Personal exposure to fine particulates and polycyclic aromatic hydrocarbons in an office environment by menez

Frontier of Environmental Science December 2013, Volume 2, Issue 4, PP.33-46

Personal Exposure to Fine Particulates and Polycyclic Aromatic Hydrocarbons in an Office Environment in Xi’an, China Hongmei Xu1,2, Junji Cao1,3†, Meiling Gao4, Kin Fai Ho1,5, Xinyi Niu1, Teresa L. Coons6, Steven Sai Hang Ho1,7, Gehui Wang1, Zhuzi Zhao1,2 1. Key Lab of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710075, China 2. University of Chinese Academy of Sciences, Beijing, 100049, China 3. Institute of Global Environmental Change, Xi’an Jiaotong University, Xi'an, 710054, China 4. University of California, Berkeley, USA 5. School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China 6. Washington State University, USA 7. Hong Kong Premium Services and Research Laboratory, Lai Chi Kok, Kowloon, Hong Kong, China †Email:

cao@loess.llqg.ac.cn

Abstract This study was conducted to evaluate the relationships between PM2.5 and associated polycyclic aromatic hydrocarbons (PAHs) in indoor and outdoor environments, identify likely PAH sources, determine personal exposures, and estimate the toxicity and carcinogenic risks. Monitoring was conducted in Xi’an, China on consecutive weekdays (July 6 to 24, 2009) from 8am to 8 pm. The average PM2.5 personal exposure mass concentration (66.4 μg m-3) was lower than that outdoors (80.5 μg m-3), but the average total PAH concentration in the personal exposure samples (179.8 ng m-3) was higher than outdoors (114.9 ng m-3). In addition, two distinct relationships between personal exposure and outdoor PAH concentrations were observed; these could be explained by the subjects’ time-activity patterns. PAHs toxicity risks were estimated from the BaP-equivalent concentrations in the personal samples and determined to be 45.8 ng m-3 on average. Applying the unit risk method, an estimated 8 cancer cases (range: 2 to 30) per million office workers would be expected from the inhalation of PM2.5-bound PAHs. Keywords: PM2.5; PAH; Personal Exposure; Toxicity Risk; Office Workers

1 INTRODUCTION Rapid and sustained economic and population growth in China has led to frequent air pollution episodes and increased incidences of respiratory disease [1,2,3]. Two sources of fine particulate matter (PM2.5, PM with aerodynamic equivalent diameters ≤ 2.5 μm) exposure, ambient air pollution and household air pollution, were the fourth and fifth leading death risks in China, respectively [4]. Total PM2.5 burden in China–the combination of ambient air pollution, household air pollution, and second-hand tobacco smoke–is very large [4]. An estimated 300,000 deaths annually are attributed to urban air pollution in China alone [5]. Much of PM2.5 is produced by anthropogenic activities. PM2.5 has been found to be especially toxic to humans because these particles are small enough to penetrate deeply into the lungs where they then can be transferred into the - 33 http://www.ivypub.org/fes/

bloodstream [1]. PM2.5-associated PAHs have also gained attention owing to their toxicity, carcinogenicity and mutagenicity [6,7]. Several studies have demonstrated an association between specific PAHs and early genetic damage associated with breast and lung carcinogenesis [8,9]. Outdoors, PAHs are generated from various natural sources, such as forest fires and volcanic eruptions, but they are also produced from anthropogenic sources, mainly motor vehicle exhaust, the incomplete combustion of fossil fuels for heat or power generation, and fugitive emissions from industries [10,11,12]. Indoor PAHs are produced from cooking and from wood and coal burning for heat; they also can be transferred indoors either from nearby sources or long-range transport [13,14,15]. Modern humans spend most of their lives indoors [13,16], but few studies have assessed the relationship between ambient PM2.5 or PAH concentrations and personal exposure. Investigations of exposures in an urban office environment can provide important insights into the overall exposure to PM2.5 and to PAHs and the health implications of that exposure for office workers. Hence, the aims of this study were to evaluate the relationships between PM2.5 and associated PAHs in indoor and outdoor environments, identify likely PAH sources, determine personal exposures, and estimate the toxicity and carcinogenic risks from the exposure to PAHs.

2 MATERIALS AND METHODS 2.1 Participant Selection Four participants (identified as AA, BB, CC, and DD) were selected from four different offices in the Institute of Earth Environment, Chinese Academy of Sciences (IEECAS, 34°13'49.68"N, 108°52'59.05"E). Located in the Hi-Tech Zone in urban Xi’an, the Institute hosts scientists and graduate students, some of whom both live and work there. The selected participants (non-smokers, female, ages 24 to 29) spent their time in similar indoor microenvironments and worked in the same building complex. During the study, the participants maintained activity logs to document the amount of time spent in different locations and sources of direct exposure, such as cooking or being in an area where people were smoking.

2.2 Sample Collection PM2.5 personal exposure filter samples were collected continuously and simultaneously for the four participants on weekdays (July 6 to 24, 2009) from 8 am to 8 pm local time (total 12 hr). Samples were collected using URG-2000 PM2.5 personal sampling devices (URG Corp., Chapel Hill, USA) each of which consisted of a filter-holder containing a 25-mm quartz filter (QM/A®, Whatman Inc., UK), a mini-PM2.5 cyclone, and a 3 L min-1 AirLite Sample Pump. Before sampling, the quartz filters were pre-combusted at 800C for at least 4 hr to remove adsorbed organic vapors. A blank filter was collected for each batch to account for contamination from handling and the weighing steps. The pumps were wrapped in sound-deadening material and placed in a waist pack for the participants to wear. The samplers were connected to the pumps, and the participants kept the sampling inlets within the breathing zone distance (~0.2 m from the nose and mouth). Flow rates were tested at the beginning and the end of each sampling period. The exposed sample filters were placed in petri dishes and then stored at -20C before analysis to prevent the volatilization of the PAHs. Ambient PM2.5 samples were also collected from 8 am to 8 pm local time (in parallel with the personal sampling) with the use of a URG-3000N ambient sampler that was deployed on the rooftop of IEECAS building complex (~10 m above the ground and 30 m from road traffic). This ambient sampling device used 37-mm quartz filters (QM/A®, Whatman Inc., UK), and operated at a standard flow rate 22 L m-1. The start and end times were recorded in a sampling log along with notes on unusual weather or traffic events. After sampling, the ambient aerosol filters were removed, equilibrated, weighed, and stored using the same methods as those for personal exposure samples. A total of 15 samples were collected from each of the four participants; this resulted in a total of 60 personal exposure and 15 outdoor samples for the gravimetric analyses. - 34 http://www.ivypub.org/fes/

2.3 Analyses All quartz sample filters were weighed before and after sampling to determine the accumulated PM2.5 mass concentrations. The filters were weighed using a Sartorius ME 5-F electronic microbalance (±1 μg sensitivity, Sartorius, Gottingen, Germany)[17]. The equilibration and weighing steps were repeated until a difference of < 5 µg was achieved. Due to the high PM2.5 mass correlations among the four individuals [18], one punch (0.5 cm2) from each personal exposure filter were combined (total 2.0 cm2) for the PAH analyses of the personal samples. Two punches (each punch was 0.5 cm2; 1.0 cm2 in total) were taken from each outdoor sample to provide sufficient mass for the ambient PAHs analysis. Solvent extraction (SE) followed by gas chromatography/mass spectrometry (GC/MS) was used to determine the PAH concentrations. Filter punches were extracted three times, each time with 5 mL of a mixture of dichloromethane/ methanol (2:1, v/v) for 10 min with ultrasonication. After concentration, the extracts were incubated with 50 μL of N,O-bis-(trimethylsilyl)trifluoroacetamide with 1% trimethylsilyl chloride and 10 μL of pyridine at 70C for 3 hr. The derivatized extracts were analyzed with a Agilent 4890 5975 gas chromatography/mass selective detector system (Agilent Technologies, Inc., Santa Clara, CA. USA). The GC/mass spectrometer GC/MS response factors were determined using authentic standards. Average recoveries of all the standards were ~70%. Detailed information on the procedures used for PAHs pretreatment and analysis along with QA/QC information has been presented in Wang et al. [19] . Field blank filters were analyzed using these same procedures. The results of the blank analyses showed no serious contamination (< 5.0% of the PAH concentrations of samples). The data reported are all corrected for the blanks. Thirteen PAHs were identified and quantified in this study; these were fluorine (FLO, 3-ring), phenanthrene (PHE, 3-ring), anthracene (ANT, 3-ring), fluoranthene (FLU, 4-ring), pyrene (PYR, 4-ring), benzo[a]anthracene (BaA, 4-ring), chrysene and triphenylene (CT, 4-ring), benzo[b]fluoranthene (BbF, 5-ring), benzo[k]fluoranthene (BkF, 5-ring), benzo[a]pyrene (BaP, 5-ring), indeno[1,2,3-cd]pyrene (IcdP, 6-ring), dibenzo[a,h]anthracene (DahA, 5-ring), and benzo[g,h,i]perylene (BghiP, 6-ring).

2.4 Air Exchange Rate Experiment An experiment was conducted to determine the rate at which outdoor air was transferred into the office environment from the air conditioning system and from leaks in doors, windows, etc; this was done to understand the role of the air exchange in terms of PAH exposure. Carbon dioxide gas (gas cylinder, 5000 ppm CO2) was released into an office with the windows and doors closed in the building complex. The CO2 source was removed when the concentration reached 5000 ppm in the office. A handheld Q-TRAK air quality real-time instrument (TSI Inc., MN, USA) was used to measure the CO2 concentrations. Multiple locations in the office were measured to ensure CO2 was well-mixed throughout the room. The air conditioner was then turned on high until the CO2 concentration fell below the background, indoor level (700 ppm). The air exchange rate (AER) was calculated based on the following equation [20,21]: C(t) = C(0)e-kt

where C(0) is the initial concentration of CO2, C(t) is the concentration of CO2 after time t, and k is a rate constant (that is, the AER) in units of reciprocal time.

3 RESULTS AND DISCUSSION 3.1 Exposure to PM2.5 1) Personal-outdoor Associations of PM2.5 Concentrations - 35 http://www.ivypub.org/fes/

The arithmetic mean mass concentrations of the four personal exposure PM2.5 samples ranged from a low of 58.6 μg m-3 (subject CC) to a high of 73.5 (BB) μg m-3, and these were generally lower than outdoor PM2.5 concentrations, which averaged 80.5 μg m-3 (Table 1). Ratios of personal exposure to outdoor mass concentrations (P/O) ranged from 0.7 to 0.9. The P/O ratios less than unity can be interpreted as an indication that the PM2.5 loadings were lower in the offices compared with the outdoor air, that is, lower exposure indoors compared with outdoors. A scatter-plot of personal versus outdoor PM2.5 mass concentrations is presented in Fig. 1. Overall, the PM2.5 mass concentrations showed a strong correlation between the personal exposure and outdoor samples (R = 0.81), with the R values for the four subjects ranging from 0.79 to 0.87. The slope of the regression (0.6) implies that the filters on the air conditioners removed some of the PM or that the PM was prevented from entering the offices by some other means. The intercept (24.3) of the regression might imply that there is a background source for indoor PM. 200

AA BB CC DD

-3

Personal exposure PM2.5 (ug m )

200

150

100

Y= 0.6X + 24.3 R=0.81 N=52 P<0.0001

0 0

100

150

200

250

0 300

-3

Outdoor PM2.5 (ug m ) FIG. 1 RELATIONSHIP BETWEEN PERSONAL EXPOSURE (P) AND OUTDOOR (O) PM 2.5 MASS CONCENTRATIONS TABLE 1 PERSONAL EXPOSURE (P) AND OUTDOOR (O) PM 2.5 MASS CONCENTRATIONS IN XI’AN Type of Sample

PM2.5 concentration (μg m-3) a

P/O ratio Mean

Range

Subject AA

69.6

25.9 – 181.3

0.9

0.83

Subject BB

73.5

30.6 – 186.0

0.9

0.87

Subject CC

58.6

28.4 – 123.6

0.7

0.86

Subject DD

63.9

26.0 – 114.7

0.8

0.79

Outdoor

80.5

32.3 – 236.8

N/Ac

N/A

N is the number of samples

R is the P/O correlation coefficient

NA is not applicable

- 36 http://www.ivypub.org/fes/

Regulatory standards have not been established in China for either personal exposure or indoor PM2.5 concentrations, and few studies have focused on personal exposure to PM in office settings. Nevertheless, the results from our study can be compared with those from other areas. Summer PM2.5 concentrations reported by Sangiorgi et al. [22] for various office settings in Milan, Italy were 14.5, 13.3, 20.0, and 23.3 μg m-3, while the corresponding outdoor PM2.5 concentrations were 19.5, 20.2, 32.1, and 37.0, respectively. The US EPA also completed the collection phase of the cross-sectional Building Assessment Survey and Evaluation (BASE) study in 2000 [23]. The PM2.5 indoor concentrations from that study ranged from 1.3 to 24.8 μg m-3 in 100 office buildings across the USA, with a geometric mean of 7.2 μg m-3, and the outdoor concentrations ranged from 4.5 to 47.4 μg m-3, with a geometric mean of 14.7 μg m-3 [23]. A detailed study of PM2.5 distributions in three non-residential indoor environments (museum, print industry, and office) in Athens, Greece found mass concentrations of 20.3, 65.0, and 30.7 μg m-3, respectively [24]. In comparison, the PM2.5 mass loadings in the personal exposure samples from our study were much higher than all of those just mentioned. 2) Impacts of the Time Spent Outdoors and Office Air Exchange Rate The participants spent the majority of their time indoors (average = 93%, range: 89–97%); the percentages of time spent outdoors were 7, 3, 5, and 11% for subjects AA, BB, CC, and DD, respectively (Fig. 2). The correlation coefficients (R values) for linear regressions of the personal exposure PM2.5 mass concentrations versus the time spent outdoors by the participants (four inset figures in Fig. 2) were 0.75, 0.34, 0.32, and -0.16, indicating modest or no correlations between the outdoor activity time and personal PM2.5 exposure [25,26]. This is likely because the variability in personal exposure PM2.5 mass was as much a result of the differences between the indoor/outdoor PM2.5 loadings as the amount of time spent outdoors [26,27]. Moreover, it's worth mentioning that DD, who spent the greatest percentage of time outdoors, showed a negative correlation between variables, which also was the weakest of the relationships. Furthermore, the activity logs indicate that DD was the most mobile of the subjects, and that person also spent more time moving between microenvironments where the PM2.5 loadings were likely variable.

Time spent outdoor (%)

Y=0.1 X + 2.9 R=0.34 N=6 P=0.5095

0 0

100

150

0 0

100

150

200

Y=-0.03 X + 11.2 R=-0.16 N=11 P=0.6346

200

100

150

200 -3

Personal exposure PM2.5 (ug m )

Y=0.2 X - 3.4 R=0.75 N=11 P=0.0076

Time spent outdoor (%)

-3

Time spent outdoor (%)

Time spent outdoors (hour)

Time spent outdoors (%) Time spent outdoor (%)

Personal exposure PM2.5 (ug m )

CC Y=0.3 X - 2.3 R=0.32 N=6 P=0.5311

25 20

-3

Personal exposure PM2.5 (ug m ) 0 0

100

150

200 -3

Personal exposure PM2.5 (ug m )

Time spent outdoors (%)

Time spent outdoors (hour)

0 AA

Participant FIG. 2 RELATIONSHIPS BETWEEN THE PERSONAL EXPOSURE TO PM2.5 AND TIME SPENT OUTDOORS

The activity logs showed that the participants’ office windows and doors were always closed and the air conditioners were always turned on high. The high R values (0.79–0.87, Fig.1) for the linear regressions of outdoor versus personal exposure PM2.5 mass concentrations indicate the offices had good ventilation and frequent air exchange [28]. Indeed, the average AER was 1.36 hr-1 for the four offices in the study. This value is comparable to other indoor microenvironments - 37 http://www.ivypub.org/fes/

in China where air exchange rates were 1.37 hr-1 in a classroom, 1.91 hr-1 in a reading room, and 1.22 hr-1 in a dormitory and in an urban area California (USA) where the air-exchange rate in summer was 1.13 hr-1 [21,29]. If the AER for an office is low, indoor air pollutants can accumulate to levels that could pose health risks. However, in our study, PM2.5 was typically higher for the outdoor air samples than for the personal samples, and a modest air exchange rate would be beneficial to the office workers because it would prevent the infiltration of the outdoor air. On the other hand, as illustrated below, exposure to other pollutants such as PAHs, also are affected by human activities as well as the AER.

3.2 Exposure to PAHs Thirteen PAHs were detected in all samples, and the average concentrations and standard deviations of the sums of these PAHs (ΣPAHs ) were 179.8 ± 157.7 ng m-3 and 114.9 ± 116.2 ng m-3 in the personal exposure and ambient PM2.5 samples, respectively (Table 2 and Fig. 3). The PAHs for daily average personal exposure samples ranged from 35.0 (23 July) to 555.8 ng m-3 (10 July) while the PAHs for ambient PM2.5 ranged from 31.0 (22 July) to 487.9 ng m-3 (14 July). A time-series plot shows that the variations in the PAH concentrations in the two different kinds of samples were not synchronous (Fig. 3). The average P/O ratio for ΣPAHs was 1.6 and ranged from 0.2 to 6.5. Indeed, the P/O ratios for were less than 1.0 on only four of the sampling days (26.7% of the samples), and therefore, in contrast to the PM2.5 loadings discussed above, most of the personal exposure samples had higher PAH concentrations than the outdoor ones. TABLE 2 CONCENTRATIONS OF 3- to 6-RING PAHS IN PERSONAL EXPOSURE AND OUTDOOR SAMPLES Personal Exposure (P) PAH Number

Average

of Rings

Outdoor (O)

Standard

-3

Average

Standard

-3

P/O

(ng m )

deviation

(ng m )

deviation

3-ring PAHs

19.9

15.5

5.8

6.1

3.4

4-ring PAHs

36.7

33.6

23.4

26.0

1.6

5-ring PAHs

75.4

68.2

51.2

53.7

1.5

6-ring PAHs

47.8

62.0

34.4

31.4

1.4

Total PAHs

179.8

157.7

114.9

116.2

1.6

500

-3

Personal exposure Outdoor concentration

500

400

300

200

100

7/2 5

7/2 3

7/2 4

7/2 2

7/2 1

7/2 0

7/1 6

7/1 7

7/1 5

7/1 4

7/1 0

7/1 3

7/8

7/9

7/6

0 7/7

PAHs concentrations (ng m )

600

-3

PAHs concentrations (ng m )

600

Date

FIG. 3 TIME SERIES OF PERSONAL EXPOSURE AND OUTDOOR PAH CONCENTRATIONS (ng m-3) IN XI’AN - 38 http://www.ivypub.org/fes/

Based on the activity logs, none of participants cooked, cleaned, or were exposed to tobacco smoke during the collection of the personal exposure samples. No obvious sources for the PAHs were noted except for the printing and computer equipment in the office. Participants spent an average of 93% of their time indoors; most of their time outdoors was spent in environments where the PAH concentrations were likely high (e.g., walking near roadways or riding buses). This time-activity pattern was reflected in the lower 12-hr average PAH concentrations in ambient PM2.5 samples compared with the personal exposure samples. Although the time spent outdoors everyday by participants was short (even zero hours on occasion for two participants who sometimes stayed in the Institute), the time outdoors usually involved the daily commute. This led to the subjects’ exposure to higher PAH concentrations from motor vehicle emissions. To the best of our knowledge, no studies to date have investigated personal exposure to PM2.5-bound PAHs near roadways in Xi’an. Fortunately, data for traffic police exposed to PAHs during the summer in Tianjin provide a point of comparison for understanding the ambient PAH concentrations found in our study [30]. The mean concentration of the sum of thirteen PAHs collected from roadway intersections in Tianjin was 867.5 ng m−3, and that was much higher than the average for samples collected on a school campus which also was in Tianjin (ΣPAHs: 19.5 ng m−3). In comparison, the personal PAHs in our study were five orders of magnitude lower than what found in Tianjin roadside samples. This suggests that personal exposure to PAHs can be strongly affected by outdoor activity patterns, and in particular, the time spent in specific microenvironments where the pollutants are in high concentrations. The mean concentrations of individual PAH in the personal exposure and outdoor samples are shown in Fig.4. IcdP was the most abundant PAH followed by BbF and BaP. The mean IcdP concentrations were 31.6 and 26.9 ng m-3 in the personal exposure and outdoor samples, respectively, and it accounted for 17.6% to 23.4% of the ΣPAHs. BaP is one of the most potent carcinogens among the known PAHs, and it has been considered a general indicator of carcinogenicity [19,31,32] ; the average BaP concentrations were 28.4 for the personal exposure samples and 21.7 ng m-3 for the outdoor samples. These levels are more than 20 times the concentration limit in the air-quality guidelines of the World Health Organization (1.0 ng m-3), and they also exceeded the BaP limit in the China National Ambient Air Quality Standards (2.5 ng m-3 for 24-hr average in PM10) [33] and in the China National Indoor Air Quality Standards (1.0 ng m-3 for 24-hr average in PM10) [34]. Note that the last two standards just referenced are for PM10 and not PM2.5 as was measured in our study; indeed, the concentrations in our samples would have been higher if we had collected and analyzed larger particles. Although the total PAH and BaP concentrations may have declined in Xi’an [19,35], the loadings are still high, and the potential for adverse health effects remains a cause for concern.

Abundance (%)

Personal exposure Outdoor concentration

Abundance (%)

ne ne ne ne ne ne ne ne ne ne ne ne ne ore hre ace the pyre hrace enyle anthe anthe ]pyre ]pyre hrace eryle flu nant anthr oran t iph uor uor o[a -cd ant ,i]p n a e u r ] l l ] l z t b]f k]f f ,h ,3 h ph z[a ben o[1,2 nz[a, zo[g zo[ zo[ ben en dibe ben ben ben ind

FIG. 4 INDIVIDUAL PAH ABUNDANCE (%) IN PERSONAL EXPOSURE AND OUTDOOR SAMPLES IN XI’AN - 39 http://www.ivypub.org/fes/

Comparisons of the PAH concentrations grouped by ring structure for the personal exposure and outdoor samples are shown in Table 2. The average contribution of 3-ring PAHs was 11.1% for the personal exposure samples, and that was much higher than in the outdoor PM2.5 samples (5.1%); in fact, the P/O ratio for 3-ring PAHs was 3.4. In contrast, the concentration percentages of 4-, 5-, and 6-ring PAHs in personal exposure and outdoor samples were much more similar (20.4 and 20.3% for 4-ring PAHs, 41.9 and 44.6% for 5-ring PAHs, 26.6 and 30.0% for 6-ring PAHs, respectively). The average P/O ratios for the 4-, 5- and 6-ring PAHs ranged from 1.6 to 1.4; and they varied inversely with the PAHs’ boiling points; that is, lower P/O ratios were observed for the PAHs with higher boiling points. This difference in P/O ratios is most likely because the 3- and 4-ring PAHs (molecular weight, MW < 252) typically exist in both the vapor and particulate phases while the 5- and 6-ring PAHs (MW ≥ 252) are mainly in the particulate phase [7,32,36]. According to gas-particle distribution theory, the 5- and 6-ring PAHs should be more stable and less volatile than the 3-ring PAHs. This means that compared with the higher MW PAHs, the 3-ring PAHs are more likely to vaporize in the warm summer air and then infiltrate into the offices through the doors and windows. In our study, the average outdoor temperatures reached 31.1C; this was approximately 7C higher than in the offices (mean 24.4C). Hence, setting aside the differences in the PAH emission sources and other factors, a larger fraction of the 3-ring PAHs would condense onto particles in the cooler office air compared with the warmer outdoor environment. Comparisons with the results of previous studies of personal exposure to PM2.5 and associated PAHs shows that the exposure in Xi’an is much lower than in Beijing (559.4 ng m-3 in 2007 winter) [37] but higher than in Guangzhou or Tianjin, China [13,30], Shizuoka, Japan [38], Bangkok, Thailand [39], and Porto, Portugal [40]. The level of exposure in Xi’an is ten to one hundred times higher than what is typical in the USA [41,42], and this high level of the personal exposure to PAHs deserves serious attention in future air pollution and human health studies.

3.3 Implications for PAH Sources A scatter plot of the total PAH concentration outdoors versus personal exposure (Fig. 5a) shows two different relationships, one with R = 0.61 (line I) and the other R = 0.94 (line II). The difference in the slopes of lines I and II (0.18 and 4.57) indicates that there were two types of exposure to PAHs, and these were most likely a function of the individuals’ time-activity patterns. This finding is important because it illustrates how normal day-to-day activities can influence one’s exposure to this group of pollutants. For regression line I (below the 1:1 diagonal line), all of the personal exposure PAH concentrations were much higher than the matching outdoor data. Although our outdoor monitoring site did not capture the roadside PAH concentrations, the high personal exposure PAHs can best be explained by the relatively long time (>1 hr) the participants spent outdoors each day; this included time spent commuting in heavily trafficked areas where PAH concentrations were likely high. Regression line II (above the 1:1 diagonal line) reflected relatively shorter outdoor exposure times (<1 hr each day on average); this relationship was seen for participants on days when they did not commute or when they spent the entire day indoors where PAH concentrations were most likely low. Diagnostic ratios of atmospheric PAHs with similar MWs have been used for source identification studies [43,44]. The personal exposure samples from our study had average values of 0.24 for ANT/(ANT+PHE) and 0.62 for IcdP/(IcdP+BghiP); in comparison, the corresponding ratios were ~0.11 and 0.75 for the outdoor samples (Fig. 5b). The bulk of the outdoor data plotted around the vertical line at 0.1 for ANT/(ANT+PHE), and this indicates that the contributions of petrogenic and pyrogenic sources to the outdoor PAHs were roughly equal. In contrast, most of the personal exposure samples plotted in the center of Fig. 5b, and this is consistent with a predominant influence from pyrogenic sources. Almost all of the data points plotted above the upper horizontal line at 0.5 for the IcdP/(IcdP+BghiP) ratio, indicating that most of the samples had strong influences from grass, wood, and coal combustion although some of them evidently also were affected by petroleum combustion. - 40 http://www.ivypub.org/fes/

（b）

600

Ⅰ Ⅱ

400

300

Y= 0.18 X + 36.83 R=0.61 N=10 P=0.0592

200

Pyrogenic Personal exposure Outdoor

1.0

1:1 line

Y= 4.57 X - 79.93 R=0.94 N=5 P=0.0158

-3

Outdoor PAHs (ng m )

500

Petrogenic 1.2

IcdP/(IcdP+BghiP)

（a）

Grass, wood and coal combustion 0.8

0.6

0.4

Petroleum combustion 100

0.2

Petrogenic 0 0

100

200

300

400

500

600

0.0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-3

Personal exposure PAHs (ng m )

ANT/(ANT+PHE)

FIG. 5(a) CORRELATIONS OF OUTDOOR AND PERSONAL EXPOSURE PAH CONCENTRATIONS; (b) CORRELATIONS BETWEEN PAH DIAGNOSTIC RATIOS [ANT/(ANT+PHE) AND IcdP/(IcdP+BghiP)] FOR PERSONAL EXPOSURE AND OUTDOOR SAMPLES

3.4 Toxicity and Carcinogenic Risk of PAHs in Personal PM2.5 It is well established that many PAHs are mutagenic and carcinogenic, and their health risks can be assessed by calculating BaP-equivalent ([BaP]eq) concentrations [9]. The widely used procedures of the Office of Environmental Health Hazard Assessment (OEHHA) of the California Environmental Protection Agency (CalEPA) are often used to calculate inhalation cancer risks [45,46]. The [BaP]eq for each personal exposure sample was calculated from the PM2.5-bound PAH concentration combined with the toxicity equivalency factors (TEFs) of target compounds [47,48] as shown in equation (2). Σ[BaP]eq = Σ (Ci ×TEFi)

(2)

-3

where Ci is the concentration of target compound i (ng m ), and TEFi is the TEF of the target compound i. The inhalation cancer risk associated with exposure to the PAHs can be calculated as follows: Inhalation cancer risk = Σ[BaP]eq × UR[BaP]

(3)

where UR[BaP] (unit risk), which is the inhalation cancer unit risk factor of BaP, which is defined as the number of people at risk of contracting cancer from the inhalation of a BaP equivalent concentration of 1 ng m-3 in a lifetime of 70 years. The UR[BaP] value from the CalEPA is 1.1 × 10-6 (unit risk) [45,46]. Assuming that the career of a typical employee spans ~35 years; and adjusting for evenings, weekends, and holidays; that employee would spend ~12 years in the office environment. Therefore, the estimated average UR[BaP] value for the subjects in our study would be 1.8 × 10-7 (unit risk). As part of our effort to evaluate the health effects of the PAHs, we calculated the individual [BaP]eq concentration levels and the relative contributions for each of the thirteen measured PAHs in the personal exposure samples (Fig. 6). Fig. 6 shows that the [BaP]eq values for the various PAH species ranged from 0.02 (ANT) to 28.4 (BaP) ng m-3 (with a mean value for the PAHs of 3.5 ng m-3). Thus, the contributions from the individual PAHs to the total [BaP]eq concentrations (Σ[BaP]eq) ranged from 0.004% for ANT to 61.9% for BaP. The [BaP]eq levels were dominated by BaP (28.4 ng m-3 or 61.9%) and DahA (10.2 ng m-3 or 22.2%); these two compounds accounted for more than 80% of the total [BaP]eqs. The contributions of 5+6-ring PAHs to the Σ[BaP]eq concentrations followed the order BaP > DahA > IcdP > BbF > BkF > BgihP; these compounds amounted to ~99.5% of the total due to their high absolute concentrations and high TEF values: the 3+4-ring PAHs amounted to only 0.5% of Σ[BaP]eq. These results attest to a distinctly higher human-health risk for the PAHs with MW ≥ 252 (~2 to 4 orders of magnitude higher) when compared with the MW < 252 PAHs. - 41 http://www.ivypub.org/fes/

6.89% 6.9 %

61.9 %

22.2 % 22.18%

61.88%

0.8 % 0.35% 0.01% 0% 0.02% 0.09% 0.31% 6.3 % 6.34% 1.9% 1.9 %

FLO PHE ANT FLU PYR BaA CT BbF BkF BaP IcdP DahA BghiP

FIG. 6 PERCENTAGES (%) OF [BaP]eq FOR INDIVIDUAL PAH SPECIES IN PERSONAL EXPOSURE SAMPLES (SEE TEXT FOR DESCRIPTION OF PAH ABBREVIATIONS)

Furthermore, the mean Σ[BaP]eq for the entire personal exposure sampling period was 45.8 ± 43.0 ng m-3 (range: 8.7–164.6 ng m-3): the highest value was found on 10 July and the lowest on 23 July. The maximum Σ[BaP]eq value was more than 3.5 times the average. The excess inhalation cancer risk in the Xi’an urban office environment for a typical career of 12 years averaged 8.3 × 10-6 (range: 1.6 × 10-6 to 3.0 × 10-5). The median value of total inhalation risk was 6.9×10-6, with 6.0×10−6 and 1.0×10-5 for the 5th and 95th percentiles, respectively. Therefore, an estimated mean of 8 (range: 2 to 30) cases of cancer per million office workers in Xi'an can be expected from the inhalation of PM2.5-bound PAHs. The Xi’an Statistical Yearbook [49] indicates that the total number of persons employed in enterprises, institutions, agencies and related organizations in Xi’an was approximately 1.35 million at the end of 2009. Therefore, an estimated 11 cancer cases for these working employees can be attributed to the inhalation of PM2.5-bound PAHs. We should note that this number of cases is most likely an underestimate because the assessment is based on summertime PAH concentrations, which are lower than that in other seasons [19]. This extremely high Σ[BaP]eq value and the corresponding health risks should not to be neglected in Xi’an. Finally, it is important to note that the levels of PAHs and other contaminants in the offices investigated here are surely much lower than in many other work environments, and therefore, the investigations of PAH exposures should be expanded to include other workplaces where the impacts are likely to be greater.

4 CONCLUSIONS This study on personal exposure to PM2.5 and PAHs in Xi’an, China highlights the importance of understanding and quantifying PAH sources and in determining how the exposures are affected by personal activity patterns. The personal exposure PM2.5 mass concentrations for four subjects averaged over 15 days ranged from 58.6 to 73.5 μg m-3 (with the average of 66.4 μg m-3), and these were generally lower than the outdoor concentrations, which averaged 80.5 μg m-3. Overall, the mass concentrations showed a strong correlation between outdoor and personal exposure (R = 0.81), and the slope of the regression for these two sets of samples implies that some of the outdoor PM was removed by the air conditioning system or in other ways prevented from entering the offices. The averages of the sums of the thirteen PAHs investigated were 179.8 ±157.7 and 114.9 ±116.2 ng m-3 in the personal exposure (P) and outdoor (O) samples, respectively. The PAHs P/O correlations evidently were driven by the individual’s time-activity patterns. The average P/O ratio for individual PAHs was 1.6 and ranged from 0.2 to 6.5. The mean Σ[BaP]eq concentration for the ensemble of all personal exposure samples was 45.8 ± 43.0 ng m-3 (range: 8.7 to 164.6 ng m-3). The PAHs diagnostic ratios indicate that the main sources of PAHs were anthropogenic, especially coal - 42 http://www.ivypub.org/fes/

combustion and motor vehicle emissions. The excess inhalation cancer risk derived from Σ[BaP]eq indicates that 8 persons (range: 2 to 30) per million office workers in Xi'an would develop cancer due to their exposure to PM2.5-bound PAHs. It is important to note that the PM2.5 and PAH concentrations in the offices in this study are doubtlessly much lower than in many other workplace environments, and so the cancer risks estimated here are likely toward the lower end of the risk spectrum. The study also was conducted during the summer when the PAH concentrations were relatively low, so the overall risks are likely higher. It is also worth emphasizing that this study highlights the potential impacts of PM2.5 and PAHs from mobile sources; the study participants evidently were exposed during their commute despite the typically short duration of exposure. Targeted sampling of specific microenvironments and further investigations of time-activity patterns would benefit future studies and help determine the greatest PAH-related health risks.

ACKNOWLEDGMENTS This study was supported by National Gongyi Project (201209007), Shaanxi Project (2012KTZB03-01), and the funding from “US National Science Foundation East Asia Pacific Summer Institutes Program”.

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Authors 1

Hongmei Xu (1986-), female, Chinese, a

2†

Junji Cao (1971-), male, Chinese, Doctor, professor of Key Lab

PhD Candidate of Key Lab of Aerosol

of Aerosol Science & Technology, SKLLQG, Institute of Earth

Science & Technology, SKLLQG, Institute

Environment, Chinese Academy of Sciences and part-time

of Earth Environment, Chinese Academy of

professor of Institute of Global Environmental Change, Xi’an

Sciences

Chinese

Jiaotong University. His research interests are PM2.5 and

Academy of Sciences. Her research interests

carbonaceous aerosols, their origins, and effects on climate; and

are inorganic and organic compounds in

indoor air pollutants and their effects on historical artifacts.

aerosol particles, their origins, and the

Email: cao@loess.llqg.ac.cn

and

University

human health effects; personal exposure and related health risk assessment and PM2.5 source apportionment. Email: xuhongmei@ieecas.cn - 45 http://www.ivypub.org/fes/

Meiling Gao (1984-), female, USA, a PhD Candidate of

Steven Sai Hang Ho (1975-), male, Chinese, Doctor, Chief

University of California, Berkeley, USA. Her research interests are

Executive Officer of Hong Kong Premium Services and Research

air pollutants in indoor and outdoor environments, and the effects

Co. and part-time professor of Institute of Earth Environment,

of built environment on disparities in exposures and health in both

Chinese Academy of Sciences. His research experiences are in

China and USA.

environmental sciences and analytical chemistry.

Kin Fai Ho (1974-), male, Chinese, Doctor, assistant professor

Gehui Wang (1968-), male, Chinese, Professor of the Key Lab of

School of Public Health and Primary Care, The Chinese University

Aerosol Science & Technology, SKLLQG, Institute of Earth

of Hong Kong and part-time professor of Key Lab of Aerosol

Environment, Chinese Academy of Sciences. His research interests

Science & Technology, SKLLQG, Institute of Earth Environment,

are atmospheric chemistry, especially the physical and chemical

Chinese Academy of Sciences. His research interests are aerosol

characteristics of organic aerosols in the atmosphere and their

chemistry and health, especially the physical and chemical

impacts on climate and human health.

characteristics of gases and aerosols in the atmosphere from different sources. 5

Zhuzi Zhao (1985-), female, Chinese, a PhD Candidate of Key

Lab of Aerosol Science & Technology, SKLLQG, Institute of

Xinyi Niu (1990-), female, Chinese, Master degree of Department

Earth Environment, Chinese Academy of Sciences and University

of Civil and Structural Engineering, Hong Kong Polytechnic

of Chinese Academy of Sciences. Her research interest is the

University. Her research interests are air pollutants, including

carbonaceous aerosol and its origins in remote regions (e.g., Tibet

aerosol and gases in indoor environment.

and Qinghai Lake).

Teresa L. Coons (1985-), female, USA, Master degree of science

in Department of Civil, Environmental, and Architectural Engineering, Washington State University in 2009. Her research interest is personal exposure and spatial variability of PM2.5 in Colorado and China.

- 46 http://www.ivypub.org/fes/