Munschy Catherine

Bely Nadege

Héas-Moisan Karine

Olivier Nathalie

Pollono Charles

Chouvelon Tiphaine

Catherine Munschy
email: cmunschy@ifremer.fr

A large diversity of organohalogen contaminants reach the meso and bathypelagic organisms in the Bay of Biscay (northeast Atlantic)

Keywords: Deep-sea, Crustaceans, Fish, Persistent organic pollutants, Contaminants of emerging concern, Species -specific profiles

Deep-sea ecosystems play a key role in the cycling and vertical transfer of matter and energy in oceans. Although the contamination of deep-sea demersal and benthic organisms by persistent organic pollutants has been proven, deep pelagic species have been far less studied. To fill these gaps, we studied the occurrence of a large variety of hydrophobic organic contaminants including polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), legacy and alternative brominated flame retardants (BFRs) and per-and polyfluoroalkyl substances (PFASs) in crustaceans and fish species collected in the Bay of Biscay, northeast Atlantic. The results highlighted the global predominance of PCBs in fish, followed by OCPs, PFASs and PBDEs, with highly variable concentrations among species. Most of the chlorinated or brominated contaminants showed increasing concentrations with increasing δ15N values, while most PFASs showed inverse trends. The contaminant profiles and diagnostic ratios revealed species-specific metabolic capacities and peculiar contribution of highly-brominated BFRs.

Highlights

► Organohalogen contaminants were ubiquitous in deep pelagic crustaceans and fish. ► PCBs were predominant in fish followed by OCPs, PFASs and PBDEs. ► BFR profiles were peculiar with high contributions of BDE-209 and DBDPE. ► Specific ratios highlight species-specific metabolic capacities. ► Long-chain PFCAs showed biodilution with increasing δ 15 N values.

Introduction

The deep-sea pelagic environment (< 200 m) is one of the largest ecosystems on Earth and supports a high diversity and abundance of marine species, especially in the bathyal horizon (< 2000 m) [START_REF] Rogers | Environmental Change in the Deep Ocean[END_REF]. In particular, meso-(< 1000 m) and bathypelagic (1000-2000 m) communities represent essential components of oceanic biomass and important prey for higher trophic levels including large pelagic fish (tunas, sharks), marine mammals and seabirds. They play a key role in the cycling and vertical transfer of matter and energy in oceans [START_REF] Bernal | Diet and feeding strategies of mesopelagic fishes in the western Mediterranean[END_REF][START_REF] Bianchi | Diel vertical migration: Ecological controls and impacts on the biological pump in a one-dimensional ocean model[END_REF][START_REF] Catul | A review on mesopelagic fishes belonging to family Myctophidae[END_REF]. As a consequence of their strong diel vertical migrations (DVM) during which some species [START_REF] Chouvelon | High interspecies variability in elemental composition of the twilight zone fauna varies implications for predators and exploitation by humans[END_REF][START_REF] Eduardo | Distribution, vertical migration, and trophic ecology of lanternfishes (Myctophidae) in the Southwestern Tropical Atlantic[END_REF][START_REF] Takahashi | Organochlorine and butyltin residues in mesopelagic myctophid fishes from the western North Pacific[END_REF] feed in surface waters (epipelagic zone, 0-200m) at night and move back to meso-and bathypelagic zones during the day, meso-and bathypelagic organisms release particulates, organic matter and associated contaminants via faecal pellet egestion and may therefore increase transfers from surface waters to deeper horizons [START_REF] Belcher | Respiration rates and active carbon flux of mesopelagic fishes (Family Myctophidae) in the Scotia Sea, Southern Ocean[END_REF][START_REF] Bernal | Diet and feeding strategies of mesopelagic fishes in the western Mediterranean[END_REF]. Furthermore, their upward migration, during which they become available to surface predators, leads to the transfer of organic matter and contaminants accumulated in their tissues from deep horizons back to epipelagic layers. In addition to their essential role in biogeochemical cycles, mesopelagic organisms have also raised interest regarding their exploitation as new resources for human consumption as well as the fish meal and oil industry [START_REF] Berntssen | Processing Mixed Mesopelagic Biomass from the North-East Atlantic into Aquafeed Resources; Implication for Food Safety[END_REF][START_REF] Grimaldo | Investigating the potential for a commercial fishery in the Northeast Atlantic utilizing mesopelagic species[END_REF].

Although deep-sea ecosystems have been studied for decades, most studies focused on deep demersal or benthic communities and rarely on deep pelagic organisms, especially those from the ocean "twilight zone" (200-1000 m), which thus remain the most understudied ones. Recent publications have therefore highlighted the urgent need to increase knowledge in various research areas for these deep pelagic ecosystems, including the fate and impact of organic contamination [START_REF] Martin | Study the twilight zone before it is too late[END_REF][START_REF] Sanganyado | Organic pollutants in deep sea: Occurrence, fate, and ecological implications[END_REF]. Indeed, oceans and deep waters in particular are final sinks for anthropogenic wastes, including chemicals produced from industrial, urban, domestic and agricultural uses [START_REF] Froescheis | The deep-sea as a final global sink of semivolatile persistent organic pollutants? Part I: PCBs in surface and deep-sea Electronic copy available at: https://ssrn.com/abstract=4123446 dwelling fish of the North and South Atlantic and the Monterey Bay Canyon (California)[END_REF][START_REF] Looser | The deep-sea as a final global sink of semivolatile persistent organic pollutants? Part II: organochlorine pesticides in surface and deep-sea dwelling fish of the North and South Atlantic and the Monterey Bay Canyon (California)[END_REF][START_REF] Zhang | Poly-and Perfluoroalkyl Substances in Seawater and Plankton from the Northwestern Atlantic Margin[END_REF]. Contaminant sources to oceans are numerous and include mainly (80%) land-based but also sea-based activities. Atmospheric transport, continental inputs via rivers and runoff as well as direct discharges contribute to their widespread occurrence in oceans [START_REF] Landrigan | Human Health and Ocean Pollution[END_REF][START_REF] Ramu | Occurrence of organochlorine pesticides, polychlorinated biphenyls and polybrominated diphenyl ethers in deep-sea fishes from the Sulu Sea[END_REF][START_REF] Tornero | Chemical contaminants entering the marine environment from seabased sources: A review with a focus on European seas[END_REF]. Although deep-sea ecosystems are remote from direct anthropogenic sources of pollutants, various studies have shown that persistent hydrophobic organic contaminants are transported to deep oceanic waters, including the hadal trenches [START_REF] Cui | Occurrence of Halogenated Organic Pollutants in Hadal Trenches of the Western Pacific Ocean[END_REF][START_REF] Dasgupta | Toxic anthropogenic pollutants reach the deepest ocean on Earth[END_REF][START_REF] Jamieson | Bioaccumulation of persistent organic pollutants in the deepest ocean fauna[END_REF][START_REF] Takahashi | Organohalogen compounds in deep-sea fishes from the western North Pacific, off-Tohoku, Japan: Contamination status and bioaccumulation profiles[END_REF][START_REF] Webster | Halogenated persistent organic pollutants in relation to trophic level in deep sea fish[END_REF]. Because of their high hydrophobicity, long half-lives and longdistance transport, persistent organic pollutants (POPs) and other substances showing similar properties are of particular concern in our global environment [START_REF] Cousins | Why is high persistence alone a major cause of concern?[END_REF][START_REF] Jones | Persistent Organic Pollutants (POPs) and Related Chemicals in the Global Environment: Some Personal Reflections[END_REF].

Despite their regulation for decades and the remoteness of deep ecosystems from direct sources, the transport of legacy POPs to the deep sea has been proven, and various deep-sea species have been shown to be prone to high exposure to these contaminants, leading to their bioaccumulation at higher levels than in shallower water organisms [START_REF] Froescheis | The deep-sea as a final global sink of semivolatile persistent organic pollutants? Part I: PCBs in surface and deep-sea Electronic copy available at: https://ssrn.com/abstract=4123446 dwelling fish of the North and South Atlantic and the Monterey Bay Canyon (California)[END_REF][START_REF] Looser | The deep-sea as a final global sink of semivolatile persistent organic pollutants? Part II: organochlorine pesticides in surface and deep-sea dwelling fish of the North and South Atlantic and the Monterey Bay Canyon (California)[END_REF][START_REF] Mormede | Horizontal and vertical distribution of organic contaminants in deepsea fish species[END_REF]Ramu et al., 2006 and references therein) and making chemical contamination by POPs one of the anthropogenic pressures in the deep sea [START_REF] Stemmler | Evidence of the return of past pollution in the ocean: A model study[END_REF]. Among the legacy POPs, polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) are by far the mostly-studied organic contaminants in deep ecosystems [START_REF] Covaci | Anthropogenic and Naturally Occurring Organobrominated Compounds in Two Deep-Sea Fish Species from the Mediterranean Sea[END_REF][START_REF] Ramu | Occurrence of organochlorine pesticides, polychlorinated biphenyls and polybrominated diphenyl ethers in deep-sea fishes from the Sulu Sea[END_REF][START_REF] Romero-Romero | Biomagnification of persistent organic pollutants in a deep-sea, temperate food web[END_REF][START_REF] Storelli | Polychlorinated biphenyl and organochlorine pesticide contamination signatures in deep-sea fish from the Mediterranean Sea[END_REF][START_REF] Takahashi | Organohalogen compounds in deep-sea fishes from the western North Pacific, off-Tohoku, Japan: Contamination status and bioaccumulation profiles[END_REF][START_REF] Webster | Halogenated persistent organic pollutants in relation to trophic level in deep sea fish[END_REF]. However, most of these studies relate to demersal and benthic species living near or on the bottom floor of oceans (most of the references above), while true deep pelagic species are more seldom considered. Other substances with similar properties as POPs are of similar concern, as very few data on their occurrence and fate in deep-sea ecosystems are available so far.

Among them are alternative flame-retardants such as those used in the replacement of legacy compounds, for example, BTBPE (1,2-bis (2,4,6-tribromophenoxy)ethane) and DBDPE (decabromodiphenylethane), which replaced penta-and deca-BDE respectively. Per-and polyfluoroalkyl substances (PFASs), including the regulated long-chain perfluorocarboxylic acids (PFCAs) in particular, represent another under-studied class of compounds, although increasing concern has been recognised for this vast family of less hydrophobic compounds for whom oceans constitute the final reservoir [START_REF] Armitage | Modeling the Global Fate and Transport of Perfluorooctanoic Acid (PFOA) and Perfluorooctanoate (PFO) Emitted from Direct Sources Using a Multispecies Mass Balance Model[END_REF][START_REF] Yamashita | Perfluorinated acids as novel chemical tracers of global circulation of ocean waters[END_REF]. Their transport to deep seas mainly via advection and settling particles has indeed been recently emphasised [START_REF] Sanchez-Vidal | Delivery of unprecedented amounts of perfluoroalkyl substances towards the deep-sea[END_REF][START_REF] Sanganyado | Organic pollutants in deep sea: Occurrence, fate, and ecological implications[END_REF][START_REF] Zhang | Poly-and Perfluoroalkyl Substances in Seawater and Plankton from the Northwestern Atlantic Margin[END_REF].

Despite their importance for ocean health and services and their exposure to various anthropogenic threats, deep-sea ecosystems and deep pelagic ones, in particular, are still poorly studied, including the "twilight zone" towards which concerns have been recently raised regarding climate change and human exploitation [START_REF] Martin | Study the twilight zone before it is too late[END_REF]. Specifically, information on organic contaminant occurrence and understanding of their bioaccumulation and biomagnification in deep pelagic food webs are necessary to better assess organic contaminants' ecological impacts [START_REF] Sanganyado | Organic pollutants in deep sea: Occurrence, fate, and ecological implications[END_REF] and assess health risks potentially associated with human exploitation of these deep resources [START_REF] Grimaldo | Investigating the potential for a commercial fishery in the Northeast Atlantic utilizing mesopelagic species[END_REF][START_REF] Wiech | Undesirables in Mesopelagic Species and Implications for Food and Feed Safety-Insights from Norwegian Fjords[END_REF]. In this context, this study aimed to investigate the accumulation of organohalogen contaminants (OCs) in meso-and bathypelagic species from the Bay of Biscay, northeast Atlantic, focusing on crustaceans and fish. The studied contaminants include a large diversity of organic contaminant families such as the legacy POPs listed in the Stockholm Convention (i.e. PCBs, OCPs, PBDEs and PFASs such as perfluorooctane sulfonate -PFOS and perfluorohexanoic acid -PFHxA) and other regulated contaminants (i.e. long-chain PFCAs). The contamination was notably studied using the stable carbon and nitrogen isotope compositions (δ 13 C and δ 15 N values) concomitantly analysed on organisms, as respective trophic tracers of organic matter sources sustaining them and of their trophic position within the deep pelagic community studied. The results are expected to serve as a benchmark in future studies and are of prime interest to characterise and evaluate the chemical exposure of various organisms having a central role in marine ecosystems. This study provides another light on the contamination of the species living in the twilight zone in addition to the previously published results on major and trace elements analysed in the same samples [START_REF] Chouvelon | High interspecies variability in elemental composition of the twilight zone fauna varies implications for predators and exploitation by humans[END_REF].

Materials and methods

Sampling

Samples were collected on the French slope of the Bay of Biscay (NE Atlantic) during the annual EVHOE fishery survey, on board the Ifremer R/V Thalassa in October 2017

(https://doi.org/10.17600/17002300). Fish (11 species) and crustacean (3 species) samples were collected at night using a 25 m vertical opening pelagic trawl in the deep scattering layer (ca 800 m depth in the water column; 1330 m bottom floor). All samples were collected during the same haul of 60 min at a speed of approximately 4 knots. The selected fish individuals belonged to the most abundant species, including one species of Sternoptychidae and three species of Myctophidae, two of the most abundant mesopelagic fish families globally [START_REF] Catul | A review on mesopelagic fishes belonging to family Myctophidae[END_REF][START_REF] Valinassab | Lantern fish (Benthosema pterotum) resources as a target for commercial exploitation in the Oman Sea[END_REF].

Handling of samples was conducted on-board using rigorous protocols to avoid external contamination. Samples were stored at -20 °C until further processing in the laboratory. To obtain sufficient material for the quantification of OCs, the whole bodies of individuals belonging to the same species were pooled by specimens of similar sizes (Table 1). Considering the sizes reported in the literature, most fish except Aphanopus carbo were adult fish. A small piece of white muscle (< 3% of individual total weight) was also collected for the analysis of stable isotopes of carbon and nitrogen as trophic tracers. Whenever possible, fish individuals' sexes were determined and noted in the composition of each pool; all pools were made of both male and female individuals except for Serrivomer beanii (males only) and Stomias boa (females only). All fish stomachs were emptied from their major visible content; however, most stomachs were found to be empty, suggesting either a delay between the sampling and the last feeding or a fast stomach emptying. When large enough, fish were analysed individually; this was the case for 3 samples of Serrivomer beanii, 2 samples of Stomias boa and 3 samples of Aphanopus carbo (Table 1). After pooling, the samples were homogenised using a blender with stainless steel arms, freeze-dried and finely ground up with a ball mill MM400 (Retsch) using bowls and marbles with a zirconium oxide coating. Immediately after freeze-drying, the moisture percentage was determined in each sample; they varied between 69% and 78% in crustaceans and between 64% and 88% in fish (Table 1).

Chemical analyses

Extractable organic matter, used as a proxy for total lipid content (TLC), was determined gravimetrically using 500 mg of sample extracted with a mixture of hexane and acetone (80:20 v:v) using pressurised liquid extraction (PLE). The extracts were evaporated to dryness and TLC was expressed in % of dry weight (dw).

PCBs, OCPs and BFRs were determined as described by Munschy et al. (2020a). Briefly, 5-10 g of samples were extracted by PLE with dichloromethane, followed by gel permeation chromatography, a silica and alumina adsorption chromatography column and a two-dimensional HPLC system with two columns coupled in series. Analyses were performed by gas chromatography (Agilent 6890, Palo Alto, CA, USA) coupled to high-resolution mass spectrometry (AutoSpec Ultima, Waters Corp.). BDE-209, DBDPE and BTBPE were analysed using an Agilent 7890B gas chromatograph coupled to a triple quadrupole mass spectrometer Waters Xevo TQS-µ (Millford, US) using atmospheric pressure chemical ionisation operated in the positive mode. The samples were analysed for 35 PCBs ranging from tri-to decachlorinated congeners, including the 12 dioxin-like (dl-) PCBs , the 6 indicator (i-) PCBs various OCPs (p,o,o,p,p,dieldrin,aldrin,HCHs and hexachlorobenzene -HCB, referred to as ∑ OCPs later in the text) and BFRs including 36 PBDE congeners from tri-to decabrominated ones (Table S5) and non-PBDE BFRs (HBB -hexabromobenzene, BB-153 -2,2′,4,4′,5,5′-hexabromobiphenyl, BTBPE, DBDPE).

PFASs were determined according to Munschy et al. (2020a). Briefly, 1 g of sample was extracted using

Statistical analyses

All statistical analyses were performed using StatSoft Statistica software v 13.3 with a significance level (α) of < 0.05. Concentrations below the limits of quantification (LOQs) were assigned as missing values (i.e. counted as zero in the sums), and only compounds quantified in more than 50% of the samples were considered for statistical analyses. Data were tested for normality using the Shapiro-Wilk's test and parametric or non-parametric tests were performed depending on a normal distribution.

Correlations (e.g. between total lipid content and POP concentrations and between contaminant concentrations) were tested using simple linear regression coefficients and Spearman's rank correlation test was used to evaluate the strength and direction of relationships. Data comparisons (biological parameters, POP concentrations and ratios) across groups were performed using non-

Electronic copy available at: https://ssrn.com/abstract=4123446

parametric tests (Mann-Whitney: MW-and one-way ANOVA Kruskal-Wallis's: KW -test to compare independent groups) for non-normally distributed data. Results were considered significant only when both tests gave significant results. Principal component analysis (PCA) was performed on normalised concentrations to avoid the concentration effect.

Results and discussion

Trophic markers

The detailed results obtained for trophic markers on this deep pelagic community were presented in [START_REF] Chouvelon | High interspecies variability in elemental composition of the twilight zone fauna varies implications for predators and exploitation by humans[END_REF]. The values specifically obtained for the samples here analysed for organic contaminants (a selection of those analysed for chemical elements by [START_REF] Chouvelon | High interspecies variability in elemental composition of the twilight zone fauna varies implications for predators and exploitation by humans[END_REF] are summarised in Table 1. Briefly, δ 13 C values ranged from -20.30‰ to -18.26‰, with no significant differences between crustaceans and fish. This relatively small variability for δ 13 C values (~2‰ difference) indicates similar carbon sources sustaining the species [START_REF] Chouvelon | High interspecies variability in elemental composition of the twilight zone fauna varies implications for predators and exploitation by humans[END_REF]. The δ 15 N values showed more variability, ranging from 9.24‰ to 12.23‰ (Table 1). This range suggests a difference of at least one trophic level (following the expected mean difference of 3.4‰ per trophic level, [START_REF] Post | Using Stable Isotopes to Estimate Trophic Position: Models, Methods, and Assumptions[END_REF] among species of the studied food web. δ 15 N values were significantly different (MW, p = 0.0017) between crustaceans (9.58 ± 0.28‰ on average, n = 5) and fish (10.76 ± 0.91‰, n = 28).

Total lipid contents (TLCs)

The TLCs exhibited high variations among taxa and species, ranging from 4.3 ± 0.9% dw (n = 3) in Pasiphaea sivado to 51% dw in Ephyrina figueirai (n = 1) for crustaceans and, for fish, from 6.1 ± 0.1% dw (n = 3) in Xenodermichthys copei to 41.9 ± 9.6% dw (n = 3) in Notoscopelus kroeyeri (Table 2). A high diversity in TLCs was found between the crustacean species (rsd 130%), while the fish species could be observation) with a less mature stage for the smaller individuals. Concomitantly to the maturity stage, ontogenic differences may also explain the difference observed in the lipid contents of Stomias boa samples, as energy reserves were shown to be positively correlated with size at the fish species level [START_REF] Anthony | Lipid content and energy density of forage fishes from the northern Gulf of Alaska[END_REF][START_REF] Cargnelli | Notes: Fish Energetics: Larger Individuals Emerge from Winter in Better Condition[END_REF]. However, at the scale of the fish community analysed here, TLCs showed a significant linear inverse relationship with fish lengths (p = 0.014), indicating a higher energy content for the smaller species. Classically, TLCs showed an inverse significant linear relationship (p < 0.001) with humidity percentages [START_REF] Spitz | Proximate composition and energy content of forage species from the Bay of Biscay: high-or low-quality food?[END_REF].

TLC values were similar to those reported previously in the literature, even though different extraction methods were used (chloroform:methanol:water (1:2:1) in Sen [START_REF] Şen Özdemir | Neutral and polar lipid fatty acids in five families of demersal and pelagic fish from the deep Northwest Atlantic[END_REF]ether-ethyl in Spitz et al., 2010 versus hexane andacetone (80:20 v:v) for our samples).

Bioaccumulation of organohalogen contaminants in the deep pelagic ecosystem

Organic contaminant concentrations and relative contributions show high inter-species variabilities

The concentrations of the various OC families analysed are presented in Table 2 in both dw (all contaminants) and lw (for PCBs, OCPs and PBDEs) and details for each compound are given in Tables S3 to S6.

In both crustaceans and fish species, PCBs showed high detection frequencies. Most PCB congeners showed detection frequencies of 100%, except for CB-77 and CB-189 (97%), CB-126 and CB-169 (91% and 58% of the samples, respectively) (Table S3), whilst CB-81 was seldom detected above the LOQ (6% of the samples). CBs -29, -30, -112 and -114 were never detected. Among OCPs, dieldrin, endrin, and mirex were detected in all samples, similarly to the DDT isomer p,p'-DDE, whilst the other DDT isomers showed detection frequencies in the 88-94% range (Table S4). Among HCHs, β-HCH was detected in 100% of the samples, above γ-HCH (73%), α-HCH (58%) and δ-HCH (6%). HCB and PeCB were detected in 97% and 52% of the samples, respectively. The other OCPs, namely, aldrin, isodrin, α-endosulfan, β-endosulfan and endosulfan sulphate, were never detected. were the most frequently detected (> 70% of the samples),

while S4). PFHpS and PFHxA were below LOQs in all samples, PFHxS was detected in one sample only and close to the LOQ.

Globally, concentrations (calculated on the mean values of replicates per species) ranged from 11.28 to 100.07 ng g -1 dw, 1.20 to 62.49 ng g -1 dw, 0.12 to 3.49 ng g -1 dw and 3.07 to 55.69 ng g -1 dw for ∑ PCBs, ∑ OCPs, ∑ PBDEs and ∑ PFASs, respectively (Table 2). In crustaceans, the intra-species variability of concentrations was low between the 3 Pasiphaea sivado replicate pools (6-11% rsd for PFASs, PCBs and OCPs and 45% for PBDEs), but huge variations were found at the inter-species level, with rsd values of 55, 67, 107 and 97% for PFASs, PCBs, OPCs and PBDEs, respectively. The different OC families' contributions showed also some variations between crustacean species. PFASs showed the highest contamination levels of all OC families in Pasiphaea sivado (mean of 23.83 ± 2.70 ng g -1 dw, representing 65% of the OCs) followed by PCBs (11.28 ± 0.69 ng g -1 dw, 31%), OCPs (1.20 ± 0.69 ng g -1 dw, 3%) and PBDEs (0.12 ± 0.05 ng g -1 dw, 0.3%). This species showed the lowest contamination levels of PCBs, OCPs and PBDEs, i.e. 6 times, 10-30 times and 5 times lower, respectively, than the concentrations determined in Sergia robusta and Ephyrina figueirai. These OC relative contributions In fish, PCBs presented the highest concentrations (range of 18.62 ng g -1 dw to 115.37 ng g -1 dw, mean of 54.42 ± 28.57 ng g -1 dw calculated on the replicates), followed by OCPs (5.69-98.57 ng g -1 dw, mean of 21.73 ± 21.26 ng g -1 dw, of which 83% were DDTs), PFASs (1.54-37.25 ng g -1 dw, mean of 11.95 ± 9.58 ng g -1 dw) and PBDEs (0.43-5.31 ng g -1 dw, mean of 1.57 ± 1.17 ng g -1 dw). These results agree with previous studies showing PCBs and DDTs as the major chlorinated contaminants in deep-sea fish worldwide, reflecting their high persistence and hydrophobicity, while PBDE levels are usually reported to be several orders of magnitude lower [START_REF] Koenig | Legacy and emergent persistent organic pollutants (POPs) in NW Mediterranean deep-sea organisms[END_REF][START_REF] Webster | Halogenated persistent organic pollutants in relation to trophic level in deep sea fish[END_REF].

The intra-species variability of concentrations was globally low for all contaminant families (21% rsd and -77) showed a significant linear relationship between their concentrations and TLCs. These results are somewhat surprising for lipophilic contaminants. However, TLCs determined in the present samples were a proxy of total lipids and it has been proven that lipophilic contaminant accumulation is not governed only by lipid content but also by lipid composition [START_REF] Xie | Global occurrence, bioaccumulation factors and toxic effects of polychlorinated biphenyls in tuna: A review[END_REF]. Our results suggest complex relationships between the species' lipidic composition and the various studied chlorinated and brominated OC families and would argue in favour of more investigations into the specific tissue biochemical composition of species. Despite this lack of significant correlations, concentrations of lipophilic OCs were normalised to TLCs to compare the concentrations between replicate samples within a species (intra-species variability) and between species (inter-species variability). Normalising the concentrations to TLCs did not decrease the intra-species variability (30, 29 and 39% for PCBs, OCPs and PBDEs respectively) nor the inter-species variability (73-75%). However, these results were highly dependent on the species; the intra-species variability decreased highly for Argyropelecus olfersii (ratio between the concentrations in the two samples of 1.0, 1.4 and 1.0 in lw versus 1.4, 1.9 and 1.5 in dw for PCBs, OCPs and PBDEs, respectively), while the concentrations in Notoscopelus kroeyeri were highly variable whether they were expressed in dw (60-75%) or lw (64-80%). When both taxa were compared, only PFAS and PBDE concentrations (in ng g -1 dw) showed significant differences (KW and MW) between crustaceans and fish (PFASs higher in crustaceans p = 0.0034, PBDEs higher in fish p = 0.0021). Although PCBs and OCPs showed higher levels in fish than in crustaceans, the lack of significant differences between both taxa could be explained by both the high inter-species variability within each taxon and the smaller difference in concentrations between taxa.

PFASs exhibited the highest contribution among the OC families in the crustacean species Pasiphaea sivado (65 ± 2% on average), while PCB contribution was the highest in all fish species (between 47% and 72%, with a mean of 62 ± 10%). PFAS contribution decreased significantly with both δ 15 N values (p = 0.0001) and TLC (p = 0.004), reflecting a relationship with the trophic magnification factors (TMFs) of the studied contaminants, which are reported to be globally lower for PFASs than for PCBs [START_REF] Won | Importance of accurate trophic level determination by nitrogen isotope of amino acids for trophic magnification studies: A review[END_REF] and suggesting a potential link with the biochemical compositions of the studied species. Unlike the lipophilic contaminants studied here (i.e. PCBs, OCPs and PBDEs), PFASs have an affinity for specific proteins and phospholipids [START_REF] Armitage | Development and evaluation of a mechanistic bioconcentration model for ionogenic organic chemicals in fish[END_REF][START_REF] Ng | Bioconcentration of Perfluorinated Alkyl Acids: How Important Is Specific Binding?[END_REF]. PFASs presented the highest relative concentrations in the crustacean species that showed the lower TLC (lipophilic contaminants being consequently less predominant), namely Pasiphaea sivado, while the lowest PFAS relative contribution (17%) was found in the crustacean species Ephyrina figueirai, which showed the highest TLC (and the highest lipophilic contaminant contribution). However, the two fish species

Serrivomer beanii and Xenodermichthys copei, despite them having been reported to have lower protein contents than the other studied fish species sampled from the Bay of Biscay [START_REF] Spitz | Proximate composition and energy content of forage species from the Bay of Biscay: high-or low-quality food?[END_REF], showed higher PFAS contribution than the other fish (30 ± 8% versus 10 ± 6% in the other species), a result that could rather be explained by their lower trophic level (see section 3.3.6).

OC concentrations are in the range of those reported in other deep pelagic species in the NE Atlantic

Although PCB, OCP and PBDE concentrations in deep-sea organisms from various oceanic regions have been published previously, most of the data refer to bathydemersal and benthopelagic species, i.e.

living and feeding close to the bottom seafloor. In addition, the studied periods refer to sampling dates of more than 10 years ago which could bias the comparison for the legacy POPs. Data on contaminants of emerging concern such as the ones we report here are still very scarce, making comparisons impossible. With these precautions in mind, the following are some comparisons with previously published data focusing specifically on deep pelagic species.

∑ 6 PCB and ∑ 15 PBDE concentrations were determined in the muscles of 4 deep pelagic fish species similar to ours (namely Benthosema glaciale, Xenodermichthys copei, Argyropelecus hemigymnus, Gonostoma bathyphilum) and collected at 1200-1500 m depths in a submarine canyon in the south Bay of Biscay in 2012-2013 ranged between 134 and 756 ng g -1 lw and between <LOD and 23 ng g -1 lw, respectively [START_REF] Romero-Romero | Biomagnification of persistent organic pollutants in a deep-sea, temperate food web[END_REF]. These levels compare with our concentration ranges (i.e., 31.2-1072.9 ng g -1 lw and 0.92-43.37 ng g -1 lw for PCBs and PBDEs respectively). ∑ 7 ICES PCB (i.e. the International Council for the Exploration of the Sea PCBs, the major and mostly-used congeners) was found in mean concentrations of between 91.6 ± 116 and 613 ± 739 ng g -1 lw in the muscle of adult

Aphanopus carbo (black scabbardfish) collected from the west of Scotland in 2006-2012 and of between 267 ± 150 and 521 ± 301 ng g -1 lw in their livers [START_REF] Webster | Halogenated persistent organic pollutants in relation to trophic level in deep sea fish[END_REF], which compares closely to our results in whole fish (524-651 ng g -1 lw), although younger individuals were considered in our study. In the same individuals, the ∑ 9 PBDEs were between 1.1 ± 3.0 and 42.5 ± 26.4 ng g -1 lw in the flesh and between 2.4 ± 3.9 and 25.8 ± 8.2 ng g -1 lw in the liver [START_REF] Webster | Halogenated persistent organic pollutants in relation to trophic level in deep sea fish[END_REF], while our result showed concentrations of a similar order of magnitude with 13.0-17.1 ng g -1 lw range in whole fish.

Various organic contaminant concentrations (namely, PCBs, HCB, dieldrin and DDTs) were reported in the livers of black scabbardfish collected from the NE Atlantic (from Madeira off the coasts of Marocco to Ireland) in 1999 [START_REF] Mormede | Horizontal and vertical distribution of organic contaminants in deepsea fish species[END_REF]. Surprisingly, these contaminant concentrations did not differ drastically from our data, considering the difference in time of sampling, studied areas and targeted tissues (∑ 7 ICES PCBs: 91 ng g -1 lw to 7660 ng g -1 lw versus 524-651 ng g -1 lw in our fish samples; HCB: 5.3 to 30.3 ng g -1 lw versus 11.4-18.8 ng g -1 lw; dieldrin: 22.0-40.9 ng g -1 lw versus 20.5-25.0 ng g -1 lw) except for the ∑ DDTs, which was lower in our samples (239.5-397.8 ng g -1 lw versus 384-4350 ng g -1 lw in Mormede and Davies' study), potentially reflecting a higher decrease of DDT inputs over the studied periods.

Specific congener analysis reveals untypical BFR profiles

Indicator PCBs (i-PCBs) were predominant compared to dioxin-like congeners (dl-PCBs) in all species, and i-PCB and dl-PCB concentrations were highly correlated (r = 0.93, p < 0.05). The average ratio (i-PCBs/dl-PCBs) was 7 ± 1 and showed no significant difference between taxa. Detailed PCB mean concentrations per congener and taxon are given in Table S3. The most abundant congener was CB-153 with concentrations ranging from 1.73 to 15.03 ng g -1 dw (mean of 6.663 ± 6.776 ng g -1 dw) in crustaceans and from 2.40 to 23.27 ng g -1 dw (mean of 10.71 ± 6.10 ng g -1 dw) in fish. Hexa-and heptachlorinated congeners (i.e. CB-153, CB-138, CB-180 and CB-187, each one contributing to 10-19% of the ∑ PCBs) were the most abundant ones, which is consistent with previous findings in deep-sea ecosystems [START_REF] Koenig | Legacy and emergent persistent organic pollutants (POPs) in NW Mediterranean deep-sea organisms[END_REF][START_REF] Romero-Romero | Biomagnification of persistent organic pollutants in a deep-sea, temperate food web[END_REF][START_REF] Storelli | Polychlorinated biphenyl and organochlorine pesticide contamination signatures in deep-sea fish from the Mediterranean Sea[END_REF][START_REF] Takahashi | Organohalogen compounds in deep-sea fishes from the western North Pacific, off-Tohoku, Japan: Contamination status and bioaccumulation profiles[END_REF][START_REF] Webster | Halogenated persistent organic pollutants in relation to trophic level in deep sea fish[END_REF]. The i-PCBs contributed to 47% of the ∑ PCBs while dl-PCBs counted for 7% of the ∑ PCBs, pointing out the importance of determining more than the classic 18 congeners to better assess total PCB bioaccumulation in marine organisms. Congeners with 5 and more chlorine atoms showed the highest cross-correlations, which underline their similar sources and behaviours.

DDTs were by far the most abundant OCPs in all species (0.53-86.23 ng g -1 dw range, mean of 16.35 ± 18.90 ng g -1 dw), followed by dieldrin (0.25-6.83 ng g -1 dw range, mean of 1.96 ± 1.34 ng g -1 dw) > HCB (0.32-3.93 ng g -1 dw range, mean of 1.07 ± 0.91 ng g -1 dw) > endrin (0.028-0.73 ng g -1 dw range, mean of 0.25 ± 0.19 ng g -1 dw) = ∑ HCHs (0.01-0.61 ng g -1 dw range, mean of 0.20 ± 0.18 ng g -1 dw) (Table S4). These results bring evidence that DDT is still a major organochlorine pesticide in marine ecosystems, which is in line with its global past usage and environmental persistence [START_REF] Li | Sources and pathways of selected organochlorine pesticides to the Arctic and the effect of pathway divergence on HCH trends in biota: a review[END_REF]. ∑ DDTs showed significant positive correlations with all other organochlorine pesticides except ∑ HCHs, possibly related to HCH physico-chemical properties and environmental behaviour (Salvado et al., 2019). The highest correlations were between ∑ DDTs and mirex (0.91) while dieldrin and endrine showed weaker ones (0.70 and 0.42, respectively).

Among DDTs, the p,p'-DDE isomer was the most prevalent in all samples (80 ± 11% of ∑ DDTs), in accordance with the common profiles observed in marine biota including deep-sea organisms [START_REF] Koenig | Legacy and emergent persistent organic pollutants (POPs) in NW Mediterranean deep-sea organisms[END_REF][START_REF] Ramu | Occurrence of organochlorine pesticides, polychlorinated biphenyls and polybrominated diphenyl ethers in deep-sea fishes from the Sulu Sea[END_REF][START_REF] Storelli | Polychlorinated biphenyl and organochlorine pesticide contamination signatures in deep-sea fish from the Mediterranean Sea[END_REF]. The o,p'-DDT/p,p'-DDT concentration ratio was 0.36 ± 0.17, on average, in all fish species and showed high inter-species variations (0.03-0.55 range).

This ratio is commonly used to distinguish DDT sources, with values in the 0.2-0.3 range in technical DDT [START_REF] Kalantzi | The global distribution of PCBs and organochlorine pesticides in butter[END_REF]) whereas a ratio above 0.34 is usually attributed to DDT's origin from dicofol acaricide impurities (Suarez et al., 2013). This ratio was particularly low in Stomias boa (0.03 ± 0.01) because of peculiar low contributions of o,p'-DDT (0.4 ± 0.2% versus 3.3 ± 1.9% in the other fish species). These results show that the use of this ratio should be interpreted with caution and suggest that species-specific parameters may also influence DDT isomeric profiles.

BFR profiles were dominated by BDE-209 (mean contribution of 38% of the 12 summed congeners quantified in more than 50% of the samples) followed by BDE-47 (21%), BDE-155 (19%) and BDE-154 (14%). The other mostly-detected congeners (i.e. 119, contributed each to less than 10%, on average, to the summed 12 BDEs. As BDE-47 is generally reported as the major PBDE congener in biota, the present PBDE profile is therefore atypical due to the high contribution of BDE-209. The BDE-209 congener is usually reported as poorly bioaccumulable in fish because of its very high log K ow (12.1, [START_REF] Kelly | Hydroxylated and methoxylated polybrominated diphenyl ethers in a Canadian Arctic marine food web[END_REF], high molecular size and degradation propensity via metabolism (Stapleton et al. 2004a[START_REF] Roberts | Species-Specific Differences and Structure-Activity Relationships in the Debromination of PBDE Congeners in Three Fish Species[END_REF]. Following our results, this highly brominated congener has been previously identified at higher abundance (17% of ∑ PBDEs) in deep-sea organisms compared to those from the shelf [START_REF] Romero-Romero | Biomagnification of persistent organic pollutants in a deep-sea, temperate food web[END_REF]. Although all fish stomachs and intestines were emptied of major debris (after visual inspection) before analysis, it cannot be ruled out that high BDE-209 concentrations were also due to non-ingested particles still present in the digestive tracts. However, the presence of a high diversity of several high-brominated congeners, as well as species-specific profiles, rather suggests BDE-209 bioaccumulation and biotransformation, as detailed in section 3.3.4 below.

Another peculiar result was the high contribution of DBDPE, quantified in 76% of the samples at concentrations as high as 16.48 ng g -1 dw in Searsia koefoedi. Similar to BDE-209, DBDPE is characterised by a very high log K ow (11.1, Covaci et al. 2011) that should limit its bioaccumulation at high levels in fish and generally leads to its biodilution in trophic webs [START_REF] Tao | Biomagnification of PBDEs and alternative brominated flame retardants in a predatory fish: Using fatty acid signature as a primer[END_REF]. However, unlike for BDE-209, no debromination of DBDPE has been reported in fish and its bioaccumulation factor was reported to be 10 times higher than BDE-209's one [START_REF] He | Bioaccumulation of polybrominated diphenyl ethers and decabromodiphenyl ethane in fish from a river system in a Electronic copy available at: https://ssrn.com/abstract=4123446 highly industrialized area, South China[END_REF], which would argue in favour of its occurrence at higher levels than BDE-209. Similar to BDE-209, the DBDPE occurrence at particularly high levels in some of the studied samples (i.e. Serrivomer beanii, Stomias boa, Aphanopus carbo and Searsia koefoedi) could be the result of undigested particles in their digestive tracts. DBDPE sources in the marine environment include plastics from electronic and electrical equipment wastes [START_REF] Stubbings | Assessment of brominated flame retardants in a small mixed waste electronic and electrical equipment (WEEE) plastic recycling stream in the UK[END_REF]. However, whether DBDPE found in some fish originated from its adsorption on particulate matter or plastics, or plastics themselves (eventually extracted following whole fish analyses) cannot be proven. In oceanic waters off the Californian coast (Monterey Bay, US), the highest concentrations of microplastics have been reported between 200 m and 600 m [START_REF] Choy | The vertical distribution and biological transport of marine microplastics across the epipelagic and mesopelagic water column[END_REF], and microplastics have been reported in the digestive tracts of mesopelagic fish feeding at these depths, although at very different occurrence frequencies depending on locations (35% in [START_REF] Boerger | Plastic ingestion by planktivorous fishes in the North Pacific Central Gyre[END_REF] 9% in [START_REF] Davison | Plastic ingestion by mesopelagic fishes in the North Pacific Subtropical Gyre[END_REF]11% in Lusher et al., 2016; 24% specifically in Myctophidae in Savoca et al., 2020;73% in Wieczorek et al., 2018). Among the various species studied by [START_REF] Wieczorek | Frequency of microplastics in mesopelagic fishes from the Northwest Atlantic[END_REF],

Serrivomer beanii and Lampanyctus macdonaldi were among those presenting the highest frequency of plastic occurrence, while Serrivomer beanii and Myctophum punctatum were two species presenting the highest number of plastic debris in their gut. Despite the digestive tracts of fish from our study being emptied from visible material before analysis, the presence of small parts of food residues (including those of plastic origin) that could have still be present in the digestive tracts (i.e. not assimilated/absorbed into the organism's tissues) is not unrealistic. The fact that high variations were sometimes found between replicates of the same species (as in Aphanopus carbo, with concentrations of 81, 4762 and 7803 pg g -1 dw in each of the three replicates made from individual fish, or in Xenodermichthys copei with < LOQ, 148 and 1940 pg g -1 dw in pooled samples) argues in favour of undigested particles with a short-time and erratic occurrence rather than a long-term accumulation in tissues. On the opposite hand, species such as Stomias boa showed high DBDPE concentrations in all

Electronic copy available at: https://ssrn.com/abstract=4123446

replicates (3075, 5963 and 7840 pg g -1 dw, rsd = 43%), while others such as Myctophum punctatum or

Lampanyctus crocodilus exhibited systematically lower concentrations (< LOQ, 42 and 193 pg g -1 dw and 436, 682 and 938 pg g -1 dw, respectively).

Interestingly, in our study, the highest DBDPE concentrations (in both dw and lw) were determined in the longest fishes studied, i.e. Serrivomer beani (64.3 ± 9.2 cm), Stomias boa (31.6 ± 3.7 cm) and

Aphanopus carbo (61.7 ± 0.6 cm). These species are all characterised by elongate shapes and therefore have potentially longer digestive tracts, which would lead to a higher retention potential in the gut. A higher occurrence of microplastics in larger fish compared to smaller ones has previously been observed in various freshwater species from a lake in Ontario, Canada (McIllwraith et al., 2021).

Despite its relatively smaller length (15 cm), Searsia koefoedi exhibited the highest concentration of all species (16.48 ng g -1 dw) but these results would need to be confirmed as only one pool of 3 individuals was analysed. However, this result is consistent with this species' non-migratory behaviour (at least towards epipelagic waters at night for feeding, but possible migrations deeper into the bathypelagic zone; Novotny, 2018), as DBDPE has been shown to be high in deeper waters [START_REF] Zhen | Decabromodiphenyl Ether versus Decabromodiphenyl Ethane: Source, Fate, and Influencing Factors in a Coastal Sea Nearing Source Region[END_REF]. The ratio between DBDPE and BDE-209 concentrations has been suggested as a useful tracer of sources and processes, with a higher DBDPE/BDE-209 ratio being observed in deep waters compared to the surface ones because of the higher affinity to fine particles and stability of DBDPE compared to BDE-209 [START_REF] Zhen | Decabromodiphenyl Ether versus Decabromodiphenyl Ethane: Source, Fate, and Influencing Factors in a Coastal Sea Nearing Source Region[END_REF]. However, using this ratio in biota has limitations and no correlation was found between BDE-209 and DBDPE in our set of samples. Among the species reputed to undergo no DVM (i.e., Arctozenus risso and Searsia koefoedi), only the latter one showed a high DBDPE/BDE-209 ratio (16 versus 1.2 in Arctozenus risso). Indeed, this ratio was highly variable between species (median value of 3.0 in all fish samples), ranging from 0.11 in Myctophum punctatum (the only species in which BDE-209 was higher than DBDPE) to 19 in Aphanopus carbo. Globally, our results highlight that mesopelagic fish could, in addition to transferring very hydrophobic contaminants to higher trophic level organisms, contribute to their transfer from surface waters to deeper waters and eventually to the bottom sea.

Chlorinated and brominated OC profiles and diagnostic ratios reveal species-specific metabolic capacities

Because PCB bioaccumulation depends on their chlorine number and position, which both are sourceand metabolism-related, PCB profiles can be examined by their number of Cl atoms and their structureactivity group (SAG) classification [START_REF] Boon | Concentration-Dependent Changes of PCB Patterns in Fish-Eating Mammals: Structural Evidence for Induction of Cytochrome P450[END_REF][START_REF] Yunker | Development and Validation of Protocols To Differentiate PCB Patterns between Farmed and Wild Salmon[END_REF]. While the lower-chlorinated congeners are associated with atmospheric transport and feeding at lower trophic levels, the heavier congeners reflect continental inputs from rivers and prey of higher trophic levels. In our samples, 3-Cl and 4-Cl showed higher contributions to the ∑ PCBs in crustaceans compared to fish, which is consistent with crustaceans' lower trophic levels (i.e. lower δ 15 N values), although the difference was significant only for the 3-Cl congeners (10 ± 5% in crustaceans versus 4 ± 5% in fish, MW and KW tests).

However, inter-species differences were high when only fish were considered, and similar contributions to those of crustaceans were found in some fish species such as Arctozenus risso, Argyropelecus olfersii and Myctophum punctatum (Fig. 1A). These species are among those showing the lowest δ 15 N values among the studied fish species, but other species with low δ 15 N values (such as

Serrivomer beanii or Xenodermichthys copei) did not show such a high 3-Cl contribution (Fig. 1A),

suggesting that the trophic level does not solely explain these results. Indeed, the lower chlorinated congeners are also the most metabolisable ones (SAG III and IV), while the most refractory ones (6-,7and 8-Cl) belong to SAG I and II groups. No significant differences were observed between taxa regarding SAG groups. The three crustacean species showed discrepancies in their PCB profiles, with Sergia robusta being characterised by higher SAG I and II group contributions (72% in total) than the other two species (52 ± 5%). Among fish species, Arctozenus risso, Argyropelecus olfersii and Myctophum punctatum showed the highest SAG III and IV (metabolisable congeners) and the lowest SAG I and II (refractory congeners) contributions. On the opposite hand, Serrivomer beanii, Xenodermichthys copei, Aphanopus carbo, Lampanyctus crocodilus and Searsia koefoedi were characterised by higher SAG I and II (6 to 8 Cl) contributions (Fig. 2). More specifically, the CB-149/CB-between hexachlorinated congeners from SAG IV and V and a typical refractory one from SAG I), showed higher values in Arctozenus risso, Argyropelecus olfersii, Myctophum punctatum and Notoscopelus kroeyeri, indicating a lower metabolic activity towards CB-149 and CB-132 in these species (Fig. 2).

The (p,p'-DDE + p,p'-DDD)/Σ DDTs ratio was 0.85 ± 0.06 in all samples, which globally indicates old DDT inputs (Suarez et al., 2013) and is consistent with the ban of DDT usage since the 1970s or 1980s in most countries worldwide [START_REF] Kalantzi | The global distribution of PCBs and organochlorine pesticides in butter[END_REF]. The p,p'-DDE isomer contribution was significantly (MW and KS p < 0.1) higher in crustaceans and particularly high in Pasiphaea sivado replicates, which was mainly due to p,p'-DDD and p,p'-DDT < LOQs in these samples. Some variations in p,p'-DDE contributions were also observed between fish species (Fig. 1B). Among Myctophidae, both

Myctophum punctatum and Notoscopelus kroeyeri exhibited similar DDT profiles (p,p'-DDE and p,p'-DDD at 65 ± 5% and 12 ± 1%, respectively) and were different from those of the third Myctophid species Lampanyctus crocodilus, in which higher p,p'-DDE (84 ± 2%) and lower p,p'-DDD (5 ± 1%) contributions were found. These results could suggest a species-specific DDT profile due to different metabolic capacities, which would be in line with the higher metabolic capacity of PCBs observed in Lampanyctus crocodilus. In addition, Lampanyctus crocodilus was the leanest of the three studied Myctophid species (by a factor of 4 to 5, Table 2), which could influence DDT isomer's relative bioaccumulation. Indeed, in the studied fish species, p,p'-DDE contribution showed a significant decrease with increasing TLC (p < 0.0001).

Regarding PBDE profiles (Fig. 1C), the nona-BDEs BDE-207 and BDE-208, the octa-BDEs BDE-202, BDE-205 and BDE-197 and the hepta-BDEs BDE 184 and BDE-183 were quantified in 18-48% of our samples, although at low levels (their total contribution was 6% of the sum of all congeners determined above LOQs). In addition, the hexa-BDEs BDE-155 and BDE-154, ranking third and fourth in our samples, have both been reported as debromination products of octa-BDEs (Stapleton et al., 2004b;[START_REF] Zeng | Gastrointestinal absorption, metabolic debromination, and hydroxylation of three commercial polybrominated diphenyl ether mixtures by common carp[END_REF]. As the nona-to hexa-brominated congeners identified in our samples are not present in technical mixtures (La [START_REF] Guardia | Detailed polybrominated diphenyl ether (PBDE) congener composition of the widely used penta-, octa-, and deca-PBDE technical flame-retardant mixtures[END_REF][START_REF] Munschy | Classic and novel brominated flame retardants (BFRs) in common sole (Solea solea L.) from main nursery zones along the French coasts[END_REF], their occurrence might be explained by either i) assimilation and further metabolisation by fish or ii) metabolisation by the prey and bioaccumulation in fish via trophic transfer. Indeed, these congeners are among those (ranging from nona-to tetra-BDEs) that have been reported in various fish species following BDE-209 metabolic degradation [START_REF] Roberts | Species-Specific Differences and Structure-Activity Relationships in the Debromination of PBDE Congeners in Three Fish Species[END_REF]. BDE-154 could result from the debromination in the meta position of BDE-183, while BDE-155 could result from successive debrominations in the meta positions of BDE-207, BDE-197 and BDE-184, which were all detected in our samples, although at low concentrations compared to their debrominated counterparts. If these congeners originate from BDE-209 metabolism, their detection at concentrations above the LOQs reveals exposure of the studied species to BDE-209. The high variability in PBDE profiles between species could therefore result from speciesspecific metabolism, as evidenced by various studies in fish [START_REF] Roberts | Species-Specific Differences and Structure-Activity Relationships in the Debromination of PBDE Congeners in Three Fish Species[END_REF][START_REF] Stapleton | In Vivo and In Vitro Debromination of Decabromodiphenyl Ether (BDE 209) by Juvenile Rainbow Trout and Common Carp[END_REF][START_REF] Yokota | Species-specific debromination of BDE99 in teleost fish: The relationship between debromination ability and bioaccumulation patterns of PBDEs[END_REF]. The results suggest that BDE-183, BDE-197 and BDE-207 could be potential intermediate debromination products of BDE-209 resulting in the formation of BDE-154, and that the removal of Br atoms in the meta position was favoured. However, no significant relationship was found between BDE-209 and either BDEs -183, -197 or -207 (although the latter two congeners showed low detection frequencies), nor with BDE-154 or BDE-155. Interestingly, BDE-154 and BDE-155 were highly correlated (n = 28, r = 0.96) in fish, which could reflect their common origin (i.e. BDE-209 biotransformation).

Specific ratios such as BDE-99/BDE-100 concentration ratios (BDE-99 being metabolised while BDE-100 is not, a low ratio is indicative of a high metabolic capacity towards BDE-99) or congener relative contributions are commonly used to reveal metabolic capacities in fish [START_REF] Koenig | Legacy and emergent persistent organic pollutants (POPs) in NW Mediterranean deep-sea organisms[END_REF][START_REF] Voorspoels | Polybrominated diphenyl ethers in marine species from the Belgian North Sea and the Western Scheidt Estuary: Levels, profiles, and distribution[END_REF]. In our samples, BDE-99/BDE-100 ratios were highly variable depending on species and were highly consistent between replicate pools within the same species. The lowest ratios were identified in Lampanyctus crocodilus (0.11 ± 0.03), while the highest were found in Argyropelecus olfersii (1.56 ± 0.56). In Xenodermichthys copei, BDE-99 was below the LOQ in the three replicate pools, suggesting high degradation of BDE-99 in this species. This ratio was not trophic level-dependent but rather highly species-dependent (inter-and intra-family). Indeed, within the Myctophydae family, high variations were found, with both Myctophum punctatum and Notoscopelus kroeyeri showing high values (1.36 ± 0.23 and 1.29 ± 0.18, respectively), while Lampanyctus crocodilus showed a mean ratio of 0.11 ± 0.03 (i.e. a higher metabolism). Concurrently, BDE-154's highest contributions were determined in Lampanyctus crocodilus (20 ± 6.2), indicating a higher degradation capacity in this species. Indeed, as BDE-154 could potentially originate from the debromination of higher-brominated congeners, its relative contribution would be indicative of the metabolic capacities of fish, with a high contribution being indicative of a higher degradation capacity into BDE-154.

Perfluorinated substances' molecular profiles are dominated by odd chain length

PFCAs

PFOS was the only PFSA detected in 100% of the samples, at concentrations ranging from 0.38 to 10.61 ng g -1 dw (mean of 3.72 ± 3.9615 ng g -1 dw) in crustaceans and between 0.350 and 10.04 ng g -1 dw (mean of 3.00 ± 2.22 ng g -1 dw) in fish. PFDS was detected in 27% of the samples (crustaceans and fish) at levels ranging from 0.04 to 0.09 ng g -1 dw (mean of 0.06 ± 0.02 ng g -1 dw). Among PFCAs, the longchain PFCAs perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), perfluorotridecanoic acid (PFTrDA) and perfluorotetradecanoic acid (PFTeDA) were detected in 100% of the samples, while perfluorooctanoic acid (PFOA) was detected in 45% of the samples. Perfluoroheptanoic acid (PFHpA) was detected in only four samples (Sergia robusta, Xenodermichthys copei and Searsia koefoedi) at a mean concentration of 0.05 ± 0.03 ng g -1 dw. The mean concentrations of the most-detected PFCA ranged from 0.18 ± 0.17 ng g -1 dw (PFOA) to 4.40 ± 4.51 ng g -1 dw (PFTrDA). PFCA concentrations ranked in the order PFTrDA > PFUnDA > PFNA = PFDA > PFTeDA > PFDoDA > PFOA, showing higher bioaccumulation with increasing carbon chain length, which is consistent with their higher BAF [START_REF] Houde | Biological monitoring of polyfluoroalkyl substances: A review[END_REF]Martin et al., 2003;[START_REF] Ng | Bioaccumulation of Perfluorinated Alkyl Acids: Observations and Models[END_REF]. In fish, all PFCA concentrations except PFOA's were: i) significantly intercorrelated and ii) correlated with PFOS concentrations but iii) not correlated to the other contaminant families. This could reflect different sources and/or bioaccumulation processes. In most samples, PFCAs were predominant compared to PFOS (by far the predominant PFSA) with a mean contribution of 75 ± 12% (mean PFCAs/PFOS ratio = 5.4 considering all species), although some variations were observed within taxon and species (Fig. 1D). PFCA contributions were significantly (p = 0.002) higher in crustaceans (89 ± 6%) than in fish (72 ± 11%). The crustacean species Ephyrina figueirai showed a peculiar high PFCA contribution (Σ PFCAs/PFOS ratio of 59) due to a low PFOS concentration (0.379 ng g -1 dw), while its ∑ PFCA concentration was similar to the ones determined in the other crustacean species Pasiphae sivado. On the opposite hand, Chauliodus sloani (although only one sample was analysed) was the only species with lower ∑ PFCA concentrations than PFOS ones, with a ∑ PFCAs/PFOS ratio of 0.75, due to a particularly high PFOS contribution (57% of ∑ PFASs). The ∑ PFCA contribution was also higher (87 ± 2%) in Serrivomer beanii, the fish species with the lowest δ 15 N values and comparable with the ratio determined in crustaceans.

The occurrence of the longer chain PFCAs (> C 8 ) in biota is commonly explained by their release in the environment as impurities from fluorotelomer and C 9 -based products [START_REF] Wang | Global emission inventories for C4-C14 perfluoroalkyl carboxylic acid (PFCA) homologues from 1951 to 2030, Part I: production and emissions from quantifiable sources[END_REF] and their subsequent higher bioaccumulation compared to the shorter chain ones [START_REF] Houde | Biological monitoring of polyfluoroalkyl substances: A review[END_REF][START_REF] Conder | Are PFCAs bioaccumulative? A critical review and comparison with regulatory lipophilic compounds[END_REF][START_REF] Ng | Bioaccumulation of Perfluorinated Alkyl Acids: Observations and Models[END_REF]. Besides, PFCAs might also originate from the in vivo biotransformation of precursors, which would increase their biomagnification in food webs (Gebbing et al., 2016). Various experimental studies showed that when selected fluorotelomer alcohol (FTOH)

precursors were administrated to fish, PFOA, PFNA, PFDA and PFHpA were formed, although with low yields [START_REF] Brandsma | Dietary exposure of rainbow trout to 8:2 and 10:2 fluorotelomer alcohols and perfluorooctanesulfonamide: Uptake, transformation and elimination[END_REF][START_REF] Butt | Biotransformation pathways of fluorotelomer-based polyfluoroalkyl substances: A review[END_REF]. However, recent results showed that PFCAs could also be formed by yet-unidentified precursor degradation [START_REF] Simmonet-Laprade | Investigation of the spatial variability of poly-and perfluoroalkyl substance trophic magnification in selected riverine ecosystems[END_REF] and suggest that direct exposure to PFCAs is not a predominant source to explain PFCA profiles in fish. The predominance of the odd-numbered PFCAs PFTrDA (C 13 ) and PFUnDA (C 11 ) has been previously reported in marine fish worldwide [START_REF] Fujii | Long-chain perfluoroalkyl carboxylic acids in Pacific cods from coastal areas in northern Japan: A major source of human dietary exposure[END_REF][START_REF] Fujii | Levels and profiles of long-chain perfluoroalkyl carboxylic acids in Pacific cod from 14 sites in the North Pacific Ocean[END_REF]Munschy et al., 2020b;[START_REF] Schultes | Temporal Trends (1981-2013) of Per-and Polyfluoroalkyl Substances and Total Fluorine in Baltic cod (Gadus morhua)[END_REF] and references therein) and explained by direct inputs from industrial releases [START_REF] Gewurtz | Perfluoroalkyl acids in the Canadian environment: Multi-media assessment of current status and trends[END_REF]Simonnet-Laprade et al., 2019) and/or by the degradation of precursors (FTOHs), either in the atmosphere, soil or organisms, followed by preferential accumulation of the longer chain length PFCAs (i.e. C 11 > C 10 and C 13 > C 12 ). However, FTOH degradation leads to 10-times more abundant even chain length PFCAs than odd chain length PFCAs [START_REF] Franklin | How reliable are field-derived biomagnification factors and trophic magnification factors as indicators of bioaccumulation potential? Conclusions from a case study on per-and polyfluoroalkyl substances[END_REF][START_REF] Gebbink | Perfluoroalkyl Acids (PFAAs) and Selected Precursors in the Baltic Sea Environment: Do Precursors Play a Role in Food Web Accumulation of PFAAs?[END_REF]. In our samples, the mean (C 11 + C 13 )/(C 10 + C 12 ) ratio was 4.2 ± 1.4, showing a higher occurrence of odd chain length PFCAs in all species (no significant difference was observed between taxa). [START_REF] Washington | Nontargeted mass-spectral detection of chloroperfluoropolyether carboxylates in New Jersey soils[END_REF] used the (C 11 + C 13 ) -(C 10 + C 12 ) values to reveal PFAS sources in soils, allowing them to distinguish between direct release (higher values) and fluorotelomer degradation. In biota, this parameter could be influenced by in vivo degradation of precursors into PFCAs, which are not expected to further degrade in organisms. This ratio could therefore give an integrated view of direct exposure and subsequent bioaccumulation, combined with the effect of precursor biotransformation. Interestingly, this ratio showed strong differences between i) the crustaceans and the fish species Serrivomer beanii and Searsia koefoedi that show high values (14420 ± 3968) and ii) the other fish species that presented lower values (3243 ± 2360). The higher (C 11 + C 13 ) -(C 10 + C 12 ) values suggest that these PFCAs were less derived from precursors in crustaceans and the fish species Serrivomer beanii and Searsia koefoedi than in the other fish species. This assumption would agree with species-specific precursor biotransformation as already reported for PFOS in freshwater invertebrates and fish [START_REF] Babut | Per-and poly-fluoroalkyl compounds in freshwater fish from the Rhône River: Influence of fish size, diet, prey contamination and biotransformation[END_REF] and would suggest a lower precursor metabolism in these species.

Most of the chlorinated and brominated OCs show biomagnification across the studied food chain, while PFASs exhibit a contrasted behaviour

Despite legacy POP concentrations in deep-sea organisms (mostly demersal or benthic) having been reported in the literature, very few studies have examined their biomagnification in deep-sea food webs (but see [START_REF] Cresson | Variability of PCB burden in 5 fish and sharks species of the French Mediterranean continental slope[END_REF] and especially in the deep pelagic. In the present study, significant linear relationships were found between PCB log-transformed concentrations in lw and δ 15 N values (Table S6). However, CBs -18, -28 and -31 showed significant negative linear relationships with δ 15 N values, indicating their biodilution in the food web, while the higher chlorinated congeners (5 chlorine atoms and above) showed significant positive linear relationships (Fig. 3A, Table S7). Among DDT isomers, p,p'-DDE, p,p'-DDD and p,p'-DDT, but neither o,p'-DDT or o,p'-DDD, concentrations showed significant positive linear relationships with δ 15 N values, as well as dieldrin, endrin, HCB and mirex (Fig.

Electronic copy available at: https://ssrn.com/abstract=4123446

3A, Table S8). On the opposite hand, neither ∑ HCHs nor individual isomers showed any significant relationship. ∑ PBDEs and individual congeners, except BDEs -28, -66, -77, and -183, showed significant positive linear relationships with δ 15 N values (Fig. 3B, Table S9). Among the alternative brominated flame retardants, BB-153 showed significant positive linear relationships (p = 0.005), while HBB did not. These results agree with the biomagnification of lipophilic compounds in marine pelagic food webs reported previously, including in deep-sea ecosystems [START_REF] Romero-Romero | Biomagnification of persistent organic pollutants in a deep-sea, temperate food web[END_REF][START_REF] Takahashi | Organohalogen compounds in deep-sea fishes from the western North Pacific, off-Tohoku, Japan: Contamination status and bioaccumulation profiles[END_REF]. Indeed, the congeners showing no significant relationship with δ 15 N values are those with the lowest reported trophic magnification factors (TMFs) [START_REF] Walters | Trophic Magnification of Organic Chemicals: A Global Synthesis[END_REF]. The lack of biomagnification of the lower-chlorinated PCB congeners such as CBs -18, -28, -31, HCHs and HBB might be related to their moderate hydrophobicity and potential elimination via respiration [START_REF] Kelly | Food Web-Specific Biomagnification of Persistent Organic Pollutants[END_REF][START_REF] Takahashi | Organohalogen compounds in deep-sea fishes from the western North Pacific, off-Tohoku, Japan: Contamination status and bioaccumulation profiles[END_REF]. Besides, low TMFs might also result from the compound hydrophobicity and size, which limit their bioaccumulation (e.g. BDE-209). The limited extent of the trophic level covered by the food web studied here (i.e. one theoretical trophic level if referring to the average difference of 3.4‰ reported between two trophic levels, [START_REF] Post | Using Stable Isotopes to Estimate Trophic Position: Models, Methods, and Assumptions[END_REF] might also have restrained the possibility of detecting high contaminant biomagnification for lipophilic compounds [START_REF] Brandsma | Tracing organophosphorus and brominated flame retardants and plasticizers in an estuarine food web[END_REF][START_REF] Won | Importance of accurate trophic level determination by nitrogen isotope of amino acids for trophic magnification studies: A review[END_REF].

Peculiar results were obtained for BDE-209 and DBDPE: both compounds are superhydophobic ones and their concentrations (in lw) showed contrasting relationships with δ 15 N values; while BDE-209 concentrations were not significantly related to δ 15 N values, DBDPE exhibited biomagnification (Fig.

3B, Table S9), which could be due to its presence at high levels in Stomias boa, Aphanopus carbo and Searsia koefoedi (see section above).

Among PFASs, individual PFCAs showed a significant decrease with increasing δ 15 N values when both crustaceans and fish were considered, while PFOS showed no significant trend. However, no significant trend was detected in fish only, whether individual PFCAs or PFOS were considered (Fig. 3C, Table S10), which shows that the significant relationship was due to the influence of the high concentrations observed in crustaceans. This lack of observed biomagnification for both PFOS and PFCAs in fish contrasts with some previously reported results. Indeed, various PFASs, including PFOS and long-chain

PFCAs have been reported to biomagnify in marine trophic webs [START_REF] Loi | Trophic Magnification of Poly-and Perfluorinated Compounds in a Subtropical Food Web[END_REF][START_REF] Munoz | Evidence for the Trophic Transfer of Perfluoroalkylated Substances in a Temperate Macrotidal Estuary[END_REF][START_REF] Pan | Legacy and alternative per-and polyfluoroalkyl substances in a subtropical marine food web from the Beibu Gulf, South China: Fate, trophic transfer and health risk assessment[END_REF][START_REF] Tomy | Fluorinated organic compounds in an eastern Arctic marine food web[END_REF], but some opposing results lacking evidence of long-chain PFCA biomagnification have also been reported when only piscivore food webs were considered [START_REF] Du | Bioaccumulation, trophic transfer and biomagnification of perfluoroalkyl acids (PFAAs) in the marine food web of the South China Sea[END_REF][START_REF] Kelly | Perfluoroalkyl Contaminants in an Arctic Marine Food Web: Trophic Magnification and Wildlife Exposure[END_REF][START_REF] Mazzoni | Trophic Magnification of Legacy (PCB, DDT and Hg) and Emerging Pollutants (PFAS) in the Fish Community of a Small Protected Southern Alpine Lake[END_REF][START_REF] Miranda | Perfluoroalkyl Substances in the Western Tropical Atlantic Ocean[END_REF][START_REF] Pan | Legacy and alternative per-and polyfluoroalkyl substances in a subtropical marine food web from the Beibu Gulf, South China: Fate, trophic transfer and health risk assessment[END_REF]. This has partially been explained by PFCA's high aqueous solubility (due to the carboxylate functional group) and preferential distribution in blood, leading to their efficient respiratory elimination via blood-water exchange in the gills [START_REF] Kelly | Perfluoroalkyl Contaminants in an Arctic Marine Food Web: Trophic Magnification and Wildlife Exposure[END_REF]. Our results show the complexity of interpretation of PFAS bioaccumulation along marine trophic webs in a given ecosystem, as the observed results could be reflecting different accumulation and/or depuration processes depending on species and potential metabolic capacities towards precursors.

PCBs and PBDEs exceed OSPAR BACs in the majority of samples

To identify marine regions of potential environmental concern, OSPAR (Oslo/Paris Convention for the Protection of the Marine Environment of the North-East Atlantic) defined Background Assessment Concentrations (BACs) for PCBs (OSPAR, 2017). BACs are used as thresholds to assess whether concentrations are close to background levels. Although these values were initially defined in the muscle of flatfish in coastal areas, a comparison was made with the present set of samples based on the determination of concentrations in whole fish. All samples showed higher concentrations (by a factor of 11-24 on average) than the corresponding BACs for CBs -138 (0.09 ng g -1 ww), -153 (0.10 ng g -1 ww) and -180 (0.11 ng g -1 ww), while CBs -52, -105 and -118 levels were above the BACs in 86% of the samples (by a factor of 3, 2 and 5, respectively). CBs -28 and -156 were above BACs in 57% of the samples (3 and 1.5 times respectively). Similarly, a BAC of 0.065 ng g -1 lw was recommended for each PBDE congener BDEs -28, -47, -66, -85, -99, -100, -126, -153, -154, -183 and -209 (OSPAR, 2021)

Conclusions and implications for higher trophic level consumers

The results obtained in the present study bring evidence of the contamination of deep-sea pelagic organisms from the Bay of Biscay by both legacy POPs and substances of emerging concern, showing that major organohalogen contaminant families (whether chlorinated, brominated or fluorinated) reach meso-and bathypelagic ecosystems. Despite being regulated for decades, PCBs were the major organic contaminant family in fish followed by OCPs, making chlorinated organic contaminants the major contributors to the targeted halogenated ones. On the opposite hand, PBDEs contributed the least to the contaminant load in both taxa. PFASs ranked third in fish while in crustaceans, PFAS and chlorinated contaminant contributions were similar. The significant contribution of PFASs (and among them the long-chain ones) to the load of organic contaminants in the studied deep-sea species, in addition to the lack of data on a large number of emerging contaminants, emphasises the importance of considering this family of compounds together with the legacy POPs in future studies.

Altogether, contaminant profiles and specific ratios suggest that the studied species exhibited metabolic capacities, especially towards PBDEs, and that the metabolic activity was highly speciesdependent. Selective bioaccumulation of the investigated OC families was evidenced and shown to be related to taxa and species, trophic parameters and potential metabolic capacities. While most chlorinated and brominated contaminants showed biomagnification along the studied trophic assemblage, most PFASs showed biodilution.

This high inter-species variability observed in terms of OC concentrations induce important consequences in terms of matter fluxes in oceanic ecosystems. Variability in species abundance will have a direct impact on the total amount of the different OCs that will be spatially transferred in the environment during vertical migration, as well as transfer to higher trophic level through food webs.

For example, in oceanic waters of the Bay of Biscay, the lipid-rich Myctophid species N. kroeyeri was shown to largely dominate the diet of oceanic common dolphins (55% by mass of fresh reconstructed diet, [START_REF] Pusineri | Food and Feeding Ecology of the Common Dolphin (Delphinus delphis) in the Oceanic Northeast Atlantic and Comparison with Its Diet in Neritic Areas[END_REF] while the lean Alepocephalid X. copei is not consumed at all. At a similar fresh mass of prey ingested, the consumption of N. kroeyeri thus represents a much higher intake of PCBs, OCPs and PBDEs for common dolphins than if they consumed X. copei (1.8 to 2.6 higher on average depending on OCs). On the other hand, N. kroeyeri provides 6 times less PFASs than X. copei at equivalent fresh mass ingested. Finally, in the perspective of the developpement of fishing activities targeting these mesopelagic ressources, our study pinpoints a potential issue regarding matter transfers, considering an exploitation of a selection of species and given the high inter-species variability in OC concentrations.

In conclusion, our results provide essential data for understanding and predicting some impacts of anthropogenic activities on deep pelagic ecosystems, filling a gap regarding the need to increase knowledge on the fate of human-induced organic contamination in the deep ocean. These original results may also allow a better assessment of contaminant vertical transport and transfer to higher trophic levels. In the actual context of climate change and global increase of human pressures, which might affect contaminant cycle dynamics and increase chemical pressures, it appears crucial to better monitor, characterise and understand chemicals' behaviour in offshore marine environments including in the deep sea. To these ends, more efforts are still needed to further assess the impact of the anthropogenic chemical contamination on deep-sea species and, ultimately, on ecosystem functioning. Concentrations of organochlorinated compounds (A) and organobrominated compounds (B) were log-transformed and expressed in ng g -1 lw and pg g -1 lw respectively; PFAS concentrations (C) were log-transformed and expressed in ng g -1 dw. Significant relationships are indicated by dashed lines when significant for crustaceans and fish together (and for fish alone as well), by continuous lines when significant for fish only, by dotted lines when significant for crustaceans and fish only (i.e. not for fish alone). General linear model statistical parameters are given in Tables S7-S10.

  could be partially explained by TLC values, as Pasiphae sivado, with the lowest TLC values, was hence expected to show lower bioaccumulation of lipophilic OCs such as PCBs, OCPs and PBDEs. In the two other crustacean species, chlorinated OCs (and PCBs in particular) were predominant, while PBDEs contributed the least. The contaminant concentrations and TLCs in crustaceans showed significant correlations for ∑ DDTs (p < 0.0001), endrine (p = 0.015), HCB (p = 0.003), ∑ HCHs (p = 0.024) and ∑ PBDEs (p = 0.010). However, the significance was driven by the high differences in TLCs found between the 3 studied crustacean species (4 ± 1%, 15% and 51% in Pasiphaea sivado, Sergia robusta and Ephyrina figueirai, respectively), while no correlation was evidenced for the three replicates of Pasiphaea sivado. When normalised to TLCs, OCP concentrations were still lower in Pasiphaea sivado versus the other two species (both being similar), while PCB concentrations were still higher in Sergia robusta > Pasiphaea sivado > Ephyrina figueirai. PBDE concentrations were similar in both Sergia robusta and Pasiphaea sivado (not determined in Ephyrina figueirai because of a matrix effect). PFAS concentrations showed similar levels in Pasiphaea sivado and Ephyrina figueirai but a two times higher level in Sergia robusta.

Fig. 1 .Fig. 2 .

 12 Fig.1. Relative contributions (% of the summed compounds) of (A) individual PCBs (presented per number of chlorine atoms), (B) DDTs (5 isomers, DDDs in green, DDTs in red/orange), (C) PBDEs (12 congeners, tri-, tetra, penta-, hexa-and deca-Br congeners are presented in blue, green, orange, purple and brown, respectively) and (D) PFASs (odd-chain PFCAs in green, even-chain PFCAs in orange) in deep pelagic crustacean and fish species collected in the Bay of Biscay in October 2017. Species names according to Table1. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3 .

 3 Fig. 3. Relationships between organic contaminant concentrations and δ 15 N values (‰) in crustaceans (black dots) and fish (white dots) collected in deep pelagic waters of the Bay of Biscay in October 2017. Concentrations of organochlorinated compounds (A) and organobrominated compounds (B) were log-transformed and expressed in ng g -1 lw and pg g -1 lw respectively; PFAS concentrations (C) were log-transformed and expressed in ng g -1 dw. Significant relationships are indicated by dashed lines when significant for crustaceans and fish together (and for fish alone as well), by continuous lines when significant for fish only, by dotted lines when significant for crustaceans and fish only (i.e. not for fish alone). General linear model statistical parameters are given in TablesS7-S10.

  Sergia robusta and Ephyrina figueirai as well as in the Papalepididae Arctozenus risso, the Sternoptychidae Argyropelecus olfersii, the Myctophidaes Myctophum punctatum and Notoscopelus kroeyeri, the Stomiidae Stomias boa and the Platytroctidae Searsia koefoedi. These results agree with the energy densities reported by[START_REF] Spitz | Proximate composition and energy content of forage species from the Bay of Biscay: high-or low-quality food?[END_REF] in various forage fish species from the Bay of Biscay. Except in Stomias boa for which the replicate made from 3 individuals showed extremely different values compared to the two other replicates (made of 1 individual each), TLCs were fairly similar between replicate pool samples of the same species, with an average rsd of 24% (12-34% range excluding Stomias boa). The TLC values in Stomias boa replicates (all female individuals) showed a higher rsd (69%), with high TLC values of 17.6% dw and 19.5% dw for the two 35 cm and 32 cm individuals respectively, whilst the replicate made from 3 individuals of 27.7 ±

	distinguished between low-TLC species (Serrivomer beanii, Xenodermichthys copei, Lampanyctus
	crocodilus, Chauliodus sloani and Aphanopus carbo) and the other species. High lipid contents (i.e.
	above 15% dw) were determined in the crustaceans

1.5 cm (on average) exhibited a much lower TLC value, i.e. 2.7% dw. The only noticeable difference noted during dissection was a slight difference between the maturity stages (based on gonad visual

  the highest variabilities(44-75% in dw, 64-80% in lw) were obtained between Notoscopelus kroeyeri replicates. The inter-species variability (calculated on the species means) was between 43% (PCBs) and 87% (PFASs) depending on the OC family. Xenodermichthys copei and Myctophum punctatum were the least-contaminated species in PCBs, OCPs and PBDEs while Notoscopelus kroeyeri showed the lowest PFAS concentrations. The highest levels were determined in Chauliodus sloani for PCBs, in Stomias boa for OCPs and PBDEs and Searsia koefoedi for PFASs.Only a limited number of lipophilic OCs (i.e. dieldrin, endrin, ∑ HCHs and each isomer, HCB) showed significant (p < 0.0001 to 0.022) positive correlations with TLCs, while ∑ DDTs, ∑ PCBs (whether i-PCBs,

on average for PFASs and 29, 38% and 36% for PCB, OCP and PBDE concentrations in dw). For all contaminant families, dl-PCBs or ∑ all congeners were considered) and ∑ PBDEs did not. Very few individual PCB congeners

 i.e

. the less-chlorinated ones) and individual PBDEs (BDEs -66

  53% (100 times) of the samples, respectively. BDE-183 was barely above the BAC (3% of the sample by 1.6 times) and BDE-85 was never detected above the LOQ. In addition, Environmental Assessment Criteria (EACs, in lw) defined as concentrations below which biological effects are unlikely to occur have also been established in fish. EACs were exceeded only for CB-118 (25 ng g -1 lw) in 30% of the samples (Lampanyctus crocodilus, Chauliodus sloani, Stomias boa and Aphanopus carbo), in agreement with the OSPAR intermediate assessment conducted within the period1995 -2015 (OSPAR, 2017)).

	. The
	BACs were exceeded for the predominant congeners BDEs -47, -9, -100 and -154 in more than 80% of

the samples (by 33, 7, 17 and 27 times, respectively), while

BACs were exceeded in 34% (by 1.4 times, on average), 44% (1.4 times), 44% (1.8 times), 63% (3 times) and

Electronic copy available at: https://ssrn.com/abstract=4123446

Electronic copy available at: https://ssrn.com/abstract=4123446

Acknowledgements

The authors thank the crew of the Ifremer R/V Thalassa and all colleagues involved in the collection of samples at sea during EVHOE 2017 (https://doi.or g/10.17600/17002300). Claire Steinberg (Ifremer, BE, Master internship) is gratefully acknowledged for her help in preparing the samples, as well as Benoit Lebreton and Gaël Guillou from the "Plateforme de Spectrométrie Isotopique" of the LIENSs laboratory at La Rochelle (France) for their assistance during carbon and nitrogen stable isotope analyses. Finally, we thank Aourell Mauffret and Nathalie Wessel from the team of descriptor 8 of the Marine Strategy Framework Directive at Ifremer for their support during the study.

Direction de l'Eau et de la Biodiversité-MTE/DEB") within a monitoring programme for the European Marine Strategy Framework Directive. Additional financial backing was provided by the European project SUMMER "Sustainable Management of Mesopelagic Resources" (grant agreement ID: 817806).

Funding sources

This research was funded by the French Ministry of Ecology ("Ministère de la Transition Écologique /

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