Article pubs.acs.org/est
Perfluoroalkyl Acids (PFAAs) and Selected Precursors in the Baltic Sea Environment: Do Precursors Play a Role in Food Web Accumulation of PFAAs? Wouter A. Gebbink,*,†,∥ Anders Bignert,‡ and Urs Berger†,§ †
Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University, SE 10691, Stockholm, Sweden Swedish Museum of Natural History, SE 10691, Stockholm, Sweden § Department of Analytical Chemistry, Helmholtz Centre for Environmental Research − UFZ, DE 04318 Leipzig, Germany ‡
S Supporting Information *
ABSTRACT: The present study examined the presence of perfluoroalkyl acids (PFAAs) and selected precursors in the Baltic Sea abiotic environment and guillemot food web, and investigated the relative importance of precursors in food web accumulation of PFAAs. Sediment, water, zooplankton, herring, sprat, and guillemot eggs were analyzed for perfluoroalkane sulfonic acids (PFSAs; C4,6,8,10) and perfluoroalkyl carboxylic acids (PFCAs; C6−15) along with six perfluorooctane sulfonic acid (PFOS) precursors and 11 polyfluoroalkyl phosphoric acid diesters (diPAPs). FOSA, FOSAA and its methyl and ethyl derivatives (Me- and EtFOSAA), and 6:2/6:2 diPAP were detected in sediment and water. While FOSA and the three FOSAAs were detected in all biota, a total of nine diPAPs were only detected in zooplankton. Concentrations of PFOS precursors and diPAPs exceeded PFOS and PFCA concentrations, respectively, in zooplankton, but not in fish and guillemot eggs. Although PFOS precursors were present at all trophic levels, they appear to play a minor role in food web accumulation of PFOS based on PFOS precursor/PFOS ratios and PFOS and FOSA isomer patterns. The PFCA pattern in fish could not be explained by the intake pattern based on PFCAs and analyzed precursors, that is, diPAPs. Exposure to additional precursors might therefore be a dominant exposure pathway compared to direct PFCA exposure for fish.
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INTRODUCTION Perfluoroalkane sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs) are major classes of perfluoroalkyl acids (PFAAs), which have been recognized as environmental pollutants due to their persistent and, for long chain homologues, bioaccumulative properties.1 There are, however, also less persistent per- and polyfluoroalkyl substances (PFASs) that can be degraded to PFAAs. Identified perfluoro-octane sulfonic acid (PFOS) precursors include methyl and ethyl perfluorooctane sulfonamidoethanols (Me- and EtFOSE) and sulfonamides (Me- and EtFOSA).2,3 On the other hand, fluorotelomer-based chemicals can be degraded to PFCAs, and these precursors include polyfluoroalkyl phosphoric acid esters (PAPs).4 PFAAs are found globally in fish and wildlife, including different trophic levels within food webs. Accumulation of PFAAs has been studied in food webs from different ecosystems, and C6,8 PFSAs and C8−15 PFCAs were commonly detected in species such as plankton, invertebrates, prey and predator fish species, and piscivorous bird species.5−8 Besides being exposed to PFAAs by predation of prey species, predator exposure to precursors could be an additional pathway of PFAA exposure following precursor biodegradation. This is considered an indirect exposure to PFAAs. Given that there are a large © XXXX American Chemical Society
number of different potential precursors produced, the precursor contribution to wildlife PFAA exposure could contribute substantially. However, there is little data on the fate and behavior of precursors (other than FOSA) in food webs and, consequently, also on the extent of precursor contribution to PFAA exposure. Individual studies have reported on the presence of both PFOS and PFCA precursors in biota as well as in the abiotic environment. For example, MeFOSAA and EtFOSAA (degradation products of Me- and EtFOSE) were reported in fish,9 while diPAPs have been found in sediment and water10 as well as in mussels and fish.11,12 Numerous studies have reported on PFAAs in the abiotic and biotic Baltic Sea environment,13−15 however, there is no information on the presence of precursors other than FOSA in this ecosystem. Guillemots (Uria aalge) are top predators in an aquatic food web in the Baltic Sea, and these birds feed primarily on herring (Clupea harengus membras) and sprat (Sprattus sprattus),16 which in turn feed primarily on zooplankton.17 A food web schematic is shown in Supporting Received: March 9, 2016 Revised: May 11, 2016 Accepted: May 18, 2016
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DOI: 10.1021/acs.est.6b01197 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
sonication, the samples were centrifuged (5 min at 3000 rpm) and the extract was transferred to a separate tube. This extraction procedure was repeated twice. The combined extracts were concentrated to ∼1 mL under a stream of nitrogen and diluted with 10 mL Milli-Q water. Water samples (1 L, unfiltered) were spiked with internal standards (500 pg each). Solid phase extraction (SPE) WAX cartridges (150 mg, 6 mL, Waters) were conditioned with 6 mL methanol and 6 mL water. The water samples as well as the sediment and biota extracts were loaded onto the WAX columns and the columns were washed with 1 mL 2% aqueous formic acid and then with 2 mL water. The columns were dried by applying a vacuum and by centrifugation before neutral compounds were eluted with 3 mL methanol (fraction 1). The ionic compounds were subsequently eluted with 4 mL of a solution of 1% ammonium hydroxide in methanol (fraction 2). Both fractions were dried under a stream of nitrogen and the residuals were redissolved in 150 μL of methanol. The extracts were filtered for 5 min at 13 000 rpm using centrifugal filters (modified nylon 0.2 μm, 500 μL, VWR International) and 13C8−PFOA and 13C8−PFOS (500 pg each) were added as recovery internal standards prior to ultraperformance liquid chromatography-tandem mass spectrometry (UPLC/MS/MS) analysis. Fraction 1 was analyzed for FOSAs, while fraction 2 was analyzed twice, first for PFSAs, PFCAs, and FOSAAs and then for diPAPs. For all instrumental analyses, separation was carried out on an Acquity UPLC system (Waters) equipped with a BEH C18 analytical column (50 × 2.1 mm, 1.7 μm particle size, Waters). Information on the mobile phases and gradient programs for the different UPLC methods can be found in the SI (Tables S4 and S5). Connected to the UPLC system was a Xevo TQ-S triple quadrupole mass spectrometer (Waters) operated in negative ion electrospray ionization (ESI−) mode. The capillary voltage was set at 3.0 kV, and the source and desolvation temperatures were 150 and 350 °C, respectively. The desolvation and cone gas flow (nitrogen, > 99.998%) were set at 650 L/h and 150 L/h, respectively. Compoundspecifically optimized cone voltages and collision energies are listed in SI Table S1. Quantification was performed using an internal standard approach. Calibration curves (nine points) covered concentrations over 4 orders of magnitude, that is, for PFAAs 0.03− 300 pg/μL and for precursors 0.003−30 pg/μL. Analytes lacking an analogous mass-labeled standard were quantified using the internal standard with the closest retention time (SI Table S1). Quantification was performed using the precursor− product ion multiple reaction monitoring (MRM) transitions reported in SI Table S1. For all precursor compounds an additional product ion was monitored for confirmation. PFPeDA was quantified using the PFTeDA calibration curve. For diPAPs for which no authentic standards were available (i.e., 4:2/6:2, 6:2/10:2, 8:2/10:2, 6:2/12:2, 8:2/12:2, 6:2/14:2 diPAPs), a technical mixture was used to optimize MRM channels and for confirmation of retention times.20 Quantification of these diPAPs was based on calibration curves of authentic diPAP standards with similar chain length (SI Table S1). Results for these compounds should be considered semiquantitative. For PFOS and FOSA, linear and sumbranched isomers were chromatographically separated and quantified individually. Sum-branched and linear PFOS were quantified using branched and linear external calibration standards, respectively, and using m/z 99 as product ion.
Information (SI) Figure S1. Exposure of Baltic Sea guillemots to PFAAs has been monitored (via retrospective egg analysis) for decades,18 however, it was estimated that the PFOS burden in eggs could not be fully explained by the direct dietary intake of PFOS.13 Holmström and Berger13 hypothesized that the dietary intake of precursors and subsequent degradation could have contributed to PFOS burdens in guillemots (see SI Figure S1 for direct and indirect (precursor) exposure pathways). However, data on precursors in the species of the guillemot food web are limited. The PFOS precursor FOSA is present in the Baltic Sea environment, including in water and prey fish,14,15 but to what extent guillemots and lower trophic level species are exposed to other PFOS and PFCA precursors, and what role precursors could play in food web accumulation of PFAAs, remains unclear. The objective of this study was to determine the presence of PFAAs and selected precursors (including isomers) in the Baltic Sea abiotic environment and in the guillemot food web (zooplankton−herring/sprat−guillemot) and to assess the relative importance of precursors in food web accumulation of PFAAs at different trophic levels. Field-based sediment-water partition coefficients and field-based bioaccumulation factors of precursors were determined and compared to PFAAs in order to get a better insight into the environmental fate of precursors.
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MATERIALS AND METHODS Chemicals and Reagents. Target PFASs included in the present study were C4,6,8,10 PFSAs (including branched and linear PFOS), C6−15 PFCAs, branched and linear FOSA, FOSAA and their methyl and ethyl derivatives (Me- and EtFOSA; Me- and EtFOSAA), and 11 diPAPs (4:2/4:2, 4:2/ 6:2, 6:2/6:2, 6:2/8:2, 8:2/8:2, 6:2/10:2, 8:2/10:2, 6:2/12:2, 10:2/10:2, 8:2/12:2, 6:2/14:2 diPAPs). A total of 17 isotopically labeled standards were used in this study. Details on all chemical standards used in this study can be found in SI Table S1. All solvents and reagents were of the highest commercial purity and employed as received. Samples. All samples were collected in the Baltic Proper region in the Baltic Sea in 2013 or 2014 (see SI Figure S2 and Tables S2 and S3 for sampling details). Water (n = 4, 1 L) and surface sediment (approximately top 5 cm, n = 4, 50 g) samples were collected in summer 2013 near Landsort Island, northern Baltic Proper. Zooplankton (bulk sample, n = 4, 0.5 g) was collected in summer 2014 at a depth between 30 and 100 m with a 90 μm mesh net near Landsort Island. Herring (n = 10) and sprat (n = 10) were collected in spring and autumn 2013, respectively, near Utlängen Island, southern Baltic Proper, and guillemot eggs (n = 10) were collected in spring 2013 from Stora Karlsö, central Baltic Proper. Whole body prey fish and guillemot eggs were homogenized, and all samples were stored at −20 °C. The sediment samples were dried in a desiccator at room temperature to constant weight and homogenized prior to extraction. Although not all samples were collected from the same location, comparable PFAA concentrations in water samples throughout the Baltic Proper indicate that there is an even distribution of PFAAs in this region.15 Sample Preparation and Analysis. The extraction and cleanup of the samples is based on published methods.19−21 Briefly, sediment (5 g), zooplankton (0.5 g), prey fish (1.5 g), and guillemot egg (1 g) samples were spiked with labeled internal standards (500 pg each, see SI Table S1 for all internal standards used) and extracted by sonication (15 min) using methanol (sediment) or acetonitrile (biota samples). After B
DOI: 10.1021/acs.est.6b01197 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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0.00017 (0.00006) 0.0023 (0.0003) 0.0072 (0.0011) 0.22 (0.02) 0.23 (0.02)
