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Fs established prior to the construction of municipal solid waste incinerators in China
Chemosphere 86 (2012) 300–307
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Baseline soil levels of PCDD/Fs established prior to the construction of municipal solid waste incinerators in China Hong-mei Liu, Sheng-yong Lu ⇑, Alfons G. Buekens, Tong Chen, Xiao-dong Li, Jian-hua Yan, Xiao-Jun Ma, Ke-fa Cen State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou 310027, China
a r t i c l e
i n f o
Article history: Received 9 March 2011 Received in revised form 13 September 2011 Accepted 20 October 2011 Available online 25 November 2011 Keywords: PCDD/Fs Baseline level Hierarchical cluster analysis Soils Principal component analysis
a b s t r a c t In order to determine the baseline contamination by polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in different areas in China, prior to the construction of municipal solid waste incinerators (MSWIs), a total of 32 representative soil samples was collected near 16 incinerators and analyzed for their PCDD/F concentrations. The PCDD/F baseline concentrations in the soil samples ranged from 0.32 to 11.4 ng I-TEQ kg 1 (dry matter), with average and median value of 2.73 and 2.24 ng I-TEQ kg 1 (dry matter), respectively, and a span between maximum and minimum recorded value of 36. The PCDD homologues predominated in 26 out of 32 soil samples, with the ratio (PCDDs)/ (PCDFs) ranging from 1.1 to 164; however in the other 6 samples, PCDF homologues were larger, with the same ratio varying from 0.04 to 0.8. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to examine PCDD/F amount and profile in these soil samples, and their possible associations with known emission sources: in this process 6 really distinct isomer fingerprints were identified. Background PCDD/F levels and profiles were comparable to those found in soils from China and other countries and indicate a rather low baseline PCDD/F contamination of soils. The present data provide the tools for future assessment of a possible impact of these MSWIs. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), in brief, dioxins, are emitted to the atmosphere by a wide variety of thermal processes. Among these thermal sources, PCDD/F emissions from municipal solid waste incinerators (MSWIs) have received extensive attention from the scientific community as well as from environmental regulators, and any links between emissions and their effects on soil and herbage, (Alcock et al., 1999; US EPA, 2001; Kim et al., 2005; Oh et al., 2006; Kobayashi et al., 2008; Kulkarni et al., 2008) or even on cow milk (Liem et al., 1991) have been evaluated. PCDD/Fs are semi-volatile and show high values for the organic carbon/water partition coefficient (Koc = 0.41) and octanol/water partition coefficient (Log Kow > 5.0), (Fries, 1995a,b). Hence, they accumulate in media rich in organic carbon, such as soils and sediments (Adriaens et al., 1995; Brzuzy and Hites, 1995; Kjeller et al., 1996; Meneses et al., 2002; Kanematsu et al., 2006). Dioxins-from soils may also transfer to the food chain. This pathway is important for assessing general exposure of the population, since more than
⇑ Corresponding author. Tel.: +86 571 87952628; fax: +86 571 87952438. E-mail address: [email protected] (S.-y. Lu). 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.10.033
90% of the PCDD/F human uptake is by food, or by herbage and fodder for animals (Fries, 1995a,b; Ma, 2002; Ma et al., 2002; Baars et al., 2004; Kao et al., 2007); the most important contributor was identified as the background soil concentration proper (Meneses et al., 2002). In China MSWIs are considered to be third in importance as source of dioxins emissions (UNEP, 2005), coming after the production of iron and steel and heating & power generation. In 1989 the first large incinerator plant was built in Mainland China, i.e. a Martin stoker plant in Shenzhen. More recently, industrial development and enhanced living standards in China inflated the volume and improved the fuel quality of municipal solid waste (MSW), and the number of MSWI plants has gradually increased, especially in affluent cities. In 2008, already 74 MSWIs were operating, with an average treatment capacity of 612 tons/day (CSY, 2008). It is estimated that 200 MSWIs with total daily treatment capacity of 100,000 tons will be in service by 2015 (Cheng et al., 2007). At present, studies on PCDD/Fs in China have focused on air/ particle distribution in the atmosphere and on soils in the vicinity of waste incineration plants (Shi et al., 2008; Yan et al., 2008; Xu et al., 2009a, b; Li et al., 2010); data for the baseline contamination of PCDD/Fs in soils, however, is still lacking. This study was carried out to determine this baseline contamination. Such monitoring is
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passed though a 2-mm sieve. About 500 g soil of each sample was finally homogenized through a 60-mesh sieve, and refrigerated until analysis.
useful for future assessment of the eventual environmental impact of those plants. In addition, the study provides valuable information about baseline concentrations and profiles of PCDD/F in soils, prior to the construction in various parts of China of 16 new MSWIs.
2.2. Analytical method Extraction and clean-up procedures of soil samples, as well as analytical determination of PCDD/Fs, were carried out as described in previous research projects (Yan et al., 2008; Li et al., 2010). About 10 g (dry matter) of soil sample (60-mesh) were used for each PCDD/Fs analysis. A selective pressurized liquid extraction (SPLE) method was used for sample extraction, using a fully automated ASE 300 system (Dionex, Sunnyvale, CA, USA). Extraction conditions and procedures referred to the SPLE method with slight modification (Eljarrat et al., 2003). Briefly, a 100 mL extraction cell was used and the ratio sample: alumina: copper was 5:5:1. Before extraction each sample was spiked with a mixture of 13C12-labelled PCDD/Fs compound stock solution (5 lL) and clean-up standard (5 lL). The extracts from ASE were subsequently submitted to rotary evaporation and to a multilayer silicagel column clean-up procedure, following US EPA 1613 (US EPA, 1994). The extracts were blowdown to 20 lL under a gentle stream of nitrogen (N2), and 5 lL of 13 C12-labelled PCDD/Fs internal standard solution were added before the dioxins analyzed by high-resolution gas chromatography with high-resolution mass spectrometry (HRGC/HRMS JEOL JMS800D) using a DB-5MS column (60 m 0.25 mm 0.25 lm). The toxic 2,3,7,8-substituted PCDD/Fs (referred to as congeners) as well as the tetra- to octa-chlorinated homologue groups were identified based on an isotope ratio within ±15% of the theoretical values and signal to noise ratios of equal or greater than 2.5; quantification of PCDD/Fs was performed by an isotope dilution method using relative response factors previously obtained from five calibration standard solutions. Recoveries of internal standards, as determined against external standard, generally varied between 70% and
2. Material and methods 2.1. Sample collection During 2006–2009, 16 target MSWI facilities were selected prior to their construction, as shown in Fig. 1. They are located in 5 different provinces including Sichuan, Hubei, Fujian, Zhejiang and Shanghai. A total of 32 soil samples were collected at fixed sampling points, situated around the 16 incinerator plants and taking the main wind direction into account (Fig. 1). The sampling points were selected at a distance of 200 m and of 1000 m from every target incinerator stack, under the dominant wind direction. Among these 16 target MSWI facilities 11 (F1–F11; sites S1–S22) were located in suburban areas, 2 MSWIs (F12–F13; sites S23– S26) were located in residential and commercial areas, and the others were located in industrial areas (F14–16; sites S27–S32). The exact position of the sampling points was recorded by a handheld GPS device (Meridian Color, Thales Navigation, USA). The soil samples analyzed were constituted by mixing five different aliquots in equal amounts (one in the center + one in each in the four main directions situated of 5 m to the center). Sampling was carried out by inserting a cylindrical steel corer (24 cm 4 cm, length internal diameter, supplied from Eijkelkamp, Holland) down to a depth of 10 cm. Approximately 1.5 kg of soil was taken at each site. The soils were subsequently dried in a ventilated room until constant weight, and plant materials, such as roots and leaves, were manually removed. Then the soils were ground and
(134/1.22, 184/2.30)
F12,F13 F4
(42/0.35)
F1,F2
F10,F11 (2876/4.52, 2835/4.75) (473/3.67, 118/0.98) F8,F9 (511/2.22) F16 Hubei F7
Shanghai
F3
(723/3.09)
(82/0.56, 400/6.79)
(60/2.31)
Sichuan
F14,F15 (1272/3.39, 528/3.62)
Zhejiang Fujian F6
F5 (1026/1.91)
(818/2.16)
Main Wind Direction
China 200m 1000m Target MSWI Soil Sampling Point
Fig. 1. Special distribution of the soil sampling sites and MSWI facilities in this study, with brackets including average PCDD/F concentrations/I-TEQ of each facility, ng kg
1
.
PCDD/Fs
F1
F2
F3
302
Table 1 PCDD/F baseline concentrations in soil samples prior to construction of 16 new MSWI plant (ng g
1
). F4
F5
F6
F7
F8
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
S12
S13
S14
S15
S16
2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDD OCDD 2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF
ND ND ND ND ND 9.28 30.69 1.94 ND ND 1.13 1.20 ND ND 8.26 ND ND
ND ND ND ND ND 7.11 50.15 1.11 ND ND 1.26 0.58 ND ND 6.54 ND ND
0.75 3.98 3.54 4.12 3.54 10.86 198.21 2.49 10.19 8.63 5.40 5.61 3.09 5.78 11.69 4.26 9.13
ND 0.79 0.67 0.58 1.25 3.69 53.59 1.41 1.45 1.30 1.41 1.40 1.05 1.38 3.63 1.19 4.80
ND ND 0.30 1.29 1.08 8.20 27.66 1.10 1.73 1.98 1.61 2.35 1.23 2.96 9.83 1.53 6.30
ND ND ND 1.16 0.80 6.82 16.30 0.74 1.58 1.66 1.25 1.75 1.35 1.43 7.15 1.29 3.87
ND ND ND ND 0.16 0.66 7.80 0.23 0.38 0.32 0.40 0.42 0.07 0.38 1.36 ND 0.88
ND ND ND ND 0.09 1.09 37.97 0.20 0.32 0.26 0.26 0.28 0.07 0.24 1.13 ND 1.18
0.02 0.01 0.01 0.02 0.06 0.40 41.52 13.45 ND 0.32 0.27 0.09 0.06 0.06 0.20 0.10 0.15
0.20 0.05 ND 0.10 0.26 0.96 43.67 13.05 0.24 0.70 0.91 0.44 0.21 0.29 1.27 0.30 1.08
ND ND 0.32 1.06 1.86 26.90 816.79 1.23 0.67 0.95 1.36 0.83 0.41 1.46 4.29 ND ND
ND ND 0.38 0.93 2.21 20.87 461.69 0.64 0.99 0.80 0.40 0.91 0.26 0.90 3.94 ND ND
0.35 0.25 2.24 1.88 4.08 2.86 9.76 0.68 2.39 0.32 0.30 2.38 0.77 2.61 3.73 2.84 6.24
0.06 0.57 0.59 0.52 1.07 3.12 18.91 0.29 0.34 0.93 0.80 0.74 9.01 0.56 1.52 0.79 1.93
ND 0.45 0.41 0.84 0.98 18.09 961.33 0.96 1.33 1.60 1.34 1.49 0.44 1.36 5.78 1.35 6.66
ND 0.35 0.66 0.92 1.20 43.90 4505.18 0.26 0.33 0.48 0.69 0.67 0.32 0.57 3.37 0.68 3.42
TCDD PeCDD HxCDD HpCDD OCDD TCDF PeCDF HxCDF HpCDF OCDF P PCDDs + RPCDFs PCDDs/PCDFs ratio I-TEQ
2.89 1.58 2.84 17.62 30.69 5.56 3.36 2.78 11.78 ND
5.21 1.74 5.38 7.3 50.15 4.39 1.44 2.18 7.93 ND
34.49 20.20 30.75 21.93 198.21 109.18 95.38 44.40 25.71 9.13
16.77 7.63 7.30 7.45 53.59 78.17 10.86 15.99 8.57 4.80
28.50 31.37 87.09 50.81 27.66 110.23 179.76 81.74 54.37 6.30
22.07 51.52 70.93 32.77 16.30 42.14 42.69 41.13 40.02 3.87
0.96 0.61 1.30 1.02 7.80 4.27 3.26 3.76 2.36 0.88
1.27 1.84 1.67 1.87 37.97 5.81 2.52 2.50 1.19 1.18
1.70 0.11 0.25 1.07 41.52 612.44 3.39 0.65 0.37 0.15
4.98 1.59 1.92 2.47 43.67 1322.00 6.36 3.53 2.09 1.08
13.96 6.98 40.13 72.86 816.79 57.61 12.70 11.10 7.39 ND
4.87 9.25 20.67 59.14 461.69 19.16 7.64 8.47 5.79 ND
1.82 1.46 9.10 3.87 9.76 7.08 6.34 7.94 6.57 6.24
0.78 1.81 3.80 5.68 18.91 5.34 4.53 13.67 2.92 1.93
3.72 6.26 11.61 53.28 961.33 14.37 13.30 13.29 12.17 6.66
1.33 2.38 11.24 107.09 4505.18 7.34 4.36 5.98 7.10 3.42
79.1 2.37 0.63
85.72 4.38 0.48
589.38 1.08 11.40
211.13 0.78 2.18
657.83 0.52 2.50
363.44 1.14 1.93
26.22 0.80 0.37
57.82 3.38 0.32
661.65 0.07 1.63
1389.69 0.04 2.18
1039.52 10.71 2.49
596.68 13.53 1.82
60.18 0.76 2.35
59.37 1.09 2.26
1095.99 17.33 3.09
4655.42 164.09 5.95
Average Average Average Average
62.7 19.71 82.41 0.56
RPCDDs RPCDFs RPCDD/Fs I-TEQ
PCDD/Fs
2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDD OCDD 2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF
199.16 201.10 400.26 6.79
F9
209.51 301.13 510.64 2.22
F10
28.16 13.87 42.02 0.35
F11
49.64 976.03 1025.67 1.91
F12
753.17 64.93 818.10 2.16
F13
28.50 31.28 59.78 2.31
F14
2831.71 43.99 2875.71 4.52
F15
F16
S17
S18
S19
S20
S21
S22
S23
S24
S25
S26
S27
S28
S29
S30
S31
S32
ND 0.60 0.75 1.00 1.19 45.12 4504.88 0.83 0.82 1.46 0.93 0.90 0.74 0.91
ND 0.49 0.50 0.88 1.13 18.52 847.45 1.02 0.98 1.15 1.21 1.19 0.33 1.31
0.14 0.49 1.51 0.89 1.02 12.76 247.34 1.97 1.73 2.39 3.78 3.72 0.50 3.33
0.08 0.40 1.26 0.90 0.92 11.40 257.35 2.25 1.48 2.20 3.00 2.84 0.37 2.48
ND ND 0.85 0.52 0.47 3.09 105.69 0.57 0.79 1.44 1.10 0.80 0.22 0.75
ND ND 0.57 0.11 0.23 2.32 59.64 0.26 0.30 0.29 0.39 0.19 0.06 0.30
ND 0.24 0.23 0.65 0.43 3.81 57.80 0.61 0.63 0.54 0.81 0.73 0.25 0.51
ND 0.35 0.31 0.62 0.40 6.09 83.33 1.24 1.09 0.88 1.23 1.27 0.46 0.57
0.15 0.77 0.72 0.89 0.97 4.10 61.68 0.97 1.18 1.26 1.15 1.08 0.72 1.41
0.25 0.95 0.67 0.57 1.00 5.03 78.11 1.46 1.17 1.32 1.29 1.17 0.49 1.57
0.13 0.51 0.99 1.37 1.96 37.62 1392.68 1.15 0.87 0.86 1.26 1.23 0.66 1.02
0.25 0.69 0.68 1.00 1.30 18.82 776.79 1.56 2.15 0.84 2.37 1.40 0.49 1.03
ND 0.36 0.89 0.61 0.79 3.37 43.01 0.51 0.66 0.35 1.27 0.98 0.58 1.02
ND 2.85 3.12 2.86 4.67 29.75 838.60 1.49 3.38 1.1 4.48 2.79 2.91 4.3
ND ND 1.18 1.9 2.2 16.95 241.38 3.24 5.08 2.37 4.58 3.74 0.34 2.33
ND ND 0.46 0.99 1.56 14.64 780.38 0.35 0.68 0.86 1.41 1.43 0.2 1.33
H.-m. Liu et al. / Chemosphere 86 (2012) 300–307
S1
485.13 42.82 527.95 3.62
615.59 107.69 723.28 3.09
879.35 20.52 2.23 978.27 13.85 6.07
2.3. Data analysis
1197.67 74.26 1271.92 3.39
1618.52 26.96 3.64
320.76 152.49 473.25 3.67 2784.59 50.01 2834.60 4.75
ND: the concentration measured blow the detection limits, the detection level is 0.01 ng kg
93.38 24.66 118.04 0.98
1
, the same to the following data.
100.73 33.66 134.39 1.22
117.13 66.63 183.76 2.30
204.34 1.75 2.44 163.17 1.77 2.16 158.13 2.70 1.46 110.64 3.51 0.97 76.32 8.10 0.47 159.75 2.90 1.48 457.25 2.46 3.38 489.25 1.83 3.95 985.5 15.68 2.70 4683.69 113.46 6.79
303
110%, and all satisfied the requirements of US EPA 1613. Laboratory and field blanks were routinely analyzed once a month. The target compounds were all tetra- to octa-CDD/Fs. The temperature program of the capillary column was as follows: (1) 150 °C holding for 1 min; (2) increased to 190 °C at 25 °C min 1; (3) increased at 3 °C min 1 to 280 °C, hold for 20 min. The injection volume was 1 lL by automatic split injection. The MS was operated at a resolution of 10,000 under positive EI conditions (38 eV electron energy), and the data were obtained in the selective ion-monitoring mode. All isotope standards were purchased from Cambridge Isotope Laboratories, Inc. (USA).
925.32 9.21 3.13
77.62 2.93 1.16
567.2 2.25 3.94
1.97 8.85 15.56 31.73 780.38 2.58 8.80 8.31 11.11 10.06 48.39 25.92 35.28 41.72 241.38 93.12 24.21 24.21 21.73 11.24 2.99 7.47 15.36 47.98 838.60 7.19 7.92 31.05 11.35 8.36 1.90 0.73 4.61 7.61 43.01 4.41 3.42 4.85 4.08 3.00 11.89 5.84 10.92 13.88 61.68 25.06 13.00 9.32 6.52 5.06 6.59 5.89 12.98 53.49 847.45 18.91 14.74 11.68 8.95 4.82 4.22 6.00 11.50 116.17 4504.88 10.83 10.23 10.43 6.27 3.16
TCDD PeCDD HxCDD HpCDD OCDD TCDF PeCDF HxCDF HpCDF OCDF P PCDDs + RPCDFs PCDDs/PCDFs ratio I-TEQ P Average PCDDs P Average PCDFs P Average PCDD/Fs Average I-TEQ
6.83 9.77 23.03 29.51 247.34 46.52 29.69 30.32 37.37 28.87
14.96 13.55 12.78 26.40 257.35 42.87 26.90 24.53 25.29 12.62
3.95 0.49 4.09 4.60 105.69 16.83 7.06 6.93 7.47 2.64
0.78 0.81 2.07 4.63 59.64 3.27 1.65 1.20 1.83 0.44
6.10 4.97 7.44 9.79 57.80 7.64 6.44 3.63 4.43 2.40
3.65 5.78 7.95 14.64 83.33 14.60 11.46 6.17 7.05 3.50
14.96 8.23 11.93 16.82 78.11 31.70 15.17 12.79 6.40 8.23
5.56 8.59 29.41 124.39 1392.68 20.04 12.74 9.18 8.43 7.50
6.75 6.83 8.66 35.67 776.79 30.85 20.60 25.01 10.49 3.67
7.92 3.12 8.36 3.29 0.94 5.06 4.19 ND 4.82 3.41 ND 3.16 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF
18.66 2.49 28.87
12.83 1.79 12.62
3.67 0.91 2.64
0.88 0.18 0.44
2.48 0.33 2.40
3.54 0.30 3.50
3.29 1.06 8.23
3.34 1.07 7.50
5.07 0.74 3.67
2.06 0.86 3.00
11.2 1.61 11.24
4.95 0.87 10.06
H.-m. Liu et al. / Chemosphere 86 (2012) 300–307
All experimental results are expressed on a dry weight basis. The 2,3,7,8-TCDD toxic equivalents (I-TEQ) are calculated using NATO/CCMS factors, as the Chinese Government has adopted this toxicity scheme (MEPC, 2001a, 2001b). All PCDD/Fs data are normalized to the sum of [PCDDs] + [PCDFs] = 1 before the multivariate analysis of homologue and congener patterns. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to evaluate similarities and differences within the PCDD/Fs homologue patterns of the selected soil samples. HCA first served to identify homogeneous groups of samples and then was performed again according to the furthest neighbor between groups cluster method with the squared Euclidean distance measure method, derived from the PCA scores. Each sample was assigned a score after PCA analysis. Statistical analysis was performed using the SPSS 16.0 SOFTWARE package.
3. Results and discussion 3.1. PCDD/F concentrations The baseline concentrations of PCDD/Fs in soil samples, taken prior to the construction of 16 MSWI facilities in China, are summarized in Table 1. TEQ values (sum concentration of tetra- to octa-PCDD/Fs) range from 0.32 to 11.40 ng I-TEQ kg 1 (26.2– 4680 ng kg 1), with average and median value of 2.73 and 2.24 ng I-TEQ kg 1 (650 and 116 ng kg 1), and a span ratio between maximum and minimum recorded value of 36 and 180, respectively. The samples can be subdivided into three I-TEQ groups: those with low I-TEQ (<1 ng I-TEQ kg 1, i.e. S1, S2, S7, S8, S22 and S23), average samples, and high samples (>4 ng ITEQ kg 1, i.e. S3, S16, S17, and S30). Typically, individual data figures internally deviate by two orders of magnitude. Least variable is 1,2,3,4,7,8-HxCDF, with a span of only 21; second comes I-TEQ with 36. The following also show a low span (60–70): 2,3,7,8TCDD, 2,3,7,8-TCDF, and 1,2,3,6,7,8-HxCDF. Conversely, OCDD is remarkably variable, with a span of 580. The Ratio of PCDDs to PCDFs shows the largest variance, with more than 4000. There is limited difference, however, between the various types of surroundings. On average, both suburban and industrial areas are 5.3 times more PCDD/Fs polluted than residential areas, yet only a factor 1.56 and 1.9 when expressed in I-TEQ values. For most congeners and isomer groups any distinction between such averages is less than a factor two. The difference is made by OCDD (a factor 8.6 and 9.7) and by TCDF (sites S9 and S10, with an exceptional profile). Average isomer fingerprints differ only marginally, yet industrial areas are higher weight average chlorinated. A box plot of soil samples collected from different areas is depicted in Fig. 2. The average PCDD/F concentration in residential and commercial areas, 1.76 ng I-TEQ kg 1, is slightly lower than that at the suburban areas and industrial areas, 2.74 and
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H.-m. Liu et al. / Chemosphere 86 (2012) 300–307
Fig. 2. A box-plot of soil samples collected from different areas.
3.2. Comparison with worldwide PCDD/F levels In order to gain perspective on the relative extent of contamination of PCDD/Fs at the different sampling sites, the recorded levels were compared to international soil guidelines and regulations, which specify maximum acceptable levels according to different land uses (Leung et al., 2007). As yet, China has no soil guidelines for PCDD/Fs. In this study, the TEQ values of most soil samples (about 78%) are below the Canadian guideline for agricultural land use (4 ng TEQ kg 1) (CCME, 2003). Based on German guidelines for dioxins in soils (Schulz, 1993), most soils in this study could be
4
(b)
S13
Group 4
3
Factor 2 (17.3%)
3.36 ng I-TEQ kg 1, respectively. In addition, the range of PCDD/F concentrations is small, except for samples S13, S16 and S17. The most toxic congener, 2,3,7,8-TCDD, is identified in 9 out of the 32 samples, a value of 0.75 ng kg 1 clearly standing out in S3. This sample shows also the highest concentration for ten out of seventeen PCDD/F congeners. Conversely, among the 17 congeners investigated, OCDD is generally the highest in concentration (5 exceptions are: S4, S5, S6, S9, S10) ranging from 7.8 to 4505 ng kg 1 and accounting for 22–99% of the sum of the seventeen congeners in all soil samples (ATSDR, 1998). This distribution is similar to those in background soils observed in previous investigations (Domingo et al., 2001; Oh et al., 2006; Yan et al., 2008; Liu and Liu, 2009). High-chlorinated congeners are primarily bound to aerosols or to particulate matter and show the greatest tendency to bioaccumulate. PCDD homologues predominate in 26 out of 32 soil samples, with a PCDDs to PCDFs ratio ranging from 1.1 to 164, and indicating a typical background profile; Previous research indicated that dioxins in background soils tend to have an atmospheric fingerprint (high chlorinated PCDDs and low levels of chlorinated PCDFs), compared to soils close to active MSWIs, which show more PCDFs than PCDDs (Schuhmacher et al., 1997; Domingo et al., 2001; Oh et al., 2006; Yan et al., 2008; Liu and Liu, 2009), with the PCDDs to PCDFs ratio ranging 0.04–0.8. Possibly, those deviant baseline soils had been contaminated by anthropological sources of PCDD/Fs, such as metallurgical processes, waste combustion (Hagenmaier et al., 1994; Wagrowski and Hites, 2000) or hitherto unidentified sources. The highest soil concentration (11.4 ng TEQ kg 1) was observed in sample S3 in the vicinity of the F2 incinerator, situated in farmland close to an oil factory. However, another soil site near the same incinerator S4, was located upwind of the oil factory. Sample S17 was located in open area near a highway; however, this location was a pond in the past.
2
S14
Group 2
S19
S5
1
S29
Group 1 S21 S8
0
-1
-2
Group 5
S7
S20
S28 S30 S32 S15 S16 S17 S18 S22 S27 S10 S11S12 S9
S3 S26 S25
S6
S24S4
S23
S31
S2
Group 6
Group 3
-2
S1
-1
0
1
2
3
4
Factor 1 (48.6%) Fig. 3. Plot of hierarchical cluster analysis (a) and principal component analysis (b) of soil samples.
used safely, as the guidelines recommend that no restrictions be placed on use of soil with dioxin concentrations below 5 ppt (ng kg 1, based on dioxin TEQS9). However, at concentrations between 5–20 ppt, such as the soils in the sites S3, S16, S17 and S22 of this study, management systems should be implemented to reduce PCDD/F pollutions and dust (Fig. 2). The recorded baseline level exceeds the Dutch and Swedish guidelines for agricultural land use (10 ng TEQ kg 1) (MfE/MoH, 1997; BMU, 1999) only for soil site S3, while the concentrations and 2,3,7,8-TCDD at the all sampling sites are below the US guideline (1000 ng TEQ kg 1 and 39 ng kg 1, respectively) (Kimbrough et al., 1984; US EPA, 2000). In this study, the PCDD/F baseline levels and profiles were comparable to those found in soils in the vicinity of the construction of new hazardous waste incinerators (MWIs) by Schuhmacher et al. (1997 and 2002), with baseline concentrations ranging from 0.12–17.2 ng TEQ kg 1, and higher than those in Beijing (Li et al., 2004). Oh et al. (2006), Zheng et al. (2008), Kim et al. (2008), Zhang
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100
100
(a)
Group 1 (n=13) Group 2 (n=12) Group 3 (n=2)
80
(a)
80
Group 1 (n=13) Group 2 (n=12) Group 3 (n=2)
60
30
65
25
60
15
45
Percent (%)
50
OCDF
1,2,3,4,7,8,9-HpCDF
25 20 15 10
OCDF
1,2,3,4,7,8,9-HpCDF
1,2,3,7,8,9-HxCDF
1,2,3,4,6,7,8-HpCDF
2,3,4,6,7,8-HxCDF
1,2,3,6,7,8-HxCDF
1,2,3,4,7,8-HxCDF
2,3,4,7,8-PeCDF
1,2,3,7,8-PeCDF
OCDD
2,3,7,8-TCDF
0
1,2,3,4,6,7,8-HpCDD
5 1,2,3,7,8,9-HxCDD
et al. (2009) and Xu et al. (2009a,b) summarized reports on previous investigations of PCDD/F concentrations in soils, collected from various areas including China and other countries. Generally, the PCDD/F baseline levels observed in this study are similar or even slightly higher than PCDD/F concentrations previously reported to be present in soils near MSWIs of a number of countries, such as in Adige Valley, Italy (Caserini et al., 2004), in Catalonia, Spain (Domingo et al., 2001; Schuhmacher et al., 2003). Zhou et al. (2010) monitored PCDD/F concentrations in Beijing agricultural soils, which varied form 0.26 to 5.74 ng TEQ kg 1. In comparison to the investigation in soils in the vicinity of a MSWI during 2006–2007 by Yan et al. (2008) and Xu et al. (2009a,b) in China, which concentrations ranged from 0.39–6.37 ng TEQ kg 1 with average of 1.36 ng TEQ kg 1, some soil PCDD/F concentrations in this study were comparable to or slight higher for total concentration and I-TEQ. The PCDD/F concentrations observed in the present study were higher than those found in soil samples collected near MSWIs in Italy, Taiwan, Catalonia and Tarragona in Spain (Domingo et al., 2001; Cheng et al., 2003; Schuhmacher et al., 2003; Caserini et al., 2004); they were consistent with those found in Norway (Andersson and Ottesen, 2008), yet lower or far lower than those found in Korea (Oh et al., 2006;) and Spain (Domingo et al., 2000, 2002). Overall, the concentrations of PCDD/Fs are at the lower end for rural areas (1–5 ng TEQ kg 1), indicating low contamination of the baseline soils prior to the construction of new MSWIs (Rotard et al., 1994; Alcock and Jones, 1996).
30
1,2,3,6,7,8-HxCDD
Fig. 4. PCDD/F homologue patterns of soil samples in each group, with error bars indicating the plus standard deviations.
35
1,2,3,4,7,8-HxCDD
OCDF
HpCDF
HxCDF
PeCDF
TCDF
OCDD
HpCDD
HxCDD
PeCDD
TCDD
5
1,2,3,4,6,7,8-HpCDF
2,3,4,6,7,8-HxCDF
Group 4 (n=2) Group 5 (n=2) Group 6 (n=1)
40
2,3,7,8-TCDD
10
1,2,3,7,8,9-HxCDF
1,2,3,6,7,8-HxCDF
1,2,3,7,8-PeCDF
2,3,4,7,8-PeCDF
OCDD
2,3,7,8-TCDF
(b)
55
20
0
1,2,3,4,7,8-HxCDF
35
1,2,3,7,8,9-HxCDD
Group 4 (n=2) Group 5 (n=2) Group 6 (n=1)
1,2,3,4,6,7,8-HpCDD
OCDF
HpCDF
HxCDF
PeCDF
TCDF
PeCDD
(b)
0
1,2,3,7,8-PeCDD
40
OCDD
2 HpCDD
5 HxCDD
4
TCDD
10
0
Percent (%)
6
1,2,3,6,7,8-HxCDD
15
1,2,3,4,7,8-HxCDD
20
20
2,3,7,8-TCDD
40
40
1,2,3,7,8-PeCDD
Percent (%)
Percent (%)
60
Fig. 5. PCDD/F congener concentration profiles of soil samples in each group, with error bars indicating the plus standard deviations.
3.3. Multivariate analysis HCA and PCA have been widely applied to analyze homologue profiles of PCDD/Fs in various environmental media as well as in the original sources of various PCDD/F homologues (Yan et al., 2008). Similarities and differences in homologue patterns are shown in Fig. 3a, and the scope plot of the component scores for the first two factors is shown in Fig. 3b. Based on the three principal components extracted from PCA, the first two principal components explain 65.9% of total variance (Fig. 3b). A large variation of homologue patterns is observed among six groups of samples (Fig. 3). The first principal component accounts for 48.6% of total variance and positively correlates with HxCDD, HpCDF, PeCDD, PeCDF, and HxCDF, while the second principal component accounts for 17.3% of total variance mainly correlates with OCDD and HpCDD. Based on the six groups categorized by HCA and PCA, the homologue and 17 congener concentration profiles of PCDD/Fs are depicted in Figs. 4 and 5, respectively. Because a variety of sources
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introduce complex blends of PCDD/Fs in the environment, no single congener can be used to attribute the occurrence of PCDD/Fs in a sample to a specific source (Alcock and Jones, 1996). As shown in Fig. 3, PCDD/F homologue patterns in half of the soil samples collected in the same area, aggregate in the same clusters, but others gathered in different ones. The results of PCA and HCA indicate that half of soil samples collected would be polluted from similar sources of PCDD/F, while the other would be exposed to different PCDD/F emission sources, such as vehicle traffic, open burning of the waste, pesticides, industrial activities. Significant differences in the PCDD/F homologues and congeners were found in soils between six groups (Figs. 4 and 5, respectively). In Fig. 4, Group 1 is dominated by OCDD homologues (82.9 ± 9.6% in average), with low levels of low-chlorinated PCDDs and highchlorinated PCDFs, i.e. a typical background soil (Hagenmaier et al., 1994). Group 2 is still high in OCDD, yet additionally shows substantial TCDD and lower-chlorinated PCDFs. This profile is similar (Fig. 5) to that of the rice field soils (Leung et al., 2007) and also resembles unleaded gas-fueled vehicle profiles (US EPA, 2001). Group 3 (Soil samples S9 and S10) exhibits a highly unusual TCDF-dominated homologue pattern, TCDF-accounting for 93.8 ± 1.8% of total PCDD/Fs; yet, its toxic congener profile is still OCDD-dominated. These two samples may have been polluted by open burning of crop residues contaminated by pesticides, such as 5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide and 2,4-dichlorophenoxy butyl ester. (Zhang et al., 2011). For Groups 4 and 5 the PCDF-levels are higher than PCDD-levels, resembling soils contaminated by hazardous waste incinerators or other thermal sources (Hagenmaier et al., 1994). Penta- and hexaCDD/F homologues mark in Group 5, i.e. S5 and S6 (Fig. 4a), as in the effluent of a medical waste incinerator (Li et al., 2010). Group 6 has a single soil sample (S1), characterized by high-chlorinated PCDD/Fs, like the impurities in CNP and PCP on PCDD/Fs (Kiguchi et al., 2007). 4. Conclusions In this study the baseline contamination by PCDD/Fs is established in soils, prior to the construction of 16 new MSWIs in China. The results show that the background contamination levels are rather low, yet remarkably different. The average values for residential vs. suburban and industrial areas are quite similar, yet, each group shows remarkable internal spread in amount of PCDD/Fs, less so in I-TEQ value. In addition, a comparison of homologues and congeners as well as multivariate analysis of soil samples indicate that a typical ‘‘background profile’’ resembles in part of the soil samples, while others are exposed different emission sources. For different municipal solid waste incinerators, the present data will be used in future assessment, to determine the possible impact of operating the new MSWIs, and the results obtained can prove of interest for further studies on PCDD/F concentrations in soils. Acknowledgments This work was supported by National State Basic Research Program of China (973 Program, No. 2011CB201500), National Project of Scientific and Technical Supporting Program (2007BAC27B04), Zhejiang University Y.C. Tang Disciplinary Development Fund, and Program of Introducing Talents of Discipline to University (No. B08026). References Adriaens, P., Fu, Q., Grbic-Galic, D., 1995. Bioavailability and transformation of highly chlorinated dibenzo-p-dioxins and dibenzofurans in anaerobic soils and sediments. Environ. Sci. Technol. 29, 2252–2260.
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Baseline soil levels of PCDD/Fs established prior to the construction of municipal solid waste incinerators in China Hong-mei Liu, Sheng-yong Lu ⇑, Alfons G. Buekens, Tong Chen, Xiao-dong Li, Jian-hua Yan, Xiao-Jun Ma, Ke-fa Cen State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou 310027, China
a r t i c l e
i n f o
Article history: Received 9 March 2011 Received in revised form 13 September 2011 Accepted 20 October 2011 Available online 25 November 2011 Keywords: PCDD/Fs Baseline level Hierarchical cluster analysis Soils Principal component analysis
a b s t r a c t In order to determine the baseline contamination by polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in different areas in China, prior to the construction of municipal solid waste incinerators (MSWIs), a total of 32 representative soil samples was collected near 16 incinerators and analyzed for their PCDD/F concentrations. The PCDD/F baseline concentrations in the soil samples ranged from 0.32 to 11.4 ng I-TEQ kg 1 (dry matter), with average and median value of 2.73 and 2.24 ng I-TEQ kg 1 (dry matter), respectively, and a span between maximum and minimum recorded value of 36. The PCDD homologues predominated in 26 out of 32 soil samples, with the ratio (PCDDs)/ (PCDFs) ranging from 1.1 to 164; however in the other 6 samples, PCDF homologues were larger, with the same ratio varying from 0.04 to 0.8. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to examine PCDD/F amount and profile in these soil samples, and their possible associations with known emission sources: in this process 6 really distinct isomer fingerprints were identified. Background PCDD/F levels and profiles were comparable to those found in soils from China and other countries and indicate a rather low baseline PCDD/F contamination of soils. The present data provide the tools for future assessment of a possible impact of these MSWIs. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), in brief, dioxins, are emitted to the atmosphere by a wide variety of thermal processes. Among these thermal sources, PCDD/F emissions from municipal solid waste incinerators (MSWIs) have received extensive attention from the scientific community as well as from environmental regulators, and any links between emissions and their effects on soil and herbage, (Alcock et al., 1999; US EPA, 2001; Kim et al., 2005; Oh et al., 2006; Kobayashi et al., 2008; Kulkarni et al., 2008) or even on cow milk (Liem et al., 1991) have been evaluated. PCDD/Fs are semi-volatile and show high values for the organic carbon/water partition coefficient (Koc = 0.41) and octanol/water partition coefficient (Log Kow > 5.0), (Fries, 1995a,b). Hence, they accumulate in media rich in organic carbon, such as soils and sediments (Adriaens et al., 1995; Brzuzy and Hites, 1995; Kjeller et al., 1996; Meneses et al., 2002; Kanematsu et al., 2006). Dioxins-from soils may also transfer to the food chain. This pathway is important for assessing general exposure of the population, since more than
⇑ Corresponding author. Tel.: +86 571 87952628; fax: +86 571 87952438. E-mail address: [email protected] (S.-y. Lu). 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.10.033
90% of the PCDD/F human uptake is by food, or by herbage and fodder for animals (Fries, 1995a,b; Ma, 2002; Ma et al., 2002; Baars et al., 2004; Kao et al., 2007); the most important contributor was identified as the background soil concentration proper (Meneses et al., 2002). In China MSWIs are considered to be third in importance as source of dioxins emissions (UNEP, 2005), coming after the production of iron and steel and heating & power generation. In 1989 the first large incinerator plant was built in Mainland China, i.e. a Martin stoker plant in Shenzhen. More recently, industrial development and enhanced living standards in China inflated the volume and improved the fuel quality of municipal solid waste (MSW), and the number of MSWI plants has gradually increased, especially in affluent cities. In 2008, already 74 MSWIs were operating, with an average treatment capacity of 612 tons/day (CSY, 2008). It is estimated that 200 MSWIs with total daily treatment capacity of 100,000 tons will be in service by 2015 (Cheng et al., 2007). At present, studies on PCDD/Fs in China have focused on air/ particle distribution in the atmosphere and on soils in the vicinity of waste incineration plants (Shi et al., 2008; Yan et al., 2008; Xu et al., 2009a, b; Li et al., 2010); data for the baseline contamination of PCDD/Fs in soils, however, is still lacking. This study was carried out to determine this baseline contamination. Such monitoring is
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passed though a 2-mm sieve. About 500 g soil of each sample was finally homogenized through a 60-mesh sieve, and refrigerated until analysis.
useful for future assessment of the eventual environmental impact of those plants. In addition, the study provides valuable information about baseline concentrations and profiles of PCDD/F in soils, prior to the construction in various parts of China of 16 new MSWIs.
2.2. Analytical method Extraction and clean-up procedures of soil samples, as well as analytical determination of PCDD/Fs, were carried out as described in previous research projects (Yan et al., 2008; Li et al., 2010). About 10 g (dry matter) of soil sample (60-mesh) were used for each PCDD/Fs analysis. A selective pressurized liquid extraction (SPLE) method was used for sample extraction, using a fully automated ASE 300 system (Dionex, Sunnyvale, CA, USA). Extraction conditions and procedures referred to the SPLE method with slight modification (Eljarrat et al., 2003). Briefly, a 100 mL extraction cell was used and the ratio sample: alumina: copper was 5:5:1. Before extraction each sample was spiked with a mixture of 13C12-labelled PCDD/Fs compound stock solution (5 lL) and clean-up standard (5 lL). The extracts from ASE were subsequently submitted to rotary evaporation and to a multilayer silicagel column clean-up procedure, following US EPA 1613 (US EPA, 1994). The extracts were blowdown to 20 lL under a gentle stream of nitrogen (N2), and 5 lL of 13 C12-labelled PCDD/Fs internal standard solution were added before the dioxins analyzed by high-resolution gas chromatography with high-resolution mass spectrometry (HRGC/HRMS JEOL JMS800D) using a DB-5MS column (60 m 0.25 mm 0.25 lm). The toxic 2,3,7,8-substituted PCDD/Fs (referred to as congeners) as well as the tetra- to octa-chlorinated homologue groups were identified based on an isotope ratio within ±15% of the theoretical values and signal to noise ratios of equal or greater than 2.5; quantification of PCDD/Fs was performed by an isotope dilution method using relative response factors previously obtained from five calibration standard solutions. Recoveries of internal standards, as determined against external standard, generally varied between 70% and
2. Material and methods 2.1. Sample collection During 2006–2009, 16 target MSWI facilities were selected prior to their construction, as shown in Fig. 1. They are located in 5 different provinces including Sichuan, Hubei, Fujian, Zhejiang and Shanghai. A total of 32 soil samples were collected at fixed sampling points, situated around the 16 incinerator plants and taking the main wind direction into account (Fig. 1). The sampling points were selected at a distance of 200 m and of 1000 m from every target incinerator stack, under the dominant wind direction. Among these 16 target MSWI facilities 11 (F1–F11; sites S1–S22) were located in suburban areas, 2 MSWIs (F12–F13; sites S23– S26) were located in residential and commercial areas, and the others were located in industrial areas (F14–16; sites S27–S32). The exact position of the sampling points was recorded by a handheld GPS device (Meridian Color, Thales Navigation, USA). The soil samples analyzed were constituted by mixing five different aliquots in equal amounts (one in the center + one in each in the four main directions situated of 5 m to the center). Sampling was carried out by inserting a cylindrical steel corer (24 cm 4 cm, length internal diameter, supplied from Eijkelkamp, Holland) down to a depth of 10 cm. Approximately 1.5 kg of soil was taken at each site. The soils were subsequently dried in a ventilated room until constant weight, and plant materials, such as roots and leaves, were manually removed. Then the soils were ground and
(134/1.22, 184/2.30)
F12,F13 F4
(42/0.35)
F1,F2
F10,F11 (2876/4.52, 2835/4.75) (473/3.67, 118/0.98) F8,F9 (511/2.22) F16 Hubei F7
Shanghai
F3
(723/3.09)
(82/0.56, 400/6.79)
(60/2.31)
Sichuan
F14,F15 (1272/3.39, 528/3.62)
Zhejiang Fujian F6
F5 (1026/1.91)
(818/2.16)
Main Wind Direction
China 200m 1000m Target MSWI Soil Sampling Point
Fig. 1. Special distribution of the soil sampling sites and MSWI facilities in this study, with brackets including average PCDD/F concentrations/I-TEQ of each facility, ng kg
1
.
PCDD/Fs
F1
F2
F3
302
Table 1 PCDD/F baseline concentrations in soil samples prior to construction of 16 new MSWI plant (ng g
1
). F4
F5
F6
F7
F8
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
S12
S13
S14
S15
S16
2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDD OCDD 2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF
ND ND ND ND ND 9.28 30.69 1.94 ND ND 1.13 1.20 ND ND 8.26 ND ND
ND ND ND ND ND 7.11 50.15 1.11 ND ND 1.26 0.58 ND ND 6.54 ND ND
0.75 3.98 3.54 4.12 3.54 10.86 198.21 2.49 10.19 8.63 5.40 5.61 3.09 5.78 11.69 4.26 9.13
ND 0.79 0.67 0.58 1.25 3.69 53.59 1.41 1.45 1.30 1.41 1.40 1.05 1.38 3.63 1.19 4.80
ND ND 0.30 1.29 1.08 8.20 27.66 1.10 1.73 1.98 1.61 2.35 1.23 2.96 9.83 1.53 6.30
ND ND ND 1.16 0.80 6.82 16.30 0.74 1.58 1.66 1.25 1.75 1.35 1.43 7.15 1.29 3.87
ND ND ND ND 0.16 0.66 7.80 0.23 0.38 0.32 0.40 0.42 0.07 0.38 1.36 ND 0.88
ND ND ND ND 0.09 1.09 37.97 0.20 0.32 0.26 0.26 0.28 0.07 0.24 1.13 ND 1.18
0.02 0.01 0.01 0.02 0.06 0.40 41.52 13.45 ND 0.32 0.27 0.09 0.06 0.06 0.20 0.10 0.15
0.20 0.05 ND 0.10 0.26 0.96 43.67 13.05 0.24 0.70 0.91 0.44 0.21 0.29 1.27 0.30 1.08
ND ND 0.32 1.06 1.86 26.90 816.79 1.23 0.67 0.95 1.36 0.83 0.41 1.46 4.29 ND ND
ND ND 0.38 0.93 2.21 20.87 461.69 0.64 0.99 0.80 0.40 0.91 0.26 0.90 3.94 ND ND
0.35 0.25 2.24 1.88 4.08 2.86 9.76 0.68 2.39 0.32 0.30 2.38 0.77 2.61 3.73 2.84 6.24
0.06 0.57 0.59 0.52 1.07 3.12 18.91 0.29 0.34 0.93 0.80 0.74 9.01 0.56 1.52 0.79 1.93
ND 0.45 0.41 0.84 0.98 18.09 961.33 0.96 1.33 1.60 1.34 1.49 0.44 1.36 5.78 1.35 6.66
ND 0.35 0.66 0.92 1.20 43.90 4505.18 0.26 0.33 0.48 0.69 0.67 0.32 0.57 3.37 0.68 3.42
TCDD PeCDD HxCDD HpCDD OCDD TCDF PeCDF HxCDF HpCDF OCDF P PCDDs + RPCDFs PCDDs/PCDFs ratio I-TEQ
2.89 1.58 2.84 17.62 30.69 5.56 3.36 2.78 11.78 ND
5.21 1.74 5.38 7.3 50.15 4.39 1.44 2.18 7.93 ND
34.49 20.20 30.75 21.93 198.21 109.18 95.38 44.40 25.71 9.13
16.77 7.63 7.30 7.45 53.59 78.17 10.86 15.99 8.57 4.80
28.50 31.37 87.09 50.81 27.66 110.23 179.76 81.74 54.37 6.30
22.07 51.52 70.93 32.77 16.30 42.14 42.69 41.13 40.02 3.87
0.96 0.61 1.30 1.02 7.80 4.27 3.26 3.76 2.36 0.88
1.27 1.84 1.67 1.87 37.97 5.81 2.52 2.50 1.19 1.18
1.70 0.11 0.25 1.07 41.52 612.44 3.39 0.65 0.37 0.15
4.98 1.59 1.92 2.47 43.67 1322.00 6.36 3.53 2.09 1.08
13.96 6.98 40.13 72.86 816.79 57.61 12.70 11.10 7.39 ND
4.87 9.25 20.67 59.14 461.69 19.16 7.64 8.47 5.79 ND
1.82 1.46 9.10 3.87 9.76 7.08 6.34 7.94 6.57 6.24
0.78 1.81 3.80 5.68 18.91 5.34 4.53 13.67 2.92 1.93
3.72 6.26 11.61 53.28 961.33 14.37 13.30 13.29 12.17 6.66
1.33 2.38 11.24 107.09 4505.18 7.34 4.36 5.98 7.10 3.42
79.1 2.37 0.63
85.72 4.38 0.48
589.38 1.08 11.40
211.13 0.78 2.18
657.83 0.52 2.50
363.44 1.14 1.93
26.22 0.80 0.37
57.82 3.38 0.32
661.65 0.07 1.63
1389.69 0.04 2.18
1039.52 10.71 2.49
596.68 13.53 1.82
60.18 0.76 2.35
59.37 1.09 2.26
1095.99 17.33 3.09
4655.42 164.09 5.95
Average Average Average Average
62.7 19.71 82.41 0.56
RPCDDs RPCDFs RPCDD/Fs I-TEQ
PCDD/Fs
2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDD OCDD 2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF
199.16 201.10 400.26 6.79
F9
209.51 301.13 510.64 2.22
F10
28.16 13.87 42.02 0.35
F11
49.64 976.03 1025.67 1.91
F12
753.17 64.93 818.10 2.16
F13
28.50 31.28 59.78 2.31
F14
2831.71 43.99 2875.71 4.52
F15
F16
S17
S18
S19
S20
S21
S22
S23
S24
S25
S26
S27
S28
S29
S30
S31
S32
ND 0.60 0.75 1.00 1.19 45.12 4504.88 0.83 0.82 1.46 0.93 0.90 0.74 0.91
ND 0.49 0.50 0.88 1.13 18.52 847.45 1.02 0.98 1.15 1.21 1.19 0.33 1.31
0.14 0.49 1.51 0.89 1.02 12.76 247.34 1.97 1.73 2.39 3.78 3.72 0.50 3.33
0.08 0.40 1.26 0.90 0.92 11.40 257.35 2.25 1.48 2.20 3.00 2.84 0.37 2.48
ND ND 0.85 0.52 0.47 3.09 105.69 0.57 0.79 1.44 1.10 0.80 0.22 0.75
ND ND 0.57 0.11 0.23 2.32 59.64 0.26 0.30 0.29 0.39 0.19 0.06 0.30
ND 0.24 0.23 0.65 0.43 3.81 57.80 0.61 0.63 0.54 0.81 0.73 0.25 0.51
ND 0.35 0.31 0.62 0.40 6.09 83.33 1.24 1.09 0.88 1.23 1.27 0.46 0.57
0.15 0.77 0.72 0.89 0.97 4.10 61.68 0.97 1.18 1.26 1.15 1.08 0.72 1.41
0.25 0.95 0.67 0.57 1.00 5.03 78.11 1.46 1.17 1.32 1.29 1.17 0.49 1.57
0.13 0.51 0.99 1.37 1.96 37.62 1392.68 1.15 0.87 0.86 1.26 1.23 0.66 1.02
0.25 0.69 0.68 1.00 1.30 18.82 776.79 1.56 2.15 0.84 2.37 1.40 0.49 1.03
ND 0.36 0.89 0.61 0.79 3.37 43.01 0.51 0.66 0.35 1.27 0.98 0.58 1.02
ND 2.85 3.12 2.86 4.67 29.75 838.60 1.49 3.38 1.1 4.48 2.79 2.91 4.3
ND ND 1.18 1.9 2.2 16.95 241.38 3.24 5.08 2.37 4.58 3.74 0.34 2.33
ND ND 0.46 0.99 1.56 14.64 780.38 0.35 0.68 0.86 1.41 1.43 0.2 1.33
H.-m. Liu et al. / Chemosphere 86 (2012) 300–307
S1
485.13 42.82 527.95 3.62
615.59 107.69 723.28 3.09
879.35 20.52 2.23 978.27 13.85 6.07
2.3. Data analysis
1197.67 74.26 1271.92 3.39
1618.52 26.96 3.64
320.76 152.49 473.25 3.67 2784.59 50.01 2834.60 4.75
ND: the concentration measured blow the detection limits, the detection level is 0.01 ng kg
93.38 24.66 118.04 0.98
1
, the same to the following data.
100.73 33.66 134.39 1.22
117.13 66.63 183.76 2.30
204.34 1.75 2.44 163.17 1.77 2.16 158.13 2.70 1.46 110.64 3.51 0.97 76.32 8.10 0.47 159.75 2.90 1.48 457.25 2.46 3.38 489.25 1.83 3.95 985.5 15.68 2.70 4683.69 113.46 6.79
303
110%, and all satisfied the requirements of US EPA 1613. Laboratory and field blanks were routinely analyzed once a month. The target compounds were all tetra- to octa-CDD/Fs. The temperature program of the capillary column was as follows: (1) 150 °C holding for 1 min; (2) increased to 190 °C at 25 °C min 1; (3) increased at 3 °C min 1 to 280 °C, hold for 20 min. The injection volume was 1 lL by automatic split injection. The MS was operated at a resolution of 10,000 under positive EI conditions (38 eV electron energy), and the data were obtained in the selective ion-monitoring mode. All isotope standards were purchased from Cambridge Isotope Laboratories, Inc. (USA).
925.32 9.21 3.13
77.62 2.93 1.16
567.2 2.25 3.94
1.97 8.85 15.56 31.73 780.38 2.58 8.80 8.31 11.11 10.06 48.39 25.92 35.28 41.72 241.38 93.12 24.21 24.21 21.73 11.24 2.99 7.47 15.36 47.98 838.60 7.19 7.92 31.05 11.35 8.36 1.90 0.73 4.61 7.61 43.01 4.41 3.42 4.85 4.08 3.00 11.89 5.84 10.92 13.88 61.68 25.06 13.00 9.32 6.52 5.06 6.59 5.89 12.98 53.49 847.45 18.91 14.74 11.68 8.95 4.82 4.22 6.00 11.50 116.17 4504.88 10.83 10.23 10.43 6.27 3.16
TCDD PeCDD HxCDD HpCDD OCDD TCDF PeCDF HxCDF HpCDF OCDF P PCDDs + RPCDFs PCDDs/PCDFs ratio I-TEQ P Average PCDDs P Average PCDFs P Average PCDD/Fs Average I-TEQ
6.83 9.77 23.03 29.51 247.34 46.52 29.69 30.32 37.37 28.87
14.96 13.55 12.78 26.40 257.35 42.87 26.90 24.53 25.29 12.62
3.95 0.49 4.09 4.60 105.69 16.83 7.06 6.93 7.47 2.64
0.78 0.81 2.07 4.63 59.64 3.27 1.65 1.20 1.83 0.44
6.10 4.97 7.44 9.79 57.80 7.64 6.44 3.63 4.43 2.40
3.65 5.78 7.95 14.64 83.33 14.60 11.46 6.17 7.05 3.50
14.96 8.23 11.93 16.82 78.11 31.70 15.17 12.79 6.40 8.23
5.56 8.59 29.41 124.39 1392.68 20.04 12.74 9.18 8.43 7.50
6.75 6.83 8.66 35.67 776.79 30.85 20.60 25.01 10.49 3.67
7.92 3.12 8.36 3.29 0.94 5.06 4.19 ND 4.82 3.41 ND 3.16 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF
18.66 2.49 28.87
12.83 1.79 12.62
3.67 0.91 2.64
0.88 0.18 0.44
2.48 0.33 2.40
3.54 0.30 3.50
3.29 1.06 8.23
3.34 1.07 7.50
5.07 0.74 3.67
2.06 0.86 3.00
11.2 1.61 11.24
4.95 0.87 10.06
H.-m. Liu et al. / Chemosphere 86 (2012) 300–307
All experimental results are expressed on a dry weight basis. The 2,3,7,8-TCDD toxic equivalents (I-TEQ) are calculated using NATO/CCMS factors, as the Chinese Government has adopted this toxicity scheme (MEPC, 2001a, 2001b). All PCDD/Fs data are normalized to the sum of [PCDDs] + [PCDFs] = 1 before the multivariate analysis of homologue and congener patterns. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to evaluate similarities and differences within the PCDD/Fs homologue patterns of the selected soil samples. HCA first served to identify homogeneous groups of samples and then was performed again according to the furthest neighbor between groups cluster method with the squared Euclidean distance measure method, derived from the PCA scores. Each sample was assigned a score after PCA analysis. Statistical analysis was performed using the SPSS 16.0 SOFTWARE package.
3. Results and discussion 3.1. PCDD/F concentrations The baseline concentrations of PCDD/Fs in soil samples, taken prior to the construction of 16 MSWI facilities in China, are summarized in Table 1. TEQ values (sum concentration of tetra- to octa-PCDD/Fs) range from 0.32 to 11.40 ng I-TEQ kg 1 (26.2– 4680 ng kg 1), with average and median value of 2.73 and 2.24 ng I-TEQ kg 1 (650 and 116 ng kg 1), and a span ratio between maximum and minimum recorded value of 36 and 180, respectively. The samples can be subdivided into three I-TEQ groups: those with low I-TEQ (<1 ng I-TEQ kg 1, i.e. S1, S2, S7, S8, S22 and S23), average samples, and high samples (>4 ng ITEQ kg 1, i.e. S3, S16, S17, and S30). Typically, individual data figures internally deviate by two orders of magnitude. Least variable is 1,2,3,4,7,8-HxCDF, with a span of only 21; second comes I-TEQ with 36. The following also show a low span (60–70): 2,3,7,8TCDD, 2,3,7,8-TCDF, and 1,2,3,6,7,8-HxCDF. Conversely, OCDD is remarkably variable, with a span of 580. The Ratio of PCDDs to PCDFs shows the largest variance, with more than 4000. There is limited difference, however, between the various types of surroundings. On average, both suburban and industrial areas are 5.3 times more PCDD/Fs polluted than residential areas, yet only a factor 1.56 and 1.9 when expressed in I-TEQ values. For most congeners and isomer groups any distinction between such averages is less than a factor two. The difference is made by OCDD (a factor 8.6 and 9.7) and by TCDF (sites S9 and S10, with an exceptional profile). Average isomer fingerprints differ only marginally, yet industrial areas are higher weight average chlorinated. A box plot of soil samples collected from different areas is depicted in Fig. 2. The average PCDD/F concentration in residential and commercial areas, 1.76 ng I-TEQ kg 1, is slightly lower than that at the suburban areas and industrial areas, 2.74 and
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H.-m. Liu et al. / Chemosphere 86 (2012) 300–307
Fig. 2. A box-plot of soil samples collected from different areas.
3.2. Comparison with worldwide PCDD/F levels In order to gain perspective on the relative extent of contamination of PCDD/Fs at the different sampling sites, the recorded levels were compared to international soil guidelines and regulations, which specify maximum acceptable levels according to different land uses (Leung et al., 2007). As yet, China has no soil guidelines for PCDD/Fs. In this study, the TEQ values of most soil samples (about 78%) are below the Canadian guideline for agricultural land use (4 ng TEQ kg 1) (CCME, 2003). Based on German guidelines for dioxins in soils (Schulz, 1993), most soils in this study could be
4
(b)
S13
Group 4
3
Factor 2 (17.3%)
3.36 ng I-TEQ kg 1, respectively. In addition, the range of PCDD/F concentrations is small, except for samples S13, S16 and S17. The most toxic congener, 2,3,7,8-TCDD, is identified in 9 out of the 32 samples, a value of 0.75 ng kg 1 clearly standing out in S3. This sample shows also the highest concentration for ten out of seventeen PCDD/F congeners. Conversely, among the 17 congeners investigated, OCDD is generally the highest in concentration (5 exceptions are: S4, S5, S6, S9, S10) ranging from 7.8 to 4505 ng kg 1 and accounting for 22–99% of the sum of the seventeen congeners in all soil samples (ATSDR, 1998). This distribution is similar to those in background soils observed in previous investigations (Domingo et al., 2001; Oh et al., 2006; Yan et al., 2008; Liu and Liu, 2009). High-chlorinated congeners are primarily bound to aerosols or to particulate matter and show the greatest tendency to bioaccumulate. PCDD homologues predominate in 26 out of 32 soil samples, with a PCDDs to PCDFs ratio ranging from 1.1 to 164, and indicating a typical background profile; Previous research indicated that dioxins in background soils tend to have an atmospheric fingerprint (high chlorinated PCDDs and low levels of chlorinated PCDFs), compared to soils close to active MSWIs, which show more PCDFs than PCDDs (Schuhmacher et al., 1997; Domingo et al., 2001; Oh et al., 2006; Yan et al., 2008; Liu and Liu, 2009), with the PCDDs to PCDFs ratio ranging 0.04–0.8. Possibly, those deviant baseline soils had been contaminated by anthropological sources of PCDD/Fs, such as metallurgical processes, waste combustion (Hagenmaier et al., 1994; Wagrowski and Hites, 2000) or hitherto unidentified sources. The highest soil concentration (11.4 ng TEQ kg 1) was observed in sample S3 in the vicinity of the F2 incinerator, situated in farmland close to an oil factory. However, another soil site near the same incinerator S4, was located upwind of the oil factory. Sample S17 was located in open area near a highway; however, this location was a pond in the past.
2
S14
Group 2
S19
S5
1
S29
Group 1 S21 S8
0
-1
-2
Group 5
S7
S20
S28 S30 S32 S15 S16 S17 S18 S22 S27 S10 S11S12 S9
S3 S26 S25
S6
S24S4
S23
S31
S2
Group 6
Group 3
-2
S1
-1
0
1
2
3
4
Factor 1 (48.6%) Fig. 3. Plot of hierarchical cluster analysis (a) and principal component analysis (b) of soil samples.
used safely, as the guidelines recommend that no restrictions be placed on use of soil with dioxin concentrations below 5 ppt (ng kg 1, based on dioxin TEQS9). However, at concentrations between 5–20 ppt, such as the soils in the sites S3, S16, S17 and S22 of this study, management systems should be implemented to reduce PCDD/F pollutions and dust (Fig. 2). The recorded baseline level exceeds the Dutch and Swedish guidelines for agricultural land use (10 ng TEQ kg 1) (MfE/MoH, 1997; BMU, 1999) only for soil site S3, while the concentrations and 2,3,7,8-TCDD at the all sampling sites are below the US guideline (1000 ng TEQ kg 1 and 39 ng kg 1, respectively) (Kimbrough et al., 1984; US EPA, 2000). In this study, the PCDD/F baseline levels and profiles were comparable to those found in soils in the vicinity of the construction of new hazardous waste incinerators (MWIs) by Schuhmacher et al. (1997 and 2002), with baseline concentrations ranging from 0.12–17.2 ng TEQ kg 1, and higher than those in Beijing (Li et al., 2004). Oh et al. (2006), Zheng et al. (2008), Kim et al. (2008), Zhang
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100
100
(a)
Group 1 (n=13) Group 2 (n=12) Group 3 (n=2)
80
(a)
80
Group 1 (n=13) Group 2 (n=12) Group 3 (n=2)
60
30
65
25
60
15
45
Percent (%)
50
OCDF
1,2,3,4,7,8,9-HpCDF
25 20 15 10
OCDF
1,2,3,4,7,8,9-HpCDF
1,2,3,7,8,9-HxCDF
1,2,3,4,6,7,8-HpCDF
2,3,4,6,7,8-HxCDF
1,2,3,6,7,8-HxCDF
1,2,3,4,7,8-HxCDF
2,3,4,7,8-PeCDF
1,2,3,7,8-PeCDF
OCDD
2,3,7,8-TCDF
0
1,2,3,4,6,7,8-HpCDD
5 1,2,3,7,8,9-HxCDD
et al. (2009) and Xu et al. (2009a,b) summarized reports on previous investigations of PCDD/F concentrations in soils, collected from various areas including China and other countries. Generally, the PCDD/F baseline levels observed in this study are similar or even slightly higher than PCDD/F concentrations previously reported to be present in soils near MSWIs of a number of countries, such as in Adige Valley, Italy (Caserini et al., 2004), in Catalonia, Spain (Domingo et al., 2001; Schuhmacher et al., 2003). Zhou et al. (2010) monitored PCDD/F concentrations in Beijing agricultural soils, which varied form 0.26 to 5.74 ng TEQ kg 1. In comparison to the investigation in soils in the vicinity of a MSWI during 2006–2007 by Yan et al. (2008) and Xu et al. (2009a,b) in China, which concentrations ranged from 0.39–6.37 ng TEQ kg 1 with average of 1.36 ng TEQ kg 1, some soil PCDD/F concentrations in this study were comparable to or slight higher for total concentration and I-TEQ. The PCDD/F concentrations observed in the present study were higher than those found in soil samples collected near MSWIs in Italy, Taiwan, Catalonia and Tarragona in Spain (Domingo et al., 2001; Cheng et al., 2003; Schuhmacher et al., 2003; Caserini et al., 2004); they were consistent with those found in Norway (Andersson and Ottesen, 2008), yet lower or far lower than those found in Korea (Oh et al., 2006;) and Spain (Domingo et al., 2000, 2002). Overall, the concentrations of PCDD/Fs are at the lower end for rural areas (1–5 ng TEQ kg 1), indicating low contamination of the baseline soils prior to the construction of new MSWIs (Rotard et al., 1994; Alcock and Jones, 1996).
30
1,2,3,6,7,8-HxCDD
Fig. 4. PCDD/F homologue patterns of soil samples in each group, with error bars indicating the plus standard deviations.
35
1,2,3,4,7,8-HxCDD
OCDF
HpCDF
HxCDF
PeCDF
TCDF
OCDD
HpCDD
HxCDD
PeCDD
TCDD
5
1,2,3,4,6,7,8-HpCDF
2,3,4,6,7,8-HxCDF
Group 4 (n=2) Group 5 (n=2) Group 6 (n=1)
40
2,3,7,8-TCDD
10
1,2,3,7,8,9-HxCDF
1,2,3,6,7,8-HxCDF
1,2,3,7,8-PeCDF
2,3,4,7,8-PeCDF
OCDD
2,3,7,8-TCDF
(b)
55
20
0
1,2,3,4,7,8-HxCDF
35
1,2,3,7,8,9-HxCDD
Group 4 (n=2) Group 5 (n=2) Group 6 (n=1)
1,2,3,4,6,7,8-HpCDD
OCDF
HpCDF
HxCDF
PeCDF
TCDF
PeCDD
(b)
0
1,2,3,7,8-PeCDD
40
OCDD
2 HpCDD
5 HxCDD
4
TCDD
10
0
Percent (%)
6
1,2,3,6,7,8-HxCDD
15
1,2,3,4,7,8-HxCDD
20
20
2,3,7,8-TCDD
40
40
1,2,3,7,8-PeCDD
Percent (%)
Percent (%)
60
Fig. 5. PCDD/F congener concentration profiles of soil samples in each group, with error bars indicating the plus standard deviations.
3.3. Multivariate analysis HCA and PCA have been widely applied to analyze homologue profiles of PCDD/Fs in various environmental media as well as in the original sources of various PCDD/F homologues (Yan et al., 2008). Similarities and differences in homologue patterns are shown in Fig. 3a, and the scope plot of the component scores for the first two factors is shown in Fig. 3b. Based on the three principal components extracted from PCA, the first two principal components explain 65.9% of total variance (Fig. 3b). A large variation of homologue patterns is observed among six groups of samples (Fig. 3). The first principal component accounts for 48.6% of total variance and positively correlates with HxCDD, HpCDF, PeCDD, PeCDF, and HxCDF, while the second principal component accounts for 17.3% of total variance mainly correlates with OCDD and HpCDD. Based on the six groups categorized by HCA and PCA, the homologue and 17 congener concentration profiles of PCDD/Fs are depicted in Figs. 4 and 5, respectively. Because a variety of sources
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introduce complex blends of PCDD/Fs in the environment, no single congener can be used to attribute the occurrence of PCDD/Fs in a sample to a specific source (Alcock and Jones, 1996). As shown in Fig. 3, PCDD/F homologue patterns in half of the soil samples collected in the same area, aggregate in the same clusters, but others gathered in different ones. The results of PCA and HCA indicate that half of soil samples collected would be polluted from similar sources of PCDD/F, while the other would be exposed to different PCDD/F emission sources, such as vehicle traffic, open burning of the waste, pesticides, industrial activities. Significant differences in the PCDD/F homologues and congeners were found in soils between six groups (Figs. 4 and 5, respectively). In Fig. 4, Group 1 is dominated by OCDD homologues (82.9 ± 9.6% in average), with low levels of low-chlorinated PCDDs and highchlorinated PCDFs, i.e. a typical background soil (Hagenmaier et al., 1994). Group 2 is still high in OCDD, yet additionally shows substantial TCDD and lower-chlorinated PCDFs. This profile is similar (Fig. 5) to that of the rice field soils (Leung et al., 2007) and also resembles unleaded gas-fueled vehicle profiles (US EPA, 2001). Group 3 (Soil samples S9 and S10) exhibits a highly unusual TCDF-dominated homologue pattern, TCDF-accounting for 93.8 ± 1.8% of total PCDD/Fs; yet, its toxic congener profile is still OCDD-dominated. These two samples may have been polluted by open burning of crop residues contaminated by pesticides, such as 5-chloro-N-(2-chloro-4-nitrophenyl)-2-hydroxybenzamide and 2,4-dichlorophenoxy butyl ester. (Zhang et al., 2011). For Groups 4 and 5 the PCDF-levels are higher than PCDD-levels, resembling soils contaminated by hazardous waste incinerators or other thermal sources (Hagenmaier et al., 1994). Penta- and hexaCDD/F homologues mark in Group 5, i.e. S5 and S6 (Fig. 4a), as in the effluent of a medical waste incinerator (Li et al., 2010). Group 6 has a single soil sample (S1), characterized by high-chlorinated PCDD/Fs, like the impurities in CNP and PCP on PCDD/Fs (Kiguchi et al., 2007). 4. Conclusions In this study the baseline contamination by PCDD/Fs is established in soils, prior to the construction of 16 new MSWIs in China. The results show that the background contamination levels are rather low, yet remarkably different. The average values for residential vs. suburban and industrial areas are quite similar, yet, each group shows remarkable internal spread in amount of PCDD/Fs, less so in I-TEQ value. In addition, a comparison of homologues and congeners as well as multivariate analysis of soil samples indicate that a typical ‘‘background profile’’ resembles in part of the soil samples, while others are exposed different emission sources. For different municipal solid waste incinerators, the present data will be used in future assessment, to determine the possible impact of operating the new MSWIs, and the results obtained can prove of interest for further studies on PCDD/F concentrations in soils. Acknowledgments This work was supported by National State Basic Research Program of China (973 Program, No. 2011CB201500), National Project of Scientific and Technical Supporting Program (2007BAC27B04), Zhejiang University Y.C. Tang Disciplinary Development Fund, and Program of Introducing Talents of Discipline to University (No. B08026). References Adriaens, P., Fu, Q., Grbic-Galic, D., 1995. Bioavailability and transformation of highly chlorinated dibenzo-p-dioxins and dibenzofurans in anaerobic soils and sediments. Environ. Sci. Technol. 29, 2252–2260.
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