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Published in final edited form as: Chemosphere. 2020 Aug 13;263:127954. doi: 10.1016/j.chemosphere.2020.127954

Addition of lemon before boiling chlorinated tap water: A strategy to control halogenated disinfection byproducts

Jiaqi Liu a,b, Christie M Sayes b,*, Virender K Sharma a,*, Yu Li c, Xiangru Zhang d
PMCID: PMC8134856  NIHMSID: NIHMS1703113  PMID: 32854008

Abstract

Chlorine disinfection is required to inactivate pathogens in drinking water, but it inevitably generates potentially toxic halogenated disinfection byproducts (halo-DBPs). A previous study has reported that the addition of ascorbate to tap water before boiling could significantly decrease the concentration of overall halo-DBPs in the boiled water. Since the fruit lemon is rich in vitamin C (i.e., ascorbic acid), adding it to tap water followed by heating and boiling in an effort to decrease levels of halo-DBPs was investigated. We examined three approaches that produce lemon water: (i) adding lemon to tap water at room temperature, termed “Lemon”; (ii) adding lemon to boiled tap water (at 100°C) and then cooling to room temperature, termed “Boiling + Lemon”; and (iii) adding lemon to tap water then boiling and cooling to room temperature, termed “Lemon + Boiling”. The concentrations of total and individual halo-DBPs in the resultant water samples were quantified with high-performance liquid chromatography-tandem mass spectrometry and the cytotoxicity of DBP mixtures extracted from the water samples was evaluated in human epithelial colorectal adenocarcinoma Caco-2 cells and hepatoma HepG2 cells. Our results show that the “Lemon + Boiling” approach substantially decreased the concentrations of halo-DBPs and the cytotoxicity of tap water. This strategy could be applied to control halo-DBPs, as well as to lower the adverse health effects of halo-DBPs on humans through tap water ingestion.

Keywords: Disinfection byproducts, DBPs, Lemon, Boiling, Cytotoxicity

Graphical Abstract

graphic file with name nihms-1703113-f0001.jpg

1. Introduction

Chlorine is widely used as a disinfectant in drinking water treatment plants, but it inevitably reacts with constituents of source water like bromide, iodide, and natural organic matter (NOM) to generate halogenated disinfection byproducts (halo-DBPs), including chloro-, bromo- and iodo-DBPs (Nicholas et al., 2021; Jiang et al., 2020; Liu et al., 2020a; Wang et al., 2020; Zhang et al., 2020; Dong et al., 2019; Kimura et al., 2019; Hu et al., 2018; Mao et al., 2018; Yan et al., 2018; Bond and Graham, 2017; Jiang et al., 2017; Gan et al., 2015; Hua et al., 2015; Gonsior et al., 2014; Sharma et al., 2014; Zhai et al., 2014). These halo-DBPs have been reported to be cytotoxic, genotoxic, mutagenic, growth inhibitive and developmentally toxic (Han and Zhang, 2018; Cortés and Marcos, 2018; Wagner and Plewa, 2017; Li et al., 2016; Procházka et al., 2015; Liu and Zhang, 2014; Yang and Zhang, 2013). Tap water is required to contain chlorine residual in order to protect against microbial regrowth in drinking water distribution systems. However, such a residual chlorine may continue to react with organic matter and generate halo-DBPs during the transportation of drinking water. In 2015, nearly 21 million people in the United States (~ 7% of total population) received public tap water that violated health-based safety standards, e.g., the monitored levels of DBPs failed to meet the guidelines set by the U. S. Environmental Protection Agency (Allaire et al., 2018). A long-term exposure to halo-DBPs via daily tap water ingestion has raised a great public health concern.

Household water treatment approaches could be applied to remove DBPs and subsequently improve the quality of tap water. One of the approaches is boiling. Significantly, boiling (or heating to a higher-than-room temperature) of tap water has been demonstrated to be effective in decreasing the concentration of DBPs in tap water (Liu et al., 2020b; Shi et al., 2017; Liu et al., 2015; Pan et al., 2014; Zhang et al., 2013). In addition to boiling, another strategy a consumer can implement is the addition of vitamin C. In some countries, people drink lemon water, which is usually made by adding lemon pieces or juice squeezed from a lemon into tap water or iced water. Lemon is rich in vitamin C (i.e., ascorbic acid), which is an essential nutrient for humans. Our recent study showed that the addition of sodium ascorbate followed by boiling could decrease the concentrations of overall halo-DBPs in simulated tap water samples (Liu et al., 2020b). This prompted the investigation of a new strategy for controlling DBPs in tap water: combining the effects of lemon and boiling.

Here, we proposed three different approaches to producing lemon water, i.e., (i) adding lemon to tap water at room temperature; (ii) adding lemon to boiled tap water (at 100°C) and cooling to room temperature; (iii) adding lemon to tap water (at room temperature), then boiling (at 100°C), and cooling to room temperature. These three types of lemon water were compared in terms of total and individual halo-DBPs concentrations and cytotoxicity levels against the human epithelial colorectal adenocarcinoma (Caco-2) cells and hepatoma (HepG2) cells. These two cell-types have been applied in toxicological studies of DBPs and disinfected drinking waters (Liu et al., 2020a; Wu et al., 2019; Melo et al., 2016; Pals et al., 2017; Zhang et al., 2012).

2. Materials and methods

2.1. Chemicals, solvents, reagents, tap water and lemons

For chemical analysis, bromoacetic acid and 3,5-dibromo-4-hydroxybenzaldehyde were purchased from Alfa Aesar (Haverhill, MA, USA). Chloroacetic acid, 2,4,6-tribromophenol, iodoacetic acid, dibromoacetic acid, bromochloroacetic acid, dichloroacetic acid and bromobutenedioic acid were acquired from Sigma‒Aldrich (St. Louis, MO, USA). Water (Optima LC/MS grade), acetonitrile (Optima LC/MS grade), methyl tert-butyl ether (HPLC grade), and other chemicals and solvents were obtained from Fisher Chemical (Hampton, NH, USA).

For cell culture and toxicity tests, Eagle’s Minimum Essential Medium (EMEM), Dulbecco’s Modified Eagle’s Medium with nutrient mixture F-12 (DMEM), fetal bovine serum (FBS), penicillin-streptomycin solution (10,000 I.U./mL), Dulbecco’s phosphate buffered saline (PBS), and sterile distilled water were of Gibco brand and purchased from Thermo Fisher Scientific (Waltham, MA, USA). The EMEM and DMEM were supplemented with 10% FBS and 1% penicillin-streptomycin solution before use.

Tap water (with the characteristics shown in Supplementary Materials Table S1) was collected at a faucet in a residential area in Texas, USA. Organic lemons (Eureka type, 65–88 g each, product of the USA) were bought from a nearby grocery store. Prior to experimentation, each lemon was peeled and pureed with a vegetable chopper. The puree was used for experiments within 10 min after preparation.

2.2. Preparation of lemon water samples

Three approaches of making lemon water were investigated, i.e., adding lemon to tap water at room temperature (termed “Lemon”); adding lemon to boiled tap water at 100°C (termed “Boiling + Lemon”); and adding lemon to tap water and then boiling (termed “Boiling + Lemon”). Water samples were cooled to room temperature before analysis; boiled water without lemon (termed “Boiling”) and the tap water without boiling or lemon were also analyzed as controls. A schematic diagram of sample preparation is shown in Fig. S1. Each water sample was prepared as 1.1 L and contained in a 4 L glass beaker. The chlorine residual in tap water was 1.46 mg/L as Cl2, measured per the Standard Method (APHA et al., 2012). Lemon was added at 7.0 g/L. Considering that 100.0 g lemon (without peel) contains 53 mg vitamin C (U.S. Department of Agriculture, 2018), the amount of lemon added was equivalent to 3.71 mg/L vitamin C (in the form of ascorbic acid), which is the stoichiometric amount for quenching the chlorine residual (Equation 1) (Bedner et al., 2004; Albert Zhang, 2013):

C6H8O6+ HOCl → C6H6O6+HCl+ H2O Equation 1

After treatment, each sample was filtered through 0.45 μm filter, added with ultrapure water to the initial volume to compensate water evaporation, and subjected to chlorine residual measurement. The concentrations of chlorine residual were undetectable in the “Boiling”, “Lemon”, “Boiling + Lemon”, and “Lemon + Boiling” samples. Before analysis, the chlorine residual in tap water (without boiling or lemon) was quenching with 105% stochiometric amount of sodium thiosulfate.

2.3. Identification and quantitation of halo-DBPs

The five water samples in Fig. S1 were pretreated with a liquid-liquid extraction technique (details are given in Supplementary Materials Text S1) and analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) (Liu et al., 2020a). Each pretreated water sample was injected into the MS/MS with an electrospray ionization (ESI) source (Thermo Scientific TSQ Quantum Access Max) at 10 μL/min. The chloro-, bromo- and iodo-DBPs in the sample were detected with precursor ion scans (PISs) of m/z 35/37, m/z 79/81 and m/z 127, respectively. The instrument was operated at negative ESI mode and the operation parameters are given in Table S2.

The MS/MS was connected to a HPLC (Thermo Scientific Ultimate 3000) with a Waters XSelect HSS T3 column (100 × 2.1 mm, 2.5 μm particle size). The mobile phase was operated at 0.30 mL/min for a run time of 18 min with varying percentages of acetonitrile and water: 0 min, 10% acetonitrile and 90% water; 1 min, 10% acetonitrile and 90% water; 12 min, 90% acetonitrile and 10% water; 13 min, 10% acetonitrile and 90% water; and 18 min, 10% acetonitrile and 90% water. HPLC-MS/MS full scans were conducted at m/z ranges of 100–210, 200–310, 300–410, and 400–500 to cross check each pair of ions or ion clusters detected by MS/MS PISs m/z 79/81 and m/z 35/37. Each ion or ion cluster, corresponding to a halo-DBP, was further analyzed with HPLC-MS/MS selected reaction monitoring (SRM) scan and product ion scan (with parameters in Table S2) to determine the structure. The standard compounds of proposed DBPs were purchased and analyzed for confirmation. To determine the error of the HPLC-MS/MS analysis, two tap water samples without boiling or lemon were collected, pretreated, and analyzed.

2.4. Cell culture and cytotoxicity assessment

Prior to toxicity assessment, each water sample in Fig. S1 was concentrated using a liquid-liquid extraction technique (Texts S1). A series of toxicity test solutions (with different concentration factors relative to the initial water sample) were prepared by dissolving the organic extracts obtained from a water sample in different volumes of cell culture medium.

The human intestinal Caco-2 (HTB-37) and liver HepG2 (HB-8065) cells were acquired from American Type Culture Collection (ATCC, Manassas, VA, USA). Caco-2 cells (passages 39–46) were cultured in DMEM in an incubator set at 37 °C and 5% CO2. The culture medium was changed every two days. The cells of ~70% confluency were seeded at 4 × 104 cells/cm2 in 96-well plates and incubated for 48 h to facilitate cell adherence. Then, the medium in each well was replaced by a test solution (i.e., the concentrated water sample) or fresh DMEM (as control). Cells were incubated for another 24 h and the viability of Caco-2 cells in each sample was measured using the Promega (Madison, WI, USA) CellTiter 96 AQueous One Solution Cell Proliferation Assay (containing 3-(4,5-dimethyl-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) salt), per the method adopted in a previous study (Liu et al., 2020a). The cell culture and toxicity test procedures for HepG2 cells (passages 8–16) were the same as those for Caco-2 cells, except that EMEM was used instead of DMEM.

2.5. Dose-response curve fitting and statistical analysis

Cell viability data was processed using Sigma Plot 14.0 (Systat Software, San Jose, CA, U.S.). The dose (i.e. concentration factor) and response (i.e. cell viability) relationship of each water sample against either Caco-2 or HepG2 cells was obtained by fitting the experimental data to a four-parameter logistic curve (Yang and Zhang, 2013). A bootstrap statistical approach developed by Wagner and Plewa (2017) was used to generate a series of LC50 values for the sample from replicate tests. Cytotoxicity index, which is commonly used to determine the toxicity potency of a water sample, was defined as the reciprocal of LC50 multiplied by 1000 (Pan et al., 2014; Wagner and Plewa, 2017; Liu et al., 2020b). The cytotoxicity rank order of the five water samples against either Caco-2 or HepG2 cells were determined through ANOVA all pair-wise analysis of cytotoxicity indexes.

3. Results and Discussion

3.1. Comparison of total halo-DBPs in tested water samples

In this study, the total concentrations of chloro-, bromo- and iodo-DBPs in a water sample were quantified and compared via the total ion intensities (TIIs) of PIS spectra of m/z 35 (from m/z 90–500), m/z 79 (from m/z 100–500) and m/z 127 (from m/z 130–500), respectively. The TII values of PIS spectra of m/z 35, m/z 79 and m/z 127 can be approximately proportional to the total quantity of polar chloro-, bromo- and iodo-DBPs in a water sample, and have been demonstrated to be strongly positively correlated to the total organic chlorine, total organic bromine, and total organic iodine in the water sample, respectively (Liu et al., 2017; Cai et al., 2016; Liu et al., 2015; Pan et al., 2015). Figs. S2–S4 show the spectra of MS/MS PISs of m/z 35, m/z 79 and m/z 127 of the tap water sample (without boiling or lemon) obtained from duplicate measurements. Experimental errors of TII measurement were 1.4%−4.8%.

Figs. S5−S8 show the MS/MS PIS spectra of m/z 35, m/z 79 and m/z 127 of five water samples, from which the TII values were calculated and showed in Fig. 1. The TIIs of chloro-DBPs in water samples follow a descending rank order of “Without boiling or lemon” ≈ “Lemon” > “Boiling” ≈ “Boiling + Lemon” > “Lemon + Boiling”. Whereas the TIIs of bromo- and iodo-DBPs both follow a descending rank order of “Without boiling or lemon” ≈ “Lemon” > “Boiling” > “Boiling + Lemon” > “Lemon + Boiling”. The added lemon provides vitamin C at the stochiometric amount to the chlorine residual in tap water. The difference in TIIs of halo-DBPs in un-boiled tap water samples with and without lemon is within the range of experimental error. This indicates that the antioxidants in lemon neither reduced the formed halo-DBPs nor reacted with chlorine residual to generate more halo-DBPs.

Fig. 1.

Fig. 1.

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Total ion intensities (TIIs) of (a) chloro-, (b) bromo- and (c) iodo-DBPs of five water samples detected by MS/MS precursor ion scans (PISs). The experimental errors of TII measurement were 1.4%−4.8% (Fig. S2–S4).

The total concentrations of halo-DBPs were decreased in boiling. The boiling process of a water sample involves heating (from room temperature to 100 °C), boiling (at 100 °C) and cooling down (from 100 °C to room temperature) (Fig. S1). Halo-DBPs continued to form during the subsequent steps from the reactions among chlorine residual, NOM, bromide and iodide in water. In addition, thermal hydrolysis, decomposition, and volatilization of generated halo-DBPs were also possible competing reactions in the system (Pan et al., 2014; Liu et al., 2015; Liu et al., 2020b). When lemon was added after boiling before cooling, i.e., the “Boiling + Lemon” sample (Fig. S1d), the continued formation of halo-DBPs was inhibited in the cooling period. Comparatively, when lemon was added before heating, i.e., the “Lemon + Boiling” sample (Fig. S1e), the elimination of formation of DBPs was achieved in the whole heating-boiling-cooling process (Table S3). This could explain that the total concentrations of chloro-, bromo- and iodo-DBPs in the three boiled water samples follow the observed order as “Boiling” ≥ “Boiling + Lemon” > “Lemon + Boiling”.

3.2. Individual halo-DBPs detected in water samples

In total, 28 halo-DBPs were detected in tap water (without boiling or lemon) and nine DBPs were confirmed with standards (Table S4). The concentrations of each DBP in different samples are compared, based on the peak areas of the corresponding ion clusters, in HPLC-MS/MS SRM chromatograms (Fig. 2). Results show that for each DBP, the concentrations in the un-boiled tap water samples with and without lemon were approximately the same, i.e., the difference was within the range of experimental error (Table S4). Results suggest that the components in lemon did not react with the detected halo-DBPs. The 28 halo-DBPs could be divided into four groups (Groups A–D in Fig. 2).

Fig. 2.

Fig. 2.

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Comparison of concentrations of the detected halo-DBPs in five water samples. The peak area of each DBP (in HPLC-MS/MS SRM chromatograms) in tap water without lemon or boiling was defined as 100%, and concentrations of the DBP in the other samples were expressed as the percentages of the peak area in the corresponding sample to the peak area in the tap water sample. The nine DBPs marked with asterisks were confirmed with standard compounds, while others were tentatively proposed.

Group A consists of 15 DBPs including all detected iodo-DBPs and halophenols. The concentrations of these DBPs follow the rank order of “Without boiling or lemon” ≈ “Lemon” > “Boiling” > “Boiling + Lemon” > “Lemon + Boiling”, consistent with the variation trends of TIIs of bromo- and iodo-DBPs. During boiling, halophenols first hydrolyzed and sequentially degraded to haloaliphatic acids (Pan et al., 2014). Group B of halo-DBPs includes five bromoaliphatic acids and chloroacetic acid. Their concentrations follow the rank order of “Boiling” > “Without boiling or lemon” ≈ “Lemon” > “Boiling + Lemon” > “Lemon + Boiling”. These six haloaliphatic acids could be the decomposition products of halophenols during boiling in the presence of chlorine residual. Increases of the five bromoaliphatic acids during boiling (without lemon) were also observed previously (Liu et al., 2015). Group C of DBPs includes dihalo-hydroxybenzaldehydes and dihaloacetic acids. Their concentrations follow the rank order of “Boiling” > “Boiling + Lemon” > “Lemon + Boiling” > “Without boiling or lemon” ≈ “Lemon”. Boiling enhanced the yields of these DBPs and the addition of lemon (before boiling) could not control the increase of their formation, indicating that chlorine residual was not a major factor for generating them. Dihaloacetic acids could be produced from the thermal decomposition of halophenols; dihalo-hydroxybenzaldehydes could be generated from the degradation of their aromatic precursors during boiling (Pan et al., 2014). Group D includes chloro-, bromo-salicylic acids and dibromoacetic acid. Their concentrations follow the rank order of “Boiling” > “Boiling + Lemon” > “Without boiling or lemon” ≈ “Lemon” ≥ “Lemon + Boiling”. Compared with Group C, boiling also enhances the formation of these three DBPs, but adding lemon before boiling effectively inhibit their formation, suggesting that these DBPs are partially generated by chlorine residual in tap water.

3.3. Comparative cytotoxicity of different water samples

Fig. 3 shows the cytotoxicity of five water samples against Caco-2 and HepG2 cells. At the same concentration factor, a water sample showing a higher viability is less cytotoxic than the sample with a lower viability. The LC50 values and cytotoxicity indexes of each water sample against Caco-2 and HepG2 cells are listed in Tables 1 and 2. The LC50 values of tap water (without boiling or lemon) against Caco-2 cells (29.6×) was lower than that against HepG2 cells (41.7×), indicating that Caco-2 cells were more sensitive than HepG2 cells to the DBP mixture extracted from tap water. The results from both cell types consistently show that the cytotoxicity indexes of five water samples followed the descending rank order of “Without boiling or lemon” ≈ “Lemon” > “Boiling” > “Boiling + Lemon” > “Lemon + Boiling”. This trend is consistent with the variations of TIIs of bromo- and iodo-DBPs in the water samples and similar to the rank order of TIIs of chloro-DBPs, except that the TII of chloro-DBPs in “Boiling” sample and the same as that in “Boiling + Lemon” sample. As toxicity indexes were correlated to TIIs of the water samples, linear and quadratic regression analyses were conducted to determine the relations of TIIs (of chloro-, bromo- and iodo-DBPs) versus toxicity indexes (against Caco-2 and HepG2 cells). As shown in Fig. 4, the toxicity indexes of five water samples were strongly positively related to the TIIs of chloro-, bromo- and iodo-DBPs, i.e., R2 was 0.857–0.927 when linear curve fitting was used (Fig. 4a–f), and R2 was 0.903–0.961 when quadratic curve fitting was used (Fig. 4g–l).

Fig. 3.

Fig. 3.

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Concentration factor‒response curves of the cytotoxicity against the human (a) intestinal Caco-2 and (b) liver HepG2 cells of five water samples. Each data point presents the average and standard deviation.

Table 1.

Induction of cytotoxicity in human intestinal Caco-2 cells by five water samples.

Water sample Concentration factor range (×-fold) LC50 (×-fold)a Cytotoxicity indexb R2 c
Without boiling or lemon 1–100 29.6±3.0 33.9±3.4 0.995
Boiling 1–120 47.8±4.1 21.0±1.8 0.996
Lemon 1–100 31.1±3.3 32.4±3.5 0.997
Boiling + Lemon 1–120 59.5±0.9 16.8±0.3 0.998
Lemon + Boiling 1–200 90.8±5.2 11.0±0.6 0.991
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a

A series of LC50 values for each sample were obtained from replicate tests using a bootstrap statistical approach developed by Wagner and Plewa (2017). The data present the average and standard deviation.

b

The cytotoxicity index was calculated as the reciprocal of the LC50 value × 1000.

c

This is the regression coefficient of the concentration factor-response curve of each water sample in Fig. 3a.

Table 2.

Induction of cytotoxicity in human liver HepG2 cells by five water samples.

Water sample Concentration factor range (×-fold) LC50 (×-fold)a Cytotoxicity indexb R2c
Without boiling or lemon 1–150 41.7±3.0 21.3±1.3 0.999
Boiling 1–200 71.2±5.5 14.1±1.1 0.999
Lemon 1–100 48.8±3.0 20.5±1.3 0.992
Boiling + Lemon 1–200 84.6±1.3 11.8±0.2 0.995
Lemon + Boiling 1–250 131.8±3.3 7.6±0.2 0.996
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a

A series of LC50 values for each sample were obtained from replicate tests using a bootstrap statistical approach developed by Wagner and Plewa (2017). The data present the average and standard deviation.

b

The cytotoxicity index was calculated as the reciprocal of the LC50 value × 1000.

c

This is the regression coefficient of the concentration factor-response curve of each water sample in Fig. 3b.

Fig. 4.

Fig. 4.

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Relationships of toxicity index and total ion intensity (TII) derived from five water samples: (a–f) linear curve fitting; (g–l) quadratic curve fitting. Charts (a–c) and (g–i) show the correlations of toxicity index against Caco-2 cells and TIIs of chloro-, bromo- and iodo-DBPs. Charts (d–f) and (j–l) show the correlations of toxicity index against HepG2 cells and TIIs of chloro-, bromo- and iodo-DBPs. The coefficients y and x in each equation indicate toxicity index and TII, respectively.

Adding lemon without boiling did not significantly change the cytotoxicity of tap water; whereas the treatments of “Boiling”, “Boiling + Lemon” and “Lemon + Boiling” decreased the cytotoxicity of tap water by 38%, 51% and 67% against Caco-2 cells, respectively, and 34%, 44% and 64% against HepG2 cells, respectively. These results indicated that adding lemon followed by boiling was the most effective way of detoxifying tap water.

4. Conclusions

Vitamin C in lemon effectively quenched the chlorine residual but could not change the concentrations of total chloro-, bromo- and iodo-DBPs in tap water. Thus, adding lemon alone could not detoxify the mixture of overall DBPs in tap water. However, lemon addition combined with boiling decreased the concentrations of overall halo-DBPs and most of the detected halo-DBPs in tap water. Compared with the practice of adding lemon to boiled tap water, adding lemon to tap water before boiling performed better in detoxifying tap water because it prevented the formation of more halo-DBPs at higher-than-room temperature during the entire heating-boiling-cooling process. This study suggests a new strategy to produce lemon water with low levels of halo-DBPs, which could also be a promising approach to lowering the adverse effects of halo-DBPs through ingestion of tap water by humans.

Supplementary Material

Supplemental materials

Highlights.

  • Adding lemon without boiling had a neligible effect on the level of overall DBPs

  • Adding lemon without boiling did not detoxify the halo-DBPs in tap water

  • Lemon combined with boiling decreased the total level of halo-DBPs in tap water

  • Boiling followed by lemon addition detoxified halo-DBPs to some extent

  • Adding lemon before boiling is a better strategy to detoxify halo-DBPs in tap water

Acknowledgements

Dr. Jiaqi Liu was supported by the U.S. National Institutes of Health institutional training grant T32 ES026568. This study was also supported by the C. Gus Glasscock, Jr. Endowed Fund for Excellence in Environmental Sciences in the College of Arts and Sciences at Baylor University. The authors thank Dr. George Cobb for the support in HPLC-MS/MS spectra analysis and Ms. Sahar Pradhan for aid in cell cultivation.

Footnotes

Appendix A. Supplementary data

Supplementary data related to this article is available free of charge via the Internet at http://www.journals.elsevier.com/chemosphere.

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