Fate of Parabens and Their Metabolites in Two Wastewater Treatment

Article pubs.acs.org/est

Fate of Parabens and Their Metabolites in Two Wastewater Treatment Plants in New York State, United States Wei Wang† and Kurunthachalam Kannan*,†,‡ †

Wadsworth Center, New York State Department of Health, and Department of Environmental Health Sciences, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201-0509, United States ‡ Biochemistry Department, Faculty of Science, Experimental Biochemistry Unit, King Fahd Medical Research Center and Bioactive Natural Products Research Group, King Abdulaziz University, Jeddah, Saudi Arabia S Supporting Information *

ABSTRACT: Little is known about the occurrence and fate of parabens and their metabolites in wastewater treatment plants (WWTPs). In this study, mass loadings, removal efficiencies, and environmental emission of six parabens, four of their metabolites (4-hydroxy benzoate, 3,4-dihydroxy benzoate, methyl-protocatechuate, and ethyl-protocatechuate) and benzoic acid were studied based on the concentrations determined in wastewater influent, primary effluent, final effluent, suspended particulate matter (SPM), and sludge collected from two WWTPs (denoted as WWTPA and WWTPB) in the Albany area of New York State. The median respective concentrations of sum of parabens (Σparabens = 6 parent compounds) and paraben-metabolites (Σmetabolites = 4 metabolites) were 73.1−158 and 5460−10,000 ng/L in influents, and 1.96−5.57 and 2060−2550 ng/L in final effluents. The concentrations of Σmetabolites were significantly higher than those of Σparabens in sludge and SPM. The removal efficiencies for parabens (89.6−99.9%) were higher than those for their metabolites (25.9−90.6%). The respective mass loadings of parabens and their metabolites were 46.3 and 6210 mg/d/1000 people for WWTPA and 176 and 63,100 mg/d/1000 people for WWTPB. The environmental emission of parabens and their metabolites through WWTP discharges was 4.85−6.16 and 1270−2050 mg/d/1000 people, respectively.

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INTRODUCTION Parabens, the esters of 4-hydroxybenzoic acid, are extensively used as antimicrobial preservatives in cosmetics, food packaging, and pharmaceuticals.1 Parabens are also used in products such as cigarettes, varnishes, glues, animal feed, and healthcare products.2 Exposure of humans to parabens has been associated with adverse health outcomes,3 as methyl- (MeP), ethyl- (EtP), propyl- (PrP), butyl- (BuP), and benzyl-parabens (BzP) possess estrogenic properties.4 Removal of the ester group from a paraben moiety does not eliminate its estrogenic effects. Both in vitro and in vivo studies have shown that the common metabolite of parabens, 4-hydroxybenzoic acid (4-HB), is estrogenic.5 In addition, hydroxylation of 4-HB to 3,4dihydroxybenzoic acid (3,4-DHB) has been reported in studies of laboratory animals.6,7 Similarly, benzoic acid is used as a preservative in cosmetics and pharmaceuticals.8 4-HB can be formed from benzoic acid by abiotic transformation,9 and is recognized as a nonspecific marker of parabens.10 Methyl protocatechuate (OH-MeP) and ethyl protocatechuate (OHEtP) can be formed via hydroxylation of corresponding parabens, a common mechanism of transformation of many xenobiotics.11 Parabens and their metabolites, including OHMeP, OH-EtP, 4-HB, and 3,4-DHB are excreted in urine and © XXXX American Chemical Society

eventually go down the drain to wastewater treatment plants (WWTPs). Two earlier studies have reported the occurrence of parabens in WWTPs.3,12 These studies, however, were focused on the formation of halogenated products of parabens in WWTPs rather than the removal and fate of these estrogenic chemicals. Further, none of the earlier studies determined 3,4-DHB, OHMeP, OH-EtP and benzoic acid, which are the major metabolites of parabens, in aquatic environments. The primary goal of this study was to determine the mass loading and fate of parabens and their metabolites in WWTPs. Loadings, removal efficiencies, and environmental emission of parabens and their metabolites were determined based on the concentrations measured in influent, primary effluent, final effluent, suspended particulate matter (SPM), and sewage sludge collected from two WWTPs in the Albany area of New York State. This is the first study to describe the fate of parabens and their metabolites, including benzoic acid, OH-MeP, OH-EtP, and Received: November 10, 2015 Revised: December 22, 2015 Accepted: January 4, 2016

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DOI: 10.1021/acs.est.5b05516 Environ. Sci. Technol. XXXX, XXX, XXX−XXX

Article

Environmental Science & Technology

Sludge samples were extracted by solid−liquid extraction and then by a SPE method. Briefly, ∼0.1 g of freeze-dried sludge was spiked with a mixture of internal standards (20 ng) prior to extraction. Sludge samples were vortex-mixed for 1 min and extracted with 5 mL of methanol/water mixture (5:3 V/V) by shaking in an orbital shaker for 60 min. Extracts were centrifuged at 4500g for 5 min (Eppendorf Centrifuge 5804; Hamburg, Germany), supernatant was collected in a polypropylene (PP) tube, and the extraction was repeated twice. The supernatants were combined and concentrated to ∼3 mL under a gentle stream of nitrogen and then diluted to 10 mL with Milli-Q water that contained 0.2% formic acid (pH 2.5). The extract was purified by passage through SPE cartridges, as described above. For SPM, the entire content in the preweighed glass fiber filter (obtained from centrifugation and filtration of 100 mL of influents, primary effluents, and final effluents) was transferred into a preweighed PP tube, freezedried, spiked with the internal standards, and extracted as described above for sludge samples. The final volume of the extract was 1 mL, and 10 μL of the extract was injected into a high-performance liquid chromatograph-tandem mass spectrometer (HPLC−MS/MS). Instrumental Analyses. The target analytes were determined with an Agilent 1260 HPLC (Agilent Technologies, Inc., Santa Clara, CA) interfaced with an Applied Biosystems QTRAP 4500 mass spectrometer (ESI-MS/MS; Applied Biosystems, Foster City, CA). An analytical column (Pinnacle DBAQ C18 1.9 μm, 50 mm × 2.1 mm column; Restek Corporation, Bellefonte, PA), connected to a Javelin guard column (Betasil C18, 20 mm × 2.1 mm) was used for chromatographic separation. The negative ion multiple reaction-monitoring (MRM) mode was used. The mobile phase comprised 100% methanol (A) and Milli-Q water that contained 0.1% formic acid (B). The MS/MS parameters were optimized by infusion of individual compounds into the MS through a flow injection system (Table S3). The MRM transitions of ions monitored are listed in Table S4. Nitrogen was used as both a curtain and a collision gas. Quality Assurance and Quality Control (QA/QC). Contamination that arose from laboratory materials and solvents was evaluated by the analysis of procedural blanks. Trace levels of MeP, EtP, PrP, BuP, OH−MeP, and 4-HB were found in procedural blanks, ranging in concentrations from 0.02 ± 0.005 ng/mL for OH−MeP to 0.81 ± 0.53 ng/mL for 4-HB. A background subtraction (average value) was performed for the quantification of concentrations of compounds that were present in blanks. With each set of 20 samples analyzed, a procedural blank, a spiked blank, two pairs of matrix spiked samples (spiked at 20 ng and 40 ng for parabens and 1000 and 2000 ng for 4-HB and benzoic acid) and one duplicate sample were analyzed. Quantification of parabens was performed by an isotope-dilution method, based on the response of 13C12-MeP (for OH-MeP and MeP), 13C12-EtP (for EtP and OH-EtP), 13 C12-PrP (for PrP), 13C12-BuP (for BuP), 13C12-BzP (for BzP), 13 C12-HepP (for HepP), and 13C12-4-HB (for 4-HB and 3,4DHB), except for benzoic acid. Benzoic acid was quantified by an external calibration method, and the recovery of this compound through the analytical procedures was between 87% and 105% (calculated from matrix spiked samples). Instrumental calibration was verified by the injection of 10 calibration standards, ranging in concentrations from 0.01 to 100 ng/mL for parabens, from 0.01 to 1000 ng/mL for 4-HB, and from 0.01 to 100 μg/mL for benzoic acid, and the regression

3,4-DHB, in both solid and aqueous fractions of wastewater. The fraction of each of the parabens sorbed to SPM was calculated for the estimation of mass loadings and environmental emissions. The relationship and composition ratios of parabens and their metabolites through the wastewater treatment processes also were evaluated.

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MATERIALS AND METHODS Chemicals and Reagents. Formic acid (98.2%) was purchased from Sigma-Aldrich (St. Louis, MO), and methanol (HPLC grade) was purchased from Mallinckrodt Baker (Phillipsburg, NJ). Milli-Q water was prepared by an ultrapure water system (Barnstead International; Dubuque, IA). 4-HB and n-isomers of MeP, EtP, PrP, BuP, BzP, and HepP were purchased from AccuStandard, Inc. (New Haven, CT). OHMeP, OH-EtP, and 3,4-DHB were purchased from SigmaAldrich (St. Louis, MO). The chemical structures of parabens analyzed in this study are shown in the Supporting Information Table S1. 13C12-MeP, 13C12-EtP, 13C12-PrP, 13C12-BuP, 13C12BzP, 13C12-HepP and 13C12-4-HB were purchased from Cambridge Isotope Laboratories (Andover, MA). The working standards were prepared by serial dilution of stock solutions with methanol prior to use. Sample Collection and Preparation. Detailed information regarding the sample collection from two WWTPs is provided in Table S2. Briefly, 24-h composite wastewater samples, including raw wastewater (influent), primary-treated wastewater (primary effluent), final effluent, and sludge were collected consecutively over a seven-day period, from July 12 to 18, 2013, from two WWTPs in the Albany area of New York State. Composite sampling consists of a collection of numerous individual discrete samples taken at regular intervals over the sampling period of 24 h to represent the average performance, with collected samples refrigerated until transport. The two plants are denoted as WWTPA (population served ∼15 000) and WWTPB (population served ∼100 000), which had treatment capacities of 9.5 and 132 million liters daily (MLD), respectively. Both WWTPs used activated sludge treatment including aeration tanks and biological processes. The activated sludge (3.9% solid, determined gravimetrically) samples (combined sludge produced after primary and secondary treatments) were collected for seven consecutive days from WWTPA and four consecutive days from WWTPB. All samples were collected in certified precleaned (with solvents) amber glass jars with Teflon-faced caps, shipped to the laboratory, and stored in a refrigerator at 4 °C until extraction. The hydraulic retention times at these WWTPs were between 12 and 16 h. The wastewater samples (100 mL) were centrifuged at 5000g for 10 min, and the supernatant was filtered through a glass fiber filter (37 mm, pore size 1 μm; GE Osmonics, Inc., Minnetonka, MN) to separate SPM. Wastewater samples (100 mL) were spiked with a mixture of labeled internal standards of the target compounds (20 ng) prior to extraction. The aqueous samples were extracted by passage through Oasis MCX 3 cm3 (60 mg; Waters, Milford, MA) solid-phase extraction (SPE) cartridges. Prior to use, the cartridges were conditioned with 5 mL of methanol and 5 mL of Milli-Q water, and wastewater samples were loaded at ∼1 mL/min. Cartridges were allowed to dry for ∼30 min under vacuum and then eluted with 9 mL of methanol. The eluents were combined and concentrated to 1 mL under a gentle stream of nitrogen using a TurboVap Evaporator (Zymark, Inc., Hopkinton, MA). B


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Table 1. Concentrations of Parabens and Their Metabolites in Wastewater (Aqueous/Dissolved Fraction) and Sludge from Two Centralized Wastewater Treatment Plants in Albany Area, New York, USA, in July 2013a water (ng/L)

sludge (ng/g dry wt)

WWTPA influent

primary effluent

WWTPB final effluent

influent

0.14/0 0.14−0.14 0.30/71.4 0.14−1.47 1.16/71.4 0.36−4.90 0.61/71.4 0.36−3.55 0.071/14.3 0.071−0.34 0.071/28.6 0.071−0.62 19.1/100 8.60−215 7.33/85.7 0.36−25 1780/100 555−5530 265/100 109−1550 71.0/0 71.0−71.0 5.57/ 1.37−7.93 2060/ 729−7290

97.9/100 18.3−320 2.75/100 0.50−66.8 20.9/100 8.19−42.3 7.25/100 3.46−112 0.071/28.6 0.071−0.27 0.071/28.6 0.071−0.17 66.0/100 28.7−102 32.0/71.4 0.36−176 5280/100 3890−293000 720/100 43.8−2270 71.0/0 71−71 158/ 30.6−471 5460/ 4370−295000

median/df range MeP EtP PrP BuP BzP HepP OH-MeP OH-EtP 4-HB 3,4-DHB benzoic acid Σparabens Σmetabolites a

36.8/100 21.7−56.4 4.00/100 2.17−8.4 12.9/100 9.69−113 5.80/100 3.15−21.4 0.071/42.9 0.071−0.22 0.11/57.1 0.071−0.31 128/100 12.7−346 78.2/71.4 0.36−340 8820/100 1460−41100 1010/100 220−1960 71.0/0 71.0−71.0 73.1/ 52.4−161 10000/ 1760−43300

0.14/28.6 0.14−9.38 0.54/71.4 0.14−11.2 2.12/71.4 0.36−120 0.58/71.4 0.36−6.66 0.071/0 0.071−0.071 0.071/28.6 0.071−0.12 82.9/100 21.9−478 6.87/57.1 0.36−156 4397/100 1110−5760 556/100 202−3170 71.0/0 71.0−71.0 3.51/ 1.14−145 4950/ 1340−9450

primary effluent

final effluent

WWTPA

0.14/28.6 0.14−1.73 0.14/14.3 0.14−0.29 0.51/71.4 0.14−1.10 0.14/42.9 0.14−0.76 0.071/14.3 0.071−0.27 0.071/14.3 0.071−0.11 35.6/100 9.01−84.5 23.7/71.4 0.36−39.6 2080/100 633−4040 232/100 107−427 71.0/42.9 71−133 1.96/ 1.08−2.70 2550/ 848−4590

41.6/100 35.3−68.8 2.54/100 1.74−4.80 1.38/100 0.60−2.62 0.57/66.7 0.36−2.63 0.071/0 ND 0.071/16.7 0.071−0.12 67.9/100 49.7−80.3 0.36/16.7 0.36−8.18 1020/100 125−1300 189/100 101−255 2920/100 1730−4170 46.0/ 38.9−78.9 1260/ 331−1610

median/df range 0.14/33 0.14−7.68 0.21/50 0.14−1.57 0.44/50 0.36−0.87 0.55/50 0.36−2.61 0.071/0 ND 0.071/0 ND 14.3/100 1.53−56.9 10.4/67 0.36−32.9 1530/100 253−4670 192/100 54.2−338 71.0/0 71−71 2.47/ 1.14−8.85 1690/ 626−4870

WWTPB

median/df range 58.5/100 24.3−87.4 5.13/100 1.6−12.0 2.93/66.7 0.36−4.64 11.2/100 0.55−19.0 0.071/0 ND 0.15/66.7 0.071−0.17 14.6/100 5.55−20.0 0.36/33.3 0.36−0.55 1870/100 1450−3820 79.4/100 72.3−294 4690/100 3360−35500 94.3/ 27.0−107 1960/ 1550−4120

Notation: df = detection frequency; ND = not detected.

coefficient (R) of all calibration curves was >0.99. Recoveries of parabens in spiked matrices ranged from 52 ± 16% for OHMeP to 109 ± 9.5% for BzP in sludge and SPM samples, and from 70.3 ± 12.8% for OH-EtP to 105 ± 14.7% for 4-HB in the aqueous (i.e., dissolved phase) fraction (Table S4). Duplicate analysis of randomly selected samples yielded a coefficient variation (CV) of OH-MeP (2.17%) > OH-EtP (1.29%) > 4-HB (0.42%), which is possibly related to the solubility of chemicals. These values were not calculated for EtP, BuP, PrP, BzP, or HepP because of their low detection rates in both wastewater and SPM. The high proportion of benzoic acid in SPM can be attributed to its low water solubility (2493 mg/L) and high sorption potential, whereas the low proportion of OH-MeP, OH-EtP, and 4-HB in SPM can be explained by their high water solubility (OH-MeP 43 300 mg/L; OH-EtP 14 120 mg/L; 4-HB 14 500 mg/L). Further, MeP, OH-MeP, OH-EtP, 4-HB, and 3,4-DHB were

Figure 1. Mean concentrations of parabens and their metabolites in sewage sludge samples collected from WWTPs in the USA, compared with those reported in other countries.21−23

information is available on the treatment processes used in these countries. No earlier studies have reported OH-MeP, OH-EtP, 3,4-HB, and benzoic acid in sludge samples. It is worth noting that significantly higher concentrations of paraben metabolites (median, 1260, 331−1610 ng/g, dry wt, in WWTPA; and median, 1960, 1550−4120 ng/g, dry wt, in WWTPB) than parent parabens (median, 46.0, 38.9−78.9 ng/g, dry wt, for WWTPA; and median, 94.3, 27.0−107 ng/g, dry wt, for WWTPB) were found in sludge, although 4-HB can be derived from sources other than paraben degradation/ metabolism. Disposal of sludge onto land can be a source of contamination by parabens and their metabolites. Parabens and Their Metabolites in Suspended Particulate Matter. This is the first report of the occurrence of four paraben metabolites and benzoic acid in SPM. MeP was

Table 2. Mass Loading, Environmental Emission, and Removal Efficiency of Parabens and Their Metabolites in Two WWTPs from New York State, USAa mass load (mg/d/1000 people)

emission via WWTPs (mg/d/1000 people)

analyte

WWTPA

WWTPB

WWTPA

WWTPB

MeP EtP PrP BuP BzP HepP OH-MeP OH-EtP 4-HB 3,4-DHB benzoic acid Σparabens Σmetabolites

20.0 2.05 14.3 4.30 0.09 5.59 77.1 50.4 5570 508 101 46.3 6210

113 16.5 17.9 28.2 0.15 0.14 55.1 45.7 62100 839 275 176 63100

1.83 0.35 1.24 1.24 0.08 0.11 23.0 4.43 1040 204 145 4.85 1270

3.71 0.32 0.98 0.91 0.12 0.12 24.6 17.6 1810 192 273 6.16 2050

average % removal Ib WWTPA 99.6 92.6 91.0 89.6 NC NC 85.0 90.6 79.8 73.8 NC

± ± ± ±

0.13 10.6 4.96 12.5

± ± ± ±

16.7 14.0 11.2 10.1

average % removal IIc

WWTPB 99.9 94.8 97.6 98.0 NC NC 46.1 25.9 60.6 67.8 NC

± ± ± ±

1.45 12.8 2.18 2.41

± ± ± ±

17.7 19.4 23.4 3.65

WWTPA 95.8 89.8 88.5 70.8 NC NC 61.4 67.5 71.0 68.9 NC

± ± ± ±

7.78 10.9 7.66 15.7

± ± ± ±

18.9 17.2 36.3 33.0

WWTPB 95.2 90.1 95.0 91.1 NC NC 45.8 78.5 56.4 82.7 NC

± ± ± ±

5.81 18.0 2.62 4.86

± ± ± ±

15.3 18.1 33.8 29.3

a

Notation: NC: not calculated. Because of the low detection rates for BzP, HepP, and benzoic acid in wastewater and low detection rates for EtP, PrP, BuP, BzP, HepP, in particulate samples, the removal rate was not calculated. bRemoval efficiency was calculated based on the concentrations of parabens and their metabolites determined in influent and effluent water (aqueous fraction). cRemoval efficiency calculated based on the parabens and metabolites determined in influent water, effluent water, and the fraction determined in SPM. E


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Figure 2. Contribution (%) of individual parabens to total concentrations (sum of six parent and four metabolite concentrations) determined in wastewater (influent, primary effluent, and final effluent), SPM (influent-P, primary effluent-P, and final effluent-P) and sludge samples from two WWTPs.

of paraben-metabolites in both WWTPs were >500 times higher than those of the parent parabens, which suggested that these metabolites originate from other sources in addition to transformation of parabens. For instance, 4-HB can be derived from commercial products that contain benzoic acid as well as in naturally occurring plant products (e.g., wine, tea). Elevated 4-HB concentrations in WWTPB, which treats effluents from a larger population, suggest sources from direct human excretion of 4-HB. The average mass loadings of 3,4-DHB and benzoic acid were 1.5 times higher in WWTPB (839 and 275 mg/d/ 1000 people) than in WWTPA (508 and 101 mg/d/1000 people). The mean mass loadings of MeP and BuP were 6 times higher in WWTPB (113 and 28.2 mg/day/1000 people) than in WWTPA (20.0 and 4.30 mg/day/1000 people). The differences in mass loadings between the two plants can be related to specific sources, especially sources originating from direct human excretion (WWTPB treats wastewater for 6-times greater population than WWTPA). The mass loadings of parent parabens in WWTPs were similar to those reported in Denmark (2750 mg/d/1000 people) (Figure S1) but lower than those reported in France (30400 mg/day/1000 people),26,27 although SPM was not analyzed in studies from Denmark and France. However, this is the first study to report the mass loading of parabens and their metabolites in the United States. Environmental Emission of Parabens and Their Metabolites through WWTP Discharges. The total mass of parabens and their metabolites discharged through WWTP final effluents and sewage sludge was calculated on the basis of the concentrations measured in final effluents, the fraction of analytes found in SPM and activated sludge, by the daily flow of effluents, total sludge production rate, and the population served by the WWTPs. The emission of 4-HB was the highest in WWTPA and WWTPB, respectively (1040 and 1810 mg/ day/1000 people) which was followed by 3,4-DHB (204 and 192 mg/day/1000 people) and benzoic acid (145 and 273 mg/ day/1000 people) (Table 2). The respective emission rates of OH−MeP for two WWTPs were 23.0 and 24.6, and those for OH-EtP were 4.43 and 17.6 mg/d/1000 people. Although there is a considerable removal of 4-HB and 3,4-DHB, 269− 2689 and 60.0−730 mg/d/1000 people, respectively, were released into the environment through the final effluent and sewage sludge disposal. MeP emission rates from WWTPs were

found to sorb to SPM at proportions as high as 21.9%, 15.4%, 13.8%, 3.48%, and 35.9% of the total mass found in influents, respectively. Therefore, estimation of mass loadings of parabens and metabolites based only on the analysis of dissolved fractions of wastewater can significantly underestimate the total loadings by as much as 36%. In contrast, >96% of the loadings of 4-HB were found in the aqueous fraction. Removal of Parabens and Their Metabolites in WWTPs. Little is known about the fate of parabens and their metabolites in WWTPs. Because of their moderate hydrophobicity and their ability to sorb to organic fractions, parabens were reported to partition to particulate fractions.21,25 On the basis of the concentrations of parabens and their metabolites measured in influents and final effluents, the removal efficiencies were calculated; it was found that 73.8% to 99.6% of parabens were removed in WWTPA and 25.9% to 99.9% in WWTPB (Table 2). The average removal efficiency of parent parabens (89.6−99.6% in WWTPA and 94.8−99.9% in WWTPB) was similar to that reported as >90% in other studies.2 The removal efficiencies of four paraben metabolites in WWTPs, ranged from 73.8% (3,4-DHB) to 90.6% (OHEtP) in WWTPA and 25.9% (OH-EtP) to 67.8% (3,4-DHB) in WWTPB, respectively. BzP and HepP were not significantly removed from WWTPs (0 to 34.5%), which might be an artifact of the low detection rates of these two compounds in influents. However, by taking into account the fraction of parabens and their metabolites determined in SPM, the removal efficiency was calculated at 95.5% for MeP, 90.0% for EtP, 91.8% for PrP, 89.8% for BuP, 75.8% for 3,4-DHB, 73.0% for OH-EtP, 63.5% for 4-HB, and 50.4% for OH−MeP. Mass Loadings of Parabens in WWTPs. The total mass of parabens and their metabolites discharged into WWTPs was estimated based on the measured concentrations in influents, daily flow rate of wastewater, and the population served by the WWTPs. The total loadings of parabens and their metabolites in WWTPA (6210 mg/d/1000 people), which serves a smaller population (∼15 000 people), were 10 times lower than those calculated for WWTPB (63100 mg/d/1000 people) (Table 2), which served a larger population (∼100 000 people). However, the median mass loadings of six parent parabens were 46.3 and 176 mg/d/1000 people for WWTPA and WWTPB, respectively, which suggested that the majority of the variation in loading originated from the metabolites of parabens. The mass loadings F


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more, considering the bioaccumulation and toxic potential of these metabolites in aquatic organisms, further studies are needed to assess the environmental fate of these metabolites. In summary, mass loadings, removal efficiencies, and environmental emission were correlated and compared between parent parabens and their metabolites in two WWTPs in the Albany area of New York State. Parent parabens were significantly removed from WWTPs; however, relatively lower removal efficiencies were found for paraben metabolites. The median daily loadings of paraben metabolites were 100−400 times higher than those of parent parabens; consequently, the discharge rates of paraben metabolites through WWTPs were 300 times higher than the parent parabens. The discharge of 4-HB was found to be the highest among the compounds analyzed (1037; 1811 mg/day/1000 people). A significant increase in the ratio of metabolites to parent parabens was found in the mass flow, which indicated degradation of parabens to metabolites. Between 92% and 98% of parabens and 53% and 79% of paraben metabolites were lost or transformed in the wastewater treatment process, and sorption to sludge accounted for a minor proportion. The environmental emission for paraben metabolites (1270−2050 mg/d/1000 people) was higher than for parent parabens (4.85−6.16 mg/d/1000 people). This is the first study to report the fate and transport of four paraben metabolites in domestic WWTPs. A greater mass loading and a low removal rate were found for the metabolites of parabens in WWTPs.

1.83 and 3.71 mg/day/1000 people for WWTPA and WWTPB, respectively. The high emission rates of paraben metabolites (1270−2050 mg/d/1000 people) warrant further studies due to their potential aquatic toxicity.28 Fate of Parabens and Their Metabolites in the WWTP Processes. The composition profiles of parabens and their metabolites from various steps in wastewater treatment processes are presented in Figure 2. Paraben-metabolites are the largest contributors to total paraben load in influent, primary effluent, final effluent, SPM, and sludge from both WWTPs. Specifically, 4-HB was the predominant compound in both wastewater (>85%) and sludge (>77%), whereas 4-HB and 3,4 DHB collectively accounted for >75% of the total paraben plus paraben-metabolites load in SPMs. The contribution of metabolites to total paraben plus parabenmetabolites load ranged from 97.9 to 99.9% among influent, primary influent, and final effluent in wastewater samples from both WWTPs, whereas in the SPM, the contribution decreased in the following order: influent (95.2−97.8%) > primary influent (84.0−92.6%) > final effluent (81.4−91.3%). On the basis of the daily mass flows of parabens and their metabolites, a significant proportion of parabens was found lost in WWTPs (Figure S2). The mass out was estimated as 0.04− 0.21 g/day for parent parabens and 14.2−213 g/day for metabolites, which were 1.57−8.03% and 20.6−46.8%, respectively, of parent parabens and their metabolites estimated to enter the plants (i.e., mass in). The removal mechanisms of parabens and their metabolites in WWTPs are expected to vary, depending on the chemical structure, sorption, treatment methods, and season, among other factors. The ratio of metabolites to parent parabens increased from 136 in mass in to 350 in mass out for WWTPA, whereas that for WWTPB increased from 34.4 to 1030, which suggested that parabens are transformed to metabolites during WWTP processes, and the metabolites are resistant to further degradation. The higher ratios found in WWTPA influent and in WWTPB final effluent suggested multiple sources (∼5% industrial waste for WWTPA and ∼25% for WWTPB) of target chemicals and transformations during WWTP processes. The ratio of metabolites to parent paraben concentration was lower in sludge from the two WWTPs studied (27.5 for WWTPA and 20.8 for WWTPB). Further investigation is needed to identify and/or quantify the transformation byproducts (e.g., chlorinated derivatives) of parabens and their metabolites during wastewater treatments. Although this is the first study to report the fate of parabens and their metabolites in wastewater, SPM, and sludge, our study has some limitations. First, the samples were analyzed several weeks/months after the collection. Although samples were stored at 4 °C until analysis, potential degradation of target chemicals during storage is not known. Second, some metabolites such as 4-HB, have sources other than the metabolism of parabens. 4-HB is present in some plant products and can be released directly into WWTPs through human excretion. Thus, the mass loading estimates for the metabolites are confounded by the existence of multiple sources of origin. However, it should be noted that the validity of our results is not affected by the lack of that information pertaining to sources, and the high loads and emissions of such compounds are of significant interest for future studies. The low removal rates and large emission rates of parabenmetabolites suggest that they are discharged into surface waters in large amounts and can play a role in antimicrobial resistance in WWTPs (due to their antimicrobial properties). Further-

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.5b05516. Additional information as noted in the text includes details of analytical methods, information regarding target chemicals and structures (Table S1), information regarding WWTPs (Table S2), HPLC−MS/MS parameters used in the analysis (Table S3) and summary statistics for MRM, LOQs, and recoveries of target chemicals through the analytical method (Table S4). Chart of mass loadings, mass flows, and metabolites ratio plot for parabens and their metabolites in WWTP processes (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Phone: +1 518 474 0015; fax: +1 518-473- 2895; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to thank the WWTP facilities and Mr. Jingchuan Xue for assistance with the sample collection.

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REFERENCES

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Fate of Parabens and Their Metabolites in Two Wastewater Treatment

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