Science of the Total Environment 493 (2014) 481–486

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Identification of priority organic compounds in groundwater recharge of China Zhen Li, Miao Li, Xiang Liu ⁎, Yeping Ma, Miaomiao Wu School of Environment, Tsinghua University, Beijing 100084, China

H I G H L I G H T S • • • •

We developed a comprehensive ranking system to identify priority organic compounds. We developed two different ranking lists of organic compounds. 151 OCs were selected as the candidate organic compounds and ranked. Nonylphenol, erythromycin and ibuprofen were the highest priority OCs.

a r t i c l e

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Article history: Received 24 January 2014 Received in revised form 2 June 2014 Accepted 2 June 2014 Available online xxxx Editor: Eddy Y. Zeng Keywords: Priority organic compounds Groundwater recharge A comprehensive ranking system Reclaimed water

a b s t r a c t Groundwater recharge using reclaimed water is considered a promising method to alleviate groundwater depletion, especially in arid areas. Traditional water treatment systems are inefficient to remove all the types of contaminants that would pose risks to groundwater, so it is crucial to establish a priority list of organic compounds (OCs) that deserve the preferential treatment. In this study, a comprehensive ranking system was developed to determine the list and then applied to China. 151 OCs, for which occurrence data in the wastewater treatment plants were available, were selected as candidate OCs. Based on their occurrence, exposure potential and ecological effects, two different rankings of OCs were established respectively for groundwater recharge by surface infiltration and direct aquifer injection. Thirty-four OCs were regarded as having no risks while the remaining 117 OCs were divided into three groups: high, moderate and low priority OCs. Regardless of the recharge way, nonylphenol, erythromycin and ibuprofen were the highest priority OCs; their removal should be prioritized. Also the database should be updated as detecting technology is developed. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Groundwater recharge using reclaimed water has been rapidly developed around the world in order to replenish decreasing groundwater resources and declining water table. Groundwater recharge can be accomplished by various methods: surface spreading, soil aquifer treatment system, vadose zone injection and direct injection (U S Environmental Protection Agency, 2004). These methods can be categorized as either surface percolation or direct aquifer injection. In China, during 2008 there was 3000 × 104 t reclaimed water to be recharged. It is, however, difficult to remove all the contaminants in reclaimed water completely (Calderon-Preciado et al., 2011; Matamoros and Salvado, 2012), meaning that some of them such as endocrine disrupting chemicals (EDCs), pharmaceuticals, perfluorochemicals (PFCs) and antibiotics (Karthikeyan and Meyer,

⁎ Corresponding author. Tel.: +86 10 62772485; fax: +86 10 62785685. E-mail address: [email protected] (X. Liu).

http://dx.doi.org/10.1016/j.scitotenv.2014.06.005 0048-9697/© 2014 Elsevier B.V. All rights reserved.

2006; Al-Khashman, 2009; Teijon et al., 2010; Karnjanapiboonwong et al., 2011) were introduced into groundwater, thereby posing risks to groundwater and humans. Different pollutants would impose different degrees of risk to groundwater due to their varied behaviors and fates during recharge. For instance, those pollutants which can be removed by adsorption and degradation, may not pose risks to the safety of the groundwater environment even if the concentration is high in reclaimed water. However, other pollutants that are present at low concentrations in reclaimed water and that do not undergo transformations on entering the aquifer, may also pose greater risk to groundwater (Zhang et al., 2011; Debroux et al., 2012; Lapworth et al., 2012). For these reasons rather priority pollutants should deserve our first concern in wastewater treatment plants (WWTPs) that are supplying reclaimed water to groundwater. Several researchers have carried out evaluations using various methodologies, of which three methodologies were most commonly adopted for screening. The most popular method is a comprehensive scoring system, for example, Kumar and Xagoraraki (2010) provided a ranking list of 100 OCs in surface water and finished drinking water

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by using this method. The other two most popular methods were step by step screening based on multi-criteria (Boxall et al., 2003; Besse et al., 2008; Eriksson et al., 2008; Perazzolo et al., 2010; Jean et al., 2012) and mathematical simulations (Jonsson et al., 1989; Munoz et al., 2008; Voigt and Bruggemann, 2008). In those studies, the target environment media were surface water (Mitchell et al., 2002; Sanderson et al., 2004; Arnot and Mackay, 2008; Besse et al., 2008; Besse and Garric, 2008; Kumar and Xagoraraki, 2010; Perazzolo et al., 2010; Sui et al., 2012), drinking water (Kumar and Xagoraraki, 2010; Schriks et al., 2010), sludge (Eriksson et al., 2008) and soil (Jeong and An, 2012). However to the best of our knowledge studies on screening for priority chemical substances in groundwater have rarely been reported. Also, due to the difference of usage amounts, environmental conditions and levels of treatment technology, priority contaminants vary by country. In China only one study (Sui et al., 2012) had focused on priority pollutant screening in the water environment. In that study, 39 pharmaceuticals were ranked based on consumption, removal performance in WWTPs and potential ecological effects. Seventeen pharmaceuticals were screened out as priority pollutants. In this study, we developed a ranking system based on OCs' occurrence in either reclaimed water or WWTP effluent of China, exposure potential and potential ecological effects. This approach was applied to groundwater recharge using reclaimed water by surface percolation and direct aquifer injection in China.

transportability of an OC are represented by its degradation half-life and soil organic carbon adsorption coefficients (KOC), respectively. The attribute “persistence” only considers biological effect. The third criterion “ecological effects” contains two factors: bioaccumulation (E1) and eco-toxicity (E2). The octanol/water partitioning coefficient (KOW), which indicates the lipophilicity of OCs, is used to estimate bioaccumulation, as it has been correlated with bioconcentration factor for different compounds (Schriks et al., 2010). The eco-toxicity is estimated by the lethal concentrations for 50% kill (LC50) of the aquatic indicator species (fish, daphnid and green algae which represent three trophic levels) of an OC (He et al., 2014). And in this study, only acute toxicity is considered. 2.1.2. Scoring For different criteria and attributes, different utility functions were applied (Table 1), some of which were modified from the utility functions used by Kumar and Xagoraraki (2010). The score of one criterion was calculated using Eq. (1), where Si was the score of the corresponding criterion, Wi,j was the importance weight of each component, and Uj was the value obtained from corresponding utility function of the component. For the three criteria “occurrence”, “exposure potential” and “ecological effects”, two components were involved and considered to be equally important.

Si ¼ 2. Methods

n X U j  W i; j :

ð1Þ

j¼1

2.1. Ranking system

The overall score of an OC was calculated using Eq. (2), where Soverall represented the overall score of the OC, and Wi represented the importance weight of each criterion. Similarly, to avoid any judgment bias all the criteria were also considered equally important, so Wi was assigned a value of 1/3 for groundwater recharge through surface percolation. The “exposure potential” criterion is not applicable for groundwater recharge by direct aquifer, so the value of Wi was set as 1/2 for the other two criteria.

2.1.1. Criteria The ranking of OCs in this study was based on the overall scores of three different criteria: occurrence in the reclaimed water or WWTP effluent of China, exposure potential and ecological effects. Table 1 presents the information about different attributes of multiple criteria. The “occurrence” (O) is represented by the “prevalence” attribute (O1) and “magnitude” attribute (O2) of an OC. The two attributes are represented as the frequency of detection and the concentration of an OC in reclaimed water or WWTP effluent, respectively. Because the amount of infiltration is mostly affected by adsorption and degradation of pollutants during recharge, the second criterion “exposure potential” (P) is represented by two attributes: (1) persistence (P1) and (2) transportability (P2) of an OC. Assuming that groundwater was extracted from the recharge site, when OCs in groundwater recharged by direct aquifer injection were ranked, the criterion “exposure potential” does not undergo treatment, as pollutants in groundwater recharged by this method aren't adsorbed or degraded in vadose zone. The persistence and

Soverall ¼

3 X Si  W i :

ð2Þ

i¼1

The illustration of the scoring for one OC (erythromycin) was shown in Table A.1. 2.2. Data collection All the data collected are presented in Table A.2.

Table 1 Criteria, attributes and corresponding utility functions used to prioritize OCs in groundwater recharge. Criteria

Attributes

Utility functions

Occurrence (O)

Prevalence(O1)(%) Magnitude(O2)(ng/L)

Exposure potential(P)

Persistence (P1)(1)

U(O1) = max(f / 100)i, where f represents frequency of detection of anith chemical in water. U(O2) = (C − Cmin) / (Cmax − Cmin)i, where C represents concentration of anith chemical in reclaimed water or WWTPs effluent, Cmax and Cmin represent maximum and minimum concentration values, obtained from the overall list of OCs considered. U(P1) = 1, if t1/2 b 0(A), “0.8” for category “B” (0–1), “0.6” for category “C”(1–2), “0.4” for category “D”(2–3), and “0.2” for category “X” (N3). U(P2), which is equals to “1” for category “A” (1–2), “0.8” for category “B”(2–3), “0.6” for category “C”(3–4), “0.4” for category “D” (4–5), and “0.2” for category “X” (N5). U(E1) = 1, if log KOW N 3; U(E1) = 0, if log KOW b 3a. 3 1 UðE2Þ ¼ ∑  UðE2Þk ; k¼1 3 ðLC Þ −ðLC Þ UðE2Þk ¼ 1− ðLC5050Þ i −ðLC5050min : Þ

Transportability (P2)(l/mg) Ecological effects(E)

Bioaccumulation (E1)(1) Ecotoxicity (E2) (mg/L)

max

min

Note: A: lower exposure potential; B: low exposure potential; C: moderate exposure potential; D: high exposure potential; and X: higher exposure potential. a If the pollutant has log KOWof more than 3.0, it was indicated to be potentially bioaccumulated (Perazzolo et al., 2010; Schriks et al., 2010).

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2.2.1. Occurrence This ranking was based on studies carried out in China between 2004 and 2013. Studies were selected in the Web of Knowledge using “China”, “effluent * OR wastewater * OR reclaimed water *” and “occurrence * OR determination * OR detection *”as the topics. Studies which failed to provide specific values were not taken into account and 27 documents(Cao et al., 2005; Kloepfer et al., 2005; Peng et al., 2006; Chang et al., 2007; Zeng et al., 2007; Xiao et al., 2008; Li et al., 2009; Duong et al., 2010; Huang et al., 2010; Lv et al., 2010; Ma and Shih, 2010; Zhao et al., 2010a,b; Zhou et al., 2010; Chang et al., 2011; Chen et al., 2011; Li and Zhang, 2011; Liu et al., 2011; Sui et al., 2011; Sun et al., 2011; Tong et al., 2011; Yang et al., 2011; Zhang et al., 2011a,b; Gao et al., 2012; Ye et al., 2012; Zhou et al., 2012; Yuan et al., 2013) were selected for reference. If an OC, such as E1, was reported in several studies, the average concentration was calculated. The detection frequency of an OC was also takenfrom these studies, and the maximum detection frequency was calculated if a particular OC was reported in more than one study. The utility function of an OC was assigned to be 0.5, if in these studies the detection frequency of the OC was not reported.

2.2.2. Exposure potential The degradation half-life and KOC were calculated using Estimations Programs Interface for Windows (EPI) (US Environmental Protection Agency (USEPA), 2012) designed by EPA (Environmental Protection Agency). This software predicts the behavior of chemical substances in biological or environmental systems based on their physical, chemical and environmental properties. Biodegradability data were modeled using “BIOWINv4.1”, developed jointly with the “Office of Pollution Prevention and Toxics” and by the “Syracuse Research Corporation”. The Quantitative Structure Activity Relationship (QSAR) type modeling method incorporates the Biodegradation Probability Program, recommended in the “European Chemical Bureau”. We used ultimate biodegradability as the sole selection criterion. In the software the ratings correspond to different time units as follows: 5-hours, 4-days, 3-weeks, 2-months, 1-longer. It should be noted that the ratings are only semi-quantitative and not half-lives. KOC data were modeled using the “KOCWIN v2.00”. We used Koc from the PCKOCWIN (version 1) as the sole selection criterion. PCKOCWIN estimates Koc solely with a QSAR using first-order Molecular Connectivity Index. In the EPI software, the data of seven OCs were not available and except for occurrence the values of utility functions were assigned to be 0.5.

8%

EDCs 27%

PFCs Antibiotics

23%

Pesticides

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2.2.3. Ecological effects KOW and LC50 were also obtained by the EPI (US Environmental Protection Agency (USEPA), 2012). Because there are no toxicity data for most chemicals, LC50 were modeled using “ECOSAR”. This software estimates 96-h EC50 for green algae, 48-h LC50 for daphnid and 96-h LC50 for fish. These estimations were based on the structure activity analysis of these compounds. We used the LC50 or EC50 calculated by Neutral Organic SAR. If the values calculated by Neutral Organic SAR were not available, the values modeled by ECOSAR Class were employed. 3. Results and discussion 3.1. Overall ranking EDCs, PFCs, antibiotics, pharmaceuticals (excluding antibiotics), pesticides, polycyclic aromatic hydrocarbons (PAHs) and personal care products (PCPs) were the main OC groups in our study (Fig. 1). EDCs, antibiotics and pharmaceuticals were the main contaminants, and accounted for 27%, 23% and 21% of the OCs studied, respectively. This indicates that in recent years these three pollutant groups were paid more attention than other groups. According to the scoring, 151 OCs were divided into four groups: groups I, II and III included 117 OCs in all that had average concentrations above the limit of detection and group IV included 34 OCs whose concentrations in reclaimed water or WWTP effluent were below the limit of detection. OCs in group IV do not access groundwater and so do not pose any risks to either the environment or humans. Groups I, II and III were categorized as high, moderate and low priority OCs, respectively and in each group there were 39 OCs. This ranking is a relative scale of importance rather than an absolute scale. This means that high priority OCs should be more concerned about than moderate and low priority OCs and if time and financial resources are enough, attentions should also be paid to moderate and low priority OCs. The primary purpose of this categorization was to help researchers and policymakers (1) identify priority OCs in groundwater recharge that deserve our first concern in WWTPs, (2) identify priority OCs that need further study and (3) establish effective policies and strategies. Regardless of whether reclaimed water was recharged through surface spreading or direct aquifer injection, nonylphenol (NP), with an average concentration of 947.79 ng/L, was the highest priority OC. This contrasts with the results studied by Kumar and Xagoraraki (2010) in which NP was ranked after bisphenol A. That may be due to different usages between countries. Also we based our study on groundwater, while the other study was focused on surface water in the United States from 2002 to 2009. NP, erythromycin and ibuprofen were the three highest priority OCs and were classified as EDC, antibiotic and pharmaceutical, respectively. As shown in Table A.2, the average concentrations of these three pollutants were all more than 150 ng/L and for all the OCs investigated the concentrations of only seven pollutants were more than 150 ng/L. Also the three pollutants show high ecological toxicity. In that study carried out by Sui et al. (2012) in surface water of China, erythromycin, diclofenac acid and ibuprofen were the highest priority OCs and these OCs were also in the high priority OC group in this study. This indicates that high priority OCs in the surface water may also be given high concerns in groundwater.

PAHs 11%

Pharmaceuticals

7% PCPs 3%

21%

Fig. 1. Percentage contribution of each group to the total number of investigated OCs.

3.2. Each pollutant class and ranking group Fig. 2 shows that, in each ranking group, the contribution of each contaminant class was different and that the OCs differed as the recharging method differed. When the surface spreading recharge method was used, pharmaceuticals contributed most to high priority OCs, for 12 of the 39 high priority OCs representing 31% followed by EDCs, which accounted for 21%

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Fig. 2. Contribution of each pollutant class to each ranking group in groundwater recharge by (a) surface spreading and (b) direct aquifer injection.

of high priority OCs (group I). These results suggest that pharmaceuticals and EDCs should be given more concern in WWTPs to ensure the security of groundwater. Using direct aquifer injection recharge method, pharmaceuticals and EDCs were again the main high priority OCs, accounting 28% and 23%, respectively, closely followed by PAHs (21%). Regardless of the recharge method, pharmaceuticals and EDCs accounted for the majority of the high priority OCs which may be due to the large number and high risk of candidate pharmaceuticals and EDCs. This does not mean that attention should not be paid to the moderate and low priority OCs. If time and financial resources are enough,

we should focus on removing the moderate and low priority OCs in reclaimed water or effluent of WWTPs. The occurrence of PFCs and PAHs in the high priority OC class differed depending on the recharge method, as shown in Fig. 2. There were more PFCs and less PAHs in the high priority OC class when surface spreading recharge method was used rather than direct aquifer injection; the results were reverse for the moderate priority OCs class. This indicates that priority OCs varied with the recharging method. For example, phenanthrene was at the 40th when the surface spreading method was used, but ranked eighth when the direct

Fig. 3. Percentage of each pollutant class in each ranking group in groundwater recharge by (a) surface spreading and (b) direct aquifer injection.

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aquifer injection method was used. This may be because pollutants like phenanthrene are easily absorbed and so the criterion “exposure potential” was important in the screening. In the direct injection method, the criterion “exposure potential” wasn't taken into account, such that the criteria “occurrence” and “ecological effects” of the OCs were the main factors that influenced the risk. Fig. 3 shows the proportions of the seven kinds of pollutants in each priority group. EDCs were distributed almost equally. Out of all EDCs, Table A.3 shows that removal of NP, 17α-hydroxyprogesterone and 4-tert-octylphenol from reclaimed water should be a priority if recharged through surface spreading; NP, bisphenol A and 4-tertoctylphenol should be given priority concern in reclaimed water if recharged by direct aquifer injection. Regardless of whether recharge was by surface spreading or direct aquifer injection, perfluorooctanoate (PFOA) was the highest priority PFC, followed by perfluoropentanoate (PFHxA) and perfluoroheptanoate (PFHpA). For groundwater recharge by surface spreading, PFOA, PFHxA and PFHpA were in the high priority OC group that needed most attention for removal, while using another recharge method, only PFOA was in group I and PFHxA and PFHpA were moderate priority OCs. Thirty-three percent of PFCs investigated could not be detected. However, due to high stability in the environment, degradation of PFCs by heat, light, micro-organisms and higher organisms is difficult, and these pollutants can be accumulated in vivo and can be biomagnified through the food chain (Kelly et al., 2009; Tomy et al., 2009), such that concentrations of PFCs are eventually high in high ecological niche organisms, which will ultimately result in toxic effects to ecosystems and humans (Renner, 2001). Therefore, PFCs pose risks to groundwater even if the concentration is low and more attention should be paid, if time and cost are sufficient. More than 80% of antibiotics were in groups II and III, while nearly 60% of pharmaceuticals were in groups III and IV for both recharge methods. This is not an excuse for complacence as regards antibiotics and pharmaceuticals. Certain antibiotics, for example, erythromycin, josamycin and ofloxacin, were high priority OCs, while some pharmaceuticals, such as ibuprofen, diclofenac and indomethacin, deserve attention. Pesticides and PAHs occurred most frequently in high and moderate priority OC groups and should be a priority for removal in WWTPs. The majority of PCPs in our study were musk and antimicrobials. Group I and II comprised 67% of PCPs if recharge by surface spreading and 75% if recharge by direct aquifer injection. If groundwater recharge through surface spreading triclocarban, musk ketone and triclosan were the three highest priority PCPs, while through direct aquifer injection triclocarban, galaxolide and triclosan were the three highest priority PCPs. 3.3. Uncertainty As the candidate OCs were those for which concentration data were available, the uncertainties were mainly attributed to the data gaps of ecological effects and exposure potential. The EPI model could not provide data for seven OCs (gatifloxacin, 4-hydroxy-androst-4-ene-17dione, moxifloxacin, 17α-boldenone, spiramycin, tylosin tartrate and perfluorobutanesulfonate). All attributes of the seven OCs, apart from criterion “occurrence” were assigned as 0.5. There were also data gaps in the criterion “occurrence” in the current database; this database will need to be updated frequently as both OC monitoring and treatment technology of WWTPs were improved. Also, the database needs to be updated systematically as new contaminants are discovered. Numerous factors, which influence groundwater recharge process, could not be all considered in this study. For instance, biodegradation, chemical degradation, hydrolysis and photolysis may take place, but only the biodegradation effect was considered. However, other factors may have contributed to the degradation of some OCs. For example, diclofenac is degraded by direct photolysis and self-sensitization in the aquatic environment (Zhang et al., 2011a,b) while halogenated VOCs are susceptible to abiotic degradation by iron (Butler and Hayes,

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1999). Also, in this study only degradation was considered in the soil, but time was not taken into account. Arora et al. (2013) have studied that biogeochemical process and redox reactions are often characterized by high temporal variability. In the future, the relationship between degradation and time will be studied to get a generalize method which would represent the influence of time to the biogeochemical process. In this study, only acute toxicity was considered and chronic toxicity was excluded. Finally, additional human health effects (for example, endocrine effects) need to be taken into account in the future study. 4. Conclusion We developed a comprehensive ranking system for identifying priority OCs in groundwater recharge using reclaimed water for China based on three criteria: occurrence in reclaimed water or WWTP effluent in China, exposure potential and ecological effects. According to the scorings, 117 OCs were divided into three groups (high, moderate and low priority OCs); 34 OCs were regarded as having no risk. Regardless of whether reclaimed water was recharged by surface spreading or direct aquifer injection, NP, erythromycin and ibuprofen were the three highest priority OCs which were EDC, antibiotic and pharmaceutical, respectively. Compared with other studies, OCs receiving high concerns in surface water should also be given prior consideration in groundwater. This database needs to be constantly updated as new pollutants are discovered. Also, concentration data also need to be updated as water treatment methods and monitoring technology improve. Conflict of interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work. There is no professional or other personal interest of any nature or kind in any product, service and company. Acknowledgments The authors thank the Special Environmental Research Funds for Public Welfare (No. 201209053) and the National Natural Science Foundation of China (No. 51378287) for the financial support of this work. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scitotenv.2014.06.005. References Al-Khashman O. Chemical evaluation of Ma'an sewage effluents and its reuse in irrigation purposes. Water Resour Manag 2009;23:1041–53. Arnot JA, MacKay D. Policies for chemical hazard and risk priority setting: can persistence, bioaccumulation, toxicity, and quantity information be combined? Environ Sci Technol 2008;42:4648–54. Arora B, Mohanty BP, Mcguire JT, Cozzarelli IM. Temporal dynamics of biogeochemical processes at the Norman Landfill site. Water Resour Res 2013;49:6909–26. Besse JP, Garric J. Human pharmaceuticals in surface waters implementation of a prioritization methodology and application to the French situation. Toxicol Lett 2008;176: 104–23. Besse JP, Kausch-Barreto C, Garric J. Exposure assessment of pharmaceuticals and their metabolites in the aquatic environment: application to the French situation and preliminary prioritization. Hum Ecol Risk Assess 2008;14:665–95. Boxall A, Fogg LA, Kay P, Blackwell PA, Pemberton EJ, Croxford A. Prioritisation of veterinary medicines in the UK environment. Toxicol Lett 2003;142:207–18. Butler EC, Hayes KF. Kinetics of the transformation of trichloroethylene and tetrachloroethylene by iron sulfide. Environ Sci Technol 1999;33:2021–7. Calderon-Preciado D, Matamoros V, Bayona JM. Occurrence and potential crop uptake of emerging contaminants and related compounds in an agricultural irrigation network. Sci Total Environ 2011;412:14–9. Cao ZH, Wang YQ, Ma YM, Xu Z, Shi GL, Zhuang YY, et al. Occurrence and distribution of polycyclic aromatic hydrocarbons in reclaimed water and surface water of Tianjin, China. J Hazard Mater 2005;122:51–9.

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