Gabriel Munoz

Hélène Budzinski

Marc Babut

Jérémy Lobry

Jonathan Selleslagh

Nathalie Tapie

Pierre Labadie
email: pierre.labadie@u-bordeaux.fr

Temporal variations of perfluoroalkyl substances partitioning between surface water, suspended sediment, and biota in a macrotidal estuary

Keywords:

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are highly fluorinated chemicals used in a variety of applications and consumer products [START_REF] Robel | Closing the Mass Balance on Fluorine on Papers and Textiles[END_REF][START_REF] Tokranov | How Do We Measure Poly-and Perfluoroalkyl Substances (PFASs) at the Surface of Consumer Products?[END_REF], which can result in their emission to the environment [START_REF] Wang | Toward a comprehensive global emission inventory of C4-C10 perfluoroalkanesulfonic acids (PFSAs) and related precursors: focus on the life cycle of C8-based products and ongoing industrial transition[END_REF]). Due to concerns on environmental and health impacts of PFASs, monitoring surveys have assessed the extent of contamination of aquatic ecosystems [START_REF] Lindim | Estimating emissions of PFOS and PFOA to the Danube River catchment and evaluating them using a catchment-scale chemical transport and fate model[END_REF][START_REF] Campo | Analysis of the presence of perfluoroalkyl substances in water, sediment and biota of the Jucar River (E Spain). Sources, partitioning and relationships with water physical characteristics[END_REF][START_REF] Loos | Analysis of emerging organic contaminants in water, fish and suspended particulate matter (SPM) in the Joint Danube Survey using solid-phase extraction followed by UHPLC-MS-MS and GC-MS analysis[END_REF] and water sources [START_REF] Hu | Detection of poly-and perfluoroalkyl substances (PFASs) in US drinking water linked to industrial sites, military fire training areas, and wastewater treatment plants[END_REF][START_REF] Boone | Per-and polyfluoroalkyl substances in source and treated drinking waters of the United States[END_REF]. Certain PFASs such as perfluorooctane sulfonate (PFOS) are found at widespread scale, including in the open ocean and polar regions [START_REF] Yeung | Vertical Profiles, Sources and Transport of PFASs in the Arctic Ocean[END_REF][START_REF] Rigét | Temporal trends of persistent organic pollutants in Arctic marine and freshwater biota[END_REF].

The long-chain perfluoroalkyl carboxylates (PFCAs) and perfluoroalkane sulfonates (PFSAs) are of particular concern due to persistent, toxic, and bioaccumulative properties [START_REF] Gomis | Comparing the toxic potency in vivo of longchain perfluoroalkyl acids and fluorinated alternatives[END_REF][START_REF] Shi | Probing the differential tissue distribution and bioaccumulation behavior of per-and polyfluoroalkyl substances of varying chain-lengths, isomeric structures and functional groups in crucian carp[END_REF]. In homologous series of PFCAs and PFSAs, the logarithm of the bioaccumulation factor (Log BAF) and the number of perfluoroalkyl carbon atoms were shown to be linearly correlated over a certain chain length range [START_REF] Hong | Bioaccumulation characteristics of perfluoroalkyl acids (PFAAs) in coastal organisms from the west coast of South Korea[END_REF][START_REF] Kwadijk | Distribution of Perfluorinated Compounds in Aquatic Systems in the Netherlands[END_REF][START_REF] Xu | Bioaccumulation and trophic transfer of perfluorinated compounds in a eutrophic freshwater food web[END_REF]. The perfluoroalkyl chain length was also suggested as a key controlling factor of PFCA and PFSA sorption onto sediment or suspended particulate matter (SPM) [START_REF] Ahrens | Distribution of polyfluoroalkyl compounds in water, suspended particulate matter and sediment from Tokyo Bay, Japan[END_REF]Labadie and Chevreuil, 2011a;[START_REF] Zhang | Determination and partitioning behavior of perfluoroalkyl carboxylic acids and perfluorooctanesulfonate in water and sediment from Dianchi Lake, China[END_REF].

Significant progress has been achieved in recent years to elucidate the environmental fate of PFASs, but there still exist significant data gaps regarding their temporal dynamics in aquatic ecosystems. Hitherto, temporal surveys of biota have essentially focused on long-term and interannual variations, over typically 20-30 years (e.g., [START_REF] Kratzer | Reprint of: Temporal trends of polyfluoroalkyl compounds (PFCs) in liver tissue of grey seals (Halichoerus grypus) from the Baltic Sea, 1974-2008[END_REF][START_REF] Rigét | Trends of perfluorochemicals in Greenland ringed seals and polar bears: Indications of shifts to decreasing trends[END_REF]. Interannual studies are of fundamental interest to evaluate the impact of recent regulations implying restrictions on C8-based PFASs use, commerce, and/or production. Besides, seasonal surveys can provide insightful knowledge on the variability of PFAS levels and profiles at smaller time scales. Available data on intra-annual variability of PFASs remain, however, limited [START_REF] Cai | Temporal trends and transport of perfluoroalkyl substances (PFASs) in a subtropical estuary: Jiulong River Estuary, Fujian, China[END_REF][START_REF] Chen | Occurrence and seasonal variations of per-and polyfluoroalkyl substances (PFASs) including fluorinated alternatives in rivers, drain outlets and the receiving Bohai Sea of China[END_REF][START_REF] Kong | Multimedia fate modeling of perfluorooctanoic acid (PFOA) and perfluorooctane sulphonate (PFOS) in the shallow lake Chaohu, China[END_REF][START_REF] Pignotti | Seasonal variations in the occurrence of perfluoroalkyl substances in water, sediment and fish samples from Ebro Delta (Catalonia, Spain)[END_REF][START_REF] Zhao | Seasonal variations and spatial distributions of perfluoroalkyl substances in the rivers Elbe and lower Weser and the North Sea[END_REF].

Although PFAS partitioning studies and biomonitoring surveys have been conducted, few were spatially or temporally integrated (i.e., realized at the exact same place and time period, respectively) or repeated in time to account for temporal variability (Labadie and Chevreuil, 2011b;[START_REF] Powley | Polyfluorinated chemicals in a spatially and temporally integrated food web in the Western Arctic[END_REF]. Deriving partitioning coefficients from a limited number of field replicates can provide useful preliminary data regarding the environmental fate of pollutants, but there are some caveats. Not accounting for temporal variability may raise questions on the level of representativeness of the reported partitioning coefficients. In estuarine ecosystems, for instance, biogeochemical parameters can greatly vary both spatially and temporally [START_REF] Sottolichio | A synthesis on seasonal dynamics of highly-concentrated structures in the Gironde estuary[END_REF][START_REF] Selleslagh | Seasonal succession of estuarine fish, shrimps, macrozoobenthos and plankton: Physico-chemical and trophic influence. The Gironde estuary as a case study[END_REF]. Such variations may, in turn, lead to non-negligible fluctuations in the field partitioning of contaminants. Certain endpoints can have a direct bearing on chemical substances management (e.g., REACH criterion for very bioaccumulative substances: BAF >5000) as well as on the management of water bodies (e.g., environmental quality standards set by the E.U. Water Framework Directive). The variability of in situ partitioning should, therefore, be accounted for to make well informed decisions.

In this study, we set out to evaluate the temporal variations of PFAS levels and partitioning behaviors. A one-year monitoring survey was launched on a monthly basis at a single study-site within a highly turbid macrotidal estuary. The specific objectives of the present study were as follows: i) examine potential seasonal variations in PFAS levels and profiles in a highly turbid environment; ii) investigate the partitioning behavior of selected PFASs between abiotic and biotic compartments; and iii) conduct a preliminary assessment of PFAS biomagnification at the base of the estuarine food web.

Materials and methods

Chemicals and standards

A full list of chemicals and solvents is provided in the Supporting Information (SI). Analyte names, acronyms, and structures are also provided in the SI (Table S1). Certified PFAS native compounds and isotope-labeled internal standards were all purchased from Wellington Laboratories, Inc. (BCP Instruments, Irigny, France). The targeted PFASs included PFCAs (PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnDA, PFDoDA, PFTrDA, and PFTeDA), PFSAs (PFBS, PFHxS, PFHpS, L-PFOS, and PFDS), perfluorooctane sulfonamide (FOSA) and N-alkylated related compounds (MeFOSA, EtFOSA), N-alkylated perfluorooctane sulfonamide acetic acids (MeFOSAA, EtFOSAA), and 6:2 fluorotelomer sulfonate (6:2 FTSA).

Note that in this paper, "PFOS" refers to the sum of the linear (L-PFOS) and branched (Br-PFOS) isomers. 13 C2-PFHxA 13 C4-PFOA, 13 C2-PFDA, 13 C2-PFUnDA, 13 C2-PFDoDA, 18 O2-PFHxS, 13 C4-PFOS, d3-N-MeFOSAA, 13 C8-FOSA, d3-N-MeFOSA, d5-N-EtFOSA and 13 C2-6:2 FTSA were the internal standards used in the present study.

Study site and sample collection

At the northernmost tip of the Aquitaine coastline, the Gironde estuary (SW France) is a macrotidal estuary resulting from the confluence of the Garonne and Dordogne rivers, the combined flows of which feed into the estuary at Bec d'Ambès (SI Fig. S1). The Gironde flows over 70 km in a general northwestern direction through landscapes alternating natural wilderness, small municipalities, and agricultural areas, before entering the Bay of Biscay near Le Verdon. The Gironde is characterized by a fairly permanent maximum turbidity zone, resulting from the mixing of fresh water inflows (from the Garonne and Dordogne rivers and smaller tributaries) and saltwater wedges from incoming tides [START_REF] Sottolichio | A synthesis on seasonal dynamics of highly-concentrated structures in the Gironde estuary[END_REF]. This estuary is of great ecological value, being an important transit point for several diadromous fish and a nursery area for numerous marine fish during their juvenile stage [START_REF] Lobry | Diversity and stability of an estuarine trophic network[END_REF].

The temporal survey was carried out on a monthly basis from October 2012 to October 2013 at Pauillac (Gironde, France). Located on the left-side bank of the Gironde estuary, the municipality lies approximately 20 km downstream from the confluence of the Garonne and Dordogne rivers and 50 km upstream from the mouth of the estuary (SI Figure S1). Sample collection was carried out at a pier exterior to the marina (Latitude 45.19845°D, Longitude -0.74259°D) during the last two hours of the rising tide, at dates selected for medium tidal coefficients (mean: 55 ± 8) as described by [START_REF] Tapie | Contamination des écosystèmes aquatiques par les PCB et PBDE : Application à l'estuaire de la Gironde[END_REF]. Physical chemical parameters such as water temperature, pH, or salinity were measured on site (SI Table S2).

Water sampling was conducted at high tide, using a 1 L high density polyethylene bottle rinsed 3 times with the site surface water prior to sampling and storage in a cooling box. Upon arrival at the laboratory, the water samples were passed through GF/F (0.7 μm) Whatman glass microfiber filters (previously baked at 400°C for 6h and weighed) using Nalgene ® polyethylene filtration units.

The filtrate was stored at -20°C until analysis. Filters were freeze-dried (24 h) and weighed (to determine the suspended solid amount) prior storage at -20°C until analysis.

A cone-shaped WP-2 net (mesh: 200 μm) was deployed to collect the organisms considered in this study, starting two hours before high tide. Every 5-10 minutes, the net was hauled in and emptied above stacked sieves (mesh sizes: 2 mm, 500 μm and 200 μm). White shrimp (Palaemon longirostris), brown shrimp (Crangon crangon), and mysids (Mysidacea, ind.) were collected and sorted out in the field. Following sacrifice, the catch was stored in 50 mL polypropylene centrifuge tubes. Any other species were returned immediately to the water. Copepods (Copepoda, ind.)

were preserved in a 10 L bottle containing water from the estuary. In the laboratory, the copepod catch was poured in 4 L glass beakers and mixed (1:1 v/v) with Volvic spring water adjusted to the adequate salinity [START_REF] Tapie | Contamination des écosystèmes aquatiques par les PCB et PBDE : Application à l'estuaire de la Gironde[END_REF]. After the decantation of particles and dead animals, live copepods were retrieved from the medium and left overnight in 4 L glass beakers containing Volvic spring water (adjusted to the adequate salinity) and equipped with submerged aerators and an overhanging light source. Particle-free copepods were finally recovered in the 200 μm mesh and stored in 15 mL polypropylene centrifuge tubes. Biota samples were freeze-dried (72 h) and finely ground with pestle and mortar.

Sample extraction and instrumental analysis

Internal standards were added to the samples at the beginning of the extraction procedure (50 μL of a 20 ng mL -1 internal standard mix in methanol). The extraction methods for water and biota samples are described elsewhere [START_REF] Munoz | Spatial distribution and partitioning behavior of selected poly-and perfluoroalkyl substances in freshwater ecosystems: A French nationwide survey[END_REF]Munoz et al., 2017a [START_REF] Munoz | Spatial distribution and partitioning behavior of selected poly-and perfluoroalkyl substances in freshwater ecosystems: A French nationwide survey[END_REF].

Quality assurance and quality control

Method performance was evaluated through the analysis of replicate (n = 3) spiked samples.

Spike recoveries were in the range of 53-115% for Vittel mineral water, 60-119% for reference sediment (surrogate for SPM), and 52-119% for brown trout filets from the Kerguelen archipelago (Southern Ocean). Suitable whole-method precision was obtained, with relative standard deviations (RSD) below 25% (SI Table S3).

In addition, a non-spiked reference matrix (NIST SRM 1947 Lake Michigan Fish Tissue) was analyzed in parallel to the samples to evaluate method trueness. The values determined for PFOS were between 79-96% of those of NIST or Environment Canada [START_REF] Reiner | Determination of perfluoroalkyl acid concentrations in biological standard reference materials[END_REF], with suitable precision (SI Figure S2).

Instrumental blanks remained free of analytes and ISs. Procedural blanks were performed with 0.5 L of Vittel spring water for water samples and with 10 mL of MeOH for SPM and biota samples, submitted to their respective procedures (SI Table S4). Limits of detection (LODs) were in the range of 0.002-0.15 ng L -1 , 0.001-0.13 ng g -1 dw, and 0.001-0.10 ng g -1 ww for surface water, SPM, and biota samples, respectively. R (R version 2.15.3, R Core Team, 2013) and Sigmaplot TM 12.5 (Systat Software) softwares were used to conduct data analysis. Correlations between PFAS levels in the water column and relevant environmental parameters were investigated through the calculation of Spearman's rank order coefficients. Statistical significance was set at p<0.05.

Results and discussion

Seasonal variability of hydro-physical parameters

Water temperatures ranged from 6.6-8.7°C during winter months to 19-25.7°C during summer months. The estimated water flow rate at Pauillac ranged from 170 to 4,700 m 3 s -1 over the overall study period (SI Figure S3) and from 251 to 1,847 m 3 s -1 for the specific days of sampling (SI Table S2). The lowest salinities were observed from January to June (0-2.7‰) under high flow rate conditions, while the highest salinities (4.5-11.6‰) were observed from July to December (SI Figure S4). There was no clear seasonal pattern for the SPM, which was subject to wide variations (130-1,900 mg L -1 ).

Seasonal variations of PFAS levels and profiles in the water column

In surface water (dissolved phase), C5-C10 PFCAs, PFBS, PFHxS, and PFOS displayed the highest detection frequencies (100%) (Table 1). The 6:2 fluorotelomer sulfonate (6:2 FTSA) was also recurrently detected (75%). Occurrence data are in agreement with a 2014 survey conducted at large spatial scale in this estuary (Munoz et al. 2017b). The median ∑PFASs was 6.2 ng L -1 , close to the 7.9 ng L -1 median reported at French nationwide scale for 133 rivers and lakes [START_REF] Munoz | Spatial distribution and partitioning behavior of selected poly-and perfluoroalkyl substances in freshwater ecosystems: A French nationwide survey[END_REF]. Summed PFAS levels varied up to a factor of 3x, between 3.5 ng L -1 (March 2013) and 11 ng L -1 (December 2012). Dissolved PFAS levels are relatively stable (Figure 1a), compared to some other riverine hydrosystems in France (Labadie and Chevreuil, 2011b). This might be due to a "buffering effect" of riverine inputs through estuarine mixing processes, associated with relatively long water residence times in the estuary (~ 20-85 days) [START_REF] Castaing | Temps de résidence des eaux et des suspensions dans l'estuaire de la Gironde[END_REF]. The PFAS molecular pattern was dominated by C5-C8 PFCAs, PFHxS, and PFOS with limited variations across the time period of this study, each group accounting respectively for 47±12%, 14±3%, and 17±5% of the summed PFAS levels (Figure 1b).

We observed a median dissolved PFOS concentration in surface water of 1.1 ng L -1 (mean = 1.04 ± 0.33 ng L -1 , range: 0.48-1.6 ng L -1 ), a relatively low level compared to some major hydrosystems worldwide [START_REF] Pan | Worldwide distribution of novel perfluoroether carboxylic and sulfonic acids in surface water[END_REF]. The median PFOS level in the present survey is also about 20 times lower than that in the Seine River downtown Paris (Labadie and Chevreuil, 2011b). The relatively lower PFOS concentrations may be due to higher dilution capability, lower urban and industrial inputs compared to the Paris region, and much higher SPM loads acting as a sink for long-chain PFASs.

The fluctuations of ΣPFASs and compound-specific abundance in the suspended sediment are

shown in Figure 2. The PFAS concentrations in SPM samples varied by less than one order of magnitude (up to 4.3x) during the present study (ΣPFASs range: 1.3-5.6 ng g -1 dw; median = 2.7 ng g -1 dw) (Figure 2a). The congener profiles also remained consistent during the time period of this study (Figure 2b). PFOS was the predominant compound, at 58±7% of ΣPFASs on average.

Of these, nearly 70% could be attributed to the linear isomer, in agreement with the distribution of PFOS isomers in sediments and likely reflecting both historical electrofluorination sources and the higher sediment-water partition coefficient (KD) of L-PFOS [START_REF] Houde | Fractionation and bioaccumulation of perfluorooctane sulfonate (PFOS) isomers in a lake Ontario food web[END_REF]Labadie and Chevreuil, 2011b).

In the water column (dissolved phase + SPM), PFCAs and PFOS levels were highly correlated to each other and to ΣPFASs (SI Table S5). In contrast, 6:2 FTSA was related in a negative fashion to ΣPFASs, suggesting particular sources and/or different environmental fate. The presence of 6:2 FTSA has been linked with industrial locations and firefighting foam impacted sites, for instance via the degradation of precursors to 6:2 FTSA present in aqueous film-forming foam formulations [START_REF] D'agostino | Certain perfluoroalkyl and polyfluoroalkyl substances associated with aqueous film forming foam are widespread in Canadian surface waters[END_REF][START_REF] Dauchy | Mass flows and fate of per-and polyfluoroalkyl substances (PFASs) in the wastewater treatment plant of a fluorochemical manufacturing facility[END_REF][START_REF] Field | Properties, occurrence, and fate of fluorotelomer sulfonates[END_REF]. In addition, 6:2 FTSA itself could be biotransformed to fluorotelomer unsaturated carboxylates and PFCAs [START_REF] Zhang | Biotransformation potential of 6: 2 fluorotelomer sulfonate (6: 2 FTSA) in aerobic and anaerobic sediment[END_REF][START_REF] Shaw | Degradation and defluorination of 6:2 fluorotelomer sulfonamidoalkyl betaine and 6: 2 fluorotelomer sulfonate by Gordonia sp. strain NB4-1Y under sulfur-limiting conditions[END_REF].

Dissolved PFOS or PFCA levels were not significantly correlated to daily flow rate, which differs from previous observations in the river Seine (Labadie and Chevreuil, 2011b). This indicates that inputs from diffuse sources such as atmospheric deposition may be important compared to those of point sources in this estuary. ΣPFASs was correlated to monthly rainfall (Spearman's rho = 0.58), as were short-chain PFCAs (Spearman's rho = 0.55), which seems to substantiate the prevalence of diffuse sources. The examination of PFHpA/PFOA ratios in the dissolved phase revealed higher values from July to October (1.02-1.35), months that displayed the highest rainfall to flow rate ratios (SI Figures S5-S6). According to literature precedent, this may indicate an increase of the relative importance of atmospheric wet deposition at these sampling dates [START_REF] Simcik | Ratio of Perfluorochemical Concentrations as a Tracer of Atmospheric Deposition to Surface Waters[END_REF]. Conversely, PFHpA/PFOA ratios decreased in the narrow range of 0.45-0.51 from February to April-a potential outcome of the dilution of atmospheric inputs under high river flow conditions.

SPM-water partitioning

KD values were determined by dividing the PFAS concentration in the SPM (in ng kg -1 dw) by that of the dissolved phase (in ng L -1 ), when the analyte was found in both matrices. The average Log KD was in the range of 2.0-3.8 for C7-C11 PFCAs and 1.9-3.4 for C6-C8 PFSAs (Table 2). Log KD values varied within a rather limited range at the water year scale. For instance, the Log KD of L-PFOS averaged 3.3±0.2 (range = 3.1-3.8), and that of PFOA was 2.4±0.2 (range = 2.2-2.7) (SI

Figure S7).

The sediment organic carbon-partitioning coefficient (KOC) was derived from the KD value and SPM organic carbon fraction, foc (range: 1.6-2.7%). Average Log KOC was in the range of 3.6-5.2

for the compounds considered (Table 2).

The particle-related PFAS fraction (φ) was determined by dividing the PFAS concentration in the SPM by that in the water column (i.e., dissolved phase + SPM). For PFSAs, φ varied from 6.5±2%

for PFHxS to 62±14% for L-PFOS (Figure 3). For PFCAs, φ increased with perfluoroalkyl chain length (power law fitting, SI Figure S8), concurring with previous observations by Ahrens et al.

(2010) in the Tokyo Bay. Relatively higher φ values were observed in our case. For instance, the φ value of PFDA was in the range of 50-87% in the Gironde estuary, compared to 23±5.7% in Tokyo Bay [START_REF] Ahrens | Distribution of polyfluoroalkyl compounds in water, suspended particulate matter and sediment from Tokyo Bay, Japan[END_REF]. This may be related to the much higher suspended solid concentrations than those reported in the Tokyo Bay (130-1900 vs. 3-5 mg L -1 ). Other potentially influencing parameters of the suspended sediment-water partitioning of PFASs include sorbent characteristics (e.g., geochemical composition of the SPM, especially organic carbon content) and water quality parameters [START_REF] Higgins | Sorption of perfluorinated surfactants on sediments[END_REF][START_REF] Jeon | Effects of salinity and organic matter on the partitioning of perfluoroalkyl acid (PFAs) to clay particles[END_REF].

Bioaccumulation and biomagnification

In invertebrates, the mean ΣPFASs [in ng g -1 wet weight of the whole body (ww w-b)] was as follows: copepods (2.9±0.8 ng g -1 ww w-b); mysids (7.2±2.0 ng g -1 ww w-b); white shrimps (4.5±1.2 ng g -1 ww w-b); brown shrimps (11±2 ng g -1 ww w-b). These levels fall in the same order of magnitude as those observed by [START_REF] Loi | Trophic magnification of poly-and perfluoroalkyl compounds in a subtropical food web[END_REF] in Mai Po Marshes (Hong Kong) for zooplankton and shrimps (~3-4 ng g -1 ww w-b).

Seasonal variations of ΣPFASs for copepods and mysids are shown in the SI (Figure S9). Over the time period of this study, ΣPFASs varied only up to a factor of 2.5x for zooplankton and 2.3x

for shrimps, further suggesting the relative stability of PFAS levels in this ecosystem. The increasing ΣPFAS trend observed for mysids in the spring-summer months may be attributed to the increase in prey density (i.e., copepods). In addition, shifts in mysid communities from

Neomysis integer to Mesopodopsis slabberi typically occur from April to August [START_REF] David | Long-term changes of the zooplankton variability in a turbid environment: the Gironde estuary (France)[END_REF]. Grazing of vegetal particulate organic matter or periphyton may be another key PFAS exposure route for mysids in the spring-summer months, especially for Mesopodopsis slabberi -Neomysis integer being rather carnivorous and feeding primarily on copepods in the Gironde estuary [START_REF] David | The paradox high zooplankton biomass-low vegetal particulate organic matter in high turbidity zones: What way for energy transfer?[END_REF].

In zooplankton, PFOS dominated the PFAS pattern (SI Figure S10). The mean contribution of PFOS to the ΣPFASs was 56±7 % for copepods and 60±8 % for mysids. This agrees with observations by [START_REF] Loi | Trophic magnification of poly-and perfluoroalkyl compounds in a subtropical food web[END_REF] who reported a mean PFOS abundance of ~57% for zooplankton.

Interestingly, FOSA was the dominant congener in white shrimps, followed by PFOS (35±5 and 30±8 % of ΣPFASs, respectively). The distinctive PFAS pattern observed in shrimps may be a consequence of a low metabolic capacity to transform FOSA and FOSA-like compounds to PFOS.

Another indication to support this hypothesis is the relatively high abundance observed for Nalkylated perfluorooctane sulfonamide acetic acids (~9% of ΣPFASs) in shrimps (SI Figure S10). When applicable, bioaccumulation factors (BAFs) were calculated as the ratio of the concentration in biota (ng kg -1 ww) to that in the water (ng L -1 ) (dissolved phase) for each species and each sampling date (Table 2). Mean Log BAFs were generally comparable in zooplankton and shrimps, in contrast to observations from Taihu Lake (China) where Log BAFs were ~0.6-1.6 log units higher in shrimps than in zooplankton [START_REF] Xu | Bioaccumulation and trophic transfer of perfluorinated compounds in a eutrophic freshwater food web[END_REF]. An illustration of the year-round variations of Log BAFs for PFOS, PFNA, and FOSA is provided in Figure 4. Log BAFs remained relatively constant, suggesting that PFAS concentrations in zooplankton and nekton were under nearequilibrium conditions with those in the dissolved phase.

Exceedances to the "very bioaccumulative" (vB) criterion set in Annex XIII of REACH (bioconcentration factor > 5,000) were observed for L-PFOS, PFUnDA, and FOSA (mean Log BAF = 3.4-3.9, 3.7-4.1, and 4.1-5.0, respectively) (Table 2). Log BAFs increased linearly with increasing perfluoroalkyl chain length, each additional CF2 moiety contributing to an increase of 0.32-0.44 log units for PFCAs and 0.71-1.0 log units for PFSAs (SI Figure S11). These trends are in agreement with observations for other model organisms [START_REF] Kwadijk | Distribution of Perfluorinated Compounds in Aquatic Systems in the Netherlands[END_REF]Labadie and Chevreuil, 2011a;[START_REF] Ahrens | Stockholm Arlanda Airport as a source of per-and polyfluoroalkyl substances to water, sediment and fish[END_REF]. Biota to suspended sediment accumulation factors (BSSAF) were in the range of 0.3-29 for the compounds considered (Table 2).

Biomagnification factors (BMF = Cpredator/Cprey) were tentatively assessed for mysids/copepods (SI suggesting that these compounds may undergo biomagnification at the first trophic levels of the estuarine food web. Such results are consistent with previous findings by Munoz et al. (2017a), who provided evidence for the apparent biomagnification of these PFASs in the Gironde estuary when the whole estuarine trophic web was considered.

Conclusions

The present survey explored the year-round variations of a wide range of PFASs in a macrotidal estuary. PFAS levels and profiles varied within a rather limited range over the time period of the study. PFAS concentrations in surface water were not significantly correlated to flow rate, suggesting the prevalence of diffuse PFAS sources at this site. Field-based distribution coefficients (i.e., KD, KOC, and BAF) were moderately affected by seasonal variations. The magnitude of the suspended solid loads in this highly turbid estuary implies that, in the water column, long-chain perfluoroalkyl carboxylates and sulfonates are mainly bound to the SPM (φ > 60%). From an ecotoxicological standpoint, this could entail different PFAS exposure pathways for organisms dwelling in the maximum turbidity zone of estuaries, for instance via the ingestion of particulate organic matter by deposivores or suspensivores. Biomagnification factors (BMFs mysids/copepods) were consistently >1 (95% confidence interval) for PFOS, FOSA, and certain long-chain perfluoroalkyl carboxylates, suggesting the biomagnification of these compounds at the base of the estuarine food web.

  [START_REF] Tomy | Fluorinated organic compounds in an eastern arctic marine food web[END_REF] also reported EtFOSA concentrations greatly exceeding those of PFOS for shrimps (Pandalus borealis and Hymenodora glacialis) from an Eastern Arctic marine food web. The biotransformation of other perfluorooctanesulfonamide-based PFASs (not targeted in the present survey) could also have played a role in the observed FOSA levels (Mejia-Avendaño et al. 2016; Barzen-Hanson et al. 2017).

Figure S12 ).

 S12 Figure S12). With the exception of PFHxS, average BMFs were >1, the highest values being

Figure 1 .

 1 Figure 1. Seasonal variations of ΣPFASs in the dissolved phase (a) and corresponding composition profiles

Figure 2 .

 2 Figure 2. Seasonal variations of ΣPFASs in the suspended sediment (a) and corresponding composition

Figure 3 .

 3 Figure 3. Average particle-related fraction (φ = ratio of the PFAS concentration determined in the SPM to

Figure 4 .

 4 Figure 4. Variations of the bioaccumulation factor (Log BAF = Cbiota/Cwater) illustrated in the case of mysids

Table 1 .

 1 Summary of PFAS detection frequencies (%) and concentrations (ng L -1 ) in surface water samples from the present survey (dissolved phase). Compounds that were not detected are not shown.

		Detection Frequency Concentration range*
		%	ng L -1
	PFBA	50	0.39-2.0
	PFPeA	100	0.26-2.4
	PFHxA	100	0.46-2.0
	PFHpA	100	0.24-1.4
	PFOA	100	0.40-1.9
	PFNA	100	0.09-0.27
	PFDA	100	0.06-0.22
	PFUnDA	50	0.02-0.04
	PFBS	100	0.26-0.69
	PFHxS	100	0.58-1.3
	PFHpS	92	0.02-0.07
	Br-PFOS	100	0.23-0.79
	L-PFOS	100	0.25-0.80
	ΣPFOS**	100	0.48-1.6
	FOSA	75	0.01-0.05
	6:2 FTSA	75	0.05-0.52

*Min-max of samples >LOD. **Sum of branched and linear isomers.

for perfluorooctane sulfonamide (FOSA), perfluorooctane sulfonate (L-PFOS), and perfluorononanoate

Acknowledgments

This study was carried out within the PFC-Gironde CNRS project (EC2CO-Ecodyn INSU), with financial support from the French National Research Agency (ANR). The study was conducted in the frame of the Investments for the future Program, within the Cluster of Excellence COTE (ANR-10-LABX-45). The authors also acknowledge funding from the Aquitaine Regional Council and the European Union (CPER A2E project and ERDF). The authors wish to thank Virginie Bocquet, Mariange Cornet, Patrick Pardon, Gwenaël Abril, and Dominique Poirier for their contribution.

Year-round daily data of salinity and turbidity at Pauillac were supplied by MAGEST (Réseau de surveillance automatisée du système estuarien Garonne-Dordogne-Gironde). IdEx Bordeaux (ANR-10-IDEX-03-02) provided the PhD grant allocated to G. Munoz.

PFHxS

1.9 ± 0.3 3.7 ± 0.3 2.0 ± 0.2 1.3 ± 0.9 1.9 ± 0.4 0.9 ± 0.5 1.9 ± 0.2

L-PFOS

3.4 ± 0.2 5.0 ± 0.2 3.4 ± 0.2 1.4 ± 0.9 3.9 ± 0.2 3.8 ± 2.2 3.4 ± 0.2 1.2 ± 0.7 3.9 ± 0.1 4.6 ± 1.9

EtFOSAA ---1.1 ± 0.5 -0.9 -1.9 ± 1.3 -1.9 ± 1.6

L-FOSA 3.5 ± 0.2 5.3 ± 0. 21


Magali Boespflug

Bruno Mazieres

French Consumer Co-operatives: Pioneers of French Modern Distribution

Purpose

This research aims at explaining how consumer co-operatives have been pioneers of modern distribution in France. These companies issued from the 19 th century socialist utopia provided the basis for both modern marketing and Corporate Social Responsibility (CSR) principles. Using an historical approach, we will introduce the different cooperative innovations that were finally adopted by the main actors of the French distribution sector.

The case: French consumer co-operatives

The choice of this specific type of company has been motivated by different reasons. First, it is a very old form of distribution. Indeed, even if it has been developed on a larger scale and on a sustainable way by the Rochdale Society of Equitable Pioneers in England during the 19 th century, the very first one was developed in Lyon (France) in 1835 by the "Canuts" [silk industry workers]. This form of cooperative originated in social movements led by unsatisfied customers. Then, its legal status is original for a consumer co-operative belongs to its customers (the so-called members or co-operators) in charge of marketing goods at a fair price and ensuring the sustainability of the co-operative. Lastly, consumer co-operatives have been leaders of the French distribution sector from the 19 th century to the 1980s.

Methodology

Data collection was based on both primary and secondary sources. Relevant information was taken from literature about the cooperative sector and the French distribution industry. We also had access to the archives of Coop Atlantique (the most important remaining French consumer co-operative) and public archives. This documentary research work was completed by several semi-directive individual interviews and focus groups with different consumer co-operative stakeholders, such as customers, cooperators, employees, and managers (active and retired). We also organized and were part of seminars on co-operatives, which gave us the opportunity to interact with both professional (co-operative managers or members of cooperative federations) and academic (researchers in History, Economy, Marketing and Semiology) stakeholders.

Consumer co-operatives as pioneers

We were able to identify two fields in which French consumer co-operatives could be considered as pioneers in France: marketing practices and societal orientation.

Consumer co-operatives as pioneers in marketing practices

Consumer co-operatives are behind numerous marketing innovations regarding price, product, distribution or promotion policies. In terms of price, a first idea came directly from the roots of consumer co-operatives. Indeed, first members were workers unable to buy food items made too expensive by the industrialization of France and its effect on the reduction of food-crop production. As

a result, co-operatives were created to offer products sold at a "fair price", that is, lower than their competitors (for this purpose, price studies were conducted as soon as 1921). This price strategy can still be found today in the practices of many French distributors, such as Leclerc, and in the development of many price comparison tools. Moreover, after the First World War, co-operatives implemented a system of cooperative rebate: the more a co-operator will purchase, the more he will get rebate (in cash or gifts). This is clearly the ancestor of our fidelity cards and loyalty programs widely used nowadays in the distribution area. As regards products, consumer co-operatives introduced the brand "Coop" in 1922. That was the very first private label used in the French distribution sector; today, all distribution groups have developed their own brands. Moreover, Coop products were developed and produced within the co-operatives: many factories and warehouses were dedicated to a wide range of private label products (chocolate, coffee, wine, etc.) This integration strategy is now spread in the whole French distribution sector, with concepts such as quality lines (Carrefour Group) or the "producer and retailer" slogan (Les Mousquetaires Group). In terms of distribution, consumer co-operatives have always sought to address the customers' needs for convenience. First, they have always valued convenience stores, which was not the case of the rest of the sector some decades ago; this store format is yet developing once more in France due to the increasing consumers' need for closeness. Besides, a home delivery service using mobile stores has been proposed for many years, long before the e-commerce and the concept of drive-thru supermarket. Finally, regarding communication strategy, consumer co-operatives have proposed various actions with can be considered precursors of modern customer relationship management tools. As early as in the 1920s, vouchers were proposed to co-operators so as to increase their loyalty. In 1928, the very first issue of "Le coopérateur de France" [The French co-operator] was published: this periodical provided clients with advertisements, local and regional cooperative information and useful tips on health, cooking, gardening, etc. and it can be seen as a vintage version of our current newsletters or magazines.

Consumer co-operatives as pioneers in CSR practices

French co-operatives are precursors in Corporate Social Responsibility since they have always applied the cooperative principles developed by the International Co-operative Alliance (ICA) in 1895. These guidelines are used by co-operatives to put their values into practice: democracy, responsibility, solidarity, sustainability, transparency, closeness and service. First, democracy is the core and distinctive value of the cooperative model. Thus, co-operators run their company directly or obliquely through the election of representatives. That enables customers to rebalance their bargaining power within their co-operative. Responsibility is key element of a co-operative because members are invited to be part of the everyday life of their company. Also, consumer co-operatives have always taken care of developing their communication towards co-operators in order to increase their involvement. Solidarity is exercised in favor of different stakeholders: social conditions have often been more favorable to employees compared to what happens in other distribution companies (for example, when mergers occur, or co-operatives have to close, the safeguarding of jobs is a priority). Also, cooperatives have always been community-oriented, providing support for local associations, etc. Sustainability can be observed inside the co-operative status (as it is owned by its members and cannot be sold without their agreement) or in their commitment in social or environmental actions (as an example, the increasing offering of local or organic products). Transparency towards members and community is achieved through different actions. First, co-operators are consulted in annual general meetings. Then, consumer co-operatives developed the "Laboratoire coopératif" [Cooperative laboratory] in 1955. One of its missions was to conduct independent analyses not only on Coop products but also on competitors' products in order to give co-operators and consumer associations relevant information. Closeness has always been part of consumer co-operatives. The localization of the points of sale provides an extended geographical coverage, even in rural areas. Moreover, this local anchoring is strengthened by a large local food product offering and the use of short food supply chains, making co-operatives real players in regional development. A significant number of innovative services has been provided by consumer co-operatives: credit activity, sport and recreational activities and vacation centers (1920s), consumer protection and travel agency (1970s), food and nutrition education programs for youth (from 1977 onwards).

Discussion

Despite significant contributions in marketing and CSR since the 19 th century in France, today's consumer co-operatives represent a very marginal share of the French market when they used to be leaders up to the 1980s. The largest remaining one, Coop Atlantique, has no more than 4,000 employees. This evolution might be largely due to a communication too much focused on current cooperators and not enough on other stakeholders such as customers (that are potential co-operators), government authorities, etc. Thus, the competitors of co-operatives have taken up these marketing and CSR innovations and have implemented large communication campaigns on these issues. However, co-operatives could be back in emphasizing their core values. In terms of marketing, they have to communicate on their still-living historical and activist dimension. Societally speaking, they need to insist on their distinctive added values of democracy and their involvement towards members and community, which is already at stake in the development of new innovative models of much smaller size like cooperative groceries.