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Pollution level, inhalation exposure and lung cancer risk of ambient atmospheric polycyclic aromatic hydrocarbons (PAHs) in Taiyuan, China
Environmental Pollution 173 (2013) 150e156
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Pollution level, inhalation exposure and lung cancer risk of ambient atmospheric polycyclic aromatic hydrocarbons (PAHs) in Taiyuan, China Zhonghuan Xia a, b, *, Xiaoli Duan c, Shu Tao a, Weixun Qiu a, Di Liu a, Yilong Wang a, Siye Wei a, e, Bin Wang a, Qiujing Jiang d, Bin Lu d, Yunxue Song d, Xinxin Hu d a
Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China Department of Environmental Science and Engineering, School of Geography Science, Nanjing Normal University, Nanjing 210046, China Department of Environmental Pollution and Health, Chinese Academy of Environmental Sciences, Beijing 100012, China d Taiyuan Environment Science Research and Design Institute, Taiyuan 030024, China e College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 June 2012 Received in revised form 24 September 2012 Accepted 16 October 2012
Passive air samplers were deployed to collect both gas and particulate phase polycyclic aromatic hydrocarbons in Taiyuan between 2009 and 2010. Annual average concentrations of BaP equivalent concentration (B[a]Peq) in background, rural and urban areas were 2.90 0.29, 23.2 30.8 and 27.4 28.1 ng/m3, respectively, with higher concentration in the winter than in other seasons. The median B[a]Peq concentrations of annual inhalation exposure were estimated to be in the range of 103e347 ng/d for all population groups in rural as well as in urban areas. The median values of incremental lifetime cancer risk (ILCR) induced by whole year inhalation exposure for all groups were basically larger than 106, with higher values in winter than in other seasons and in urban than in rural area. In the same season and area, the ILCR of adults was larger than other age groups and that of females was a little higher than males. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Polycyclic aromatic hydrocarbons Pollution level Inhalation exposure Lung cancer risk Taiyuan
1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are a group of fusedring aromatic compounds that are formed during the incomplete combustion of organic material (McGrath et al., 2007). PAHs have generated considerable interest ever since they were recognized as a carcinogenic class of compounds in the late twenties (Okona-Mensah et al., 2005). Several individual PAHs such as benzo(a)pyrene (BaP), chrysene (CHR), indeno(1,2,3- c,d)pyrene (IcdP) and benzo(b)fluoranthene (BbF) have produced carcinogenic, mutagenic, and genotoxic effects in animal experiments (DeutschWenzel et al., 1983). In recent years, environmental PAH concentrations have increased in many industrialized and developing countries. In China, the PAHs emissions contributed over 20% of the total global PAH emissions in 2004 (Zhang et al., 2008) and the high emissions have resulted in heavy contamination of various environmental media, especially ambient air (Zhang et al., 2007). Lung cancer has been ranked as the fourth and fifth leading causes of cancer death
* Corresponding author. E-mail address: [email protected] (Z. Xia). 0269-7491/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.envpol.2012.10.009
in Chinese males and females, respectively (Jiang et al., 2008) due to serious air pollution. Causes of human lung cancer have always been associated with the inhalation exposure to PAHs (Chen and Liao, 2006). Therefore, exposure and health risk assessment of atmospheric PAHs is very essential for effective environmental management (Asante-Duah, 2002). So far, researches concerning respiratory exposure and lung cancer risk assessment of PAHs are quite limited in China (Bai et al., 2009; Zhang et al., 2009). Taiyuan, the capital of Shanxi Province and an old industrial city, becomes one of the most polluted cities in China and PAHs may be a threat to the health of local residents (Zhang et al., 2009) mainly due to the high intensity of pollutant emission (Zhang et al., 2009). Thus, assessing the health risk level of citizens in Taiyuan associated with environmental exposure to PAHs is quite urgent. PAHs concentrations of foods consumed by local residents in Taiyuan were monitored in 2008 and the incremental lifetime cancer risks (ILCRs) were found to be larger than 104 at the 74.5th, 78.7th, 60.6th, 77.4th, 75.3th, 79.5th, 60.8th and 77.9th percentile for children, adolescents, adults and seniors of male as well as the above groups of female, respectively (Xia et al., 2010), implying significant dietary cancer risk. However, lung cancer risk level induced by inhalation exposure to atmospheric PAHs for citizens in Taiyuan is currently unavailable.
Z. Xia et al. / Environmental Pollution 173 (2013) 150e156
The objective of this study is to determine the pollution level, quantify the inhalation exposure and further score the incremental lifetime cancer risk for citizens in Taiyuan, investigating the changes in both exposure and risk for different seasons, areas and population groups. To determine the overall uncertainty in predicted risks, the uncertainty resulting from the assessment of exposure was propagated through the risk characterization process using the Monte Carlo simulation. Moreover, a detailed sensitivity analysis was conducted to identify the input variables that were critical to the accuracy of the risk assessment. 2. Materials and methods 2.1. Sampling Passive air samplers with PUF disk and glass fiber filter (GFF) were used to collect PAHs in the gas and particulate phases, respectively. Detailed calibration method and uptake rates of this sampler were described previously (Tao et al., 2009). Volume concentrations of PAHs were calculated based on calibration equations derived in Supporting Material (S.2, Equation S1 and S2). Passive air samplers were deployed at 25 background, rural and urban sites in Taiyuan, the capital of Shanxi Province and an old industrial city in China (S.1, Fig. S1 and Table S1), in the spring, summer-autumn and winter between 2009 and 2010. The sampling periods were 70, 155 and 140 days for spring, summereautumn, and winter, respectively, and the sampling period in the winter included the residential heating time. Two identical samplers were deployed at each site on rooftops or open areas to avoid airflow obstruction (1.5e20 m heights). Detailed information on atmospheric sampling sites was presented in Supporting Material (S.1, Table S1). After sampling, all PUF disks were stored at 18 C. GFFs were equilibrated in a desiccator (25 C) for 24 h and weighed before and after the sampling, in accordance with USEPA Method (1980). Before sampling, the PUF disks were cleaned by extracting them in a Soxhlet with a 1:1 mixture of n-hexane and acetone for 8 h and the GFFs were cleaned by baking them in a furnace at 450 C for 4 h. 2.2. Analytical procedure PUF disks were Soxhlet extracted with150 ml 1:1 mixture of n-hexane and acetone at 52 C for 8 h. GFFs were subjected to microwave extraction (MARS2Xpress, CEM, USA) with 25 ml 1:1 mixture of n-hexane and acetone, being heated to 100 C at 10 C/min and then held for 10 min. After concentration with a vacuum rotary evaporator (R-201, Shanghai, China) at 37 C, total extracts were transferred to the alumina silica gel column for purification. The eluted mixture from the column during cleanup was first concentrated to near dryness. The residue was then transferred and diluted with n-hexane and brought to exactly 1.0 ml by nitrogen blowdown (Eyela MG-1000) at room temperature (25 C). The samples were sealed in vials and stored at 4 C before analysis. Quantitative analysis of the air sample extracts was done by gas chromatography with mass spectrometer detector (Agilent 6890GC/5973MSD). A 30 m 0.25 mm i.d. 0.25 mm film thickness HP-5MS capillary column (Agilent Technology) was used. GC temperature was programmed from an initial 60 C before commencing at 5 C/min up to 280 C, with a final holding time of 20 min. Helium was used as the carrier gas. A 1.0 ml aliquot of the extract was injected while the injector port was held at 280 C and operated in splitless mode at a flow rate of 1.0 ml/min. The head column pressure was 30 kPa. The mass spectrometer was operated in scan mode with an electron impact ionization of 70 eV, an electron multiplier voltage of 1288 V, and an ion source of 230 C. Concentrations were determined for 15 PAHs in all samples. They were acenaphthene (ACE), acenaphthylene (ACY), fluorine (FLO), phenanthrene (PHE), anthracene (ANT), fluoranthene (FLA), pyrene (PYR), benz(a)anthracene (BaA), chrysene (CHR), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), dibenz(a,h)anthracene (DahA), indeno(1,2,3-cd)pyrene (IcdP) and benzo(g,h,i)perylene (BghiP). 2.3. Quality control Quantification was performed by the internal standard method using 2-fluoro1,10 -biphenyl and p-terphenyl-d14 (2.0 mg/ml; J&K Chemical, Beijing, China). All solvents used were analytical grade (Beijing Chemical Reagent, Beijing, China) and purified by distillation prior to use. Alumina and silica gel (80e200 mesh; Dikma, China) were heated at 650 C in a muffle furnace (DLII-9, Beijing, China) for 10 h, kept in a sealed desiccator, and reactivated at 130 C for 4 h immediately prior to use. All glassware was cleaned using an ultrasonic cleaner (KQ-500B, Kunshan, China) and heated to 400 C for 6 h. The field and laboratory blanks were analyzed, and the concentration of target PAHs in the field blanks were higher than laboratory blanks and more than one order of magnitude lower than real samples for both PUF disks and GFFs. All the results of air samples were field blank corrected. Recovery of individual PAHs ranged from 78% to 103% with a mean value of 89% for PUF disks, whereas that varied from
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80% to 101% with a mean value of 88% for GFFs. Data analyzed in the article were not corrected for recoveries. The detection limits were in the range of 0.172e1.23 ng/ml. 2.4. Inhalation exposure estimates The carcinogenic risk of a PAHs mixture is often expressed by its BaP equivalent concentration (B[a]Peq). The B[a]Peq of atmospheric PAHs (BEC) was calculated according to Equation (1): BEC ¼
n X
Ci TEFi
(1)
i¼1
where Ci ¼ concentration of PAH congener i; TEFi ¼ the toxicity equivalency factor (TEF) of PAH congener i (S.3, Table S2). For individual PAH concentration, when a result was below the limit of detection (LOD), the value was assumed to be half of the respective LOD. The carcinogenic potencies of 15 PAHs were estimated as the sum of each individual B[a]Peq. We treated C, which followed lognormal distribution, in Equation (1) probabilistically. Taiyuan consists of background, rural and urban areas. There are no citizens living in background area. In both rural and urban areas, the citizens were divided into eight population groups according to the age and gender: children (4e10 years), adolescents (11e17 years), adults (18e60 years), and seniors (61e70 years) of male as well as the above groups of female. Daily inhalation exposure level (E) for each population group was calculated as follows: E ¼
n X
BECi IR Ti
(2)
i¼1
where Ti ¼ daily exposure time span in the ith area (S4); BECi ¼ B[a]Peq in the ith area (ng/m3); IR ¼ inhalation rate (m3/day) (S4, Table S13). We treated BEC and IR, which followed lognormal and normal distribution, respectively, in Equation (2) probabilistically. Detailed information on inhalation exposure calculation was presented in Supporting Material (S4). 2.5. Cancer risk estimates The incremental lifetime cancer risk (ILCR) of population groups in Taiyuan caused by PAHs inhalation exposure was calculated based on Equation (3). ILCR ¼ SF E EF ED CF=ðBW ATÞ
(3)
where ILCR ¼ the incremental lifetime cancer risk of the inhalation exposure (dimensionless); SF ¼ the cancer slope factor for BaP inhalation exposure [a lognormal distribution with a geometric mean of 3.14 (mg kg1 day1)1 and a geometric standard deviation of 1.80](Chen and Liao, 2006); E ¼ the daily inhalation exposure level (ng/d); EF ¼ the exposure frequency (day/year) (S.5); CF ¼ conversion factor (106 mg/ng); BW ¼ body weight (kg) (S.5, Table S13); AT ¼ average lifespan for carcinogens (25550 day). We treated SF E and BW, which obeyed lognormal, lognormal and normal distribution, respectively, in Equation (3) probabilistically. Detailed information on cancer risk calculation was presented in Supporting Material (S.5). 2.6. Uncertainty analysis A Monte Carlo simulation using matlab6.5 software was implemented to deal with the uncertainties in the risk assessment in this study. We performed independent runs at 1000, 3000, 5000, and 10,000 iterations with each parameter sampled independently from the appropriate distribution at the start to test the convergence and the stability of the numerical output. The result showed that 5000 iterations are sufficient to ensure the stability of results. As the results manifested the effects of uncertainty in the input parameter statistics on the estimation, sensitivity analysis using matlab6.5 software could be done to find the variables that affect the risk most. Rank correlation coefficients between each input variable and the output (risk) were calculated, and then by squaring the output variance and normalizing it to 100%, the contribution of each input variable to the output (risk) variance was assessed, and the sensitivity of each input variable relative to one another was evaluated.
3. Results and discussion 3.1. Pollution level of atmospheric PAHs Atmospheric concentrations (particulate þ gas phase) of PAHs in Taiyuan are shown in Fig. 1 and the detailed results are presented in Supporting Material (S.3, Table S3eS11). In background area, the concentrations (particulate þ gas phase) of total 15 PAHs and BaPeq were in the range of 57.5 5.32e73.6 2.22 and
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Fig. 1. Atmospheric concentrations (particulate þ gas phase) of PAHs. A: total 15 PAHs; B: BaPeq. The data are presented as arithmetic means plus arithmetic standard deviations.
1.13 0.08e5.69 0.30 ng/m3, respectively, in different seasons and the whole year (Fig. 1). In rural area, the both phase concentrations of total 15 PAHs and BaPeq were in the range of 164 149e232 237 and 19.3 27.4e29.3 33.7 ng/m3, respectively, whereas that in urban area were in the range of 176 93e253 167 and 14.0 16.8e40.5 46.4 ng/m3, respectively, for the above periods (Fig. 1). In each season, the concentrations of BaPeq in both rural and urban areas were larger than 2.5 ng/m3, the Chinese national standard. In background area, the BaPeq were less than 2.5 ng/m3 in the spring and summereautumn but greater than 2.5 ng/m3 in both the winter and the whole year, and were larger than 1 ng/m3, the WHO guideline (Ravindra et al., 2008) for each season, indicating serious air pollution in Taiyuan (Fig. 1). According to the season, the ranking of both 15 PAHs and BaPeq in decreasing order was: winter, spring and summereautumn in background area, whereas that in urban area was: winter, summereautumn and spring (Fig. 1). In rural area, with respect to the season, the ranking of 15 PAHs in decreasing order was: spring, winter and summere autumn, while that of BaPeq in decreasing order was: winter, spring and summereautumn (Fig. 1). The fact that concentration of PAHs was basically higher in the winter than in other seasons was also reported by other researches (Zhou et al., 2005) and the possible reason might be the residential heating resulting more biomass and domestic coal combustion as well as the unfavorable atmospheric diffusion and degradation conditions during the
winter (Liu et al., 2008). In rural area, the total 15 PAHs in the spring was a litter higher than that in the winter (Fig. 1) due to a large number of straw burning in this season. According to the region, the ranking of both 15 PAHs and BaPeq in decreasing order for all seasons except spring was: urban, rural and background area (Fig. 1), which was consistent with other reports (Gigliotti et al., 2005; Liu et al., 2008). The ratio between PAHs concentrations in urban and rural areas was w1.05 (209 ng/m3 in urban, 199 ng/m3 in rural) in Taiyuan (Fig. 1), which was close to the ratio in North China Plain (1.23) (870 ng/m3 in urban, 710 ng/m3 in rural) (Liu et al., 2008), but much lower than that in Europe and America, such as Birmingham, UK (w4) (28.7 ng/m3 in urban, 6.88 ng/m3 in rural) (Smith and Harrison, 1996), New Jersey, USA (w7) (17.0 ng/m3 in urban, 2.54 ng/m3 in rural) (Gigliotti et al., 2005), Massachusetts, USA (w46) (47.2 ng/m3 in urban, 1.03 ng/ m3 in rural) (Allen et al., 1996) and Toronto, Canada (w3) (26.5 ng/ m3 in urban, 7.91 ng/m3 in rural) (Motelay-Massei et al., 2005). In both Taiyuan and North China Plain, the low efficient practices in biomass and coal combustion in rural area resulted in higher PAHs emission than coal combustion and vehicle emission in urban area, and additionally centralized heating system and utilization of natural gas in urban area decreased the need for biomass or domestic coal burning, leading to much lower ratio of PAHs concentrations between urban and rural areas in comparison with that in Europe and America. In the spring, a lot of straw burning in rural area resulted heavy pollution, causing the ratio of PAHs contents between urban and rural areas less than 1 (Fig. 1). The comparison of atmospheric PAHs concentrations among Taiyuan and other regions are presented in Supporting Material (S.3, Table S12). For rural area, the concentration of gas phase PAHs in Taiyuan was much higher than that in Birmingham, UK in the summer, and in Toronto, Canada in all seasons (S.3, Table S12); the particulate phase PAHs level in Taiyuan was higher than that in Beijing, which is a highly polluted city in China, in all seasons except winter, and was much higher than that in Kuala Lumpur, Malaysia in the whole year, and in both Birmingham, UK and Massachusetts, USA in the summer whereas in the winter was lower than that in Tianjin, which is also a heavily polluted industrial city in China (S.3, Table S12); the concentration of total PAHs (gas þ particulate phase) in Taiyuan was much higher than that in Birmingham, UK in the summer, and in New Jersey, USA in the whole year whereas was lower than that in North China Plain in the whole year, which is a highly contaminated region including Beijing and Tianjin (S.3, Table S12). For urban area, the concentration of gas phase PAHs in Taiyuan was higher than that in Seoul, Korea in the whole year, and in Birmingham, UK in the summer, and in Toronto, Canada in all seasons whereas was lower than that in Birmingham, UK in the winter (S.3, Table S12); the particulate phase PAHs level in Taiyuan was higher than that in Beijing, China in the spring, summer and autumn, and was much higher than that in Qingdao, China in all seasons, and in both Hong Kong, China and Birmingham, UK in the summer and winter, and in both Seoul, Korea and Kuala Lumpur, Malaysia in the whole year, and in Massachusetts, USA in the summer, and in São Paulo, Brazil in the winter whereas was lower than that in both Beijing and Tianjin in the winter (S.3, Table S12); the concentration of total PAHs (gas þ particulate phase) in Taiyuan was much higher than that in both Seoul, Korea and New Jersey, USA in the whole year, and in Birmingham, UK in the summer and winter whereas was lower than that in North China Plain in the whole year (S.3, Table S12). Overall, Taiyuan was heavily PAHs contaminated compared with other regions in the word, and the possible reasons might be the high intensity of pollutant emission, special geographical location and adverse weather conditions (Zhang et al., 2009; Xia et al., 2010).
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3.2. Daily inhalation exposure to PAHs The cumulative probability distributions of the calculated inhalation exposure to PAHs for population groups of Taiyuan are depicted in Fig. 2 and in S.6, Fig. S3. In the spring, the median B[a] Peq concentrations of inhalation exposure were estimated to be in the range of 40.8e121.5 ng/d for different population groups (Fig. 2; S.6, Fig. S3); and that were found to be in the range of 81.7e265 ng/ d in the summereautumn (Fig. 2; S.6, Fig. S3); and were in the range of 150e518 ng/d in the winter (Fig. 2; S.6, Fig. S3); and were in the range of 104e347 ng/d in the whole year (Fig. 2; S.6, Fig. S3). According to the season, the ranking of exposure in decreasing order was: winter, summereautumn and spring in both rural and urban areas (Fig. 2; S.6, Fig. S3), which was in accordance with the ranking of geometric mean of atmospheric B[a]Peq. In all seasons, the inhalation exposure for each population group was larger in urban than in rural area (Fig. 2; S.6, Fig. S3) for the reason that geometric mean of atmospheric B[a]Peq in urban area was greater. In the same season and area, with respect to the age, the ranking of exposure in decreasing order was: adults, adolescents, seniors and children for both males and females (Fig. 2; S.6, Fig. S3), which was consistent with the ranking of inhalation rate for different age groups (S4, Table S13). According to gender, males showed higher exposure dose than females in all age groups for the same season and area (Fig. 2; S.6, Fig. S3) due to the fact that inhalation rate of males were larger than females (S4, Table S13). However, if we considered the exposure time of adult females spent in the kitchen, the female adults might show higher exposure dose than male adults due to the emissions of PAHs from cooking oil and food and
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the PAHs from wood and coal burning (Yoon et al., 2007; Zhang et al., 2009) in urban and especially in rural area. As we assume that the daily exposure time for the population in Taiyuan were one day (S.4) whereas most of population may be not in outdoor in whole day, the ambient exposure might be smaller than the calculated results. Reports concerning PAHs inhalation exposure are rather limited. In Tianjin, China, the average values of daily B[a]Peq exposure doses for urban children and adults in the outdoor settings were estimated to be 322 and 519 ng/d, respectively (Bai et al., 2009) whereas that for the two age groups in urban area of Taiyuan were 246 and 462 ng/d, respectively (Fig. 2; S.6, Fig. S3). The main reason for the higher exposure dose in Tianjin was that the B[a]Peq concentrations in the autumn and winter, which was surely much higher than in the spring and summer, was adopted as the annual average in the calculation of exposure (Bai et al., 2009), whereas the calculation of exposure in Taiyuan was based on the average B[a]Peq concentrations of spring, summereautumn and winter. In Taiwan, the median B[a]Peq concentration of inhalation exposure to environmental PAHs were estimated to be 1590 and 1628 ng/d for children and adults, respectively (Chen and Liao, 2006). Far higher exposure dose in Taiwan was probably due to two reasons. Firstly, the samples were collected from pollution sources of traffic, industrial and rural areas in Taiwan, whereas those were not collected from pollution sources in Taiyuan. The pollution sources in Taiwan was heavily polluted by PAHs, with the median values of total PAHs and B[a]Peq at traffic settings being 10611 and 159 ng/m3, respectively (Chen and Liao, 2006). Secondly, the BaPeq values were calculated based on 21 compounds in Taiwan (Chen and Liao,
Fig. 2. Probability distributions of daily inhalation B[a]Peq exposure for population groups in Taiyuan. A: rural male adults; B: rural female adults; C: urban male adults; D: urban female adults.
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2006), whereas that were calculated based on 15 compounds in Taiyuan, lacking CYC, BeP, NAP, PER, COR, BbC. 3.3. Lung cancer risk assessment According to the USEPA (1980), a one in a million chance of additional human cancer over a 70 year lifetime (ILCR ¼ 106) is the level of risk considered acceptable or inconsequential, since this compares favorably with risk levels from some ‘normal’ human activities such as diagnostic X-rays, fishing, etc (Asante-Duah, 2002); whereas additional lifetime cancer risk of one in ten thousand or greater (ILCR ¼ 104) is considered serious, and there is high priority for paying attention to such health problem. The cumulative probability distributions of the calculated ILCR for population groups in Taiyuan are presented in Fig. 3 and in S.7, Fig. S4. In the spring, the median values of ILCR were estimated to be in the range of 7.52 108e6.79 107 for different population groups (Fig. 3; S.7, Fig. S4); and that for the above groups were in the range of 3.17 107e3.31 106 in the summere autumn (Fig. 3; S.7, Fig. S4); and were in the range of 5.41 107e5.89 106 in the winter (Fig. 3; S.7, Fig. S4); and were in the range of 9.80 107e1.03 105 in the whole year (Fig. 3; S.7, Fig. S4). For whole year inhalation exposure to PAHs, ILCR values at the 42.3th, 41.4th, 50.6th, 50.0th, 8.12th, 8.98th, 50.6th and 48.9th percentile for boys, girls, male adolescents, female adolescents, male adults, female adults, male seniors and female seniors, respectively, were larger than 106 in rural area (Fig. 3; S.7, Fig. S4) whereas that in urban area were larger than 106 at the 23.9th,
23.4th, 33.8th, 33.1th, 1.42th, 1.60th, 33.0th and 31.4th percentile for the above groups, respectively (Fig. 3; S.7, Fig. S4), indicating high potential carcinogenic risk. Therefore it is necessary to take appropriate measures to control the lung cancer risk due to respiratory PAHs exposure in Taiyuan. With respect to the season, the ranking of ILCR in decreasing order was: winter, summer-autumn and spring in both rural and urban areas (Fig. 3; S.7, Fig. S4), which was consistent with the ranking of exposure (Fig. 2; S.6, Fig. S3). In all seasons, the ILCR for each population group was larger in urban than in rural area (Fig. 3; S.7, Fig. S4) due to the fact that the exposures dose was larger in urban area (Fig. 2; S.6, Fig. S3). In the same season and area, according to the age, the ranking of ILCR in decreasing order basically was: adults, children, seniors and adolescent for both males and females (Fig. 3; S.7, Fig. S4), which was not consistent with the ranking of exposure (Fig. 2; S.6, Fig. S3). Although the inhalation exposure of children was less than that of both adolescents and seniors (Fig. 2; S.6, Fig. S3), the body weight of children was much lower (S.5, Table S14), resulting in higher ILCR value (Fig. 3; S.7, Fig. S4). Other reports also found that children were a population group sensitive to the health risks of pollutants (Martí-Cid et al., 2008) and their health issues should be paid more attention. Although the inhalation exposure of seniors was less than that of adolescents (Fig. 2; S.6, Fig. S3), the exposure duration of seniors was greater, resulting in higher ILCR value in most cases (Fig. 3; S.7, Fig. S4). In the same season and area, according to gender, females showed a little higher ILCR values than males in all age groups except adults (Fig. 3; S.7, Fig. S4), which was not in accordance with exposure results (Fig. 2; S.6, Fig. S3). Although the
Fig. 3. Cumulative probability of respiratory incremental lifetime cancer risk for population groups in Taiyuan. A: rural male adults; B: rural female adults; C: urban male adults; D: urban female adults.
Z. Xia et al. / Environmental Pollution 173 (2013) 150e156
exposure of females was less than that of males (Fig. 2; S.6, Fig. S3), the body weight of females was much lower (S.5, Table S14), resulting in higher ILCR value (Fig. 3; S.7, Fig. S4). Researches on lung cancer risk assessment for PAHs are quite limited. The median value of ILCR for general urban citizens in Tianjin was estimated to be 2.2 104 (Bai et al., 2009), being higher than that in Taiyuan (1.51 105) (Fig. 3; S.7, Fig. S4) owing to larger inhalation exposure in Tianjin (Bai et al., 2009), and the reason for larger exposure dose in Tianjin was analyzed in Section 3.2. The geometric mean of inhalation ILCRs for children and adults in Taiwan were 6.47 106 and 1.04 104, respectively (Chen and Liao, 2006) whereas that for the two age groups in Taiyuan were 1.74 106 and 7.95 106, respectively (Fig. 3; S.7, Fig. S4). The ILCR values in Taiwan were higher than that in Taiyuan for the same reason of larger exposure dose, and the reasons for higher exposure dose in Taiwan was also analyzed in Section 3.2. An Euler atmospheric transport model was applied to evaluate lung cancer risk for the Chinese population caused by inhalation exposure to PAHs based on a high-resolution emission inventory (Zhang et al., 2009). The arithmetic mean value of ILCR in 2003 for general residents was 6.5 106 in China and was larger than 1.79 104 in Shanxi Province (Zhang et al., 2009) whereas that in Taiyuan for the year of 2009e2010 was 2.58 105 (Fig. 3; S.7, Fig. S4), indicating that the lung cancer risk for residents in Taiyuan was much higher than the average level in China. A large number of small-scale coke ovens have been closed under the Coal Law since 2004 in Shanxi Province resulting sharp drop of PAHs concentration, and this might be the reason for much lower ILCR in Taiyuan in 2009e2010 compared to that in Shanxi Province in 2003. 3.4. Sensitivity analysis The sensitivity analysis results on the ILCR for population groups in Taiyuan are depicted in the form of the percentile contribution to variance (Fig. 4; S.8, Fig. S5). The two most influential variables that contributed most to the total variance of risk for all population groups were the same: the daily inhalation exposure level (E) and the cancer slope factor for BaP inhalation exposure (SF) (Fig. 4; S.8, Fig. S5). Average contributions for E and SF counted about 72% and 37%, respectively, whereas body weight (BW) only contributed 9% on average (Fig. 4; S.8, Fig. S5). Other researches also found that cancer slope factor of BaP and daily PAH exposure level were the most important factors in health risk assessment (Chen and Liao, 2006). So based on the sensitivity results, we can improve the accuracy of the risk assessment by improving the accuracy of E and SF, especially the accuracy of E.
Fig. 4. Sensitivity analysis results on respiratory incremental lifetime cancer risk assessment for adults in Taiyuan.
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4. Conclusions The Pollution level of ambient PAHs in Taiyuan was serious, with the annual average concentrations of BaPeq being larger than both the Chinese national standard and the WHO guideline. The concentration of PAHs showed seasonal variation, with the pollution level in winter being more serious than in other seasons. There were high potential lung cancer risks for population in Taiyuan owing to the inhalation exposure of PAHs. The ILCR values was higher in winter than in other seasons, in urban than in rural area, for adults than for other age groups, and for females than for males. The daily inhalation exposure level and the cancer slope factor for BaP inhalation exposure had the greater impact than body weight on the ILCR. Acknowledgments This study was jointly supported by the Ministry of Chinese Environmental Protection (200809101), National Natural Science Foundation of China (40730737 and 41001344), National Basic Research Program of China (2007CB407301), Priority Academic Program Development of Jiangsu Higher Education Institutions funded project (164320H101), Scientific Research Foundation of the High-level Personnel of Nanjing Normal University (2012105XGQ0102) and China Postdoctoral Science Foundation funded project (20090460128 and 201003002). Appendix A. Supplementary material Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.envpol.2012.10.009. References Allen, J.O., Dookeran, N.M., Smith, K.A., Sarofim, A.D., Taghizadeh, K., Lafleur, A.L., 1996. Measurement of polycyclic aromatic hydrocarbons associated with sizesegregated atmospheric aerosols in Massachusetts. Environmental Science and Technology 30, 1023e1031. Asante-Duah, K., 2002. Public Health Risk Assessment for Human Exposure to Chemicals. Kluwer, Netherlands. Bai, Z.P., Hu, Y.D., Yu, H., Wu, N., You, Y., 2009. Quantitative health risk assessment of inhalation exposure to polycyclic aromatic hydrocarbons on citizens in Tianjin, China. Bulletin of Environmental Contamination and Toxicology 83, 151e154. Chen, S., Liao, C., 2006. Health risk assessment on human exposed to environmental polycyclic aromatic hydrocarbons pollution sources. Science of the Total Environment 366 (1), 112e123. Deutsch-Wenzel, R.P., Brune, H., Grimmer, G., Dettbarn, G., Misfeld, J., 1983. Experimental studies in rat lungs on the carcinogenicity and dose-response relationships of eight frequently occurring environmental polycyclic aromatic hydrocarbons. Journal of the National Cancer Institute 71, 539e544. Gigliotti, C.L., Totten, L.A., Offenberg, J.H., Dachs, J., Reinfelder, J.R., Nelson, E.D., Glenn IV, T.R., Eisenreich, S.J., 2005. Atmospheric concentrations and deposition of polycyclic aromatic hydrocarbons to the Mid-Atlantic east coast region. Environmental Science and Technology 39, 5550e5559. Jiang, J.M., Liu, B.Q., Nasca, P.C., Chen, J.S., Zeng, X.P., Wu, Y.P., Zou, X.L., Zhao, P., Li, J.Y., 2008. Age-related effects of smoking on lung cancer mortality: a nationwide case-control comparison in 103 population centers in China. Annals of Epidemiology 18 (6), 484e491. Liu, S.Z., Tao, S., Liu, W.X., Dou, H., Liu, Y.N., Zhao, J.Y., Little, M.G., Tian, Z.F., Wang, J.F., Wang, L.G., Gao, Y., 2008. Seasonal and spatial occurrence and distribution of atmospheric polycyclic aromatic hydrocarbons in rural and urban areas of the North Chinese plain. Environmental Pollution 156, 651e656. Martí-Cid, R., Llobet, J.M., Castell, V., Domingo, J.L., 2008. Evolution of the dietary exposure to polycyclic aromatic hydrocarbons in Catalonia, Spain. Food and Chemical Toxicology 46, 3163e3171. McGrath, T.E., Wooten, J.B., Geoffrey, C.W., Hajaligol, M.R., 2007. Formation of polycyclic aromatic hydrocarbons from tobacco: the link between low temperature residual solid (char) and PAH formation. Food Chemistry and Toxicology 45, 1039e1050. Motelay-Massei, A., Harner, T., Shoeib, M., Diamond, M., Stern, G., Rosenberg, B., 2005. Using passive air samplers to assess urbanerural trends for persistent organic pollutants and polycyclic aromatic hydrocarbons. 2. Seasonal trends for
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PAHs, PCBs, and organochlorine pesticides. Environmental Science and Technology 39, 5763e5773. Okona-Mensah, K.B., Battershill, J., Boobis, A., Fielder, R., 2005. An approach to investigating the importance of high potency polycyclic aromatic hydrocarbons(PAHs) in the induction of lung cancer by air pollution. Food and Chemical Toxicology 43, 1103e1116. Ravindra, K., Sokhi, R., Grieken, R.V., 2008. Atmospheric polycyclic aromatic hydrocarbons: source attribution, emission factors, and regulation. Atmospheric Environment 42, 2895e2921. Smith, D.J.T., Harrison, R.M., 1996. Concentrations, trends and vehicle source profile of polynuclear aromatic hydrocarbons in the U.K. atmosphere. Atmospheric Environment 30 (14), 2513e2525. Tao, S., Cao, J., Wang, W.T., Zhao, J. i. Y., Wang, W., Wang, Z.H., Cao, H.Y., Xing, B.S., 2009. A passive sampler with improved performance for collecting gaseous and particulate phase polycyclic aromatic hydrocarbons in air. Environmental Science & Technology 43, 4124e4129. Xia, Z.H., Duan, X.L., Qiu, W.X., Liu, D., Wang, B., Tao, S., Jiang, Q.J., Lu, B., Song, Y.X., Hu, X.X., 2010. Health risk assessment on dietary exposure to polycyclic aromatic hydrocarbons (PAHs) in Taiyuan, China. Science of the Total Environment 408, 5331e5337.
Yoon, E., Park, K., Lee, H., Yang, J.H., Lee, C., 2007. Estimation of excess cancer risk on time-weighted lifetime average daily intake of PAHs from food ingestion. Human and Ecological Risk Assessment 13 (3), 669e680. Zhang, Y.X., Dou, H., Chang, B., Wei, Z.C., Qiu, W.X., Liu, S.Z., Liu, W.X., Tao, S., 2008. Emission of polycyclic aromatic hydrocarbons from indoor straw burning and emission inventory updating in China. Annals of the New York Academy of Sciences 1140, 218e227. Zhang, Y.X., Tao, S., Cao, J., Coveney, R.M., 2007. Emission of polycyclic aromatic hydrocarbons in China by county. Environment Science & Technology 41, 683e687. Zhang, Y.X., Tao, S., Shen, H.Z., Ma, J.M., 2009. Inhalation exposure to ambient polycyclic aromatic hydrocarbons and lung cancer risk of Chinese population. Proceedings of the National Academy of Sciences of the United States of America 106 (50), 21063e21067. Zhou, J.B., Wang, T.G., Huang, Y.B., Mao, T., Zhong, N.N., 2005. Size distribution of polycyclic aromatic hydrocarbons in urban and suburban sites of Beijing, China. Chemosphere 61, 792e799. Indoor Air Quality Standards (GB/T 18883-2002, 2003-03-01), Ministry of Environmental Protection of China; http://www.zhb.gov.cn. USEPA Method 5 of 40 CFR Part 60; 1980. http://www.epa.gov/ttn/emc/methods/method5.html.
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Pollution level, inhalation exposure and lung cancer risk of ambient atmospheric polycyclic aromatic hydrocarbons (PAHs) in Taiyuan, China Zhonghuan Xia a, b, *, Xiaoli Duan c, Shu Tao a, Weixun Qiu a, Di Liu a, Yilong Wang a, Siye Wei a, e, Bin Wang a, Qiujing Jiang d, Bin Lu d, Yunxue Song d, Xinxin Hu d a
Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China Department of Environmental Science and Engineering, School of Geography Science, Nanjing Normal University, Nanjing 210046, China Department of Environmental Pollution and Health, Chinese Academy of Environmental Sciences, Beijing 100012, China d Taiyuan Environment Science Research and Design Institute, Taiyuan 030024, China e College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 June 2012 Received in revised form 24 September 2012 Accepted 16 October 2012
Passive air samplers were deployed to collect both gas and particulate phase polycyclic aromatic hydrocarbons in Taiyuan between 2009 and 2010. Annual average concentrations of BaP equivalent concentration (B[a]Peq) in background, rural and urban areas were 2.90 0.29, 23.2 30.8 and 27.4 28.1 ng/m3, respectively, with higher concentration in the winter than in other seasons. The median B[a]Peq concentrations of annual inhalation exposure were estimated to be in the range of 103e347 ng/d for all population groups in rural as well as in urban areas. The median values of incremental lifetime cancer risk (ILCR) induced by whole year inhalation exposure for all groups were basically larger than 106, with higher values in winter than in other seasons and in urban than in rural area. In the same season and area, the ILCR of adults was larger than other age groups and that of females was a little higher than males. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Polycyclic aromatic hydrocarbons Pollution level Inhalation exposure Lung cancer risk Taiyuan
1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are a group of fusedring aromatic compounds that are formed during the incomplete combustion of organic material (McGrath et al., 2007). PAHs have generated considerable interest ever since they were recognized as a carcinogenic class of compounds in the late twenties (Okona-Mensah et al., 2005). Several individual PAHs such as benzo(a)pyrene (BaP), chrysene (CHR), indeno(1,2,3- c,d)pyrene (IcdP) and benzo(b)fluoranthene (BbF) have produced carcinogenic, mutagenic, and genotoxic effects in animal experiments (DeutschWenzel et al., 1983). In recent years, environmental PAH concentrations have increased in many industrialized and developing countries. In China, the PAHs emissions contributed over 20% of the total global PAH emissions in 2004 (Zhang et al., 2008) and the high emissions have resulted in heavy contamination of various environmental media, especially ambient air (Zhang et al., 2007). Lung cancer has been ranked as the fourth and fifth leading causes of cancer death
* Corresponding author. E-mail address: [email protected] (Z. Xia). 0269-7491/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.envpol.2012.10.009
in Chinese males and females, respectively (Jiang et al., 2008) due to serious air pollution. Causes of human lung cancer have always been associated with the inhalation exposure to PAHs (Chen and Liao, 2006). Therefore, exposure and health risk assessment of atmospheric PAHs is very essential for effective environmental management (Asante-Duah, 2002). So far, researches concerning respiratory exposure and lung cancer risk assessment of PAHs are quite limited in China (Bai et al., 2009; Zhang et al., 2009). Taiyuan, the capital of Shanxi Province and an old industrial city, becomes one of the most polluted cities in China and PAHs may be a threat to the health of local residents (Zhang et al., 2009) mainly due to the high intensity of pollutant emission (Zhang et al., 2009). Thus, assessing the health risk level of citizens in Taiyuan associated with environmental exposure to PAHs is quite urgent. PAHs concentrations of foods consumed by local residents in Taiyuan were monitored in 2008 and the incremental lifetime cancer risks (ILCRs) were found to be larger than 104 at the 74.5th, 78.7th, 60.6th, 77.4th, 75.3th, 79.5th, 60.8th and 77.9th percentile for children, adolescents, adults and seniors of male as well as the above groups of female, respectively (Xia et al., 2010), implying significant dietary cancer risk. However, lung cancer risk level induced by inhalation exposure to atmospheric PAHs for citizens in Taiyuan is currently unavailable.
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The objective of this study is to determine the pollution level, quantify the inhalation exposure and further score the incremental lifetime cancer risk for citizens in Taiyuan, investigating the changes in both exposure and risk for different seasons, areas and population groups. To determine the overall uncertainty in predicted risks, the uncertainty resulting from the assessment of exposure was propagated through the risk characterization process using the Monte Carlo simulation. Moreover, a detailed sensitivity analysis was conducted to identify the input variables that were critical to the accuracy of the risk assessment. 2. Materials and methods 2.1. Sampling Passive air samplers with PUF disk and glass fiber filter (GFF) were used to collect PAHs in the gas and particulate phases, respectively. Detailed calibration method and uptake rates of this sampler were described previously (Tao et al., 2009). Volume concentrations of PAHs were calculated based on calibration equations derived in Supporting Material (S.2, Equation S1 and S2). Passive air samplers were deployed at 25 background, rural and urban sites in Taiyuan, the capital of Shanxi Province and an old industrial city in China (S.1, Fig. S1 and Table S1), in the spring, summer-autumn and winter between 2009 and 2010. The sampling periods were 70, 155 and 140 days for spring, summereautumn, and winter, respectively, and the sampling period in the winter included the residential heating time. Two identical samplers were deployed at each site on rooftops or open areas to avoid airflow obstruction (1.5e20 m heights). Detailed information on atmospheric sampling sites was presented in Supporting Material (S.1, Table S1). After sampling, all PUF disks were stored at 18 C. GFFs were equilibrated in a desiccator (25 C) for 24 h and weighed before and after the sampling, in accordance with USEPA Method (1980). Before sampling, the PUF disks were cleaned by extracting them in a Soxhlet with a 1:1 mixture of n-hexane and acetone for 8 h and the GFFs were cleaned by baking them in a furnace at 450 C for 4 h. 2.2. Analytical procedure PUF disks were Soxhlet extracted with150 ml 1:1 mixture of n-hexane and acetone at 52 C for 8 h. GFFs were subjected to microwave extraction (MARS2Xpress, CEM, USA) with 25 ml 1:1 mixture of n-hexane and acetone, being heated to 100 C at 10 C/min and then held for 10 min. After concentration with a vacuum rotary evaporator (R-201, Shanghai, China) at 37 C, total extracts were transferred to the alumina silica gel column for purification. The eluted mixture from the column during cleanup was first concentrated to near dryness. The residue was then transferred and diluted with n-hexane and brought to exactly 1.0 ml by nitrogen blowdown (Eyela MG-1000) at room temperature (25 C). The samples were sealed in vials and stored at 4 C before analysis. Quantitative analysis of the air sample extracts was done by gas chromatography with mass spectrometer detector (Agilent 6890GC/5973MSD). A 30 m 0.25 mm i.d. 0.25 mm film thickness HP-5MS capillary column (Agilent Technology) was used. GC temperature was programmed from an initial 60 C before commencing at 5 C/min up to 280 C, with a final holding time of 20 min. Helium was used as the carrier gas. A 1.0 ml aliquot of the extract was injected while the injector port was held at 280 C and operated in splitless mode at a flow rate of 1.0 ml/min. The head column pressure was 30 kPa. The mass spectrometer was operated in scan mode with an electron impact ionization of 70 eV, an electron multiplier voltage of 1288 V, and an ion source of 230 C. Concentrations were determined for 15 PAHs in all samples. They were acenaphthene (ACE), acenaphthylene (ACY), fluorine (FLO), phenanthrene (PHE), anthracene (ANT), fluoranthene (FLA), pyrene (PYR), benz(a)anthracene (BaA), chrysene (CHR), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), dibenz(a,h)anthracene (DahA), indeno(1,2,3-cd)pyrene (IcdP) and benzo(g,h,i)perylene (BghiP). 2.3. Quality control Quantification was performed by the internal standard method using 2-fluoro1,10 -biphenyl and p-terphenyl-d14 (2.0 mg/ml; J&K Chemical, Beijing, China). All solvents used were analytical grade (Beijing Chemical Reagent, Beijing, China) and purified by distillation prior to use. Alumina and silica gel (80e200 mesh; Dikma, China) were heated at 650 C in a muffle furnace (DLII-9, Beijing, China) for 10 h, kept in a sealed desiccator, and reactivated at 130 C for 4 h immediately prior to use. All glassware was cleaned using an ultrasonic cleaner (KQ-500B, Kunshan, China) and heated to 400 C for 6 h. The field and laboratory blanks were analyzed, and the concentration of target PAHs in the field blanks were higher than laboratory blanks and more than one order of magnitude lower than real samples for both PUF disks and GFFs. All the results of air samples were field blank corrected. Recovery of individual PAHs ranged from 78% to 103% with a mean value of 89% for PUF disks, whereas that varied from
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80% to 101% with a mean value of 88% for GFFs. Data analyzed in the article were not corrected for recoveries. The detection limits were in the range of 0.172e1.23 ng/ml. 2.4. Inhalation exposure estimates The carcinogenic risk of a PAHs mixture is often expressed by its BaP equivalent concentration (B[a]Peq). The B[a]Peq of atmospheric PAHs (BEC) was calculated according to Equation (1): BEC ¼
n X
Ci TEFi
(1)
i¼1
where Ci ¼ concentration of PAH congener i; TEFi ¼ the toxicity equivalency factor (TEF) of PAH congener i (S.3, Table S2). For individual PAH concentration, when a result was below the limit of detection (LOD), the value was assumed to be half of the respective LOD. The carcinogenic potencies of 15 PAHs were estimated as the sum of each individual B[a]Peq. We treated C, which followed lognormal distribution, in Equation (1) probabilistically. Taiyuan consists of background, rural and urban areas. There are no citizens living in background area. In both rural and urban areas, the citizens were divided into eight population groups according to the age and gender: children (4e10 years), adolescents (11e17 years), adults (18e60 years), and seniors (61e70 years) of male as well as the above groups of female. Daily inhalation exposure level (E) for each population group was calculated as follows: E ¼
n X
BECi IR Ti
(2)
i¼1
where Ti ¼ daily exposure time span in the ith area (S4); BECi ¼ B[a]Peq in the ith area (ng/m3); IR ¼ inhalation rate (m3/day) (S4, Table S13). We treated BEC and IR, which followed lognormal and normal distribution, respectively, in Equation (2) probabilistically. Detailed information on inhalation exposure calculation was presented in Supporting Material (S4). 2.5. Cancer risk estimates The incremental lifetime cancer risk (ILCR) of population groups in Taiyuan caused by PAHs inhalation exposure was calculated based on Equation (3). ILCR ¼ SF E EF ED CF=ðBW ATÞ
(3)
where ILCR ¼ the incremental lifetime cancer risk of the inhalation exposure (dimensionless); SF ¼ the cancer slope factor for BaP inhalation exposure [a lognormal distribution with a geometric mean of 3.14 (mg kg1 day1)1 and a geometric standard deviation of 1.80](Chen and Liao, 2006); E ¼ the daily inhalation exposure level (ng/d); EF ¼ the exposure frequency (day/year) (S.5); CF ¼ conversion factor (106 mg/ng); BW ¼ body weight (kg) (S.5, Table S13); AT ¼ average lifespan for carcinogens (25550 day). We treated SF E and BW, which obeyed lognormal, lognormal and normal distribution, respectively, in Equation (3) probabilistically. Detailed information on cancer risk calculation was presented in Supporting Material (S.5). 2.6. Uncertainty analysis A Monte Carlo simulation using matlab6.5 software was implemented to deal with the uncertainties in the risk assessment in this study. We performed independent runs at 1000, 3000, 5000, and 10,000 iterations with each parameter sampled independently from the appropriate distribution at the start to test the convergence and the stability of the numerical output. The result showed that 5000 iterations are sufficient to ensure the stability of results. As the results manifested the effects of uncertainty in the input parameter statistics on the estimation, sensitivity analysis using matlab6.5 software could be done to find the variables that affect the risk most. Rank correlation coefficients between each input variable and the output (risk) were calculated, and then by squaring the output variance and normalizing it to 100%, the contribution of each input variable to the output (risk) variance was assessed, and the sensitivity of each input variable relative to one another was evaluated.
3. Results and discussion 3.1. Pollution level of atmospheric PAHs Atmospheric concentrations (particulate þ gas phase) of PAHs in Taiyuan are shown in Fig. 1 and the detailed results are presented in Supporting Material (S.3, Table S3eS11). In background area, the concentrations (particulate þ gas phase) of total 15 PAHs and BaPeq were in the range of 57.5 5.32e73.6 2.22 and
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Fig. 1. Atmospheric concentrations (particulate þ gas phase) of PAHs. A: total 15 PAHs; B: BaPeq. The data are presented as arithmetic means plus arithmetic standard deviations.
1.13 0.08e5.69 0.30 ng/m3, respectively, in different seasons and the whole year (Fig. 1). In rural area, the both phase concentrations of total 15 PAHs and BaPeq were in the range of 164 149e232 237 and 19.3 27.4e29.3 33.7 ng/m3, respectively, whereas that in urban area were in the range of 176 93e253 167 and 14.0 16.8e40.5 46.4 ng/m3, respectively, for the above periods (Fig. 1). In each season, the concentrations of BaPeq in both rural and urban areas were larger than 2.5 ng/m3, the Chinese national standard. In background area, the BaPeq were less than 2.5 ng/m3 in the spring and summereautumn but greater than 2.5 ng/m3 in both the winter and the whole year, and were larger than 1 ng/m3, the WHO guideline (Ravindra et al., 2008) for each season, indicating serious air pollution in Taiyuan (Fig. 1). According to the season, the ranking of both 15 PAHs and BaPeq in decreasing order was: winter, spring and summereautumn in background area, whereas that in urban area was: winter, summereautumn and spring (Fig. 1). In rural area, with respect to the season, the ranking of 15 PAHs in decreasing order was: spring, winter and summere autumn, while that of BaPeq in decreasing order was: winter, spring and summereautumn (Fig. 1). The fact that concentration of PAHs was basically higher in the winter than in other seasons was also reported by other researches (Zhou et al., 2005) and the possible reason might be the residential heating resulting more biomass and domestic coal combustion as well as the unfavorable atmospheric diffusion and degradation conditions during the
winter (Liu et al., 2008). In rural area, the total 15 PAHs in the spring was a litter higher than that in the winter (Fig. 1) due to a large number of straw burning in this season. According to the region, the ranking of both 15 PAHs and BaPeq in decreasing order for all seasons except spring was: urban, rural and background area (Fig. 1), which was consistent with other reports (Gigliotti et al., 2005; Liu et al., 2008). The ratio between PAHs concentrations in urban and rural areas was w1.05 (209 ng/m3 in urban, 199 ng/m3 in rural) in Taiyuan (Fig. 1), which was close to the ratio in North China Plain (1.23) (870 ng/m3 in urban, 710 ng/m3 in rural) (Liu et al., 2008), but much lower than that in Europe and America, such as Birmingham, UK (w4) (28.7 ng/m3 in urban, 6.88 ng/m3 in rural) (Smith and Harrison, 1996), New Jersey, USA (w7) (17.0 ng/m3 in urban, 2.54 ng/m3 in rural) (Gigliotti et al., 2005), Massachusetts, USA (w46) (47.2 ng/m3 in urban, 1.03 ng/ m3 in rural) (Allen et al., 1996) and Toronto, Canada (w3) (26.5 ng/ m3 in urban, 7.91 ng/m3 in rural) (Motelay-Massei et al., 2005). In both Taiyuan and North China Plain, the low efficient practices in biomass and coal combustion in rural area resulted in higher PAHs emission than coal combustion and vehicle emission in urban area, and additionally centralized heating system and utilization of natural gas in urban area decreased the need for biomass or domestic coal burning, leading to much lower ratio of PAHs concentrations between urban and rural areas in comparison with that in Europe and America. In the spring, a lot of straw burning in rural area resulted heavy pollution, causing the ratio of PAHs contents between urban and rural areas less than 1 (Fig. 1). The comparison of atmospheric PAHs concentrations among Taiyuan and other regions are presented in Supporting Material (S.3, Table S12). For rural area, the concentration of gas phase PAHs in Taiyuan was much higher than that in Birmingham, UK in the summer, and in Toronto, Canada in all seasons (S.3, Table S12); the particulate phase PAHs level in Taiyuan was higher than that in Beijing, which is a highly polluted city in China, in all seasons except winter, and was much higher than that in Kuala Lumpur, Malaysia in the whole year, and in both Birmingham, UK and Massachusetts, USA in the summer whereas in the winter was lower than that in Tianjin, which is also a heavily polluted industrial city in China (S.3, Table S12); the concentration of total PAHs (gas þ particulate phase) in Taiyuan was much higher than that in Birmingham, UK in the summer, and in New Jersey, USA in the whole year whereas was lower than that in North China Plain in the whole year, which is a highly contaminated region including Beijing and Tianjin (S.3, Table S12). For urban area, the concentration of gas phase PAHs in Taiyuan was higher than that in Seoul, Korea in the whole year, and in Birmingham, UK in the summer, and in Toronto, Canada in all seasons whereas was lower than that in Birmingham, UK in the winter (S.3, Table S12); the particulate phase PAHs level in Taiyuan was higher than that in Beijing, China in the spring, summer and autumn, and was much higher than that in Qingdao, China in all seasons, and in both Hong Kong, China and Birmingham, UK in the summer and winter, and in both Seoul, Korea and Kuala Lumpur, Malaysia in the whole year, and in Massachusetts, USA in the summer, and in São Paulo, Brazil in the winter whereas was lower than that in both Beijing and Tianjin in the winter (S.3, Table S12); the concentration of total PAHs (gas þ particulate phase) in Taiyuan was much higher than that in both Seoul, Korea and New Jersey, USA in the whole year, and in Birmingham, UK in the summer and winter whereas was lower than that in North China Plain in the whole year (S.3, Table S12). Overall, Taiyuan was heavily PAHs contaminated compared with other regions in the word, and the possible reasons might be the high intensity of pollutant emission, special geographical location and adverse weather conditions (Zhang et al., 2009; Xia et al., 2010).
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3.2. Daily inhalation exposure to PAHs The cumulative probability distributions of the calculated inhalation exposure to PAHs for population groups of Taiyuan are depicted in Fig. 2 and in S.6, Fig. S3. In the spring, the median B[a] Peq concentrations of inhalation exposure were estimated to be in the range of 40.8e121.5 ng/d for different population groups (Fig. 2; S.6, Fig. S3); and that were found to be in the range of 81.7e265 ng/ d in the summereautumn (Fig. 2; S.6, Fig. S3); and were in the range of 150e518 ng/d in the winter (Fig. 2; S.6, Fig. S3); and were in the range of 104e347 ng/d in the whole year (Fig. 2; S.6, Fig. S3). According to the season, the ranking of exposure in decreasing order was: winter, summereautumn and spring in both rural and urban areas (Fig. 2; S.6, Fig. S3), which was in accordance with the ranking of geometric mean of atmospheric B[a]Peq. In all seasons, the inhalation exposure for each population group was larger in urban than in rural area (Fig. 2; S.6, Fig. S3) for the reason that geometric mean of atmospheric B[a]Peq in urban area was greater. In the same season and area, with respect to the age, the ranking of exposure in decreasing order was: adults, adolescents, seniors and children for both males and females (Fig. 2; S.6, Fig. S3), which was consistent with the ranking of inhalation rate for different age groups (S4, Table S13). According to gender, males showed higher exposure dose than females in all age groups for the same season and area (Fig. 2; S.6, Fig. S3) due to the fact that inhalation rate of males were larger than females (S4, Table S13). However, if we considered the exposure time of adult females spent in the kitchen, the female adults might show higher exposure dose than male adults due to the emissions of PAHs from cooking oil and food and
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the PAHs from wood and coal burning (Yoon et al., 2007; Zhang et al., 2009) in urban and especially in rural area. As we assume that the daily exposure time for the population in Taiyuan were one day (S.4) whereas most of population may be not in outdoor in whole day, the ambient exposure might be smaller than the calculated results. Reports concerning PAHs inhalation exposure are rather limited. In Tianjin, China, the average values of daily B[a]Peq exposure doses for urban children and adults in the outdoor settings were estimated to be 322 and 519 ng/d, respectively (Bai et al., 2009) whereas that for the two age groups in urban area of Taiyuan were 246 and 462 ng/d, respectively (Fig. 2; S.6, Fig. S3). The main reason for the higher exposure dose in Tianjin was that the B[a]Peq concentrations in the autumn and winter, which was surely much higher than in the spring and summer, was adopted as the annual average in the calculation of exposure (Bai et al., 2009), whereas the calculation of exposure in Taiyuan was based on the average B[a]Peq concentrations of spring, summereautumn and winter. In Taiwan, the median B[a]Peq concentration of inhalation exposure to environmental PAHs were estimated to be 1590 and 1628 ng/d for children and adults, respectively (Chen and Liao, 2006). Far higher exposure dose in Taiwan was probably due to two reasons. Firstly, the samples were collected from pollution sources of traffic, industrial and rural areas in Taiwan, whereas those were not collected from pollution sources in Taiyuan. The pollution sources in Taiwan was heavily polluted by PAHs, with the median values of total PAHs and B[a]Peq at traffic settings being 10611 and 159 ng/m3, respectively (Chen and Liao, 2006). Secondly, the BaPeq values were calculated based on 21 compounds in Taiwan (Chen and Liao,
Fig. 2. Probability distributions of daily inhalation B[a]Peq exposure for population groups in Taiyuan. A: rural male adults; B: rural female adults; C: urban male adults; D: urban female adults.
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2006), whereas that were calculated based on 15 compounds in Taiyuan, lacking CYC, BeP, NAP, PER, COR, BbC. 3.3. Lung cancer risk assessment According to the USEPA (1980), a one in a million chance of additional human cancer over a 70 year lifetime (ILCR ¼ 106) is the level of risk considered acceptable or inconsequential, since this compares favorably with risk levels from some ‘normal’ human activities such as diagnostic X-rays, fishing, etc (Asante-Duah, 2002); whereas additional lifetime cancer risk of one in ten thousand or greater (ILCR ¼ 104) is considered serious, and there is high priority for paying attention to such health problem. The cumulative probability distributions of the calculated ILCR for population groups in Taiyuan are presented in Fig. 3 and in S.7, Fig. S4. In the spring, the median values of ILCR were estimated to be in the range of 7.52 108e6.79 107 for different population groups (Fig. 3; S.7, Fig. S4); and that for the above groups were in the range of 3.17 107e3.31 106 in the summere autumn (Fig. 3; S.7, Fig. S4); and were in the range of 5.41 107e5.89 106 in the winter (Fig. 3; S.7, Fig. S4); and were in the range of 9.80 107e1.03 105 in the whole year (Fig. 3; S.7, Fig. S4). For whole year inhalation exposure to PAHs, ILCR values at the 42.3th, 41.4th, 50.6th, 50.0th, 8.12th, 8.98th, 50.6th and 48.9th percentile for boys, girls, male adolescents, female adolescents, male adults, female adults, male seniors and female seniors, respectively, were larger than 106 in rural area (Fig. 3; S.7, Fig. S4) whereas that in urban area were larger than 106 at the 23.9th,
23.4th, 33.8th, 33.1th, 1.42th, 1.60th, 33.0th and 31.4th percentile for the above groups, respectively (Fig. 3; S.7, Fig. S4), indicating high potential carcinogenic risk. Therefore it is necessary to take appropriate measures to control the lung cancer risk due to respiratory PAHs exposure in Taiyuan. With respect to the season, the ranking of ILCR in decreasing order was: winter, summer-autumn and spring in both rural and urban areas (Fig. 3; S.7, Fig. S4), which was consistent with the ranking of exposure (Fig. 2; S.6, Fig. S3). In all seasons, the ILCR for each population group was larger in urban than in rural area (Fig. 3; S.7, Fig. S4) due to the fact that the exposures dose was larger in urban area (Fig. 2; S.6, Fig. S3). In the same season and area, according to the age, the ranking of ILCR in decreasing order basically was: adults, children, seniors and adolescent for both males and females (Fig. 3; S.7, Fig. S4), which was not consistent with the ranking of exposure (Fig. 2; S.6, Fig. S3). Although the inhalation exposure of children was less than that of both adolescents and seniors (Fig. 2; S.6, Fig. S3), the body weight of children was much lower (S.5, Table S14), resulting in higher ILCR value (Fig. 3; S.7, Fig. S4). Other reports also found that children were a population group sensitive to the health risks of pollutants (Martí-Cid et al., 2008) and their health issues should be paid more attention. Although the inhalation exposure of seniors was less than that of adolescents (Fig. 2; S.6, Fig. S3), the exposure duration of seniors was greater, resulting in higher ILCR value in most cases (Fig. 3; S.7, Fig. S4). In the same season and area, according to gender, females showed a little higher ILCR values than males in all age groups except adults (Fig. 3; S.7, Fig. S4), which was not in accordance with exposure results (Fig. 2; S.6, Fig. S3). Although the
Fig. 3. Cumulative probability of respiratory incremental lifetime cancer risk for population groups in Taiyuan. A: rural male adults; B: rural female adults; C: urban male adults; D: urban female adults.
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exposure of females was less than that of males (Fig. 2; S.6, Fig. S3), the body weight of females was much lower (S.5, Table S14), resulting in higher ILCR value (Fig. 3; S.7, Fig. S4). Researches on lung cancer risk assessment for PAHs are quite limited. The median value of ILCR for general urban citizens in Tianjin was estimated to be 2.2 104 (Bai et al., 2009), being higher than that in Taiyuan (1.51 105) (Fig. 3; S.7, Fig. S4) owing to larger inhalation exposure in Tianjin (Bai et al., 2009), and the reason for larger exposure dose in Tianjin was analyzed in Section 3.2. The geometric mean of inhalation ILCRs for children and adults in Taiwan were 6.47 106 and 1.04 104, respectively (Chen and Liao, 2006) whereas that for the two age groups in Taiyuan were 1.74 106 and 7.95 106, respectively (Fig. 3; S.7, Fig. S4). The ILCR values in Taiwan were higher than that in Taiyuan for the same reason of larger exposure dose, and the reasons for higher exposure dose in Taiwan was also analyzed in Section 3.2. An Euler atmospheric transport model was applied to evaluate lung cancer risk for the Chinese population caused by inhalation exposure to PAHs based on a high-resolution emission inventory (Zhang et al., 2009). The arithmetic mean value of ILCR in 2003 for general residents was 6.5 106 in China and was larger than 1.79 104 in Shanxi Province (Zhang et al., 2009) whereas that in Taiyuan for the year of 2009e2010 was 2.58 105 (Fig. 3; S.7, Fig. S4), indicating that the lung cancer risk for residents in Taiyuan was much higher than the average level in China. A large number of small-scale coke ovens have been closed under the Coal Law since 2004 in Shanxi Province resulting sharp drop of PAHs concentration, and this might be the reason for much lower ILCR in Taiyuan in 2009e2010 compared to that in Shanxi Province in 2003. 3.4. Sensitivity analysis The sensitivity analysis results on the ILCR for population groups in Taiyuan are depicted in the form of the percentile contribution to variance (Fig. 4; S.8, Fig. S5). The two most influential variables that contributed most to the total variance of risk for all population groups were the same: the daily inhalation exposure level (E) and the cancer slope factor for BaP inhalation exposure (SF) (Fig. 4; S.8, Fig. S5). Average contributions for E and SF counted about 72% and 37%, respectively, whereas body weight (BW) only contributed 9% on average (Fig. 4; S.8, Fig. S5). Other researches also found that cancer slope factor of BaP and daily PAH exposure level were the most important factors in health risk assessment (Chen and Liao, 2006). So based on the sensitivity results, we can improve the accuracy of the risk assessment by improving the accuracy of E and SF, especially the accuracy of E.
Fig. 4. Sensitivity analysis results on respiratory incremental lifetime cancer risk assessment for adults in Taiyuan.
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4. Conclusions The Pollution level of ambient PAHs in Taiyuan was serious, with the annual average concentrations of BaPeq being larger than both the Chinese national standard and the WHO guideline. The concentration of PAHs showed seasonal variation, with the pollution level in winter being more serious than in other seasons. There were high potential lung cancer risks for population in Taiyuan owing to the inhalation exposure of PAHs. The ILCR values was higher in winter than in other seasons, in urban than in rural area, for adults than for other age groups, and for females than for males. The daily inhalation exposure level and the cancer slope factor for BaP inhalation exposure had the greater impact than body weight on the ILCR. Acknowledgments This study was jointly supported by the Ministry of Chinese Environmental Protection (200809101), National Natural Science Foundation of China (40730737 and 41001344), National Basic Research Program of China (2007CB407301), Priority Academic Program Development of Jiangsu Higher Education Institutions funded project (164320H101), Scientific Research Foundation of the High-level Personnel of Nanjing Normal University (2012105XGQ0102) and China Postdoctoral Science Foundation funded project (20090460128 and 201003002). Appendix A. Supplementary material Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.envpol.2012.10.009. References Allen, J.O., Dookeran, N.M., Smith, K.A., Sarofim, A.D., Taghizadeh, K., Lafleur, A.L., 1996. Measurement of polycyclic aromatic hydrocarbons associated with sizesegregated atmospheric aerosols in Massachusetts. Environmental Science and Technology 30, 1023e1031. Asante-Duah, K., 2002. Public Health Risk Assessment for Human Exposure to Chemicals. Kluwer, Netherlands. Bai, Z.P., Hu, Y.D., Yu, H., Wu, N., You, Y., 2009. Quantitative health risk assessment of inhalation exposure to polycyclic aromatic hydrocarbons on citizens in Tianjin, China. Bulletin of Environmental Contamination and Toxicology 83, 151e154. Chen, S., Liao, C., 2006. Health risk assessment on human exposed to environmental polycyclic aromatic hydrocarbons pollution sources. Science of the Total Environment 366 (1), 112e123. Deutsch-Wenzel, R.P., Brune, H., Grimmer, G., Dettbarn, G., Misfeld, J., 1983. Experimental studies in rat lungs on the carcinogenicity and dose-response relationships of eight frequently occurring environmental polycyclic aromatic hydrocarbons. Journal of the National Cancer Institute 71, 539e544. Gigliotti, C.L., Totten, L.A., Offenberg, J.H., Dachs, J., Reinfelder, J.R., Nelson, E.D., Glenn IV, T.R., Eisenreich, S.J., 2005. Atmospheric concentrations and deposition of polycyclic aromatic hydrocarbons to the Mid-Atlantic east coast region. Environmental Science and Technology 39, 5550e5559. Jiang, J.M., Liu, B.Q., Nasca, P.C., Chen, J.S., Zeng, X.P., Wu, Y.P., Zou, X.L., Zhao, P., Li, J.Y., 2008. Age-related effects of smoking on lung cancer mortality: a nationwide case-control comparison in 103 population centers in China. Annals of Epidemiology 18 (6), 484e491. Liu, S.Z., Tao, S., Liu, W.X., Dou, H., Liu, Y.N., Zhao, J.Y., Little, M.G., Tian, Z.F., Wang, J.F., Wang, L.G., Gao, Y., 2008. Seasonal and spatial occurrence and distribution of atmospheric polycyclic aromatic hydrocarbons in rural and urban areas of the North Chinese plain. Environmental Pollution 156, 651e656. Martí-Cid, R., Llobet, J.M., Castell, V., Domingo, J.L., 2008. Evolution of the dietary exposure to polycyclic aromatic hydrocarbons in Catalonia, Spain. Food and Chemical Toxicology 46, 3163e3171. McGrath, T.E., Wooten, J.B., Geoffrey, C.W., Hajaligol, M.R., 2007. Formation of polycyclic aromatic hydrocarbons from tobacco: the link between low temperature residual solid (char) and PAH formation. Food Chemistry and Toxicology 45, 1039e1050. Motelay-Massei, A., Harner, T., Shoeib, M., Diamond, M., Stern, G., Rosenberg, B., 2005. Using passive air samplers to assess urbanerural trends for persistent organic pollutants and polycyclic aromatic hydrocarbons. 2. Seasonal trends for
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