composites, as well as high concentrations of non-carbon species. These results indicate that this composite bears specific further study. Correlations with Climatic Factors and Chemical Composition. The mutagenic potencies pooled for all samples

show a significant negative correlation with temperature (r ) -0.60). The correlation coefficient increases to r ) -0.91 if the January-April composites at Massachusetts are excluded. When the data from all sites were pooled, weak inverse correlations were found for mutagenic potency with bimonthly averages of particulate sulfate, OC, and PM2.5 mass concentrations, while a weak positive correlation was found with particulate nitrate. Mutagenic potency was not significantly correlated with bimonthly averages of precipitation, humidity, and EC or non-carbon mass concentrations.

Discussion Seasonal and Spatial Trends in Mutagenicity. This study is the first to report systematic seasonal and spatial variations in human cell mutagenic potency (per µg OC) of ambient respirable particles. In general, mutagenic potencies at each site were significantly higher in winter than in summer, except for the beginning of the year at the Massachusetts sites (Figure 3). Mutagenic potencies in upstate New York appear to be ∼2-fold higher than in Massachusetts (Figures 3 and 6a). Since the mutagenic potency differs for the same amount of OC, these variations represent changes in the composition of the particles rather than changes in the ambient OC concentrations. Human cell mutagen density (per m3 of air) exhibits similar seasonal trends and increases by ∼1.5-2fold from rural areas to nearby urban centers (Figures 5 and 6b). The seasonal variations in mutagen density of respirable particles in the Northeast are driven by mutagenic potency rather than ambient OC concentrations. In contrast, the spatial variations in mutagen density are driven by OC concentrations, which increase from the rural locations to the urban ones. This gradient of mutagen density with urbanization suggests that local emission sources could be VOL. 33, NO. 24, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 4. Spatial (a) and seasonal (b-f) trends in ambient concentrations of organic carbon (OC) and elemental carbon (EC) in respirable airborne particles collected in the northeastern United States during 1995 (47). Site abbreviations are the same as Figure 3. Population densities: BR, 200/km2; RO, 2500/km2; QB, no inhabitants in 90 km2; RD, 1000/km2; KS, 5000/km2.

FIGURE 5. Seasonal (a-e) and spatial (f-k) trends in mutagen density [IMF (× 106)/m3 of air] of respirable airborne particles collected in the northeastern United States during 1995. Error bars represent 95% confidence intervals; different letters indicate a significant difference at this 95% confidence level (see Figure 3). Site abbreviations are the same as Figure 3. responsible for at least a portion of the mutagenicity of these particles. 4412

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The correlation analysis indicates that the seasonal variations in mutagenic potency are associated with changes

FIGURE 6. (a) Carbon-weighted annual average of 1995 mutagenic potency [IMF (× 106)/µg of EOC] ( standard error of the mean. (b) Annual average of 1995 mutagen density [IMF (× 106)/m3 of air] ( standard error of the mean. in ambient temperature, especially at the sites in upstate New York (r ) -0.95). The correlation coefficient for the Massachusetts sites is lower but still significant (r ) -0.40), indicating that for the period of January-April in Massachusetts the inverse correlation with temperature is weaker and that there are other as yet undetermined influences on the mutagenic potency. The inverse correlation with temperature could be due to indirect effects, such as seasonal changes in emission sources (e.g., heating or wood-burning in winter) or in meteorological conditions, affecting mixing of particles or photochemical transformation of mutagens. Direct effects of temperature on mutagens may also be important, e.g., partitioning of mutagens between the gas phase and the particulate phase. Gas-particle partitioning of PACs, for example, is inversely correlated with ambient temperature (48-50). Comparisons with Bacterial Mutagenicity Studies. The seasonal and spatial trends we observed in the northeastern United States are consistent with variations in the bacterial mutagenicity of airborne particles and concentrations of particle-phase PACs observed at other locations with similar climates (e.g., ref 10). Seasonal patterns in locations with cold winters have shown significant inverse correlations with temperature (e.g., refs 14 and 17). Bacterial mutagenicity per cubic meter of air and PAC concentrations in Sapporo, Japan, were tracked over the years 1974-1992 (20). During each of these years, both bacterial mutagenicity and PAC concentrations were highest in the winter and lowest in the summer. Hannigan et al. (19) found that the bacterial mutagenicity per cubic meter of air in the Los Angeles area was highest in winter but observed no clear trend in mutagenicity per microgram of OC. However, some studies in warmer locations such as Brazil (18) and Spain (51) found higher bacterial mutagenicity during warmer months, indicating that the character of airborne particles in warmer climates may differ from colder locations. The various seasonal trends observed in these studies were attributed to seasonal changes in emission sources and atmospheric conditions (e.g., inversion layers, photochemical processes, and adsorption rates of mutagens).

Significant spatial variations have also been found in the bacterial mutagenicity and PAC concentrations of particulate matter collected simultaneously at multiple locations (e.g., refs 10, 14, 18, and 19). In general, the types of locations, listed in increasing order of mutagenicity, were background, rural, residential, industrial, and urban center areas. These spatial differences were explained by proximity to primary emission sources (e.g., vehicle exhaust) at the urban sites, higher particle concentrations, or higher mutagen content. Alfheim et al. (13) found that, in addition to being more mutagenic than background sites, airborne particles at urban sites were significantly (1.5-3 times) more mutagenic than at nearby suburban sites. de Raat et al. (12) found that bacterial mutagenicity of airborne particle samples increased not only from unpolluted to highly polluted sites but also on a gradient among locations with increasing urbanization. These findings indicate that bacterial mutagenicity is correlated with urban development. Previous Human Cell Studies. Hornberg et al. measured the sister chromatid exchanges induced in human tracheal epithelial cells by PM2.5 and PM10 collected in the RhineRuhr region of Germany during the winter of 1996 (52). Samples collected at a rural site exhibited lower genotoxicity per m3 of air than those from industrial and urban sites. This finding is consistent with the spatial trends in mutagen density we observed in the current study. The current study uses methods and materials identical to those used by Hannigan et al. in the Los Angeles basin during 1993 (23). In the Los Angeles study, no systematic seasonal pattern was found in the human cell mutagenic potency of respirable particles. OC concentrations were high in the winter and low in the summer (the opposite of the trend in the Northeast). The seasonal and spatial variations in mutagen density in the Los Angeles area followed the trends in OC concentrations. It was concluded that the mutagenic potency of the respirable particles was probably governed by primary particle emissions from ubiquitous sources and that if photochemical processes were important then they must occur in both summer and winter. The human cell mutation assay used in both of these studies has provided data on the mutagenicity of respirable airborne particles in three urban areas across the United States: Los Angeles, CA; Boston, MA; and Rochester, NY. The comparison of these studies indicates that the human cell mutagenic potency of respirable particles in the northeastern United States is similar in magnitude to that of southern California (23) but that the spatial and temporal trends in the mutagenicity in each urban area appear to be different. The average mutagenic potency measured at sites across the Los Angeles basin (∼0.15 IMF × 106/µg of EOC) was similar to the average over all of the northeastern sites (∼0.12 IMF × 106/µg of EOC). The Los Angeles values were lower than the average mutagenic potency measured in New York and higher than the average values measured in Massachusetts. Within each region (Los Angeles, upstate New York, and Massachusetts), the mutagenic potency appeared to be uniform among sites within distances of ∼100 km. However, both the bimonthly composites and the annual averages of mutagenic potency (per µg of EOC) varied significantly over greater distances (e.g., between upstate New York and Massachusetts sites). These variations can be related to different conditions at each location, particularly climate and heating practices. This comparison suggests that the temperature variations in the temperate climate of southern California are not extreme enough, or more likely the winters are not cold enough, to have a strong influence on the human cell mutagenic potency of the respirable particles. In contrast, it appears that the cold winters in the Northeast are associated with significant increases in mutagenic potency. VOL. 33, NO. 24, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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The results of this study indicate that the human cell mutagenicity (both per µg of organic carbon and per m3 of air) of respirable particles in the northeastern United States is strongly correlated with seasonally varying temperatures, consistent with previous studies. Differences among the sites that cannot be explained by temperature variations, such as the lower mutagenicity in Massachusetts at the beginning of 1995 as compared to the New York sites, suggest that factors other than temperature are also likely to be important. The spatial pattern of mutagen density (per m3 of air) further shows that human exposure to airborne mutagens at these sites increases with population density and urban development. These findings in the human cell assay are similar to the urban/rural spatial gradients previously found for lung cancer (4), bacterial mutagenicity (12), and PAC concentrations (10). While these data are not sufficient to draw causal connections between ambient respirable particles and health risks, they are consistent with the hypothesis that particulate air pollution may contribute to lung cancer risk. Further chemical analysis is in progress to determine whether contributions from specific types of emission sources or concentrations of specific human cell mutagens can explain the differences found in the respirable particle samples collected in the northeastern United States.

Acknowledgments The authors are grateful for the efforts of Frances Lew at MIT and Alex Lunts at Rochester, who helped operate the sampling equipment, and Mark DuCombe of the Massachusetts Department of Environmental Protection, who helped with sample unloading. The authors would also like to thank the following people and organizations: Mark Utell and Ray Gibb of the University of Rochester helped initiate the sampling program in New York; Lynn Salmon and Mike Hannigan at Caltech provided support with sampling equipment and supplies; the Massachusetts Department of Environmental Protection generously provided access and support at the Quabbin Site, as did Bill Pula of the Metropolitan District Commission in Quabbin State Park; Len Rucker and James Blomley (Reading Municipal Light Department) and Daniel Lieberman (Boston University Office of Environmental Health and Safety) graciously allowed us to site our equipment on their rooftops and provided on-going assistance; Lawrence Donhoffner and Lita Doza-Corpus at Gentest Corporation performed the human cell assays; Koli Taghizadeh and Elaine Plummer of the Center for Environmental Health Sciences (CEHS) at MIT for help with laboratory techniques. Funding for this study was provided by the following grants from the National Institute for Environmental Health Sciences (NIEHS): Superfund Hazardous Substances Basic Research (SF P42-ESO4675), CEHS Core grant (P30-ESO2109), and Mutagenic Effects of Air Toxicants (MEAT) (P01-ESO7168).

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Received for review May 25, 1999. Revised manuscript received September 10, 1999. Accepted September 14, 1999. ES9905997

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