Effect of Body Condition on Tissue Distribution of Perfluoroalkyl

Article pubs.acs.org/est

Effect of Body Condition on Tissue Distribution of Perfluoroalkyl Substances (PFASs) in Arctic Fox (Vulpes lagopus) Camilla Bakken Aas,†,‡ Eva Fuglei,† Dorte Herzke,§ Nigel G. Yoccoz,‡ and Heli Routti*,† †

Norwegian Polar Institute, Fram Centre, 9296 Tromsø, Norway Department of Arctic and Marine Biology, UiT The Arctic University of Norway, 9037 Tromsø, Norway § Norwegian Institute for Air Research, Fram Centre, 9296 Tromsø, Norway ‡

S Supporting Information *

ABSTRACT: Arctic animals undergo large seasonal fluctuations in body weight. The effect of body condition on the distribution and composition of 16 perfluoroalkyl substances (PFASs) was investigated in liver, blood, kidney, adipose tissue, and muscle of Arctic foxes (Vulpes lagopus) from Svalbard (n = 18, age 1−3 years). PFAS concentrations were generally highest in liver, followed by blood and kidney, while lowest concentrations were found in adipose tissue and muscle. Concentrations of summed perfluorocarboxylic acids and perfluoroalkyl sulfonates were five and seven times higher, respectively, in adipose tissue of lean compared to fat foxes. In addition, perfluorodecanoate (PFDA) and perfluoroheptanesulfonate (PFHpS) concentrations in liver, kidney, and blood, and, perfluorononanoate (PFNA) in liver and blood, were twice as high in the lean compared to the fat foxes. The ratio between perfluorooctane sulfonamide (FOSA) and its metabolite perfluorooctanesulfonate (PFOS) was lowest in liver, muscle, and kidney, while significantly higher proportions of FOSA were found in adipose tissue and blood. The results of the present study suggest that toxic potential of exposure to PFAS among other pollutants in Arctic mammals may increase during seasonal emaciation. The results also suggest that body condition should be taken into account when assessing temporal trends of PFASs.

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nological effects, and neurotoxicity.7,9 Metabolic disruption has been associated with PFASs’ ability to interfere with peroxisome proliferator-activated receptors (PPAR),10 which are key regulators of lipid metabolism.11 PPARs are naturally activated by fatty acids, but also several PFAS, which are structurally similar to fatty acids, having a strong hydrophobic body and polar headgroup, induce PPARs.10,12 Many Arctic species undergo seasonal energy-demanding periods due to variation in temperature and food availability as well as cost of migration, reproduction and molting.13,14 The use of fat reserves during these emaciation periods leads to remobilization of lipophilic POPs from fat to blood and further to vital organs as well as up-concentration in the residual adipose tissue.15,16 This process also leads to increased induction of xenobiotic metabolizing enzymes15 and formation of metabolites of POPs,17 which together with increased tissue concentrations of POPs can cause increased toxic stress. In contrast to lipophilic POPs, PFASs have high affinity to proteins18,19 and the subgroups PFCAs and PFSAs are not subject to biotransformation.20 The few studies reporting PFAS

INTRODUCTION Perfluoroalkyl substances (PFASs) are synthetic chemicals used for various industrial purposes since 1950s. The use and production of perfluorooctanesulfonate (PFOS), its salts and perfluorooctane sulfonyl fluoride (PFOSF) have been restricted by the Stockholm convention since 2009, while restrictions of long-chained perfluorocarboxylic acids (PFCAs) and their precursors are currently moving toward restrictions and bans on use and production in Europe and North-America.1 The most commonly detected groups of PFASs in biota are perfluoroalkyl sulfonates (PFSAs), including PFOS, and PFCAs.2 Many PFASs are highly persistent in the environment, and they are transported to remote areas such as the Arctic. In Arctic marine food webs PFOS and C9−C11 PFCAs, in particular their linear isomers,3 have similar biomagnification capacity as lipophilic persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs) and p,p′-dichlorodiphenyldichloroethylene (DDE),4,5 while PFASs biomagnify to a lesser extent in Arctic terrestrial food webs.6 In fact, PFOS has been reported at higher concentrations (on wet weight basis) than PCBs in plasma of polar bears (Ursus maritimus).7,8 The high concentrations of PFASs in Arctic apex predators are of great concern due to their potential health effects. Chronic exposure to PFASs has been related to metabolic disruption, developmental toxicity, thyroid disruption, immu© 2014 American Chemical Society

Received: Revised: Accepted: Published: 11654

June 28, 2014 September 5, 2014 September 12, 2014 September 12, 2014 dx.doi.org/10.1021/es503147n | Environ. Sci. Technol. 2014, 48, 11654−11661

Environmental Science & Technology

Article

Samples of liver, kidney, abdominal adipose tissue, and muscle were wrapped in aluminum foil, and all the samples were stored at −20 °C until further use. Analysis of PFASs. The analysis of PFASs, including perfluorooctane sulfonamide (FOSA), perfluorobutanoate (PFBA), perfluoropentanoate (PFPA), perfluorohexanoate (PFHxA), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), perfluorodecanoate (PFDcA), perfluoroundecanoate (PFUnA), perfluorododecanoate (PFDoA), perfluorotridecanoate (PFTriA), perfluorotretradecanoate (PFTeA), perfluorohexanesulfonate (PFHxS), perfluoroheptanesulfonate (PFHpS), linear and branched PFOS isomers, and perfluorodecanesulfonate (PFDcS), was conducted at the Norwegian Institute for Air Research (NILU). The samples were extracted, cleaned-up, and analyzed according to the method described by Hanssen et al.,27 although there were some modifications. In short, to all samples (1−2 g) 20 ng of 0.1 ng/μL isotopically labeled internal standards were added. Internal standards included MPFHxS (PFHxS18O2), MPFOS (13C4PFOS), MPFOA (13C 4PFOA), MPFNA (13C5 PFNA), MPFHxA (13C2PFDA), MPFUnDA (13C2PFUnDA) and MPFDoDA (13C2PFDoDA) were of >98% purity and were obtained from Wellington Laboatories Inc. (Guelph, Ontaria, Canada). Acetonitrile was added to the samples followed by ultrasonic bath and centrifuged for sedimentation (2000 rpm). The supernatant was concentrated to 1 mL using a RapidVap (Rapid Vap; Labconco corp., Kansas city, MO, U.S.A.). ENVICarb 120/400 (Supelco, PN, U.S.A.) and glacial acetic acid was added to the extract and mixed thoroughly.28 The mixture was centrifuged (10 000 rpm), and the supernatant was transferred to an auto injector vial where 20 μL recovery standard 3,7dimethyl-branched perfluorodecanoate (bPFDA), 97% purity (ABCR, Karlsruht, Germany) was added. Prior to the UHPLCMS/MS analysis an aliquot of the extract was transferred into a liquid chromatography-vial together with 2 mM ammonium acetate in water precleaned with two inline solid phase extraction cartridges with hydrophilic−lipohilic balanced (HLB) material. (NH4OAc, ≥ 99%, Sigma-Aldrich, St. Louis, MO, U.S.A.) in a 50/50 mixture. PFASs were analyzed by UHPLC-MS/MS.27 Branched PFOS isomers were quantified against the linear PFOS standard. Quality was assessed according to Hanssen et al.27 In order to control for background contamination, a procedural blank with no matrix was run with every 10 samples. Limit of detection (LOD) was defined as signal-to-noise ratio of three. In case a signal was detected in blanks, LOD was defined as three times signal in blank (Supporting Information (SI) Table S1). None of the blanks in this study had contamination. Recovery of the mass labeled internal standards ranged for liver between 45 and 125%, for adipose tissue 35−125% and for blood, kidney, and muscle between 50 and 115%. A certified reference material was run with every 10 samples to ensure quality of the analysis. The control used for liver, kidney, muscle, and adipose tissue, was pike IRMM-427, sample ID 0119. SRM recovery for blood varied between 88 and 107% and for fish tissue between 77 and 109% for the target compounds. For the blood sample, a serum control was used (SRM 1958, NIST, Gaithersburg, MD, U.S.A.). Stable Isotope Analysis (SIA) of δ13C and δ15N. To assess the possible confounding effect of diet on PFAS exposure, stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) in muscle were analyzed.29 Muscle SIA is expected to

tissue distribution in marine mammals including harbor seals (Phoca vitulina),21,22 polar bears,23 and beluga whales (Delphinapterus leucas)4 indicate that these compounds accumulate mainly to protein rich body compartments such as liver, kidney, and blood. However, it is not known how body condition affects tissue concentrations and distribution of PFASs. This knowledge is crucial in order to understand whether seasonal emaciation leads to increased concentrations of PFASs, which may further increase the toxic potential of the chemical cocktail to which the animals are exposed. This is especially important with regard to the metabolic disruption potency of PFASs. The Arctic fox (Vulpes lagopus) is an opportunistic predator going through extreme seasonal fluctuations in their fat content, which may vary from zero to 40% of their body mass.24 The average fat content in Svalbard Arctic fox population is highest in late autumn/early winter and lowest in late winter/spring.24 However, during periods of food deprivation (winter, spring) some foxes have still extensive fat reserves, due to their opportunistic feeding habits. This species is thus an ideal model to study the effect of body condition on contaminant distribution. The aim for this study is thus to examine the effect body condition on concentrations and patterns of PFSAs and PFCAs within and between five different body compartments of Arctic foxes from Svalbard. In addition, we looked at the effect of tissue and body condition on the ratios between PFOS and its parent compound FOSA, as well as between linear and branched PFOS. As the Artic fox in Svalbard has a highly variable diet,25 which may further influence PFAS accumulation, we also analyzed stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) as dietary tracers to avoid the confounding effect of diet. In our knowledge, this is the first study reporting the effect of body condition on distribution and concentration of PFASs.

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EXPERIMENTAL SECTION Sample Collection. Arctic fox carcasses were collected from trappers on Spitsbergen, Svalbard, mainly around Isfjorden area (77.8−79.1°N, 13−17°E). Baited dead fall traps (that kills the animals instantly) were used during the annual recreational harvest between first of November and 15th of March in 2010/2011 (n = 13) and 2011/2012 (n = 5). The collection of carcasses from the trappers and the further storing (frozen) until autopsy were organized through the annual monitoring program of the Norwegian Polar Institute (by E. Fuglei). All foxes were weighed, sex-determined, and skinned before the final dissection. Body condition was evaluated according to a subjective fat index ranging from 0 to 4 (none to extensive) based on visual inspection of the skinned carcasses.24 The foxes were divided into lean (n = 8) and fat (n = 10) according to their body condition. The average (range) body condition was 1.1 (1−2) and 3.7 (3−4) for the lean and fat foxes, respectively. The lean foxes weighted on average 2863 g (2400−3550) and the fat ones 4250 g (3500−5200). The age of the Arctic foxes was determined by counting the annuli in the cementum of a sectioned canine tooth.26 Intentionally young individuals were chosen and possible marks from reproduction on the uterus of the vixens was examined to avoid possible confounding effects of sex due to reproduction. Both groups contained only young foxes without reproductive marks (mean age for lean and fat foxes 1.6 (1−3) and 1.2 (1− 2) years) of both sexes (M/F for lean = 4/4 and fat = 7/3, respectively). Whole blood was collected from the heart. 11655

dx.doi.org/10.1021/es503147n | Environ. Sci. Technol. 2014, 48, 11654−11661


Article

Figure 1. Percent compositions of ∑-perfluoroalkyl substances (PFASs) and ∑-perfluorocarboxylic acids (PFCAs) within each tissue in lean (n = 8) and fat (n = 10) Arctic foxes from Svalbard.

Individual)). Age and gender were not included as explanatory variables since the study only included young foxes that had not reproduced. As our study is based on planned comparisons of tissue and body condition, the interactions between them were kept in all models. From the two pool of models, we selected the most parsimonious models for each response variable with the lowest value of Akaike’s Information Criterion corrected for small sample size (AICc).34 The selected models were further applied for individual and summed PFCAs and PFSAs, the ratios of PFOS/FOSA and the ratio of branched and linear PFOS. As the models selected included only the interaction body condition/tissue, and other models considered in this study included it too by design, we did not use model averaging, since it would not have modified our estimates of the main term body condition: tissue. One outlier was removed in the analysis of PFOS/FOSA, however, removing this value did not have large effects on the estimates but estimates were likely more robust without this outlier. PFOS used in the models for individual compounds, ∑PFASs and ∑PFSAs was based on the sum of branched and linear PFOS. To assess the uncertainty and significance of the effects of explanatory variables on PFAS concentrations MCMCglmm (MCMCglmm, Marcov Chain Monte Carlo Sampler simulations for Bayesian estimations of Generalized Linear Mixed Models) package35 was used to calculate the 95% confidence intervals (CI) of the back-transformed effect. 500 000 MCMC iterations were used, retaining every fifth value in the chain, and the back-transformed values of the chains were used to calculate confidence intervals. Using this approach takes into account that simply back-transforming parameters result in biased estimates of mean effects. Assumptions of constant variance and approximate normal distribution of residuals were determined through plots of residuals against fitted values and normal-and quantile-quantile plots.36 To meet the assumptions, all PFAS concentrations were log-transformed prior to the analyses. A constant (0.05) was added to take the few nondetected compounds into account, and the constant was chosen so as to have residuals approximately normally distributed. Back-transformed parameter estimates with 95% CI for the estimated values are given in the text. As the back-transformed effect estimates represent multiplicative change, the result was considered significant if the 95% CI did not cross 1.

provide dietary information from the previous one to two months in the Arctic fox.29 Approximately 1 g (cm3) of muscle tissue was dried for 2−3 days at 60 °C before it was ground into a fine powder in a bread-mill homogenizer (TissueLyzerll, Qiagen Gmbh, Hilden, Germany) and 0.4 mg (±0.05 mg) fine powder was put into a tin container. Stable isotope analysis was performed at the Stable Isotopes in Nature Laboratory (SINLAB), New Brunswick, Canada as previously described by Ehrich et al.30 In short, samples were combusted in a Carlo Erba NC2500 Elemental Analyzer before delivery to a Finnigan MatDelta Pluss mass spectrometer (Thermo Finnigan, Bremen, Germany). Stable isotope signatures are expressed as parts per thousand (‰) relative to a standard as follows [(Rsample/ Rstandard) − 1] × 1000, where R is the fraction of heavy to light isotopes (13C/12C and 15N/14N). As standards for δ13C and δ15N, Peedee belemnite carbonate and atmospheric nitrogen were used, respectively.31 As δ13C reflects the lipid content of the tissue sample, the model based normalization for muscular tissue was used to correct the value of δ13C for lipid content in the samples with a C/N ratio between 3.5 and 7.30 Data Analysis. Statistical analyses were carried out by using the statistical program R, version 3.0.2 (R Core Team, 2013). Compounds detected in >60% of the samples in a given tissue were used for statistical analyses. Nondetected values of the compounds used in the analysis were set to be half the LOD (SI Table S1). LOD is expressed as the concentration derived from the lowest measure that can be detected with reasonable certainty for a given analytical procedure.32 The tissues with detected samples of less than 60% were removed from the mixed models for the given compounds. Furthermore, the given compound was removed from the ∑PFCA and ∑PFSA analyses. Linear mixed-effects models were applied using the R-library lme4,33 which were used to analyze the effect of tissue, body condition and diet on distribution of PFASs in Arctic fox tissues. We used the same model for summed and individual PFCAs and PFSAs on the basis of model selection with lntransformed ∑PFCAs and ∑PFSAs as response variables, respectively. The possible explanatory variables included in the global models, applied as fixed effects were tissue (liver, blood, kidney, adipose tissue, and muscle), body condition (lean and fat), δ15N and δ13C, while individual was applied as a random effect (∼body condition × tissue + δ13C + δ15N + (1| 11656



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Figure 2. Concentrations (ng/g wet weight) of individual and sum (Σ) perfluoroalkyl sulfonates (PFSAs) and perfluorocarboxylic acids (PFCAs), in liver (Li), blood (Bl), kidney (Ki), adipose tissue (Ad), and muscle (Mu) of lean (dark gray, n = 8) and fat (white, n = 10) Arctic foxes form Svalbard.

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RESULTS AND DISCUSSION

Arctic fox tissues, while PFNA was the dominating PFCA, followed by PFUnDA and PFTrDA (Figure 1, SI Table S3). PFTrDA was observed at similar concentrations as PFUnDA in all tissues except adipose tissue, where PFTrDA was detected in less than 60% of samples. These findings are consistent with previous studies on Arctic predators.8,23,37 PFHxS and PFOA were detected in all tissues, although at lower concentrations than PFOS, PFNA, and PFUnDA (Figure 1, SI Table S3). In addition, PFDA, PFDoDA, PFTeDA, FOSA, and PFHpS were detected in most tissues except in adipose tissue. Additionally, PFTeDA was not detected in blood and FOSA was not detected in muscle. Odd-numbered PFCAs were found in greater abundance than the even-numbered in all tissues, and concentrations of odd-numbered PFCAs decreased with increasing chain length,

Model Selection. The result from the model selection showed that the most parsimonious models explaining the variation of ΣPFCAs and ΣPFSAs contained tissue and body condition as fixed factors and individual as random variable (log(PFAS + 0.05) ≈ tissue × body condition, SI Table S2). The relationship between body condition and tissue showed great evidence to explain the variation of PFASs. δ15N or δ13C were not included in the most parsimonious models indicating that PFAS variation was not significantly explained by the dietary traces (SI Table S2). Tissue Concentrations of PFSAs and PFCAs. PFSAs were found in higher concentration in all tissues compared to PFCAs (Figure 1). PFOS was the dominating PFAS in all 11657



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Figure 3. Percent compositions of perfluorooctane sulfonamide (FOSA) and perfluorooctanesulfonate (PFOS) and composition between linear and branched PFOS within each tissue in lean (n = 8) and fat (n = 10) Arctic foxes from Svalbard.

with PFNA being the major one (Figure 1, SI Table S3). These trends are in agreement with previous findings on Arctic foxes, polar bears, and seabirds.23,37−39 PFBS, PFDcS, PFHxA, and PFHpA were not detected in any of the tissue samples of Arctic foxes. PFBS, PFHxA, and PFHpA are neither considered bioaccumulative nor biomagnifying, and are usually not detected in wildlife samples.40 Comparisons with recent studies from Greenland indicate that hepatic concentrations of the main PFASs in the present Arctic foxes were approximately one tenth compared to polar bears and at a similar range compared to ringed seals.39 Compared to a previous study on Arctic foxes from the Canadian Arctic37 hepatic concentrations of the major PFASs (PFNA, PFDA, PFUnDA, and PFOS) were two to three times higher compared to the present study. The difference may be explained by the young age of the foxes in the present study or other environmental factors. Generally, the highest concentrations of PFASs were found in the liver, followed by blood and kidney and the lowest concentrations in adipose tissue and muscle (Figure 2, SI Tables S3−S4). These findings are in accordance with previous literature on mammalian predators.4,22,23 It is well established that PFASs go through enterohepatic recirculation, and accumulate mostly in the liver.9 Furthermore, the distribution of PFASs is affected by localized proteins.19,41 In detail, PFASs have great affinity to liver fatty acid-binding protein (L-FABP), which partly explains their high concentration in the liver.9,41−43 Additionally, recent modeling studies suggest that PFASs have great affinity toward phospholipids.19,44 These are found in large quantities in the liver, and may contribute to the high concentrations of PFASs in this organ.19,44 Blood had the second highest concentrations of PFASs (Figure 2, SI Table S3). This is likely due to the affinity of PFASs to albumin.18,19,41,45,46 Reabsorption of PFASs from the gut and urine by passive diffusion and organic anion transporters (OATs) into the blood probably plays a significant role for the high concentrations and the long half-life of PFASs in blood.47 Phospholipids, L-FABPs, and OATs are found in the kidney, which may explain the high concentration of PFASs in this organ.19 Furthermore, the high concentrations of PFASs in the kidney (Figure 2, SI Table S3) may also indicate excretion of these compounds through urine,48 or simply reflect the high flow of blood through this organ.49

Concentration ratios of PFASs were similar between Arctic fox tissues (Figure 1). These findings are in agreement with a previous study on harbor seals.21 However, these results are not in agreement with the PFAS composition in polar bears, in which longer-chained PFCAs are found in adipose tissue while shorter-chained PFCAs are found in liver and blood.23 Effect of Body Condition on PFSAs and PFCAs. Concentrations of overall and individual PFASs differed between lean and fat foxes (Figure 2). For ∑PFSAs, lean foxes had seven times [95% CI: 2.5, 18] higher concentration of ∑PFSAs in adipose tissue than fat foxes. The trend for ∑PFCAs was similar: adipose tissue of lean individuals had 5fold [95% CI: 2.3, 9.3] higher concentrations of ∑PFCAs than fat foxes. Additionally, lean foxes had over two times [95% CI: 1.1, 4.4] higher concentrations of ∑PFCAs in liver, blood, and kidney (Figure 2). Muscles were not significantly affected by body condition, as lean individuals only had 1.3 times [95% Cl: −0.6, 2.5] higher concentrations of ∑PFCAs than fat foxes. Analysis on individual compounds showed that C9−C11 chain length PFCAs and C6−C7 chain length PFSAs were the compounds mostly affected by decreased body condition (Figure 2). Lean foxes had twice as high [95% CI: 1.2, 4.4] concentrations of PFNA in liver, blood, and adipose tissue compared to fat foxes. Concentrations of PFDA were two times [95% CI: 1.3, 3.6] higher in liver, kidney, and blood of lean individuals compared to the fat foxes. Six times [95% CI: 2.2, 23] higher concentration of PFUnDA was found in adipose tissue of the lean foxes compared to the fat individuals. For PFHxS, adipose tissue was the only tissue affected by body condition, with lean foxes having three times [95% CI: 1.1, 12] higher concentration of PFHxS than fat foxes. Liver, kidney, and blood of lean foxes had two times [CI: 1.0, 4.2] higher concentrations of PFHpS than fat foxes. Concentrations of FOSA, PFOS, PFOA, PFDoDA, PFTrDA, and PFTeDA were not affected by body condition in any tissue analyzed in our study. Similarly, studies on sea otter (Enhydra lutris nereis) and harbor seals showed that PFOS and PFOA measured in liver were not affected by body condition.50,51 This is further supported in a study on male mink (Neovison vison) where it was found that concentrations of PFHxS, PFOS, PFOA, PFUnDA, PFDoDA, and PFTrDA in the liver was not affected by body condition.52 However, in the same study, PFNA and PFDA were also found not to correlate to body 11658



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with decreasing body condition. The large seasonal variability in fat content in arctic mammals24,60−62 may thus affect tissue concentrations of PFASs and increase their potential effects during seasonal emaciation. The effects are not only related to the increased concentration of PFASs, but also to increased concentration of other POPs in target organs during decreased body condition which may further increase toxicity.15 Essentially, PFASs interfere with the PPAR-pathway by binding to PPARs, and liver-FABPs, which is directly involved in the transportation of fatty acids to the PPAR.63 Interference with the PPAR-pathway may further lead to disruption of whole body energy metabolism.64,65 Future studies should focus on toxicity in animals in relation to body condition in order to map if decreased body condition amplify the possible effects of PFASs along with lipohilic POPs. The results also suggest that these large annual changes in body condition must be taken into account when performing time-trend analyses and other studies on PFASs.

condition in the liver, while higher hepatic concentrations of these compounds were found in the present foxes. The results from this study clearly show that adipose tissue concentrations of several PFASs vary with body condition. This may be explained by an up-concentration of the compound within the adipose tissue i.e. PFASs are not mobilized with the fat and therefore become more concentrated as the total mass of the adipose tissue diminishes. A possible explanation for the increased concentrations in kidney, liver, and blood may be the lowered intake of food during fasting.53 Fasting leads to reduced resting metabolic rate53 and reduced excretion of contaminants, which again causes increased half-life and increased accumulation of contaminants.16 This may further explain why PFCAs with a carbon-chain between C9−C11 are more affected by decreased body condition than the PFCAs with a shorter chain-length. The shorter chain length PFCAs are more water-soluble54 and more eliminated through urine.55,56 PFCAs with a carbon-chain between C9−C11, are more hydrophobic and favor biliary enterohepatic recirculation.55,56 However, it is unclear why the long chain length PFCAs were not affected by body condition as the hydrophobicity increases with the increasing chain length. One additional aspect unknown to the authors is the body condition of the investigated foxes earlier in life. It is not known if the foxes with little body fat did have larger fat reserves or if they were characterized by a lean body-condition through their whole life. However, it is not know if the “fat” individuals did experience under-nourishment earlier in life. Ratio of FOSA and PFOS. The estimated ratio between FOSA and its metabolite PFOS were 0.0037 [CI: 0.001, 0.013] in liver, muscle and kidney, while over ten times higher ratios were found in adipose tissue and blood, 0.042 [CI: 0.004; 0.40] and 0.068 [CI: 0.007, 0.66], respectively (Figure 3). This suggests biotransformation of FOSA to PFOS may be catalyzed by enzymes in liver, kidney and muscle of the Arctic fox. Body condition had no effect on the ratio between FOSA and PFOS (Figure 3). This was surprising, as activity of xenobiotic metabolizing enzymes was expected to be enhanced in the lean foxes.15The relative amount of FOSA to PFOS was similar to previous observations in polar bears but lower compared to seals and whales.57 Ratio of Branched and Linear PFOS. Kidney was the organ with the highest relative abundance of branched PFOS (32%), while the remaining tissues contained ∼20% of branched PFOS (Figure 3). Nevertheless, the branched and linear PFOS composition did not differ significantly between tissues (Figure 3). Body condition did not have an effect on the proportion either. However, it should be noted that our results are semiquantitative because we did not carried out isomerspecific analyses. Branched PFOS were found in much higher proportion in Arctic foxes compared to polar bears, where branched PFOS varied between ∼0% to 25% depending on tissue.58 Moreover, the composition of branched and linear PFOS varied between tissues in polar bears,58 whereas no difference between tissues was observed in the Arctic foxes of the present study. Interspecies variation in metabolism of precursors, uptake and half-lives of branched and linear PFOS48,59 may explain the contrasting result in this study compared with polar bears.58 Implications. Lean Arctic foxes had increased concentrations of ΣPFSAs and ΣPFCAs in adipose tissue compared to fat foxes. Additionally, concentrations of PFDA and PFHpS in liver, kidney, and blood, and PFNA in liver and blood increased

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ASSOCIATED CONTENT

S Supporting Information *

Limit of detections and concentrations for individual PFASs in each tissue, and, the result of model selection as well as parameter estimates from all mixed models. This material is available free of charge via the Internet at http://pubs.acs.org/.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +4777750541; e-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Local hunters at Svalbard and the Governor of Svalbard are acknowledged for collection of the arctic fox carcasses. We thank Norwegian Veterinary Institute in Tromsø, in particular Torill Mørk, for laboratory facilities, help and guidance with autopsies. We would like to thank the NILU staff for the assistance with the chemical analyses. We thank Anette Wold for technical help in sample preparation, and the staff of SINLAB (University of New Brunswick, Canada) for performing the mass spectrometer analysis for stable isotopes. We thank Lisa Helgason and Jan Ove Bustnes for their constructive comments on the manuscript. This study was funded by the Fram Centre Hazardous Substances Program and the Norwegian Polar Institute.

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REFERENCES

(1) OECD OECD/UNEP Global PFC Group. Synthesis paper on per- and polyfluorinated chemicals (PFCs), Environment, Health and Safety, Environment Directorate, OECD; Paris, 2013. (2) Butt, C. M.; Berger, U.; Bossi, R.; Tomy, G. T. Levels and trends of poly- and perfluorinated compounds in the arctic environment. Sci. Total Environ. 2010, 408 (15), 2936−2965. (3) Powley, C. R.; George, S. W.; Russell, M. H.; Hoke, R. A.; Buck, R. C. Polyfluorinated chemicals in a spatially and temporally integrated food web in the Western Arctic. Chemosphere 2008, 70 (4), 664−672. (4) Kelly, B. C.; Ikonomou, M. G.; Blair, J. D.; Surridge, B.; Hoover, D.; Grace, R.; Gobas, F. A. P. C. Perfluoroalkyl contaminants in an

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