Lena Driehaus

Thierry Nalpas
email: thierry.nalpas@univ-rennes1.fr

Jean-François Ballard

Interaction between deformation and sedimentation in a multidecollement thrust zone: analogue modelling and application to the Sub-Andean thrust belt of Bolivia

Keywords: Compressive system, Decollement, Synkinematic sedimentation, Experiment, Incahuasi

Fold and thrust belts are influenced by the presence of decollement levels, as well as the amount of shortening and synkinematic sedimentation. These parameters are studied at the scale of a thrust belt using a field approach, combined with analogue and numerical modelling. In this study, we use analogue modelling to test the evolution of a single structure during sedimentation in a domain containing three prekinematic decollement levels. The development of this structure in the analogue experiments shows that the expression of the deformation is strongly dependent on sedimentation rate: (i) the structure propagates forward in an overall asymmetric shape if the sedimentation rate is slower than the uplift velocity, or (ii) the structure grows vertically and its vergence changes at the surface if the sedimentation rate is similar to the uplift velocity, or (iii) the structure grows

Introduction

The deformation observed in compressive systems such as fold and thrust belts is influenced by the presence of decollement levels (e.g. [START_REF] Dunn | Structural styles and hydro-carbon potential of the sub-Andean thrust belt of southern Bolivia[END_REF][START_REF] Labaume | Diagenesis-dependence of cataclastic thrust fault zone sealing in sandstones. Example from the Bolivian Sub-Andean Zone[END_REF][START_REF] Sepehr | The impact of cover rock rheology on the style of folding in the Zagros fold-thrust belt[END_REF][START_REF] Verges | Multiple detachment folding in Pusht-e Kuh arc, Zagros: Role of mechanical stratigraphy[END_REF], which exhibit low basal friction related to lithology (marl, shale, coal and evaporite) and/or overpressure conditions (e.g. [START_REF] Cobbold | Seepage forces, important factors in the formation of horizontal hydraulic fractures and bedding-parallel fibrous veins ("beef" and "cone-in-cone[END_REF][START_REF] Cobbold | Structural consequences of fluid overpressure and seepage forces in the outer thrust belt of the Niger Delta[END_REF]. These systems have been investigated in previous analogue studies that show the importance of the basal angle of the wedge and the shortening rate (e.g. [START_REF] Smit | Deformation of brittle-ductile thrust wedges in experiments and nature[END_REF], as well as the presence of decollement levels in controlling coupling/decoupling processes (e.g. [START_REF] Couzens-Schultz | Duplex style and triangle zone formation: insights from physical modeling[END_REF][START_REF] Massoli | Structural evolution of a fold and thrust belt generated by multiple décollements: analogue models and natural examples from the Northern Apennines (Italy)[END_REF] and synkinematic sedimentation [START_REF] Leturmy | Piggyback basin development above a thin-skinned thrust belt with two detachment levels as a function of interactions between tectonic and superficial mass transfer: the case of the Subandean Zone (Bolivia)[END_REF]. The relationship between sedimentation and thrust geometry at the scale of a single structure has been studied using analogue modelling with one prekinematic ductile layer [START_REF] Nalpas | Influence de la charge sédimentaire sur le développement d'anticlinaux synsédimentaires. Modélisation analogique et exemples de terrain (Bordure sud du bassin de Jaca)[END_REF][START_REF] Casas | Analogue models of transpressive systems[END_REF][START_REF] Barrier | Influence of syntectonic sedimentation on thrusts geometry. Field examples from the Iberian Chain (Spain) and analogue modeling[END_REF]Nalpas et al.;2003;[START_REF] Gestain | Rôle des niveaux incompétents syncinématiques sur l'évolution des structures chevauchantes[END_REF][START_REF] Barrier | Impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures: Insights from analogue modelling[END_REF].

However, only one study has been carried out at the scale of a single structure with two prekinematic ductile layers [START_REF] Pichot | Influence of synkinematic sedimentation in a thrust system with two decollement levels; analogue modeling[END_REF], so there is a continuing debate about the vergence of the thrusts as well as the evolution of deformation at depth and at the surface in relation to mass transfer.

This study makes use of analogue modelling to investigate the formation and evolution of a compressive structure with a mechanical stratigraphy comprising three prekinematic decollement levels (ductile layers) accoding to (i) the amount of shortening and (ii) the synkinematic rate of mass transfer. The results of this experimental approach are then compared with a field example (the Subandean thrust-belt).

Experimental procedure

In this study, we apply the classical techniques used for brittle-ductile analogue modelling experiments developed by the Experimental Tectonics Laboratory of Géosciences Rennes (Université de Rennes 1, France). These techniques have been described in previous studies dealing

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3 with the use of a velocity discontinuity (VD; e.g. [START_REF] Malavieille | Modélisation expérimentale des chevauchements imbriqués: application aux chaînes de montagnes[END_REF][START_REF] Balé | Tectonique cadomienne en Bretagne nord[END_REF][START_REF] Ballard | Propagation des chevauchements audessus des zones de décollement : Modèles expérimentaux[END_REF][START_REF] Allemand | Symétrie et asymétrie des rifts et mécanismes d'amincissement de la lithosphère[END_REF], the use of silicone and sand [START_REF] Faugère | Modélisation expérimentale de la distension continentale[END_REF], and also various scaling issues [START_REF] Davy | Experiments on shortening of a 4-layer model of continental lithosphere[END_REF][START_REF] Weijermars | Rheological and tectonic modeling of salt provinces[END_REF]. Brittle layers (pre-and synkinematic) are represented by dry Fontainebleau quartz sand, with an internal friction angle of 30-35° [START_REF] Krantz | Measurements of friction coefficients and cohesion for faulting and fault reactivation in laboratory models using sand and sand mixtures[END_REF] and a density (ρ) of approximately 1,500 kg/m 3 . The weak ductile layers (e.g. salt, clay) are represented by i) pink silicone putty 70 009 (Rhône Poulenc, France) with a viscosity (µ) of around 10 4 Pa⋅s at 20°C and a density (ρ) close to 1,400 kg/m 3 , and ii) transparent silicone putty SGM 36 (Dow Corning, USA) with a viscosity (µ) of around 10 4 Pa⋅s at 20°C and a density (ρ) close to 1,000 kg/m 3 .

Silicone putty is commonly used to model salt, but it has also been used to model overpressured shales (e. g. [START_REF] Cohen | Sedimentation and shale tectonics of the northwestern Niger Delta front[END_REF][START_REF] Wu | Two-dimensional analog modelling of fold and thrust belts: Dynamic interactions with syncontractional sedimentation and erosion[END_REF]. To take into account overpressures and pore fluids in decollement levels such as shales, physical modelling techniques have been developed using compressed air injected into beeswax microspheres (e.g. [START_REF] Cobbold | Fluid pressure and effective stress in sandbox models[END_REF][START_REF] Cobbold | Sandbox modelling of thrust wedges with fluid-assisted detachments[END_REF][START_REF] Mourgues | Some tectonic consequences of fluid overpressures and seepage forces as demonstrated by sandbox modelling[END_REF][START_REF] Zanella | Physical modelling of chemical compaction, overpressure development, hydraulic fracturing and thrust detachments in organic-rich source rock Original Research[END_REF]. The implementation of these techniques is complicated and remains impractical for experiments with three decollement levels, explaining why such an approach is not adopted here.

The experimental apparatus consists of a fixed wall screwed to a rigid and fixed basal plate, over which another wall fixed to a thin mobile basal plate is pushed at a constant rate (Fig. 1a). The two other sides are free and supported by sand to ensure uniform stresses. The displacement of the basal mobile plate induces a velocity discontinuity (VD) at its border, which localizes the deformation at the base of the model, (cf. Malavielle, 1984;[START_REF] Balé | Tectonique cadomienne en Bretagne nord[END_REF][START_REF] Ballard | Approche géologique et mécanique des décollements dans la croûte supérieure[END_REF]. In our experiments, we use a VD to simulate only one structure, with the VD representing the zone localizing the deformation at the base of the model. The VD may represent either a basement fault, (e.g. [START_REF] Richard | Experiments on simultaneous faulting and folding above a basement wrench fault[END_REF] or, in an imbricate thrust system, the tip line of a basal decollement (Boyer and Elliot, 1982;[START_REF] Casas | Analogue models of transpressive systems[END_REF]. The experiment is set up in a 100 x 60 cm sandbox, wide enough to allow the model to be cut into several vertical slices after each phase of deformation without border effects (see below).

To facilitate comparisons with natural examples such as the Bolivian Subandean fold and thrust belt, where several decollement levels are present, we set up experiments composed of a four-layer brittle-ductile system. The prekinematic pile consists of layers including, from bottom to top: 1 cm of purple silicone (lower decollement level); 1.2 cm of black and white sand; 0.8 cm of transparent silicone (middle decollement level); and 3 cm of black and white sand. The layer of black and white

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sand is composed of two 1.5 cm layers separated by a thin layer (0.3 cm) of silicone to facilitate flexural slip (Fig. 1a). The synkinematic pile is composed of blue and white sand layers of different thicknesses. To simulate synkinematic mass transfer, both sedimentation and erosion are simulated.

Sedimentation is simulated using fresh sand (blue and white) that is continuously sprinkled manually onto the model during the shortening (e.g. [START_REF] Cobbold | Sedimentary basins and crustal thickening[END_REF][START_REF] Baby | Etude géométrique et expérimentale d'un bassin transporté: exemple du synclinorium de l'Alto Beni (Andes centrales)[END_REF][START_REF] Storti | Influence of syntectonic sedimentation on thrust wedges in analogue models[END_REF][START_REF] Barrier | Influence of syntectonic sedimentation on thrusts geometry. Field examples from the Iberian Chain (Spain) and analogue modeling[END_REF]. Erosion is simulated by removing sand with a vacuum cleaner. To define the amount of sedimentation, we use the dimensionless parameter R = Vs/Vu, where R is the ratio between the rate of the sedimentation (Vs) and the velocity of uplift of the structure (Vu) (see [START_REF] Barrier | Influence of syntectonic sedimentation on thrusts geometry. Field examples from the Iberian Chain (Spain) and analogue modeling[END_REF][START_REF] Pichot | Influence of synkinematic sedimentation in a thrust system with two decollement levels; analogue modeling[END_REF]. To define the amount of erosion, we use a dimensionless parameter E = Ve/Vu, where E is the ratio between the velocity of the erosion (Ve) and the velocity of uplift of the structure (Vu). The switchover between erosion and sedimentation corresponds to a base level in the stratigraphic sense (Posamentier et al., 1988;Posamentier and Vail, 1988), which implies that the system is being eroded above the base level, with transit occurring along this level and sedimentation below. Different sedimentation modes are chosen to represent the range of possible sedimentation rates within natural basins (Fig. 1b). In the first series of experiments, models are performed without sedimentation (R = 0), the second series with sedimentation and erosion (R = 1/2 and E = 1/4), the third series with sedimentation alone (R = 1) and the fourth series with a high sedimentation/uplift ratio (R = 2). The variations of mass transfer between our experiments are comparable to different geographic positions in the Bolivian Subandean fold and thrust belt, ranging from the western zone with erosion, through the central foredeep with a high sedimentation rate to the eastern zone with a low sedimentation rate.

Table 1 presents the geometric and dynamic scaling of the models. The scale ratios for dimensions and stress between the models and nature are of the same order of magnitude (10 -5 ), and the shortening rate is imposed by the scaling laws. A velocity of 1 cm/h is used for displacement of the piston, mobile basal plate and wall, along with the associated velocity discontinuity (VD).

Photographs of the model surface are taken at regular time intervals (every 15 min) to observe the development of the structure. Sand layers are made up of various colours; black and white for the prekinematic layers, and blue and white for the synkinematic layers (the colour of the sand does not modify its behaviour). After deformation, the internal structures and their time-evolution are observed in a series of cross-sections cut parallel to the compression direction and perpendicular to the VD. The experiments are conducted in three steps of shortening: i) compression of 5 cm; ii) compression of 7.5 cm; and iii) compression of 10 cm. All the cross-sections extracted after each

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step are taken at a distance of at least 5 cm from the lateral border of the model, in order to avoid boundary effects. The deformation is not affected by stopping between steps. This is verified by an experiment in which 10 cm of shortening in one step yields the same amount of deformation as the experiment performed in 3 shortening steps. Although a total of twenty experiments were performed to test the reproducibility (denoted Bode 1 to Bode 20), only the results of four experiments are presented here.

To simplify the description of the silicone/sand pile of the model, we use the following terminology (Fig. 2). From bottom to top, the prekinematic layers are called: lower silicone layer; lower sand layer; middle silicone layer; middle sand layer; upper silicone layer; upper sand layer. The layers added during the experiment are termed synkinematic sand layers. The thrusts are named according to the sand layers affected and their geometry in relation to the VD inducing shear displacement [START_REF] Ballard | Approche géologique et mécanique des décollements dans la croûte supérieure[END_REF]. For example, a synthetic thrust occurs when the hanging wall moves in a direction opposite to the movement of the mobile plate, and an antithetic thrust is characterized by the hanging wall moving in the same direction as the mobile plate. Therefore, as shown in Figure 2, the thrusts are referred to as follows, from bottom to top: lower synthetic thrust; middle antithetic thrust; upper synthetic thrust. The faults are colour coded to highlight the movement of the faults for each step of deformation (Fig. 3). The forward or backward propagation of the deformation is defined with respect to the previous structure considered (Fig. 2).

Results of analogue modelling experiments

3.1. Shortening without sedimentation, R = 0 (Fig. 3a)

The main feature observed in this experiment is the synthetic vergence of all thrusts, associated with a forward propagation of the deformation.

More precisely:

-After 5 cm of shortening (Fig. 3a1), the lower and middle sand layers are affected by synthetic thrusts generating penetration of the lower and middle sand layers into the middle and upper silicone layers, respectively. The upper sand layer is affected by a synthetic thrust with a very shallow dip.

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6 -After 7.5 cm of shortening (Fig. 3a2), the anticline in the lower sand layer is amplified and associated with an accumulation of silicone forming a ridge in the lower silicone layer near the VD.

The lower and middle synthetic thrusts grow in amplitude and are rotated anticlockwise. The upper synthetic thrust is still active, and a pop-up structure develops in front of the thrust (in yellow in Fig. 3a2).

-After 10 cm of shortening (Fig. 3a3), the lower and middle synthetic thrusts have undergone anticlockwise rotation and become no longer active. In addition, a new lower synthetic thrust develops (in yellow in Fig. 3a3). The upper synthetic thrust and the associated pop-up structure are still active. The layers are affected by an amplification of the folding.

Shortening with synkinematic sedimentation and erosion

, R = 1/2, E = 1/4 (Fig. 3b)
The main feature of this experiment is the change in vergence of the middle and upper antithetic thrusts after 10 cm of shortening.

More precisely:

-After 5 cm of shortening (Fig. 3b1), the lower sand layer is affected by a synthetic thrust of flat geometry that penetrates the middle silicone layer. The middle and upper sand layers are affected by an antithetic thrust. Firstly, the middle antithetic thrust penetrates slightly into the upper silicone layer, and then, while showing a steeper dip, it connects up with the upper antithetic thrust. The upper sand layer is slightly eroded on the crest of the ramp anticline. The synkinematic layers show onlap geometry on the hanging wall of the upper thrust, and toplap geometry below the base of the thrust in the footwall.

-After 7.5 cm of shortening (Fig. 3b2), the deformation is similar to that observed for 5 cm of shortening with the same synthetic and antithetic thrusts. The lower synthetic thrust shows a large penetration into the middle silicone layer. An amplification of the the middle and upper antithetic thrusts induces more uplift and erosion on the crest of the ramp anticline in the upper sand layer.

The synkinematic layers show the same overall geometry with increasing deformation.

-After 10 cm of shortening (Fig. 3b3), a change in the vergence of the deformation is observed. The lower synthetic thrust penetrates deeply into the middle silicone layer, while an incipient lower antithetic thrust is developed (in yellow in Fig. 3b3). The lower synthetic thrust is deformed, in 3.3. Shortening with synkinematic sedimentation, R = 1 (Fig. 3c)

The main feature of this experiment is that all the sand layers are affected by thrusts of opposite vergence developing a typical fish-tail structure.

More precisely:

-After 5 cm of shortening (Fig. 3c1), the lower sand layer is affected by a lower synthetic thrust that penetrates the middle silicone layer. The middle sand layer is affected by a middle antithetic thrust that penetrates into the upper silicone layer. The upper sand layer is affected by an upper synthetic steeply dipping thrust with an incipient upper antithetic fault in its hanging wall. This faulting pattern with opposing vergence is typical of a fish-tail structure. The synkinematic layers show onlap geometry on the hanging wall of the upper thrust, and toplap geometry below the base of the thrust in the footwall.

-After 7.5 cm of shortening (Fig. 3c2), the lower antithetic thrust penetrates deeply into the middle silicone layer. The middle antithetic thrust has ceased growing and a new steeply dipping antithetic thrust is formed cutting the upper sand layer and affecting the synkinematic layers. The upper synthetic thrust ceases and a new upper antithetic thrust cuts the previous synthetic thrust and synkinematic layers. The synkinematic layers show onlap geometry in the direction of the anticline crest.

-After 10 cm of shortening (Fig. 3c3), the lower synthetic thrust penetrates deeply into the middle silicone layer without anticline growth. The growth of the middle antithetic thrust continues until it is cut by a new synthetic thrust. This thrust has variable dip, the lower part being nearly horizontal, and the upper part steeply dipping (in yellow in Fig. 3c3). The vertical amplification of the The synkinematic layers show onlap geometry in the direction of the anticline crest.

3.4. Shortening with synkinematic sedimentation, R = 2 (Fig. 3d)

The main feature of this experiment is that all sand layers are affected by thrusts with opposing vergence, thus developing a typical fish-tail structure. Finally, at the end of the shortening, the deformation shows a double vergence.

More precisely:

-After 5 cm of shortening (Fig. 3d1), the lower sand layer is affected by a lower synthetic thrust that penetrates into the middle silicone layer. The middle sand layer is affected by a middle antithetic thrust that penetrates into the upper silicone layer. The upper sand layer is affected by a major upper synthetic thrust and an incipient antithetic thrust. Although such a fault pattern with opposing vergence is typical of a fish-tail structure, there is less folding and uplift in this case than previously observed (Fig. 3c1). The synkinematic layers show a progressive decrease in the thickness of the hanging wall in the direction of the upper synthetic thrust (in green in Fig. 3d1), and a nearly constant thickness on its footwall. The thrusts near the piston in the middle and upper sand layers are due to boundary effects at the beginning of the experiment (in grey in Fig. 3d).

-After 7.5 cm of shortening (Fig. 3d2), the deformation is similar to that observed for 5 cm of shortening. The lower synthetic thrust shows deep penetration into the middle silicone layer. The growth of the middle antithetic thrust continues and an incipient middle antithetic fault is formed.

The upper synthetic and antithetic thrusts are still active, associated with the development of a new incipient antithetic thrust. The synkinematic layers show the same overall geometry as before.

-After 10 cm of shortening (Fig. 3d3), the lower synthetic thrust penetrates deeply into the middle silicone layer, and the lower sand layer is also affected by an new anthitetic thrust. The middle antithetic thrust is cut by a middle synthetic thrust. The upper sand layer and the synkinematic layers are affected by a synthetic and an anthitetic thrust, as well as a new synthetic thrust. These associated faults induce a double vergence in the deformation, and the synkinematic layers display a relatively constant thickness.

3.5. Time-evolution of structure uplift (Fig. 4)

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The time-evolution of the anticline crest uplift, which is associated with the thrusts, affects the lower and upper sand layers in completely different ways depending on the R ratio. The maximum uplift of the upper sand layer anticline is observed when the sedimentation rate is equal to the uplift velocity (R = 1), and the minimum uplift is observed when there is no sedimentation (R = 0). On the contrary, the maximum uplift of the lower sand layer structure is observed when there is no sedimentation (R = 0) and minimum uplift occurs when the sedimentation rate is equal to or greater than the velocity of uplift (R = 2 or 1). It is important to note that the amplitude of the uplift is nearly the same (around 4 cm) for the lower and upper sand structure when there is no sedimentation (R = 0). When the sedimentation rate is equal to the uplift velocity (R = 1), the amplitude of the uplift in the upper sand layer is three times that of the lower sand layer (around 7.5 cm and 2.5 cm, respectively). Note that, when the sedimentation/uplift ratio is intermediate between these two cases (R = 1/2, E = 1/4), the amplitude of the uplift is also intermediate. When the sedimentation rate is double the uplift velocity (R = 2), the uplift of the lower sand layer structure decreases to its minimum amplitude, while the uplift of the upper sand layer structure is lower than for R = 1 and R = 1/2, with E = 1/4, as noted by [START_REF] Barrier | Impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures: Insights from analogue modelling[END_REF].

Discussion

Influence of initial mechanical stratigraphy

The initial mechanical stratigraphy is characterized by the presence of interbedded silicone layers and sand layers that allow decoupling between the sand layers.

Firstly, a typical flat lower thrust is developed because the lower sand layers penetrate into the middle detachment level (see Fig. 5 for main features of experiments after 10 cm of shortening).

The geometry of the upper reverse fault is dependent on the sedimentation/uplift ratio (e.g. [START_REF] Pichot | Influence of synkinematic sedimentation in a thrust system with two decollement levels; analogue modeling[END_REF][START_REF] Barrier | Impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures: Insights from analogue modelling[END_REF], and shows a maximum dip when R = 1 or 2 (Fig. 3a1,b1, c1, d1 and 5, see α < β). Secondly, two superposed thrusts with opposite vergence create a fish-tail structure when the interbedded silicone layer acts as a decollement level (Figs. 3c1 andd1). These fish-tail structures are created only when sedimentation occurs during deformation (for R = 1 and 2). In the experiment with low ratios of sedimentation and erosion with respect to uplift of the structure (R = 1/2, E = 1/4), a fish-tail structure is only present between the lower and middle sand layers (Fig. 3b). In the experiment without sedimentation, no fish-tail structures are created (Fig. 3a). Therefore, the presence of decollement levels is a necessary but insufficient condition to

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10 produce such fish-tail structures. Thirdly, the presence of a decollement level allows the deformation to propagate forward of the main upper structure (Figs. 3a2 anda3), provided there is no sedimentation. Finally, we suggest it is necessary to have an initial mechanical stratigraphy with several decollement levels to create specific features such as fish-tail structures and forward propagation of the deformation. However, the presence of several decollement levels is insufficient to explain the geometric evolution and variability of the structures.

Influence of shortening

Increasing shortening induces major deformation in the model, creating structures with a marked uplift (Fig. 4), and an increase in the thrust throw. Firstly, during the increase in the amount of shortening, two possible trends of development can be observed. When there is no sedimentation, the model develops an overall asymmetric shape (Figs. 3a1 to a3). Alternatively, in the experiment with sedimentation, the shape of the model evolves from asymmetric to doubly vergent (Figs. 3b3, c1 to c3, and d1 to d3). Secondly, increased shortening enhances the penetration of thrusts into the overlying silicone layer. Thirdly, although increased shortening allows the deformation to propagate forward (Figs. 3a2 anda3), this can only take place in the absence of sedimentation. Finally, we suggest that increased shortening is necessary to ensure an evolution in the overall shape of the model, but is not sufficient to explain why this evolution is possible.

Influence of synkinematic sedimentation

The geometry of the structure is highly dependent on the sedimentation/uplift ratio (Figs. 3 and5).

Without sedimentation, the geometry of structures is similar in the lower, middle and upper layers insofar as they display the same synthetic vergence. Any increase in the shortening is accommodated by a forward propagation of the deformation (Figs. 3a and5a). By contrast, with sedimentation, the geometry of the structures is different in the lower, middle and upper layers with different vergence. Also there is no propagation of the deformation during shortening, and all the structures are stacked above the VD (Figs. 3b, c, d and5b, c).

With sedimentation, the geometry of the faults shows a fish-tail structure for the lower and middle sand layers when R = 1/2 with ongoing erosion (E = 1/4), and for all layers when R = 1 and 2 (Figs. 3 and5). This implies that more fish-tail structures are developed when the sedimentation rate is higher. Such an effect may be related to an increase in normal stress induced by the synkinematic

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layers, which increases the strength of the interbedded sand layers. In this way, the differential strength between the sand and silicone layers increases, thereby making it easier for the sand layers to penetrate the silicone layers.

During deformation, the overall shape of the model changes from asymmetric to doubly vergent, with an increase in shortening that is only observed with synkinematic sedimentation. With an increase in sedimentation with respect to uplift (R = 1 to 2), the model shows an increasingly prominent doubly vergent shape.

In agreement with previous experimental studies (e.g. Tondji-Biyo, 1995;[START_REF] Nalpas | Influence de la charge sédimentaire sur le développement d'anticlinaux synsédimentaires. Modélisation analogique et exemples de terrain (Bordure sud du bassin de Jaca)[END_REF][START_REF] Barrier | Influence of syntectonic sedimentation on thrusts geometry. Field examples from the Iberian Chain (Spain) and analogue modeling[END_REF][START_REF] Nalpas | Effects of rate and nature of synkinematic sedimentation on the growth of compressive structures constrained by analogue models and field examples[END_REF][START_REF] Pichot | Influence of synkinematic sedimentation in a thrust system with two decollement levels; analogue modeling[END_REF][START_REF] Barrier | Impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures: Insights from analogue modelling[END_REF], synkinematic sedimentation strongly influences the uplift of compressive growth structures. When R = 0, the effect of shortening in the lower and upper layers is the same, being associated with forward propagation of the deformation without major uplift. The maximum uplift is found in the experiment with R = 1 (Figs. 3, 4 and5), but it is noteworthy that, when the uplift of the upper structure increases, the lower structure undergoes less uplift (Fig. 4). When R = 1, the effect of shortening in the lower and upper layers is different: the lower layer propagates horizontally, while the upper layer grows vertically. The uplift of the lower structure is inhibited by the weight of the sediments, which explains why there is minor uplift for R = 2, and major uplift for R = 0.

Comparison with natural examples

The structural style of the Bolivian Subandean foothills is characterized by elongated N-S trending tight folds in the Chaco Basin (Figs. 6a andb). The geometry of the fold and thrust belt is mainly controlled by lithology and the presence of three main potential decollement levels [START_REF] Baby | Structure de la Zone Subandine de Bolivie: infuence de la géométrie des séries sédimentaires antéorogéniques sur la propagation des chevauchements[END_REF][START_REF] Baby | Geometric and kinematic evolution of passive roof duplexes deduced from cross section balancing: example from the foreland thrust system of the southern Bolivian Subandean Zone[END_REF][START_REF] Moretti | Hydrocarbon generation in relation to thrusting in the Sub Andean zone from 18 to 22 degrees S, Bolivia[END_REF][START_REF] Giraudo | Pre-Silurian control in the genesis of the central and southern Bolivian fold belt[END_REF][START_REF] Moretti | Compartmentalisation of fluid migration pathways in the sub-Andean Zone, Bolivia[END_REF]. The basal decollement level is located in the Kirusillas shales (Late Silurian). The middle decollement levels are identified at Icla (Early Devonian) and Los Monos (Late Devonian), where potential decollement is controlled by the clay content of the formations involved. The decollement levels partly disconnect the deformation observed at the surface (Tertiary to Lower Carboniferous series) from that occurring at depth (Devonian sandstones, Huamampampa, Fig. 6c). The upper decollement level, which is the thinnest, is located in the Ipaguazu Formation, which is composed of gypsum and shales (Triassic). Fluid overpressure in maturing source rocks may have an effect on detachments and the propagation of deformation in compressive systems (Cobbold and Rodrigues, [START_REF] Cobbold | Structural consequences of fluid overpressure and seepage forces in the outer thrust belt of the Niger Delta[END_REF]), but we do not discuss this possibility here because we have only analysed the geometry of isolated structures.

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The Chaco Basin is a classical foreland basin in a retro arc position [START_REF] Uba | Facies analysis and basin architecture of the Neogene Subandean synorogenic wedge, southern Bolivia[END_REF]2006).

Tertiary sedimentation is regarded as taking place in a foreland basin sequence during the Late Oligocene to Early Miocene. The base of this sequence is represented by the unconformable fluvial Petaca Formation (Late Oligocene to Early Miocene), which may be attributed to sedimentation in a forebulge-backbulge depocentre. The overlying Yecua Formation (Middle to Late Miocene) corresponds to the onset of active deformation and large-scale subsidence in response to thrust-belt loading on a regional scale (distal foredeep). The overlying Tariquia Formation (Late Miocene) is concomitant with the onset of deposition of Andean derived sediment in the medial-foredeep depocentre. In our study area, eastward from the Incahuasi structure (Fig. 6b), these formations may be considered as of relatively constant thickness and are thus pre-tectonic. In the western part of our study area, westward from the Incahuasi structure (Fig. 6b), these formations are of variable thickness and may be considered as syn-tectonic.

The Guandacay Formation (Late Miocene to Early Pliocene) and Emborozu Formation (Late Pliocene to Pleistocene) are coeval with the propagation of the deformation front in the Subandean Zone and thus represent true syntectonic deposits associated with the emplacement of the folds and thrusts in our studied area (Incahuasi structure). Their thickness can vary between 1000 -3500 m.

The age of the Guandacay Formation corresponds to the peak of shortening calculated by [START_REF] Moretti | Hydrocarbon generation in relation to thrusting in the Sub Andean zone from 18 to 22 degrees S, Bolivia[END_REF].

As hydrocarbon exploration in Bolivia targets a deep-seated reservoir below the main upper decollement (Devonian Los Monos Formation), some of these N-S trending tight folds have been drilled and some seismic data exists. The quality of seismic data in the Subandean Zone is poor and this hinders clear imaging of the deep-seated structures. Therefore, it is difficult to interpret the seismic data, which often give rise to misleading interpretations. Among the folds in the area, the Incahuasi anticline shows some interesting features. Three exploration wells drilled on the anticline axis confirm that the top of the Huamampampa Formation is offset by at least 1 km to the east with respect to the surface anticline axial plane (Fig. 7) as evidenced by sampling and dipmeter data acquired during drilling. The surface Incahuasi structure is overturned towards the west and shows a vergence contrary to that of most other folds in the Subandean Zone (Fig. 6). The main backthrust that accommodates this overfolding is rooted in the basal shale of the Los Monos Formation, close A comparison between the Incahuasi subsurface data and the analogue experiments (inverted crosssection of the model of figure 3b3) allows us to propose an interpretation of the Incahuasi structure in a cross-section showing the evolution of the thrust in time and space (Fig. 7). The overall evolution corresponds to an inversion of the vergence of the thrust. The first fault propagation fold is cut and displaced passively along with the hanging wall of the newly formed thrust fault.

Therefore, the change in the vergence of the Incahuasi fold may be explained by the influence of sedimentation rate. A comparison can also be made between the experimental results and subsurface data for the whole cross-section of the Subandean system (Fig. 6b). We propose that, in the eastern part, the structures of Camiri, Carohuaycho Los Huesos, Caipipendi and Charagua are characterized by major asymmetric geometries and propagation of deformation in front of the thrust, which is characteristic of the experiment with low sedimentation rate (Figs. 3a and5a). The central zone corresponding to the Incahuasi structure shows a drastic change in vergence direction, which is comparable to the experiment with a medium rate of sedimentation (Figs. 3b and5b). The western structures of Ilinchunpa and Inau are characterized by a double vergence and vertical propagation of the deformation, corresponding to the experiment with high sedimentation rate (Figs. 3c3, d3; and5c).

Thus, this lateral variation in the structures (see also [START_REF] Baby | Geometric and kinematic evolution of passive roof duplexes deduced from cross section balancing: example from the foreland thrust system of the southern Bolivian Subandean Zone[END_REF][START_REF] Moretti | Hydrocarbon generation in relation to thrusting in the Sub Andean zone from 18 to 22 degrees S, Bolivia[END_REF][START_REF] Giraudo | Pre-Silurian control in the genesis of the central and southern Bolivian fold belt[END_REF][START_REF] Moretti | Compartmentalisation of fluid migration pathways in the sub-Andean Zone, Bolivia[END_REF] is consistent with an increase in shortening from east to west and a decrease in rate of sedimentation from the hinterland toward the foreland.

Conclusions

The experimental results presented here suggest that: [START_REF] Barrier | Influence of syntectonic sedimentation on thrusts geometry. Field examples from the Iberian Chain (Spain) and analogue modeling[END_REF]. E is the ratio between the erosion rate, Ve, and the velocity of structure uplift, Vu (E = Ve/Vu). [START_REF] Ypfb-Sergeomin | [END_REF]. (b) Cross-section of the Subandean fold and thrust belts across the Incahuasi structure (using surface and subsurface data), the names correspond to the main structures. (c) Stratigraphic column of the Bolivian Subandean Zone [START_REF] Moretti | Compartmentalisation of fluid migration pathways in the sub-Andean Zone, Bolivia[END_REF], interpreted in terms of mechanical stratigraphy, compared with structures obtained in the analogue experiments.

  thickening of the lower silicone layer near the VD. New middle and upper synthetic thrusts cut the previous middle and upper antithetic thrusts. The previous middle and upper antithetic thrusts are slightly rotated clockwise and displaced passively on the hanging wall of the newly formed middle and upper synthetic thrusts. The synkinematic layers deposited during the growth of these synthetic thrusts show onlap geometry on their hanging wall, thus sealing the previous antithetic thrust. These layers also show toplap geometry below the base of the synthetic thrust in the footwall.

  centre of the model is associated with a verticalization of the prekinematic layers.

  with the Huamampampa quartzites. The dipmeter data in wells confirm the fact that the deep-seated thrust system affecting the Huamampampa Formation also faces towards the west (hinterland). Geological cross-sections constrained by field and several wells data confirm that the Incahuasi thrust, facing towards the east, has been passively rotated by the emplacement of the backthrust (Figs.6 and 7), which postdates the Incahuasi thrust, in the same way as reproduced by analogue modelling(Figs. 3b).

  Figure 7 compares the subsurface data, their interpretation and the interpreted cross-section of a model, showing the positive contribution of analogue modelling to an improved interpretation of the seismic lines.

  Figure and Table captions

Figure 1 :

 1 Figure 1: (a) Experimental apparatus and (b) sketch of the homogeneous and local synkinematic sedimentation. R is the ratio between the sedimentation rate, Vs, and the velocity of structure uplift,Vu (R = Vs/Vu, see[START_REF] Barrier | Influence of syntectonic sedimentation on thrusts geometry. Field examples from the Iberian Chain (Spain) and analogue modeling[END_REF]. E is the ratio between the erosion rate, Ve, and the

Figure 2 :

 2 Figure 2: Cross-section showing the terminology used in the description of the experiments.

Figure 3 :Figure 4 :

 34 Figure 3: Cross-sections of experiments for 5, 7.5, 10 cm of shortening. a1 to a3: for R = 0; b1 to b3; for R = 1/2 and E = 1/4; c1 to c3: for R = 1; d1 to d3: for R = 2. The colour coding used is green for a fault active only at the beginning of deformation, red for a fault active throughout deformation and yellow for a fault active at the end of deformation. "Bode" and "Repa" denote different experiments.

Figure 5 :

 5 Figure 5: Schematic cross-section of experiments after 10 cm of shortening showing the main features of the structures.

Figure 6 :

 6 Figure 6: (a) Geological map of Bolivia showing location of the interpreted seismic line (YPFB-

Figure 7 :

 7 Figure 7: (a) Subsurface data (seismic line and well) for the Incahuasi structure. (b) Interpretation of the Incahuasi structure (c) Inverted cross-section of experiment b after 10 cm of shortening (see figure 3b3).

•

  With décollement levels, models of compressive system show fish-tail structure• Synkinematic sedimentation favour vertical uplift and double vergence in thrust structure • Models allow to better interpret seismic lines in compressive systems• The evolution of Subandean structures is related to shortening and mass transfer

Table 1 :

 1 Scaling of parameters between nature and models. L, g, ρ, µ, V, t, and σ represent the length, acceleration due to gravity, density, viscosity, shortening rate, time and stress, respectively.

	M A N U S C R I P T

Acknowledgements:

We acknowledge Total for financial support. Special thanks are due to J.-J. Kermarrec for his


I Blanchet-Letrouvé
email: isabelle.blanchet-letrouve@ac-nantes.fr

A Zalouk-Vergnoux

A Vénisseau

M Couderc

B Le Bizec

C Herrenknecht

C Mouneyrac

L Poirier

Dioxin-like, non-dioxin like PCB and PCDD/F contamination in European eel 1 (Anguilla anguilla) from the Loire estuarine continuum: spatial and biological 2 variabilities 3 4

Introduction 30

Since the 1980s, monitoring studies in European countries have shown the decline of glass 31 eels arriving in the coastal waters and estuaries (ICES, 2006). The disappearance of the 32 prepubertal European eel (Anguilla anguilla) occurred as well a few decades earlier and 33 stocks were estimated to be divided by ten [START_REF] Dekker | Did lack of spawners cause the collapse of the European eel, Anguilla anguilla? 537[END_REF][START_REF] Moriarty | Management of the European Eel[END_REF]. 34

Several factors were brought forward to explain this decrease such as overfishing, obstacles to 35 migration [START_REF] Robinet | Sublethal Effects of Exposure to Chemical Compounds: A Cause 613 for the Decline in Atlantic Eels?[END_REF], pathogens (Palstra et al., 2007b), climate change 36 [START_REF] Castonguay | Is there a role of ocean 529 environment in American and European eel decline?[END_REF] and contaminants [START_REF] Geeraerts | Reproduction of European eel 558 jeopardised by high levels of dioxins and dioxin-like PCBs?[END_REF]Palstra et al., 2007a; and rivers and a significant food resource [START_REF] Perraudeau | L'estuaire de la Loire: un territoire en développement durable? 611 Rennes[END_REF]. Significant levels 62 of PCBs were detected in European eels from the Gironde and Adour estuary (France) (Tapie 63 et al., 2011), in the Mondego estuary (Portugal) [START_REF] Nunes | PCDD/Fs and dioxin-595 like PCBs in sediment and biota from the Mondego estuary (Portugal)[END_REF], in the rivers of Italy 64 [START_REF] Mezzetta | Concentration of DL-588 PCBs in fish from market of Parma city (north Italy): Estimated human intake[END_REF] and could be responsible for migration or reproduction impairments 65 [START_REF] Van Ginneken | PCBs and 641 the energy cost of migration in the European eel (Anguilla anguilla L.)[END_REF]. Assessing PCB contamination of the European eel is therefore of 66 great interest since their level is threatening public health, beyond a maximal value (European 67 Union, 2011) and is also a potential risk for its own health (for review, Geeraerts and 68 Belpaire, 2010). The present study aims to assess PCB contamination of the European eel 69 from the Loire estuary (France) which the basin (117,800 km 2 ) drains a lot of tributaries. 70

Moreover, the Loire estuary runs through important urban sites (Nantes, Saint-Nazaire) with 71 shipping, industrial and agricultural activities. It displays a diffusive pollution including a 72 mixture of contaminants such as heavy metals (Grobois et al., 2012), pesticides (Marchand et 73 al., 2004), PAHs and PCBs [START_REF] Hubaux | PCB dans 571 les milieux aquatiques: enjeux de gestion et lacunes dans les connaissances[END_REF]. For European eels, this estuary 74 constitutes one of the most important continental migration path of glass eels. The 75 preservation of its chemical quality is therefore essential for eel health. However, a real lack 76 of data on the POPs contamination levels of European eels exists in this ecosystem. Only few 77 individuals, sampling on the whole Loire river, have been analyzed in the French PCB 78 framework (ONEMA, 2012). These results cannot be sufficiently representative of eels living 79 in the estuary. In the present study, dl-PCB, ndl-PCB and PCDD/F levels were investigated in 80 European eels fished in the Loire estuary. This work was set out to reach three objectives : 81 i)to get a representative trend of PCB contaminants over life stages, from glass eels to silver 82 eels; ii) to assess spatial PCB contamination variations on yellow individuals (similar size 83 class distributions), along three different Loire estuary sites (Fig. 1), iii) to evaluate health 84 risks for local consumers with PCDD/F and dl-PCB TEQs quantification according to WHO 85 recommendations (van den Berg et al., 2006). 86 87 2. Material and methods 88

Sampling sites 89

As shown in Fig. 1, three sampling sites were selected in this study. Varades is a small city 90 (about 3550 locals), located upstream in the estuary at the limit of the salinity (100 km from 91 the Loire mouth); it also presents few industrial activities and is particularly under agricultural 92 pressure. The intermediate site is close to an important city, Nantes (about 600,000 locals) 93

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10. 1016/j.scitotenv.2013.11.037 located at 50 km from the mouth, characterized by an industrial harbor and an urban zone 94 including two incineration factories. The third site, Cordemais, is downstream of Nantes with 95 a strong influence of the North Atlantic Ocean and is well-known for its industrial activities, 96 particularly the presence of a coal-fired power plant and closed to an industrial complex 97 including oil refineries. These three sampling sites were chosen in order to represent the 98 estuary displaying different kinds of human activities. 99

Sampled animals 100

During one year and a half, i.e. from May 2009 to January 2011, European eels were 101 captured by local fishermen according to the fishing authorizations, in the three sampling sites 102 described above. Using specific methods, 62 yellow and silver eels were collected with fyke 103 and stow nets respectively. The aim of the sampling procedure was to evaluate the potential 104 spatial variability of contaminant levels in eels on these 3 different sites, to upstream from 105 downstream. Consequently, 16 yellow eels were captured in Varades, 16 in Nantes and 17 in 106

Cordemais. The captured eels were preferentially selected in order to obtain a similar size 107 class distribution, i.e. about 4 to 5 eels per size class and par site. To evaluate the trend in 108 contaminant level over life stage, glass eels and 13 silver eels were also captured. Individuals 109 were transported to the laboratory in aerated 200 L tanks filled with water from the sampling 110 site. They were maintained in the laboratory few hours until dissection under a natural 111 photoperiod (L15/D9) and at a temperature around 12 ± 2 °C, equivalent to the fishing site 112 conditions. Glass eels were collected with a specific fishing net (authorized mesh size) in 113 January 2011 in the estuary entry, near Cordemais. These glass eels had no pigment and 114 corresponded to a stage before the onset of the feeding [START_REF] Elie | Définition des limites des différents stades 542 pigmentaires durant la phase civelle d'anguilles Anguilla sp.(poisson téléostéen 543 anguilliforme)[END_REF]. They were directly 115 frozen at -20°C in aluminum foil after fishing and later divided into two different pools. 116 117 2.3. Biometric parameters and life stages of the biological samples 118 Eels were anesthetized in a water bath of 10 L added with 1.5 to 2 mL of clove oil solution 119 dissolved in ethanol (70%), according to the weight of eels (Palstra et al., 2007a). Once 120 anesthetized, the body length (BL in mm) and the body weight (BW in g) of each European 121 eel were measured. The animals were then sacrificed, skinned and dissected in order to collect 122 filets and otoliths. Biometric parameters were recorded to evaluate the Fulton's condition 123

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10. 1016/j.scitotenv.2013.11.037 factor (K= (BW x 10 5 ) / BL 3 with BW and BL respectively expressed as g and mm) (Fulton, 124 1904). 125

The otoliths were utilized to determine the age of the organisms. The pair of otoliths named 126 sagitta were removed from the eel's head. After extraction, otoliths were cleaned of all organic 127 membranes in distilled water, dried with ethanol, and then stored in Eppendorf tubes. The 128 otoliths were later embedded in synthetic resin (Synolithe), and then polished to the nucleus 129 with a polishing wheel (Streuers Rotopol-35) using two different grits of sandpaper (1200 and 130 2400). Fine polishing was done by hand with alumina (1µm grain) on a polishing cloth. 131

Etching was done using 10% EDTA. A drop of this solution was applied on the mold during 132 fifteen minutes. Then, the otoliths were rinsed with distilled water and stored in dry condition. 133

Yearly increments were revealed by staining with a drop of 5% Toluidine blue on the otolith 134 and letting it dry. Growth rings were then counted under binocular magnifier. The age of each 135 eel was determined by the number of increments starting from the nucleus, which was 136 considered as year 1 of the eel's life. The otolithometry was realized in partnership with the 137 IRSTEA (Cestas, France). Silver stage was determined by macroscopic characteristics such as 138 the differentiated lateral line (presence of black corpuscules), a contrasting skin color (dark 139 dorsal surface and a white ventral surface), the ocular diameter and the pectoral fin length. 140 141 2.4. PCB and PCDD/F analysis 142

Eel filets and pools of glass eels were analyzed for 18 PCBs (n= 62 and 2 pools of glass eels). 143 Among them, 12 are dl-PCBs (#77; 81; 105; 114; 118; 123; 126; 156; 157; 167; 169; 189) and 144 6 are ndl-PCBs (#28; 52; 101; 138; 153; 180). Ndl-PCB and dl-PCB levels in eel filets and 145 pools of glass eels were expressed as a sum of all congeners. In order to assess a potential 146 health risk, PCDD/F analyses were achieved on 11 out of 62 eels (5 yellow and 6 silver 147 individuals) and on the 2 pools of glass eels. The PCDD/Fs analyzed were the 17 congeners 148 regulated by the European Union (EC/1259/2011). PCB and PCDD/F levels were expressed 149 by congeners or as a sum of all congeners in ng.g -1 dry, lipid or wet weight (dw, lw or ww). 150

Reagents and Chemicals 151

All organic solvents (Promochem) were Picograde ® quality. Silica (Fluka), sodium sulfate 152 (Merck), and sulfuric acid (SDS) were of superior analytical quality. Native and 13 C-labeled 153 standards were purchased from Cambridge Isotope Laboratories (CIL) and Wellington 154

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10. 1016/j.scitotenv.2013.11.037 Laboratory. Standard solutions were prepared in toluene. All reference solutions were stored 155 in darkness at a temperature < 6°C. 156

Sample preparation procedure 157

Eel filets and pools of glass eels were homogenized, weighed and freeze-dried. Five grams of 158 filets and pools of glass eels were cut, dehydrated, and milled using a turbo-mixer with glass 159 bowl. Each experiment was realized with disposable material. Then, samples were powdered 160 and transferred into cells in order to be extracted by Accelerated Solvent Extraction (ASE) 161 using a Dionex ASE 300. Before extraction, eighteen 13 C-labelled PCB congeners were added 162 to the samples for internal standard calibration and quantification by the isotope dilution 163 method. Pressure and temperature were set to 100 bars and 120°C respectively. The extraction 164 solvent was a mixture of toluene/acetone 70:30 (v/v), and three successive extraction cycles 165

(5 min each) were performed. The extract was evaporated to dryness by rotary evaporation 166 (40°C), allowing the gravimetric determination of the fat content, in order to assess the filet 167 lipid weight (LW in % of wet weight). The extracts were dissolved in 25 mL of hexane for 168 sample clean-up. 169 Three purification steps were then performed, using successively acid silica, Florisil ® and 170 celite/carbon columns. After removal of fat on the first silica gel column activated with 171 sulfuric acid, PCBs were separated from PCDDs/PCDFs on the second Florisil ® column. The 172 separation of coplanar (non-ortho) PCBs from non coplanar PCBs was achieved on an 173 activated mixture of Florisil ® / Carbopack C/Celite 545 (overnight at 130°C). After the 174 addition of external standards for the recovery calculation ( 13 C 12 -PCB #111 for PCBs), final 175 sample extracts were evaporated under a nitrogen stream to dryness and reconstituted in 20 176 L, 50 L and 10 L of toluene for coplanar PCBs, non coplanar PCBs and PCDD/Fs 177 respectively. 178

GC-HRMS measurement 179

PCB and PCDD/F measurements were performed by gas chromatography coupled to high 180 resolution mass spectrometry (GC-HRMS) using an 7890A gas chromatograph (Agilent) 181 coupled to a JMS 700D or a JMS 800D double electromagnetic sector high resolution mass 182 spectrometer (Jeol, Tokyo, Japan). A DB5MS (30 m x 0.25 mm x 0.25 µm) capillary column 183 (J&W) was used in the splitless mode. The GC program for PCBs was 120°C (3 min), 184 20°C/min to 170°C (0 min), 3°C/min to 245 °C (0 min) and finally 20°C/min to 275°C 185

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037

(7 min). Ionization was achieved in the electron ionization mode (42 eV electron energy). The 186 spectrometric resolution was set at 10,000 (10% valley), and the signal acquisition was 187 performed in the Single Ion Monitoring (SIM) mode focusing on the two most abundant 188 signals from each target molecular ion ( 35 Cl and 37 Cl isotopic contributions). Signals were 189 integrated by JEOL Diok software (v.4). The detection and quantification limits (LOD and 190 LOQ respectively) Table 1 shows biometric parameters of the European eels collected in the Loire estuary 219 according to life stage, sampling site and size class. The increase of BW is positively 220 correlated with the increase of BL whatever the life stage (yellow or silver), and the sampling 221 site. The linear regression equations for yellow eels are: Varades BL=126.18 lnBW-154.9 222 R²=0.97 (n=16); Nantes BL=152.8 lnBW-292.5 R²=0.97 (n=16); Cordemais BL=113.14 223 lnBW-105.2 R²=0.98 (n=17) and those of silver eels was BL=220.94 lnBW-685.9 R²=0.98 224 (n=13). The age of eels is associated to BL and BW, only for yellow individuals from 225 Cordemais (BL=60.9 Age+109.2 R²=0.77 (n=17)). No significant correlation was observed 226 for yellow individuals from others sites and for silver eels. Fulton's condition factor values 227 (K) are roughly similar in the range of the different size classes studied as well as according to 228 the sampling site and the life stage, with values ranging from 0.13 to 0.17. According to 229 [START_REF] Feunteun | Management and restoration of European eel population (Anguilla anguilla): An 548 impossible bargain[END_REF], these values are representative of eel good health of in the Loire estuary. 230 Such values are similar to the Fulton's condition factor found in other studies about European 231 areas [START_REF] Gravato | Comparative study 561 about the effects of pollution on glass and yellow eels (Anguilla anguilla) from the estuaries of Minho, Lima and Douro Rivers (NW Portugal)[END_REF]Palstra et al., 2007b;[START_REF] Tapie | PBDE and PCB 626 contamination of eels from the Gironde estuary: From glass eels to silver eels[END_REF]. Nevertheless, better eel 232 conditions were calculated in some other studied sites like the River Rhine watershed and 233 Lake Ijsselmeer [START_REF] Haenen | 568 The health status of European silver eels, Anguilla anguilla, in the Dutch River Rhine 569 Watershed and Lake IJsselmeer[END_REF]. 234 3.2 Influence of life stage, sampling site and size class on dl and ndl-PCB levels 235

Table 1 shows the PCB levels (dl and ndl-PCBs) according to the life stage, the sampling site 236 and the size class. As it was already reported in a previous work [START_REF] Tapie | PBDE and PCB 626 contamination of eels from the Gironde estuary: From glass eels to silver eels[END_REF], PCB 237 levels determined for glass eels were higher than the limit of quantification of the analytical 238 methods. The sums of dl and ndl-PCBs are 3.7±1.9 ng.g -1 dw and 15.2±4.2 ng.g -1 dw 239 respectively. These levels could be the result of a contamination via the food web during the 240 leptocephali stage (plankton) and to a direct exposure from the aquatic compartment. Another 241 hypothesis could be an intergenerational transfer of contaminants (Palstra and van den 242 Thillart, 2011). 243

Regarding yellow eels, the PCB contamination increases and becomes significantly higher 244 compared to glass eels whatever the sampling site and the size class considered. Regarding 245 each site, the trends of ndl and dl-PCB levels expressed as ng.g -1 dw or lw are similar and 246

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037

showed no significant difference according to the size classes. This observation could be 247 attributed to the low sample number per size class. Nevertheless, it is possible to conclude that 248 PCB levels were not correlated to BL and BW, except for eels from Nantes (Table 1). 249

Considering the results depicted for eels from Nantes and the eel ecology (bottom dwelling 250 fish), the increasing contamination with BL and BW could be attributed to the continental 251 phase longevity and consequently to the time spent in the estuary environment, in close 252 contact with potentially contaminated sediments. It could be also related to the trophic chain 253 based on a more or less contaminated food. 254

Regarding the silver eels, dl-PCB levels, expressed as ng.g -1 dw, were significantly higher 255 than results for yellow eels from Varades and Cordemais. Considering the same unit, ndl-PCB 256 levels for silver eels were significantly higher than levels for yellow eels from Varades only. 257

Considering dl-and ndl-PCB levels expressed as ng.g -1 lw, the results tend to decrease but are 258 only significantly different to those for yellow eels from Nantes, and whatever all the size 259 classes. This results can be explained by the highly lipid content in silver eels leading to a 260 dilution of the contaminants. 261

In a previous work [START_REF] Tapie | PBDE and PCB 626 contamination of eels from the Gironde estuary: From glass eels to silver eels[END_REF], a review about marker PCB levels in Anguilla 262 anguilla filets was achieved from the literature. Marker PCB congeners are #28, 52, 101, 118, 263 138, 153 and 180. To compare with this synthetic review , the values obtained in this study 264 for the last congeners were summed, , and expressed as ng.g -1 ww and lw (Table 1). The PCB 265 congener #118 is usually used as a marker PCB until now (ANSES, 2011). The percentage of 266 this congener was relatively constant and represented an average of 9.39 ± 2.7 % of total PCB 267 marker level. 268

At the international scale, eels from the Loire estuary appear to be more contaminated than 269 those from some other sites in Poland, Ireland, Spain, Italy and the UK (Bordajandi et al., 270 2003;[START_REF] Corsi | Contamination and 531 sub-lethal toxicological effects of persistent organic pollutants in the European eel 532 (Anguilla anguilla) in the Orbetello lagoon (Tuscany, Italy)[END_REF][START_REF] Mchugh | The occurrence of 585 persistent chlorinated and brominated organic contaminants in the European eel 586 (Anguilla anguilla) in Irish waters[END_REF][START_REF] Santillo | Swimming in Chemicals Widespread. 622 Presence of Brominated Flame Retardants and PCBs in eels (Anguilla anguilla) 623 from Rivers and Lakes in 10 European Countries[END_REF]. However, other sites are 271 more contaminated than the Loire estuary (twice to 10 times higher), i.e. the River Elbe in 272 Czech Republic and Germany, the Tevere and Gagliarino rivers in Italy, Flanders in Belgium 273 and different lakes in Finland [START_REF] Belpaire | What can we learn from monitoring 512 PCBs in the European eel? A Belgian experience[END_REF][START_REF] Maes | Spatial variations and temporal trends between 1994 and 578 2005 in polychlorinated biphenyls, organochlorine pesticides and heavy metals in 579 European eel (Anguilla anguilla L.) in Flanders, Belgium[END_REF]Tulonen and Vuorinen, 274 1996;[START_REF] Van Der Oost | Biomonitoring 638 aquatic pollution with feral eel (Anguilla anguilla) I. Bioaccumulation: biota-sediment 639 ratios of PCBs, OCPs, PCDDs and PCDFs[END_REF]. Throughout France, eels from the Loire estuary are slightly 275 more contaminated than those from the Vacares lagoon and about three times more than those 276 from the Thau pound [START_REF] Oliveira Ribeiro | Bioaccumulation of polychlorinated 598 biphenyls in the eel (Anguilla anguilla) at the Camargue Nature Reserve -France. 599[END_REF][START_REF] Santillo | Swimming in Chemicals Widespread. 622 Presence of Brominated Flame Retardants and PCBs in eels (Anguilla anguilla) 623 from Rivers and Lakes in 10 European Countries[END_REF], whereas they are 277

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037 less contaminated than eels from the Rhone River (about ten times less) and the Gironde 278 estuary (about two times less, whatever the life stage and the size class) [START_REF] Tapie | PBDE and PCB 626 contamination of eels from the Gironde estuary: From glass eels to silver eels[END_REF]. 279

In the study of [START_REF] Tapie | PBDE and PCB 626 contamination of eels from the Gironde estuary: From glass eels to silver eels[END_REF], a significant decrease of marker-PCB levels expressed as 280 ng.g -1 dw was observed for eels exceeding 600 mm. These authors hypothesized that this 281 decrease could be induced by two parameters regarding the sexual maturity of the individuals 282 of this size class. On the one hand, eels could be at the onset of the silvering and coming from 283 upstream areas, less contaminated. On the other hand, silver eels could be already in 284 starvation and start to mobilize lipid stores as fuel energy to ensure the sexual maturation and 285 swimming towards spawning areas. This mobilization of lipids was already proposed to 286 explain a decrease in lipid contents observed in filets of eels larger than 800 mm (Durif et al., 287 2005). In this present work, no decrease is observed for eels with length superior than 600 288 mm whatever the unit expression. . 289 290 In order to evaluate the correlations between biometric parameters and PCB levels as well as 291 the sampling site effect, a principal component analysis (PCA) was performed by using 292 biometric parameters (age, BW, BL and LW) and dl and ndl-PCB levels expressed as ng.g -1 293 dw. Since silver eels are not strictly territorial, due to their downstream migration, they could 294 be originated from other sites than sampling ones. For that reason, the PCA was performed 295 with yellow eels only. As it was shown in the Table 1, the size class distributions between the 296 3 studied sites are comparable. Consequently, it is possible to study and discuss the presence 297 of an eventual sampling site effect on yellow eel impregnation. 298

The correlation loading and sample representation are shown on figure 2 (respectively Fig. 2 A 299 and Fig. 2 B). The first two principal components (respectively PC1 and PC2) describe 300 82.97% of the total variability among eels. PC1 and PC2 represent respectively 62.65 and 301

20.32%. 302

The correlation loading (Fig. 2A) highlights that biometric parameters (BW, BL and age) are 303 correlated to each other as it was depicted in Table 1. Concerning LW, it appears to be quite 304 correlated to both levels of dl-and ndl-PCBs. This observation was expected and already 305 well-known according to the lipophilic properties of PCBs (van der [START_REF] Van Der Oost | Biomonitoring 638 aquatic pollution with feral eel (Anguilla anguilla) I. Bioaccumulation: biota-sediment 639 ratios of PCBs, OCPs, PCDDs and PCDFs[END_REF]. 306

Regarding the sample presentation in Fig. 2B, the eels are relatively clustered according to the 307 three different sampling sites. The comparison of Fig. 2A and Fig. 2B underlines that eels from 308

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037

Varades are the lowest contaminated by dl and ndl-PCBs closely related with lower LW. The 309 eels from Nantes and some of those from Cordemais are more contaminated, showing a 310 higher LW. However, eels from Nantes present a higher heterogeneity. The inter-site 311 differences observed could be also related to differences of biometric parameters such as the 312 BL and the age, characterizing a different exposition time (9.8 ± 1.9 years for eels from 313 Nantes compared to 4.4 ± 1.4 years and 5.9 ± 1.9 years for eels from Cordemais and Varades, 314 respectively). 315 Moreover, Varades is a small city (about 3550 locals), relatively preserved, located upstream 316 in the estuary, and with few industrial activities. It is probably for these reasons that the eels 317 from this sampling site are less contaminated than the others. Nantes is indeed an important 318 city (about 600000 locals) and Cordemais is downstream of Nantes and well-known for its 319 industrial activities. In this study, the living area of eels seems to affect their contamination 320 level as it was already shown in the Gironde estuary [START_REF] Tapie | PBDE and PCB 626 contamination of eels from the Gironde estuary: From glass eels to silver eels[END_REF]. These inter-site 321 differences would be highlighted in the next section dealing with eels PCB fingerprints. 322 323 3.3 PCB fingerprints in eels according to the sampling site and life stage 324 A sampling site effect has been previously demonstrated (Fig. 2). A second PCA was then 325 performed using individual PCB levels expressed as ng.g -1 dw. For the same reason that 3.2 326 paragraph, this second PCA was realized with yellow eels only. Consequently, this PCA was 327 useful in order to evaluate the influence of the sampling site on PCB fingerprints in yellow 328

eels. 329

The result of the PCA correlation loading is shown in Fig. 3A Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037

of Cl atoms in meta-and para-positions are important, the upper their localization is. Ndl-340 PCBs are considered as particularly persistent and present in the environment, representing 341 about 50% of all of the PCB congeners found in food from animal origin (AFSSA, 2006). 342

According to Fig. 3A, they were well distributed around the right part of the correlation circle 343 and among all the other PCBs, emphasizing their qualitative representativeness of all the PCB 344 congeners [START_REF] Cariou | Prediction 525 of the PCDD/F and dl-PCB 2005-WHO-TEQ content based on the contribution of six 526 congeners: Toward a new screening approach for fish samples?[END_REF]. 345 Fig. 3B enhances this result showing the accumulation patterns of marker-PCBs in yellow eels 346 from the three sampling sites comparatively to those in the glass and silver eels. 347

Concerning the main congener #153, it contributes to an average of 42% of the contamination 348 of the yellow eels whatever the sampling site. This PCB is interesting because it is non 349 metabolizable and a tracer of bioaccumulation process. The percentages of this congener are 350 not significantly different for glass and silver eels compared to yellow eels from Varades but 351 they are lower than those found for yellow eels from Cordemais and Nantes. 352

Considering the sampling site influence, an inter-site variability is observed, particularly for 353 eels from Cordemais which display patterns with significantly lower relative proportion of 354 PCBs #28 and 118 whereas the relative proportion of #180 is significantly higher than those 355 of the other sites. About eels from Nantes, the relative proportion of the PCB #101 is 356 significantly higher to the detriment of the #180 with a relative proportion significantly lower. 357

Finally, the PCB #180 is the only one able to discriminate the sampling sites. Its proportion is 358 higher in Cordemais eels, lower in Nantes eels and intermediate in Varades eels. For the other 359 marker-PCBs (#153, 138 and 52), no significant specific trend is observed according to the 360 sampling site. 361

The PCB contamination variability between the three sampled sites could be partially 362 explained by the anthropogenic activities existing in the area. Indeed, Varades is a relatively 363 small city, marked by several agricultural activities where PCB sources are probably less 364 important than in Nantes or Cordemais. On the contrary, Nantes is an important urban and 365 industrial city, with an important economic and demographic development, where two 366 incinerator factories and various maritime and industrial activities exist. A lot of domestic, 367 industrial and agricultural effluents are discharged into the Loire estuary more or less 368 previously depolluted in sewage treatment plants. Cordemais presents another profile because 369 it is a very small rural city but dominated by its economic and industrial activities, directly 370

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10. 1016/j.scitotenv.2013.11.037 based on the presence of the Loire estuary such as a coal-fired power plant and close to an 371 industrial complex which includes oil refineries. 372

The PCB sources are therefore multiple along the estuary and the PCB contamination of this 373 ecosystem could be done following atmospheric or aquatic routes. This complexity prevents 374 from establishing easy correlations between the congener profiles and the sources. Motelay-375 Massei et al. (2004) showed, in the Seine river basin, that less chlorinated PCB congeners are 376 transported over longer distances from the source sites because of their longer residence time 377 in the atmosphere, whereas the heaviest PCBs tend to be adsorbed on particles and to settle 378 near production sources. Therefore, our results could suggest that eels from Cordemais were 379 living closer to a PCB source than eels from the other sites. 380

Moreover, the Loire estuary presents strong hydrodynamic, sedimentary and abiotic 381 parameters [START_REF] Dauvin | The main characteristics, problems, and prospects for Western European coastal 535 seas[END_REF]. Today, the effects of the tide can be observed within 97 km from 382 the estuary mouth and the salinity moves upstream. This modifies also the temperature from 383 the mouth of the estuary to the upstream front of the salinity which varies of 5°C from 384 downstream to upstream. The Loire estuary is also characterized by a fluid mud which 385 extends over 20 km; it is an important factor in the rapid sedimentation of the estuary, so the 386 turbidity varies from 2 g.L -1 at the surface to 20 g.L -1 near the bottom. All these parameters 387 (salinity, turbidity, temperature and tidal amplitude) could affect the exposition level of PCBs 388 potentially present in the estuary, and their chemical bioavailability for eels. Moreover, the 389 biological variability of eel PCB levels could also be explained by differences of diets, 390 ecology, physiology or metabolism capacities in relation to polyhaline, mesohaline and 391 oligohaline ecozones. 392

Regarding the difference of the relative proportions found for silver eels compared to yellow 393 eels, the only significant one is for PCB #28 which is higher in silver eels compared to yellow 394 eels whatever the sampling site considered. The patterns of silver eels are closer to those of 395 eels from Nantes, then Varades, whereas they display many significant differences 396 comparatively to those of eels from Cordemais: all the relative proportions are significantly 397 different except the one of PCB #138. 398 Finally, concerning the glass eels, a contrasting pattern is noticed, underlying a different 399 bioaccumulation phenomenon, characterized mainly by an important proportion of less 400 chlorinated PCBs to the detriment to the heaviest PCBs. This was already shown in a previous 401 study [START_REF] Tapie | PBDE and PCB 626 contamination of eels from the Gironde estuary: From glass eels to silver eels[END_REF] in which congeners 28, 50, 52, 101, 118 represented 51% of 402 Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037 accumulation pattern for glass eels sampled in the Gironde estuary. Comparatively, the 403 relative proportion of these congeners (without the PCB #50 not analyzed in this study) 404 represent 53% for glass eels in our study. The less chlorinated PCBs are transported over 405 longer distances from the PCB sources sites because of their longer residence time in the 406 atmosphere [START_REF] Motelay-Massei | Distribution 592 and spatial trends of PAHs and PCBs in soils in the Seine River basin, France[END_REF]. Moreover, in aquatic environments, these PCBs 407 that are more polar, are found to be dominant in dissolved phase and particulate organic 408 matter [START_REF] Cailleaud | Seasonal 517 variation of hydrophobic organic contaminant concentrations in the water-column of 518 the Seine Estuary and their transfer to a planktonic species Eurytemora affinis 519 (Calanoïd, copepod). Part 2: Alkylphenol-polyethoxylates[END_REF]. Glass eels come from the oceanic platform after the 409 metamorphosis of larvae leptocephali stage. These transparent larvaes move with currents 410 (pelagic comportment) for months, or years, in seawaters far from important pollution 411 sources. During their travel, the larvae were mainly contaminated by feeding uptake. When 412 they approach the continental shelf claim, the metamorphosis in glass eels occurs. They stop 413 then to feed and the contamination is then by direct exposure which leads to a pattern similar 414 to that of water column dominated by less chlorinated compounds. It is likely that the specific 415 PCB pattern of glass eels could be the result of these two phenomena. Another hypothesis is 416 the transfer of PCBs from adult eels to eggs and, consequently, to glass eels, low chlorinated 417 PCBs being more efficiently transferred than the heavy chlorinated ones [START_REF] Bargar | Maternal transfer of contaminants: case study of the 508 excretion of three polychlorinated biphenyl congeners and technical-grade 509 endosulfan into eggs by white leghorn chickens (Gallus domesticus)[END_REF]418 Verreault, 2006). 419

PCDD/F, PCB levels and public health 420

Mean PCDD/F and dl-PCB levels expressed according to the 2005 WHO recommendations 421 were 5.21 ± 1.78 and 9.88 ± 4.14 pg.g -1 WHO 2005 PCDD/F and dl-PCB TEQ (toxic 422 equivalents) ww for yellow (n=5) and silver individuals (n=6) respectively. Glass eels 423 depicted a mean level significantly lower (0.27 ± 0.03 pg.g -1 WHO 2005 PCDD/F and dl-PCB 424 TEQ ww). The maximum level established for the level of PCDD/Fs in eel filets is currently 425 3.5 pg.g -1 WHO 2005 PCDD/F TEQ ww and 10 pg.g -1 WHO 2005 PCDD/F and dl-PCB TEQ wet 426 weight (European Union, 2011). These values were not reached regarding the yellow eels. 427 Nevertheless, in the case of silver ones, biological variability was high and 4 out of 6 studied 428 eels displayed WHO 2005 PCDD/F and dl-PCB TEQ values higher than 10 pg WHO 2005 429 PCDD/F and dl-PCB TEQ per gram of wet filet. 430

Regarding the congeners # 28, 52, 101, 138, 153 and 180 (ndl-PCB), sampled eels did not 431 present levels superior than the 2005 WHO recommendation of 300 ng.g -1 ww. Silver eels and 432 yellow individuals from Nantes depicted the highest levels (mean of 204.6 ± 113.3 and 175.7 433 ± 90.7 ng.g -1 ww, respectively), but few individuals (3/29) presented concentrations higher 434

Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10. 1016/j.scitotenv.2013.11.037 than the recommended level (Table 1). Yellow individuals from Cordemais presented 435 intermediate levels (mean of 117.9 ± 47.7 ng.g -1 ww) and those from Varades the lowest ones 436 (mean of 75.5 ± 25.2 ng.g -1 ww). 437

Our results indicate a potential exposure to PCBs through eel consumption in this estuary, and 438 especially with silver ones. The French Food Safety Agency proposed a tolerable daily intake 439 (TDI) of 10 ng/ kg body weight/day (for the 6 ndl-PCB congeners), which represents 700 440 ng/day for a 70 kg person or 150 ng/day for a child of 15 kg (under 3 years) (French Food 441 Safety Agency, 2010). We could thus recommend to limit the consumption of eel from the 442 Loire estuary to one portion (150 g) per month for the general population, which represent an 443 average dietary daily intake of 694 ng/day. This is more restricted than the French Food 444 Safety Agency recommendations which limit the consumption of PCB bioaccumulating fish 445 to two portions per month for the general population. Specific recommendations (a portion of 446 60 g every two months) exist for the most sensitive populations (pregnant and breastfeeding 447 women, young and adolescent girls, women of childbearing age, and children under 3) and are 448 in agreement with our results, representing an average dietary daily intake of 139 ng/day. 449 A national study assessing the PCB impregnation of freshwater fish consumers performed on 450 six investigation sites including the Loire (French Food Safety Agency, 2011), revealed that 451 only 13% of participants (on a total of 606 amateur anglers and members of their households 452 and 16 professional anglers) are strong PCB-bioaccumulator freshwater fish consumers, with 453 a moderate consumption frequency of 1 time per month. Among the strong PCB-454 bioaccumulator freshwater fish species, eel is consumed with a mean annual frequency of 2.6 455 times per year. Considering these local practices and our results, a dietary daily intake of ndl-456 PCBs varying from 22 to 504 ng/day with a mean of 150 ng/day could be estimated. The TDI 457 value is not exceeded and the risk seems then to be moderate for an adult consumer but really 458 present for the most sensitive populations. Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10. 1016/j.scitotenv.2013.11.037 agricultural pressure) appeared less contaminated than the two other sites, i.e. Nantes (an 466 important city) and Cordemais (a town hosting a coal-fired power station). Regarding the 467 PCB patterns, the sampled sites of Varades and Nantes could be associated to urban 468 influences whereas the one of Cordemais, more impacted by heavy chlorinated PCBs, would 469 be nearer from a PCB industrial source. Compared to other international or national areas, the 470 ndl-PCB levels in eels from Loire estuary show an intermediate contamination. Our results 471 indicate a potential exposure to PCBs through eel consumption, and especially with silver 472 ones. According to TDI value, the consumption must be limited to once per month for the 473 general population and to once every two month for the most sensitive ones. 474

Apart from an eventual sanitary problem, the contamination of eels could lead to damages for 475 the eel population by affecting their reproduction and by a transfer of pollutants to eggs. 476 Indeed, since these compounds are lipophilic, the results showed that the PCB levels are 477 correlated to the lipid content in the filets. Lipids are essential compounds for the migration 478 reproduction [START_REF] Van Ginneken | PCBs and 641 the energy cost of migration in the European eel (Anguilla anguilla L.)[END_REF] and for both fat deposition in the oocytes and later 479 incorporation of vitellogenic stores in eggs. Moreover, acclimation of eels to seawater, 480 silvering process and reproduction migration are under different endocrine controls and fuel 481 consuming. This energetic cost is described to increase significantly when lipid filets of 482 swimming eels are charged in PCB mixture (after intraperitoneally injection of 5000 ng g -1 483 PCB # 153, 7 ng g -1 PCB # 126 and 50 ng g -1 PCB # 77) [START_REF] Thillart | Artificial Maturation and Reproduction of the 629 European Eel. Spawning Migration of the European Eel[END_REF]. PCB levels 484 determined in eels from the Loire estuary could thus potentially have an impact on the 485 reproduction success of European eels. 486

The comparison of eel biomonitoring studies highlighted heterogeneity in sampled 487 individuals. To better correlate studies at the international level, it appears necessary to 488 standardize parameters such as age, length, sex and sexual maturation stage. To preserve this 489 endangered species and such as recommended by scientists [START_REF] Van Ginneken | PCBs and 641 the energy cost of migration in the European eel (Anguilla anguilla L.)[END_REF], the 490 environmental quality of its habitats should be restored and protected. Considering our results, 491 the European eels from the Loire estuary appeared moderately contaminated compared to eels 492 from other major international estuaries, suggesting a moderate PCB contamination of the 493 Loire estuarine system. These conditions could contribute therefore to preserve genitors.

  Dioxin-like, non-dioxin like PCB and PCDD/F contamination in European eel (Anguilla anguilla) from the Loire estuarine continuum: spatial and biological variabilities I. Blanchet Letrouvé, A. Zalouk Vergnoux, A. Vénisseau, M. Couderc, B. Le Bizec, Pierre Elie, C. Herrenknecht, Catherine Mouneyrac, L. Poirier To cite this version: I. Blanchet Letrouvé, A. Zalouk Vergnoux, A. Vénisseau, M. Couderc, B. Le Bizec, et al.. Dioxin-like, non-dioxin like PCB and PCDD/F contamination in European eel (Anguilla anguilla) from the Loire estuarine continuum: spatial and biological variabilities. Science of the Total Environment, 2014, 472, p. 562 -p. 571. 10.1016/j.scitotenv.2013.11.037. hal-00993492

  are calculated by JEOL Diok software according to the regulation for 191 dioxin compounds analysis (LOD=LOQ at Signal/Noise=3). A LOD is calculated for each 192 congener and each sample (according to the sample mass). 193 2.4.4 Toxic equivalency calculation 194 Toxic Equivalent Quotient values (TEQ) were calculated according to the 2005 World Health 195 Organization Toxic Equivalency Factors (van den Berg et al., 2006) and basically expressed 196 on a fresh weight basis. 197 2.4.5. Quality assurance/quality control 198 All these procedures integrated quality control parameters to fulfill the requirements of the 199 Commission Directive 2002/69/EC and 2002/70/EC of July 2002, laying down the sampling 200 methods and the methods of analysis for the official control of dioxins and the determination 201 of dl-PCBs in foodstuffs and feedingstuffs respectively. Moreover, all analyses were 202 performed upon a double quality management system associated with an accreditation system 203 according to the ISO 17025:2005 standard for analytical measurements. 204 2.5. Statistical analysis 205 The Shapiro-Wilk and the Kolmogorov-Smirnov tests were employed to determine the 206 normality of the results. Consequently to these tests, non-parametric tests (Kruskal-Wallis and 207 pair-wise comparison tests) were used in order to highlight significant differences of PCB 208 levels and fingerprints in filets of eels with different life stages and from different sites. The 209 significant level of each test was determined according to Bonferroni correction (corrected 210 significant level of 0.005). To compare PCB levels in eel filets from different sites and 211 facilitate their discrimination, Principal Component Analysis (PCA) were performed. 212 WHO 2005 PCDD/F and dl-PCB TEQ values were compared according to life stages using 213 Mann-Whitney test at a significant level of 5%. All statistical treatments were realized with 214

  . The first two principal 330 components of the PCA (respectively PC1 and PC2) describe 85.74% of the total variability 331 among eels. PC1 and PC2 respectively represent 68.85 and 16.89%. This figure highlights 332 that the first principal component is positively correlated to all the individual PCB levels. The 333 second one is negatively correlated to low chlorinated PCBs and positively correlated to 334 highly chlorinated ones. 335 Each PCB congener is represented around the right part of the correlation circle. Nevertheless, 336 the repartition of the different PCBs seems to be due to their chemical structure, i.e. the 337 number and the position of Cl atoms. Low chlorinated PCBs with few Cl atoms in meta and 338 para-positions are in the right bottom of the circle. The more the number of total Cl atoms and 339

  a first assessment of the PCB contamination of a European eel population 462 fraction from the Loire estuary, along a hundred-km long portion of ecosystem. The 463 quantitative and qualitative contents of PCBs in eel filets are different depending on their life 464 stage and the sampling sites. The eels sampled in the site next to Varades (small city under 465

  to express their special thanks to the region Pays de la Loire and the 497 AADPPMFEDLA (Association Agréée Départementale des Pêcheurs Professionnels 498 Maritimes et Fluviaux en Eau Douce de Loire-Atlantique) for their technical and financial 499 support. 500 501

Figure 1 :Figure 2 :

 12 Figure 1: Studied area: the Loire estuary (France). Three sampling locations (Cordemais; Nantes and Varades)

Figure 3 :

 3 Figure 3: Representation of PCB patterns. A: correlation loadings of Principal Component Analysis of dl and ndl-PCB muscle levels expressed in ng.g -1 dw in yellow eels from 3 sampling sites (n = 49): Varades, Nantes and Cordemais (dl-PCBs: black circles; ndl-PCBs: white circles); B: Relative proportion (in %) of marker-PCBs in eel filets according to the life stage and the sampling site.

  Figure captions Click here to download Figure: Figure captions.docx Author-produced version of the article published in Science of the Total Environment, 2014, 472, 562-571The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037

Table 1 :

 1 Means and standard deviations of PCB levels (dl, ndl and marker) and biometric parameters (Body Length BL, Body Weight BW, Lipid Weight LW), Fulton's condition factor (K) and age of sampled European eels (n = 62) from the three studied sites in the Loire estuary according to life stage and size classes.

	Life stage	Sampling site	Size class (mm)	n	BL (mm)	BW (g)	Age (year)	LW (%)	K	dl-PCB levels (ng.g -1 dw)	ndl-PCB levels (ng.g -1 dw)	dl-PCB levels (ng.g -1 lw)	ndl-PCB levels (ng.g -1 lw)	ndl-PCB levels (ng.g -1 ww)	Marker-PCB levels (ng.g -1 ww)	Marker-PCB levels (ng.g -1 lw)
	Glass eels		< 200	pools	≤ 90	62±12	< 1	4.0 ± 0.8	n.d.	3.7±1.9	15.2±4.2	18.6±8.3	78±26	3.0±0.4	3.5±0.2	89±21
			200-300		279±14	30±3	5.2±0.8	4.9±2.3	0.14±0.02	41.4±12.4	253.7±78.1	286.9±69.2	1764±458	79.7±28.6	86.8±31.3	1918±491
			300-400		349±31	59±17	5.7±1.8	6.4±4.9	0.14±0.01	37.6±9.3	228.0±46.9 349.3±372.9	1183±510	72.7±22.2	79.3±24.7	1284±546
		Varades
			400-500		433±26	111±21	5.6±1.8	6.0±4.4	0.14±0.01	48.2±6.5	261.0±12.0 334.5±198.8 1770±1006	76.7±14.2	84.5±15.2	1953±1111
			500-600		533±31	207±2	9.0±2.1	10.1±11.7 0.14±0.02	29.0±13.8	195.1±118.1 169.7±121.4	1041±619	69.1±58.8	74.6±63.0	1132±682
			300-400		366±37	81±28	8.6±0.7	10.4±5.7	0.16±0.02	71.8±15.7	448.5±78.5 266.8±131.2	1657±722	144.8±49.1	158.3±54.7	1810±799
	Yellow eels	Nantes	400-500 500-600		452±33 546±24	129±30 259±49	9.5±0.5 10.5±1.2	10.2±3.2 11.2±6.7	0.14±0.01 0.16±0.01	82.2±10.3 97.8±31.0	482.2±74.4 278.5±103.6 542.8±171.3 344.4±135.5	1669±797 1909±767	151.9±16.4 180.8±77.2	166.6±17.3 199.0±84;5	1827±852 2100±828
			>600		678±63	551±183	11.0±3.9	11.6±8.9	0.17±0.03	134.9±82.9	734.6±401.9 488.0±244.5 2706±1365 252.0±187.9 278.6±210.0 2986±1508
			200-300		272±10	26±2	3.1±0.7	6.6±2.8	0.13±0.01	45.6±11.4	326.7±78.8 238.7±126.2	1291±490	95.8±23.5	102.3±25.1	1910±1258
			300-400		342±36	61±19	3.8±0.6	12.0±3.6	0.15±0.02	61.8±22.7	403.8±166.4 172.5±45.5	1130±378	135.7±63.1	146.2±67.7	1217±401
		Cordemais
			400-500		455±17	147±12	5.5±0.4	7.7±3.3	0.16±0.01	46.1±6.7	307.3±42.6	191.1±68.8	1275±476	88.1±21.0	94.9±22.4	1372±508
			500-600		522±11	227±22	6.3±1.0	15.0±6.8	0.16±0.00	76.1±17.2	479.3±68.9	185.1±54.4	1170±285	164.8±37.0	177.9±40.9	1263±312
	Silver eels		>500	13	659±124 517±344	12.4±3.8	25.6±3.5	0.16±0.01	93.7±56.3	463.2±244.6 161.6±96.1	800±425	204.6±113.3 229.0±130.3	895±485
				n.d.: non determined

Table Click here to download Table: Table 1.docx

 Click Author-produced version of the article published in Science of the TotalEnvironment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037

Author-produced version of the article published in Science of the TotalEnvironment, 2014, 472, 562-571 The original publication is available at http://www.sciencedirect.com/science/journal/00489697 10.1016/j.scitotenv.2013.11.037

Acknowledgments 496

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