Science of the Total Environment 490 (2014) 153–160
Contents lists available at ScienceDirect
Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Occurrence and source apportionment of PAHs in highly vulnerable karst system Yixian Shao a,b,1, Yanxin Wang a,⁎, Xiaoqing Xu c,2, Xiao Wu a,3, Zhou Jiang a,4, Shanshan He a,5, Kun Qian a a b c
State Key Laboratory of Biogeology and Environmental Geology, School of Environmental Studies, China University of Geosciences, Wuhan 430074, PR China Geological Research Center for Agricultural Applications, China Geological Survey, Zhejiang 311203, PR China North China Power Engineering Co., Ltd. of China Power Engineering Consulting Group, Beijing 100120, PR China
H I G H L I G H T S • • • •
High levels of PAHs were detected at Guozhuang karst water system of northern China. Low and high molecular PAHs were dominant in groundwater and topsoil, respectively. Positive correlation between TOC and PAHs concentration was observed in topsoil. Coal combustion and coke production were the major sources of PAHs in groundwater.
a r t i c l e
i n f o
Article history: Received 3 April 2014 Received in revised form 29 April 2014 Accepted 29 April 2014 Available online xxxx Editor: D. Barcelo Keywords: PAHs Karst Groundwater Suspended solids PMF
a b s t r a c t The concentration and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in topsoil, groundwater and groundwater suspended solids (SS) at Guozhuang karst water system of northern China were investigated. The total concentration of PAHs ranged from 622 to 87,880 ng/g dry weight in topsoil, from 4739 to 59,314 ng/g dry weight in SS, and from 2137 to 9037 ng/L in groundwater, with mean values of 17,174 ng/g, 11,990 ng/g and 5020 ng/L, respectively. High concentrations of PAHs were mainly observed in the coal mining industrial area and the discharge area. The composition of PAHs indicated that low molecular weight PAHs were predominant in groundwater samples, the content of medium molecular weight PAHs was elevated in SS, and carcinogenic high molecular weight PAHs were frequently detected in topsoil. The high contents of low-medium molecular weight PAHs in groundwater and SS suggested relatively recent local sources of PAHs that were transported into the aquifer via leakage of contaminated surface water and/or infiltration of PAH-containing precipitation. The results of evaluating sources of PAHs using ratios of specific PAH compounds showed that PAHs mainly originated from coal and wood combustion. Furthermore, five sources were identified by positive matrix factorization (PMF) model, and the contribution to the total loadings of groundwater PAHs were: 2% for unburnt oil, 32% for coal combustion, 22% for vehicle emission, 27% for biomass combustion and 18% for coke production, respectively. Furthermore, strong correlations of total PAHs with total organic carbon (TOC) in topsoil indicated coemission of PAHs and TOC. Poor correlations of PAHs with dissolved organic carbon (DOC) in groundwater indicated that other factors exert stronger influences. Therefore, PAHs might have posed a major threat to the quality of potable groundwater in Guozhuang karst water system. © 2014 Published by Elsevier B.V.
1. Introduction
⁎ Corresponding author. Tel.: +86 027 67883998; fax: +86 027 87481030. E-mail addresses: [email protected] (Y. Shao), [email protected] (Y. Wang), [email protected] (X. Xu), [email protected] (X. Wu), [email protected] (Z. Jiang), [email protected] (S. He), [email protected] (K. Qian). 1 Tel.: +86 15926206008. 2 Tel.: +86 13476195754. 3 Tel.: +86 13545039811. 4 Tel.: +86 15927379456. 5 Tel.: +86 15926393650.
http://dx.doi.org/10.1016/j.scitotenv.2014.04.128 0048-9697/© 2014 Published by Elsevier B.V.
Polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants that occur widely in atmosphere, water, soil and other environmental media (Maioli et al., 2011; Yang et al., 2013). The occurrence and source apportionment of PAHs in various environmental samples are of great importance due to their toxic and carcinogenic properties and their relatively long lifetime in the environment (Callén et al., 2013; Nielsen et al., 1996). Hundreds of PAHs are formed and released during incomplete combustion or pyrolysis of organic matter in industrial processes and other human activities. Large
154
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
emissions and wide distributions of PAHs in the surface water and soils as well as sediments have been reported worldwide (García-Flores et al., 2013; Guo et al., 2007; Zhang et al., 2007). The highest concentrations of PAHs are generally found around coke producing plants and urban centers (Liu et al., 2013). Owing to their low aqueous solubility and hydrophobic nature, PAHs tend to associate with particulate material, including suspended solids in groundwater (Tolosa et al., 2004). In China, previous studies have been focused on the distribution and sources of PAHs in coastal water and sediments (Mai et al., 2003; Wang et al., 2013b), but there has been little information about PAHs' occurrence in suspended solids and groundwater, especially in northern China where coal mining, coal processing and utilization have been intensively developed during the past five decades. Previous studies in Shanxi Province of northern China showed that this province is one of the areas with high PAH emission, due to the effect of coal mining and industries (Liu et al., 2009). The catchment of Guozhuang karst water system for this study is severely affected by coal mining processing and combustion. Statistical surveys indicate that there are four coal mines around the karst water system with a total production of 4 million tons of coal each year (Bo, 2002), and the wastewater discharge was 30 million tons each year, including 20 million tons of industrial wastewater (Yang, 2011). Thus, an investigation on the distribution of PAHs in the study area will help improve environmental management for PAH pollution control.
Furthermore, the study area is a karst system that provides large amounts of high-quality groundwater for local drinking water and industrial water supply. However, karst systems are known for their high vulnerability to be contaminated from surface water or wastewater due to their high hydraulic conductivities and strong surface water–groundwater interaction (Heinz et al., 2009). And the additionally thin soil layers with limited retardation capacity make karst systems more sensitive to be contaminated. Thus, taking the Guozhuang karst water system as a case study area, the objective of this study is to assess the sources and behavior of PAHs in karst water system, investigating their concentrations and spatial distribution in topsoil, SS and groundwater. This study is the first effort in environmental hydrogeology studies to understand the effect of coal industries on PAH contamination of highly vulnerable karst water resource. The Guozhuang karst water system for this study is located in the south of Shanxi Province of northern China (Fig. 1), with an area of 5600 km2 where 25% of the Ordovician carbonate rocks of the karst aquifer outcrop. The study area has a semi-arid climate, with an annual average air temperature of 9–14 °C. According to the hydrogeological characteristics of the system, four regions were selected for our sampling. Region 1 (R1) is the recharge area, where the Ordovician carbonate aquifers are overlain by Carboniferous–Permian coal-bearing clastic rocks. Region 2 (R2) is the leakage segment of the Fenhe river, where
Fig. 1. The study areas and sampling locations in the Guozhuang karst water system, Shanxi Province, northern China.
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
the river water infiltrate into the karst aquifers via fractures and karst pores in the river bed. Region 3 (R3) is along the leaking Shuangchi river where there are clusters of coal-washing and coke production plants. Region 4 (R4) is the discharge area of the system. Sampling soils and groundwater from the four different regions can provide a holistic picture of the distribution of PAHs in this large-scale karst water system. 2. Materials and methods 2.1. Chemicals A mixture of 16 PAH stock standards: naphthalene(Nap), acenaphthene(Ace), acenaphthylene(Acy), fluorene(Flu), 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), dibenzo[a,h] anthracene(DiA), indeno[1,2,3-cd]pyrene(InP) and benzo[ghi] perylene(BghiP) was purchased from AccuStandara (100 mg/L, USA, solvent: dichloromethane). Other solvents included methanol, n-hexane, and dichloromethane (analytical grade, CNWBOND, Germany). Anhydrous sodium sulfate was heated at 450 °C in a muffle furnace for 4 h and stored in the sealed desiccator prior to be used. Silica gel and alumina were extracted by Sohxlet for 48 h, and dried in an oven for 12 h, then 3% deionized water was added. Before use, all glasswares were rinsed in sulfuric acid potassium dichromate lotion and heated at 180 °C for 4 h. 2.2. Analytical methods 2.2.1. Topsoil samples Topsoil samples were taken near the groundwater sampling wells over the entire catchment area using stainless steel shovels and spoons. All topsoil samples were air-dried at room temperature, sieved through a 100-mesh sieve (0.15 mm), and then stored in desiccators for analysis. For the determination of PAHs, 5 g of soil samples to which 5 g of anhydrous sodium sulfate was added was extracted in a Soxhlet apparatus fitted with a 150 mL flask. 120 mL of dichloromethane solution was added to the flask and the entire apparatus was heated for 24 h at 45 °C. After extraction, the extract was transferred to the clean-up procedure.
papers were extracted using the same Soxhlet extraction as for the topsoil samples. 2.2.4. Clean-up procedure The extracts were subsequently transferred to the top of a chromatographic column (30 cm × 10 mm i.d.) filled with 6 cm silica gel, 3 cm alumina and 3 cm anhydrous sodium sulfate for cleanup. And 20 mL mixed solution of dichloromethane/n-hexane (1:1, V: V) was used to elute PAHs. The eluate was collected to a 50 mL pear-shaped flask, the final volume was 0.5 mL after rotary evaporation and nitrogen flush. 2.2.5. PAH analysis Concentrations of PAHs were analyzed using an Agilent GC 6850 gas chromatograph equipped with a DB-5 MS capillary column (30 m × 250 μm × 0.25 mm, Agilent Co., USA), operating with helium carrier gas (1 mL/min), coupled to an Agilent MD 5975 mass spectrometer (MS). 1 μL aliquots were injected using an auto-sampler in splitless mode with a venting time of 0.75 min. The GC oven temperature was programmed to hold 80 °C for 1 min, then increased to 200 °C at 10 °C/min, which was held for 2 min increase to 290 °C at 4 °C/min, and finally to maintain 290 °C for 10 min. The injector and detector temperatures were 280 °C. 2.2.6. PMF model PMF is a receptor modeling tool developed in the early 1990s by Paatero and Tapper (1994), which utilizes non-negativity constraints for obtaining physically realistic meanings. PMF runs on a matrix of individual PAH compound concentrations, and the model principle is briefly explained here. PMF defines that a n × m data matrix X (chemical species concentrations (n) measured at sites (m)) can be factored into a (n × p) matrix G (source contributions) and a (p × m) matrix F (source profiles) with a residual matrix E (n × m):
X ¼ GF þ E: The elements eij of matrix E (n × m) indicates the residual value not accounted for by the modeled data value xij, i.e.,
xij ¼ 2.2.2. Groundwater samples Groundwater samples were collected in May 2013 from 22 boreholes across the catchment area. The groundwater was filtrated with a vacuum Sartorius filtration apparatus and Whatman glass microfiber filters with a pore size of 0.45 μm. The cartridges used for solid-phase extraction were C 18 (500 mg, 6 mL, CNWBOND, Germany). PAHs were extracted from groundwater (1 L) added with 100 mL methane (10%) as an organic modifier. Before the sample loading, the solid-phase adsorbent was pre-conditioned with 6 mL of dichloromethane, 6 mL of methanol and 6 mL of water. The samples were introduced to the cartridges by means of PTFE tubes at flow rates of 5 mL/min. After sample loading, the solid phase was washed with 6 mL of water. Cartridges were then dried for more than 30 min under Supelco vacuum manifold (Sigma-Aldrich), which allowed for the parallel extraction of up to 12 samples and the adsorbent were then eluted with 12 mL of 1:1 (v/v) mixtures of dichloromethane and n-hexane. 2.2.3. Suspended solids samples Suspended solids samples were collected from 2 L groundwater filtrating with a vacuum Sartorius filtration apparatus and Whatman organic glass micro-fiber filters with a pore size of 0.45 μm. All SS samples were air-dried at room temperature in a desiccator. The weighed filter
155
p X
g ik f kj þ eij
k¼1
where xij is the jth species concentration measured in the ith sample, gik is the kth source's contribution to sample i, and fkj is the jth element's concentration in source k. eij is the residual associated with the jth species concentration measured in the ith sample. Our PMF analysis was carried out using the US EPA PMF 3.0 model (US EPA, 2008). 2.2.7. Quality control and statistical analyses All data were subject to strict quality control procedures. Four surrogate standards (naphthene-d8, acenaphthene-d10, phenanthrene-d10 and chrysene-d12) were added to all samples to monitor the procedures of sample extraction, cleanup and analysis. The average recoveries of surrogate standards varied from 78% to 101%, 83% to 105% and 91% to 110% in groundwater, suspended solids and topsoil samples, respectively. One laboratory blank and one duplicate were run with every 10 samples. Statistical analyses of PAH concentrations in the environmental samples for different regions to obtain correlation coefficients between PAHs and TOC as well as mean and standard deviation of replicated spiked standard solutions were done using PASW statistics 18 (SPSS Inc., USA) and Origin 8.
156
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
Table 1 Residual levels of PAHs in the groundwater, suspended solids in groundwater and soil from Guozhuang karst system. PAHs
NaP Acy Ace Flu Phe Ant Fla Pyr BaA Chr BbF BkF BaP DiA InP BghiP ΣPAHs
Groundwater (ng/L) n = 22
Suspended solids (ng/g, dw) n = 22
Soil (ng/g, dw) n = 15
Range
Mean
SD
Range
Mean
SD
Range
Mean
SD
90–400 ND — 217 217–1320 340–2407 563–4258 257–2000 213–673 187–443 ND — 423 ND — 277 ND — 477 ND — 357 ND — 400 ND ND ND 2137–9037
148 27.7 531 934 1400 963 308 240 185 120 83.6 69 18.2 ND ND ND 5020
63.6 71.6 314 600 1042 491 119 68.7 207 134 182 140 85.3 ND ND ND 2050
ND — 1660 ND — 1168 ND — 1290 ND — 2677 827–3854 652–3051 770–11,135 687–8619 ND — 7601 ND — 4978 ND — 7280 ND — 5567 ND ND ND ND 4739–59,314
693 429 122 1235 1791 1347 2140 1867 1098 682 330 253 ND ND ND ND 11,990
365 489 308 549 681 545 2077 1580 1949 1254 1552 1187 ND ND ND ND 11,072
19.9–3340 ND — 617 11.9–2932 25.8–3147 39.2–5069 21.9–2730 32.8–6760 34.3–6761 70.5–7712 45.2–10,814 73–25,958 53.6–9584 65.6–4922 48.2–9175 ND — 2383 65.1–3797 622–87,880
533 94 332 458 1163 575 1014 1007 1171 1409 3473 1231 1128 2058 554 967 17,174
919 159 748 816 1590 811 1905 1820 2046 2787 6725 2548 1663 2983 759 1237 26,210
Note: ND not detected. Σ PAHs-total concentration of the 16 PAHs.
3. Results and discussion
3.2. Distribution patterns of PAHs
3.1. Residual levels of PAHs
In order to distinguish the proportions of low molecular, medium molecular and high molecular (LM, MM and HM) PAHs in different environment media, sixteen PAH compounds were divided into three groups: 2 + 3 rings, 4-rings and 5 + 6 rings. Fig. 2 showed the triangular diagram of percentage average concentrations of different ring number PAHs in different sampling stations. The percentage of LM PAHs to total PAHs was higher than that of MM and HM in groundwater stations, indicating that low molecular PAHs were predominant in groundwater samples, and dominated by phenanthrene, accounting for about 27% of the total 16 PAHs. MM PAHs were also detected with low detection frequencies, and HM PAHs such as six-ring PAHs were not detected. All PAHs analyzed in our study show relatively high octanol–water partition coefficients, with the only exception of lightest PAHs such as naphthalene (log Kow 3.4 to 4). Therefore they are likely to be found in both soil and SS in which they may occur as mobile constituents, rather than in the aqueous phase in which they show a very low solubility (Quesada et al., 2014). Since low molecular PAHs were commonly
The total and individual concentrations of 16 PAHs in groundwater, SS and topsoil samples from Guozhuang karst water system were listed in Table 1. Most types of PAHs were detected in the groundwater with a mean concentration of 5020 ng/L. The levels of phenanthrene (1400 ng/L) was the highest and account for 27.9% of total PAHs. Three-ring PAHs were predominant among individual PAHs, and six-ring PAHs were not detected. This tendency was similar to the water samples from the lower Mississippi River and the Gulf of Mexico in the US (Mitra and Bianchi, 2003). Most of the 16 EPA priority parent PAHs were present in a majority of SS samples. The total concentrations of PAHs in SS samples varied from 4739 to 59,314 ng/g, with an average concentration of 11,990 ng/g, which were much lower than the river water SS levels in the Daliao River watershed (21,725 ng/g) (Guo et al., 2007). Probably owing to absorption on SS for PAHs and different SS contents, in terms of individual PAHs in the SS, the composition characteristic was different from that in groundwater. Four-ring PAHs such as fluoranthene and pyrene were predominant among individual PAHs, account for 33.4%. The total PAH concentration in topsoil varied greatly depending on the sampling location and ranged from 622 to 87,880 ng/g with an average concentration of 17,174 ng/g, much higher than that of topsoil samples from Ammer River of Germany (8770 ng/g) which flows through farmlands or small towns with some industrial activities such as metal processing, electronics, and furniture production (Liu et al., 2013). And it was about 9 times higher than that from the Liangtan River (2040 ng/g) along a recently urbanized and industrialized area of China (Liu et al., 2013). The PAH composition of the topsoil samples from Guozhuang was different from that of groundwater and SS. All PAHs including six-ring PAHs were detected in topsoil samples. The levels of benzo[b]fluoranthene were the highest (73 to 25,959 ng/g), account for 20.2% of total PAHs. The abnormally high PAH concentration in the topsoil of our study area clearly indicates the effect of intensive mining activities. It can then be expected that the PAHs, especially the low molecular weight PAHs (Liang et al., 2008), deposited in soil would be washed out during the rainy season, to contaminate causing groundwater contaminated.
Fig. 2. Triangular diagram of percentage average concentrations of the 16 PAHs in groundwater, suspended solids and soil samples.
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
detected in our groundwater samples, their possible sources might be SS that were transported into groundwater together with PAHs which were later mobilized into aqueous phase. Such a PAH composition might also reflect a relatively recent local source of PAHs that were transported into the aquifer via processes like wastewater discharge, adhesion on suspended solids and surface water leakage rather than atmospheric deposition. In SS, although LM PAHs were most abundant, the content of MM PAHs increased gradually. The average percentage of MM PAHs to total PAHs ranged from 32.3% to 62.8%. And HM PAHs such as five- and six-ring PAHs suspected to be carcinogenic were detected with high frequencies in topsoil samples, which were very similar to the Liangtan River (Liu et al., 2013). HM PAHs in the topsoil may be due to the greater affinity of high molecular weight PAHs for the solid matrix. The variability of PAHs patterns in the topsoil samples indicated that there were likely different sources of PAHs along the Guozhuang karst water system. In contrast to the stable and diffuse characteristics of PAH sources in early industrialized countries, the sources of PAHs at Guangzhuang appeared to be more diversified. Another observation was that the concentrations of 4-ring PAHs in soil samples were substantially lower than those in SS, which was also found in the Pearl River (Luo et al., 2006). This observation suggested that low-medium molecular PAHs could be removed from the soil phase during deposition and early diagenesis and then transported into the aquifer together with SS. Numerous studies showed that low molecular PAHs are acutely toxic, while high-ring PAHs are considered to be genotoxic (Perugini et al., 2007). So our results showed that the drinking water in Guozhuang karst water system had been polluted by less toxic PAHs at low concentration levels. This result was similar to that of a previous study of riverine waters from Llobregat hydrographic basin in Catalonia, northern Spain (Olivella et al., 2006). Different patterns of PAH composition in groundwater, SS and soil were also found in other regions, such as the Caspian Sea (Tolosa et al., 2004) and Tijuana of Mexico (García-Flores et al., 2013). Since low molecular weight PAHs are less hydrophobic relative to high molecular weight PAHs, they tend to be more enriched in the aqueous phase, leading to a greater proportion of MM and HM PAHs in SS and soil. Besides, HM PAHs are more resistant to degradation processes in soil (Simarro et al., 2013).
157
The sum of all measured compounds of groundwater and SS in the four sampling areas were summarized in Fig. 3. The differences between
the R1, R2 and R3 (except R4) were found to be statistically significant by Student's t test (p b 0.05). In general, PAH concentrations were higher in groundwater and SS samples from the sampling areas R3 and R4 than those from R1 and R2. The highest concentrations were detected in R3 could be related to the discharge of coking wastewater into the river water which may later leak into the subsurface. With a relatively high groundwater flow rate and strong interaction with surface water, karst aquifers are particularly vulnerable to be contaminated (Simmleit and Herrmann, 1987). PAHs in coking wastewater originate not only from processes of coke production but also from purification processes of industrial by-products, such as ammonium, benzene, and tar. Thus, The concentration of PAHs in coking wastewater could be as high as 8710 μg/L (Zhang et al., 2013), and have been identified as a source for groundwater PAH contamination in northern China (Wang et al., 2013a). Our sampling area R1 is the recharge area, where the Ordovician karst aquifers are partially overlain by Carboniferous–Permian coalbearing strata. The PAHs in groundwater samples from R1 may originate from raw coal. Though the concentration of PAHs in raw coal of Shanxi is high, ranging from 162 to 270 μg/g (Yan et al., 2013), these PAHs embedded inside cavities or pores of the cross-linked network of coal were probably not able to be reached by water, but can be only extracted by organic solvents by swelling (Jonker et al., 2005). Our sampling area R2 is along the leaking Fenhe river and there is almost no coal industry. The PAHs in groundwater may mainly originate from the recharge area and automobile exhaust emission. As a result, the contents of PAHs in samples from R1 and R2 were lower than those from R3 and R4. The sources of PAHs are formed mainly via two mechanisms: fuel-combustion (pyrolytic) and discharge of crude oil related material (petrogenic), and may be identified by ratios of individual PAH compounds based on peculiarities in PAH composition and distribution pattern as a function of the emission source (Zhang et al., 2004). In order to survey the sources of PAHs in Guozhuang karst water system, Ant/Ant + Phe versus Fla/Fla + Pyr was plotted (Fig. 4). Usually, The Ant content in petroleum products is lower than that of Phe. However, it can be produced in the process of combustion (Zhang et al., 2012). So Ant/Ant + Phe ratios higher than 0.1 indicate pyrolytic origin, whereas values lower than 0.1 indicate petrogenic origin; Fla/Fla + Pyr ratio less than 0.5 being defined as the petrogenic origin, whereas the ratios higher than 0.5 corresponded to wood or coal combustion (Doong and Lin, 2004; Guo et al., 2007). Fig. 4 illustrated that PAHs in groundwater, SS and topsoil mainly originated from wood and coal combustion, and PAHs in very few topsoil samples originated from petroleum
Fig. 3. Box-whisker plots of the total PAH concentrations in groundwater (ng/L) and suspended solids (μg/g). (PR1,R3 = 0.001, PR1,R4 = 0.189, PR2,R3 = 0.021, PR2,R4 = 0.141, α = 0.05 in groundwater. PR1,R3 = 0.017, PR1,R4 = 0.564, PR2,R3 = 0.015, PR2,R4 = 0.531, α = 0.05 in suspended solids).
Fig. 4. Plot of the isomeric ratio Ant/Ant + Phe vs Fla/Fla + Pyr.
3.3. Spatial distributions of PAHs
158
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
Fig. 5. Source profiles obtained from PMF model.
combustion. As a matter of fact, coal is one of the most important source of energy in our study area. 3.4. Source of PAHs Although the compositions and ratios of selected PAH compounds can be taken as indirect indicators of PAH sources, the relationships among different factors and their percentage of contribution to contamination were not clear. In this study, PMF model was used to better understand the PAH sources in Guozhuang karst water system. The PMF analysis used individual PAH concentrations as input data and run in robust mode to keep outliers from unduly influencing the results. For each dataset the number of factors was varied, each time running the model 20 times starting from a different initial seed. This was done to better understand the variability of the PMF analysis. There are also no strict rules for determining the number of factors. The tentative identification of the factor profiles was based on the molecular markers in different sources. By comprehensively considering the characteristics of anthropogenic activities that may release PAHs into the environment in our study area, five factors (oil, coal combustion, vehicle, biomass combustion and coal tar) were selected as the possible sources of PAHs in
Guozhuang karst water system. Factor profiles of individual PAH compounds in the five factors from the PMF model output were given in Fig. 5. The source 1 profile was dominated by Phe and Ant, moderately weighted by Nap, Acy and Ace, and a little Chr, BbF. The petrogenic PAHs are characterized by the predominance of 2 and 3-ring PAHs (Yunker et al., 2002). So the source 1 was identified as unburnt petroleum (oil). 4 to 5 ring PAHs had a high loading in the source 2 profile, including Pyr, BaA, Chr, BbF and BkF, which are typical markers for coal combustion (Huang et al., 2013; Kannan et al., 2005; Qin et al., 2014), indicating the effects of coal combustion. The source 3 profile mainly consisted by high molecular weight PAHs. Among these PAHs, Fla, Pyr, BbF, BkF were identified as markers of traffic tunnels (Liu et al., 2010b). Among the other compounds in this profile, the concentration of InP was the highest, which has been identified as typical tracers of vehicle emission of PAHs (Harrison et al., 1996; Hu et al., 2013; Larsen and Baker, 2003). The source 4 profile had predominant loadings of Acy and BbF, with some loadings of Nap. Acy has been commonly used as an indicator of wood combustion (Zuo et al., 2007). Incomplete combustion of biomass has also been assigned as the source for Nap (Grover et al., 2012). Thus the source 4 could be identified as
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
159
Fig. 6. Relationship between TOC/DOC and total concentration of 16 PAHs in groundwater and topsoil at Guozhuang karst water system including coefficient of determination (R2), number of points (N), and probability (p) (regression slope t test, α = 0.05).
biomass combustion. The source 5 profile was dominated by Acy, Phe and BbF, and moderately weighted by Fla, Pyr, BaA, and Chr. It has been reported Acy and Phe were the main components of coal products (Jiao et al., 2012; Lee et al., 2005). On the other hand, Fla and Phe were sometimes used as indicators for coke oven sources (Liu et al., 2010a; Zuo et al., 2007). Therefore, the source 5 may indicate the effects of coke production. The average contributions of each source to total PAHs in groundwater samples were calculated. The relative contributions for the 1– 5 factors were 2%, 32%, 22%, 27%, 18%, respectively. Therefore, the major sources of PAHs in groundwater were categorized in this study as pyrogenic origin, especially coal combustion that accounts for 50% (source 2 plus 5). At Guozhuang, coal has been used for home heating in the winter. And like many other areas in northern China, a large amount of consumption in both industrial and domestic sectors may have made coal the primary contributor to PAHs in the environment.
3.5. Relationship between TOC/DOC and PAHs Organic matter plays an important role in the partitioning and retention of organic contaminant (Agarwal and Bucheli, 2011). Fig. 6 showed the relationship between TOC/DOC content and total concentration of 16 PAHs. The input of PAHs to groundwater did not seem to be linked to the input of DOC (R2 = 0.11, p = 0.08). As compared to suspended solids, the DOC concentration might be too low to influence PAH concentrations in water. Another probable interpretation is that PAHs and DOC were either not transported to the groundwater from the same sources or, if they are, the factors driving their mobilization might differ. Instead, a major fraction of PAHs would enter the groundwater via direct atmospheric deposition to surface water that may then leak into the aquifer. And PAHs and DOC would undergo different geochemical processes in the karst aquifer such as adsorption and biodegradation. Our observations might illustrate the importance of direct input of PAHs from the air and surface water to groundwater and geochemical processes of PAHs in this type of aquatic environment of strong surface water–groundwater interaction. And the mobilization of PAHs in the aquifer could be related to particle-facilitated transport (Schwarz et al., 2011). In topsoil, strongly significant positive correlations between TOC and total concentration of PAHs were observed (R2 = 0.89, p b 0.0001). It would seem intuitive that the TOC and PAHs were co-emitted with wastewater at Guozhuang karst water system. High TOC in topsoil to some extent resulted in decreased degradation of HM PAHs in soil due to the strong adsorption (Hinga, 2003), leading to higher abundance of the HM PAHs in topsoil.
4. Conclusions To our knowledge, this study is the first effort to investigate the occurrence and origins of PAHs in karst water systems in northern China. At Guozhuang, the distribution pattern of total PAHs was different in different environmental media. LM, MM and HM PAHs were the representative PAHs in the groundwater, suspended solids and topsoil, respectively. The samples from region R3 and R4 exhibited very high PAH concentrations, and therefore greater attention needs to be paid to these two regions in environmental management. Source apportionment of PAHs suggests a mixed origin of PAHs, but coal combustion should be the dominant source for PAHs in the soil and groundwater environment at Guozhuang.
Acknowledgments The research work was financially supported by the National Natural Science Foundation of China (No. 40902071, and No. 41120124003), the Ministry of Science and Technology of China (2012AA062602), and the Ministry of Education of China (111 project and Priority Development Projects of SRFDP (20120145130001)).
References Agarwal T, Bucheli TD. Is black carbon a better predictor of polycyclic aromatic hydrocarbon distribution in soils than total organic carbon? Environ Pollut 2011;159(1): 64–70. Bo G. Causes of flow rate decrease of Guozhuang Spring and countermeasures [J]. Water Resour Prot 2002;1:64–5. (in Chinese with English abstract). Callén M, Iturmendi A, López J, Mastral A. Source apportionment of the carcinogenic potential of polycyclic aromatic hydrocarbons (PAH) associated to airborne PM10 by a PMF model. Environ Sci Pollut Res 2013:1–13. Doong R-A, Lin Y-T. Characterization and distribution of polycyclic aromatic hydrocarbon contaminations in surface sediment and water from Gao-ping River, Taiwan. Water Res 2004;38(7):1733–44. García-Flores E, Wakida F, Espinoza-Gomez J. Sources of polycyclic aromatic hydrocarbons in urban storm water runoff in Tijuana, Mexico. Int J Environ Res 2013;7(2): 387–94. Grover IS, Sharma R, Singh S, Pal B. Polycyclic aromatic hydrocarbons in some grounded coffee brands. Environ Monit Assess 2012:1–5. Guo W, He M, Yang Z, Lin C, Quan X, Wang H. Distribution of polycyclic aromatic hydrocarbons in water, suspended particulate matter and sediment from Daliao River watershed, China. Chemosphere 2007;68(1):93–104. Harrison RM, Smith D, Luhana L. Source apportionment of atmospheric polycyclic aromatic hydrocarbons collected from an urban location in Birmingham, UK. Environ Sci Technol 1996;30(3):825–32. Heinz B, Birk S, Liedl R, Geyer T, Straub K, Andresen J, et al. Water quality deterioration at a karst spring (Gallusquelle, Germany) due to combined sewer overflow: evidence of bacterial and micro-pollutant contamination. Environ Geol 2009; 57(4):797–808. Hinga K. Degradation rates of low molecular weight PAH correlate with sediment TOC in marine subtidal sediments. Mar Pollut Bull 2003;46(4):466–74.
160
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
Hu N-J, Huang P, Liu J-H, Shi X-F, Ma D-Y, Liu Y. Source apportionment of polycyclic aromatic hydrocarbons in surface sediments of the Bohai Sea, China. Environ Sci Pollut Res 2013;20(2):1031–40. Huang W, Huang B, Bi X, Lin Q, Liu M, Ren Z, et al. Emission of PAHs, NPAHs and OPAHs from the residential honeycomb coal briquettes combustion. Energy Fuel 2013; 28(1):636–42. Jiao W, Wang T, Khim JS, Luo W, Hu W, Naile JE, et al. PAHs in surface sediments from coastal and estuarine areas of the northern Bohai and Yellow Seas, China. Environ Geochem Health 2012;34(4):445–56. Jonker MT, Hawthorne SB, Koelmans AA. Extremely slowly desorbing polycyclic aromatic hydrocarbons from soot and soot-like materials: evidence by supercritical fluid extraction. Environ Sci Technol 2005;39(20):7889–95. Kannan K, Johnson-Restrepo B, Yohn SS, Giesy JP, Long DT. Spatial and temporal distribution of polycyclic aromatic hydrocarbons in sediments from Michigan inland lakes. Environ Sci Technol 2005;39(13):4700–6. Larsen RK, Baker JE. Source apportionment of polycyclic aromatic hydrocarbons in the urban atmosphere: a comparison of three methods. Environ Sci Technol 2003; 37(9):1873–81. Lee RG, Coleman P, Jones JL, Jones KC, Lohmann R. Emission factors and importance of PCDD/Fs, PCBs, PCNs, PAHs and PM10 from the domestic burning of coal and wood in the UK. Environ Sci Technol 2005;39(6):1436–47. Liang Y, Fung PK, Tse MF, Hong HC, Wong MH. Sources and seasonal variation of PAHs in the sediments of drinking water reservoirs in Hong Kong and the Dongjiang River (China). Environ Monit Assess 2008;146(1–3):41–50. Liu WX, Dou H, Wei ZC, Chang B, Qiu WX, Liu Y, et al. Emission characteristics of polycyclic aromatic hydrocarbons from combustion of different residential coals in North China. Sci Total Environ 2009;407(4):1436–46. Liu G, Tong Y, Luong JH, Zhang H, Sun H. A source study of atmospheric polycyclic aromatic hydrocarbons in Shenzhen, South China. Environ Monit Assess 2010a; 163(1–4):599–606. Liu S, Xia X, Yang L, Shen M, Liu R. Polycyclic aromatic hydrocarbons in urban soils of different land uses in Beijing, China: distribution, sources and their correlation with the city's urbanization history. J Hazard Mater 2010b;177(1):1085–92. Liu Y, Beckingham B, Ruegner H, Li Z, Ma L, Schwientek M, et al. Comparison of sedimentary PAHs in the Rivers of Ammer (Germany) and Liangtan (China): differences between early-and newly-industrialized countries. Environ Sci Technol 2013;47(2): 701–9. Luo X-J, Chen S-J, Mai B-X, Yang Q-S, Sheng G-Y, Fu J-M. Polycyclic aromatic hydrocarbons in suspended particulate matter and sediments from the Pearl River Estuary and adjacent coastal areas, China. Environ Pollut 2006;139(1):9–20. Mai B, Qi S, Zeng EY, Yang Q, Zhang G, Fu J, et al. Distribution of polycyclic aromatic hydrocarbons in the coastal region off Macao, China: assessment of input sources and transport pathways using compositional analysis. Environ Sci Technol 2003;37(21): 4855–63. Maioli OL, Rodrigues KC, Knoppers BA, Azevedo DA. Distribution and sources of aliphatic and polycyclic aromatic hydrocarbons in suspended particulate matter in water from two Brazilian estuarine systems. Cont Shelf Res 2011;31(10):1116–27. Mitra S, Bianchi T. A preliminary assessment of polycyclic aromatic hydrocarbon distributions in the lower Mississippi River and Gulf of Mexico. Mar Chem 2003;82(3): 273–88. Nielsen T, Jørgensen HE, Larsen JC, Poulsen M. City air pollution of polycyclic aromatic hydrocarbons and other mutagens: occurrence, sources and health effects. Sci Total Environ 1996;189:41–9. Olivella M, Ribalta T, De Febrer A, Mollet J, De Las Heras F. Distribution of polycyclic aromatic hydrocarbons in riverine waters after Mediterranean forest fires. Sci Total Environ 2006;355(1):156–66.
Paatero P, Tapper U. Positive matrix factorization: a non‐negative factor model with optimal utilization of error estimates of data values. Environmetrics 1994;5(2):111–26. Perugini M, Visciano P, Giammarino A, Manera M, Di Nardo W, Amorena M. Polycyclic aromatic hydrocarbons in marine organisms from the Adriatic Sea, Italy. Chemosphere 2007;66(10):1904–10. Qin L, Han J, He X, Lu Q. The emission characteristic of PAHs during coal combustion in a fluidized bed combustor. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects 2014;36(2):212–21. Quesada S, Tena A, Guillén D, Ginebreda A, Vericat D, Martínez E, et al. Dynamics of suspended sediment borne persistent organic pollutants in a large regulated Mediterranean river (Ebro, NE Spain). Sci Total Environ 2014;473:381–90. Schwarz K, Gocht T, Grathwohl P. Transport of polycyclic aromatic hydrocarbons in highly vulnerable karst systems. Environ Pollut 2011;159(1):133–9. Simarro R, Gonzalez N, Bautista LF, Molina MC. Biodegradation of high‐molecular‐weight polycyclic aromatic hydrocarbons by a wood‐degrading consortium at low temperatures. FEMS Microbiol Ecol 2013;83(2):438–49. Simmleit N, Herrmann R. The behavior of hydrophobic, organic micropollutants in different karst water systems. Water Air Soil Pollut 1987;34(1):79–95. Tolosa I, de Mora S, Sheikholeslami MR, Villeneuve J-P, Bartocci J, Cattini C. Aliphatic and aromatic hydrocarbons in coastal Caspian Sea sediments. Mar Pollut Bull 2004;48(1): 44–60. US EPA. EPA positive matrix factorization (PMF) 3.0 fundamentals & user guide. Online available at http://www.epa.gov/heasd/products/pmf/pmf.htm, 2008. Wang Y, Xia Z, Liu D, Qiu W, Duan X, Wang R, et al. Multimedia fate and source apportionment of polycyclic aromatic hydrocarbons in a coking industry city in northern China. Environ Pollut 2013a;181:115–21. Wang Z, Wang Y, Ma X, Na G, Lin Z, Yao Z. Probabilistic ecological risk assessment of typical PAHs in coastal water of Bohai Sea. Polycycl Aromat Compd 2013b;33(4): 367–79. Yan C, Yang Y, Liu M, Nie M, Gu L, Zhou JL. Polycyclic aromatic hydrocarbons (PAHs) in Chinese coal: occurrence and sorption mechanism. Environ Earth Sci 2013:1–8. Yang X. The pollution present situation and the countermeasures of Guozhuang Spring field, Shanxi Province. Water Resour Plann Des 2011(01):23–5. Yang D, Qi S, Zhang Y, Xing X, Liu H, Qu C, et al. Levels, sources and potential risks of polycyclic aromatic hydrocarbons (PAHs) in multimedia environment along the Jinjiang River mainstream to Quanzhou Bay, China. Mar Pollut Bull 2013;76(1):298–306. Yunker MB, Macdonald RW, Vingarzan R, Mitchell RH, Goyette D, Sylvestre S. PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition. Org Geochem 2002;33(4):489–515. Zhang Z, Huang J, Yu G, Hong H. Occurrence of PAHs, PCBs and organochlorine pesticides in the Tonghui River of Beijing, China. Environ Pollut 2004;130(2):249–61. Zhang Y, Tao S, Cao J, Coveney RM. Emission of polycyclic aromatic hydrocarbons in China by county. Environ Sci Technol 2007;41(3):683–7. Zhang W, Wei C, Chai X, He J, Cai Y, Ren M, et al. The behaviors and fate of polycyclic aromatic hydrocarbons (PAHs) in a coking wastewater treatment plant. Chemosphere 2012;88(2):174–82. Zhang W, Wei C, Yan B, Feng C, Zhao G, Lin C, et al. Identification and removal of polycyclic aromatic hydrocarbons in wastewater treatment processes from coke production plants. Environ Sci Pollut Res 2013;20(9):6418–32. Zuo Q, Duan Y, Yang Y, Wang X, Tao S. Source apportionment of polycyclic aromatic hydrocarbons in surface soil in Tianjin, China. Environ Pollut 2007;147(2):303–10.
Contents lists available at ScienceDirect
Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Occurrence and source apportionment of PAHs in highly vulnerable karst system Yixian Shao a,b,1, Yanxin Wang a,⁎, Xiaoqing Xu c,2, Xiao Wu a,3, Zhou Jiang a,4, Shanshan He a,5, Kun Qian a a b c
State Key Laboratory of Biogeology and Environmental Geology, School of Environmental Studies, China University of Geosciences, Wuhan 430074, PR China Geological Research Center for Agricultural Applications, China Geological Survey, Zhejiang 311203, PR China North China Power Engineering Co., Ltd. of China Power Engineering Consulting Group, Beijing 100120, PR China
H I G H L I G H T S • • • •
High levels of PAHs were detected at Guozhuang karst water system of northern China. Low and high molecular PAHs were dominant in groundwater and topsoil, respectively. Positive correlation between TOC and PAHs concentration was observed in topsoil. Coal combustion and coke production were the major sources of PAHs in groundwater.
a r t i c l e
i n f o
Article history: Received 3 April 2014 Received in revised form 29 April 2014 Accepted 29 April 2014 Available online xxxx Editor: D. Barcelo Keywords: PAHs Karst Groundwater Suspended solids PMF
a b s t r a c t The concentration and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in topsoil, groundwater and groundwater suspended solids (SS) at Guozhuang karst water system of northern China were investigated. The total concentration of PAHs ranged from 622 to 87,880 ng/g dry weight in topsoil, from 4739 to 59,314 ng/g dry weight in SS, and from 2137 to 9037 ng/L in groundwater, with mean values of 17,174 ng/g, 11,990 ng/g and 5020 ng/L, respectively. High concentrations of PAHs were mainly observed in the coal mining industrial area and the discharge area. The composition of PAHs indicated that low molecular weight PAHs were predominant in groundwater samples, the content of medium molecular weight PAHs was elevated in SS, and carcinogenic high molecular weight PAHs were frequently detected in topsoil. The high contents of low-medium molecular weight PAHs in groundwater and SS suggested relatively recent local sources of PAHs that were transported into the aquifer via leakage of contaminated surface water and/or infiltration of PAH-containing precipitation. The results of evaluating sources of PAHs using ratios of specific PAH compounds showed that PAHs mainly originated from coal and wood combustion. Furthermore, five sources were identified by positive matrix factorization (PMF) model, and the contribution to the total loadings of groundwater PAHs were: 2% for unburnt oil, 32% for coal combustion, 22% for vehicle emission, 27% for biomass combustion and 18% for coke production, respectively. Furthermore, strong correlations of total PAHs with total organic carbon (TOC) in topsoil indicated coemission of PAHs and TOC. Poor correlations of PAHs with dissolved organic carbon (DOC) in groundwater indicated that other factors exert stronger influences. Therefore, PAHs might have posed a major threat to the quality of potable groundwater in Guozhuang karst water system. © 2014 Published by Elsevier B.V.
1. Introduction
⁎ Corresponding author. Tel.: +86 027 67883998; fax: +86 027 87481030. E-mail addresses: [email protected] (Y. Shao), [email protected] (Y. Wang), [email protected] (X. Xu), [email protected] (X. Wu), [email protected] (Z. Jiang), [email protected] (S. He), [email protected] (K. Qian). 1 Tel.: +86 15926206008. 2 Tel.: +86 13476195754. 3 Tel.: +86 13545039811. 4 Tel.: +86 15927379456. 5 Tel.: +86 15926393650.
http://dx.doi.org/10.1016/j.scitotenv.2014.04.128 0048-9697/© 2014 Published by Elsevier B.V.
Polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants that occur widely in atmosphere, water, soil and other environmental media (Maioli et al., 2011; Yang et al., 2013). The occurrence and source apportionment of PAHs in various environmental samples are of great importance due to their toxic and carcinogenic properties and their relatively long lifetime in the environment (Callén et al., 2013; Nielsen et al., 1996). Hundreds of PAHs are formed and released during incomplete combustion or pyrolysis of organic matter in industrial processes and other human activities. Large
154
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
emissions and wide distributions of PAHs in the surface water and soils as well as sediments have been reported worldwide (García-Flores et al., 2013; Guo et al., 2007; Zhang et al., 2007). The highest concentrations of PAHs are generally found around coke producing plants and urban centers (Liu et al., 2013). Owing to their low aqueous solubility and hydrophobic nature, PAHs tend to associate with particulate material, including suspended solids in groundwater (Tolosa et al., 2004). In China, previous studies have been focused on the distribution and sources of PAHs in coastal water and sediments (Mai et al., 2003; Wang et al., 2013b), but there has been little information about PAHs' occurrence in suspended solids and groundwater, especially in northern China where coal mining, coal processing and utilization have been intensively developed during the past five decades. Previous studies in Shanxi Province of northern China showed that this province is one of the areas with high PAH emission, due to the effect of coal mining and industries (Liu et al., 2009). The catchment of Guozhuang karst water system for this study is severely affected by coal mining processing and combustion. Statistical surveys indicate that there are four coal mines around the karst water system with a total production of 4 million tons of coal each year (Bo, 2002), and the wastewater discharge was 30 million tons each year, including 20 million tons of industrial wastewater (Yang, 2011). Thus, an investigation on the distribution of PAHs in the study area will help improve environmental management for PAH pollution control.
Furthermore, the study area is a karst system that provides large amounts of high-quality groundwater for local drinking water and industrial water supply. However, karst systems are known for their high vulnerability to be contaminated from surface water or wastewater due to their high hydraulic conductivities and strong surface water–groundwater interaction (Heinz et al., 2009). And the additionally thin soil layers with limited retardation capacity make karst systems more sensitive to be contaminated. Thus, taking the Guozhuang karst water system as a case study area, the objective of this study is to assess the sources and behavior of PAHs in karst water system, investigating their concentrations and spatial distribution in topsoil, SS and groundwater. This study is the first effort in environmental hydrogeology studies to understand the effect of coal industries on PAH contamination of highly vulnerable karst water resource. The Guozhuang karst water system for this study is located in the south of Shanxi Province of northern China (Fig. 1), with an area of 5600 km2 where 25% of the Ordovician carbonate rocks of the karst aquifer outcrop. The study area has a semi-arid climate, with an annual average air temperature of 9–14 °C. According to the hydrogeological characteristics of the system, four regions were selected for our sampling. Region 1 (R1) is the recharge area, where the Ordovician carbonate aquifers are overlain by Carboniferous–Permian coal-bearing clastic rocks. Region 2 (R2) is the leakage segment of the Fenhe river, where
Fig. 1. The study areas and sampling locations in the Guozhuang karst water system, Shanxi Province, northern China.
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
the river water infiltrate into the karst aquifers via fractures and karst pores in the river bed. Region 3 (R3) is along the leaking Shuangchi river where there are clusters of coal-washing and coke production plants. Region 4 (R4) is the discharge area of the system. Sampling soils and groundwater from the four different regions can provide a holistic picture of the distribution of PAHs in this large-scale karst water system. 2. Materials and methods 2.1. Chemicals A mixture of 16 PAH stock standards: naphthalene(Nap), acenaphthene(Ace), acenaphthylene(Acy), fluorene(Flu), 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), dibenzo[a,h] anthracene(DiA), indeno[1,2,3-cd]pyrene(InP) and benzo[ghi] perylene(BghiP) was purchased from AccuStandara (100 mg/L, USA, solvent: dichloromethane). Other solvents included methanol, n-hexane, and dichloromethane (analytical grade, CNWBOND, Germany). Anhydrous sodium sulfate was heated at 450 °C in a muffle furnace for 4 h and stored in the sealed desiccator prior to be used. Silica gel and alumina were extracted by Sohxlet for 48 h, and dried in an oven for 12 h, then 3% deionized water was added. Before use, all glasswares were rinsed in sulfuric acid potassium dichromate lotion and heated at 180 °C for 4 h. 2.2. Analytical methods 2.2.1. Topsoil samples Topsoil samples were taken near the groundwater sampling wells over the entire catchment area using stainless steel shovels and spoons. All topsoil samples were air-dried at room temperature, sieved through a 100-mesh sieve (0.15 mm), and then stored in desiccators for analysis. For the determination of PAHs, 5 g of soil samples to which 5 g of anhydrous sodium sulfate was added was extracted in a Soxhlet apparatus fitted with a 150 mL flask. 120 mL of dichloromethane solution was added to the flask and the entire apparatus was heated for 24 h at 45 °C. After extraction, the extract was transferred to the clean-up procedure.
papers were extracted using the same Soxhlet extraction as for the topsoil samples. 2.2.4. Clean-up procedure The extracts were subsequently transferred to the top of a chromatographic column (30 cm × 10 mm i.d.) filled with 6 cm silica gel, 3 cm alumina and 3 cm anhydrous sodium sulfate for cleanup. And 20 mL mixed solution of dichloromethane/n-hexane (1:1, V: V) was used to elute PAHs. The eluate was collected to a 50 mL pear-shaped flask, the final volume was 0.5 mL after rotary evaporation and nitrogen flush. 2.2.5. PAH analysis Concentrations of PAHs were analyzed using an Agilent GC 6850 gas chromatograph equipped with a DB-5 MS capillary column (30 m × 250 μm × 0.25 mm, Agilent Co., USA), operating with helium carrier gas (1 mL/min), coupled to an Agilent MD 5975 mass spectrometer (MS). 1 μL aliquots were injected using an auto-sampler in splitless mode with a venting time of 0.75 min. The GC oven temperature was programmed to hold 80 °C for 1 min, then increased to 200 °C at 10 °C/min, which was held for 2 min increase to 290 °C at 4 °C/min, and finally to maintain 290 °C for 10 min. The injector and detector temperatures were 280 °C. 2.2.6. PMF model PMF is a receptor modeling tool developed in the early 1990s by Paatero and Tapper (1994), which utilizes non-negativity constraints for obtaining physically realistic meanings. PMF runs on a matrix of individual PAH compound concentrations, and the model principle is briefly explained here. PMF defines that a n × m data matrix X (chemical species concentrations (n) measured at sites (m)) can be factored into a (n × p) matrix G (source contributions) and a (p × m) matrix F (source profiles) with a residual matrix E (n × m):
X ¼ GF þ E: The elements eij of matrix E (n × m) indicates the residual value not accounted for by the modeled data value xij, i.e.,
xij ¼ 2.2.2. Groundwater samples Groundwater samples were collected in May 2013 from 22 boreholes across the catchment area. The groundwater was filtrated with a vacuum Sartorius filtration apparatus and Whatman glass microfiber filters with a pore size of 0.45 μm. The cartridges used for solid-phase extraction were C 18 (500 mg, 6 mL, CNWBOND, Germany). PAHs were extracted from groundwater (1 L) added with 100 mL methane (10%) as an organic modifier. Before the sample loading, the solid-phase adsorbent was pre-conditioned with 6 mL of dichloromethane, 6 mL of methanol and 6 mL of water. The samples were introduced to the cartridges by means of PTFE tubes at flow rates of 5 mL/min. After sample loading, the solid phase was washed with 6 mL of water. Cartridges were then dried for more than 30 min under Supelco vacuum manifold (Sigma-Aldrich), which allowed for the parallel extraction of up to 12 samples and the adsorbent were then eluted with 12 mL of 1:1 (v/v) mixtures of dichloromethane and n-hexane. 2.2.3. Suspended solids samples Suspended solids samples were collected from 2 L groundwater filtrating with a vacuum Sartorius filtration apparatus and Whatman organic glass micro-fiber filters with a pore size of 0.45 μm. All SS samples were air-dried at room temperature in a desiccator. The weighed filter
155
p X
g ik f kj þ eij
k¼1
where xij is the jth species concentration measured in the ith sample, gik is the kth source's contribution to sample i, and fkj is the jth element's concentration in source k. eij is the residual associated with the jth species concentration measured in the ith sample. Our PMF analysis was carried out using the US EPA PMF 3.0 model (US EPA, 2008). 2.2.7. Quality control and statistical analyses All data were subject to strict quality control procedures. Four surrogate standards (naphthene-d8, acenaphthene-d10, phenanthrene-d10 and chrysene-d12) were added to all samples to monitor the procedures of sample extraction, cleanup and analysis. The average recoveries of surrogate standards varied from 78% to 101%, 83% to 105% and 91% to 110% in groundwater, suspended solids and topsoil samples, respectively. One laboratory blank and one duplicate were run with every 10 samples. Statistical analyses of PAH concentrations in the environmental samples for different regions to obtain correlation coefficients between PAHs and TOC as well as mean and standard deviation of replicated spiked standard solutions were done using PASW statistics 18 (SPSS Inc., USA) and Origin 8.
156
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
Table 1 Residual levels of PAHs in the groundwater, suspended solids in groundwater and soil from Guozhuang karst system. PAHs
NaP Acy Ace Flu Phe Ant Fla Pyr BaA Chr BbF BkF BaP DiA InP BghiP ΣPAHs
Groundwater (ng/L) n = 22
Suspended solids (ng/g, dw) n = 22
Soil (ng/g, dw) n = 15
Range
Mean
SD
Range
Mean
SD
Range
Mean
SD
90–400 ND — 217 217–1320 340–2407 563–4258 257–2000 213–673 187–443 ND — 423 ND — 277 ND — 477 ND — 357 ND — 400 ND ND ND 2137–9037
148 27.7 531 934 1400 963 308 240 185 120 83.6 69 18.2 ND ND ND 5020
63.6 71.6 314 600 1042 491 119 68.7 207 134 182 140 85.3 ND ND ND 2050
ND — 1660 ND — 1168 ND — 1290 ND — 2677 827–3854 652–3051 770–11,135 687–8619 ND — 7601 ND — 4978 ND — 7280 ND — 5567 ND ND ND ND 4739–59,314
693 429 122 1235 1791 1347 2140 1867 1098 682 330 253 ND ND ND ND 11,990
365 489 308 549 681 545 2077 1580 1949 1254 1552 1187 ND ND ND ND 11,072
19.9–3340 ND — 617 11.9–2932 25.8–3147 39.2–5069 21.9–2730 32.8–6760 34.3–6761 70.5–7712 45.2–10,814 73–25,958 53.6–9584 65.6–4922 48.2–9175 ND — 2383 65.1–3797 622–87,880
533 94 332 458 1163 575 1014 1007 1171 1409 3473 1231 1128 2058 554 967 17,174
919 159 748 816 1590 811 1905 1820 2046 2787 6725 2548 1663 2983 759 1237 26,210
Note: ND not detected. Σ PAHs-total concentration of the 16 PAHs.
3. Results and discussion
3.2. Distribution patterns of PAHs
3.1. Residual levels of PAHs
In order to distinguish the proportions of low molecular, medium molecular and high molecular (LM, MM and HM) PAHs in different environment media, sixteen PAH compounds were divided into three groups: 2 + 3 rings, 4-rings and 5 + 6 rings. Fig. 2 showed the triangular diagram of percentage average concentrations of different ring number PAHs in different sampling stations. The percentage of LM PAHs to total PAHs was higher than that of MM and HM in groundwater stations, indicating that low molecular PAHs were predominant in groundwater samples, and dominated by phenanthrene, accounting for about 27% of the total 16 PAHs. MM PAHs were also detected with low detection frequencies, and HM PAHs such as six-ring PAHs were not detected. All PAHs analyzed in our study show relatively high octanol–water partition coefficients, with the only exception of lightest PAHs such as naphthalene (log Kow 3.4 to 4). Therefore they are likely to be found in both soil and SS in which they may occur as mobile constituents, rather than in the aqueous phase in which they show a very low solubility (Quesada et al., 2014). Since low molecular PAHs were commonly
The total and individual concentrations of 16 PAHs in groundwater, SS and topsoil samples from Guozhuang karst water system were listed in Table 1. Most types of PAHs were detected in the groundwater with a mean concentration of 5020 ng/L. The levels of phenanthrene (1400 ng/L) was the highest and account for 27.9% of total PAHs. Three-ring PAHs were predominant among individual PAHs, and six-ring PAHs were not detected. This tendency was similar to the water samples from the lower Mississippi River and the Gulf of Mexico in the US (Mitra and Bianchi, 2003). Most of the 16 EPA priority parent PAHs were present in a majority of SS samples. The total concentrations of PAHs in SS samples varied from 4739 to 59,314 ng/g, with an average concentration of 11,990 ng/g, which were much lower than the river water SS levels in the Daliao River watershed (21,725 ng/g) (Guo et al., 2007). Probably owing to absorption on SS for PAHs and different SS contents, in terms of individual PAHs in the SS, the composition characteristic was different from that in groundwater. Four-ring PAHs such as fluoranthene and pyrene were predominant among individual PAHs, account for 33.4%. The total PAH concentration in topsoil varied greatly depending on the sampling location and ranged from 622 to 87,880 ng/g with an average concentration of 17,174 ng/g, much higher than that of topsoil samples from Ammer River of Germany (8770 ng/g) which flows through farmlands or small towns with some industrial activities such as metal processing, electronics, and furniture production (Liu et al., 2013). And it was about 9 times higher than that from the Liangtan River (2040 ng/g) along a recently urbanized and industrialized area of China (Liu et al., 2013). The PAH composition of the topsoil samples from Guozhuang was different from that of groundwater and SS. All PAHs including six-ring PAHs were detected in topsoil samples. The levels of benzo[b]fluoranthene were the highest (73 to 25,959 ng/g), account for 20.2% of total PAHs. The abnormally high PAH concentration in the topsoil of our study area clearly indicates the effect of intensive mining activities. It can then be expected that the PAHs, especially the low molecular weight PAHs (Liang et al., 2008), deposited in soil would be washed out during the rainy season, to contaminate causing groundwater contaminated.
Fig. 2. Triangular diagram of percentage average concentrations of the 16 PAHs in groundwater, suspended solids and soil samples.
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
detected in our groundwater samples, their possible sources might be SS that were transported into groundwater together with PAHs which were later mobilized into aqueous phase. Such a PAH composition might also reflect a relatively recent local source of PAHs that were transported into the aquifer via processes like wastewater discharge, adhesion on suspended solids and surface water leakage rather than atmospheric deposition. In SS, although LM PAHs were most abundant, the content of MM PAHs increased gradually. The average percentage of MM PAHs to total PAHs ranged from 32.3% to 62.8%. And HM PAHs such as five- and six-ring PAHs suspected to be carcinogenic were detected with high frequencies in topsoil samples, which were very similar to the Liangtan River (Liu et al., 2013). HM PAHs in the topsoil may be due to the greater affinity of high molecular weight PAHs for the solid matrix. The variability of PAHs patterns in the topsoil samples indicated that there were likely different sources of PAHs along the Guozhuang karst water system. In contrast to the stable and diffuse characteristics of PAH sources in early industrialized countries, the sources of PAHs at Guangzhuang appeared to be more diversified. Another observation was that the concentrations of 4-ring PAHs in soil samples were substantially lower than those in SS, which was also found in the Pearl River (Luo et al., 2006). This observation suggested that low-medium molecular PAHs could be removed from the soil phase during deposition and early diagenesis and then transported into the aquifer together with SS. Numerous studies showed that low molecular PAHs are acutely toxic, while high-ring PAHs are considered to be genotoxic (Perugini et al., 2007). So our results showed that the drinking water in Guozhuang karst water system had been polluted by less toxic PAHs at low concentration levels. This result was similar to that of a previous study of riverine waters from Llobregat hydrographic basin in Catalonia, northern Spain (Olivella et al., 2006). Different patterns of PAH composition in groundwater, SS and soil were also found in other regions, such as the Caspian Sea (Tolosa et al., 2004) and Tijuana of Mexico (García-Flores et al., 2013). Since low molecular weight PAHs are less hydrophobic relative to high molecular weight PAHs, they tend to be more enriched in the aqueous phase, leading to a greater proportion of MM and HM PAHs in SS and soil. Besides, HM PAHs are more resistant to degradation processes in soil (Simarro et al., 2013).
157
The sum of all measured compounds of groundwater and SS in the four sampling areas were summarized in Fig. 3. The differences between
the R1, R2 and R3 (except R4) were found to be statistically significant by Student's t test (p b 0.05). In general, PAH concentrations were higher in groundwater and SS samples from the sampling areas R3 and R4 than those from R1 and R2. The highest concentrations were detected in R3 could be related to the discharge of coking wastewater into the river water which may later leak into the subsurface. With a relatively high groundwater flow rate and strong interaction with surface water, karst aquifers are particularly vulnerable to be contaminated (Simmleit and Herrmann, 1987). PAHs in coking wastewater originate not only from processes of coke production but also from purification processes of industrial by-products, such as ammonium, benzene, and tar. Thus, The concentration of PAHs in coking wastewater could be as high as 8710 μg/L (Zhang et al., 2013), and have been identified as a source for groundwater PAH contamination in northern China (Wang et al., 2013a). Our sampling area R1 is the recharge area, where the Ordovician karst aquifers are partially overlain by Carboniferous–Permian coalbearing strata. The PAHs in groundwater samples from R1 may originate from raw coal. Though the concentration of PAHs in raw coal of Shanxi is high, ranging from 162 to 270 μg/g (Yan et al., 2013), these PAHs embedded inside cavities or pores of the cross-linked network of coal were probably not able to be reached by water, but can be only extracted by organic solvents by swelling (Jonker et al., 2005). Our sampling area R2 is along the leaking Fenhe river and there is almost no coal industry. The PAHs in groundwater may mainly originate from the recharge area and automobile exhaust emission. As a result, the contents of PAHs in samples from R1 and R2 were lower than those from R3 and R4. The sources of PAHs are formed mainly via two mechanisms: fuel-combustion (pyrolytic) and discharge of crude oil related material (petrogenic), and may be identified by ratios of individual PAH compounds based on peculiarities in PAH composition and distribution pattern as a function of the emission source (Zhang et al., 2004). In order to survey the sources of PAHs in Guozhuang karst water system, Ant/Ant + Phe versus Fla/Fla + Pyr was plotted (Fig. 4). Usually, The Ant content in petroleum products is lower than that of Phe. However, it can be produced in the process of combustion (Zhang et al., 2012). So Ant/Ant + Phe ratios higher than 0.1 indicate pyrolytic origin, whereas values lower than 0.1 indicate petrogenic origin; Fla/Fla + Pyr ratio less than 0.5 being defined as the petrogenic origin, whereas the ratios higher than 0.5 corresponded to wood or coal combustion (Doong and Lin, 2004; Guo et al., 2007). Fig. 4 illustrated that PAHs in groundwater, SS and topsoil mainly originated from wood and coal combustion, and PAHs in very few topsoil samples originated from petroleum
Fig. 3. Box-whisker plots of the total PAH concentrations in groundwater (ng/L) and suspended solids (μg/g). (PR1,R3 = 0.001, PR1,R4 = 0.189, PR2,R3 = 0.021, PR2,R4 = 0.141, α = 0.05 in groundwater. PR1,R3 = 0.017, PR1,R4 = 0.564, PR2,R3 = 0.015, PR2,R4 = 0.531, α = 0.05 in suspended solids).
Fig. 4. Plot of the isomeric ratio Ant/Ant + Phe vs Fla/Fla + Pyr.
3.3. Spatial distributions of PAHs
158
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
Fig. 5. Source profiles obtained from PMF model.
combustion. As a matter of fact, coal is one of the most important source of energy in our study area. 3.4. Source of PAHs Although the compositions and ratios of selected PAH compounds can be taken as indirect indicators of PAH sources, the relationships among different factors and their percentage of contribution to contamination were not clear. In this study, PMF model was used to better understand the PAH sources in Guozhuang karst water system. The PMF analysis used individual PAH concentrations as input data and run in robust mode to keep outliers from unduly influencing the results. For each dataset the number of factors was varied, each time running the model 20 times starting from a different initial seed. This was done to better understand the variability of the PMF analysis. There are also no strict rules for determining the number of factors. The tentative identification of the factor profiles was based on the molecular markers in different sources. By comprehensively considering the characteristics of anthropogenic activities that may release PAHs into the environment in our study area, five factors (oil, coal combustion, vehicle, biomass combustion and coal tar) were selected as the possible sources of PAHs in
Guozhuang karst water system. Factor profiles of individual PAH compounds in the five factors from the PMF model output were given in Fig. 5. The source 1 profile was dominated by Phe and Ant, moderately weighted by Nap, Acy and Ace, and a little Chr, BbF. The petrogenic PAHs are characterized by the predominance of 2 and 3-ring PAHs (Yunker et al., 2002). So the source 1 was identified as unburnt petroleum (oil). 4 to 5 ring PAHs had a high loading in the source 2 profile, including Pyr, BaA, Chr, BbF and BkF, which are typical markers for coal combustion (Huang et al., 2013; Kannan et al., 2005; Qin et al., 2014), indicating the effects of coal combustion. The source 3 profile mainly consisted by high molecular weight PAHs. Among these PAHs, Fla, Pyr, BbF, BkF were identified as markers of traffic tunnels (Liu et al., 2010b). Among the other compounds in this profile, the concentration of InP was the highest, which has been identified as typical tracers of vehicle emission of PAHs (Harrison et al., 1996; Hu et al., 2013; Larsen and Baker, 2003). The source 4 profile had predominant loadings of Acy and BbF, with some loadings of Nap. Acy has been commonly used as an indicator of wood combustion (Zuo et al., 2007). Incomplete combustion of biomass has also been assigned as the source for Nap (Grover et al., 2012). Thus the source 4 could be identified as
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
159
Fig. 6. Relationship between TOC/DOC and total concentration of 16 PAHs in groundwater and topsoil at Guozhuang karst water system including coefficient of determination (R2), number of points (N), and probability (p) (regression slope t test, α = 0.05).
biomass combustion. The source 5 profile was dominated by Acy, Phe and BbF, and moderately weighted by Fla, Pyr, BaA, and Chr. It has been reported Acy and Phe were the main components of coal products (Jiao et al., 2012; Lee et al., 2005). On the other hand, Fla and Phe were sometimes used as indicators for coke oven sources (Liu et al., 2010a; Zuo et al., 2007). Therefore, the source 5 may indicate the effects of coke production. The average contributions of each source to total PAHs in groundwater samples were calculated. The relative contributions for the 1– 5 factors were 2%, 32%, 22%, 27%, 18%, respectively. Therefore, the major sources of PAHs in groundwater were categorized in this study as pyrogenic origin, especially coal combustion that accounts for 50% (source 2 plus 5). At Guozhuang, coal has been used for home heating in the winter. And like many other areas in northern China, a large amount of consumption in both industrial and domestic sectors may have made coal the primary contributor to PAHs in the environment.
3.5. Relationship between TOC/DOC and PAHs Organic matter plays an important role in the partitioning and retention of organic contaminant (Agarwal and Bucheli, 2011). Fig. 6 showed the relationship between TOC/DOC content and total concentration of 16 PAHs. The input of PAHs to groundwater did not seem to be linked to the input of DOC (R2 = 0.11, p = 0.08). As compared to suspended solids, the DOC concentration might be too low to influence PAH concentrations in water. Another probable interpretation is that PAHs and DOC were either not transported to the groundwater from the same sources or, if they are, the factors driving their mobilization might differ. Instead, a major fraction of PAHs would enter the groundwater via direct atmospheric deposition to surface water that may then leak into the aquifer. And PAHs and DOC would undergo different geochemical processes in the karst aquifer such as adsorption and biodegradation. Our observations might illustrate the importance of direct input of PAHs from the air and surface water to groundwater and geochemical processes of PAHs in this type of aquatic environment of strong surface water–groundwater interaction. And the mobilization of PAHs in the aquifer could be related to particle-facilitated transport (Schwarz et al., 2011). In topsoil, strongly significant positive correlations between TOC and total concentration of PAHs were observed (R2 = 0.89, p b 0.0001). It would seem intuitive that the TOC and PAHs were co-emitted with wastewater at Guozhuang karst water system. High TOC in topsoil to some extent resulted in decreased degradation of HM PAHs in soil due to the strong adsorption (Hinga, 2003), leading to higher abundance of the HM PAHs in topsoil.
4. Conclusions To our knowledge, this study is the first effort to investigate the occurrence and origins of PAHs in karst water systems in northern China. At Guozhuang, the distribution pattern of total PAHs was different in different environmental media. LM, MM and HM PAHs were the representative PAHs in the groundwater, suspended solids and topsoil, respectively. The samples from region R3 and R4 exhibited very high PAH concentrations, and therefore greater attention needs to be paid to these two regions in environmental management. Source apportionment of PAHs suggests a mixed origin of PAHs, but coal combustion should be the dominant source for PAHs in the soil and groundwater environment at Guozhuang.
Acknowledgments The research work was financially supported by the National Natural Science Foundation of China (No. 40902071, and No. 41120124003), the Ministry of Science and Technology of China (2012AA062602), and the Ministry of Education of China (111 project and Priority Development Projects of SRFDP (20120145130001)).
References Agarwal T, Bucheli TD. Is black carbon a better predictor of polycyclic aromatic hydrocarbon distribution in soils than total organic carbon? Environ Pollut 2011;159(1): 64–70. Bo G. Causes of flow rate decrease of Guozhuang Spring and countermeasures [J]. Water Resour Prot 2002;1:64–5. (in Chinese with English abstract). Callén M, Iturmendi A, López J, Mastral A. Source apportionment of the carcinogenic potential of polycyclic aromatic hydrocarbons (PAH) associated to airborne PM10 by a PMF model. Environ Sci Pollut Res 2013:1–13. Doong R-A, Lin Y-T. Characterization and distribution of polycyclic aromatic hydrocarbon contaminations in surface sediment and water from Gao-ping River, Taiwan. Water Res 2004;38(7):1733–44. García-Flores E, Wakida F, Espinoza-Gomez J. Sources of polycyclic aromatic hydrocarbons in urban storm water runoff in Tijuana, Mexico. Int J Environ Res 2013;7(2): 387–94. Grover IS, Sharma R, Singh S, Pal B. Polycyclic aromatic hydrocarbons in some grounded coffee brands. Environ Monit Assess 2012:1–5. Guo W, He M, Yang Z, Lin C, Quan X, Wang H. Distribution of polycyclic aromatic hydrocarbons in water, suspended particulate matter and sediment from Daliao River watershed, China. Chemosphere 2007;68(1):93–104. Harrison RM, Smith D, Luhana L. Source apportionment of atmospheric polycyclic aromatic hydrocarbons collected from an urban location in Birmingham, UK. Environ Sci Technol 1996;30(3):825–32. Heinz B, Birk S, Liedl R, Geyer T, Straub K, Andresen J, et al. Water quality deterioration at a karst spring (Gallusquelle, Germany) due to combined sewer overflow: evidence of bacterial and micro-pollutant contamination. Environ Geol 2009; 57(4):797–808. Hinga K. Degradation rates of low molecular weight PAH correlate with sediment TOC in marine subtidal sediments. Mar Pollut Bull 2003;46(4):466–74.
160
Y. Shao et al. / Science of the Total Environment 490 (2014) 153–160
Hu N-J, Huang P, Liu J-H, Shi X-F, Ma D-Y, Liu Y. Source apportionment of polycyclic aromatic hydrocarbons in surface sediments of the Bohai Sea, China. Environ Sci Pollut Res 2013;20(2):1031–40. Huang W, Huang B, Bi X, Lin Q, Liu M, Ren Z, et al. Emission of PAHs, NPAHs and OPAHs from the residential honeycomb coal briquettes combustion. Energy Fuel 2013; 28(1):636–42. Jiao W, Wang T, Khim JS, Luo W, Hu W, Naile JE, et al. PAHs in surface sediments from coastal and estuarine areas of the northern Bohai and Yellow Seas, China. Environ Geochem Health 2012;34(4):445–56. Jonker MT, Hawthorne SB, Koelmans AA. Extremely slowly desorbing polycyclic aromatic hydrocarbons from soot and soot-like materials: evidence by supercritical fluid extraction. Environ Sci Technol 2005;39(20):7889–95. Kannan K, Johnson-Restrepo B, Yohn SS, Giesy JP, Long DT. Spatial and temporal distribution of polycyclic aromatic hydrocarbons in sediments from Michigan inland lakes. Environ Sci Technol 2005;39(13):4700–6. Larsen RK, Baker JE. Source apportionment of polycyclic aromatic hydrocarbons in the urban atmosphere: a comparison of three methods. Environ Sci Technol 2003; 37(9):1873–81. Lee RG, Coleman P, Jones JL, Jones KC, Lohmann R. Emission factors and importance of PCDD/Fs, PCBs, PCNs, PAHs and PM10 from the domestic burning of coal and wood in the UK. Environ Sci Technol 2005;39(6):1436–47. Liang Y, Fung PK, Tse MF, Hong HC, Wong MH. Sources and seasonal variation of PAHs in the sediments of drinking water reservoirs in Hong Kong and the Dongjiang River (China). Environ Monit Assess 2008;146(1–3):41–50. Liu WX, Dou H, Wei ZC, Chang B, Qiu WX, Liu Y, et al. Emission characteristics of polycyclic aromatic hydrocarbons from combustion of different residential coals in North China. Sci Total Environ 2009;407(4):1436–46. Liu G, Tong Y, Luong JH, Zhang H, Sun H. A source study of atmospheric polycyclic aromatic hydrocarbons in Shenzhen, South China. Environ Monit Assess 2010a; 163(1–4):599–606. Liu S, Xia X, Yang L, Shen M, Liu R. Polycyclic aromatic hydrocarbons in urban soils of different land uses in Beijing, China: distribution, sources and their correlation with the city's urbanization history. J Hazard Mater 2010b;177(1):1085–92. Liu Y, Beckingham B, Ruegner H, Li Z, Ma L, Schwientek M, et al. Comparison of sedimentary PAHs in the Rivers of Ammer (Germany) and Liangtan (China): differences between early-and newly-industrialized countries. Environ Sci Technol 2013;47(2): 701–9. Luo X-J, Chen S-J, Mai B-X, Yang Q-S, Sheng G-Y, Fu J-M. Polycyclic aromatic hydrocarbons in suspended particulate matter and sediments from the Pearl River Estuary and adjacent coastal areas, China. Environ Pollut 2006;139(1):9–20. Mai B, Qi S, Zeng EY, Yang Q, Zhang G, Fu J, et al. Distribution of polycyclic aromatic hydrocarbons in the coastal region off Macao, China: assessment of input sources and transport pathways using compositional analysis. Environ Sci Technol 2003;37(21): 4855–63. Maioli OL, Rodrigues KC, Knoppers BA, Azevedo DA. Distribution and sources of aliphatic and polycyclic aromatic hydrocarbons in suspended particulate matter in water from two Brazilian estuarine systems. Cont Shelf Res 2011;31(10):1116–27. Mitra S, Bianchi T. A preliminary assessment of polycyclic aromatic hydrocarbon distributions in the lower Mississippi River and Gulf of Mexico. Mar Chem 2003;82(3): 273–88. Nielsen T, Jørgensen HE, Larsen JC, Poulsen M. City air pollution of polycyclic aromatic hydrocarbons and other mutagens: occurrence, sources and health effects. Sci Total Environ 1996;189:41–9. Olivella M, Ribalta T, De Febrer A, Mollet J, De Las Heras F. Distribution of polycyclic aromatic hydrocarbons in riverine waters after Mediterranean forest fires. Sci Total Environ 2006;355(1):156–66.
Paatero P, Tapper U. Positive matrix factorization: a non‐negative factor model with optimal utilization of error estimates of data values. Environmetrics 1994;5(2):111–26. Perugini M, Visciano P, Giammarino A, Manera M, Di Nardo W, Amorena M. Polycyclic aromatic hydrocarbons in marine organisms from the Adriatic Sea, Italy. Chemosphere 2007;66(10):1904–10. Qin L, Han J, He X, Lu Q. The emission characteristic of PAHs during coal combustion in a fluidized bed combustor. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects 2014;36(2):212–21. Quesada S, Tena A, Guillén D, Ginebreda A, Vericat D, Martínez E, et al. Dynamics of suspended sediment borne persistent organic pollutants in a large regulated Mediterranean river (Ebro, NE Spain). Sci Total Environ 2014;473:381–90. Schwarz K, Gocht T, Grathwohl P. Transport of polycyclic aromatic hydrocarbons in highly vulnerable karst systems. Environ Pollut 2011;159(1):133–9. Simarro R, Gonzalez N, Bautista LF, Molina MC. Biodegradation of high‐molecular‐weight polycyclic aromatic hydrocarbons by a wood‐degrading consortium at low temperatures. FEMS Microbiol Ecol 2013;83(2):438–49. Simmleit N, Herrmann R. The behavior of hydrophobic, organic micropollutants in different karst water systems. Water Air Soil Pollut 1987;34(1):79–95. Tolosa I, de Mora S, Sheikholeslami MR, Villeneuve J-P, Bartocci J, Cattini C. Aliphatic and aromatic hydrocarbons in coastal Caspian Sea sediments. Mar Pollut Bull 2004;48(1): 44–60. US EPA. EPA positive matrix factorization (PMF) 3.0 fundamentals & user guide. Online available at http://www.epa.gov/heasd/products/pmf/pmf.htm, 2008. Wang Y, Xia Z, Liu D, Qiu W, Duan X, Wang R, et al. Multimedia fate and source apportionment of polycyclic aromatic hydrocarbons in a coking industry city in northern China. Environ Pollut 2013a;181:115–21. Wang Z, Wang Y, Ma X, Na G, Lin Z, Yao Z. Probabilistic ecological risk assessment of typical PAHs in coastal water of Bohai Sea. Polycycl Aromat Compd 2013b;33(4): 367–79. Yan C, Yang Y, Liu M, Nie M, Gu L, Zhou JL. Polycyclic aromatic hydrocarbons (PAHs) in Chinese coal: occurrence and sorption mechanism. Environ Earth Sci 2013:1–8. Yang X. The pollution present situation and the countermeasures of Guozhuang Spring field, Shanxi Province. Water Resour Plann Des 2011(01):23–5. Yang D, Qi S, Zhang Y, Xing X, Liu H, Qu C, et al. Levels, sources and potential risks of polycyclic aromatic hydrocarbons (PAHs) in multimedia environment along the Jinjiang River mainstream to Quanzhou Bay, China. Mar Pollut Bull 2013;76(1):298–306. Yunker MB, Macdonald RW, Vingarzan R, Mitchell RH, Goyette D, Sylvestre S. PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition. Org Geochem 2002;33(4):489–515. Zhang Z, Huang J, Yu G, Hong H. Occurrence of PAHs, PCBs and organochlorine pesticides in the Tonghui River of Beijing, China. Environ Pollut 2004;130(2):249–61. Zhang Y, Tao S, Cao J, Coveney RM. Emission of polycyclic aromatic hydrocarbons in China by county. Environ Sci Technol 2007;41(3):683–7. Zhang W, Wei C, Chai X, He J, Cai Y, Ren M, et al. The behaviors and fate of polycyclic aromatic hydrocarbons (PAHs) in a coking wastewater treatment plant. Chemosphere 2012;88(2):174–82. Zhang W, Wei C, Yan B, Feng C, Zhao G, Lin C, et al. Identification and removal of polycyclic aromatic hydrocarbons in wastewater treatment processes from coke production plants. Environ Sci Pollut Res 2013;20(9):6418–32. Zuo Q, Duan Y, Yang Y, Wang X, Tao S. Source apportionment of polycyclic aromatic hydrocarbons in surface soil in Tianjin, China. Environ Pollut 2007;147(2):303–10.
