Chemosphere 112 (2014) 289–295
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Cancer risk of polycyclic aromatic hydrocarbons (PAHs) in the soils from Jiaozhou Bay wetland Wei Yang, Yinhai Lang ⇑, Guoliang Li Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100, China College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China
h i g h l i g h t s Cancer risks for three age groups were evaluated based on Monte Carlo simulation. Sensitivity analysis was conducted to find the influential factors. Cancer risks for three age groups were at acceptable range. BaP contribute most to the total cancer risk. Food ingestion was the major exposure pathway for carcinogenic risks.
a r t i c l e
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Article history: Received 22 January 2014 Received in revised form 16 April 2014 Accepted 23 April 2014
Handling Editor: Tamara S. Galloway Keywords: PAHs Cancer risk Monte Carlo simulation Sensitivity analysis
a b s t r a c t To estimate the cancer risk exposed to the PAHs in Jiaozhou Bay wetland soils, a probabilistic health risk assessment was conducted based on Monte Carlo simulations. A sensitivity analysis was performed to determine the input variables that contribute most to the cancer risk assessment. Three age groups were selected to estimate the cancer risk via four exposure pathways (soil ingestion, food ingestion, dermal contact and inhalation). The results revealed that the 95th percentiles cancer risks for children, teens and adults were 9.11 106, 1.04 105 and 7.08 105, respectively. The cancer risks for three age groups were at acceptable range (106–104), indicating no potential cancer risk. For different exposure pathways, food ingestion was the major exposure pathway. For 7 carcinogenic PAHs, the cancer risk caused by BaP was the highest. Sensitivity analysis demonstrated that the parameters of exposure duration (ED) and sum of converted 7 carcinogenic PAHs concentrations in soil based on BaPeq (CSsoil) contribute most to the total uncertainty. This study provides a comprehensive risk assessment on carcinogenic PAHs in Jiaozhou Bay wetland soils, and might be useful in providing potential strategies of cancer risk prevention and controlling. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds with two or more fused aromatic rings carbon and hydrogen atoms. PAHs are primarily formed by incomplete combustion or pyrolysis of organic matter (Man et al., 2013; Chen et al., 2013a). Due to their potential mutagenic, carcinogenic and teratogenic effects on human health, PAHs have attracted particular concern and 16 PAHs were listed as priority pollutant by the USEPA (2003). Seven of them including benz[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene ⇑ Corresponding author at: College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China. Tel./fax: +86 532 66786308. E-mail address: [email protected] (Y. Lang). http://dx.doi.org/10.1016/j.chemosphere.2014.04.074 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved.
(BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IND) and dibenz [a,h]anthracene (DBahA) are classified as carcinogenic PAHs by the International Agency for Research on Cancer (IARC, 2010). Soil system is a good indicator of environmental pollution. Due to their ubiquity and persistence nature, PAHs are prone to enrichment in soils and retain for a long time (Lang et al., 2012). PAHs in soil may lead to direct or indirect exposure to humans. Therefore, it is necessary to assess the potential adverse health risk of PAHs in soils to protect human health. Human health risk assessment was used to quantitatively estimate the health risk levels posed by specific chemicals, and have been successfully used (Wang et al., 2011, 2013; Chen et al., 2013b; Luo et al., 2013). In the health risk assessment, deterministic risk assessments based on a single value for the exposure parameter was widely adopted (Chen et al., 2013b; Luo et al., 2013; Man et al., 2013; Li et al.,
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2014). However, this approach does not take into account the variability in measurements and the heterogeneity in a population or exposure parameter (Li et al., 2014). Thus, probabilistic approaches based on Monte Carlo simulation were conducted (Hu et al., 2007; Chiang et al., 2009; Wu et al., 2011). Jiaozhou Bay wetland is the most important coastal wetland ecosystems in Shandong Peninsula, China. This wetland provides breading grounds for many types of fish and shellfish and a resting place for migratory birds (Gu et al., 2007). However, with the rapid development of industry, aquaculture and aquiculture, Jiaozhou Bay wetland is seriously affected by anthropogenic activities (Gu et al., 2007). Pyrolytic and petrogenic sources were the main sources for the PAHs in the area (Wang et al., 2006, 2010). And the cancer risk caused by PAHs in Jiaozhou Bay wetland soils has remained scarce. There is a need to assess the health risk of PAHs in Jiaozhou Bay wetland soils. The results of this research may be useful for the local government in pollution control, remediation and human health protection. 2. Materials and methods 2.1. Sample To evaluate the PAHs pollution levels, soil samples were collected from Jiaozhou Bay wetland (Fig. 1). Sixteen surface soil samples were collected using a stainless steel soil auger on December 2012. For each site, 2 samples were taken from 2 to 5 cm and collected with a polyethylene spatula and placed in self-sealing polyethylene bags. All samples were then preserved with ice and stored at 20 °C. The samples were freeze-dried in the laboratory, and then carefully homogenized in a mortar, sieved through 100-mesh stainless steel mesh, and stored at 4 °C in glass bottles prior to analysis. 2.2. Chemical analysis For soil PAH extraction and clean-up, n-hexane, dichloromethane and silica gel were used. The standards of 16 PAHs including naphthalene (Nap), acenaphthene (Ace), acenaphthylene (Acy), fluorene (Fle), 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), indeno[1,2,3-cd]pyrene (IND), dibenz[a,h]anthracene
(DBahA), and benzo[ghi]perylene (BghiP) were purchased from Supelco (Bellefonte, USA). Ultrasonic extraction of PAHs was performed according to the procedures described by Lang et al. (2012). Briefly, (2.0 g) freeze-dried and homogenized soils were weighed and extracted three times by ultrasonication (40 kHz) with 20 mL n-hexane/dichloromethane (1:1 v:v). A mixture of deuterated PAHs compounds (acenaphthene-d10, chrysene-d12, perylene-d12 and phenanthrene-d10) as recovery surrogate standards was added into all samples to monitor the procedures of sample extraction, cleanup, and analysis. The extracts were concentrated to 1.0 mL by rotary vacuum evaporation, and an alumina/silica gel column was implemented to clean-up the extracts. The PAHs fraction was eluted with 30.0 mL dichloromethane/n-hexane (3:7 v:v), and then concentrated up to 1 ml by rotary vacuum evaporator and further to exactly 1 mL under a gentle gas stream of purified nitrogen. PAHs composition analysis for 16 PAHs was performed on an Agilent GC (6890-N)/MSD (5975B) equipped with a fused-silica HP-5MS capillary column (30 m 0.25 mm 0.25 lm). High purity helium was used as the carrier gas at a constant flow of 1.2 ml min1. The temperature program of the oven was started at 50 °C (hold 2 min), ramped to 230 °C at 8 °C min1, then, further ramped to 300 °C at 3.5 °C min1, and held for 7 min. The sample was injected splitless with the injector temperature at 290 °C. The temperatures for the ion source and interface were set at 230 °C and 250 °C, respectively. The MSD was operated in the SIM mode and electron impact energy was set at 70 eV. 2.3. Quality assurance/quality control All analytical data were subject to strict quality control. The procedural blanks, spiked blanks, and sample duplicates were determined for quality assurance and control, and no interferences were detected in the procedure blanks. The aim of spiked blank was checked for recovery efficiencies by analyzing uncontaminated soil spiked with 16 PAHs standards. In the study, the spiked blank values for 16 PAHs were 100 ng g1 and the average recoveries ranged from 70% to 106%. The five-point external calibration method was applied in the sample analysis. The detection limit (DL) of 16 PAHs was estimated from a signal-to-noise ratio of 3:1 in blank samples, and ranged from 1.05 to 6.78 ng g1 (see Supplementary Table S1). Not detected or the values below DL were treated as half of DL when proceeding statistical analysis.
Fig. 1. Sampling sites of soils in Jiaozhou Bay wetland.
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2.4. Cancer risk assessment Cancer risk expresses the likelihood of occurring cancer as a result of exposure to the potential carcinogen (Li et al., 2014). In this study, the chronic daily intake of PAHs refers to the PAHs in soils accepted by the exposure terminal (i.e., respiratory organs of the human body) and is denoted by CDI. The CDI of PAHs in other medium was not considered given that this study only focuses on the PAHs in soils. In the paper, Toxicity equivalency factor (TEF) was used to convert concentrations of carcinogenic PAHs to an equivalent concentration of BaP (BaPeq) when assessing the cancer risks posed by PAHs exposure (USEPA, 1993; Hu et al., 2007). According to the assumptions applied by Passuello et al. (2010), Man et al. (2013) and Omar et al. (2013), four exposure pathways including dermal contact, soil ingestion, food ingestion and inhalation were considered as the main pathways in this study. The CDI via four pathways were calculated using the following equations adapted from USEPA (1997), Wang et al. (2013) and Omar et al. (2013).
CDIsoil ingestion ¼ ðCSsoil IRsoil CF ED EFÞ=ðBW ATÞ
ð1Þ
where CDIsoil ingestion is the chronic daily intake associated with soil ingestion (mg kg1 d1), CSsoil is the sum of converted PAHs concentrations for 7 carcinogenic PAHs (BaA, Chr, BbF, BkF, BaP, IND and DBahA) in the soil based on toxic equivalents of BaP (mg kg1), IRsoil is the soil ingestion rate (mg d1), EF is the exposure frequency (d a1), ED is the exposure duration (a), BW is the body weight of the exposed individual (kg), AT is the average lifespan for carcinogens time (365 d/a 70a = 25 550 d), and CF is the conversion factor (1 106 kg mg1).
CDIinhalation ¼ ðCSsoil HR ED EFÞ=ðPEFsoil BW ATÞ
ð2Þ
where CDIinhalation is chronic daily intake via inhalation of soil particles (mg kg1 d1); HR is air inhalation rate (m3 d1); PEFsoil is the soil particle emission factor (1.36 109 m3 kg1).
CDIdermal contact ¼ ðCSsoil CF SA AF ABS ED EFÞ=ðBW ATÞ
ð3Þ
where CDIdermal contact is the chronic daily intake for dermal contact of soil (mg kg1 d1), SA is the surface area of the skin that contacts soil (cm2 day1), AF is the relative skin adherence factor for soil (mg cm2), and ABS is the dermal absorption factor In the study, we assumed that the cancer risk via food ingestion was resulting from the consumption of carcinogenic PAHs in fish edible tissues. The PAHs concentrations in fish were calculated based on the models described by USEPA (1998).
where the subscript i denotes dermal contact, soil ingestion, food ingestion and inhalation, correspondingly. R is the cancer risk as a result of exposure to a contaminant, CDI is the average daily exposure dose obtained from the Eqs. (1)–(5), CSF is the cancer slope factor. The total cancer risks for different age groups are the sum of risks associated with each exposure route (Chiang et al., 2009).
R ¼ Rsoil ingestion þ Rfood ingestion þ Rinhalation þ Rdermal contact
ð7Þ 6
Generally, the acceptable level for cancer risk is set to 10 –104 by the USEPA, and the risks above 104 considered unacceptable (Wang et al., 2011; Li et al., 2014). The lower end of the range of acceptable risk distribution is given by a single constraint on the 95th percentiles of risk distribution that must be equal or lower than 106 for carcinogens. (Chiang et al., 2009; Wu et al., 2011). Exposure doses for different age groups were considered in this study. According to the assumptions applied by Chen et al. (2012), three groups of people were selected to estimate the exposure dose, i.e. children (1–11 years old), teens (12–17 years old) and adults (18–70 years old). Probability distributions for the exposure parameters for the receptors are used to estimate CDI and cancer risk via four exposure pathways. In this study, the probability distribution of total concentration and BaPeq concentration in soils and fish for 16 sites were evaluated by fitting distribution functions with the assistance of Anderson–Darling test, v2-test and Kolmogorov–Smirnov test. The model parameters including exponential, gamma, normal, lognormal, logistic and Weibull distributions were considered (Wu et al., 2011). The other exposure variables for the people live in Jiaozhou Bay wetland were derived from the literatures (Table 1). 2.5. Uncertainty and sensitivity analysis Uncertainty exists in risk assessment, especially when the uncertainty arises due to the variability of individual human characteristics. To minimize the uncertainties of the above calculations, Monte Carlo simulation was applied to evaluate the cancer risk using the software Crystal Ball 7.2 (Wu et al., 2011; Chen et al., 2012; Li et al., 2014). The simulation selects a value of each variable according to its distribution function at random to calculate the cancer risk, and the model ran for 50 000 iterations. In order to determine the input variables that most affect the cancer risk assessment, a sensitivity analysis by using Spearman rank correlations is performed (Hu et al., 2007; Wu et al., 2011). 3. Results and discussion
C fish ¼ ðC soil f lipid BSAFÞ=OCsoil
ð4Þ
3.1. Health risk assessment
CDIfood ingestion ¼ ðCSfish IRfish EF EDÞ=ðBW ATÞ
ð5Þ
The total concentration for the 7 carcinogenic PAHs in Jiaozhou Bay wetland soils follow a lognormal distribution, with geometric mean 78.06 ng g1 and geometric standard deviation 58.04 ng g1. The measured total concentration for the 7 carcinogenic PAHs in soil was lower than the target value set by Dutch government for unpolluted soil (475 ng g1 dry weight for 7 carcinogenic PAHs) (Sun et al., 2013). Considering the diverse characteristics of three age groups involving EF, ET, ED, BW, and AT, the cancer risks for teens, adults and children were calculated based on Eqs. (1)–(7). The risk estimation for children, adults and teens were calculated at the 95% confidence level using the Monte Carlo simulation, and the results were shown in Fig. 2. Fig. 2(a) shows that the cancer risk of PAHs calculated by Monte Carlo simulation for children, the cancer risk ranged from 1.80 1011 to 7.01 104, with a mean of 2.85 106. The
where Cfish is fish concentration (mg kg1), Csoil is concentration of carcinogenic PAHs, soilflipid is fish lipid content (0.07), BSAF is biota to sediment accumulation factor for fish (unitless) (USEPA, 2000; USACE, 2007), OCsoil is the fraction organic carbon in sediment (0.04) (USEPA, 1998). CDIfood ingestion is the chronic daily intake associated with fish ingestion (mg kg1 d1). CSfish is the sum of converted PAHs concentrations for 7 carcinogenic PAHs in fish based on toxic equivalents of BaP (mg kg1), IRfish is the fish ingestion rate (g d1), as indicated by Urban et al. (2009) and Chu et al. (2013). The cancer risks were calculated multiplying the estimated dosage by the cancer potency factor, which was adapted from USEPA (1989).
Ri ¼ CDIi CSFi
ð6Þ
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Table 1 Risk variables considered as random variables for different age groups. Definition a
HR IRsoilb IRfishc SAd ED AFe EFf BWg ABSe CSFIngestionh CSFInhalationi CSFDermalj a b c d e f g h i j
Units
Distribution
Children
Teens
Adults
3
Log-normal Log-normal Log-normal Log-normal Uniform Log-normal Log-normal Log-normal Log-normal Log-normal Log-normal
LN(14.10, 1.72) LN(12.24, 1.90) LN(2.4, 0.24) LN(7422, 1.25) U(0, 11) LN(0.04, 3.41) LN(252, 1.01) LN(16.68, 1.48) LN(0.13, 1.26) LN(7.3, 1.56) LN(3.14, 1.8) 37.47
LN(32.13, 1.04) LN(23.85, 1.88) LN(9.9, 0.99) LN(14321, 1.18) U(0, 6) LN(0.04, 3.41) LN(252, 1.01) LN(32.41, 1.08) LN(0.13, 1.26)
LN(32.73, 1.14) LN(26.95, 1.88) LN(14.4, 1.44) LN(18182, 1.1) U(0, 52) LN(0.02, 2.67) LN(252, 1.01) LN(59.78, 1.07) LN(0.13, 1.26)
1
m d mg d1 g d1 cm2 d1 a mg cm2 d a1 kg mg kg1 d1 mg kg1 d1 mg kg1 d1
Adapted from ICRP, 1994. Adopted from USEPA, 1994 and USEPA, 1996. Adopted from Chu et al. (2013) and Urban et al. (2009). Adopted from Wu et al. (2011). Adapted from USEPA, 2001. Adopted from Central Personnel Administration, ROC (http://www.cpa.gov.tw/cpa2004/pfattend/download/EXWT93102901.doc). Adopted from Chen et al. (2012) and Wu et al. (2011). Adopted from Chen and Liao (2006). Adopted from Integrated Risk Information System (http://www.epa.gov/iris/subst/0136.htm#quaoral). Adopted from Hussain et al. (1998).
95th percentiles cancer risk for children (9.11 106) was in the USEPA acceptable range (106–104), indicating no potential for cancerous develop. For teens and adults, the cancer risk of PAHs ranged from 1.02 1011 to 2.28 104 and from 1.61 109 to 1.28 103, with a mean of 3.21 106 and 2.21 105, respectively Fig. 2(b and c). The 95th percentiles cancer risks for teens (1.04 105) and adults (7.08 105) were lower than 104, the cancer risks were at acceptable range.
3.2. Contribution of individual PAHs As shown in Fig. 3, for the three exposed age groups, the cancer risk for individual carcinogenic PAHs were presented at different level, and the risk from BaP was the highest. The higher cancer risk for BaP was also observed by Chen et al. (2013a), who evaluated toxicity of PAHs in sediments of Kaohsiung Harbor, based on BaPeq concentrations. This probably due to the high TEF value of BaP, which have considerable weight on the BaPeq. The range, mean and BaPeq of 7 carcinogenic PAHs were presented (see Supplementary Table S2). Given that BaP was the major components of the
Fig. 2. Predicted probability density functions of cancer risk for (a) children, (b) teens and (c) adults.
Fig. 3. Cancer risk of PAHs for (a) children, (b) teens and (c) adults.
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cancer risk, the influence on the total cancer risk was significant. For different age groups, the 95th percentiles cancer risks of BaP for children, teens and adult were 8.34 106, 9.56 106 and 6.67 105, respectively, in the order of adult >teens > children. This confirmed the above result presented in Section 3.1.
3.3. Contribution of individual exposure pathways The cancer risk from the individual exposure pathways (soil ingestion, food ingestion, dermal contact and inhalation) was summarized to determine the key exposure pathway for carcinogenic PAHs. The contribution for different exposure pathways at 95th percentiles were shown in Fig. 4. In this study, 95th percentiles of the cancer risk levels via food ingestion for three age groups ranged from 8.90 106 to 7.05 105 , while cancer risk levels via soil ingestion, dermal contact and inhalation ranged from 5.43 1012 to 4.79 108 , about 102 to 106 times lower than that through food ingestion. Thus, food ingestion was the most important exposure pathway, which contributes more than 99.29% to the total cancer risk for the three age groups (Fig. 4). The cancer risk caused by soil ingestion, dermal contact and inhalation were almost negligible compared with food ingestion. An earlier investigation on a study of exposure to POPs for sewage sludge application in agricultural soils also showed that the cancer risk via food ingestion was much higher than that through soil ingestion and air inhalation (Passuello et al., 2010). The great contribution of food ingestion to the total cancer risk can explain the difference in total cancer risks for three age groups. The IRfish for adults was presented at the highest level (Table 1), than the highest cancer risk obtained (see Section 2.4). 95th percentiles of the cancer risk levels via soil ingestion for children (2.13 108) was lower than that of soil ingestion for adults (6.13 108), but higher than the corresponding risk of soil ingestion for teens (1.15 108). Similar findings can be seen from the studies of Wu et al. (2011), which could be explained by high IRsoil and ED for adults. Thus, the cancer risk for adults exposed to PAHs via soil ingestion is thought to be considerably greater than that of children. For soil ingestion, dermal contact and inhalation, although IRsoil, HR and SA of teens were higher than that of children, the body weight (BW) of teens was significantly higher than children. According to Eqs. (1)–(7), the lowest risk for teen’s group was obtained, and the shorter ED also contributes to the lower cancer risk for teens. In addition, the cancer risk via dermal contact for adults (4.79 108) appeared to be greatest compared with that of children and teens. This finding was similar to the cancer risk resulted from PAHs exposure in urban surface dust of Guangzhou, China (Wang et al., 2011), probably due to the fact that
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the SA and ED of adults were higher than those of children and teens (see Table 1). 3.4. Sensitivity analysis of parameters The sensitivity analysis results on the cancer risk are shown in the form of tornado plots illustrating the spearman rank order correlation coefficients (Fig. 5). For children, teens and adults, the most contributions to variance in total cancer risk were 43.5– 44.3% in CSsoil, 51.7–52.3% in ED, respectively. These two factors reflect the carcinogenic potential caused by carcinogenic PAHs in food and the duration of time exposed to carcinogenic PAHs, which affects the CDI and cancer risk, leading to a variation in cancer risk assessment. The results were consistent with report of Wu et al. (2011), which estimated the human health risk of PAHs in the source water and drinking water of China from a national scale. Considering CSsoil and ED were the most two sensitive parameters and greatly affected the estimate of cancer risk, efforts should focus on a better definition of probability distribution for those two parameters to increase the accuracy of the results. Since BW was in the denominator of Eqs. (1)–(4), the sensitivity of BW was a slight negative value, indicating that cancer risk inversely related to BW. Similar results have been reported by other investigators (Chiang et al., 2009; Luo et al., 2013). Moreover, for parameters associated with dermal contact (relative AF (mg cm2), ABS), soil ingestion (CSFingestion and IR) and inhalation (HR and CSFinhalation) were almost 0 for three age groups. Similar findings can be seen from the studies of Luo et al. (2013). This probably due to the fact that food ingestion was the dominant pathway for three age groups (see Section 3.3), parameters associated with fish ingestion contribute most to the total uncertainty. 3.5. Uncertainty and variability analyses Uncertainties are inherent in health risk assessment, which stems from a lack of knowledge about the factors affecting exposure or toxicity assessment (Wu et al., 2011). Although Monte Carlo simulation was used to eliminate the nondeterminacy, there were still other uncertainties exist during cancer risk assessment processes. Firstly, great uncertainty exists in the step of exposure assessment. The probability distributions of exposure parameters such as BW and SA were obtained from statistical data of Chinese. However, due to limited data, other exposure parameters were directly obtained from the recommended values of USEPA and ICRP, which may be different from those in China for ethnicity differences (Hu et al., 2007; Wu et al., 2011). This may be a limit to the validity of the case presented.
Fig. 4. Contribution for different exposure pathways at 95th percentiles.
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exposure pathways, the observed cancer risks via food ingestion contribute most to the total cancer risks. Sensitivity analysis showed that CSsoil and ED were the most two sensitive parameters. The present study might provide useful information on human exposure to PAHs in Jiaozhou Bay wetland soil, and will be useful for potential strategies of cancer risk management and reduction. Acknowledgments This work was supported by Qingdao Science and Technology Development Plan (12-1-4-1-(16)-jch) and Program for New Century Excellent Talents in University (NCET-10-0758). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2014.04.074. References
Fig. 5. Sensitivity analysis of cancer risk for (a) children (b) teens (c) adults.
Secondly, due to the limited dose–response data on carcinogenicity, uncertainty exists in the cancer risk assessment of mixture PAHs for human (Wu et al., 2011). The effects of joint exposure PAHs are, to date, unknown. There may be synergistic effects, antagonistic effects, or simply additive effects. In addition, there is no biological rationale about how these elements may truly interact to cause adverse health effects. In this study, we assumed the cancer risk caused by individual PAHs were additive base on the TEF values. And the TEF values were obtained from animal experiments basis on the results of animal experiment. There might be uncertainties in the processes for transferring of results from test animal to human. In addition, deviation of this subject to even more uncertainties, probably due to the limited number of dose–response data on carcinogenicity (Vojtisek-Lom et al., 2012). The TEF are based on several measurements. But different values have been proposed on the bases of toxicological studies mentioned by some authors. For example, Larsen and Larsen (1998) suggested a TEF for BkF of 0.05, as opposed to a TEF of 0.01. Different BaPeq levels are expected to be obtained when using different TEFs. 4. Conclusion Cancer risk assessment of 7 carcinogenic PAHs based on Monte Carlo simulation was conducted to evaluate the cancer risk via soil ingestion, food ingestion, dermal contact and inhalation for three age groups. 95th percentiles cancer risks were 9.11 106, 1.04 105 and 7.08 105 for children, teens and adults, respectively. The cancer risks for three age groups were at acceptable range, there is no potential cancer risk. For 7 carcinogenic PAHs, the cancer risk caused by BaP was the highest, which probably due to their high BaPeq concentrations in soil and fish. For different
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Cancer risk of polycyclic aromatic hydrocarbons (PAHs) in the soils from Jiaozhou Bay wetland Wei Yang, Yinhai Lang ⇑, Guoliang Li Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100, China College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China
h i g h l i g h t s Cancer risks for three age groups were evaluated based on Monte Carlo simulation. Sensitivity analysis was conducted to find the influential factors. Cancer risks for three age groups were at acceptable range. BaP contribute most to the total cancer risk. Food ingestion was the major exposure pathway for carcinogenic risks.
a r t i c l e
i n f o
Article history: Received 22 January 2014 Received in revised form 16 April 2014 Accepted 23 April 2014
Handling Editor: Tamara S. Galloway Keywords: PAHs Cancer risk Monte Carlo simulation Sensitivity analysis
a b s t r a c t To estimate the cancer risk exposed to the PAHs in Jiaozhou Bay wetland soils, a probabilistic health risk assessment was conducted based on Monte Carlo simulations. A sensitivity analysis was performed to determine the input variables that contribute most to the cancer risk assessment. Three age groups were selected to estimate the cancer risk via four exposure pathways (soil ingestion, food ingestion, dermal contact and inhalation). The results revealed that the 95th percentiles cancer risks for children, teens and adults were 9.11 106, 1.04 105 and 7.08 105, respectively. The cancer risks for three age groups were at acceptable range (106–104), indicating no potential cancer risk. For different exposure pathways, food ingestion was the major exposure pathway. For 7 carcinogenic PAHs, the cancer risk caused by BaP was the highest. Sensitivity analysis demonstrated that the parameters of exposure duration (ED) and sum of converted 7 carcinogenic PAHs concentrations in soil based on BaPeq (CSsoil) contribute most to the total uncertainty. This study provides a comprehensive risk assessment on carcinogenic PAHs in Jiaozhou Bay wetland soils, and might be useful in providing potential strategies of cancer risk prevention and controlling. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds with two or more fused aromatic rings carbon and hydrogen atoms. PAHs are primarily formed by incomplete combustion or pyrolysis of organic matter (Man et al., 2013; Chen et al., 2013a). Due to their potential mutagenic, carcinogenic and teratogenic effects on human health, PAHs have attracted particular concern and 16 PAHs were listed as priority pollutant by the USEPA (2003). Seven of them including benz[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene ⇑ Corresponding author at: College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China. Tel./fax: +86 532 66786308. E-mail address: [email protected] (Y. Lang). http://dx.doi.org/10.1016/j.chemosphere.2014.04.074 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved.
(BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IND) and dibenz [a,h]anthracene (DBahA) are classified as carcinogenic PAHs by the International Agency for Research on Cancer (IARC, 2010). Soil system is a good indicator of environmental pollution. Due to their ubiquity and persistence nature, PAHs are prone to enrichment in soils and retain for a long time (Lang et al., 2012). PAHs in soil may lead to direct or indirect exposure to humans. Therefore, it is necessary to assess the potential adverse health risk of PAHs in soils to protect human health. Human health risk assessment was used to quantitatively estimate the health risk levels posed by specific chemicals, and have been successfully used (Wang et al., 2011, 2013; Chen et al., 2013b; Luo et al., 2013). In the health risk assessment, deterministic risk assessments based on a single value for the exposure parameter was widely adopted (Chen et al., 2013b; Luo et al., 2013; Man et al., 2013; Li et al.,
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2014). However, this approach does not take into account the variability in measurements and the heterogeneity in a population or exposure parameter (Li et al., 2014). Thus, probabilistic approaches based on Monte Carlo simulation were conducted (Hu et al., 2007; Chiang et al., 2009; Wu et al., 2011). Jiaozhou Bay wetland is the most important coastal wetland ecosystems in Shandong Peninsula, China. This wetland provides breading grounds for many types of fish and shellfish and a resting place for migratory birds (Gu et al., 2007). However, with the rapid development of industry, aquaculture and aquiculture, Jiaozhou Bay wetland is seriously affected by anthropogenic activities (Gu et al., 2007). Pyrolytic and petrogenic sources were the main sources for the PAHs in the area (Wang et al., 2006, 2010). And the cancer risk caused by PAHs in Jiaozhou Bay wetland soils has remained scarce. There is a need to assess the health risk of PAHs in Jiaozhou Bay wetland soils. The results of this research may be useful for the local government in pollution control, remediation and human health protection. 2. Materials and methods 2.1. Sample To evaluate the PAHs pollution levels, soil samples were collected from Jiaozhou Bay wetland (Fig. 1). Sixteen surface soil samples were collected using a stainless steel soil auger on December 2012. For each site, 2 samples were taken from 2 to 5 cm and collected with a polyethylene spatula and placed in self-sealing polyethylene bags. All samples were then preserved with ice and stored at 20 °C. The samples were freeze-dried in the laboratory, and then carefully homogenized in a mortar, sieved through 100-mesh stainless steel mesh, and stored at 4 °C in glass bottles prior to analysis. 2.2. Chemical analysis For soil PAH extraction and clean-up, n-hexane, dichloromethane and silica gel were used. The standards of 16 PAHs including naphthalene (Nap), acenaphthene (Ace), acenaphthylene (Acy), fluorene (Fle), 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), indeno[1,2,3-cd]pyrene (IND), dibenz[a,h]anthracene
(DBahA), and benzo[ghi]perylene (BghiP) were purchased from Supelco (Bellefonte, USA). Ultrasonic extraction of PAHs was performed according to the procedures described by Lang et al. (2012). Briefly, (2.0 g) freeze-dried and homogenized soils were weighed and extracted three times by ultrasonication (40 kHz) with 20 mL n-hexane/dichloromethane (1:1 v:v). A mixture of deuterated PAHs compounds (acenaphthene-d10, chrysene-d12, perylene-d12 and phenanthrene-d10) as recovery surrogate standards was added into all samples to monitor the procedures of sample extraction, cleanup, and analysis. The extracts were concentrated to 1.0 mL by rotary vacuum evaporation, and an alumina/silica gel column was implemented to clean-up the extracts. The PAHs fraction was eluted with 30.0 mL dichloromethane/n-hexane (3:7 v:v), and then concentrated up to 1 ml by rotary vacuum evaporator and further to exactly 1 mL under a gentle gas stream of purified nitrogen. PAHs composition analysis for 16 PAHs was performed on an Agilent GC (6890-N)/MSD (5975B) equipped with a fused-silica HP-5MS capillary column (30 m 0.25 mm 0.25 lm). High purity helium was used as the carrier gas at a constant flow of 1.2 ml min1. The temperature program of the oven was started at 50 °C (hold 2 min), ramped to 230 °C at 8 °C min1, then, further ramped to 300 °C at 3.5 °C min1, and held for 7 min. The sample was injected splitless with the injector temperature at 290 °C. The temperatures for the ion source and interface were set at 230 °C and 250 °C, respectively. The MSD was operated in the SIM mode and electron impact energy was set at 70 eV. 2.3. Quality assurance/quality control All analytical data were subject to strict quality control. The procedural blanks, spiked blanks, and sample duplicates were determined for quality assurance and control, and no interferences were detected in the procedure blanks. The aim of spiked blank was checked for recovery efficiencies by analyzing uncontaminated soil spiked with 16 PAHs standards. In the study, the spiked blank values for 16 PAHs were 100 ng g1 and the average recoveries ranged from 70% to 106%. The five-point external calibration method was applied in the sample analysis. The detection limit (DL) of 16 PAHs was estimated from a signal-to-noise ratio of 3:1 in blank samples, and ranged from 1.05 to 6.78 ng g1 (see Supplementary Table S1). Not detected or the values below DL were treated as half of DL when proceeding statistical analysis.
Fig. 1. Sampling sites of soils in Jiaozhou Bay wetland.
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2.4. Cancer risk assessment Cancer risk expresses the likelihood of occurring cancer as a result of exposure to the potential carcinogen (Li et al., 2014). In this study, the chronic daily intake of PAHs refers to the PAHs in soils accepted by the exposure terminal (i.e., respiratory organs of the human body) and is denoted by CDI. The CDI of PAHs in other medium was not considered given that this study only focuses on the PAHs in soils. In the paper, Toxicity equivalency factor (TEF) was used to convert concentrations of carcinogenic PAHs to an equivalent concentration of BaP (BaPeq) when assessing the cancer risks posed by PAHs exposure (USEPA, 1993; Hu et al., 2007). According to the assumptions applied by Passuello et al. (2010), Man et al. (2013) and Omar et al. (2013), four exposure pathways including dermal contact, soil ingestion, food ingestion and inhalation were considered as the main pathways in this study. The CDI via four pathways were calculated using the following equations adapted from USEPA (1997), Wang et al. (2013) and Omar et al. (2013).
CDIsoil ingestion ¼ ðCSsoil IRsoil CF ED EFÞ=ðBW ATÞ
ð1Þ
where CDIsoil ingestion is the chronic daily intake associated with soil ingestion (mg kg1 d1), CSsoil is the sum of converted PAHs concentrations for 7 carcinogenic PAHs (BaA, Chr, BbF, BkF, BaP, IND and DBahA) in the soil based on toxic equivalents of BaP (mg kg1), IRsoil is the soil ingestion rate (mg d1), EF is the exposure frequency (d a1), ED is the exposure duration (a), BW is the body weight of the exposed individual (kg), AT is the average lifespan for carcinogens time (365 d/a 70a = 25 550 d), and CF is the conversion factor (1 106 kg mg1).
CDIinhalation ¼ ðCSsoil HR ED EFÞ=ðPEFsoil BW ATÞ
ð2Þ
where CDIinhalation is chronic daily intake via inhalation of soil particles (mg kg1 d1); HR is air inhalation rate (m3 d1); PEFsoil is the soil particle emission factor (1.36 109 m3 kg1).
CDIdermal contact ¼ ðCSsoil CF SA AF ABS ED EFÞ=ðBW ATÞ
ð3Þ
where CDIdermal contact is the chronic daily intake for dermal contact of soil (mg kg1 d1), SA is the surface area of the skin that contacts soil (cm2 day1), AF is the relative skin adherence factor for soil (mg cm2), and ABS is the dermal absorption factor In the study, we assumed that the cancer risk via food ingestion was resulting from the consumption of carcinogenic PAHs in fish edible tissues. The PAHs concentrations in fish were calculated based on the models described by USEPA (1998).
where the subscript i denotes dermal contact, soil ingestion, food ingestion and inhalation, correspondingly. R is the cancer risk as a result of exposure to a contaminant, CDI is the average daily exposure dose obtained from the Eqs. (1)–(5), CSF is the cancer slope factor. The total cancer risks for different age groups are the sum of risks associated with each exposure route (Chiang et al., 2009).
R ¼ Rsoil ingestion þ Rfood ingestion þ Rinhalation þ Rdermal contact
ð7Þ 6
Generally, the acceptable level for cancer risk is set to 10 –104 by the USEPA, and the risks above 104 considered unacceptable (Wang et al., 2011; Li et al., 2014). The lower end of the range of acceptable risk distribution is given by a single constraint on the 95th percentiles of risk distribution that must be equal or lower than 106 for carcinogens. (Chiang et al., 2009; Wu et al., 2011). Exposure doses for different age groups were considered in this study. According to the assumptions applied by Chen et al. (2012), three groups of people were selected to estimate the exposure dose, i.e. children (1–11 years old), teens (12–17 years old) and adults (18–70 years old). Probability distributions for the exposure parameters for the receptors are used to estimate CDI and cancer risk via four exposure pathways. In this study, the probability distribution of total concentration and BaPeq concentration in soils and fish for 16 sites were evaluated by fitting distribution functions with the assistance of Anderson–Darling test, v2-test and Kolmogorov–Smirnov test. The model parameters including exponential, gamma, normal, lognormal, logistic and Weibull distributions were considered (Wu et al., 2011). The other exposure variables for the people live in Jiaozhou Bay wetland were derived from the literatures (Table 1). 2.5. Uncertainty and sensitivity analysis Uncertainty exists in risk assessment, especially when the uncertainty arises due to the variability of individual human characteristics. To minimize the uncertainties of the above calculations, Monte Carlo simulation was applied to evaluate the cancer risk using the software Crystal Ball 7.2 (Wu et al., 2011; Chen et al., 2012; Li et al., 2014). The simulation selects a value of each variable according to its distribution function at random to calculate the cancer risk, and the model ran for 50 000 iterations. In order to determine the input variables that most affect the cancer risk assessment, a sensitivity analysis by using Spearman rank correlations is performed (Hu et al., 2007; Wu et al., 2011). 3. Results and discussion
C fish ¼ ðC soil f lipid BSAFÞ=OCsoil
ð4Þ
3.1. Health risk assessment
CDIfood ingestion ¼ ðCSfish IRfish EF EDÞ=ðBW ATÞ
ð5Þ
The total concentration for the 7 carcinogenic PAHs in Jiaozhou Bay wetland soils follow a lognormal distribution, with geometric mean 78.06 ng g1 and geometric standard deviation 58.04 ng g1. The measured total concentration for the 7 carcinogenic PAHs in soil was lower than the target value set by Dutch government for unpolluted soil (475 ng g1 dry weight for 7 carcinogenic PAHs) (Sun et al., 2013). Considering the diverse characteristics of three age groups involving EF, ET, ED, BW, and AT, the cancer risks for teens, adults and children were calculated based on Eqs. (1)–(7). The risk estimation for children, adults and teens were calculated at the 95% confidence level using the Monte Carlo simulation, and the results were shown in Fig. 2. Fig. 2(a) shows that the cancer risk of PAHs calculated by Monte Carlo simulation for children, the cancer risk ranged from 1.80 1011 to 7.01 104, with a mean of 2.85 106. The
where Cfish is fish concentration (mg kg1), Csoil is concentration of carcinogenic PAHs, soilflipid is fish lipid content (0.07), BSAF is biota to sediment accumulation factor for fish (unitless) (USEPA, 2000; USACE, 2007), OCsoil is the fraction organic carbon in sediment (0.04) (USEPA, 1998). CDIfood ingestion is the chronic daily intake associated with fish ingestion (mg kg1 d1). CSfish is the sum of converted PAHs concentrations for 7 carcinogenic PAHs in fish based on toxic equivalents of BaP (mg kg1), IRfish is the fish ingestion rate (g d1), as indicated by Urban et al. (2009) and Chu et al. (2013). The cancer risks were calculated multiplying the estimated dosage by the cancer potency factor, which was adapted from USEPA (1989).
Ri ¼ CDIi CSFi
ð6Þ
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Table 1 Risk variables considered as random variables for different age groups. Definition a
HR IRsoilb IRfishc SAd ED AFe EFf BWg ABSe CSFIngestionh CSFInhalationi CSFDermalj a b c d e f g h i j
Units
Distribution
Children
Teens
Adults
3
Log-normal Log-normal Log-normal Log-normal Uniform Log-normal Log-normal Log-normal Log-normal Log-normal Log-normal
LN(14.10, 1.72) LN(12.24, 1.90) LN(2.4, 0.24) LN(7422, 1.25) U(0, 11) LN(0.04, 3.41) LN(252, 1.01) LN(16.68, 1.48) LN(0.13, 1.26) LN(7.3, 1.56) LN(3.14, 1.8) 37.47
LN(32.13, 1.04) LN(23.85, 1.88) LN(9.9, 0.99) LN(14321, 1.18) U(0, 6) LN(0.04, 3.41) LN(252, 1.01) LN(32.41, 1.08) LN(0.13, 1.26)
LN(32.73, 1.14) LN(26.95, 1.88) LN(14.4, 1.44) LN(18182, 1.1) U(0, 52) LN(0.02, 2.67) LN(252, 1.01) LN(59.78, 1.07) LN(0.13, 1.26)
1
m d mg d1 g d1 cm2 d1 a mg cm2 d a1 kg mg kg1 d1 mg kg1 d1 mg kg1 d1
Adapted from ICRP, 1994. Adopted from USEPA, 1994 and USEPA, 1996. Adopted from Chu et al. (2013) and Urban et al. (2009). Adopted from Wu et al. (2011). Adapted from USEPA, 2001. Adopted from Central Personnel Administration, ROC (http://www.cpa.gov.tw/cpa2004/pfattend/download/EXWT93102901.doc). Adopted from Chen et al. (2012) and Wu et al. (2011). Adopted from Chen and Liao (2006). Adopted from Integrated Risk Information System (http://www.epa.gov/iris/subst/0136.htm#quaoral). Adopted from Hussain et al. (1998).
95th percentiles cancer risk for children (9.11 106) was in the USEPA acceptable range (106–104), indicating no potential for cancerous develop. For teens and adults, the cancer risk of PAHs ranged from 1.02 1011 to 2.28 104 and from 1.61 109 to 1.28 103, with a mean of 3.21 106 and 2.21 105, respectively Fig. 2(b and c). The 95th percentiles cancer risks for teens (1.04 105) and adults (7.08 105) were lower than 104, the cancer risks were at acceptable range.
3.2. Contribution of individual PAHs As shown in Fig. 3, for the three exposed age groups, the cancer risk for individual carcinogenic PAHs were presented at different level, and the risk from BaP was the highest. The higher cancer risk for BaP was also observed by Chen et al. (2013a), who evaluated toxicity of PAHs in sediments of Kaohsiung Harbor, based on BaPeq concentrations. This probably due to the high TEF value of BaP, which have considerable weight on the BaPeq. The range, mean and BaPeq of 7 carcinogenic PAHs were presented (see Supplementary Table S2). Given that BaP was the major components of the
Fig. 2. Predicted probability density functions of cancer risk for (a) children, (b) teens and (c) adults.
Fig. 3. Cancer risk of PAHs for (a) children, (b) teens and (c) adults.
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cancer risk, the influence on the total cancer risk was significant. For different age groups, the 95th percentiles cancer risks of BaP for children, teens and adult were 8.34 106, 9.56 106 and 6.67 105, respectively, in the order of adult >teens > children. This confirmed the above result presented in Section 3.1.
3.3. Contribution of individual exposure pathways The cancer risk from the individual exposure pathways (soil ingestion, food ingestion, dermal contact and inhalation) was summarized to determine the key exposure pathway for carcinogenic PAHs. The contribution for different exposure pathways at 95th percentiles were shown in Fig. 4. In this study, 95th percentiles of the cancer risk levels via food ingestion for three age groups ranged from 8.90 106 to 7.05 105 , while cancer risk levels via soil ingestion, dermal contact and inhalation ranged from 5.43 1012 to 4.79 108 , about 102 to 106 times lower than that through food ingestion. Thus, food ingestion was the most important exposure pathway, which contributes more than 99.29% to the total cancer risk for the three age groups (Fig. 4). The cancer risk caused by soil ingestion, dermal contact and inhalation were almost negligible compared with food ingestion. An earlier investigation on a study of exposure to POPs for sewage sludge application in agricultural soils also showed that the cancer risk via food ingestion was much higher than that through soil ingestion and air inhalation (Passuello et al., 2010). The great contribution of food ingestion to the total cancer risk can explain the difference in total cancer risks for three age groups. The IRfish for adults was presented at the highest level (Table 1), than the highest cancer risk obtained (see Section 2.4). 95th percentiles of the cancer risk levels via soil ingestion for children (2.13 108) was lower than that of soil ingestion for adults (6.13 108), but higher than the corresponding risk of soil ingestion for teens (1.15 108). Similar findings can be seen from the studies of Wu et al. (2011), which could be explained by high IRsoil and ED for adults. Thus, the cancer risk for adults exposed to PAHs via soil ingestion is thought to be considerably greater than that of children. For soil ingestion, dermal contact and inhalation, although IRsoil, HR and SA of teens were higher than that of children, the body weight (BW) of teens was significantly higher than children. According to Eqs. (1)–(7), the lowest risk for teen’s group was obtained, and the shorter ED also contributes to the lower cancer risk for teens. In addition, the cancer risk via dermal contact for adults (4.79 108) appeared to be greatest compared with that of children and teens. This finding was similar to the cancer risk resulted from PAHs exposure in urban surface dust of Guangzhou, China (Wang et al., 2011), probably due to the fact that
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the SA and ED of adults were higher than those of children and teens (see Table 1). 3.4. Sensitivity analysis of parameters The sensitivity analysis results on the cancer risk are shown in the form of tornado plots illustrating the spearman rank order correlation coefficients (Fig. 5). For children, teens and adults, the most contributions to variance in total cancer risk were 43.5– 44.3% in CSsoil, 51.7–52.3% in ED, respectively. These two factors reflect the carcinogenic potential caused by carcinogenic PAHs in food and the duration of time exposed to carcinogenic PAHs, which affects the CDI and cancer risk, leading to a variation in cancer risk assessment. The results were consistent with report of Wu et al. (2011), which estimated the human health risk of PAHs in the source water and drinking water of China from a national scale. Considering CSsoil and ED were the most two sensitive parameters and greatly affected the estimate of cancer risk, efforts should focus on a better definition of probability distribution for those two parameters to increase the accuracy of the results. Since BW was in the denominator of Eqs. (1)–(4), the sensitivity of BW was a slight negative value, indicating that cancer risk inversely related to BW. Similar results have been reported by other investigators (Chiang et al., 2009; Luo et al., 2013). Moreover, for parameters associated with dermal contact (relative AF (mg cm2), ABS), soil ingestion (CSFingestion and IR) and inhalation (HR and CSFinhalation) were almost 0 for three age groups. Similar findings can be seen from the studies of Luo et al. (2013). This probably due to the fact that food ingestion was the dominant pathway for three age groups (see Section 3.3), parameters associated with fish ingestion contribute most to the total uncertainty. 3.5. Uncertainty and variability analyses Uncertainties are inherent in health risk assessment, which stems from a lack of knowledge about the factors affecting exposure or toxicity assessment (Wu et al., 2011). Although Monte Carlo simulation was used to eliminate the nondeterminacy, there were still other uncertainties exist during cancer risk assessment processes. Firstly, great uncertainty exists in the step of exposure assessment. The probability distributions of exposure parameters such as BW and SA were obtained from statistical data of Chinese. However, due to limited data, other exposure parameters were directly obtained from the recommended values of USEPA and ICRP, which may be different from those in China for ethnicity differences (Hu et al., 2007; Wu et al., 2011). This may be a limit to the validity of the case presented.
Fig. 4. Contribution for different exposure pathways at 95th percentiles.
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exposure pathways, the observed cancer risks via food ingestion contribute most to the total cancer risks. Sensitivity analysis showed that CSsoil and ED were the most two sensitive parameters. The present study might provide useful information on human exposure to PAHs in Jiaozhou Bay wetland soil, and will be useful for potential strategies of cancer risk management and reduction. Acknowledgments This work was supported by Qingdao Science and Technology Development Plan (12-1-4-1-(16)-jch) and Program for New Century Excellent Talents in University (NCET-10-0758). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2014.04.074. References
Fig. 5. Sensitivity analysis of cancer risk for (a) children (b) teens (c) adults.
Secondly, due to the limited dose–response data on carcinogenicity, uncertainty exists in the cancer risk assessment of mixture PAHs for human (Wu et al., 2011). The effects of joint exposure PAHs are, to date, unknown. There may be synergistic effects, antagonistic effects, or simply additive effects. In addition, there is no biological rationale about how these elements may truly interact to cause adverse health effects. In this study, we assumed the cancer risk caused by individual PAHs were additive base on the TEF values. And the TEF values were obtained from animal experiments basis on the results of animal experiment. There might be uncertainties in the processes for transferring of results from test animal to human. In addition, deviation of this subject to even more uncertainties, probably due to the limited number of dose–response data on carcinogenicity (Vojtisek-Lom et al., 2012). The TEF are based on several measurements. But different values have been proposed on the bases of toxicological studies mentioned by some authors. For example, Larsen and Larsen (1998) suggested a TEF for BkF of 0.05, as opposed to a TEF of 0.01. Different BaPeq levels are expected to be obtained when using different TEFs. 4. Conclusion Cancer risk assessment of 7 carcinogenic PAHs based on Monte Carlo simulation was conducted to evaluate the cancer risk via soil ingestion, food ingestion, dermal contact and inhalation for three age groups. 95th percentiles cancer risks were 9.11 106, 1.04 105 and 7.08 105 for children, teens and adults, respectively. The cancer risks for three age groups were at acceptable range, there is no potential cancer risk. For 7 carcinogenic PAHs, the cancer risk caused by BaP was the highest, which probably due to their high BaPeq concentrations in soil and fish. For different
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