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A Nationwide Distribution of Per- and Polyfluoroalkyl Substances (PFASs) in Outdoor Dust in Mainland China From Eastern to Western Areas Yiming Yao, Hongwen Sun, Zhiwei Gan, Hongwei Hu, Yangyang Zhao, Shuai Chang, and Qi-Xing Zhou Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 11 Mar 2016 Downloaded from http://pubs.acs.org on March 11, 2016
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Environmental Science & Technology
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A Nationwide Distribution of Per- and
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Polyfluoroalkyl
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Outdoor Dust in Mainland China From
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Eastern to Western Areas
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Yiming Yao,a Hongwen Sun,*, a Zhiwei Gan,b Hongwei Hu,a Yangyang Zhao,a Shuai Chang,a Qixing Zhoua
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a
Substances
(PFASs)
in
MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental
Science and Engineering, Nankai University, Tianjin 300071, China. b
Department of Environmental Science and Engineering, Sichuan University, Chengdu, Sichuan,
610065, China 38 Tongyan Road, Jinnan District, Tianjin 300350, China TEL: 86-22-23509241 Email:
[email protected] ABSTRACT ART
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ABSTRACT From eastern to western areas, per- and polyfluoroalkyl substances (PFASs) were detected at substantial levels in the outdoor dust across mainland China. Urban samples generally showed higher levels compared with rural samples. Compared with neutral PFASs, ionizable PFASs (C4-C12 perfluoroalkyl carboxylic acids and C4, C8 perfluoroalkyl sulfonic acids) were more abundant, with the highest total concentration up to 1.6E2 ng/g and perfluorooctanoic acid (PFOA) being a predominant analogue. Fluorotelomer alcohols (FTOHs) and polyfluoroalkyl phosphoric acid diesters (DiPAPs) were both detected in most samples with total concentrations of 0.12-32 and 0.030-20 ng/g, respectively. Perfluorooctane sulfonamidoethanols/sulfonamides (FOSE/As) were detected at low frequencies (< 30%). In addition to partitioning to organic moiety, specific adsorption onto mineral particles can be important for PFASs to bind onto outdoor dust, especially for short-chain ionizable PFASs. The eastern plain areas were characterized by a higher contribution of long-chain ionizable PFASs; whereas the western high plateau areas were characterized by the dominating contribution of short-chain analogues. The difference suggests that the long range atmospheric transport potential of PFASs from source regions to the inland is probably limited by the increase in altitude, and different sources from its adjacent regions may influence the western border area of China.
INTRODUCTION Per- and polyfluoroalkyl substances (PFASs) are a class of chemicals broadly applied to various kinds of industrial and commercial products that require surface protection. Their uses include textile coating, paper treatment, pesticide and fire-fighting foam.1 Due to their widespread use and subsequent emissions, PFASs, especially perfluoroalkyl acids (PFAAs), have been detected not only in environmental matrices from populated urban areas2 but also in samples from remote Arctic regions and mountaintops.3-5 PFAAs were proposed to undergo long-range transport to the Arctic regions through a combination of ocean currents and atmosphere.6 However, for continental interiors with high altitude, long-range atmospheric transport (LRAT) is the only practicable way.4 This usually involves gas-phase degradation of volatile PFASs and subsequent precipitation of the produced ionizable PFASs (iPFASs) to the surface environment. As major volatile precursors of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs), fluorotelomer alcohols (FTOHs) and perfluoroalkyl sulfonamidoethanols/sulfonamides (FOSE/As) are ubiquitously detected in urban and remote atmospheres,7-9 albeit with remarkably low concentrations in atmospheric particulate matter as reported in field studies.9-11 FTOHs, in fact, have been shown to be able to partition effectively to organic12, 13 and mineral14 surfaces of particulate matter; FOSE/As have also been proposed to occur in the finest atmospheric particles.15 However, the occurrence of particle-phase neutral PFASs (nPFASs) may still need support from field data on a large scale. In addition, polyfluoroalkyl phosphoric acid diesters (DiPAPs), as fluorotelomer-based substances, have been widely used in food packaging for surface treatment16 and in personal care products.17 DiPAPs have been detected in wastewater treatment plant (WWTP) sludge at levels much higher than those of perfluorooctanoic acid (PFOA).18 The biodegradation of DiPAPs can contribute to the environmental burden of PFCAs and their human exposures,19, 20 and substantial levels of DiPAPs
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have been detected in surface water21, 22 and human serum.17, 18, 23 DiPAPs were measured in indoor
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Atmospheric particulate matter acts as a sink to accumulate atmospheric contaminants and brings the
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dust at much higher levels than other PFASs, wherein 6:2 and 8:2 DiPAP were the predominant analogues.24 Even so, the atmospheric fate of this new class of precursors is still vague. Therefore, the occurrence of DiPAPs in atmospheric particulate matter is of great interest.
associated contaminants to the earth’s surface via dry deposition. The settled outdoor dust especially the fine particles (1-50 µm) can also migrate globally via re-suspension.25 As a result, the re-migration of outdoor dust can contribute to the LRAT potential of contaminants via atmospheric re-suspension and re-entrainment. PFASs have been worldwide detected in wet deposition, which is deemed to be an efficient way of eliminating atmospheric PFASs.26-28 Comparatively, higher levels of PFAAs have been found in surface runoff than in rainfall,28-30 which indicates that particle-phase PFAAs on the land surface may contribute to the high PFAS levels in surface runoff. Long-chain PFCAs (>C7) and perfluorooctane sulfonic acid (PFOS) were reported to occur in street dust at substantial levels,31 and they showed a different compositional profile compared with WWTP influents and effluents.32 Even so, not enough attention has been paid to outdoor dust in terms of PFASs. In particular, the occurrence of short-chain PFAAs and nPFASs in this particulate matter can be important when accounting for their atmospheric fate and LRAT potential. China is an emerging hotspot for the production of PFAS-based products and their consumption, yet the exact inventory involved in this market has remained largely uncharacterized. As a matter of fact, imbalanced urbanization levels have resulted in a higher population density and faster economic growth in the eastern part of mainland China. Thus, the transport of PFASs from these source areas to remote western inland areas is anticipated but the extent is unknown. So far, few studies have reported the occurrence of PFASs in the atmosphere of mainland China, and the available data can hardly account for the whole map.33 Data are even rare for PFASs in particulate matter such as outdoor dust. Therefore, a distribution map of both iPFASs and nPFASs covering a large scale can be of great significance. In the present study, a nationwide outdoor dust sampling campaign was carried out across a wide range of altitudes from near sea level to over 3600 m. A total of 23 PFASs were analyzed, including PFCAs, PFSAs, FTOHs and FOSE/As, as well as DiPAPs and several possible ionizable intermediates.
MATERIALS AND METHODS Sample Collection. Sampling of outdoor dust was performed in winter from February to March in 2013. A total of 92 outdoor samples were collected from mainland China covering all administrative provinces except Macau. The provinces officially fall under 6 administrative divisions (http://www.xzqh.org/quhua), and samples from both urban and rural areas were collected from each region except for Northeast China, where only urban samples were collected. Detailed information on the sampling sites is given in Table S1 in the supporting information (SI). Settled dust on the sill outside windows or on the outer wall surface of a building 1 m above the ground was swept and collected into a polypropylene plastic (PP) tube using a disposable pig-bristle brush. Each sample was collected from multiple spots at one location. After collection, all PP tubes were
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sealed in polypropylene bags separately and transported to a laboratory for storage at – 20 ˚C until
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Sample Preparation. Repeated ultrasonic extraction with methanol34 was used for the dust samples
analysis.
with modifications. Approximately 500 mg of each sieved dust sample (< 150 µm) was prepared in a 15 mL PP tube. Prior to extraction, 5 ng of each mass-labeled internal standard listed in the SI was spiked. The sample was then shaken for 1 min using a vortex mixer and allowed to settle for 2 min before adding the solvent. Having soaked in 5 mL methanol for 15 min, the sample was further extracted with sonication for 30 min. After centrifugation at 3500 g, the supernatant was collected and a second aliquot of 5 mL methanol was added to repeat the procedure. The two methanol extracts were combined and possible water residue was removed by anhydrous sodium sulfate. The extract was further reduced to a volume of 0.5 mL in a calibrated PP tube by evaporation under a gentle stream of nitrogen. The concentrate was cleaned by being gently shaken with 25 mg dispersive EnviCarb (120/400 mesh, CNW Technologies, GmbH, Düsseldorf, Germany) and then centrifuged at 15,000 g for 10 min. A 100-µL aliquot of the supernatant was transferred into an autosampler vial before analysis, and in this manner a second aliquot was prepared.
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Sample characterization. As limited by sample amount, 67 out of 92 outdoor samples were
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Instrumental Analysis. A gas chromatography-mass spectrometer (GC/MS) was used for the analysis
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Quality Assurance and Control. All samples were randomly numbered and analyzed in duplicate. All
characterized for their particle size distribution, total organic carbon (TOC) content and elemental composition. Details are given in the SI.
of nPFASs. For iPFASs, a high-performance liquid chromatograph-tandem mass spectrometer (HPLC-MS/MS) was used. Both instruments were from Agilent Technologies. PAPs were also analyzed with the HPLC-MS/MS, but they were analyzed separately with a different gradient method. Details of the instrumental methodologies and information on the chemicals involved are given in the SI.
the analyzed PFASs were normalized against the recovery of the corresponding mass-labeled internal standard added prior to extraction, which was deemed to be necessary and effective at correcting matrix effects in dust samples.31 Specific information on the normalization is shown in Table S2. For quantification, three internal calibration curves were prepared from sequential concentrations (20-1000 ng/L, 100 to 5000 ng/L and 5 to 100 µg/L) of external standards, and the concentration of internal standards was kept as 10 µg/L. The linearity and repeatability of these calibration curves were confirmed prior to each set of determinations, and the standard deviations from the theoretical values were less than 20%. Limit of detection (LOD) was derived from the peak value with the signal-to-noise ratio (SNR) equaling three and limit of quantification (LOQ) was from the peak value with SNR equaling ten. Concentrations below LOD were achieved for all instrumental and procedural blanks, which demonstrated that a low PFAS background level existed in this HPLC-MS/MS system and that no contamination during sample pretreatment occurred. Matrix recoveries were conducted at three dose levels (0.5 ng, 5 ng and 50 ng), and the mean recovery ranged from 89% to 104% and 74% to 103% for LC-MS/MS and GC-MS analytes, respectively, with standard deviations (SD) less than 20% (details in Table S4). Due to low blank levels (
