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Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan
Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan Jabir Hussain Syed a, Riffat Naseem Malik b, Jun Li c,n, Gan Zhang c, Kevin C. Jones d a
Environmental Biology Laboratory, Department of Plant Sciences, Quaid-I-Azam University, Islamabad 45320, Pakistan Environmental Biology and Ecotoxicology Laboratory, Department of Environmental Sciences, Quaid-I-Azam University, Islamabad 45320, Pakistan c State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China d Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK b
art ic l e i nf o
a b s t r a c t
Article history: Received 11 March 2013 Received in revised form 1 June 2013 Accepted 6 June 2013
An initial survey of the concentrations of polychlorinated biphenyl (PCB) compounds in air and soils across industrial and agricultural areas of Punjab Province, Pakistan, was conducted from January to March 2011. The total concentration of all PCBs ( oSigma 431 PCBs) ranged from 34 to 389 pg m 3 in air and from 7 to 45 ng g 1 dry weight in soils, where both ranges were similar to the average ranges in other areas of the world. PCBs were elevated across industrial regions near urban and industrial sources. Consistently low air concentrations of PCBs at the agricultural sites suggest that they are less widespread or uniformly distributed in the Pakistani atmosphere. The calculated air and soil fugacity fraction values indicated that soils are a potential secondary source of PCBs in agricultural areas, whereas they are in equilibrium or atmospheric deposition in industrial and urban areas. TEQ concentrations of dioxin-like PCBs for soil samples met the Canadian standard. However, local authorities should address the human health threats from urban and industrial soils in Punjab Province, Pakistan. & 2013 Elsevier Inc. All rights reserved.
Keywords: Air Soil Polychlorinated biphenyls (PCBs) Air–soil exchange fluxes Punjab Province
1. Introduction Polychlorinated biphenyls (PCBs) are a group of semi-volatile organic compounds (SVOCs) that are toxic in nature and also persistent because they do not readily undergo degradation when released into the environment. This group of persistent organic compounds (POPs) is of concern for humans and wildlife because of their toxicity and bioaccumulation capacity (Axmon et al., 2008; Lunder et al., 2010). PCBs have been released into the environment by open burning, waste incineration, vaporization from contaminated surfaces and products containing PCBs, and improper disposal or leakage of oil from transformers and capacitors (Breivik et al., 2002a). Because of their toxicity and resistance to degradation, the production and use of PCBs is banned in many countries. PCB levels in the environment have been declining slowly, and it has been estimated that PCB emissions during 2005 were approximately only 10 percent of those released in 1970 (Breivik et al., 2007). PCBs that have a close structural relationship to dioxins and furans and that can exhibit high levels of toxicity are called dioxinlike PCBs. Four coplanar polychlorinated biphenyls (cop-PCBs: CB-77, -81, -126, -169) and eight mono-ortho-PCBs (CB-105, -114,
n
Corresponding author. Fax: +86 20 8529 0706. E-mail address: [email protected] (J. Li).
-118, -123, -156, -157, -167, -189) share similar chemical structures and a common mechanism of toxic action as those of seven polychlorinated dibenzodioxins (PCDDs) and ten polychlorinated dibenzofurans (PCDFs) (Van den Berg et al., 2006; Matthews et al., 2008). Dioxin-like PCBs are never found as individual congeners but occur as complex mixtures with only some congeners exhibiting 2,3,7,8-TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)-like toxicity. Co-PCBs have different sources compared to the collection of PCBs that dominate the Aroclor technical mixtures (Breivik et al., 2002a, 2002b). Multiplication of the concentration of a dioxin-like PCB congener by its toxicity equivalent factor (TEF) gives the toxic equivalent (TEQ) concentration of that congener in a sample. Summation of the toxic equivalent concentrations (TEQs) of the twelve 2,3,7,8-substituted congeners gives the total toxic equivalents. This allows the reduction of a large dataset to a single number. There are several different TEQ schemes in use that assign different TEF values to congeners. Until recently, the most widely used TEQ system was prepared by a North Atlantic Treaty Organization (NATO) committee on challenges to modern society; that system is known as the International Toxicity Equivalency Factor (I-TEF) system (Kutz et al., 1990). Air–soil exchange is known to be one of the key processes that controls the presence and levels of PCBs in the environment. These compounds are thought to move towards equilibrium between soil and air and are continuously recycled (Wania and Mackay, 1993; Backe et al., 2004). Monitoring the distribution of these
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Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
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chemicals in different environmental compartments such as soil and air and evaluating their movement is required to predict their potential health effects. Dry and wet deposition from atmosphere to soil and volatilization from soil to air are the most important processes that affect the levels of PCBs in those environmental compartments, although it was reported by Harner et al. (1995) that diffusive gaseous transport of contaminants was the most important pathway for the transfer of PCBs from soil to the atmosphere. Soils have an important role in supplying, receiving and global cycling of persistent organic pollutants in the environment (Meijer et al., 2003). Soil properties such as organic matter content are important factors affecting the air–soil partitioning of organic chemicals. It has also been shown that the levels of chemicals in soil are affected by seasonal temperature variations (Cabrerizo et al., 2011). A fugacity model has been developed by Mackay (1991) to explain the equilibrium partitioning process among the environmental compartments. With the help of fugacity quotients and mass transfer coefficients, the movement of SVOCs between the environmental compartments has been studied by several authors (Cousins and Jones, 1998; Harner et al., 2001; Backe et al., 2004; Masih et al., 2012). Although the levels, distribution, sources and air–soil exchange properties of PCBs have been widely studied for many developed or developing countries, this is not the case for Pakistan. There have been only a few studies from Pakistan in which the concentrations of PCBs in various environmental compartments have been documented (Sanpera et al., 2002, 2003; Eqani et al., 2011, 2012a). However, there is no information available regarding atmospheric concentrations of PCBs where the polyurethane foam passive air sampler (PUF-PAS) technique and the air–soil exchange of these persistent compounds were used to estimate the role of secondary sources in the country. To our knowledge, this is the very first study conducted to evaluate the POP levels in the atmosphere of Pakistan. The study area is the most important region in the subcontinent that is associated with a population of more than 100 million people. Notwithstanding its importance for the region, Punjab Province has never been studied in detail for the occurrence of SVOCs such as PCBs. This study was thus conducted to investigate the levels, sources, distribution and variations in PCB concentrations in both soil and air and in conjunction with each other and to examine air–soil exchange fluxes using the appropriate fugacity fractions. The importance of the assessment of air and soil PCB
concentrations together with the fugacity fractions was also highlighted.
2. Materials and methods 2.1. Air sampling Ten (10) sampling locations were selected for deploying Polyurethane FoamPassive Air Samplers (PUF-PAS). The study area (Punjab Province) was divided into two zones: an industrial zone, including highly populated industrialized cities such as Faisalabad, Sheikhupura and Lahore (the provincial capital), and an agricultural zone, including the cotton-growing areas of Pakistan (Fig. 1). Five PAS were deployed on the roofs of one-floor buildings in five locations in the industrial zone: Faisalabad (FSD), Sheikhupura (SHK), Shahdra (SHR), Lahore (LHR) and Phool Nagar (PN). Five more PAS were deployed on the roofs of one-floor houses in various locations in the agricultural zone: Sahiwal (SHW), Cheechawatni (CHW), Mianchanu (MCH), Khanewal (KHW) and Kabirwala (KBW). Locations of each sampling site are given in the Supplementary data in Table A1. All the PUF disks, which included ten samples, three field blanks and three transportation blanks, were pre-extracted using dichloromethane (DCM) and acetone at the State Key Laboratory of Organic Geochemistry, Guangzhou, China, and transferred by express-mail service to Pakistan in sealed, solvent-cleaned glass jars. The design and deployment of the PUF-PAS has been discussed in detail elsewhere (Jaward et al., 2005). Transportation PUF disk blanks were kept sealed in the glass jars throughout the sampling period and labeled as transportation blanks with the date. In the case of field blanks, PUF disks were taken to the chosen sites, opened with clean gloves for 5 min, sealed again in the glass jars and labeled as field blanks. Each of the samplers was assembled at the deployment sites to avoid contamination during transportation. A PUF-PAS unit was deployed at each sampling location for eight weeks between January 22 and March 19, 2011. At the completion of the deployment period, the PUF disks were retrieved, resealed and returned to Guangzhou, where they were stored frozen at –20 °C until they were analyzed. The concentrations of PCBs in air were estimated over the sampling period by assuming sampling rates and partitioning for a sample unit. A standard sampling rate of 3.5 m3 air/day per sampler was determined in previous calibration studies (Shoeib and Harner, 2002). The air/sampler partitioning was estimated as a factor of 2 to 3 for a 10 °C temperature difference, but it was neglected in the present study because similar temperature conditions prevailed in the different cities of Punjab Province throughout the sampling period (Jaward et al., 2005).
2.2. Soil sampling Fifty surface soil samples (five composite soil samples from each PUF-PAS deployment sites) were collected from the ten sampling stations. At each sampling station, one surface soil sample was taken from a 0 to 5 cm depth at the exact location of the PUF-PAS sampler; the four other samples were collected at similar depths within a 500 m radius of the sampler in different directions. All the soil samples were collected using a hand trowel and placed in polyethylene bags and then brought to the Environmental Biology Lab at Quaid-i-Azam University
Fig. 1. Map showing sampling stations from Punjab Province, Pakistan.
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
J.H. Syed et al. / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎ Islamabad, Pakistan. Samples were freeze-dried, sieved through a 2 mm sieve and then transferred to Guangzhou where they were stored frozen until they were analyzed. 2.3. Extraction and analysis The 20-g soil and PUF samples were Soxhlet-extracted for 24 h with DCM (DCM obtained from Merck and Co., Inc.). A mixture of surrogate standards of 2,4,5, 6-tetrachloro-m-xylene (TCmX) and decachlorobiphenyl (PCB-209) were added to each of the samples prior to extraction. Activated copper granules were added to the collection flask to remove any elemental sulfur that could have been present. The extract was concentrated, solvent-exchanged to hexane (hexane obtained from Merck and Co., Inc.) and purified on an 8 mm i.d. alumina/silica column. The column was packed, from the bottom to top, with neutral alumina (3 cm, 3 percent deactivated), neutral silica gel (3 cm, 3 percent deactivated), 50 percent sulfuric acid silica (3 cm), and anhydrous sodium sulfate (1 cm). The column was eluted with 50 ml of DCM/ hexane (1:1, v:v). Before use, the neutral alumina, neutral silica gel, and anhydrous sodium sulfate were Soxhlet-extracted for 48 h with DCM and then heated for 12 h at 250, 180, and 450 1C, respectively. The eluted fraction was concentrated to 0.2 ml under a gentle high-purity nitrogen stream after adding 25 μl of dodecane as a solvent keeper. A known quantity of PCB-54 was added as an internal standard prior to GC-EIMS analysis. 2.4. Chromatographic analysis Thirty-one PCB congeners, specifically PCB-28, PCB-74, PCB-70, PCB-44, PCB-49, PCB-37, PCB-60, PCB-52, PCB-66, PCB-77, PCB-82, PCB-87, PCB-99, PCB-101, PCB118, PCB-114, PCB-126, PCB-105, PCB-138, PCB-153, PCB-187, PCB-179, PCB-169, PCB-156, PCB-128, PCB-166, PCB-158, PCB-183, PCB-189, PCB-170 and PCB-180 were analyzed by GC-EI-MS. A 50 m capillary column (Varian, CP-Sil 8 CB, 50 m, 0.25 mm, 0.25 μm) was used. The injector temperature was 250 1C. The initial oven temperature was set at 150 1C for 3 min, then the temperature was raised to 290 1C at a rate of 4 1C/min, and held for 10 min. PCBs were determined in selected ion mode (SIM). The temperature of the MSD source and the quadruple was 230 1C and 150 1C, respectively. The MS was used in SIM mode with two ions monitored for each target compound group in a specific window. All the PCBs were quantified using HP-Chemstation to confirm the peaks. 2.5. Quality control/quality assurance
total PCBs in the atmosphere ranged from 34 to 389 pg m 3. It is important to note that PCB-28 was the dominant congener, accounting for 22 percent of the total PCBs, followed by PCB-37 and PCB-49, which accounted for 17 percent and 8 percent, respectively. The trends of different homologs of PCBs detected in the air samples from Punjab Province were as follows: tri-CBs4tetra-CBs4penta-CBs4hexaCBs4hepta-CBs. Dioxin-like PCB (dl- PCB) congeners including PCB77, -126, -169, -105, -114, -118, -156, -170, -180, -189, which are very important, ranged between 7 and 55 pg m 3. The compositional profiles of the PCBs in each PUF sample are illustrated in Supplementary data Fig. A1. The results showed that the tri- and tetra-CBs were the major components, constituting 37 percent and 29 percent of the total concentration (o Sigma4 31 PCBs), respectively. For high molecular weight PCBs (penta-, hexaand hepta-CBs), the relative contributions were 22 percent, 7 percent and 5 percent of the oSigma 431 PCB concentration, respectively. This prominent composition pattern was dominated by tri-CBs. This result is consistent with the composition characteristics of PCBs in the atmosphere from those of other regions (Bruhn et al., 2003; Sundqvist et al., 2004; Jaward et al., 2004a; Manodori et al., 2007; Zhang and Lohmann, 2010). However, this pattern was slightly different from composition characteristics of PCBs in the atmosphere of Asia (Jaward et al., 2005; Zhang et al., 2008a,2008b; Li et al., 2012), where tetra-CBs were the dominant homolog. The explanation of the observed composition pattern is most likely related to the emission from sources related to the production and consumption history of PCBs from all over Asia, as previously explained by Hogarh et al. (2012). Compared to the levels of PCBs in other parts of the world (Supplementary data Table A2), the levels of PCBs in Punjab
Table 1 Descriptive statistics of PCBs congeners in air (pg m-3) and soil (ng/g) samples.
All analytical procedures were monitored using strict quality assurance and control measures. Laboratory blanks (7), field blanks (3) and transportation blanks (3) were processed the same way as samples. There were no significant differences between analyte concentrations in the laboratory, field and transportation blanks, indicating contamination was negligible during transport, storage, and analysis. The average surrogate recoveries for TCmX and PCB-209 were 577 4% and 77 7 9% for air samples and 617 7% and 71 711% for soil samples, respectively. The instrumental detection limit (IDLs) values were calculated using the lowest standards extrapolated to the corresponding amount of analyte that would generate a signal-to-noise ratio of 3:1. Measurements less than the IDLs were considered as not detected (ND). The method detection limits (MDLs) were assigned as the average values of the blanks plus 3 standard deviations of blank values. When the compounds were not detected in the blanks, a standard of three times the IDLs was used to calculate the MDLs. MDLs ranged from 0.04 to 0.1 pg m 3 for air samples and from 0.4 to 1 pg g 1 for soil samples. Reported values were corrected according to the recovery ratios and blank values. 2.6. Fugacity calculations In this study, the fugacities of a compound in the soil (fs) and air (fa) phases were calculated according to Harner et al. (2001). The fugacity fractions near 0.5 indicate equilibrium. Fractions 40.5 indicate net volatilization from the soil into air, whereas values o 0.5 indicate net deposition from air to soil. Due to uncertainties and the propagation of errors in the calculation using Eq. (1), fugacity fractions between 0.3 and 0.7 were not considered to differ significantly from equilibrium (Harner et al., 2001). f f ¼ f s =ðf s þ f a Þ
3
ð1Þ
3. Results and discussion 3.1. Atmospheric concentrations and congener profile The total air concentration for all 31 PCBs and the concentration for each PCB congener are summarized in Table 1. The concentrations of
Air samples (n¼ 10) (pg m 3)
Soil Samples (n¼ 50) (ng g 1)
Mean 7std.
Range
H/L
Mean 7 std.
Range
H/L
PCB-28 PCB-37 PCB-52 PCB-49 PCB-44 PCB-74 PCB-70 PCB-66 PCB-60 PCB-77 PCB-101 PCB-99 PCB-87 PCB-82 PCB-118 PCB-114 PCB-105 PCB-126 PCB-153 PCB-138 PCB-158 PCB-166 PCB-128 PCB-156 PCB-169 PCB-179 PCB-183 PCB-180 PCB-170 PCB-189 PCB-187
257 39 167 18 4.17 8.0 9.7 7 9.5 4.7 7 9.8 0.8 7 1.0 1.6 7 2.8 2.6 7 3.9 4.6 7 8.9 3.6 7 4.1 2.5 7 4.1 2.0 7 1.0 1.9 7 3.1 5.5 7 9.2 2.6 7 4.7 1.17 1.0 1.9 7 1.7 6.4 7 9.1 2.6 7 4.3 2.4 7 3.9 0.2 7 0.27 0.38 7 0.94 0.62 7 0.98 0.4 7 0.8 1.6 7 1.8 0.17 0.2 0.2 7 0.4 0.5 7 0.8 4.7 7 1.6 0.127 0.12 0.30 7 0.50
3.2–130 0.66–50 0.61–26 1.9–34 0.15–32 0.1–2.9 0.1–8.7 0.1–11 0.15–28 0.05–11 0.31–12 0.77–4.4 0.15–9.6 0.31–28 0.1–15 0.1–2.5 0.05–6.0 0.1–28 0.05–13 0.05–11.4 0.05–0.9 0.05–3.0 0.05–3.2 0.05–2.5 0.1–4.5 ND–0.71 ND–1.0 ND–2.3 0.46–6.2 ND–0.41 ND–1.5
39 76 43 18 212 29 87 108 189 226 9 6 64 91 146 25 120 283 264 228 18 60 64 50 45 – – – 13 – –
1.2 7 1.4 1.5 7 1.7 0.3 7 1.2 2.0 7 1.1 0.3 7 0.5 0.2 7 0.2 0.3 7 0.3 0.3 7 0.2 0.5 7 0.5 0.2 7 0.1 0.5 7 0.2 0.2 7 0.1 0.2 7 0.1 0.3 7 0.3 0.3 7 0.3 0.3 7 0.28 0.4 7 0.17 1.8 7 1.1 0.90 7 1.6 1.3 7 2.5 0.277 0.20 0.137 0.10 0.487 0.74 0.22 7 0.22 0.357 0.32 0.137 0.17 0.22 7 0.31 0.88 7 1.6 1.3 7 0.96 0.317 0.16 0.38 7 0.65
0.37–5.0 0.22–6.0 0.05–0.7 1.2–5.0 0.01–1.8 0.02–0.6 0.02–1.0 0.02–0.8 0.01–1.4 0.01–0.5 0.19–1.0 0.04–0.4 0.01–0.5 0.09–1.0 0.03–1.2 0.07–1.0 0.28–0.8 0.29–3.5 0.08–5.4 0.06–8.4 0.04–0.7 0.02–0.3 0.03–2.5 0.02–0.8 0.04–1.0 o MDL–0.6 o MDL–1.1 0.10–5.4 0.62–4.0 0.09–0.6 0.02–2.2
14 27 14 4 180 30 50 40 140 50 5 10 50 11 41 14 3 12 67 140 17 15 83 40 25 – – 54 6 7 110
ΣPCBs
1207 120
34–390
Congeners
11
187 11
6.7–45
7
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
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Province were similar to or lower than the reported data from the rural, urban and suburban areas of Japan and Korea. In addition, PCB concentrations were observed to be much lower in the current study compared to the rural and urban areas of China, where the Chinese results were monitored under the GAPs network (Hogarh et al., 2012). PCB concentrations (12,100 pg m 3) from a recent study monitored by the GAPs network in the agricultural regions with close proximity to industrial sources and dump sites in India (Pozo et al., 2011) were found to be much higher compared to the present study. Similar trends were found in the rural, urban and background air samples from 97 sites in China (Zhang et al., 2008a,2008b) where PCB levels (250 pg m 3) were reported to be significantly higher in contrast to the levels from Punjab Province during the current study. The average background concentrations of PCBs measured by various groups from regions around the world (Europe, America, Asia and Australia) were lower compared to this study except for Central America, where PCB levels were reported to be much higher (Li et al., 2010). 3.2. PCB levels and congener profiles in soils Basic descriptive statistical values of total PCB concentrations and 31 PCB congener's concentrations for 50 soil samples in Punjab Province are listed in Table 1. o Sigma4 31 PCBs ranged from 7 to 45 ng g 1 (dw), with a mean concentration of 18 ng g 1 (dw). Among all the PCB congeners, the top three chlorinated congeners were CB-126 followed by CB-37 and CB-170. With regard to the profile of PCB homologs, the dominant homologs in urban, industrial and agricultural soils of Punjab Province were penta-CBs (25 percent), followed by tetra-CBs (23 percent) and hexa-CBs (18 percent); these three congeners accounted for almost 70 percent of the total PCB concentration (Supplementary data Fig. A1). PCB homolog patterns in Punjab soils were similar to those in global background soil, which is dominated by hexa-CBs (46 percent) and penta-CBs (27 percent) (Meijer et al., 2003). However, the patterns differed from those in Chinese background/rural soil (Ren et al., 2007), which may be due to the presence of a higher quantity of lower PCB congeners in Chinese PCB products (tri-CBs: 40.4 percent; tetra-CBs: 31.1 percent) compared to global products (tri-CBs: 25.2 percent; tetra-CBs: 24.7 percent) (Wu et al., 2011) and the long-range transmission of lower chlorinated PCBs from other areas (Meijer et al., 2003; Ren et al., 2007; Fu et al., 2008b).
agricultural sites including CHW, MCH, SHW, KHW and KBW contributed only 35 percent of the total PCB concentrations in all the soil samples. This is almost half of the industrial and urban level (70 percent), which is consistent with the result from China (Ren et al., 2007) and reflects the influence of urban and industrial sources on environmental PCBs. Local authorities should pay attention to this effect because industrial plants may become more significant sources for PCBs pollution in surface soils in Punjab Province. The spatial distribution of the different PCB classes in all air samples can be clearly observed in Fig. 2. PCBs have been used as a technical mixture containing 70 percent tri, tetra and pentachlorinated biphenyls, with tri-chlorinated biphenyls as the dominant homolog (Eqani et al., 2012b). The results indicated a relatively high proportion of lower chlorinated PCBs in the air samples collected from Punjab Province, especially in the industrial and urban areas, such as Shahdara (SHR) and Lahore (LHR), where these PCB congeners are being added to the atmosphere via off-gassing. Current global air concentrations of PCBs are mainly the result of emissions from diffusive urban sources (Breivik et al., 2002a). A potentially important source of PCBs for developing countries is electronic waste (Wong et al., 2008). High concentration of tri-CBs at three sites, Shahdara, Lahore and Sheikhupura, originated from electric waste disposal points near these urban and industrial sites. Tri-CBs are mainly used in electrical appliances and paint additives. Therefore, contamination by these congeners may be triggered by the disposal of electric waste that is openly dumped and burned in the surrounding areas
3.3. Spatial distribution and potential sources The highest PCB concentrations occurred at industrial and urban sites including SHR, SHK and LHR, which contributed 25 percent, 15 percent and 12 percent, respectively, of the total PCB concentration among all soil samples. In these industrial and urban areas, the paint industry, carbonless copy paper, cable insulation companies and workshops for burning electric cable for metal reclamation were widely distributed; this may explain the high values. In Taiwan, a similar conclusion was drawn by Huang et al. (1992) who found soil samples were heavily polluted by the incineration of electric wires for metal reclamation. Fu et al. (2003) also noted that the combustion of PVCs, vehicle fuels, and other chemical processes were emission sources of PCBs. Previous studies reported the urban fractionation of PCBs in soils. Motellay-Massey et al. (2004) found that PAHs and PCBs in soils from an urbanized area were 1–2 orders of magnitude higher than those in rural sites. The urban fractionation was also found in soil samples from Shanghai, China along a short (200 km) urban– rural transect (Ren et al., 2007). An urban fractionation effect can also be observed in the present study. As Fig. 2 shows, the mean value of total PCB concentrations in the soils of rural and
Fig. 2. Spatial distribution map of PCBs in air and soil sampling stations.
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
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5
of cities, such as SHR, LHR, and SHK, for various reasons including electric power generation. Urban PCB sources also include offgassing from closed systems, such as older equipment (e.g., transformers that contain large quantities of PCB fluids) (Breivik et al., 2002a), and polyvinylchloride (PVC) manufacturing. These sites are also located in urban areas where different pollutants, such as paints, oils and other waste material, are dumped and reduce the quality of the ecosystem (Farooq et al., 2011). On the other hand, tetra-CBs and penta-CBs were also found with greater frequency and at relatively high concentrations in industrial and urban sites such as Lahore and Shahdara. Significant sources of these chlorinated congeners may include steel manufacturing units and coal burning during the iron ore sintering process (Buekens et al., 2001; Biterna and Voutsa, 2005), as practiced in many industrial cities such as Lahore, Faisalabad, Sheikhupura and Shahdara. 3.4. Air–soil exchange of PCBs Fugacity fractions (ff) were calculated using PCB air and soil concentrations. When fugacities from the different compartments are approximately equal, the compartments are close to equilibrium, but if there is a large disparity then there will be a tendency for the compound to move from one compartment to the other to establish equilibrium conditions. This analysis reveals sites that are air sources (secondary sources), air sinks (soil that is undersaturated relative to air), or near equilibrium for different PCB congeners. It also shows patterns in PCB distribution or fractionation. This analysis may yield insight into the role of primary emissions and the potential of these sites to act as secondary sources for certain congeners. In the present study, fugacity fractions for six different PCB congeners (PCB-28, -52, -101, -138, -153, and -180) were calculated for the ten sampling sites in Punjab Province. The atmospheric (pg m 3) and mean soil concentrations (ng g 1 dw) for several selected PCBs from all sampling stations are presented in Fig. 3; these were used to calculate the fugacities. The fugacity fractions that were calculated for all sampling sites and selected PCB congeners are displayed in Fig. 3. The ff covers a wide range of values, indicating that some soils are net recipients of PCBs from the atmosphere, while other soils are net sources at particular sampling stations. Fugacity fractions from industrial and urban sampling sites including LHR, SHR and SHW showed equilibrium and/or atmospheric deposition status for all the samples, which clearly indicate the higher levels of PCBs in the atmosphere of these areas. The resulting lower fugacity values at these sites reflected industrial and urban activities as a primary potential source of PCBs in the urban areas of the study area. In contrast, higher fugacity fractions from agricultural and suburban areas indicated the equilibrium and/or volatilization from soil to atmosphere, which reflected the higher PCB levels in the soils of these areas. Areas with or near background concentrations of PCB in the soil have most likely been subjected to longrange transport of PCBs rather than short-range transport from local sources. The long-range transport mechanism may result in a preference for lighter congeners due to the increased time in the atmosphere (Wania and Mackay, 1993). These areas are most likely closer to air–soil equilibrium because the processes are not affected by recent high input of PCBs. As for PCB congeners, the fugacity fraction values for lighter PCBs including PCB 28 and 52 ranged between 0.0–0.7 and 0.2–0.7, respectively, showing a lower fractionation trend in the LMW PCBs in most of the sampling sites. Estimated soil–air fugacity ratios showed that lighter congeners had a tendency toward equilibrium and/or deposition from air to soil in all the samples. In the case of other congeners, such as PCB 101, 138, 153 and 180, fugacity
Fig. 3. Fugacity fractions of selected PCB congeners in air and soil samples. The whiskers on the plot represent the range of ff values; the dashed lines at ff ¼0.3 and 0.7 represent uncertainty in the equilibrium condition based on errors propagated in the ff calculation (Harner et al., 2001).
fractions showed enriched patterns close to equilibrium and/or volatilization from soils to air at most of the sampling stations in Punjab Province (Fig. 3). It is important to note that large values of ff identify the net flux direction (i.e., identifying the role of soil as a “source” to the air), and the larger the ff, the greater the flux potential. However, the absolute quantity of PCBs associated with this flux is proportional to the concentrations of PCBs in soil and also depends on meteorological factors. This could partly be explained by faster volatilization rates of lighter congeners and a larger fraction of heavier congeners left in the soil. 3.5. Dioxin-like PCBs and TEQ fluxes The WHO published recommended TEFs, including values for the dioxin-like PCBs; this system is usually referred to as the WHO-TEF scheme, as shown in Table 2. The average WHO-TEQ values for three non-ortho (PCB-77, -126, -169), mono-ortho (PCB105, -114, -118, -156, -189) and di-ortho (PCB-170, -180) PCBs were calculated using WHO-TEF, as reported by Van den Berg et al. (2006). The WHO-TEQ of PCBs varied from 0 to 3 pg m 3 (0.6 pg m 3) in all air samples. The highest oSIGMA 4TEQ levels were found at sampling locations MCH-PUF (3 pg m 3), CHW-PUF (2 pg m 3), and SHR-PUF (1 pg m 3), with much lower levels in the PUFs collected from other cities (Supplementary data Fig. A2).
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
J.H. Syed et al. / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
6
Improper incineration seems to be a possible source of release of dioxin-like PCBs in the atmosphere of these sites. The investigation of PCB pollution in the atmosphere of Punjab Province during this study showed that mean concentrations of TEQs are low compared to other developing nations (Subramanian et al., 2007; Zhang et al., 2008a,2008b). The lower values of the WHO-TEQ in the present study are perhaps due to the lower ambient temperature conditions during the deployment period of the passive samplers. For all soil samples, the dioxin-like PCBs concentrations ranged from 3 to 14 ng g 1 (dw) and accounted for 35 percent of total PCB concentrations. Table 2 shows the statistical values for TEQ concentrations for individual dioxin-like PCBs and the total dioxin-like PCBs in soils from different sampling areas in Punjab. CB-169 and CB-77 had the highest TEQ values for Punjab Province with mean values of 10 and 2 ng kg 1, respectively. The total TEQ concentration of dioxin-like PCBs in soil samples ranged from 1 to 31 ng kg 1 (mean of 13 ng kg 1) among all sampling sites. Compared with other areas of the world, the TEQ concentration for Punjab Province, Pakistan, was 13 ng kg 1, which was much higher than that for Dalian (1.372 ng kg 1). The values for Taiyun and Harbin, China, were 0.006 and 0.009 ng kg 1, respectively (Wang et al., 2008; Fu et al., 2009; Ma et al., 2009). The TEQ values obtained from Punjab Province were very high, and the CCME claims that these values are not safe (CCME, 2007). Local authorities should be made aware of this threat to human health, especially for urban and industrial soils in Punjab Province, Pakistan.
4. Conclusions This is the very first systematic study on PCB levels, profile, and distribution in surface soils and air from ten cities in Pakistan. The study provides POP data for Punjab Province, one of the most developed and populated provinces in Pakistan. The results highlight that PCB contamination should be considered an important environmental issue due to excessive PCB use in the industrial sectors. Compared with the levels of PCBs in other parts of the world, the levels of PCBs in Punjab Province were similar to or lower than the reported data from those areas. Higher levels of tri-CBs in urban and industrial areas, such as SHR, LHR and SHK, may have originated from electric waste disposal points near these urban and industrial sites. The calculated soil/air fugacity quotients indicate that soils are a potential secondary source of PCBs in agricultural areas, whereas industrial and urban areas show equilibrium and/or atmospheric deposition status. TEQ values of dioxin-like PCBs for soil samples obtained from Punjab Province were very high and CCME recommends that these values are not safe. Local authorities should address this threat to human health, especially in urban and industrial areas of Punjab Province, Pakistan. Table 2 TEQ concentrations (ng/kg) of dioxin-like PCBs in soils from Punjab Province. Congeners
Mean
Min
Max
TEFs
PCB-77 PCB-105 PCB-114 PCB-118 PCB-126 PCB-156 PCB-169 PCB-189 PCB-170 PCB-180
1.89 0.02 0.01 0.01 0.05 0.01 10.51 0.01 0.13 0.01
0.00 ND ND 0.00 0.01 0.00 1.20 0.00 0.06 0.00
14.40 0.08 0.10 0.04 0.10 0.02 31.08 0.02 0.40 0.05
0.0001 0.00003 0.00003 0.00003 0.1 0.00003 0.03 0.00003 0.0001 0.00001
PCBs
12.65
1.40
31.32
Acknowledgments This work was supported by the Chinese Academy of Sciences (No. KZCX2-YW-GJ02). We acknowledge the Higher Education Commission, Pakistan (HEC), for providing financial support under the International Research Support Initiative Program (IRSIP), and we thank Mr. Bashir Ahmad (M. Phil Student, QAU) for his assistance during field sampling.
Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.ecoenv.2013.06.005.
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Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
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Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan Jabir Hussain Syed a, Riffat Naseem Malik b, Jun Li c,n, Gan Zhang c, Kevin C. Jones d a
Environmental Biology Laboratory, Department of Plant Sciences, Quaid-I-Azam University, Islamabad 45320, Pakistan Environmental Biology and Ecotoxicology Laboratory, Department of Environmental Sciences, Quaid-I-Azam University, Islamabad 45320, Pakistan c State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China d Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK b
art ic l e i nf o
a b s t r a c t
Article history: Received 11 March 2013 Received in revised form 1 June 2013 Accepted 6 June 2013
An initial survey of the concentrations of polychlorinated biphenyl (PCB) compounds in air and soils across industrial and agricultural areas of Punjab Province, Pakistan, was conducted from January to March 2011. The total concentration of all PCBs ( oSigma 431 PCBs) ranged from 34 to 389 pg m 3 in air and from 7 to 45 ng g 1 dry weight in soils, where both ranges were similar to the average ranges in other areas of the world. PCBs were elevated across industrial regions near urban and industrial sources. Consistently low air concentrations of PCBs at the agricultural sites suggest that they are less widespread or uniformly distributed in the Pakistani atmosphere. The calculated air and soil fugacity fraction values indicated that soils are a potential secondary source of PCBs in agricultural areas, whereas they are in equilibrium or atmospheric deposition in industrial and urban areas. TEQ concentrations of dioxin-like PCBs for soil samples met the Canadian standard. However, local authorities should address the human health threats from urban and industrial soils in Punjab Province, Pakistan. & 2013 Elsevier Inc. All rights reserved.
Keywords: Air Soil Polychlorinated biphenyls (PCBs) Air–soil exchange fluxes Punjab Province
1. Introduction Polychlorinated biphenyls (PCBs) are a group of semi-volatile organic compounds (SVOCs) that are toxic in nature and also persistent because they do not readily undergo degradation when released into the environment. This group of persistent organic compounds (POPs) is of concern for humans and wildlife because of their toxicity and bioaccumulation capacity (Axmon et al., 2008; Lunder et al., 2010). PCBs have been released into the environment by open burning, waste incineration, vaporization from contaminated surfaces and products containing PCBs, and improper disposal or leakage of oil from transformers and capacitors (Breivik et al., 2002a). Because of their toxicity and resistance to degradation, the production and use of PCBs is banned in many countries. PCB levels in the environment have been declining slowly, and it has been estimated that PCB emissions during 2005 were approximately only 10 percent of those released in 1970 (Breivik et al., 2007). PCBs that have a close structural relationship to dioxins and furans and that can exhibit high levels of toxicity are called dioxinlike PCBs. Four coplanar polychlorinated biphenyls (cop-PCBs: CB-77, -81, -126, -169) and eight mono-ortho-PCBs (CB-105, -114,
n
Corresponding author. Fax: +86 20 8529 0706. E-mail address: [email protected] (J. Li).
-118, -123, -156, -157, -167, -189) share similar chemical structures and a common mechanism of toxic action as those of seven polychlorinated dibenzodioxins (PCDDs) and ten polychlorinated dibenzofurans (PCDFs) (Van den Berg et al., 2006; Matthews et al., 2008). Dioxin-like PCBs are never found as individual congeners but occur as complex mixtures with only some congeners exhibiting 2,3,7,8-TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)-like toxicity. Co-PCBs have different sources compared to the collection of PCBs that dominate the Aroclor technical mixtures (Breivik et al., 2002a, 2002b). Multiplication of the concentration of a dioxin-like PCB congener by its toxicity equivalent factor (TEF) gives the toxic equivalent (TEQ) concentration of that congener in a sample. Summation of the toxic equivalent concentrations (TEQs) of the twelve 2,3,7,8-substituted congeners gives the total toxic equivalents. This allows the reduction of a large dataset to a single number. There are several different TEQ schemes in use that assign different TEF values to congeners. Until recently, the most widely used TEQ system was prepared by a North Atlantic Treaty Organization (NATO) committee on challenges to modern society; that system is known as the International Toxicity Equivalency Factor (I-TEF) system (Kutz et al., 1990). Air–soil exchange is known to be one of the key processes that controls the presence and levels of PCBs in the environment. These compounds are thought to move towards equilibrium between soil and air and are continuously recycled (Wania and Mackay, 1993; Backe et al., 2004). Monitoring the distribution of these
0147-6513/$ - see front matter & 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ecoenv.2013.06.005
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
2
J.H. Syed et al. / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
chemicals in different environmental compartments such as soil and air and evaluating their movement is required to predict their potential health effects. Dry and wet deposition from atmosphere to soil and volatilization from soil to air are the most important processes that affect the levels of PCBs in those environmental compartments, although it was reported by Harner et al. (1995) that diffusive gaseous transport of contaminants was the most important pathway for the transfer of PCBs from soil to the atmosphere. Soils have an important role in supplying, receiving and global cycling of persistent organic pollutants in the environment (Meijer et al., 2003). Soil properties such as organic matter content are important factors affecting the air–soil partitioning of organic chemicals. It has also been shown that the levels of chemicals in soil are affected by seasonal temperature variations (Cabrerizo et al., 2011). A fugacity model has been developed by Mackay (1991) to explain the equilibrium partitioning process among the environmental compartments. With the help of fugacity quotients and mass transfer coefficients, the movement of SVOCs between the environmental compartments has been studied by several authors (Cousins and Jones, 1998; Harner et al., 2001; Backe et al., 2004; Masih et al., 2012). Although the levels, distribution, sources and air–soil exchange properties of PCBs have been widely studied for many developed or developing countries, this is not the case for Pakistan. There have been only a few studies from Pakistan in which the concentrations of PCBs in various environmental compartments have been documented (Sanpera et al., 2002, 2003; Eqani et al., 2011, 2012a). However, there is no information available regarding atmospheric concentrations of PCBs where the polyurethane foam passive air sampler (PUF-PAS) technique and the air–soil exchange of these persistent compounds were used to estimate the role of secondary sources in the country. To our knowledge, this is the very first study conducted to evaluate the POP levels in the atmosphere of Pakistan. The study area is the most important region in the subcontinent that is associated with a population of more than 100 million people. Notwithstanding its importance for the region, Punjab Province has never been studied in detail for the occurrence of SVOCs such as PCBs. This study was thus conducted to investigate the levels, sources, distribution and variations in PCB concentrations in both soil and air and in conjunction with each other and to examine air–soil exchange fluxes using the appropriate fugacity fractions. The importance of the assessment of air and soil PCB
concentrations together with the fugacity fractions was also highlighted.
2. Materials and methods 2.1. Air sampling Ten (10) sampling locations were selected for deploying Polyurethane FoamPassive Air Samplers (PUF-PAS). The study area (Punjab Province) was divided into two zones: an industrial zone, including highly populated industrialized cities such as Faisalabad, Sheikhupura and Lahore (the provincial capital), and an agricultural zone, including the cotton-growing areas of Pakistan (Fig. 1). Five PAS were deployed on the roofs of one-floor buildings in five locations in the industrial zone: Faisalabad (FSD), Sheikhupura (SHK), Shahdra (SHR), Lahore (LHR) and Phool Nagar (PN). Five more PAS were deployed on the roofs of one-floor houses in various locations in the agricultural zone: Sahiwal (SHW), Cheechawatni (CHW), Mianchanu (MCH), Khanewal (KHW) and Kabirwala (KBW). Locations of each sampling site are given in the Supplementary data in Table A1. All the PUF disks, which included ten samples, three field blanks and three transportation blanks, were pre-extracted using dichloromethane (DCM) and acetone at the State Key Laboratory of Organic Geochemistry, Guangzhou, China, and transferred by express-mail service to Pakistan in sealed, solvent-cleaned glass jars. The design and deployment of the PUF-PAS has been discussed in detail elsewhere (Jaward et al., 2005). Transportation PUF disk blanks were kept sealed in the glass jars throughout the sampling period and labeled as transportation blanks with the date. In the case of field blanks, PUF disks were taken to the chosen sites, opened with clean gloves for 5 min, sealed again in the glass jars and labeled as field blanks. Each of the samplers was assembled at the deployment sites to avoid contamination during transportation. A PUF-PAS unit was deployed at each sampling location for eight weeks between January 22 and March 19, 2011. At the completion of the deployment period, the PUF disks were retrieved, resealed and returned to Guangzhou, where they were stored frozen at –20 °C until they were analyzed. The concentrations of PCBs in air were estimated over the sampling period by assuming sampling rates and partitioning for a sample unit. A standard sampling rate of 3.5 m3 air/day per sampler was determined in previous calibration studies (Shoeib and Harner, 2002). The air/sampler partitioning was estimated as a factor of 2 to 3 for a 10 °C temperature difference, but it was neglected in the present study because similar temperature conditions prevailed in the different cities of Punjab Province throughout the sampling period (Jaward et al., 2005).
2.2. Soil sampling Fifty surface soil samples (five composite soil samples from each PUF-PAS deployment sites) were collected from the ten sampling stations. At each sampling station, one surface soil sample was taken from a 0 to 5 cm depth at the exact location of the PUF-PAS sampler; the four other samples were collected at similar depths within a 500 m radius of the sampler in different directions. All the soil samples were collected using a hand trowel and placed in polyethylene bags and then brought to the Environmental Biology Lab at Quaid-i-Azam University
Fig. 1. Map showing sampling stations from Punjab Province, Pakistan.
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
J.H. Syed et al. / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎ Islamabad, Pakistan. Samples were freeze-dried, sieved through a 2 mm sieve and then transferred to Guangzhou where they were stored frozen until they were analyzed. 2.3. Extraction and analysis The 20-g soil and PUF samples were Soxhlet-extracted for 24 h with DCM (DCM obtained from Merck and Co., Inc.). A mixture of surrogate standards of 2,4,5, 6-tetrachloro-m-xylene (TCmX) and decachlorobiphenyl (PCB-209) were added to each of the samples prior to extraction. Activated copper granules were added to the collection flask to remove any elemental sulfur that could have been present. The extract was concentrated, solvent-exchanged to hexane (hexane obtained from Merck and Co., Inc.) and purified on an 8 mm i.d. alumina/silica column. The column was packed, from the bottom to top, with neutral alumina (3 cm, 3 percent deactivated), neutral silica gel (3 cm, 3 percent deactivated), 50 percent sulfuric acid silica (3 cm), and anhydrous sodium sulfate (1 cm). The column was eluted with 50 ml of DCM/ hexane (1:1, v:v). Before use, the neutral alumina, neutral silica gel, and anhydrous sodium sulfate were Soxhlet-extracted for 48 h with DCM and then heated for 12 h at 250, 180, and 450 1C, respectively. The eluted fraction was concentrated to 0.2 ml under a gentle high-purity nitrogen stream after adding 25 μl of dodecane as a solvent keeper. A known quantity of PCB-54 was added as an internal standard prior to GC-EIMS analysis. 2.4. Chromatographic analysis Thirty-one PCB congeners, specifically PCB-28, PCB-74, PCB-70, PCB-44, PCB-49, PCB-37, PCB-60, PCB-52, PCB-66, PCB-77, PCB-82, PCB-87, PCB-99, PCB-101, PCB118, PCB-114, PCB-126, PCB-105, PCB-138, PCB-153, PCB-187, PCB-179, PCB-169, PCB-156, PCB-128, PCB-166, PCB-158, PCB-183, PCB-189, PCB-170 and PCB-180 were analyzed by GC-EI-MS. A 50 m capillary column (Varian, CP-Sil 8 CB, 50 m, 0.25 mm, 0.25 μm) was used. The injector temperature was 250 1C. The initial oven temperature was set at 150 1C for 3 min, then the temperature was raised to 290 1C at a rate of 4 1C/min, and held for 10 min. PCBs were determined in selected ion mode (SIM). The temperature of the MSD source and the quadruple was 230 1C and 150 1C, respectively. The MS was used in SIM mode with two ions monitored for each target compound group in a specific window. All the PCBs were quantified using HP-Chemstation to confirm the peaks. 2.5. Quality control/quality assurance
total PCBs in the atmosphere ranged from 34 to 389 pg m 3. It is important to note that PCB-28 was the dominant congener, accounting for 22 percent of the total PCBs, followed by PCB-37 and PCB-49, which accounted for 17 percent and 8 percent, respectively. The trends of different homologs of PCBs detected in the air samples from Punjab Province were as follows: tri-CBs4tetra-CBs4penta-CBs4hexaCBs4hepta-CBs. Dioxin-like PCB (dl- PCB) congeners including PCB77, -126, -169, -105, -114, -118, -156, -170, -180, -189, which are very important, ranged between 7 and 55 pg m 3. The compositional profiles of the PCBs in each PUF sample are illustrated in Supplementary data Fig. A1. The results showed that the tri- and tetra-CBs were the major components, constituting 37 percent and 29 percent of the total concentration (o Sigma4 31 PCBs), respectively. For high molecular weight PCBs (penta-, hexaand hepta-CBs), the relative contributions were 22 percent, 7 percent and 5 percent of the oSigma 431 PCB concentration, respectively. This prominent composition pattern was dominated by tri-CBs. This result is consistent with the composition characteristics of PCBs in the atmosphere from those of other regions (Bruhn et al., 2003; Sundqvist et al., 2004; Jaward et al., 2004a; Manodori et al., 2007; Zhang and Lohmann, 2010). However, this pattern was slightly different from composition characteristics of PCBs in the atmosphere of Asia (Jaward et al., 2005; Zhang et al., 2008a,2008b; Li et al., 2012), where tetra-CBs were the dominant homolog. The explanation of the observed composition pattern is most likely related to the emission from sources related to the production and consumption history of PCBs from all over Asia, as previously explained by Hogarh et al. (2012). Compared to the levels of PCBs in other parts of the world (Supplementary data Table A2), the levels of PCBs in Punjab
Table 1 Descriptive statistics of PCBs congeners in air (pg m-3) and soil (ng/g) samples.
All analytical procedures were monitored using strict quality assurance and control measures. Laboratory blanks (7), field blanks (3) and transportation blanks (3) were processed the same way as samples. There were no significant differences between analyte concentrations in the laboratory, field and transportation blanks, indicating contamination was negligible during transport, storage, and analysis. The average surrogate recoveries for TCmX and PCB-209 were 577 4% and 77 7 9% for air samples and 617 7% and 71 711% for soil samples, respectively. The instrumental detection limit (IDLs) values were calculated using the lowest standards extrapolated to the corresponding amount of analyte that would generate a signal-to-noise ratio of 3:1. Measurements less than the IDLs were considered as not detected (ND). The method detection limits (MDLs) were assigned as the average values of the blanks plus 3 standard deviations of blank values. When the compounds were not detected in the blanks, a standard of three times the IDLs was used to calculate the MDLs. MDLs ranged from 0.04 to 0.1 pg m 3 for air samples and from 0.4 to 1 pg g 1 for soil samples. Reported values were corrected according to the recovery ratios and blank values. 2.6. Fugacity calculations In this study, the fugacities of a compound in the soil (fs) and air (fa) phases were calculated according to Harner et al. (2001). The fugacity fractions near 0.5 indicate equilibrium. Fractions 40.5 indicate net volatilization from the soil into air, whereas values o 0.5 indicate net deposition from air to soil. Due to uncertainties and the propagation of errors in the calculation using Eq. (1), fugacity fractions between 0.3 and 0.7 were not considered to differ significantly from equilibrium (Harner et al., 2001). f f ¼ f s =ðf s þ f a Þ
3
ð1Þ
3. Results and discussion 3.1. Atmospheric concentrations and congener profile The total air concentration for all 31 PCBs and the concentration for each PCB congener are summarized in Table 1. The concentrations of
Air samples (n¼ 10) (pg m 3)
Soil Samples (n¼ 50) (ng g 1)
Mean 7std.
Range
H/L
Mean 7 std.
Range
H/L
PCB-28 PCB-37 PCB-52 PCB-49 PCB-44 PCB-74 PCB-70 PCB-66 PCB-60 PCB-77 PCB-101 PCB-99 PCB-87 PCB-82 PCB-118 PCB-114 PCB-105 PCB-126 PCB-153 PCB-138 PCB-158 PCB-166 PCB-128 PCB-156 PCB-169 PCB-179 PCB-183 PCB-180 PCB-170 PCB-189 PCB-187
257 39 167 18 4.17 8.0 9.7 7 9.5 4.7 7 9.8 0.8 7 1.0 1.6 7 2.8 2.6 7 3.9 4.6 7 8.9 3.6 7 4.1 2.5 7 4.1 2.0 7 1.0 1.9 7 3.1 5.5 7 9.2 2.6 7 4.7 1.17 1.0 1.9 7 1.7 6.4 7 9.1 2.6 7 4.3 2.4 7 3.9 0.2 7 0.27 0.38 7 0.94 0.62 7 0.98 0.4 7 0.8 1.6 7 1.8 0.17 0.2 0.2 7 0.4 0.5 7 0.8 4.7 7 1.6 0.127 0.12 0.30 7 0.50
3.2–130 0.66–50 0.61–26 1.9–34 0.15–32 0.1–2.9 0.1–8.7 0.1–11 0.15–28 0.05–11 0.31–12 0.77–4.4 0.15–9.6 0.31–28 0.1–15 0.1–2.5 0.05–6.0 0.1–28 0.05–13 0.05–11.4 0.05–0.9 0.05–3.0 0.05–3.2 0.05–2.5 0.1–4.5 ND–0.71 ND–1.0 ND–2.3 0.46–6.2 ND–0.41 ND–1.5
39 76 43 18 212 29 87 108 189 226 9 6 64 91 146 25 120 283 264 228 18 60 64 50 45 – – – 13 – –
1.2 7 1.4 1.5 7 1.7 0.3 7 1.2 2.0 7 1.1 0.3 7 0.5 0.2 7 0.2 0.3 7 0.3 0.3 7 0.2 0.5 7 0.5 0.2 7 0.1 0.5 7 0.2 0.2 7 0.1 0.2 7 0.1 0.3 7 0.3 0.3 7 0.3 0.3 7 0.28 0.4 7 0.17 1.8 7 1.1 0.90 7 1.6 1.3 7 2.5 0.277 0.20 0.137 0.10 0.487 0.74 0.22 7 0.22 0.357 0.32 0.137 0.17 0.22 7 0.31 0.88 7 1.6 1.3 7 0.96 0.317 0.16 0.38 7 0.65
0.37–5.0 0.22–6.0 0.05–0.7 1.2–5.0 0.01–1.8 0.02–0.6 0.02–1.0 0.02–0.8 0.01–1.4 0.01–0.5 0.19–1.0 0.04–0.4 0.01–0.5 0.09–1.0 0.03–1.2 0.07–1.0 0.28–0.8 0.29–3.5 0.08–5.4 0.06–8.4 0.04–0.7 0.02–0.3 0.03–2.5 0.02–0.8 0.04–1.0 o MDL–0.6 o MDL–1.1 0.10–5.4 0.62–4.0 0.09–0.6 0.02–2.2
14 27 14 4 180 30 50 40 140 50 5 10 50 11 41 14 3 12 67 140 17 15 83 40 25 – – 54 6 7 110
ΣPCBs
1207 120
34–390
Congeners
11
187 11
6.7–45
7
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
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J.H. Syed et al. / Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Province were similar to or lower than the reported data from the rural, urban and suburban areas of Japan and Korea. In addition, PCB concentrations were observed to be much lower in the current study compared to the rural and urban areas of China, where the Chinese results were monitored under the GAPs network (Hogarh et al., 2012). PCB concentrations (12,100 pg m 3) from a recent study monitored by the GAPs network in the agricultural regions with close proximity to industrial sources and dump sites in India (Pozo et al., 2011) were found to be much higher compared to the present study. Similar trends were found in the rural, urban and background air samples from 97 sites in China (Zhang et al., 2008a,2008b) where PCB levels (250 pg m 3) were reported to be significantly higher in contrast to the levels from Punjab Province during the current study. The average background concentrations of PCBs measured by various groups from regions around the world (Europe, America, Asia and Australia) were lower compared to this study except for Central America, where PCB levels were reported to be much higher (Li et al., 2010). 3.2. PCB levels and congener profiles in soils Basic descriptive statistical values of total PCB concentrations and 31 PCB congener's concentrations for 50 soil samples in Punjab Province are listed in Table 1. o Sigma4 31 PCBs ranged from 7 to 45 ng g 1 (dw), with a mean concentration of 18 ng g 1 (dw). Among all the PCB congeners, the top three chlorinated congeners were CB-126 followed by CB-37 and CB-170. With regard to the profile of PCB homologs, the dominant homologs in urban, industrial and agricultural soils of Punjab Province were penta-CBs (25 percent), followed by tetra-CBs (23 percent) and hexa-CBs (18 percent); these three congeners accounted for almost 70 percent of the total PCB concentration (Supplementary data Fig. A1). PCB homolog patterns in Punjab soils were similar to those in global background soil, which is dominated by hexa-CBs (46 percent) and penta-CBs (27 percent) (Meijer et al., 2003). However, the patterns differed from those in Chinese background/rural soil (Ren et al., 2007), which may be due to the presence of a higher quantity of lower PCB congeners in Chinese PCB products (tri-CBs: 40.4 percent; tetra-CBs: 31.1 percent) compared to global products (tri-CBs: 25.2 percent; tetra-CBs: 24.7 percent) (Wu et al., 2011) and the long-range transmission of lower chlorinated PCBs from other areas (Meijer et al., 2003; Ren et al., 2007; Fu et al., 2008b).
agricultural sites including CHW, MCH, SHW, KHW and KBW contributed only 35 percent of the total PCB concentrations in all the soil samples. This is almost half of the industrial and urban level (70 percent), which is consistent with the result from China (Ren et al., 2007) and reflects the influence of urban and industrial sources on environmental PCBs. Local authorities should pay attention to this effect because industrial plants may become more significant sources for PCBs pollution in surface soils in Punjab Province. The spatial distribution of the different PCB classes in all air samples can be clearly observed in Fig. 2. PCBs have been used as a technical mixture containing 70 percent tri, tetra and pentachlorinated biphenyls, with tri-chlorinated biphenyls as the dominant homolog (Eqani et al., 2012b). The results indicated a relatively high proportion of lower chlorinated PCBs in the air samples collected from Punjab Province, especially in the industrial and urban areas, such as Shahdara (SHR) and Lahore (LHR), where these PCB congeners are being added to the atmosphere via off-gassing. Current global air concentrations of PCBs are mainly the result of emissions from diffusive urban sources (Breivik et al., 2002a). A potentially important source of PCBs for developing countries is electronic waste (Wong et al., 2008). High concentration of tri-CBs at three sites, Shahdara, Lahore and Sheikhupura, originated from electric waste disposal points near these urban and industrial sites. Tri-CBs are mainly used in electrical appliances and paint additives. Therefore, contamination by these congeners may be triggered by the disposal of electric waste that is openly dumped and burned in the surrounding areas
3.3. Spatial distribution and potential sources The highest PCB concentrations occurred at industrial and urban sites including SHR, SHK and LHR, which contributed 25 percent, 15 percent and 12 percent, respectively, of the total PCB concentration among all soil samples. In these industrial and urban areas, the paint industry, carbonless copy paper, cable insulation companies and workshops for burning electric cable for metal reclamation were widely distributed; this may explain the high values. In Taiwan, a similar conclusion was drawn by Huang et al. (1992) who found soil samples were heavily polluted by the incineration of electric wires for metal reclamation. Fu et al. (2003) also noted that the combustion of PVCs, vehicle fuels, and other chemical processes were emission sources of PCBs. Previous studies reported the urban fractionation of PCBs in soils. Motellay-Massey et al. (2004) found that PAHs and PCBs in soils from an urbanized area were 1–2 orders of magnitude higher than those in rural sites. The urban fractionation was also found in soil samples from Shanghai, China along a short (200 km) urban– rural transect (Ren et al., 2007). An urban fractionation effect can also be observed in the present study. As Fig. 2 shows, the mean value of total PCB concentrations in the soils of rural and
Fig. 2. Spatial distribution map of PCBs in air and soil sampling stations.
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
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of cities, such as SHR, LHR, and SHK, for various reasons including electric power generation. Urban PCB sources also include offgassing from closed systems, such as older equipment (e.g., transformers that contain large quantities of PCB fluids) (Breivik et al., 2002a), and polyvinylchloride (PVC) manufacturing. These sites are also located in urban areas where different pollutants, such as paints, oils and other waste material, are dumped and reduce the quality of the ecosystem (Farooq et al., 2011). On the other hand, tetra-CBs and penta-CBs were also found with greater frequency and at relatively high concentrations in industrial and urban sites such as Lahore and Shahdara. Significant sources of these chlorinated congeners may include steel manufacturing units and coal burning during the iron ore sintering process (Buekens et al., 2001; Biterna and Voutsa, 2005), as practiced in many industrial cities such as Lahore, Faisalabad, Sheikhupura and Shahdara. 3.4. Air–soil exchange of PCBs Fugacity fractions (ff) were calculated using PCB air and soil concentrations. When fugacities from the different compartments are approximately equal, the compartments are close to equilibrium, but if there is a large disparity then there will be a tendency for the compound to move from one compartment to the other to establish equilibrium conditions. This analysis reveals sites that are air sources (secondary sources), air sinks (soil that is undersaturated relative to air), or near equilibrium for different PCB congeners. It also shows patterns in PCB distribution or fractionation. This analysis may yield insight into the role of primary emissions and the potential of these sites to act as secondary sources for certain congeners. In the present study, fugacity fractions for six different PCB congeners (PCB-28, -52, -101, -138, -153, and -180) were calculated for the ten sampling sites in Punjab Province. The atmospheric (pg m 3) and mean soil concentrations (ng g 1 dw) for several selected PCBs from all sampling stations are presented in Fig. 3; these were used to calculate the fugacities. The fugacity fractions that were calculated for all sampling sites and selected PCB congeners are displayed in Fig. 3. The ff covers a wide range of values, indicating that some soils are net recipients of PCBs from the atmosphere, while other soils are net sources at particular sampling stations. Fugacity fractions from industrial and urban sampling sites including LHR, SHR and SHW showed equilibrium and/or atmospheric deposition status for all the samples, which clearly indicate the higher levels of PCBs in the atmosphere of these areas. The resulting lower fugacity values at these sites reflected industrial and urban activities as a primary potential source of PCBs in the urban areas of the study area. In contrast, higher fugacity fractions from agricultural and suburban areas indicated the equilibrium and/or volatilization from soil to atmosphere, which reflected the higher PCB levels in the soils of these areas. Areas with or near background concentrations of PCB in the soil have most likely been subjected to longrange transport of PCBs rather than short-range transport from local sources. The long-range transport mechanism may result in a preference for lighter congeners due to the increased time in the atmosphere (Wania and Mackay, 1993). These areas are most likely closer to air–soil equilibrium because the processes are not affected by recent high input of PCBs. As for PCB congeners, the fugacity fraction values for lighter PCBs including PCB 28 and 52 ranged between 0.0–0.7 and 0.2–0.7, respectively, showing a lower fractionation trend in the LMW PCBs in most of the sampling sites. Estimated soil–air fugacity ratios showed that lighter congeners had a tendency toward equilibrium and/or deposition from air to soil in all the samples. In the case of other congeners, such as PCB 101, 138, 153 and 180, fugacity
Fig. 3. Fugacity fractions of selected PCB congeners in air and soil samples. The whiskers on the plot represent the range of ff values; the dashed lines at ff ¼0.3 and 0.7 represent uncertainty in the equilibrium condition based on errors propagated in the ff calculation (Harner et al., 2001).
fractions showed enriched patterns close to equilibrium and/or volatilization from soils to air at most of the sampling stations in Punjab Province (Fig. 3). It is important to note that large values of ff identify the net flux direction (i.e., identifying the role of soil as a “source” to the air), and the larger the ff, the greater the flux potential. However, the absolute quantity of PCBs associated with this flux is proportional to the concentrations of PCBs in soil and also depends on meteorological factors. This could partly be explained by faster volatilization rates of lighter congeners and a larger fraction of heavier congeners left in the soil. 3.5. Dioxin-like PCBs and TEQ fluxes The WHO published recommended TEFs, including values for the dioxin-like PCBs; this system is usually referred to as the WHO-TEF scheme, as shown in Table 2. The average WHO-TEQ values for three non-ortho (PCB-77, -126, -169), mono-ortho (PCB105, -114, -118, -156, -189) and di-ortho (PCB-170, -180) PCBs were calculated using WHO-TEF, as reported by Van den Berg et al. (2006). The WHO-TEQ of PCBs varied from 0 to 3 pg m 3 (0.6 pg m 3) in all air samples. The highest oSIGMA 4TEQ levels were found at sampling locations MCH-PUF (3 pg m 3), CHW-PUF (2 pg m 3), and SHR-PUF (1 pg m 3), with much lower levels in the PUFs collected from other cities (Supplementary data Fig. A2).
Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i
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Improper incineration seems to be a possible source of release of dioxin-like PCBs in the atmosphere of these sites. The investigation of PCB pollution in the atmosphere of Punjab Province during this study showed that mean concentrations of TEQs are low compared to other developing nations (Subramanian et al., 2007; Zhang et al., 2008a,2008b). The lower values of the WHO-TEQ in the present study are perhaps due to the lower ambient temperature conditions during the deployment period of the passive samplers. For all soil samples, the dioxin-like PCBs concentrations ranged from 3 to 14 ng g 1 (dw) and accounted for 35 percent of total PCB concentrations. Table 2 shows the statistical values for TEQ concentrations for individual dioxin-like PCBs and the total dioxin-like PCBs in soils from different sampling areas in Punjab. CB-169 and CB-77 had the highest TEQ values for Punjab Province with mean values of 10 and 2 ng kg 1, respectively. The total TEQ concentration of dioxin-like PCBs in soil samples ranged from 1 to 31 ng kg 1 (mean of 13 ng kg 1) among all sampling sites. Compared with other areas of the world, the TEQ concentration for Punjab Province, Pakistan, was 13 ng kg 1, which was much higher than that for Dalian (1.372 ng kg 1). The values for Taiyun and Harbin, China, were 0.006 and 0.009 ng kg 1, respectively (Wang et al., 2008; Fu et al., 2009; Ma et al., 2009). The TEQ values obtained from Punjab Province were very high, and the CCME claims that these values are not safe (CCME, 2007). Local authorities should be made aware of this threat to human health, especially for urban and industrial soils in Punjab Province, Pakistan.
4. Conclusions This is the very first systematic study on PCB levels, profile, and distribution in surface soils and air from ten cities in Pakistan. The study provides POP data for Punjab Province, one of the most developed and populated provinces in Pakistan. The results highlight that PCB contamination should be considered an important environmental issue due to excessive PCB use in the industrial sectors. Compared with the levels of PCBs in other parts of the world, the levels of PCBs in Punjab Province were similar to or lower than the reported data from those areas. Higher levels of tri-CBs in urban and industrial areas, such as SHR, LHR and SHK, may have originated from electric waste disposal points near these urban and industrial sites. The calculated soil/air fugacity quotients indicate that soils are a potential secondary source of PCBs in agricultural areas, whereas industrial and urban areas show equilibrium and/or atmospheric deposition status. TEQ values of dioxin-like PCBs for soil samples obtained from Punjab Province were very high and CCME recommends that these values are not safe. Local authorities should address this threat to human health, especially in urban and industrial areas of Punjab Province, Pakistan. Table 2 TEQ concentrations (ng/kg) of dioxin-like PCBs in soils from Punjab Province. Congeners
Mean
Min
Max
TEFs
PCB-77 PCB-105 PCB-114 PCB-118 PCB-126 PCB-156 PCB-169 PCB-189 PCB-170 PCB-180
1.89 0.02 0.01 0.01 0.05 0.01 10.51 0.01 0.13 0.01
0.00 ND ND 0.00 0.01 0.00 1.20 0.00 0.06 0.00
14.40 0.08 0.10 0.04 0.10 0.02 31.08 0.02 0.40 0.05
0.0001 0.00003 0.00003 0.00003 0.1 0.00003 0.03 0.00003 0.0001 0.00001
PCBs
12.65
1.40
31.32
Acknowledgments This work was supported by the Chinese Academy of Sciences (No. KZCX2-YW-GJ02). We acknowledge the Higher Education Commission, Pakistan (HEC), for providing financial support under the International Research Support Initiative Program (IRSIP), and we thank Mr. Bashir Ahmad (M. Phil Student, QAU) for his assistance during field sampling.
Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.ecoenv.2013.06.005.
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Please cite this article as: Syed, J.H., et al., Levels, distribution and air–soil exchange fluxes of polychlorinated biphenyls (PCBs) in the environment of Punjab Province, Pakistan. Ecotoxicol. Environ. Saf. (2013), http://dx.doi.org/10.1016/j.ecoenv.2013.06.005i