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PCDDs and PCDFs in sewage sludges from two wastewater treatment plants in Beijing, China
Chemosphere 82 (2011) 635–638
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
PCDDs and PCDFs in sewage sludges from two wastewater treatment plants in Beijing, China Xuemei Li ⇑, Zhenshan Ke, Jizhen Dong Analysis and Measurement Center of Beijing Municipal Drainage Corporation, Beijing 100124, China
a r t i c l e
i n f o
Article history: Received 4 June 2010 Received in revised form 7 November 2010 Accepted 15 November 2010 Available online 8 December 2010 Keywords: Dioxin Furan Wastewater treatment plant Sewage sludge Distribution
a b s t r a c t The levels of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analyzed by an isotope-dilution high-resolution mass spectrometric in 16 sewage sludges, sampled from 2004 to 2009, from two municipal wastewater treatment plants (WWTPs) in Beijing. Total toxicity equivalent (TEQ) values were evaluated using the toxicity equivalent factors proposed by International for PCDD/Fs. The ITEQs for these sewage sludges were from 0.97 to 15.0 pg g 1 dry weight (dw) with a mean value 4.43 pg g 1 dw, indicating that all I-TEQs were below Chinese legislation limit value regulated for agricultural use in soils. The results from limited samples (16 samples) showed that the levels of PCDD/Fs might be correlated with the sludge age. Meanwhile, the temporal trends of PCD/Fs suggested that the I-TEQs may correlate with rainfall in the present study. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Sewage sludge, a by-product of the process in wastewater treatment plant (WWTP), accounts for 0.3–0.5% wastewater. Now, the total amount of dry wastewater sludge is about 1.3 106 tons per year and the amount was expected to increase at the rate of approximately 10% per year in China (Zhang et al., 2006). Usually, sludge is generally regarded as fertilizer because it contains high proportions of organic matters as well as nitrogen and phosphorous (Guo et al., 2009). However, some toxicants such as metals and organic contaminants which can not be removed are also taken into account because these contaminants are toxic to the wildlife and human health. Among these contaminants, the polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) called ‘‘dioxin compounds’’ are types of environmental contaminants with high carcinogenic and bioaccumulative properties. Therefore, it is necessary to take comprehensive determination to assure the level of these contaminants in sewage sludge fertilization of cultivated land will not do harm to the environment, especially to human being. PCDD/Fs enter the environment via wet and dry deposition of atmosphere, urban runoff, domestic wastewater, industrial effluents, and these compounds even can be formed during the WWTP process (Klimm et al., 1998). Klimm et al. (1998) found sludge by semi-anaerobic digestion over 192 days can produce a twofold ⇑ Corresponding author. Tel.: +86 10 8774 3466; fax: +86 10 8774 3414. E-mail address: [email protected] (X. Li). 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.11.039
increase of OCDD and HpCDD. They also found that digestion of sludge under strictly anaerobic conditions can not form PCDD/Fs, including HpCDD and OCDD. PCDD/Fs in sewage sludges were first reported in 1984 (Lamparski et al., 1984) and has been carried out in the USA, Spain, China, and so on (Eljarrat et al., 2003; Dai et al., 2007; Clarke et al., 2008). The concentrations of dioxin are reported using toxicity equivalent (TEQ) values usually within pg g 1 dry weight (dw). Some investigations suggested that the levels of dioxin-like compounds sludge had decreased in some areas such as the USA and Swedish (Rappe et al., 1998; Alvarado et al., 2001). Some factors can influence the level and distribution of PCDD/Fs in sewage sludge (Weber et al., 1997; Fuentes et al., 2007). Weber et al. (1997) found that the kind of digestion and composting can influence the PCDD/Fs levels in sewage sludge. Stevens et al. (2001) found that the type of treatment is important to the levels of PCDD/Fs. Meanwhile, Stevens et al. (2001) also suggested that diffuse, catchment based sources (domestic wastewater, runoff) rather than point sources (trade effluent discharge) are the most important contributors of PCDD/F to sludge. Therefore, we hypotheses that the levels of dioxin in sewage sludges in Beijing, China were influenced by treatment process (such as sludge age) and runoff (such as rainfall). The objective of the present study is to determine the concentrations of PCDDs and PCDFs in sewage sludges from Beijing WWTPs in China and compare the I-TEQ with the limit proposed by Chinese GB 18918-2002 ‘‘Discharge standard of pollutants for municipal wastewater treatment plant’’ for agricultural use in soils
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and the objective regulated by European Union. Meanwhile, the contribution of each contaminant in the total toxicity of the samples and influential factors were evaluated.
were defined as LOD when they were lower than LOD. The concentrations of PCDD/Fs in the real samples were not corrected by recoveries and blanks.
2. Materials and methods
3. Results and discussion
2.1. Reagents and chemicals
3.1. Concentrations of PCDD/Fs in sewage sludges
All solvents (pesticide residue grade) were purchased from Tedia Co., USA. Silica (100–200 mesh) was obtained from Qingdao Haiyang Chemical Co., China. And permeable gels (SX-3 Bio-beads, 200–400 mesh) were from Bio-Rad Co., USA. Calibration standard solution, 13C-labeled surrogate standards and injection standards complying with EPA method 1613 for PCDD/Fs analysis were from Cambridge isotope laboratories, USA.
The concentrations of PCDD/Fs (pg g 1 dw) in sewage sludge samples from plants 1 and 2 were shown in Table 2. The concentrations of PCDD/Fs varied greatly (162–178 pg g 1 dw in plant 1 and 191–1036 pg g 1 dw in plant 2) and the I-TEQ also varied greatly in plant 1 (0.97–15.0 pg g 1 dw) and plant 2 (1.91–11.0 pg g 1 dw), which might be explained by variable loads during the sample collection period at different WWTPs. The highest (15.0 pg g 1 dw) and the second I-TEQ (11.0 pg g 1 dw) were found in sewage sludge from plants 1 and 2, respectively. The I-TEQs in all sewage sludge in the present study were far below the recommended upper limits (100 pg g 1 dw) regulated by Chinese legislation GB 18918–2002 ‘‘Discharge standard of pollutants for municipal wastewater treatment plant’’ for agricultural use in soils and the safe sediment value 20 pg g 1 dw which is derived from the no observed effect concentration of 200 pg g 1 dw divided by the safety factor of 10 (Evers et al., 1996). Generally, the mean ratio RTEQPCDDs/TEQPCDFs are greater than 1 in sewage sludge samples (Eljarrat et al., 1997, 1999). However, the ratios RTEQPCDDs/TEQPCDFs ranged from 0.31 to 3.50 in plant 1 and from 0.23 to 1.14 in plant 2, and the ratios in 2 out of 16 sewage sludge samples were greater than 1. There were no correlations between capacity and PCDD/Fs concentrations in these sewage sludge samples (p > 0.05). The mean I-TEQ (2.53 pg g 1 dw) were lower in plant 1 than in plant 2 (4.60 pg g 1 dw), which might be explained by different received industrial influent (5% in plant 1 and 20% in plant 2). Meanwhile, the sludge age in plant 2 was longer than that in plant 1. These results suggested that there might be some correlations between the degree of industrial input and/or sludge age and the I-TEQ.
2.2. Sample collection Sixteen sewage sludge samples were collected from two WWTPs (plants 1 and 2) in Beijing from 2004 to 2009. The details of sewage sludge samples were shown in Table 1. The sewage sludge samples from each WWTP were packed with aluminum foil after being collected, then transferred to the laboratory and freezed-dried for 48 h before analysis. 2.3. PCDD/Fs analysis The PFDD/Fs analysis was performed according to the USEPA method 1613 at the State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy in Beijing, China. Ten grams of freezed-dried sludge were spiked with 13C-labeled surrogate standards and extracted for 24 h with toluene. The concentrated extracts were sequentially cleaned up by multi-layer silica gel, permeable gel column, and basic alumina chromatographic column. The clean-up were concentrated to 20 lL with nitrogen. 13C-labeled injection standards of PCDD/Fs were spiked to the extracts for calculation of recoveries before injecting.
3.2. Pattern of PCDD/Fs and possible sources 2.4. Instrumental analysis Samples were quantified by HRGC/HRMS using DB-5 MS capillary column (60 m 0.25 mm 0.25 lm film thickness) (Guo et al., 2009). The column temperature initiated at 80 °C (2 min), then increased to 180 °C at 15 °C min 1 and 280 °C (30 min) at 7.5 C min 1; the carrier gas was helium at 0.8 mL min 1 and the injection volume was 1 lL in splitless mode. 2.5. Quality assurance (QA) and quality control (QC) The QA and QC were described previously (Guo et al., 2009). And the recoveries of the PCDD/Fs in sewage sludge samples ranged from 50% to 90%, indicating that the extraction and clean-up of PCDD/Fs are properly. The limit of detection (LOD) was a signal to noise ratio of 3:1. And the concentrations of PCDD/Fs in samples Table 1 Detailed characteristic of the two WWTPs in the present study. WWTP
Plant 1
Plant 2
Wastewater type Sewage process
5% industrial influent
20% industrial influent Oxidation ditch
Sludge process Capacity (m3 d 1)
Activated sludge process (aerobic) Lime 4 104
Dewater 2 105
Fig. 1 presented the concentration profiles of homologues found in the sewage sludge from plants 1 and 2. The patterns of PCDD/Fs Table 2 PCDD/Fs concentration (pg g 2004 to 2009. Compounds
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 1,2,3,7,8,9-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF PCDD/Fs I-TEQ
1
dw) in sewage sludge samples from two WWTPs from
Plant 1
Plant 2
Min–max (mean)
Min–max (mean)
LOD-1.80 (0.51) LOD-11.0 (1.93) LOD-1.70 (0.67) 0.40–2.70 (1.18) LOD-1.24 (0.53) 4.7–34.9 (15.0) 26.2–408 (211) 0.8–3.70 (2.16) LOD-3.40 (1.18) LOD-4.10 (1.47) 0.5–7.0 (2.41) 0.4–3.1 (1.80) LOD-3.6 (0.84) LOD-17.5 (3.56) 4.3–17.0 (10.63) 0.5–1.8 (1.20) 8.2–53.0 (29.6) 162–718 (436) 0.97–15.0 (2.53)
LOD-1.37 (0.51) LOD-3.70 (1.04) LOD-1.21 (0.65) 0.60–2.0 (1.29) LOD-1.40 (0.68) 6.20–24.0 (14.1) 24.2–489 (175) 1.5–7.0 (3.34) LOD-4.40 (2.41) 1.40–4.60 (2.86) 1.30–7.20 (3.33) 1.10–5.90 (2.89) LOD-6.90 (1.54) LOD-4.70 (2.65) 7.30–40.0 (15.0) LOD-5.5 (1.72) 6.10–52.5 (26.3) 191–1036 (489) 1.91–11.0 (4.57)
LOD: the concentrations of PCDD/F in sewage sludge were lower than the LOD.
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among the samples from plant1 were similar with those from plant 2 except for those samples collected in 2004. The concentration homologue profiles in the sewage sludge samples showed a characteristic predominance of highly chlorinated congeners HxCDD/Fs-OCDD/Fs (86–99%) and OCDD/ Fs (76–91%, except for 39% in April, 2004) in plant 1 and HxCDD/ Fs-OCDD/Fs (87–97%) and OCDD/Fs (69–85%, except for 33% in April, 2004) in plant 2. The patterns of highly chlorinated congeners dominating in PCDD/Fs were also found in sewage sludge from Hongkong, German, and Sweden (Stevens et al., 2001) and the pattern suggested that PCPs was the major source of highly chlorinated congeners in sewage sludge (Horstmann et al., 1993). However, Eljarrat et al. (1999) suggested that the value of 1,2,3,6,7,8-HxCDD/1,2,3,4,7,8-HxCDD (>100) is a more useful indicator for technical mixture of PCP. Meanwhile, Rappe et al. (1999) have postulated that the highly chlorinated PCDD/Fs in sewage sludge but not from PCPs are formed naturally in sediment. And Stevens et al. (2001) suggested that the natural formation of highly chlorinated PCDD/Fs may also be responsible for the homologue pattern in sludges where the higher chlorinated PCDDs are dominant, as an alternative explanation to PCP contamination. The ratio of 1,2,3,6,7,8-HxCDD/1,2,3,4,7,8-HxCDD ranged from 0.70 to 13.5 in plant 1 and from 0.62 to 6.33 in plant 2 in this study. And the results were similar with those (0.58–2.57) found in 2004 (Dai et al., 2007), which suggested the PCP was not a major source of PCDD/Fs during 2004–2009. And such a pattern, in principle, suggested that the thermal process is not the primary source of contamination (Dai et al., 2007). Dai et al. (2007) suggested that household water and urban runoff may be the two important sources of PCDD/Fs in sewage sludge from Beijing WWTPs. For
3.3. Temporal trends of PCDD/Fs The temporal trends of PCDD/Fs obtained in Beijing WWTPs sewage sludge during 2004–2009 were shown in Fig. 2. The results showed a marked increase in plants 1 and 2 in 2008. Meanwhile, the TEQs were higher in April than those in October. The results may be explained by the reason that the rainfall in 2008 was the greatest from 2000 to 2009 and the rainfall was higher in April 16
plant1
plant2
12
TEQs (pg g-1dw)
Fig. 1. The concentration homologue profile in the sewage sludge samples, (a) for plant 1, (b) for plant 2.
lower chlorinated congeners PeCDD/Fs, it was almost absent in all sewage sludge samples except for the sewage sludge obtained in 2004 in the present study. OCDD and OCDF dominated in PCDDs and PCDFs in most sewage sludge samples from both plants 1 and 2, respectively. And HpCDD and HpCDF had relatively high concentrations (Fig. 1). This is in agreement with the data reported by Eljarrat et al. (2003). The concentrations of OCDF were lower than OCDD in all sewage sludge samples from plant 2 and plant 1 except for one sample obtained in October 2004. And the results were similar with the previous report, which found that OCDD concentrations were significantly greater than OCDF (OCDD/OCDF = 19.7) (de Souza and Kuch, 2005). However, OCDD concentrations were lower than OCDF in other studies (Fattore et al., 1997; Dalla et al., 2003; Martínez et al., 2007). In this study, there were no correlations between OCDD and I-TEQ, OCDF and I-TEQ (p > 0.05). However, if the data obtained in 2004 were excluded, there were correlations between OCDD and I-TEQ, OCDF and I-TEQ (p < 0.05). The results indicated that OCDF and OCDF could be regarded as the indicator to predict the I-TEQs from 2005 to 2009. Meanwhile, there were correlations between OCDD and OCDF (r2 = 0.9025; p < 0.05), OCDD and I-TEQ (r2 = 0.9409; p < 0.05) in the previous report (Clarke et al., 2008), which suggested that OCDF as well as OCDD can be regarded as the indicator to predict the I-TEQ in Australian sewage sludge (Fuentes et al., 2007; Clarke et al., 2008). The ratios of OCDD/OCDF and HpCDD/HpCDF were correlated with the digestion of sludge (de Souza and Kuch, 2005). de Souza and Kuch (2005) found that OCDD/OCDF (19.7) and HpCDD/HpCDF in actived sludge samples were higher than those (OCDD/ OCDF = 3.3; HpCDD/HpCDF = 2.1) in digested sludge. The mean ratio were 8.92 (ranging from 0.95–23.81) in plant 1 and 7.31 (3.27– 18.54) in plant 2 for OCDD/OCDF, and 1.81 (0.55–4.48) in plant 1 and 1.04 (0.48–2.31) in plant 2 for HpCDD/HpCDF in activated sludge in the present study, which was similar with those (3.3– 19.7 for OCDD/OCDF) and lower than those (2.3–10.9 for HpCDD/ HpCDF) in the previous report (de Souza and Kuch, 2005). The reason might be that the sources of PCDD/Fs were different in the previous study (de Souza and Kuch, 2005) and in the present study.
8
4
0
Apr-04
Oct-04
Apr-05 Oct-05 Jun-06
Jun-07
Oct-08 Oct-09
Fig. 2. The temporal trends of PCDD/Fs in sewage sludge samples from Beijing WWTPs from 2004 to 2009.
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The TEQ contribution of OCDD/Fs was low although OCDD/Fs concentrations were higher. OCDD/Fs correlated with TEQs during 2005–2009 and OCDF and OCDF could be regarded as the indicator to predict the I-TEQs in sewage sludge from Beijing WWTPs during 2005–2009. Acknowledgements The authors would like to acknowledge Dr. Bin Zhang and Li Guo at the State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy in Beijing, China. References
Fig. 3. The TEQ homologue profile in the sewage samples from Beijing WWTPs. (a) for plant 1, (b) for plant 2.
than in October in Beijing, China. These results were consistent with the conclusion that the urban runoff may be an important sources of PCDD/Fs in sewage sludge from Beijing WWTPs (Dai et al., 2007). Fig. 3(a) and (b) were the TEQ profiles of homologues found in the sewage sludge from plants 1 and 2, respectively. There was a large portion change of lower chlorinated TCDD/F-PeCDD/F (22– 80%) in sewage sludge from plant 2, but there was no variation of lower chlorinated TCDD/F-PeCDD/F (58–67%) in sewage sludge from plant 1. The TEQ contribution of PeCDF has decreased and the contribution of TCDD has increased in sewage sludge from plant 2. There were large variations for TEQ profiles of homologues found in the sewage sludge from plant 1 during 2004–2009, which suggested that the source of influent was not stable in plant 1. The TEQ contribution from TCDD may be lower in April than in October in sewage sludge from plant 1, however, the contribution from TCDD was higher in April than in October in sewage sludge from plant 2 between 2004 and 2005. And these results indicated that the source of PCDD/Fs may be different in plants 1 and 2. 4. Conclusions The I-TEQs in all sewage sludge samples from two WWTPs in Beijing were lower than the upper limit regulated by GB 18918– 2002 ‘‘Discharge standard of pollutants for municipal wastewater treatment plant’’ for agricultural use in soils.
Alvarado, M.J., Armstrong, S., Crouch, E., 2001. The AMSA 2000/2001 survey of dioxin-like compounds in biosolids: statistical analyses. Cambridge Environmental, Inc. Clarke, B., Porter, N., Symons, R., Blackbeard, J., Ades, P., Marriott, P., 2008. Dioxinlike compounds in Australian sewage sludge – review and national survey. Chemosphere 72, 1215–1228. Dai, J., Xu, M., Chen, J., Yang, X., Ke, Z., 2007. PCDD/F, PAH and heavy metals in the sewage sludge from six wastewater treatment plants in Beijing, China. Chemosphere 66, 353–361. Dalla, V.M., Marcomini, A., Sfriso, A., Sweetman, A.J., Jones, K.F., 2003. Estimation od PCDD/F distribution and fluxes in the Venice Lagoon, Italy: combining measurement and modeling approaches. Chemosphere 51, 603–616. de Souza, P.M., Kuch, B., 2005. Heavy metals, PCDD/F and PCB in sewage sludge samples from two wastewater treatment facilities in Rio de Janeiro State, Brazil. Chemosphere 60, 844–853. Eljarrat, E., Caixach, J., Rivera, J., 1997. Effects of sewage sludges contaminated with polychlorodibenzo-p-dioxins, dibenzofurans and biphenyls on agricultural soils. Environ. Sci. Technol. 31, 2765–2771. Eljarrat, E., Caixach, J., Rivera, J., 1999. Decline in PCDD and PCDF levels in sewage sludge from Catalonia. Environ. Sci. Technol. 33, 2493–2498. Eljarrat, E., Caixach, J., Rivera, J., 2003. A comparison of TEQ contributions from PCDDs, PCDFs and dioxin-like PCBs in sewage sludges from Catalonia, Spain. Chemosphere 51, 595–601. Evers, E.H.G., Laane, R.W.P.M., Groeneveld, G.J.J., Olie, K., 1996. Levels, temporal trends and risk of dioxins and related compounds in the Dutch aquatic environment. Organohalogen Compd. 28, 117–122. Fattore, E., Benfenati, E., Mariani, G., Fanelli, R., Evers, E.H.G., 1997. Patterns and sources of polychlorinated dibenzo-p-dioxins and dibenzofurans in sediments from the Venice Lagoon, Italy. Environ. Sci. Technol. 31, 1777–1784. Fuentes, M.J., Font, R., Gomez-Rico, M.F., Molto, J., 2007. Multivariant statistical analysis of PCDD/FS in sewage sludges from different areas of the Valencian Community (Spain). Chemosphere 67, 1423–1433. Guo, L., Zhang, B., Xiao, K., Zhang, Q.H., Zheng, M.H., 2009. Levels and distributions of polychlorinated biphenyls in sewage sludge of urban wastewater treatment plants. J. Environ. Sci. 21, 468–473. Horstmann, M., McLachlan, M.S., Reissinger, M., 1993. Investigations of the origin of PCDD/F in municipal sewage sludge. Chemosphere 27, 113–120. Klimm, C., Schramm, K.W., Henkelmann, B., Martens, D., Kettrup, A., 1998. Formation of Octa- and heptachlorodibenzo-p-dioxins during semi anaerobic digestion of sewage sludge. Chemosphere 37, 2003–2011. Lamparski, L.L., Nestrick, T.J., Stenger, V.A., 1984. Presence of chlorodibenzo dioxins in a sealed 1933 sample of dried municipal sewage sludge. Chemosphere 13, 361. Martínez, K., Abad, E., Palacios, O., Caixach, J., Rivera, J., 2007. Assessment of polychlorinated dibenzo-p-dioxins and dibenzofurans in sludges according to the European environmental policy. Environ. Int. 33, 1040–1047. Rappe, C., Andersson, R., Bonner, M., Cooper, K., Fiedler, H., Howell, F., 1998. PCDDs and PCDFs in municipal sewage sludge and effluent from potw in the state of Mississippi, USA. Chemosphere 36, 315–328. Rappe, C., Oberg, L., Andersson, R., 1999. Natural formation-A neglected source of polychlorinated dixins and dibenzofurans. Organohalogen Compd. 43, 249–253. Stevens, J., Green, N.J.L., Jones, K.C., 2001. Survey of PCDD/Fs and non-ortho PCBs in UK sewage sludges. Chemosphere 44, 1455–1462. Weber, H., Hamann, R., Disse, G., Haupt, H.J., 1997. Influence of different treatment methods for sewage sludge on the levels of chlorinated dibenzodioxins and dibenzofurans. Organohalogen Compd. 32, 394–399. Zhang, Y., Gao, D., Chen, T.B., Zheng, G.D., Li, Y.X., 2006. Economical evaluation of different techniques to treatment and dispose sewage sludge in Beijing. Ecol. Environ. 15, 234–238.
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
PCDDs and PCDFs in sewage sludges from two wastewater treatment plants in Beijing, China Xuemei Li ⇑, Zhenshan Ke, Jizhen Dong Analysis and Measurement Center of Beijing Municipal Drainage Corporation, Beijing 100124, China
a r t i c l e
i n f o
Article history: Received 4 June 2010 Received in revised form 7 November 2010 Accepted 15 November 2010 Available online 8 December 2010 Keywords: Dioxin Furan Wastewater treatment plant Sewage sludge Distribution
a b s t r a c t The levels of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analyzed by an isotope-dilution high-resolution mass spectrometric in 16 sewage sludges, sampled from 2004 to 2009, from two municipal wastewater treatment plants (WWTPs) in Beijing. Total toxicity equivalent (TEQ) values were evaluated using the toxicity equivalent factors proposed by International for PCDD/Fs. The ITEQs for these sewage sludges were from 0.97 to 15.0 pg g 1 dry weight (dw) with a mean value 4.43 pg g 1 dw, indicating that all I-TEQs were below Chinese legislation limit value regulated for agricultural use in soils. The results from limited samples (16 samples) showed that the levels of PCDD/Fs might be correlated with the sludge age. Meanwhile, the temporal trends of PCD/Fs suggested that the I-TEQs may correlate with rainfall in the present study. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Sewage sludge, a by-product of the process in wastewater treatment plant (WWTP), accounts for 0.3–0.5% wastewater. Now, the total amount of dry wastewater sludge is about 1.3 106 tons per year and the amount was expected to increase at the rate of approximately 10% per year in China (Zhang et al., 2006). Usually, sludge is generally regarded as fertilizer because it contains high proportions of organic matters as well as nitrogen and phosphorous (Guo et al., 2009). However, some toxicants such as metals and organic contaminants which can not be removed are also taken into account because these contaminants are toxic to the wildlife and human health. Among these contaminants, the polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) called ‘‘dioxin compounds’’ are types of environmental contaminants with high carcinogenic and bioaccumulative properties. Therefore, it is necessary to take comprehensive determination to assure the level of these contaminants in sewage sludge fertilization of cultivated land will not do harm to the environment, especially to human being. PCDD/Fs enter the environment via wet and dry deposition of atmosphere, urban runoff, domestic wastewater, industrial effluents, and these compounds even can be formed during the WWTP process (Klimm et al., 1998). Klimm et al. (1998) found sludge by semi-anaerobic digestion over 192 days can produce a twofold ⇑ Corresponding author. Tel.: +86 10 8774 3466; fax: +86 10 8774 3414. E-mail address: [email protected] (X. Li). 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.11.039
increase of OCDD and HpCDD. They also found that digestion of sludge under strictly anaerobic conditions can not form PCDD/Fs, including HpCDD and OCDD. PCDD/Fs in sewage sludges were first reported in 1984 (Lamparski et al., 1984) and has been carried out in the USA, Spain, China, and so on (Eljarrat et al., 2003; Dai et al., 2007; Clarke et al., 2008). The concentrations of dioxin are reported using toxicity equivalent (TEQ) values usually within pg g 1 dry weight (dw). Some investigations suggested that the levels of dioxin-like compounds sludge had decreased in some areas such as the USA and Swedish (Rappe et al., 1998; Alvarado et al., 2001). Some factors can influence the level and distribution of PCDD/Fs in sewage sludge (Weber et al., 1997; Fuentes et al., 2007). Weber et al. (1997) found that the kind of digestion and composting can influence the PCDD/Fs levels in sewage sludge. Stevens et al. (2001) found that the type of treatment is important to the levels of PCDD/Fs. Meanwhile, Stevens et al. (2001) also suggested that diffuse, catchment based sources (domestic wastewater, runoff) rather than point sources (trade effluent discharge) are the most important contributors of PCDD/F to sludge. Therefore, we hypotheses that the levels of dioxin in sewage sludges in Beijing, China were influenced by treatment process (such as sludge age) and runoff (such as rainfall). The objective of the present study is to determine the concentrations of PCDDs and PCDFs in sewage sludges from Beijing WWTPs in China and compare the I-TEQ with the limit proposed by Chinese GB 18918-2002 ‘‘Discharge standard of pollutants for municipal wastewater treatment plant’’ for agricultural use in soils
636
X. Li et al. / Chemosphere 82 (2011) 635–638
and the objective regulated by European Union. Meanwhile, the contribution of each contaminant in the total toxicity of the samples and influential factors were evaluated.
were defined as LOD when they were lower than LOD. The concentrations of PCDD/Fs in the real samples were not corrected by recoveries and blanks.
2. Materials and methods
3. Results and discussion
2.1. Reagents and chemicals
3.1. Concentrations of PCDD/Fs in sewage sludges
All solvents (pesticide residue grade) were purchased from Tedia Co., USA. Silica (100–200 mesh) was obtained from Qingdao Haiyang Chemical Co., China. And permeable gels (SX-3 Bio-beads, 200–400 mesh) were from Bio-Rad Co., USA. Calibration standard solution, 13C-labeled surrogate standards and injection standards complying with EPA method 1613 for PCDD/Fs analysis were from Cambridge isotope laboratories, USA.
The concentrations of PCDD/Fs (pg g 1 dw) in sewage sludge samples from plants 1 and 2 were shown in Table 2. The concentrations of PCDD/Fs varied greatly (162–178 pg g 1 dw in plant 1 and 191–1036 pg g 1 dw in plant 2) and the I-TEQ also varied greatly in plant 1 (0.97–15.0 pg g 1 dw) and plant 2 (1.91–11.0 pg g 1 dw), which might be explained by variable loads during the sample collection period at different WWTPs. The highest (15.0 pg g 1 dw) and the second I-TEQ (11.0 pg g 1 dw) were found in sewage sludge from plants 1 and 2, respectively. The I-TEQs in all sewage sludge in the present study were far below the recommended upper limits (100 pg g 1 dw) regulated by Chinese legislation GB 18918–2002 ‘‘Discharge standard of pollutants for municipal wastewater treatment plant’’ for agricultural use in soils and the safe sediment value 20 pg g 1 dw which is derived from the no observed effect concentration of 200 pg g 1 dw divided by the safety factor of 10 (Evers et al., 1996). Generally, the mean ratio RTEQPCDDs/TEQPCDFs are greater than 1 in sewage sludge samples (Eljarrat et al., 1997, 1999). However, the ratios RTEQPCDDs/TEQPCDFs ranged from 0.31 to 3.50 in plant 1 and from 0.23 to 1.14 in plant 2, and the ratios in 2 out of 16 sewage sludge samples were greater than 1. There were no correlations between capacity and PCDD/Fs concentrations in these sewage sludge samples (p > 0.05). The mean I-TEQ (2.53 pg g 1 dw) were lower in plant 1 than in plant 2 (4.60 pg g 1 dw), which might be explained by different received industrial influent (5% in plant 1 and 20% in plant 2). Meanwhile, the sludge age in plant 2 was longer than that in plant 1. These results suggested that there might be some correlations between the degree of industrial input and/or sludge age and the I-TEQ.
2.2. Sample collection Sixteen sewage sludge samples were collected from two WWTPs (plants 1 and 2) in Beijing from 2004 to 2009. The details of sewage sludge samples were shown in Table 1. The sewage sludge samples from each WWTP were packed with aluminum foil after being collected, then transferred to the laboratory and freezed-dried for 48 h before analysis. 2.3. PCDD/Fs analysis The PFDD/Fs analysis was performed according to the USEPA method 1613 at the State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy in Beijing, China. Ten grams of freezed-dried sludge were spiked with 13C-labeled surrogate standards and extracted for 24 h with toluene. The concentrated extracts were sequentially cleaned up by multi-layer silica gel, permeable gel column, and basic alumina chromatographic column. The clean-up were concentrated to 20 lL with nitrogen. 13C-labeled injection standards of PCDD/Fs were spiked to the extracts for calculation of recoveries before injecting.
3.2. Pattern of PCDD/Fs and possible sources 2.4. Instrumental analysis Samples were quantified by HRGC/HRMS using DB-5 MS capillary column (60 m 0.25 mm 0.25 lm film thickness) (Guo et al., 2009). The column temperature initiated at 80 °C (2 min), then increased to 180 °C at 15 °C min 1 and 280 °C (30 min) at 7.5 C min 1; the carrier gas was helium at 0.8 mL min 1 and the injection volume was 1 lL in splitless mode. 2.5. Quality assurance (QA) and quality control (QC) The QA and QC were described previously (Guo et al., 2009). And the recoveries of the PCDD/Fs in sewage sludge samples ranged from 50% to 90%, indicating that the extraction and clean-up of PCDD/Fs are properly. The limit of detection (LOD) was a signal to noise ratio of 3:1. And the concentrations of PCDD/Fs in samples Table 1 Detailed characteristic of the two WWTPs in the present study. WWTP
Plant 1
Plant 2
Wastewater type Sewage process
5% industrial influent
20% industrial influent Oxidation ditch
Sludge process Capacity (m3 d 1)
Activated sludge process (aerobic) Lime 4 104
Dewater 2 105
Fig. 1 presented the concentration profiles of homologues found in the sewage sludge from plants 1 and 2. The patterns of PCDD/Fs Table 2 PCDD/Fs concentration (pg g 2004 to 2009. Compounds
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 1,2,3,7,8,9-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF PCDD/Fs I-TEQ
1
dw) in sewage sludge samples from two WWTPs from
Plant 1
Plant 2
Min–max (mean)
Min–max (mean)
LOD-1.80 (0.51) LOD-11.0 (1.93) LOD-1.70 (0.67) 0.40–2.70 (1.18) LOD-1.24 (0.53) 4.7–34.9 (15.0) 26.2–408 (211) 0.8–3.70 (2.16) LOD-3.40 (1.18) LOD-4.10 (1.47) 0.5–7.0 (2.41) 0.4–3.1 (1.80) LOD-3.6 (0.84) LOD-17.5 (3.56) 4.3–17.0 (10.63) 0.5–1.8 (1.20) 8.2–53.0 (29.6) 162–718 (436) 0.97–15.0 (2.53)
LOD-1.37 (0.51) LOD-3.70 (1.04) LOD-1.21 (0.65) 0.60–2.0 (1.29) LOD-1.40 (0.68) 6.20–24.0 (14.1) 24.2–489 (175) 1.5–7.0 (3.34) LOD-4.40 (2.41) 1.40–4.60 (2.86) 1.30–7.20 (3.33) 1.10–5.90 (2.89) LOD-6.90 (1.54) LOD-4.70 (2.65) 7.30–40.0 (15.0) LOD-5.5 (1.72) 6.10–52.5 (26.3) 191–1036 (489) 1.91–11.0 (4.57)
LOD: the concentrations of PCDD/F in sewage sludge were lower than the LOD.
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among the samples from plant1 were similar with those from plant 2 except for those samples collected in 2004. The concentration homologue profiles in the sewage sludge samples showed a characteristic predominance of highly chlorinated congeners HxCDD/Fs-OCDD/Fs (86–99%) and OCDD/ Fs (76–91%, except for 39% in April, 2004) in plant 1 and HxCDD/ Fs-OCDD/Fs (87–97%) and OCDD/Fs (69–85%, except for 33% in April, 2004) in plant 2. The patterns of highly chlorinated congeners dominating in PCDD/Fs were also found in sewage sludge from Hongkong, German, and Sweden (Stevens et al., 2001) and the pattern suggested that PCPs was the major source of highly chlorinated congeners in sewage sludge (Horstmann et al., 1993). However, Eljarrat et al. (1999) suggested that the value of 1,2,3,6,7,8-HxCDD/1,2,3,4,7,8-HxCDD (>100) is a more useful indicator for technical mixture of PCP. Meanwhile, Rappe et al. (1999) have postulated that the highly chlorinated PCDD/Fs in sewage sludge but not from PCPs are formed naturally in sediment. And Stevens et al. (2001) suggested that the natural formation of highly chlorinated PCDD/Fs may also be responsible for the homologue pattern in sludges where the higher chlorinated PCDDs are dominant, as an alternative explanation to PCP contamination. The ratio of 1,2,3,6,7,8-HxCDD/1,2,3,4,7,8-HxCDD ranged from 0.70 to 13.5 in plant 1 and from 0.62 to 6.33 in plant 2 in this study. And the results were similar with those (0.58–2.57) found in 2004 (Dai et al., 2007), which suggested the PCP was not a major source of PCDD/Fs during 2004–2009. And such a pattern, in principle, suggested that the thermal process is not the primary source of contamination (Dai et al., 2007). Dai et al. (2007) suggested that household water and urban runoff may be the two important sources of PCDD/Fs in sewage sludge from Beijing WWTPs. For
3.3. Temporal trends of PCDD/Fs The temporal trends of PCDD/Fs obtained in Beijing WWTPs sewage sludge during 2004–2009 were shown in Fig. 2. The results showed a marked increase in plants 1 and 2 in 2008. Meanwhile, the TEQs were higher in April than those in October. The results may be explained by the reason that the rainfall in 2008 was the greatest from 2000 to 2009 and the rainfall was higher in April 16
plant1
plant2
12
TEQs (pg g-1dw)
Fig. 1. The concentration homologue profile in the sewage sludge samples, (a) for plant 1, (b) for plant 2.
lower chlorinated congeners PeCDD/Fs, it was almost absent in all sewage sludge samples except for the sewage sludge obtained in 2004 in the present study. OCDD and OCDF dominated in PCDDs and PCDFs in most sewage sludge samples from both plants 1 and 2, respectively. And HpCDD and HpCDF had relatively high concentrations (Fig. 1). This is in agreement with the data reported by Eljarrat et al. (2003). The concentrations of OCDF were lower than OCDD in all sewage sludge samples from plant 2 and plant 1 except for one sample obtained in October 2004. And the results were similar with the previous report, which found that OCDD concentrations were significantly greater than OCDF (OCDD/OCDF = 19.7) (de Souza and Kuch, 2005). However, OCDD concentrations were lower than OCDF in other studies (Fattore et al., 1997; Dalla et al., 2003; Martínez et al., 2007). In this study, there were no correlations between OCDD and I-TEQ, OCDF and I-TEQ (p > 0.05). However, if the data obtained in 2004 were excluded, there were correlations between OCDD and I-TEQ, OCDF and I-TEQ (p < 0.05). The results indicated that OCDF and OCDF could be regarded as the indicator to predict the I-TEQs from 2005 to 2009. Meanwhile, there were correlations between OCDD and OCDF (r2 = 0.9025; p < 0.05), OCDD and I-TEQ (r2 = 0.9409; p < 0.05) in the previous report (Clarke et al., 2008), which suggested that OCDF as well as OCDD can be regarded as the indicator to predict the I-TEQ in Australian sewage sludge (Fuentes et al., 2007; Clarke et al., 2008). The ratios of OCDD/OCDF and HpCDD/HpCDF were correlated with the digestion of sludge (de Souza and Kuch, 2005). de Souza and Kuch (2005) found that OCDD/OCDF (19.7) and HpCDD/HpCDF in actived sludge samples were higher than those (OCDD/ OCDF = 3.3; HpCDD/HpCDF = 2.1) in digested sludge. The mean ratio were 8.92 (ranging from 0.95–23.81) in plant 1 and 7.31 (3.27– 18.54) in plant 2 for OCDD/OCDF, and 1.81 (0.55–4.48) in plant 1 and 1.04 (0.48–2.31) in plant 2 for HpCDD/HpCDF in activated sludge in the present study, which was similar with those (3.3– 19.7 for OCDD/OCDF) and lower than those (2.3–10.9 for HpCDD/ HpCDF) in the previous report (de Souza and Kuch, 2005). The reason might be that the sources of PCDD/Fs were different in the previous study (de Souza and Kuch, 2005) and in the present study.
8
4
0
Apr-04
Oct-04
Apr-05 Oct-05 Jun-06
Jun-07
Oct-08 Oct-09
Fig. 2. The temporal trends of PCDD/Fs in sewage sludge samples from Beijing WWTPs from 2004 to 2009.
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The TEQ contribution of OCDD/Fs was low although OCDD/Fs concentrations were higher. OCDD/Fs correlated with TEQs during 2005–2009 and OCDF and OCDF could be regarded as the indicator to predict the I-TEQs in sewage sludge from Beijing WWTPs during 2005–2009. Acknowledgements The authors would like to acknowledge Dr. Bin Zhang and Li Guo at the State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy in Beijing, China. References
Fig. 3. The TEQ homologue profile in the sewage samples from Beijing WWTPs. (a) for plant 1, (b) for plant 2.
than in October in Beijing, China. These results were consistent with the conclusion that the urban runoff may be an important sources of PCDD/Fs in sewage sludge from Beijing WWTPs (Dai et al., 2007). Fig. 3(a) and (b) were the TEQ profiles of homologues found in the sewage sludge from plants 1 and 2, respectively. There was a large portion change of lower chlorinated TCDD/F-PeCDD/F (22– 80%) in sewage sludge from plant 2, but there was no variation of lower chlorinated TCDD/F-PeCDD/F (58–67%) in sewage sludge from plant 1. The TEQ contribution of PeCDF has decreased and the contribution of TCDD has increased in sewage sludge from plant 2. There were large variations for TEQ profiles of homologues found in the sewage sludge from plant 1 during 2004–2009, which suggested that the source of influent was not stable in plant 1. The TEQ contribution from TCDD may be lower in April than in October in sewage sludge from plant 1, however, the contribution from TCDD was higher in April than in October in sewage sludge from plant 2 between 2004 and 2005. And these results indicated that the source of PCDD/Fs may be different in plants 1 and 2. 4. Conclusions The I-TEQs in all sewage sludge samples from two WWTPs in Beijing were lower than the upper limit regulated by GB 18918– 2002 ‘‘Discharge standard of pollutants for municipal wastewater treatment plant’’ for agricultural use in soils.
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