Source, distribution, and health risk assessment of polycyclic aromatic hydrocarbons in urban street dust from Tianjin, China
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- Yu, B., Xie, X., Ma, L.Q. et al. Environ Sci Pollut Res (2014) 21: 2817. doi:10.1007/s11356-013-2190-z
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To better assess and understand potential health risk of urban residents exposed to urban street dust, the total concentration, sources, and distribution of 16 polycyclic aromatic hydrocarbons (PAHs) in 87 urban street dust samples from Tianjin as a Chinese megacity that has undergone rapid urbanization were investigated. In the meantime, potential sources of PAHs were identified using the principal component analysis (PCA), and the risk of residents’ exposure to PAHs via urban street dust was calculated using the Incremental Lifetime Cancer Risk (ILCR) model. The results showed that the total PAHs (∑PAHs) in urban street dust from Tianjin ranged from 538 μg kg−1 to 34.3 mg kg−1, averaging 7.99 mg kg−1. According to PCA, the two to three- and four to six-ring PAHs contributed 10.3 and 89.7 % of ∑PAHs, respectively. The ratio of the sum of major combustion specific compounds (ΣCOMB) / ∑PAHs varied from 0.57 to 0.79, averaging 0.64. The ratio of Ant/(Ant + Phe) varied from 0.05 to 0.41, averaging 0.10; Fla/(Fla + Pyr) from 0.40 to 0.68, averaging 0.60; BaA/(BaA + Chry) from 0.29 to 0.51, averaging 0.38; and IcdP/(IcdP + BghiP) from 0.07 to 0.37, averaging 0.22. The biomass combustion, coal combustion, and traffic emission were the main sources of PAHs in urban street dust with the similar proportion. According to the ILCR model, the total cancer risk for children and adults was up to 2.55 × 10−5 and 9.33 × 10−5, respectively.
KeywordsHealth risk assessmentPAHsUrban street dustUrban soilPollution source
As an important type of persistent organic pollutants (POPs), polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene, benzo[a]anthracene, and benzo[b]fluoranthene distribute widely in the atmosphere, surface water, sediments, soil, and groundwater. Because of their carcinogenicity, teratogenicity, and mutagenicity, they can cause a great and lasting threat to ecosystem safety and human health (Larsen and Baker 2003; Grote et al. 2005; Chen and Liao 2006; Luo et al. 2008). Most of PAHs originate from human activities, by-products of incomplete burning of petroleum products, and other incomplete combustions such as vehicle exhaust, coal-fired heating, and straw and fuel wood combustion (Finlayso-Pitts and Pitts 1997; Zhou et al. 2004; Li et al. 2006).
In recent years, with the development of economy and urbanization, urban areas have been expanded quickly in China and other countries. Currently, almost 50 % of the world’s population lives in urban areas, compared with only 15 % in 1900 (Joop 2007). The service function of urban soils is therefore becoming more important due to their ecological function and environmental significance (Zhou 2005). For example, urban street dust is a major reservoir and sink for various pollutants including PAHs and other organic pollutants, which has adverse effects on ecological function and service of urban soils (Zhou et al. 2004). Furthermore, urban street dust might affect public health via ingestion, dermal contact, and inhalation (Mielke 1991). In particular, the previous researches (Liu et al. 2010; Lee and Dong 2011; Lorenzi 2011; Wang et al. 2011) had reported an increasing trend of PAHs in urban soil and street dust around the world.
The International Agency for Research on Cancer (IARC) has identified PAHs as major carcinogens and cancer risk sources in urban areas. In addition, PAHs resulting from various human activities in urban areas have higher carcinogenic toxicity. This is attributed to that those in urban areas are richer in high-ring PAHs compared with those in rural areas. The carcinogenic toxicity of high-ring PAHs is greater than that of low-ring PAHs (Zhou et al. 2004; Lu et al. 2008).
During the rapid urbanization in China, many midsized cities have developed into large cities, even megacities, leading to more serious pollution due to PAHs and caused more human health risk. In the center of a city, particularly in northern China, there are increasing amounts of urban street dust containing toxic pollutants, especially PAHs. However, the potential health risk of human beings exposed to PAHs and other toxic pollutants in urban street dust is not well understood.
As one of China’s four autonomous cities, Tianjin is a megacity with 11,917 km2 area in northern China. With its rapid increase in population and economic development, Tianjin is transforming into a hub city for international shipping and logistics, modern manufacturing, and research and development, which has brought about increasingly environmental challenges. Especially, more attention has been paid to serious air pollution including urban street dust that has a direct influence on human health (Zhou et al. 2004). In order to better regulate and control potential health risk of urban residents exposed to urban street dust, we determined the concentrations and spatial distribution of ∑PAHs in Tianjin, identified main sources of PAHs in urban street dust from Tianjin, evaluated the potential health risk of Tianjin residents exposed to PAHs in urban street dust via ingestion, dermal exposure, and inhalation, and discussed pollution control strategies of the central urban area in Tianjin and other similar cities, both in China and in other countries in the world.
Materials and methods
Tianjin (39°07′ N, 117°12′ E) is a megacity adjacent to Beijing and Hebei Province in northern China. Along the coast of the Bohai Bay, Tianjin has a temperate monsoon climate and four seasons, characterized by cold, windy, dry winters affected by the vast Siberian anticyclone and hot, humid summers due to the East Asian monsoon. Its annual average temperature is 11.6–13.9 °C, annual average wind speed is 2–5 m s−1, and average annual rainfall is 360–970 mm.
Urban street dust sample of 1 g was grounded into powder with 5 g of anhydrous sodium sulfate (activated at 550 °C for 3 h). A mixed solution of 30 mL of chloromethane and hexane (1:1, v/v) was added for soaking, and ultrasonic extraction for 4 min at 25 ± 2 °C was performed. Centrifuged supernatants were collected, the extraction was repeated twice, and the combined supernatants were used. Each extract was concentrated with a rotary evaporator to 2 mL, and the solvent was exchanged to n-hexane. It was then passed through a silica column (6 g of activated silica, activated at 450 °C for 5 h), first eluted with 25 mL dichloromethane, then leached with dichloromethane and n-hexane mixed solution (2:3, v/v). The finial extracts were concentrated to almost 1.0 mL, aerated under nitrogen to 0.1 mL, then added to n-hexane to reach a volume 1.0 mL and stored at 4 °C before analysis.
PAHs determination and quality control
Aglient 5975 C gas chromatograph was equipped with Triple-Axis detector and Thermo Scientific TRACE TR-5MS GC column (30 m × 250 mm, 0.25 μm film thickness). The inlet temperature was 260 °C, and the detector temperature was 300 °C. The temperature program was listed as follows: initial temperature of 70 °C, hold for 1 min, 10 °C/min rise to 260 °C for 4 min, and 5 °C /min to 300 °C, hold for 4 min. Splitless injection was used with an injection volume of 0.1 μL and with a carrier gas of high-purity nitrogen at a flow rate of 1 mL/min. Deuterated PAHs (naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysene-d12, and perylene-d12) (J&K Chemical Ltd., USA) were used as internal standards to determine the recovery rates. The 16 PAHs analyzed included: naphthalene (Nap), acenaphthylene (Acy), acenaphthene (Ace), fluorene (Fl), phenanthrene (Phe), anthracene (Ant), fluoranthene (Fla), pyrene (Pyr), benzo[a]anthracene (BaA), chrysene (Chry), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), dibenzo[a,h]anthracene (dBaAnt), indeno[1,2,3-c,d]pyrene (IcdP), and benzo[g,h,i]perylene (BghiP) (Choi et al. 2012; Tobiszewski and Namieśnik 2012). During the sample collection, preservation, and analyses, field and laboratory blanks and standard spiked recoveries were performed to ensure quality assurance and quality control. The 16 PAHs in field and laboratory blanks were less than the detection limit. The 16 PAHs were detected using the external standard method, a method that is limited to the blank signal-to-noise ratio of three times the process of PAHs detection limit of 1 ∼ 4 μg kg−1 (dry weight), and the sample concentrations below the detection limit were treated as 0. The recoveries of PAHs varied from 75.7 to 111 % (n = 87).
PAHs from typical combustion origin can be represented by the sum of major combustion specific compounds (ΣCOMB), which include Fla, Pyr, BaA, Chry, BbF, BkF, BaP, IcdP, and BghiP. The ratio of ΣCOMB to ΣPAHs (ΣCOMB/ΣPAHs) can be used to identify the source of PAHs (Hwang et al. 2003). To avoid a single molecular marker causing susceptible impact of PAHs biodegradation behavior, the diagnostic ratios of Ant/(Ant + Phe), Fla/(Fla + Pyr), IcdP/(IcdP + BghiP), and BaA/(BaA + Chry) were also used (Yunker et al. 2002; Zhang et al. 2004; Dvorská et al. 2011).
Health risk assessment
Where Ci is the concentration of individual PAHs and TEFi is the corresponding toxic equivalency factor (Table 2).
Parameters used in cancer risk assessment
Ingestion ratio of soil (Ing R)
US EPA 2002
Exposure frequency (EF)
Wang et al. 2011;
Bartoš Tomáš et al. 2009
Exposure duration (ED)
Bartoš Tomáš et al. 2009
Body weight (BW)
Peng et al. 2011
Average life span (AT)
US EPA 2002
Dermal exposure area (SA)
US EPA 2002
Dermal adherence factor (AF)
US EPA 2002
Dermal adsorption fraction (ABS)
US EPA 2002
Inhalation ratio (Inh R)
Peng et al. 2011
Particle emission factor (PEF)
1.36 × 109
1.36 × 109
US EPA 2002
Where CSF is carcinogenic slope factor (mg kg−1 day−1)−1.
Results and discussion
Total PAH concentration and source identification
The summary of measured PAHs in urban street dust from Tianjin (micrograms per kilograms)
In this work, two to three-ring PAHs contributed 10.3 % of ∑PAHs, and four to six-ring PAHs contributed 89.7 % of ∑PAHs. Among four to six-ring PAHs, four-, five-, and six-ring PAHs contributed 20.5, 43.3, and 24.0 %, respectively. The two to three-ring PAHs sources include mainly natural sources and incomplete burning petroleum products, while the four to six-ring PAHs come from various types of complete combustions (Chen et al. 2005; Wilcke 2007; Yu et al. 2006). The concentration of four to six-ring PAHs was higher in the solid surface. On the contrary, the concentration of two to three-ring PAHs was higher in the gaseous phase (Dvoská et al. 2012). Meanwhile, the meteorological conditions are very important in diffusion of PAHs in the atmosphere. PAHs in urban street dust is not easily diffused because of various meteorological conditions, such as the low annual average temperature, annual average wind, and average annual rainfall. In general, PAHs in urban street dust had a common characteristic with high contribution (62 to 94 %) of high molecular weight PAHs (four to five rings), revealing a pyrogenic origin (Zakaria et al. 2002). The contribution of five to six-ring PAHs was extremely high, suggesting a common source of vehicle emission (Hwang et al. 2003). This result was consistent with the speciation of PAHs in gasoline vehicle soots enriched with high molecular weight PAHs, revealing a dominant influence of gasoline vehicle release (Hassanien and Abdel-Latif 2008).
Lv et al. (2010) investigated PAH contamination of suburban soils in Tianjin, and found that the mean value of ∑PAHs in soil from different districts range from 257 to 934 μg kg−1. Despite the fact that these concentrations exceeded those of the reported standard for PAHs, they were lower than those in urban street dust in Tianjin. Jiao et al. (2009) collected topsoil samples in an industrial area in Tianjin and found that the ∑PAHs concentrations ranged from 68.7 to 5,590 μg kg−1 dry weight, which were much higher than those in urban street dust in this study. The previous results showed that the concentration of ∑PAHs in soil/dust decreased in the following sequence: industrial area > urban area > suburban area, which is consistent with the data from Dalian, China (Wang et al. 2007).
The higher ΣCOMB/ΣPAHs ratio is considered as one of the characteristics of PAHs combustion sources. In this study, the mean ΣCOMB/ΣPAHs ratio was high, up to 0.64, which indicated the influence of traffic emission on PAHs concentration. Meanwhile, the mean ratio of Ant/(Ant + Phe) was 0.1, Fla/(Fla + Pyr) was 0.60, BaA/(BaA + Chry) was 0.38, and IcdP/(IcdP + BghiP) was 0.22. These results pointed out that the PAH source in Tianjin was a mixture of biomass, coal combustion, and traffic emission.
Principal component analysis
Health risk assessment
The results showed that the BaP-equivalent concentration ranged from 142.69 μg kg−1 to 10.65 mg kg−1, averaging 2.76 mg kg−1 (Table 2). In this study, the determination values of CSFingest, CSFdermal, and CSFinhalation of BaP were 7.3, 25.0, and 3.9 (mg kg−1 day−1)−1, respectively (Liu et al. 2007; Knafla et al. 2006). The cancer risk levels for children via ingestion, dermal contact, and inhalation were 1.14 × 10−5, 1.42 × 10−5, and 1.10 × 10−10, respectively, while these for adults were 3.36 × 10−5, 5.97 × 10−5, and 2.61 × 10−9, respectively. Cancer risks of inhalation for children and adults were very low, almost 105 times lower than those pathways through dermal contact and ingestion, which were negligible. Cancer risk between 10−6 and 10−4 indicated potential health risk, while greater than 10−4 suggests high potential health risk. In this study, total cancer risks for children and adults were 2.55 × 10−5 and 9.33 × 10−5, respectively, which indicated a moderate potential cancer risk, as the cancer risks were higher than the baseline value of acceptable potential cancer risk (one cancer case per million people) (Maertens et al. 2008).
The results also showed that exposure of PAHs in urban street dust were a moderate potential carcinogenic risk for residents in Tianjin. Furthermore, children often play outdoors, which may result in PAHs exposure, making children sensitive. In this study, the results were expressed by BaP-equivalent concentration rather than the total concentration. Ingestion, dermal contact, and inhalation were recognized to be the three ways of human health exposure to PAHs via urban street dust. However, the calculated risk result based on this assumption was often too conservative (Eom et al. 2007). Although many studies have shown that not all PAHs can be digested by human bodies and enter the blood circulation system from the desorption out of soil/dust particles (Eom et al. 2007; Schooten et al. 1997; Pu et al. 2004; Ounnas et al. 2009), there is no standard method to determine bioavailability of PAHs in soil/dust. If it is easy to get the bioavailable concentration of PAHs in soil/dust, we can make an evaluation of human health risks more objectively and exactly. Prolonged and high exposure of residents to PAHs can greatly affect their health, and result in many diseases such as lung cancer, bladder cancer, and skin cancer. Meanwhile, the results were established mainly by using exposure parameters of the USA. However, the exposure parameters that are appropriate for one country may not be adequate for another. The differences of dietary habits, pollution characteristics, and exposure mode between different countries could affect the toxicity of street dust to the people. Therefore, to better sustain human health in China, the government and scientists should stress the importance of establishing more applicable exposure parameters based on its own situation.
In the recent years, manufactures are being gradually moved away from urban areas in Tianjin as an industrial city. However, there is still increasing environmental pollution. In particular, types and quantity of pollutants such as PAHs, pesticides, and heavy metals entering into urban areas have increased. Coal is the main energy source in Tianjin, especially in the heating period, and biomass and coal combustion release PAHs on a large scale, serving as the primary source in urban street dust. Meanwhile, with the development of population and economics in Tianjin, motor vehicles increased rapidly, from 690,000 in 2010 to 1,700,000 in 2012. The emission of more pollutants from motor vehicles is increasingly affecting the quality of air and soil in urban areas. Hence, traffic emissions have become a most important source of PAHs in urban street dust.
In Tianjin, the green area and the per capita park green area were up to 2.2 × 108 and 8.9 m2, and the green coverage rate and the greenbelt rate reached 30.3 and 25.3 %, respectively. In particular, the center of the city has a relatively high degree of green fragmentations. These green roads, green residential areas, green parks, and their surrounding green space can greatly improve the urban microclimate by reducing road dusts, absorbing toxic gases from motor vehicles, and cleaning the air in residential areas. Due to the moderate potential health risk of PAHs in urban street dust, it is still necessary to further increase the green rate and take appropriate measures to control biomass, coal combustion, and traffic exhaust, and reduce the generation of PAHs and pollution of urban street dust in Tianjin.
In Tianjin, almost 90 % of urban street dust was heavily contaminated with PAHs. Based on ∑COMB/∑PAHs, Ant/(Ant + Phe), Fla/(Fla + Pyr), BaA/(BaA + Chry), IcdP/(IcdP + BghiP), and PCA, biomass, coal combustion, and traffic emission were the main sources of PAHs in urban street dust with the similar proportion. Total BaP-equivalent concentration instead of ∑PAHs better represent PAHs exposure due to their high levels in urban street dust. The exposure analysis was based on the exposure parameters of USA. However, the parameters used in one country may not be adequate for another. The differences of dietary habits, pollution characteristics, and exposure mode between different countries could affect the toxicity of street dust to the people. Therefore, to better protect human health in China, the government and scientists should stress the importance of establishing a more applicable exposure parameters based on its own situation.
We gratefully acknowledge that this work was financially supported by the National Natural Science Foundation of China as a key project (grant no. 21037002) and the National Key Basic Research Program (973) of China (grant no. 2011CB503802).