Delphine Bertin
email: delphine.bertin@univ-lyon1.fr

J D Ferrari

Pierre Labadie

Alexandre Sapin
email: asapin@rovaltainresearch.com

Débora Da

Silva Avelar

Rémy Beaudouin

Alexandre Péry

Jeanne Garric

Hélène Budzinski

Marc Babut

 Alexandre

Refining uptake and depuration constants for fluoroalkyl chemicals in Chironomus riparius larvae on the basis of experimental results and modelling

Keywords: Per-and polyfluoroalkyl substances, perfluorotridecanoic acid, Chironomus riparius, bioaccumulation, uptake rate, concentration-dependency

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 compounds of emerging interest;

their numerous uses and specific properties induce their global distribution in the environment [START_REF] Houde | Monitoring of Perfluorinated Compounds in Aquatic Biota: An Updated Review[END_REF][START_REF] Houde | Biological monitoring of polyfluoroalkyl substances: A review[END_REF][START_REF] Prevedouros | Sources, fate and transport of perfluorocarboxylates[END_REF]. The physicochemical

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

properties of PFASs differ substantially from those of other persistent organic pollutants (POPs). While the perfluoroalkyl moiety is hydrophobic and lipophobic [START_REF] Bhhatarai | Prediction of Aqueous Solubility, Vapor Pressure and Critical Micelle Concentration for Aquatic Partitioning of Perfluorinated Chemicals[END_REF], the functional group increases the solubility in water, and per-and polyfluoroalkyl acids are thus amphiphilic. These complex properties make it difficult to predict their bioaccumulation, even though it seems that the bioaccumulation of longer-chain PFASs is partly driven by their increasing lipophilic character [START_REF] Greaves | Brain region distribution and patterns of bioaccumulative perfluoroalkyl carboxylates and sulfonates in east greenland polar bears (Ursus maritimus). Environmental Author-produced version of the article published in cotoxicology and Environmental Safety[END_REF]. Several studies have shown the presence of PFASs in sediment [START_REF] Ahrens | Partitioning Behavior of Per-and Polyfluoroalkyl Compounds between Pore Water and Sediment in Two Sediment Cores from Tokyo Bay, Japan[END_REF][START_REF] Bao | Perfluorinated compounds in sediments from the Daliao River system of northeast China[END_REF][START_REF] Bao | Perfluorinated compounds in urban river sediments from Guangzhou and Shanghai of China[END_REF][START_REF] Higgins | Quantitative determination of perfluorochemicals in sediments and domestic sludge[END_REF][START_REF] Labadie | Partitioning behaviour of perfluorinated alkyl contaminants between water, sediment and fish in the Orge River (nearby Paris, France)[END_REF][START_REF] Myers | Fate, distribution, and contrasting temporal trends of perfluoroalkyl substances (PFASs) in Lake Ontario, Canada[END_REF][START_REF] Zushi | Time trends of perfluorinated compounds from the sediment core of Tokyo Bay, Japan (1950s-2004)[END_REF], whereas other studies have suggested the importance of sediment as a PFAS source for biota (e.g., [START_REF] Martin | Perfluoroalkyl contaminants in a food web from lake Ontario[END_REF]. However, PFAS transfer from sediment to biota is poorly understood. Only a few experimental studies have provided evidence of bioaccumulation from sediment by benthic invertebrates, namely in the oligochaete worm,

Lumbriculus variegatus [START_REF] Higgins | Bioaccumulation of perfluorochemicals in sediments by the aquatic oligochaete Lumbriculus variegatus[END_REF][START_REF] Lasier | Perfluorinated chemicals in surface waters and sediments from northwest Georgia, USA, and their bioaccumulation in Lumbriculus variegatus[END_REF][START_REF] Prosser | Bioaccumulation of perfluorinated carboxylates and sulfonates and polychlorinated biphenyls in laboratory-cultured Hexagenia spp., Lumbriculus variegatus and Pimephales promelas from field-collected sediments[END_REF], in insect Chironomus riparius [START_REF] Bertin | Bioaccumulation of perfluoralkyl compounds in midge (Chironomus riparius) larvae exposed to sediment[END_REF] and Hexagenia spp. larvae [START_REF] Prosser | Bioaccumulation of perfluorinated carboxylates and sulfonates and polychlorinated biphenyls in laboratory-cultured Hexagenia spp., Lumbriculus variegatus and Pimephales promelas from field-collected sediments[END_REF], and in an amphipod, Gammarus spp. [START_REF] Bertin | Potential exposure routes and accumulation kinetics for poly-and perfluorinated alkyl compounds for a freshwater amphipod: Gammarus spp. (Crustacea)[END_REF]. Two contamination routes were identified for C. riparius: food was the main route of exposure for perfluorinated carboxylic acids (PFCAs) with a fluorinated chain from C 11 to C 14 , and perfluorooctane sulfonamide (FOSA). For perfluoroundecanoic acid (PFUnDA), perfluorooctane sulfonate (PFOS), and 6:2 fluorotelomer sulfonic acid (6:2 FTSA), which are present in pore water (PW) and sediment, both uptake from water (i.e. respiration) and from food were involved.

Accumulated concentrations in this species fit an exponential curve which could be supported by two models: (i) a classical partition model [START_REF] Higgins | Bioaccumulation of perfluorochemicals in sediments by the aquatic oligochaete Lumbriculus variegatus[END_REF], which assumes that the PFASs concentrations in organisms and sediment at steady state are proportional; and (ii) a concentration-dependency model [START_REF] Liu | Novel Perspectives on the Bioaccumulation of PFCs -the Concentration Dependency[END_REF], which hypothesizes that the uptake kinetics involves active transport through binding to specific sorption sites, such that these sites may become saturated at high exposure concentrations. To gain a more accurate understanding of the processes underpinning the PFAS uptake mechanisms for chironomids, and to refine the uptake and depuration constants, the models proposed must be tested to determine which is the most suitable.

The aims of the present study were therefore (i) to describe PFAS elimination kinetics for chironomids, and (ii) to test the concentration dependency of the PFAS bioaccumulation for a model compound, the perfluorotridecanoic acid (PFTrDA). A combined accumulation and depuration experiment involving field sediment was implemented to address the first objective. For the second one, we conducted combined accumulation and depuration experiments at different concentrations and applied a bioaccumulation model adapted to these compounds and species that could account for realistic kinetics constants.

Bioaccumulation modeling: theoretical background

Assuming that PFAS uptake and elimination depend on the organisms' surface, the dynamics of the PFAS load in the organism are defined as follows:

𝑑(𝑄 𝑜𝑟𝑔 ) 𝑑𝑡 = 𝑆 𝑜𝑟𝑔 . 𝑘 𝑢 . 𝐶 𝑠𝑒𝑑-𝑜𝑐 -𝑆 𝑜𝑟𝑔 . 𝑘 𝑒 . 𝐶 𝑜𝑟𝑔 Eq. ( 1)

where Q org corresponds to the quantity of PFASs in and/or on the organism, S org the chironomids surface, k u (g.g ww .mm -2 .d -1 ) and k e (mm -2 .d -1 ) the uptake and elimination constants, respectively. C sed-oc (ng.g oc -1

dw ) and C org (ng.g -1 ww ) indicate the PFAS concentrations in sediment adjusted to the f oc , and in the organisms, respectively. As a consequence of growth during the test [START_REF] Péry | A modeling approach to link food availability, growth, emergence, and reproduction for the midge Chironomus riparius[END_REF], the tissue concentration dynamics is described by Eq. 2 (details in SI):

𝑑(𝐶 𝑜𝑟𝑔 ) 𝑑𝑡 = ( 1 𝐿 . 𝑘 𝑢 . 𝐶 𝑠𝑒𝑑-𝑜𝑐 - 1 𝐿 . 𝑘 𝑒 . 𝐶 𝑜𝑟𝑔 ) -𝐶 𝑜𝑟𝑔 × 𝑑(𝑉) 𝑑𝑡 × 1 𝑉 Eq. (2)
Where C org is the internal concentration, L is the chironomids length (cm), and V is the chironomid volume (cm 3 ). Note that k u and k e in Eq. ( 2) are expressed in different units than in Eq. ( 1), namely g oc .g ww .h -1 for k u and h -1 for k e .

PFAS uptake may or may not be concentration-dependent, i.e. this uptake could follow either first order kinetics or kinetics with saturation. In case of concentration-dependency, the accumulation can be viewed as an adsorption-like process, in which the chemical adsorb at binding sites, i.e. specific components of the organs where PFASs accumulate [START_REF] Liu | Novel Perspectives on the Bioaccumulation of PFCs -the Concentration Dependency[END_REF]. The binding site saturation process progressively slows down the uptake, and the steady state is reached at a lower concentration than in the case of a first order kinetics. Both the concentration in the exposure media and the number of sites remaining free control the uptake rate. The S term was introduced in order to model these two cases:

𝑆 = 1 ( 1+ 𝐶 𝑜𝑟𝑔 𝐶 50 ⁄ )
Eq. ( 3)

with C 50 representing the half-saturation concentration, i.e. the internal concentration at which the uptake is one-half of its maximum rate. When C org is low, S is close to 1, and the dynamics follow Eq. 2; conversely, when C org increases and site binding occurs, S decreases and tends to 0, meaning that the uptake is lower or stopped. The final equation is: A working solution containing all analytes, each at approximately 0.05 ng.µL -1 , was prepared in MeOH and stored at -18°C. 13 C-labelled perfluorodecanoic acid (PFDA), PFOS, and perfluorooctane sulfonamide (FOSA), each at 50 ng.µL -1 in MeOH, were supplied by Wellington Laboratories and used as internal standards (ISs). A working solution was prepared in MeOH, each containing IS at 0.1 ng.µL -1 (Table S1 in supplementary information).

LC/MS-grade MeOH and acetonitrile (ACN) were purchased from J.T. Baker via Interchim (Montluçon, France). Sodium acetate buffer (99%, ACS Reagent), ammonium hydroxide (28-30% in water), 0.2-µm nylon centrifuge tube filters, and ENVI-Carb cartridges (6 cc, 250 mg)

were obtained from Sigma-Aldrich (St Quentin Fallavier, France), whereas Strata XAW (6 ml, 200 mg) were purchased from Phenomenex (Le Pecq, France). Nitrogen (99%) was supplied by Air Liquide (Paris, France). Ultra-pure water was obtained using an Elix 10 purification system fitted with an EDS pack (Millipore, Guyancourt, France).

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

Testing strategy

Two experiments were conducted with C. riparius: an accumulation test with field and fieldspiked sediment, and an elimination test with field and field-spiked sediment (Figure S1 in SI). The decision to spike field sediment was made for testing the concentration-dependency hypothesis; spiking involved PFTrDA, the main PFAS among those detected in the field sediment used in the present study [START_REF] Munoz | Spatial distribution and partitioning behavior of selected poly-and perfluoroalkyl substances in freshwater ecosystems: A French nationwide survey[END_REF]. The elimination experiment was implemented in order to improve the accumulation kinetics modelling when concentrationdependency occurs [START_REF] Bertin | Bioaccumulation of perfluoralkyl compounds in midge (Chironomus riparius) larvae exposed to sediment[END_REF].

Field sediment

The study was conducted using sediment collected at Beurre Island (characteristics in SI).

This site is a fluvial annex of the Rhone River (eastern central France, N45°28′17.0″E4°46′43.4″) located downstream of a fluoropolymer manufacturing plant.

Since 1902, this industrial site has been used to produce hydrofluoric acid and a wide array of fluorine-based organics. Three PFAS production periods can be defined at this site: (i) polytetrafluoroethylene (PTFE) production from 1960 to 1987, (ii) fluorinated copolymers synthesis from 1981 to 1996,and (iii) polyvinylfluoridene (PVDF) production from  1981 onwards [START_REF] Dauchy | Relationship Between Industrial Discharges and Contamination of Raw Water Resources by Perfluorinated Compounds. Part I: Case Study of a Fluoropolymer Manufacturing Plant[END_REF]. Two campaigns were conducted in 2013 (March and November): 50 L of surface sediments ( 5 cm deep) were collected from the river bed with a Van-Veen grab, kept on ice, and brought to the laboratory, where they were sieved at 2 mm, pooled in a polypropylene (PP) jar, and stored at 4°C.

Sediment spiking

In order to test the concentration-dependency hypothesis, field sediments were spiked with PFTrDA, on the basis of the field sediment contamination pattern [START_REF] Munoz | Spatial distribution and partitioning behavior of selected poly-and perfluoroalkyl substances in freshwater ecosystems: A French nationwide survey[END_REF], and on the chironomids accumulation capacity [START_REF] Bertin | Bioaccumulation of perfluoralkyl compounds in midge (Chironomus riparius) larvae exposed to sediment[END_REF]. The loss of ignition (LOI) values of these sediments laid between 5.2 % and 5.4 %, corresponding to organic carbon fractions (f oc ) of 0.02 (conversion factor of 2.4 based on Craft et al.,1991). The spiking solution was prepared with a stock solution purchased from Wellington Laboratories (via BCP Instruments, Irigny, France). For each concentration, a PFTrDA solution (0.1 g.L -1 in MeOH) was added to 1.2 L of sediment and 0.4 L of clean water. The bottles were gently shaken for 6 h; the sediment was then allowed to settle for 48 h and the overlying water (OW) cautiously siphoned off. The sediment was then homogenised and subsequently reintroduced in aquaria for chironomid exposure. In the first experiment, PFTrDA was added at twice (C1) its initial concentration in the field sediment (1.64 ± 0.03 ng.g -1 dw). The accumulation phase was reduced to 2 days, in order to increase the duration of the depuration period and get more samples for this phase. For a second experiment PFTrDA was added at approximately five times (C2) the initial field sediment concentration (1.67 ± 0.48 ng.g -1 dw) and ten times (C3) the field sediment concentration (1.67 ± 0.48 ng.g -1 dw). Note that two different batches of field sediments were used for these experiments, displaying similar PFTrDA concentrations at 1.64 ± 0.03 ng.g -1 dw and 1.67 ± 0.48 ng.g -1 dw (Table S2). Sediment depth after transfer in the aquaria was approximately 5 cm.

Chironomus riparius accumulation and depuration tests

Chironomids were obtained from our laboratory cultures maintained according to standard methods (OECD, 2004;AFNOR, 2010). Experiments were conducted in the same laboratory conditions as previously described by [START_REF] Bertin | Bioaccumulation of perfluoralkyl compounds in midge (Chironomus riparius) larvae exposed to sediment[END_REF] Three aquaria (38 × 20 × 24.5 cm in polystyrene) were prepared with 4 L of homogenized sediment and 15 L of OW: one with field sediment, one with C2-spiked sediment and the last one with C3-spiked sediment. Three control aquaria were prepared in parallel with silica sand (particle size distribution: 90% 50-200 µm, 10% <50 µm). A total of 2400 L4 larvae were added to sediment and control aquaria (400 in each aquarium). After 4 days of exposure (Fig.

S1-part A), chironomids from both test and control aquaria were collected and cryopreserved, as explained below in section 3.2.6.

Elimination test

Four more aquaria were prepared, each with 4 L of homogenized sediment spiked with PFTrDA (i.e. C1) with 15 L of OW. One control aquarium was prepared with silica sand having the same characteristics and origin as in the accumulation test. A total of ca. 4.000 L4 larvae were added to the spiked-sediment aquaria (1000 in each aquarium), and 400 L4 larvae were added to the control aquarium. After 2 days of exposure, up to 400 larvae were collected in the sediment; the larvae remaining in the spiked-sediment aquarium were directly (without gut clearance phase) transferred to three aquaria (400 larvae in each aquarium) containing silicate sand and clean water for the depuration phase. Similarly, 1.200 remaining larvae from the field sediment aquaria were directly (without gut clearance phase) transferred to three aquaria prepared with silica and clean water. The organisms were collected and sacrificed after 6 h, 18 h, and 42 h of depuration (one aquarium stopped at each time); finally, 42 h after the transfer the control organisms were also sacrificed (Fig. S1 -part B).

The same design was applied to field (un-spiked) sediment.

Sample collection and organism measurements

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

The OW was sampled in 1-L polyethylene (PE) bottles and the pore water (PW) was sampled with a porous polymer micro-sampler (Rhizon® system, SDEC, Reignac-sur-Indre, France; description in SI). At the end of exposure, subsamples from sediment were deposited in PE tubes. Chironomids were collected by sieving sediment or silica at 500 µm; about 200 larvae (ca 800 mg ww or 200 mg dw) were pooled and cryopreserved in liquid nitrogen and then stored at -21°C before PFAS analysis. As C. riparius gut contents represent about 6 % of the total body weight [START_REF] Ferrari | Bioaccumulation kinetics and effects of sediment-bound contaminants on chironomids in deep waters: New insights using a low-disturbance in situ system[END_REF], and gut clearance was not feasible in the elimination test, organisms were directly sacrificed. Water and sediment samples were frozen and kept at -21°C. Additionally, initial body residue was determined by pooling and cryopreserving about 200 individuals at the start of each experiment.

Chironomid survival, length and (wet) weight were determined for each time point, including the start of each experiment. To determine the total length, four groups of ten larvae were photographed and the mean sizes determined using digital image analysis software (Jmicrovision, available free at http://www.jmicrovision.com/). The same groups were then weighed (weighing scales: Sartorius CPA225D, France) to obtain mean individual masses.

PFAS analysis

PFAS extraction

The PFAS extraction methods for OW, PW and sediment samples were similar to those described in [START_REF] Bertin | Bioaccumulation of perfluoralkyl compounds in midge (Chironomus riparius) larvae exposed to sediment[END_REF]. Briefly, PFASs were extracted from water samples using Phenomenex Strata-XAW cartridges while sonication in methanol was used for sediment samples, followed by graphitized carbon black clean-up. For the chironomid samples, the method was adapted with minor modifications: both neutral and acid analytes were eluted in a single fraction using MeOH containing 0.2% NH 4 OH (30% in water). 13 SRM 1947 fish reference matrix [START_REF] Reiner | Determination of perfluorinated alkyl acid concentrations in biological standard reference materials[END_REF].

LC-MS/MS analysis

PFASs were analysed using an Agilent 1200 LC system (Agilent Technologies, Massy, France) interfaced with an Agilent 6460 triple quadrupole mass spectrometer (details in Table S3).

Quality control and methods

Analyte recovery was determined using spiked samples (n=3) for each matrix (surface and pore water, sediment, and chironomids) within the range 50-123% (Table S4).

Replicate procedural blanks were analysed for each series of samples. PFAS concentrations were blank-corrected when applicable. For compounds present in blanks, the limits of detection (LDs) were defined as three times the standard deviation of the blank, and the limits of quantification (LQs) were set at ten times the standard deviation of the blank. For analytes not detected in the blanks, LDs (0.001-0.103 ng.g -1 or ng.L -1 ) and LQs (0.003-0.310 ng.g -1 or ng.L -1 ) were determined as the concentration with a signal-to-noise ratio of 3 and 9, respectively. This was calculated on matrices spiked at 0.3-1.1 ng.g -1 (sediment and C. riparius) and 0.7-1.4 ng.L -1 (Vittel® mineral water samples) (Table S5). The PFASs measured in SRM 1947 Lake Michigan Fish Tissue and compared with the NIST value are presented in SI (Table S6).

Data analyses and modelling

Data were checked for normality using the Shapiro-Wilk test and were analysed using the Student t-test. Experimental biota-to-sediment accumulation factors (BSAF exp ) were determined by dividing tissue concentrations (C org , ng.g -1 ww) at steady state by concentrations in sediment normalized by f oc (C sed-oc = C sed /f oc ng.g oc -1 dw) [START_REF] Ankley | Bioaccumulation of PCBs from sediments by oligochaetes and fishes: comparison of laboratory and field studies[END_REF][START_REF] Burkhard | Comparing laboratory-and field-measured biota-sediment accumulation factors[END_REF]. As lipids do not influence PFAS accumulation in tissues, it is not

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011 appropriate to adjust C org to chironomid lipid content [START_REF] Higgins | Bioaccumulation of perfluorochemicals in sediments by the aquatic oligochaete Lumbriculus variegatus[END_REF].

Concerning the bioaccumulation modelling, two different hypotheses were tested: (H1) concentration dependency (Eq. 4), and (H2) no concentration-dependency (Eq. 2). The model parameter values (depending on the hypothesis) were adjusted simultaneously in order to obtain the best fit to experimental data. The uptake and elimination coefficient (k u and k e ), the half-saturation concentration (C 50 ) and the growth rate (r) were adjusted simultaneously by minimizing the weighted least squares between the simulated and observed data. For each hypothesis, the distance and the adjusted coefficient of determination (R 2 ) were calculated.

Model calculations and data analyses were performed with R software (R-Core-team, 2012)

within the RStudio environment (Version 0.97.336).

Results

Sediment contamination

Long chain perfluoro-alkyl carboxylates were predominant in field sediments: PFUnDA (0.85 ± 0.11 ng.g dw -1 and 0.91 ± 0.26 ng.g -1 dw) and PFTrDA (1.64 ± 0.03 ng.g dw -1 and 1.67 ± 0.48 ng.g -1 dw) in March and November respectively. PFOS (0.58 ± 0.05 ng.g dw -1 and 0.36 ± 0.13 ng.g -1 dw) and FOSA (0.03 ± 0.01 ng.g dw -1 and 0.045 ± 0.02 ng.g dw -1 ) were observed at much lower concentrations. PFTrDA strongly sorbed onto sediment particles and its concentration increased with the increasing spiking level: after spiking the measured PFTrDA were 3.66 ± 0.48 ng.g -1 dw (C1); 5.83 ± 0.72 ng.g -1 dw (C2); 10.78 ± 0.64 ng.g -1 dw (C3) (Fig. S2; Table S7). PFTrDA concentrations apparently decreased during the tests by 43 % in one instance (C2); they might have decreased slightly in the other instances, by about 10%

(field, C3), to 25 % (field) (Table S6 in SI), so within the range of the analytical uncertainty.

Chironomids : survival and PFAS depuration kinetics

In the accumulation experiment, chironomid survival at each condition was 97.0%, 92.8% and

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011 96.0% for the test samples (field sediment, C2, and C3, respectively) and 97.1 ± 2.9% for the control sample. In the elimination experiment, chironomid survival was 96.4 ± 2.6% and 62.8 ± 17.7% for the test and 81.9% and 91.1 ± 4.0% for the control samples, respectively. The larva length data fit a linear growth model well (R 2 = 0.798).

Concentrations in control treatments were systematically below LDs. The chironomids accumulated two PFCAs (PFUnDA and PFTrDA) as well as PFOS and its precursor FOSA (Figure 1). For all compounds, PFAS elimination was nearly complete in 42 h. In all these experiments, the PFTrDA concentration increase in spiked sediments was more important than in chironomids (Figure 2): while the raw sediment concentration increased by Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011 a factor ≈2-3 in (C2) and ≈6 (C3), the respective increase rates in chironomids were ≈1.5 (C1), 3.4 (C2) and 5.6 (C3). This pattern was more evident when PFTrDA concentrations in sediment were adjusted to organic carbon content (Table 1). Nevertheless, the BSAFs exp resulting from the different exposure conditions ( S8; they are in the same range as for PFTrDA, between 0.006 -0.007 for PFUnDA and 0.013 -0.022 for FOSA.

Model outcomes

The model parameters (k u , k e , r and C 50 for PFTrDA in the case of H1; k u , k e and r for PFTrDA in the case of H2) were adjusted simultaneously on the basis of all results in order to obtain the best fit to the data by minimizing the weighed least squares between simulated and observed data.

The final uptake and elimination rates for PFTrDA are presented in Table 2. There was much better agreement between observed and simulated data for H1 (adjusted R² 0.978, distance 1.279; Figure 3-A) than for H2 (adjusted R² 0.655, distance 13.919; Figure 3-B).

Hypotheses k u (g oc .g ww .h -1 ) k e (h -1 ) H1 0.013  0.008 0.032  0.009 H2 0.00077  7.5*10 -5 0.0098  0.0042

Table 2 -Optimized uptake and depuration constants for PFTrDA.

Growth curves displayed in Figure 3-A and B (right-hand panels, fitted simultaneously with accumulation data) are essentially identical, as they rely on the same data. Slopes (growth rates) did not differ between the experiments, and between field and spiked sediments. PFTrDA half-life (T 1/2 ) on the basis of model H1 was 0.65 day. .

Discussion

Sediment spiking

The sediment contamination profile at the sampling site is rather unusual, with PFTrDA

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290

The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

contributing up to 36 % to the sum of PFAS concentrations [START_REF] Munoz | Spatial distribution and partitioning behavior of selected poly-and perfluoroalkyl substances in freshwater ecosystems: A French nationwide survey[END_REF], and reaching concentrations as high as 1.67 ± 0.48 ng.g -1 dw, which is comparable to [START_REF] Zushi | Time trends of perfluorinated compounds from the sediment core of Tokyo Bay, Japan (1950s-2004)[END_REF]. These authors measured this compound at 1.2 ng.g -1 (dw) in Tokyo Bay sediment.

Only a few other studies looked for this chemical (e.g. [START_REF] Zhao | Spatial distribution of perfluoroalkyl acids in surface sediments of the German Bight, North Sea[END_REF], and generally found lower concentrations than in this study. While it is therefore very difficult to confirm whether or not the spiking schedule was realistic, we considered that this was not a significant concern, given that the motivation for spiking was to determine whether or not concentration dependency occurs.

Uptake and elimination kinetics

The comparison of model performances for the two hypotheses shows a much better fit to experimental data for H1. The discussion about uptake and elimination kinetics is accordingly focused on H1 model outcomes. PFTrDA elimination by chironomids is quick even when adjusting for growth; indeed, the elimination constant equaled 0.032 ( 0.009) h -1 when calculated under the H1 hypothesis, with simultaneous optimization of both k u and k e (Table 2). This k e value is very similar to the k e value determined in our previous study [START_REF] Bertin | Bioaccumulation of perfluoralkyl compounds in midge (Chironomus riparius) larvae exposed to sediment[END_REF]) using a partition model with a correction for growth, i.e. 0.03  0.01 h -1 . Conversely, the k u value derived under the H1 hypothesis is about one order of magnitude greater than the k u derived previously (0.0015 g oc .g ww .h -1 ; [START_REF] Bertin | Bioaccumulation of perfluoralkyl compounds in midge (Chironomus riparius) larvae exposed to sediment[END_REF], emphasizing the impact of model choice. However, in the present study, the proposed model takes into account the growth dilution for both uptake and elimination phases, with the length of the organisms introduced in each term of the model equation (Eq. 4). In addition, k u and k e were estimated from the same experimental data set, and estimated together. The k u and k e obtained in the present study under the concentration-dependency hypothesis are therefore more reliable than those calculated under a passive diffusion hypothesis on the basis of the accumulation phase only, or separately for two phases. Meanwhile, the BSAF values of (BSAF exp , Table 1) did not

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011 support the concentration-dependency hypothesis. The steady state might not be reached after 2 days of exposure, and the growth dilution is not taken into account for the BSAF exp calculation, which may explain why BSAFs did not follow the expected pattern.

Our experimental results did not allow for testing the concentration-dependency hypothesis for other PPFASs, such as PFUnDA or PFOS, nor to derive kinetic BSAFs by solving analytically Eq. 2, due to the growth dilution term. Overall, these BSAFs were low, confirming some field evidence [START_REF] Babut | Per-and poly-fluoroalkyl compounds in freshwater fish from the Rhône River: influence of fish size, diet, prey contamination and biotransformation[END_REF] that chironomids would not be a significant source of PFTrDA and other PFCAs to their predators, e.g. fish.

Conclusion

The models tested herein are advantageous in that they simultaneously optimize the uptake and elimination rates while accounting for chironomid growth rate, in contrast to other studies that calculated the uptake and elimination rates from two different models [START_REF] Higgins | Bioaccumulation of perfluorochemicals in sediments by the aquatic oligochaete Lumbriculus variegatus[END_REF][START_REF] Higgins | Bioaccumulation of triclocarban in Lumbriculus variegatus[END_REF][START_REF] Van Geest | Accumulation and Depuration of Polychlorinated Biphenyls from Field-Collected Sediment in Three Freshwater Organisms[END_REF].

Reliable experimental elimination constants (k e ) were obtained for chironomids exposed to a field sediment contaminated by a PFAS mixture (PFTrDA, PFUnDA, and to a lesser extent PFOS, FOSA). Measured PFTrDA concentrations accumulated in chironomid tissues did not increase proportionally to their increase in sediment, but the resulting experimental BSAFs did not vary much. Nevertheless, bioaccumulation modeling with a simultaneous optimization of uptake and elimination rates consistently supported the hypothesis of concentrationdependency for this compound and yielded reliable uptake and elimination rates. Similar findings were reported by for shorter chain PFCAs (PFOA, PFNA, PFDA) in the green mussel (Perna viridis) [START_REF] Liu | Novel Perspectives on the Bioaccumulation of PFCs -the Concentration Dependency[END_REF], suggesting that concentration dependency could be a rather general uptake mechanism for long chain PFCAs or PFSAs.

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

  Refining uptake and depuration constants for fluoroalkyl chemicals in Chironomus riparius larvae on the basis of experimental results and modelling Delphine Bertin, Benoît J.D. Ferrari, Pierre Labadie, Alexandre Sapin, Débora da Silva Avelar, Rémy Beaudouin, Alexandre R.R. Pery, Jeanne Garric, Hélène Budzinski, Marc Babut To cite this version: Delphine Bertin, Benoît J.D. Ferrari, Pierre Labadie, Alexandre Sapin, Débora da Silva Avelar, et al.. Refining uptake and depuration constants for fluoroalkyl chemicals in Chironomus riparius larvae on the basis of experimental results and modelling. Ecotoxicology and Environmental Safety, 2018, 149, pp.284-290. 10.1016/j.ecoenv.2017.12.011. hal-01666918

Figure 1 :

 1 Figure 1: Elimination kinetics of PFASs in chironomids exposed to field sediment (unspiked:

Figure 2 :

 2 Figure 2: Biplot of PFTrDA concentrations in sediment (X-axis) and C. riparius (Y-axis);

Figure 3 -

 3 Figure 3 -Observed (symbols) and simulated (lines) PFTrDA concentrations (left hand

  Author-produced version of the article published in cotoxicology and EnvironmentalSafety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

  Author-produced version of the article published in cotoxicology and EnvironmentalSafety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

	conductivity, NO 2	-, and NH 4	+ were monitored.
	3.2.4. Accumulation test at several exposure concentrations
			. Briefly, C. riparius fourth instar
	(L4) larvae (7-day-old larvae post-hatching) were exposed to field sediment covered with
	OW, i.e., a mixture of groundwater and water purified by reverse osmosis, to reach a
	conductivity of 300 µS.cm -1 . Each experiment was conducted at 21°C under a 16:8-h light-

dark photoperiod. The OW was renewed four times per day to maintain adequate water quality and oxygenation. Ancillary parameters such as pH, dissolved oxygen concentration,

  Author-produced version of the article published in cotoxicology and EnvironmentalSafety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

C-labeled PFAS internal standards (ISs) were added before the extraction. PFASs were analyzed on freezedried tissues based on 800 mg wet weight (ww) for C. riparius and 120 mg dry weight for the

Table 1 -

 1 Table 1) did not differ much, unlike what should have occurred in case of concentration dependency, where the BSAF should decrease while the f oc adjusted PFTrDA sediment concentrations increase.Nevertheless the BSAF exp resulting from the C1 experiment was obtained after a reduced exposure time, and might thus be underestimated. PFTrDA concentrations in sediment organic matter and chironomids at T final and resulting BSAF exp BSAF exp calculated for PFUnDA, PFOS and FOSA are recorded in SI, Table

		5
	ww) [PFTrDA] in C. riparius (ng.g -1	1 2 3 4	C1 C2	C3
		0
		0	5	10	15
			[PFTrDA] in sediment at T-final (ng.g -1 dw)
	Experiments	Type	Sediment organic matter (ng oc .g -1 dw)	Chironomids (ng.g -1 ww)	BSAF exp
	Accumulation phase of the Field	65.92 ± 1.79	0.460 ± 0.141	0.007 ± 0.0039

  Author-produced version of the article published in cotoxicology and EnvironmentalSafety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011

Acknowledgements

This study was supported by the Rhone-Mediterranean and Corsica Water Agency and the Rhone-Alpes Region within the Rhone ecological restoration plan. The Aquitaine Region and the European Union [CPER A2E project] are acknowledged for their financial support. This study also benefitted from grants of the French National Research Agency (ANR) as part of the Investments for the future Program, within the Cluster of Excellence COTE [ANR-10-LABX-45]. We thank Linda Northrup (English Solutions, Voiron, France) for copyediting the text.

The laboratory experiments and analyses were mainly funded by the Rhone-Mediterranean and Corsica Water Agency and the Rhône-Alps Region within the Rhône ecological restoration plan. Additional grants were obtained from the Aquitaine Region and the European Union (CPER A2E project), and the French National Research Agency (ANR) as part of the Investments for the Future Program, within the Cluster of Excellence COTE (ANR-10-LABX-45). None of these supports were involved in the study design, nor in data processing, report writing and article submission.

Author-produced version of the article published in cotoxicology and Environmental Safety, 2018, pp. 284-290 The original publication is available at http://www.sciencedirect.com doi : 10.1016/j.ecoenv.2017.12.011


Isabelle Braud
email: isabelle.braud@irstea.fr

Jean-François Desprats

Pierre-Alain Ayral

Christophe Bouvier

Jean-Pierre Vandervaere

A method for mapping topsoil field-saturated hydraulic conductivity K fs in the Cévennes-Vivarais region using infiltration tests conducted with different techniques

CONTEXT AND OBJECTIVES

Context:

Flash floods are natural hazards that affect the Mediterranean region. They are caused by intense rainfall events but catchment characteristics, and particularly topsoil field-saturated hydraulic conductivity K sf , are also influential on the hydrological response. For distributed hydrological models, maps of K sf are useful, as K sf impacts Hortonian runoff, but they are difficult to obtain from points measurements.

Objectives:

• Propose a method to map K sf from GIS layers with application to the Cévennes-Vivarais region where infiltration measurements obtained with different methods were available (Fig. 1) • Propose a method to pool available infiltration measurements obtained with various techniques in the region for regionalization

POOLING INFILTRATION MEASUREMENTS

• Raw data show significant difference in distribution among methods (Fig. 3) so pooling the data requires specific treatments A two steps method for pooling K fs data from various methods:

• Pooling of GP and DR data by geology * land use (Desprats et al., 2010, Fig. 4) and conversion of GP data to equivalent DR data • Pooling SR and DR + TI data (Fig. 5) to get a final set of homogeneized equivalent DR +TI data set

MAPPING TOPSOIL K fs

Mapping method

• Field data analysis show that geology and land use are significant explaining factors of K fs and one value is assigned by geology * land use class (Fig. 6) • Geology and land use were used to produce a map of K fs (Fig. 7a) that is compared to a map derived from Rawls and Brakensieck (1985, RB85) pedotransfer function (Fig. 7b) based on a pedology map with associated soil data base including information about soil texture

CONCLUSIONS AND PERSPECTIVES

• A method was proposed to pool infiltration measurements of K fs obtained with different techniques • Geology and land use were found to be discriminant factors explaining the variability of K fs • Geology and land use can be used to map K fs • Perspective: use the map in a distributed hydrological model to assess if flash flood simulation is improved as compared to the use of pedotransfer functions

Figure

  Figure 3: Boxplot of original K fs data per method

Figure 7 :

 7 Figure 7: Maps of log(Kfs) for part of the Cévennes-Vivarais region using (a) the geology and land cover maps and the results of Fig. 6 and; (b) the pedology map and Rawls and Brakensieck pedotransfer function RB85.

Figure 4 :

 4 Figure 4: Boxplot of explaining variables for non-flooding (0) and flooding (1) dates. Differences are significant, p<0.001

Figure 2 :

 2 Figure 2: Photos of the various infiltration methods (a) GP; (b) DR; (c) SR; (d) TI where the disk has been removed from the tower (SDEC, SW 080 B); (e) Home-made TI from IGE.

Figure 4 :

 4 Figure 4: Regression between log(Kfs) (mm h-1) for GP and DR infiltration methods. The points are mean values per geology * land cover classes and the vertical and horizontal lines correspond to one standard deviation.

Figure 5 :

 5 Figure 5: Regression between log(Kfs) (mm h-1) for SR and DR +TI infiltration methods. The points are mean values per geology * land cover classes and the vertical and horizontal lines correspond to one standard deviation.


Branger

Ilter Rza

/ Ozcar

Isabelle Braud
email: isabelle.braud@irstea.fr

Mériem Labbas

Flora Branger

Assessing various options for rain water management in 2030 using prospective land use change scenarii and distributed hydrological modelling in the Yzeron experimental periurban catchment

    Assessing various options for rain water management in 2030 using prospective land use change scenarii and distributed hydrological modelling in the Yzeron experimental periurban catchment (ZABR/OTHU-OZCAR CZO observatory)

MODEL SET UP AND EVALUATION



  Growing urbanization : increase of surface imperviousness, modifications of water flow paths  increase of surface runoff, rise of storm peak flows and flood magnitude, reduction of groundwater recharge and increasing water pollution. • Periurban catchments = combination of natural areas, rural areas with dispersed settlements and urban areas mostly covered by built zones and spots of natural surfaces  especially affected by fast anthropogenic modifications • General guideline: European Water Framework Directive (2000) and Floods Directive (2007)  integrated and sustainable solutions needed to reduce flooding risks and river pollution at the scale of whole catchments. • Objectives: set up a distributed hydrological model to quantify the impact of urbanization and stormwater management on the longterm hydrological cycle of a medium-sized periurban watershed.  Development of the J2000P and application/evaluation in the Yzeron periurban catchment (south west of Lyon, France)  Compare various land use and rain water management scenarii • Catchment prone to quick Mediterranean-type floods • Fast growing urbanization since 1980's. In 2008, the catchment was covered by 25% of impervious surfaces, 42% of agricultural areas and 33% of forests. • Urban rainwater mainly directed to the WWTP outside of the basin through a combined sewer network.

FigureFigure 2 :

 2 Figure 1: Situation map of the Yzeron and Taffignon catchments with indications of topography, impervious areas and measurement network. The Yzeron catchment is part of the ZABR/OTHU observatory and RBV network. Monitoring started in 1990 and was enhanced in 2008 (7 rain gauges, 1 meteo station, 7 discharge stations)

Figure 3 :

 3 Figure 3: J200P model mesh.

Figure 4 :

 4 Figure 4: Observed (red) and simulated (black) daily discharge at the outlet (year XXX)

Figure 5 :

 5 Figure 5: land use map for 1990 (left). Land use map in 2030 simulated with a land use change model (Dodane et al., 2014) (right).

Table 1 : Statistical criteria comparing observed and simulated discharge at the various gauging stations 4. 2030 LAND USE AND RAIN WATER MANAGEMENT SCENARII

 1

	 1 Reference: same as
	present Tconnect=0.7
	 2 Spatialized: Tconnect
	distributed according to
	local imperviousness
	 3 Disconnection:
	distributed Tconnect and
	disconnection of recent
	urban areas

Table 2 : Catchment water balance in 2030 for three rain water management scenarii

 2

References: Labbas, 2015; Labbas et al., La Houille Blanche 2015; Dodane et al., Cybergeo, 2014.

Acknowledgements: We thank Clément Dodane for his help in using the land use change scenarii; Sven Kralisch for his help in the development of the J2000P model. The Yzeron catchment observation is supported by OTHU, Irstea, Grand Lyon and Agence de l'Eau RM&C

Conclusions:

• More differences between the rain water management scenarios than between land use change scenarios • High uncertainty in the results

• Model evaluation at all gauges (Fig. Disconnection scenario produces less surface runoff and less sewer overflows than spatialized scenario.


Soizic Morin

Betty Chaumet

Nicolas Mazzella

Transfer and distribution of diuron in biofilms and joint toxic effects by Betty Chaumet