Article pubs.acs.org/est
First Report of a Chinese PFOS Alternative Overlooked for 30 Years: Its Toxicity, Persistence, and Presence in the Environment Siwen Wang,† Jun Huang,*,† Yang Yang,† Yamei Hui,† Yuxi Ge,† Thorjørn Larssen,‡ Gang Yu,† Shubo Deng,† Bin Wang,† and Christopher Harman‡ †
State Key Joint Laboratory of Environment Simulation and Pollution Control (SKJLESPC), School of Environment, POPs Research Centre, Tsinghua University, Beijing 100084, P.R. China ‡ Norwegian Institute for Water Research (NIVA), Gaustadalléen 21, NO-0349 Oslo, Norway S Supporting Information *
ABSTRACT: This is the first report on the environmental occurrence of a chlorinated polyfluorinated ether sulfonate (locally called F-53B, C8ClF16O4SK). It has been widely applied as a mist suppressant by the chrome plating industry in China for decades but has evaded the attention of environmental research and regulation. In this study, F-53B was found in high concentrations (43−78 and 65−112 μg/L for the effluent and influent, respectively) in wastewater from the chrome plating industry in the city of Wenzhou, China. F-53B was not successfully removed by the wastewater treatments in place. Consequently, it was detected in surface water that receives the treated wastewater at similar levels to PFOS (ca. 10−50 ng/L) and the concentration decreased with the increasing distance from the wastewater discharge point along the river. Initial data presented here suggest that F-53B is moderately toxic (Zebrafish LC50-96 h 15.5 mg/L) and is as resistant to degradation as PFOS. While current usage is limited to the chrome plating industry, the increasing demand for PFOS alternatives in other sectors may result in expanded usage. Collectively, the results of this work call for future assessments on the effects of this overlooked contaminant and its presence and fate in the environment.
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INTRODUCTION The electroplating industry in China is well developed, with an estimated >15 000 factories, >500 000 employees, >5000 production lines and a production capacity of >300 million m2. A recent survey by a China market research center revealed the total industrial output value to be almost 13 000 million USD in 2008.1 During the electroplating process, especially in “hard chrome plating”, mist suppressants are indispensable for the protection of employees from exposure to the airborne, highly toxic forms of chromium. The most commonly used mist suppressants are based on perfluorooctane sulfonate acid and its salts (PFOS, C8F17SO3−). For example, the United Nations Industrial Development Organization (UNIDO) estimated that up to 10 000 kg/yr of PFOS-containing mist suppressants were being used for this purpose in Europe in 2004.2 Similarly, among the three major mist suppressants used in the Chinese market (Table 1), two of them are PFOS salts. According to the Chinese Electroplating Association, the estimated annual consumption of PFOS in China for electroplating was 30−40 t in 2007,3 which appears to be stable in recent years.4 Perfluoroalkyl ether potassium sulfonate (F-53, C8F17O4SK) was first developed as a mist suppressant for the hard chrome plating industry, by the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences in 1975.5 After successful demonstrations in four local electroplating plants in Shanghai, F-53 was found to be excellent in performance but © 2013 American Chemical Society
high in synthesis cost. F-53B is the modified version of F-53, with the replacement of one fluorine atom by a chlorine (Table 1). This modification was made to simplify the production process (see Supporting Information Figure S1), reduce the cost where chlorination is used in the last step, and prevent the use of toxic and expensive chemicals (e.g., SbCl5 and SbF3). Therefore, the commercialized product was F-53B instead of F53. For several years, this compound had remained as the only available mist suppressant in the Chinese electroplating industry, until the emergence of FC-80 (C8F17O3SK) in 1982, and FC-248 (C16H20F17O3NS) later,6 which are actually both PFOS with different counterions (see Table 1). Chrome plating is not the only industry that has made use of the special properties of PFOS (and similar compounds), and it has been extensively used in hundreds of manufacturing and industrial applications including the textile, electronic, automotive, construction and chemical processing sectors. This has resulted in significant emissions, and subsequently the discovery that it was ubiquitously present in the environment,7−11 which in turn led to concerns regarding the consequences.12 Thus PFOS has received considerable attention from environmental scientists and has been shown Received: Revised: Accepted: Published: 10163
March 4, 2013 August 7, 2013 August 16, 2013 August 16, 2013 dx.doi.org/10.1021/es401525n | Environ. Sci. Technol. 2013, 47, 10163−10170
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Table 1. Main Mist Suppressants on the Chinese Market
persistence of F-53B. To our knowledge, this is the first environmental study of F-53B after its original synthesis.5
to possess both persistent, bioaccumulative13−15 and moderately toxic16 (PBT) properties and the potential for long-range transport.17 Collectively, these issues led to a voluntary phasing out of PFOS by the primary manufacturer in Western countries in 2002, a consequent steep decline in production in those regions,18 and international controls such as inclusion in the Stockholm Convention.19 Conversely, in China, both emission inventories20 and concentrations in biota including humans21 suggested increases over the same period. Thus, as one of the only places where PFOS is still being manufactured, there has been growing pressure on China to reduce production, which appears to have peaked in 2006.4 Due to this reason, F-53B as a PFOS alternative may be expected to obtain a larger market share and potentially expand from being solely used by the metal plating industry to other industries that currently use PFOS. There is ample evidence that PFOS is environmentally persistent, bioaccumulative, and toxic to human and animals.7−16 The similarity in chemical structures between F53B and PFOS makes it reasonable to assume that they possess similar physicochemical properties and environmental behavior. However, data are lacking, with no information available on the environmental presence and potential impact of F-53B. Thus the aims of the present study were (1) to establish an analytical method for the simultaneous determination of F-53B and PFOS in wastewater including optimization of key extraction and analysis parameters; (2) to measure the concentrations of F-53B and PFOS at a wastewater treatment plant (WWTP) dedicated to an electroplating industrial park, and in receiving surface water in Southeast China; and (3) to conduct an initial assessment on the toxicity and environmental
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MATERIALS AND METHODS Chemicals. F-53B (Lot No. 20100605) was obtained from Shanghai Synica Co., Ltd. (Shanghai, China), with a purity of >98%. Potassium L-PFOS and 13C4- and 13C8-labeled L-PFOS, as recovery and injection standards (RS and IS), respectively, were purchased from Wellington Laboratories Inc. (ON, Canada). Solvents were HPLC grade (J.T. Baker, NJ), and ultrapure water was used (18 MΩ·cm, Millipore, MA). Hydrogen peroxide solution (H2O2, 30%) and ferrous sulfate heptahydrate (FeSO4·7H2O, >99% in purity) were purchased from Beijing Modern Eastern Fine-Chemical Company (Beijing, China). Acute Toxicity Test. Toxicity tests were carried out at the Key Laboratory of Ecological Effect and Risk Assessment of Chemicals, the Chinese Research Academy of Environmental Sciences, in Beijing. Fish acute toxicity was tested according to Organisation for Economic Cooperation and Development (OECD) Guideline 203,22 using zebrafish (Brachydanio rerio) as the test species. The information on estimated physicochemical properties of the test substance F-53B are presented in Supporting Information Table S3, including water solubility, logKow, pKa and vapor pressure. Exposure water had a hardness between 180 and 220 mg/L CaCO3, the pH ranged 6.7−7.5, the temperature was maintained at 23 ± 1 °C, the photoperiod was 12:12 h light:dark, and the measured dissolved oxygen (DO) was between 7.0 and 8.6 mg/L. The water was aerated for 48 h prior to the start of the test. The fish were obtained from a local market and were approximately 3 months old and 2.2 cm long. They were acclimatized for 7 days 10164
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(i) UV photodegradation: F-53B water solution was added into the reactor chamber and irradiated with a high pressure mercury lamp (220 V, 300 W) in the XPA-2 photochemical reactor (Nanjing Xujiang Electromechanic Plant, Nanjing, China). (ii) UV/H2O2 oxidation: 4.0 mL of 30% H2O2 was added into the reaction system of (i). (iii) O3 oxidation: the dosage of O3 was 3.0 g/h; and the pH of solution was 11, using the reaction system of (i). (iv) O3/H2O2 oxidation: 4.0 mL of 30% H2O2 was added into the reaction system of (iii). (v) Fenton oxidation: 250 mg/L FeSO4, 30% H2O2, pH = 3. Water Sampling and Sample Preparation. WWTPs have been considered as one of the major point source of PFOS into the aquatic environment 27,28 which includes the degradation of precursor compounds during the treatment process. This may also be the case for F-53B considering its similar application in the electroplating industry. Therefore surface water samples (5 L for each sampling point) were taken from the Oujiang River, at Wenzhou city, China (Figure 1), in
prior to testing and fed three times a week until 24 h before the test was started. Seven fish were placed in each 2 L test beaker, filled with 1500 mL of the exposure solution. Exposure water was renewed after 48 h. Seven zebrafish were randomly assigned as a control (0 mg/L) in the same exposure water. On the basis of the preliminary test results, seven nominal concentrations (1; 1.7; 2.89; 4.91; 8.35; 14.26; 24.14 mg/L) of F-53B were used, each set up in triplicate. The concentration in test water was measured at >80% of each nominal concentration before it used. Water concentrations of F-53B in the beakers with the lowest (1 mg/L) and highest (24.14 mg/L) concentrations were measured daily during this test. The median lethal dose (LC50) was calculated by sigmoidal three-parameter regression (eq 1) a y= x − x0 (1) 1 + e −( b ) where x is logarithm concentration; y is percentage mortality; and a,b,x0 are coefficients of the regression equation. Degradability Tests. Laboratory tests of “ready biodegradability” have been used as conservative surrogates for the assessment of biodegradation in actual or simulated environmental matrices, which can indicate the propensity for a chemical to be degraded in the aquatic environment.23 Amid them, the Closed Bottle Test (CBT, OECD 301D)24 is recommended as a first, simple test for the assessment of the biodegradability of organic compounds in the environment.25 The degradation process of the test substance is tracked by analysis of DO in a mineral medium inoculated with microorganisms from a mixed population. The CBT was carried out for 28 d using 250 mL sealed bottles, which were incubated in the dark at 20 ± 1 °C. The inoculum sample was obtained from a sewage treatment facility after secondary treatment in November 2012. This sample was settled for 1 h before the supernatant was taken and subsequently aerated for 5 d before use. The nutrient medium used ultrapure water, containing no metals above recommended levels and was made up using concentrations of mineral salts (8.5 mg/L KH2PO4, 21.75 mg/ L K2HPO4, 33.40 mg/L Na2HPO4·2H2O, 0.5 mg/L NH4Cl, 27.50 mg/L CaCl2, 22.50 mg/L MgSO4·7H2O, and 0.25 mg/L FeCl3·6H2O) as described by the OECD 301D. The medium was aerated for 20 min and then left to stand for 20 h before use. Three milliliters of inoculum was added to 10 L of nutrient medium to provide the final test solution which was then added to 10 test vessels. F-53B was added to make a final concentration of 3 mg/L. DO was measured in two vessels at 0, 7, 14, 21, and 28 d, and the results were used to calculate the biological oxygen demand (BOD) according to OECD Guideline 301D.24 Degradation was corrected for uptake by a blank inoculum and compared to that of a reference substance (sodium benzoate, 2 mg/L), which was processed in an identical manner to F-53B. The percentage biodegradation was derived from the BOD and the theoretical oxygen demand (ThOD) as detailed in Section S3, Supporting Information. In addition, the stability of F-53B under various advanced oxidation process (AOP) conditions was tested as described in detail by Schröder and Meesters (2005).26 Briefly, the original analyte concentration was 45 mg/L, made in ultrapure water, with a reaction vessel volume of 250 mL, in all cases. Tests proceeded for 120 min, with samples taken every 20 min, in which F-53B was determined using the analytical method described below, after dilution. The following tests were carried out.
Figure 1. Sampling sites in Wenzhou city, Zhejiang Province, China (● shows the location of sampling sites).
the vicinity of where the discharge from a municipal WWTP enters the river. This WWTP is known to receive wastewater from the electroplating industry, where both F-53B and PFOS are assumed to be in use. Wastewater samples were also collected “upstream”, at a small WWTP which treats the raw effluents of electroplating plants before they enter the municipal sewer system. These samples were taken both before and after the treatment system (see schematic in Figure 1) at different times during a single day. Tap water was also collected at this WWTP and used as field blanks, taken to the sampling site and exposed to the sampling atmosphere during the sampling process. The samples were not intended to provide a comprehensive analysis of the removal rate of F-53B at WWTPs, but instead an initial assessment of to what extent its behavior was similar to that of PFOS. Grab samples of 10165
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Figure 2. Multiple reaction monitoring (MRM) LC−MS/MS chromatograms of F-53B and PFOS spiked at the concentration of 50 ng/L in the wastewater effluent, and mass spectra of Q1 and product ion scan for both compounds.
wastewater effluent were also collected from a domestic wastewater treatment facility in Beijing, China, for the purpose of matrix effect assessment. All the water samples were collected in 500 mL polyproplyene bottles with screw caps (Vitlab, Grossostheim, Germany) and filtered through glass microfiber filters (GF/F, 47 mm, Whatman, Kent, UK) before solid phase extraction (SPE). An aliquot of 5 mL of wastewater was taken from each sample from the dedicated WWTP, due to preliminary test results, which showed high concentrations. Three field blanks consisting of 500 mL local tap water were extracted together with field samples from the WWTP. For surface water, three aliquots of 500 mL water were extracted individually and then pooled to give a single extract. As for all the other water samples taken for the concentration and matrix effect experiments, a 500 mL aliquot was used. One procedural blank consisting of 500 mL ultrapure laboratory water was set up and extracted along with each extraction batch (up to 20 field samples). Oasis HLB cartridges (6 mL, 200 mg, Waters, MA) were first conditioned with 2 × 5 mL methanol and then with 2 × 5 mL ultrapure water. Samples were introduced to the cartridges at a flow rate of 5−10 mL/min, dried and subsequently eluted with 2 × 5 mL methanol. The resulting extracts were reduced using a gentle stream of nitrogen, diluted to 1 mL with ultrapure water and filtered by a 0.22 μm nylon filter prior to analysis. The RS and IS were added at the amount of 25 ng for each sample before extraction and before instrumental analysis, respectively. Chemical Analysis. Water samples were analyzed by high performance liquid chromatography−mass spectrometry (LC− MS/MS). Target compounds were separated on an ZORBAX Eclipse XDB C18 column (5 μm × 2.1 mm × 150 mm, Agilent, CA) using an UltiMate 3000 HPLC (Dionex by Thermo Fisher Scientific Inc., MA). Detection was achieved using an API 3200 triple quadrupole mass spectrometer (AB SCIEX, ON, Canada). The injection volume was 10 μL for each sample. The column unit was held at 30 °C and the flow rate was 0.3
mL/min. Initial mobile phase condition was 40% methanol in 10 mM ammonium acetate held for 1 min. A gradient ramp followed over 6 min to 100% methanol, which was held for 3.5 min, followed by equilibrium at 40% methanol for 2.5 min. The mass spectrometer was operated in negative electrospray ionization mode with multiple reaction monitoring (MRM). The ionization was set at an ionspray voltage of −4.5 kV and at a temperature of 450 °C, using nitrogen for drying. The flows of curtain gas, collision gas, ion source gas 1 and ion source gas 2 were set at 20, 5, 30, and 60 psi, respectively. Instrumental LOQs for F-53B and PFOS in this study were 0.14 and 0.15 ng/L, respectively, and instrumental LODs were 0.04 ng/L for both. The specific quantification strategy including calibration method, internal standard information and LODs/LOQs definition is provided in Section S1, Supporting Information.
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RESULTS AND DISCUSSION Optimization of LC−MS/MS Parameters. In the MS system of this study, full scans for precursor and product ions were carried out for monitoring the transitons from both F-53B and PFOS, as shown in Figure 2. The decluster potential values were optimized to −55 and −85 V to transmit the [M − K]− (m/z 531.0) and [M − K]− (m/z 498.9) for F-53B and PFOS, respectively. For F-53B, the m/z 351.0 transition corresponding to [M − K − C2F4SO3]− was selected as the quantitative product ion due to its much stronger signal than m/z 83.0 as the confirmative one. With the comparison between product ion scans from m/z 531.0 and 533.0 (see Supporting Information Figure S2), m/z 83.0 was detected at the similar abundance in both mass spectra. Therefore, the chlorine of F53B should be excluded in the m/z 83.0 transition which would be otherwise replaced by m/z 85.0 in product ion scan from m/ z 533.0. According to the further molecular weight calculation, m/z 83.0 is presumably derived from FSO2− fragment. In addition, the transitions monitored for PFOS were m/z 80.0 (SO3 −) for quantification and m/z 98.9 (FSO3 −) for confirmation. Selected precursor and product ions for F-53B 10166
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and PFOS, together with the optimized parameters are summarized in Supporting Information Table S1. In order to prevent incorrect identification of target compounds in the matrix, the absolute intensity ratio of quantitative (Q) to confirmative (q) transition was calculated from standard solution for each analyte. The Q/q ratios in the following experiments were within 20% of the theoretical values. For the quantitative analysis of PFOS, the branched and linear isomers were coeluted and integrated as a single peak. Total PFOS (sum of branched and linear isomers) were then measured using L-PFOS standards. Chromatograms for F-53B and PFOS, spiked in the wastewater effluent, are shown in Figure 2. Both compounds were analyzed within 13 min and the variability of retention times was below 1%. Optimization of SPE Conditions. Effects of concentration and matrix were studied to optimize the SPE method for F-53B and PFOS (see Table 2). Recovery of F-53B and PFOS was
Table 3. Fish Acute Toxicity of F-53B in the OECD 203 Test LC50* (mg/L) sample F-53B 95% Confidence limits *
recovery (±SD) (%) F-53B
a
106 100 98 92 10
PFOS
(±11) (±9) (±5) (±3) (±1)
In ultrapure water and at pH 7. concentration of 50 ng/L.
106 103 99 98 17 b
(±10) (±4) (±5) (±5) (±1)
RS 88 93 92 94
(±4) (±8) (±5) (±4)
In wastewater and at the
tested at concentrations of 5, 20, 50, and 500 ng/L in ultrapure water. For both analytes, the average recovery was 100.1% with relative standard deviation of
