# Organohalogen contaminants of emerging concern in common dolphins (Delphinus delphis) from the Bay of Biscay (NE Atlantic): occurrence and 2000–2023 temporal patterns

Catherine Munschy, Yann Aminot, Florence Caurant, Willy Dabin, Audrey Mauchamp, Paula Méndez-Fernandez, Tiphaine Mille, Charles Pollono, Jérôme Spitz, Tiphaine Chouvelon

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Catherine Munschy, Yann Aminot, Florence Caurant, Willy Dabin, Audrey Mauchamp, et al. Organohalogen contaminants of emerging concern in common dolphins (Delphinus delphis) from the Bay of Biscay (NE Atlantic): occurrence and 2000–2023 temporal patterns. Environmental Pollution, 2025, 10.1016/j.envpol.2025.127290. hal-05328068

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Organohalogen contaminants of emerging concern in common dolphins (*Delphinus delphis*) from the Bay of Biscay (NE Atlantic): occurrence and 2000–2023 temporal patterns

Catherine MunschY, Yann Aminot, Florence Caurant, Willy Dabin, Audrey Mauchamp,
Paula Méndez-Fernandez, Tiphaine Mille, Charles Pollono, Jérôme Spitz, Tiphaine
Chouvelon

PII: S0269-7491(25)01664-1

DOI: https://doi.org/10.1016/j.envpol.2025.127290

Reference: ENPO 127290

To appear in: *Environmental Pollution*

Received Date: 10 July 2025

Revised Date: 15 October 2025

Accepted Date: 16 October 2025

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Please cite this article as: Munschy, C., Aminot, Y., Caurant, F., Dabin, W., Mauchamp, A., Méndez-Fernandez, P., Mille, T., Pollono, C., Spitz, J., Chouvelon, T., Organohalogen contaminants of emerging concern in common dolphins (*Delphinus delphis*) from the Bay of Biscay (NE Atlantic): occurrence and 2000–2023 temporal patterns, *Environmental Pollution*, https://doi.org/10.1016/j.envpol.2025.127290.

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Graphical abstract

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# Organohalogen contaminants of emerging concern in common dolphins (*Delphinus delphis*) from the Bay of Biscay (NE Atlantic): occurrence and 2000–2023 temporal patterns

Catherine Munschy¹*, Yann Aminot¹, Florence Caurant²,³, Willy Dabin², Audrey Mauchamp², Paula Méndez-Fernandez², Tiphaine Mille², Charles Pollono¹, Jérôme Spitz²,³, Tiphaine Chouvelon¹,²

¹ Ifremer, CCEM Contamination Chimique des Ecosystèmes Marins, 44000 Nantes, France

² Observatoire Pelagis, UAR 3462 La Rochelle Université-CNRS, F-17000 La Rochelle, France

³ Centre d'Études Biologiques de Chizé-La Rochelle, UMR 7372-Université-CNRS, La Rochelle, France

*Corresponding author: cmunschy@ifremer.fr

## Abstract

The contamination of marine mammals by legacy pollutants has been largely studied in oceans worldwide. However, international regulations have given rise to the replacement of legacy substances by alternative compounds, which represent a potential additional threat to marine mammal health and conservation. In this study, we investigated the occurrence and temporal trends of contaminants of emerging concern (CECs) in the blubber of common dolphins (*Delphinus delphis*) from the Bay of Biscay, North-East Atlantic, and in their major prey. Alternative brominated flame retardants were below the limits of quantification in all samples, while dechlorane-related compounds were identified as the major CECs, at levels of 4.6 ± 5.9 ng g⁻¹ lw, i.e. similar to or higher than those reported in various marine mammals from other oceanic regions. The concentrations of 3,6-dichlorocarbazole (3,6-CCZ), the major polyhalogenated carbazole, and of methyl-triclosan were one order of magnitude lower. The halogenated natural products, methoxylated polybrominated diphenyl ethers (MeO-BDEs), were also investigated and showed substantially higher concentrations than all CECs, i.e. 322 ± 214 ng g⁻¹ lw. Dechlorane-602, *anti*-monohydro dechlorane plus and MeO-BDEs were the only compounds showing biomagnification between small pelagic fish and dolphins. No significant differences in most CEC concentrations were found over the studied time period, indicating that these compounds are still emitted in the environment and/or have long residence times in the dolphins' blubber. Conversely, methyl-triclosan concentrations significantly decreased over the studied period. An increase in MeO-BDE concentrations in the last two decades might reveal a change in algal production in relation to global warming.

## Key Words

Marine mammals, contaminants of emerging concern, alternative flame retardants, dechloranes, polyhalogenated carbazoles, halogenated natural product.
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# 1. Introduction

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A large diversity of organohalogen contaminants of anthropogenic origin are found in the marine environment. They include the legacy contaminants, such as those regulated under the United Nations Stockholm Convention on persistent organic pollutants (POPs) (e.g. polychlorinated biphenyls [PCBs], organochlorine pesticides [OCPs] and polybrominated diphenyl ethers [PBDEs]), which have been well-studied in marine ecosystems. Due to their persistency and long-range transport, POPs have been identified in oceans worldwide (Jones, 2021; Chen et al., 2023). Moreover, their propensity to bioaccumulate in organisms and trophic webs, together with their toxicity, makes them compounds of interest with respect to their impact on marine organisms and in marine mammals in particular (Jones, 2021; Williams et al., 2023). Various contaminants of emerging concern (CECs) that have similar properties to POPs have also been identified in the marine environment, although much less data are available on their quantitative usage, occurrence and fate in marine ecosystems.

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The CECs of anthropogenic origin investigated in this study include several alternative brominated flame retardants (a-BFRs), dechlorane-related compounds (DECs) and their dechlorinated and hydroxylated metabolites, and triclosan and its metabolite methyl-triclosan. DECs have been used to replace mirex, which was banned in the US in the late 1970s and included in the Stockholm Convention on POPs in 2001, as a flame retardant in industrial and domestic products (Wang et al., 2016). Dechlorane Plus (DP) has been produced since the 1960s and was added to the Stockholm Convention list of priority pollutants in 2022 with specific exemptions. Its global emissions are due to its production (restricted to North America and China), the production and recycling of plastics and electronics containing DP, and its use in consumer products (Hansen et al., 2020). The other dechlorane-related compounds are not regulated, and even less is known about their production and use. Triclosan is a synthetic antibacterial agent used in numerous personal care products such as deodorants, toothpastes, cosmetics, and is also added to polymers and textiles in various consumer products such as toys and clothes (Fair et al., 2009; Dhillon et al., 2015). Triclosan was introduced to the market in the 1970s; its annual production was estimated at 1,500 tons globally in 1998, 350 tons of which were in Europe (Dhillon et al., 2015). Due to regulations, triclosan usage has decreased and this trend is expected to continue. Bacterial methylation of triclosan produces methyl-triclosan, and fish can also produce this metabolite, although methyl-triclosan is slightly more hydrophobic (log K<sub>ow</sub> of 5.2) than triclosan (log K<sub>ow</sub> of 4.76) (Lyndall et al., 2010).

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Other than anthropogenic contaminants, halogenated natural products (HNPs) are commonly found in marine biota due to their biosynthesis by marine algae, sponges or bacteria (Vetter, 2006). Many HNPs have similar structures and chemical properties to those of POPs and are identified at levels sometimes far beyond those of anthropogenic contaminants, including in marine mammals (Alonso et al., 2014; Barón et al., 2015). HNPs are synthesised by organisms at the base of the food chain as a defence mechanism against predators (Alonso et al., 2017). Although their potential effects on organisms occupying higher levels in the food chain have not been evidenced, due to their structural
similarities with anthropogenic contaminants, these effects cannot be ruled out. Some studies have reported the toxic potential of HNPs (Hu et al., 2011; Su et al., 2012; Bidleman et al., 2020; Michałowicz et al., 2022), but questions remain about whether marine organisms have adapted to being exposed to these compounds over time (Vetter et al., 2002; de Oliveira-Ferreira et al., 2023). Nonetheless, several HNPs such as methoxylated PBDEs (MeO-PBDEs) are considered chemicals of emerging concern (Bidleman et al., 2020). Furthermore, studying HNPs in marine organisms is important because their profiles have been successfully used as tracers of species' habitats and foraging strategies (Cossaboon et al., 2019), indicators of environmental health (de Oliveira-Ferreira et al., 2022), and indicators of climate change (Bidleman et al., 2020; Kunisue et al., 2021). The HNPs investigated in this study include two methoxylated PBDEs (MeO-PBDEs) that can be synthetised by marine algae, sponges and cyanobacteria, and several substances of mixed origins (natural and/or anthropogenic), such as polyhalogenated carbazoles (PHCZs), two bromophenols (namely, 2,4-dibromophenol [DBP] and 2,4,6-tribromophenol [TBP]), and 2,4,6-tribromoanisole (TBA).

PHCZs can be produced by fungal activity (natural origin) and also by various industrial activities such as the production of dyes, pharmaceuticals, and organic semiconductors (Wu et al., 2018; Sun et al., 2023). Various studies reported that anthropogenic sources could predominate over the natural sources for some PHCZs (Guo et al., 2017; Wu et al., 2018; Sun et al., 2023), and specific natural origins have been pinpointed in the marine environment (Zhang et al., 2023). PHCZs have dioxin-like activity and could, therefore, be of concern in terms of their impact on marine ecosystems, even at low levels (Wu et al., 2017; Riddell et al., 2015). Their stocks in marine sediments could be orders of magnitude greater than those of PCBs and PBDEs (Sun et al., 2023). TBP originates from both natural and anthropogenic (as a fungicide, wood preservative and as an intermediate and degradation product of FRs) sources and is the most widely produced bromophenol (Koch and Sures, 2018). Its degradation occurs *via* fungal activity and has also been observed in fish following microbial activity in the intestine (Halden et al., 2010), producing TBA (Bidleman et al., 2019).

Located in the northeastern Atlantic Ocean, the Bay of Biscay hosts many marine species of ecological importance, including key protected species such as the common dolphin (*Delphinus delphis*) (Laran et al., 2017). Massive mortality events of the common dolphin have been reported for several decades in the Bay of Biscay, and an increase in these events since 2016 has raised concern among scientists (Peltier et al., 2021). These high numbers of strandings on the French coastline could threaten the species' sustainability, particularly when a significant pressure of environmental pollution is added. As long-living top predators, marine mammals are particularly prone to accumulating large amounts of POPs and CECs of similar properties, and chemical contamination has harmful effects on the major physiological functions of marine mammals, such as the reproductive, immune and endocrine systems (Hall et al., 2006; Desforges et al., 2018; Murphy et al., 2018; Sonne et al., 2020; Williams et al., 2023). Therefore, marine mammals are recognised as sentinel species to evaluate the health of the oceans' ecosystem.
The present study aimed to generate new knowledge on the contamination of the common dolphin from the Bay of Biscay by selected persistent organohalogen contaminants, focusing in particular on a large selection of CECs of various origins in their blubber. Marine mammals are primarily exposed to persistent organic contaminants through their diet (Remili et al., 2023), which in the case of the common dolphin in the Bay of Biscay is mainly constituted by small pelagic fishes such as sardines (*Sardina pilchardus*), anchovies (*Engraulis encrasicolus*) and sprats (*Sprattus sprattus*) (Meynier et al., 2008; Faure et al., 2025). The contamination of these small pelagic fishes was also investigated to determine the biomagnification potential of the studied compounds. The objectives were to provide a better understanding of the chemical exposome of common dolphins in the Bay of Biscay and to investigate the temporal trends of CEC concentrations over the past 20 years.

## 2. Materials and methods

### 2.1. Sample collection

Individual carcasses were collected along the Bay of Biscay coastline (Figure 1) as part of the French Stranding Network led by the Pelagis observatory (La Rochelle, France) and under the umbrella of the French Ministry in Charge of the Environment. Freshly stranded individuals (i.e. with a decomposition state ≤3 based on the classification proposed by Kuiken and García Hartmann (1991) and more recently by IJsseldijk et al. (2019)) were collected, necropsied to identify the cause of mortality, and sampled for further analysis. Most of the stranded dolphins showed evidence of bycatch as the main cause of mortality. Some bycaught individuals directly collected by onboard observers were also considered. To limit inter-individual variability due to gender, only males were considered for analysis. In total, 3 individuals collected in 2000, 18 individuals collected in 2005–2010, and 24 individuals collected in 2020–2023 were analysed (Table S1). Each individual was sexed, measured (including total length and weight), and aged by counting the growth layer groups of teeth as described by Méndez-Fernandez et al. (2022). For lipophilic compounds, blubber is the most-contaminated tissue; it is estimated that 90% of the contaminant load is located in cetaceans’ blubber (Yordy et al., 2010; Tee et al., 2025). Therefore, the blubber was selected as the target tissue for lipophilic organic contaminant analyses and kept frozen until analysis. The blubber was always cut at the base of the dorsal fin and covered the whole thickness.

Small pelagic fish species including sprat (*Sprattus sprattus*, analysed in one pool of 9 individuals), European anchovy (*Engraulis encrasicolus*, analysed in three pools of 8, 20 and 4 individuals) and European sardine (*Sardina pilchardus*, analysed in two pools of 5 individuals each), that were representative of the lower trophic levels of common small pelagic fish, were collected by professional fishermen using pair trawling in the Bay of Biscay in February 2023. The whole bodies of the eviscerated fish (digestive tract and liver removed) were pooled for each species according to the fish length (Table S2). These species represented the dolphin’s major prey in the Bay of Biscay (Meynier et al., 2008, Faure et al., 2025), and their sizes were in the range of those targeted by dolphins (i.e. 7–12 cm for anchovy, 10–20 cm for sardine and 7–12 for sprat) (Faure et al., 2025).
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## 2.2. CEC and HNP analysis

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Sample preparation was conducted in a clean laboratory with a low-dust atmosphere and under positive pressure to prevent external contamination. The compounds full names and abbreviations are given in Table 1 and details on their CAS number, molecular formula, molecular mass and structure are given in Table S3. The target anthropogenic CECs were: i) the halogenated norbornenes (or dechlorane-related compounds -DECs) anti-DP and syn-DP, DEC-602, DEC-603 (reported summed as ΣDECs) and their dechlorinated transformation products anti-dihydro dechlorane plus (anti-Cl₁₀-DP) and anti-monohydro dechlorane plus (anti-Cl₁₁-DP), the dechlorane plus mono-adducts 1,5-DPMA and 1,3-DPMA; ii) the a-BFRs DBE-DBCH (α and β isomers), PBEB, BTBPE and DBDPE; iii) the polyhalogenated carbazoles (PHCZs) 3-CCZ, 3,6-CCZ, 1,3,6,8-CCZ, 2,3,6,7-CCZ, 3-BCZ, 2,7-BCZ, 3,6-BCZ, 1,3,6-BCZ, 1,3,6,8-BCZ, 1-B-3,6-CCZ, 18-B-3,6-CCZ; and iv) triclosan and its metabolite methyl-triclosan. Other CECs of mixed origins (namely, the bromophenols, DBP and TBP, and TBA) were also investigated. In addition, the naturally produced 6-MeO-BDE-47 and 2'-MeO-BDE-68 were determined in the same samples.

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The whole blubber samples were homogenised using cryogrinding, and sub-samples of 0.5 g taken before complete defrosting were dried overnight with anhydrous sodium sulfate and extracted using ultrasonic solid-liquid extraction using dichloromethane (DCM). Purification was achieved with gel permeation chromatography using DCM, a silica and alumina adsorption chromatography column using hexane / DCM and a two-dimensional HPLC system with a nitrophenylpropylsilica column (Nucleosil, 5 µm particles, 250 x 4.6 mm, Interchim, France), adapted from Munschy et al. (2020). Analyses (except for PHCZs, bromophenols and triclosan) were performed using gas chromatography (Agilent 6890, Palo Alto, CA, USA) coupled to high-resolution mass spectrometry (AutoSpec Ultima, Waters Corp.) and fitted with an RTX-1614 column (30 m x 0.25 mm i.d. x 0.10 µm film thickness). PHCZs 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 and fitted with a DB-5 MS column (30 m x 0.25 mm x 0.10 µm). Bromophenols and triclosan were analysed using liquid chromatography coupled to tandem mass spectrometry (LC-ESI-MS/MS) using a Waters (Waters Corp.) Acquity I-Class liquid chromatograph fitted with a BEH C₁₈ (Waters® 1.7 µm 2.1 x 150 mm) column and coupled with a Xevo TQS-µ (Waters Corp.) mass spectrometer operated in negative ionisation mode. All quantifications were done by isotopic dilution with all commercially available isotopically-labelled surrogates.

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Total lipid content values were determined gravimetrically in each blubber sample and in the prey, using DCM as the extraction solvent. All contaminant concentrations are given in ng per g of lipid weight (ng g⁻¹ lw).

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## 2.3. Quality assurance and quality control (QA/QC)
Method validation was conducted for all the studied CECs according to the Eurachem / CITAC guide (2016); all details of the validation parameters are given in the Supplementary Material (Table S4).
The results for compounds for which the accuracy was not verified (i.e. 1,3-DPMA, 1,5-DPMA and 2,3,6,7-CCZ) were considered semi-quantitative.

Strict QA/QC procedures were followed as described below. Two procedural blanks were processed with each sample batch (n = 10) throughout the whole analytical procedure. Concentrations in samples were corrected versus blanks using the mean value of the two blanks. Blank values were in the 0.002-0.019 ng g⁻¹ lw range. The LOQs calculated for each sample, taking into account the injection volume, volume of the concentrated extract prior to injection and extracted sample weight, are presented in Table 1. Intermediate precision determined during the method validation was between 4% and 23% (Table S4). The median values for the recoveries of the labelled compounds added to each sample (n = 46) prior to extraction ranged from 64% to 112%.

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## 2.4. Data analysis

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All statistical analyses were done using XLSTAT V2022.4.1. The chosen significance level was 0.05.
The data were first tested for their normality using the Shapiro-Wilks test, and non-parametric tests (i.e. Mann-Whitney and Kruskal-Wallis) were chosen for comparisons.

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In order to assess the temporal patterns of the studied compound concentrations in dolphins' blubber, a Mann-Whitney U test was used. The differences in dolphins' biological parameters (i.e. length and age) between the sampling periods were tested using the Mann-Whitney U test, in order to check if dolphins collected at different sampling periods had homogeneous biological parameters. Spearman correlations were used to determine the relationships between the compound concentrations and biological parameters (considering all individuals [n=45] for compounds that did not vary over time while only recent individuals [n = 24] were considered for the other compounds), as well as the relationships between the different compound families. The correlation between dolphins' length and age was verified using Pearson correlation.

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The ratio of the concentration of *anti*-DP / (*anti*-DP + *syn*-DP), i.e. the *fanti* value, was calculated and used to assess the differences in bioaccumulation and/or degradation of each isomer (Wu et al., 2010).

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The biomagnification factors (BMFs) were calculated as the ratio between the lipid-normalised concentrations in dolphin blubber and their prey and were used to assess the biomagnification propensity of the analysed compounds between the prey and the dolphins.

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# 3. Results

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## 3.1. Biological parameters and total lipid content of dolphins

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The mean length of individuals collected from 2005–2009 was 202 ± 13 cm (182–225 cm range, n = 18) and was not significantly different from the mean length of specimens collected during the most

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recent period (mean = 205 ± 12 cm, range = 184–226 cm, n = 24; Figure S1). The three individuals collected in 2000 were in the 180–232 cm size range. Dolphins’ ages ranged from 3 to 16 years (Figure S1). Dolphins’ lengths and ages were significantly positively correlated (Pearson ρ = 0.903, p <0.0001, n = 44). No significant differences in length or age were found between the sampling periods, which facilitated the comparison of total lipid contents or contaminant concentrations among these groups (i.e. the influence of these potential confounding factors was limited).

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In dolphins’ blubber, the total lipid content values were 71 ± 8% ww (n = 45) on average (Table 2). The total lipid content values in whole fish prey were 1.3% ww in sprat, 1.0–1.8% ww in sardine, and 1.5–2.2% ww in anchovy (Table 3).

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## 3.2. Halogenated CEC and HNP concentrations in dolphins’ blubber

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The concentrations and quantification frequencies of the various CECs and HNPs are given per sampling period in Table 2. Among CECs, *anti*-DP, *syn*-DP, DEC-602, DEC-603, *anti*-Cl₁₁-DP, 3,6-CCZ and methyl-triclosan were quantified in 58–100% of the samples, while 3-CCZ was quantified in 31% of the samples and the other target CECs were below the LOQs in all samples.

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The relationships between contaminant concentrations and dolphins’ biological characteristics (length or age) were significant only for DECs (individually or ΣDEC, Figure S2). Notably, the highest ΣDEC concentrations (21.8–25.9 ng g⁻¹ lw) were found in large (210–225 cm length) and old (12–14 years) specimen. No significant relationship was found between other CEC or HNP concentrations and age or length.

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DECs were the most frequently detected CECs and showed the highest contamination levels in dolphins (Figure 2A, Table 2). *Anti*-Cl₁₁ DP, one of the DP transformation products, showed a high occurrence as well, while *anti*-Cl₁₀ DP and DP mono-adducts (DPMA) were not detected. The ratio of *anti*-Cl₁₁ DP / *anti*-DP was 0.35 ± 0.11, and it did not vary over time or according to dolphins’ age. DEC-602 and DEC-603 accounted for 89 ± 8% and 9 ± 5% of total DECs, respectively, and no significant differences were found between the sampling periods (Figure S3). The *fanti* values were 0.58 ± 0.11 on average (n = 45) with no differences between the sampling times or dolphins’ age. Several studies reported DP and DEC-602 levels in various marine mammal species worldwide and results are presented in Table S5.

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Among the PHCZs, 3,6-CCZ showed the highest quantification frequency, while 3-CCZ was seldom detected (Table 2). All other PHCZs were below the LOQs.

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Methyl-triclosan concentrations were in a similar range as PHCZ concentrations (Figure 2B), although the concentrations were much lower (0.046 ng g⁻¹ lw) when only recent individuals were considered (see also Section 3.6). Triclosan was seldom detected (n = 4) and, therefore, not considered later.

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Among HNPs, MeO-BDE-47 showed the highest concentrations in dolphins, followed by MeO-BDE-68 (Table 2, Figure 2B).

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The inter-correlations between the various compound concentrations in recent individuals showed contrasting results (Table S6). Significant correlations were found between the ΣDEC and 3,6-CCZ (p = 0.001) concentrations, while the relationships between the ΣDEC, methyl-triclosan (p = 0.652) and HNP (p = 0.058–0.489) concentrations were not significant. The 3,6-CCZ concentrations were positively correlated with methyl-triclosan (p = 0.013) and the MeO-BDEs (p = 0.002 to <0.0001). Among the HNPs, both MeO-BDEs were highly cross-correlated (p <0.0001), while TBA showed no significant relationship with any other HNP or CECs.

### 3.3. CEC and HNP concentrations in dolphins' prey

The total lipid content values in prey (whole fish minus liver and digestive tract) were in the 1-2.2% ww (Table 3). All DEC-related compounds and anti-Cl₁₁ DP were quantified in all samples (Table 3). The ratio of anti-Cl₁₁ DP / anti-DP was 0.07 ± 0.01 on average. Interestingly and in contrast to what was observed in the dolphins' blubber, DEC profiles in prey were dominated by both DEC-602 and DEC-603, accounting for 30 ± 8% and 35 ± 2% of the ΣDECs respectively, while anti-DP and syn-DP contributions were 14 ± 3% and 21 ± 5%, respectively.

Several PHCZs were detected in 100% of the prey, and these compounds exhibited a more diverse profile than in dolphins. The 1,3,6,8-BCZ congener accounted for 43 ± 11% of ΣPHCZs on average, while 3,6-CCZ represented 39 ± 9% of ΣPHCZs. 1,3,6,8-CCZ and 3-CCZ accounted for 11 ± 6% and 9 ± 3% of ΣPHCZs respectively. Methyl-triclosan was quantified in all samples while triclosan was detected in 50% of the samples at levels close to the LOQ.

Sprats exhibited by far the highest MeO-BDE concentrations among the 3 small pelagic fish species. The MeO-BDE-47 / MeO-BDE-68 concentration ratio was four times higher in anchovies (7.9 ± 0.7) than in sprats and sardines (1.6 ± 0.7), although the difference was not significant due to the limited number of samples.

### 3.4. Biomagnification factors (BMFs)

The BMFs showed contrasting results depending on the compound (Table S7). DEC-602 and anti-Cl₁₁-DP were the only DECs that showed a BMF > 1 (7 and 2.5, respectively), while the BMFs of anti-DP, syn-DP and DEC-603 were 0.7, 0.4 and 0.6, respectively. BMFs calculated for 3-CCZ and 3,6-CCZ were 0.5 and 1.0, respectively, and 1.0 for TBA. Among MeO-BDEs, the BMFs decreased in the order of MeO-BDE-47 (BMF = 5) > MeO-BDE-68 (BMF = 2).

### 3.5. Temporal variations of CEC and HNP concentrations in dolphins' blubber

No significant differences in ΣDEC (neither in DEC-602, DEC-603, anti-DP, or syn-DP) or 3,6-CCZ concentrations were found between individuals collected in our study between different time periods (Figure 3A and 3B). Conversely, a significant decrease in methyl-triclosan concentrations was found between the samples collected in 2000 or 2005–2009 on the one hand, and those collected in 2020–2023 on the other hand (Figure 3C). TBA and the two MeO-BDEs showed significantly higher
concentrations in the more recent individuals (Figures 3D, 3E and 3F). The results of the non-parametric Mann-Whitney U tests are shown in Table S8.

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Discussion

This study reported on the concentrations of selected brominated or chlorinated compounds of
anthropogenic, natural, or mixed origin in the blubber of 45 individual dolphins over a time covering
more than two decades (from 2000 to 2023) and provided a three-time point comparison. The
biomagnification extent of the compounds was assessed using data concomitantly acquired on the
major prey species of the dolphins in the area, allowing a better understanding of these compounds'
behaviours along trophic webs.

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4.1. Alternative BFRs in common dolphins

Among the various CECs investigated in this study, a-BFRs were below the LOQs in all dolphin
samples. Various a-BFRs, including those analysed in our study, have been reported in marine
mammal species from oceans worldwide, sometimes sporadically, with the higher levels found in
Asia and the Mediterranean Sea (Sutton et al., 2019 and references therein; de Wit et al., 2020;
Zhang et al., 2022; Liu et al., 2024 and references therein). The lack of detection of the a-BFRs
targeted in our study suggests that the Bay of Biscay is not heavily contaminated by this group of
contaminants, but can also be explained by the moderate to low potential of trophic magnification of
these compounds (de Wit et al., 2020; Zhang et al., 2022).

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4.2. DEC profiles were dominated by DEC-602 in dolphins' blubber

Due to the various sampling times, marine regions, species and biological characteristics of the
individuals analysed in the previously-reported studies, the comparison of the concentrations and
profiles of DEC-related compounds in dolphins' blubber needs to be considered with caution.

In common dolphins from southern European waters in 2012, DEC-602 concentrations ranged from 1.76 to 1.92 ng g⁻¹ lw (Barón et al., 2015), which is in the range of the average concentration found in our study (4.06 ± 5.12 ng g⁻¹ lw), despite the difference in sampling times. However, the DEC profiles showed differences between the two studies, with DEC-602 dominating in our study, whereas Barón et al. (2015) reported *syn*-DP and *anti*-DP as the main isomers. As no temporal variations in DEC profiles were evidenced in our samples, the differences in DEC profiles between these two studies could be indicative of regional differences in the DEC exposure of dolphins. The predominance of DEC-602 over other DECs has been reported in harbour seals (*Phoca vitulina*) from Sweden in 2000–2016 and is consistent with the higher bioaccumulation potential of DEC-602 (Sun et al., 2022a). Interestingly, the occurrence of DEC-603 in our study was also reported in harbour seals from the coasts of Sweden, whereas this compound was not reported in individuals collected from the Gulf of Maine in the NW Atlantic (Sun et al., 2022a). Conversely, DEC-604 was
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identified in seals from the Gulf of Maine but was not detected in samples from Sweden nor in our study, suggesting that DEC profiles are region-specific.

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Because *anti*-DP has a lower bioaccumulation potential and is more degradable than *syn*-DP, the *fanti* values tend to decrease with increasing trophic levels (Wu et al., 2010), but the opposite was observed in our samples (i.e. 0.40 ± 0.07 in recent prey, n = 6, versus 0.57 ± 0.12 in recent dolphins collected in 2020–2023, n = 18, p = 0.006). The relative contribution of the *anti* isomer to the summed DPs identified in common dolphins from our study indicated its higher bioaccumulation compared to the *syn* isomer, and contrasts with previous findings in common dolphins, i.e. a *fanti* value of 0.37 (Barón et al., 2015). However, relatively high *fanti* values (i.e. >0.5) such as those found in our study have been reported in various marine mammal species from different locations worldwide, and this result was associated with low DP levels (< ng g⁻¹ lw) although no explanation was provided for in-depth understanding of this observation (Vorkamp, 2015; Wang et al., 2016). More knowledge on each isomer's accumulation and elimination kinetics in blubber would be needed to unravel the complex interrelationships involved.

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In addition to the parent DP isomers, identification of the dechlorinated transformation product *anti*-Cl₁₁-DP in dolphins' blubber at higher levels than in prey, together with the increase of the ratio *anti*-Cl₁₁-DP / *anti*-DP between prey and dolphins, suggest a higher bioaccumulation propensity of *anti*-Cl₁₁-DP accumulation along food webs (Wang et al., 2015). *Anti*-Cl₁₁-DP originates from the photo- or thermal degradation of DP, and no evidence of *in vivo* metabolisation of *anti*-DP has ever been reported, ruling out *anti*-DP degradation in dolphins, in addition to the fact that marine mammals have limited capacities to biotransform contaminants (Tanabe et al., 1988). *Anti*-Cl₁₁-DP is expected to have a lower log Kow than *anti*-DP's one (11.3, Wang et al., 2016), which, in addition to its non-metabolisation, would enhance its biomagnification potential (Walters et al., 2016). The absence of quantifiable amounts of the other transformation products of DP studied here, i.e. *anti*-Cl₁₀ DP and DP mono-adducts (DPMA), is consistent with their lower trophic magnification factors and reduced half-life (Sverko et al., 2011; Wang et al., 2015).

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### 4.3. PHCZs were found at low levels in dolphins' blubber

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Data on PHCZ concentrations in marine mammals are extremely scarce. PHCZ bioaccumulation is species-specific, and the predominance of 3,6-CCZ in common dolphins from this study agrees with previously reported results in harbour seals from San Francisco Bay, USA (Wu et al., 2017). The 3,6-CCZ is reported to be the most stable PHCZ (Deng et al., 2023), which could explain its predominance in marine mammals. However, this congener has a moderate bioconcentration factor (i.e. 490; Tu et al., 2025), which could explain its low bioaccumulation in dolphins. The concentrations determined in our study (i.e. 0.06–0.87 ng g⁻¹ lw range) were more than three orders of magnitude lower than in harbour seal blubber from the San Francisco Bay (i.e. 3,6-CCZ between 41.9 and 1416 ng g⁻¹ lw; Wu et al., 2017). In the present study, PHCZ levels were in a low range of concentrations
compared to DECs. This contrasts with the results reported by Sun et al. (2022b) in the liver of harbour seals from the south coast of Sweden, where PHCZs were found at higher levels than DECs. PHCZs are known to originate from various industrial products, but they can also be produced by natural sources. Major PHCZ industrial emissions originate from China, Australia, Japan, India, the US and Russia (Sun et al., 2023). Both chlorinated and brominated carbazoles have previously been detected in shellfish from the French Atlantic coast of the southern Bay of Biscay, and their sources have been putatively attributed to anthropogenic and natural sources, respectively (Singh et al., 2023). The chlorinated congeners, such as 3,6-CCZ, are generally associated with industrial sources such as steel production and municipal solid waste incineration (Sun et al., 2023), but natural origins have also been reported (Tu et al., 2025). In sediment cores from the Great Lakes, anthropogenic sources have been associated with low molecular mass PHCZ congeners (i.e. no more than three halogen atoms), while other congeners (such as 1,3,6,8-BCZ) were found to be abundant before industrialisation and decreased afterwards, confirming their natural origin (Guo et al., 2017). Based on current knowledge, the origins of PHCZ in environmental samples are still unclear. Interestingly, significant correlations were found in dolphins between 3,6-CCZ concentrations and anthropogenic contaminants (i.e. ΣDECs, methyl-triclosan) and the MeO-BDEs (i.e. HNPs); at the opposite, ΣDECs did not correlate with the MeO-BDEs, which could be indicative of the contaminants' sources (i.e. mixed origins versus anthropogenic origins).

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4.4. CECs were two to three orders of magnitude lower than the legacy POPs

In comparison with legacy POPs, the CEC concentrations reported here were three orders of magnitude lower than those of the PCBs identified in the same samples (12,800 ± 16,200 ng g⁻¹ lw for CB-153, personal communication), which is consistent with previously reported results for PCBs in various marine mammal species from European waters (Pierce et al., 2008; Méndez-Fernandez, 2014; Williams et al., 2023). The higher POP levels may be due to the large differences in the historical quantitative use of the contaminants (Wang et al., 2016; Li et al., 2023) and/or, for some CECs such as triclosan, to a lower propensity to bioaccumulate (Arnot et al., 2018). The total past global use of PCBs is estimated to be 1,326 ktons over a 63-year production period (1930–1993), while that of DP is thought to be one to several orders of magnitude lower. However, data on the global production of DPs are variable (e.g. 750–6,000 tons per year in 2020; Hansen et al., 2020), and ECHA reports there was no production in Europe, but importation of 90–230 tons per year (Skogeng et al., 2023). Furthermore, the production of the other dechlorane-related compounds has not been reported (Wang et al., 2016). Other studies have reported a-BFR and DEC concentrations to be several orders of magnitude lower than those of the legacy PBDEs in marine mammals from the North Atlantic (Sun et al., 2022a). Our results show that DEC concentrations were 17 (for DEC-602) to 300 (for DPs) times lower than those of mirex (66 ± 50 ng g⁻¹ lw personal communication), the compound they replaced, even though mirex has been banned since 1976 in the US and 2004 in Europe (Regulation No 850/2004). The total production of mirex was reportedly quite limited, with
2,700 tons over two decades (Li et al., 2023). However, its high persistence, bioconcentration factor, and long-range transport propensity could explain its occurrence at higher levels than DECs. Furthermore, the use and recycling of mirex-containing products have been identified as a potential current source of mirex in the environment (Rjabova et al., 2016), which might also contribute to the higher levels identified in our study in comparison to DECs.

The common predominance of persistent legacy contaminants that have been banned for several decades, over the non-regulated ones that show similar persistence, raises the question of their temporal trends in marine mammals over the coming decades. Although persistence is a key factor of contaminants' environmental concern (Cousins et al., 2019), their production volumes should undoubtedly be considered, which argues for a better global evaluation of their usage and storage volumes. Furthermore, the half-lives of CECs in marine mammals are still not known individually, which makes the understanding of their bioaccumulation and elimination kinetics more complex. It has been reported that within PCBs alone, half-lives in the blubber of the harp seal (*Pagophilus groenlandicus*) could vary from 50 to > 3,000 days depending on the congeners (Fraser et al., 2002).

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### 4.5. CECs and HNPs showed contrasted biomagnification from small pelagic fish to dolphins

BMF is a commonly-used indicator of the biomagnification propensity of organic contaminants, although this parameter could be subject to considerable variability (Wang et al., 2021). In this study, as a limited number of pools of small pelagic fishes were available for BMF calculation, the results discussed below should, therefore, be considered with caution. Of all CECs investigated here, only DEC-602 and *anti*-Cl₁₁-DP showed BMFs above 1, which explains the differences in DEC and PHCZ profiles identified in dolphins and fish, i.e. the predominance of DEC-602 in dolphins and a decrease in DEC-603, *anti*-DP and *syn*-DP between small pelagic fish and dolphins, and a more diverse profile in PHCZs in the small pelagic fish. The lack of biomagnification of DEC-603, *anti-* and *syn*-DP between the small pelagic fish and the dolphins could be partially explained by their log Kow and log Koa ranges (which are optimal for values of approximately 3.2–8 and ≥ 6.5, respectively; Kelly et al., 2007). However, most PHCZs fall into these ranges and would, therefore, be expected to biomagnify in marine mammalian food webs. The lack of biomagnification observed in our study for 3,6-CCZ contrasts with the values reported in the harbour seal by Wu et al. (2017). Although biodegradation of this stable congener would be unexpected in dolphins, the identification of 1,3,6,8-BCZ in the small pelagic fish at levels close to those of 3,6-CCZ and its absence in dolphins could suggest potential metabolism (Wu et al., 2017). Although marine mammals have limited capacities for biotransforming POPs, 1,3,6,8-BCZ is likely from natural origins, implying that dolphins have been exposed to this congener for a long time and may, therefore, have adapted to it.

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The two bromophenols were identified in the small pelagic fish at levels of 8–81 ng g⁻¹ lw, while they were below the LOQs in dolphins, which is consistent with their low BCF, although their log Kow are reported to be 4.24 and 3.48 for TBP and DBP, respectively (Koch and Sures, 2018; Bidleman et al.,
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2019). The calculated BMF of TBA was 1, confirming that this HNP does not bioaccumulate with increasing trophic levels (Losada et al., 2009).

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The BMFs of both MeO-BDEs were above 1, indicating their biomagnification along food chains.

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Although reported to be less bioaccumulative than PBDEs, MeO-BDEs have been identified as biomagnifying compounds in marine mammals (Weijs et al., 2009; Losada et al., 2009).

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### 4.6. MeO-BDE profiles are indicative of production by algae

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MeO-BDE-47 and MeO-BDE-68 were the most abundant HNPs identified in the dolphin samples.

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Both MeO-BDEs have been reported as the most studied and predominant ones in various marine mammals (Alonso et al., 2014), reaching levels as high as 151,250 ng g⁻¹ lw in the blubber of Indo-Pacific bottlenose dolphins from the Indian Ocean, while concentrations in various odontocete species from the Northern hemisphere were lower, i.e. in the range of those identified in our study (Alonso et al., 2014; Barón et al., 2015). The presence of both MeO-BDEs at relatively high levels adds to the total load of brominated compounds of potential toxicity, considering that MeO-BDEs can be biotransformed to OH-BDEs, which are more toxic than MeO-BDEs or PBDEs (Wiseman et al., 2011).

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The predominance of MeO-BDE-47 over MeO-BDE-68 suggests that algae are the major sources of MeO-BDEs in our samples (Alonso et al., 2014). This agrees with previously reported results and is typical of cetaceans from the Northern hemisphere, while the opposite has been found in dolphins from the southwestern Atlantic Ocean (Durante et al., 2024; de Oliveira-Ferreira et al., 2023). Interestingly, the higher ratio of MeO-BDE-47 / MeO-BDE-68 in anchovies than in sprat and sardines suggests that the former feed more on phytoplankton than the latter. In the Bay of Biscay, sardines were reported to feed on small to medium-sized copepods, while anchovies showed a higher plasticity in their prey (Chouvelon et al., 2014).

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TBA concentrations were one order of magnitude lower than those of the MeO-BDEs. TBA has been previously identified in dolphin blubber from Brazil, together with tribromophenol and dibromophenol that were not detected in our samples (Alonso et al., 2017). TBA concentrations did not correlate with those of any other compound, suggesting its peculiar origin and/or behaviour.

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### 4.7. Temporal stability of most CECs and increase of HNP concentrations

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The temporal stability of DECs and 3,6-CCZ over the studied time periods could result either from their continuous inputs into the marine environment and/or from their persistence in dolphins' blubber. As the blubber is considered a slow-exchange tissue (especially the external layer; Koopman, 2007), a higher delay after a decrease in environmental contamination could be expected in blubber than in other body compartments such as muscle, liver or blood. As a result, several years might be needed before a significant change in concentrations of contaminants could be detected in the blubber (e.g. a minimum of 7 years for PCBs in mature males; Hickie et al., 2011).

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The stability of DEC concentrations (either DPs, DEC-602 and DEC-603) in common dolphins over the two studied periods was similar to other studies that highlighted stable concentrations of various DEC-related compounds in marine mammals from various regions in the world over the last three decades (Aznar-Alemany et al., 2021 in the Mediterranean Sea; Sun et al., 2022a in California, the Gulf of Maine and South Sweden). These results suggest that worldwide emissions from anthropogenic uses of DECs into the marine environment are still ongoing and/or that DEC-related products have a high persistence in dolphins' blubber. A recently published study concluded on the existence of ongoing sources of DP, and to a lesser extent of DEC-602, in the European atmosphere (Skogeng et al., 2023). On the contrary, a significant increase in *anti*-DP was evidenced in humpback dolphins from the South China Sea, where high levels were observed (Zhang et al., 2022). Alternatively, a weak decrease of DPs has been reported in belugas from the St Lawrence estuary in Canada (Simond et al., 2017), and a significant decrease in several transformation products of DEC-602 and DEC-603 was identified in harbour porpoises from Sweden (Haglund and Rebryk, 2022).

As for PHCZs, studies on their temporal trends in the marine environment are lacking, but data in fish and sediment from the Great Lakes in Canada have revealed generally decreasing trends in concentrations from 2004 to 2016 (Guo et al., 2017; Wu et al., 2018). The 3,6-CCZ is reported to be the most stable PHCZ produced from natural dehalogenation of chloro- and bromo-carbazoles in sediments (Deng et al., 2023), which could explain its predominance. However, information on PHCZ sources and behaviour, including their abiotic or biotic degradation pathways, is lacking, preventing more in-depth interpretation of our results.

The HNPs TBA and the two MeO-BDEs showed a significant increase over the studied time periods. Interestingly, similar trends in MeO-BDE concentrations have been observed in melon-headed whales (*Peponocephala electra*) from the Japanese coasts and were possibly explained by a change in algal productivity associated with global warming (Kunisue et al., 2021). Evidence of the impact of climate change on the production and transport of HNPs has been recently reported, although the processes remain compound-related, and complex co-occurring factors (such as temperature, pH, salinity, nutrients) need to be considered at a regional scale (Bidleman et al., 2020).

## 5. Conclusions

This study presents original data on the contamination of common dolphins from the Bay of Biscay by various CEC families. While the targeted alternative BFRs were all below the LOQs, dechlorane-related compounds, and DEC-602 in particular, showed a high occurrence and levels in a similar range as those identified in dolphins from European waters. PHCZs showed a more complex profile in small pelagic fish than in dolphins, suggesting that PHCZs did not biomagnify. All CEC concentrations were several orders of magnitude lower than those of major POPs. Biomagnification was evidenced for some dechlorane-related compounds, including the dechlorinated transformation product *anti*-Cl₁₁-DP, but most CECs showed biodilution between small pelagic fish and dolphins.
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Stable temporal trends over 2000–2023 were identified for most CECs, suggesting their continuous
inputs and/or long residence time in dolphin blubber. In contrast, methyl-triclosan showed
significantly lower levels in the most recent years. Additional research would be needed to further
assess the trends in dechlorane-related products, some of which are not yet regulated. Interestingly,
the studied HNPs showed increasing trends in the last two decades, which might reveal that they
can be used as indicators of change in algal production in relation to global warming.

These results bring key knowledge on the present and temporal evolution of the contamination status
of common dolphins from the Bay of Biscay and represent a benchmark for future evaluation of
dolphins' chemical exposome by recently- or non-regulated contaminants. Furthermore, questions
remain about whether the total load of organohalogen contaminants in common dolphins, including
POPs, and the CECs studied here, together with numerous HNPs (those targeted here among many
other potential ones), which are all part of the chemical exposome of dolphins, could represent a
cumulative threat to their global health.

## 6. Acknowledgments

This work was supported by the Delmoges project, co-funded by the Ministry in charge of the Environment Directorates DGAMPA (Fisheries and Aquaculture) and DEB (Aquatic Biodiversity) and the Fisheries Sector Association (FFP - France Filière Pêche). Karine Héas-Moisan, Nathalie Olivier and Romane Madoulet from IFREMER are gratefully acknowledged for conducting the CEC and total lipid content analyses. We also wish to warmly thank all members of the French stranding network (RNE) and all members of the Pelagis Observatory for their continuous effort in collecting data on stranded and bycaught cetaceans.

## Data availability

The data have been deposited on SEANOE https://www.seanoe.org/data/00917/102860/
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<figure><img src="image_4.png" /></figure>
Figure 1. Sampling location of the individuals collected for organohalogen contaminants of emerging concern in blubber. Dots and triangles represent the bycaught individuals (i.e., bycaught at sea or stranded with bycatch evidence) and non-bycaught respectively. Orange, green and blue dots/triangles represent the individuals collected in 2000, 2005-2009 and 2020-2023 respectively.

Figure 2. DEC-602, 3,6-CCZ and methyl-triclosan concentrations (A) (ng g⁻¹ lw), as major compounds detected for DECs, PHCZs and triclosan and its metabolite among the CECs analysed, respectively, and MeO-BDE concentrations (B) (ng g⁻¹ lw) in the blubber of common dolphins (*Delphinus delphis*) from the Bay of Biscay. Boxplots represent the median (middle bar), 25th and 75th percentiles (top and bottom of the boxes). Red cross = mean value. Dots are maximum and minimum values, crosses are extreme values. Whiskers are Tukey ranges.

Figure 3. Concentrations (ng g⁻¹ lw) of Σ DECs (A), 3,6-CCZ (B), methyl-triclosan (C), TBA (D), 2'-MeO-BDE-68 (E) and 6-MeO-BDE-47 (F) in the blubber of common dolphins (*Delphinus delphis*) from the Bay of Biscay in 2000, 2005-2009 and 2020-2023. Red cross = mean value. Red line = median value. Significant differences at α = 0.05 are indicated by an asterisk.
<table><caption>Table 1.
Compound class, full name, abbreviation and limit of quantification (LOQ) (ng g⁻¹ lw).</caption><thead><tr><th>Compound class</th><th>Full name</th><th>Abbreviation</th><th>LOQ</th></tr></thead><tbody><tr><td rowspan="3">Halogenated norbornenes</td><td>Dechlorane Plus</td><td>DP (syn- and anti-)</td><td>0.025</td></tr><tr><td>Dechlorane 602</td><td>DEC-602</td><td>0.014</td></tr><tr><td>Dechlorane 603</td><td>DEC-603</td><td>0.015</td></tr><tr><td rowspan="4">Alternative brominated flame retardants</td><td>1,2-dibromo-4-(1,2-dibromoethyl)-cyclohexane,</td><td>DBE-DBCH (α- and β-)</td><td>0.105</td></tr><tr><td>2,3,4,5,6-pentabromoethyl benzene</td><td>PBEB</td><td>0.013</td></tr><tr><td>1,2-bis(2,4,6-tribromophenoxy)ethane</td><td>BTBPE</td><td>0.026</td></tr><tr><td>Decabromodiphenylethane</td><td>DBDPE</td><td>0.266</td></tr><tr><td rowspan="10">Polyhalogenated carbazoles</td><td>3-chlorocarbazole</td><td>3-CCZ</td><td>0.019</td></tr><tr><td>3,6-dichlorocarbazole</td><td>3,6-CCZ</td><td>0.023</td></tr><tr><td>1,3,6,8-tetrachlorocarbazole</td><td>1,3,6,8-CCZ</td><td>0.024</td></tr><tr><td>2,3,6,7-tetrachlorocarbazole</td><td>2,3,6,7-CCZ</td><td>0.019</td></tr><tr><td>3-bromocarbazole</td><td>3-BCZ</td><td>0.037</td></tr><tr><td>2,7-dibromocarbazole</td><td>2,7-BCZ</td><td>0.019</td></tr><tr><td>3,6-dibromocarbazole</td><td>3,6-BCZ</td><td>0.053</td></tr><tr><td>1,3,6-tribromocarbazole</td><td>1,3,6-BCZ</td><td>0.028</td></tr><tr><td>1,3,6,8-tetrabromocarbazole</td><td>1,3,6,8-BCZ</td><td>0.050</td></tr><tr><td>1-bromo-3,6-dichlorocarbazole</td><td>1-B-3,6-CCZ</td><td>0.026</td></tr><tr><td>1,8-dibromo-3,6-dichlorocarbazole</td><td>1,8-B-3,6-CCZ</td><td>0.028</td></tr><tr><td rowspan="2">Polychloro phenoxy phenol and transformation product</td><td>5-chloro-2-(2,4-dichlorophenoxy)phenol</td><td>Triclosan</td><td>0.142</td></tr><tr><td>2,4-dichloro-1-(4-chloro-2-methoxyphenoxy)benzene</td><td>Methyl-triclosan</td><td>0.014</td></tr><tr><td rowspan="2">Bromophenols</td><td>2,4-dibromophenol</td><td>DBP</td><td>0.139</td></tr><tr><td>2,4,6-tribromophenol</td><td>TBP</td><td>0.142</td></tr><tr><td>Bromoanisole</td><td>2,4,6-tribromoanisole</td><td>TBA</td><td>0.023</td></tr></tbody></table>
<table><caption>Table 2. Total lipid content (% ww), CEC and HNP concentrations (ng g⁻¹ lw), and quantification frequencies (%) in the blubber of common dolphins (*Delphinus delphis*) collected from the Bay of Biscay. Min-max / mean ± standard deviation are given according to the sampling time.</caption><thead><tr><th>Sampling time</th><th>Total lipid content</th><th>anti-DP</th><th>syn-DP</th><th>DEC-602</th><th>DEC-603</th><th>ΣDECs</th><th>anti-Cl<sub>11</sub>-DP</th><th>3-CCZ</th><th>3,6-CCZ</th><th>methyl-triclosan</th></tr></thead><tbody><tr><td rowspan="2">2000<br>(n=3)</td><td>52-75</td><td>0.047-0.292</td><td>&lt;LOQ-0.146</td><td>1.97-6.37</td><td>0.115-0.719</td><td>2.13-7.52</td><td>0.015-0.097</td><td>&lt;LOQ-0.026</td><td>0.072-0.196</td><td>0.098-0.258</td></tr><tr><td>63 ± 12</td><td>0.130 ± 0.140</td><td>--</td><td>3.83 ± 2.27</td><td>0.345 ± 0.327</td><td>4.37 ± 2.81</td><td>0.043 ± 0.046</td><td>--</td><td>0.135 ± 0.062</td><td>0.167 ± 0.082</td></tr><tr><td rowspan="2">2005-2009<br>(n=18)</td><td>42-84</td><td>&lt;LOQ-0.453</td><td>&lt;LOQ-0.269</td><td>0.952-23.56</td><td>&lt;LOQ-3.31</td><td>0.970-25.92</td><td>&lt;LOQ-0.171</td><td>&lt;LOQ-0.126</td><td>&lt;LOQ-0.874</td><td>&lt;LOQ-0.965</td></tr><tr><td>72 ± 9</td><td>0.194 ± 0.154</td><td>0.126 ± 0.091</td><td>5.61 ± 7.36</td><td>0.636 ± 1.032</td><td>6.32 ± 8.50</td><td>0.041 ± 0.047</td><td>0.062 ± 0.047</td><td>0.228 ± 0.243</td><td>0.323 ± 0.220</td></tr><tr><td rowspan="2">2020-2023<br>(n=24)</td><td>49-84</td><td>&lt;LOQ-0.495</td><td>&lt;LOQ-0.385</td><td>0.669-11.91</td><td>&lt;LOQ-0.896</td><td>0.716-12.51</td><td>&lt;LOQ-0.076</td><td>&lt;LOQ-0.051</td><td>&lt;LOQ-0.577</td><td>&lt;LOQ-0.099</td></tr><tr><td>71 ± 7</td><td>0.110 ± 0.110</td><td>0.099 ± 0.095</td><td>2.93 ± 2.54</td><td>0.296 ± 0.195</td><td>3.35 ± 2.75</td><td>0.029 ± 0.021</td><td>0.026 ± 0.010</td><td>0.209 ± 0.111</td><td>0.046 ± 0.027</td></tr><tr><td rowspan="2">All periods<br>(n=45)</td><td>42-84</td><td>&lt;LOQ-0.495</td><td>&lt;LOQ-0.385</td><td>0.669-23.56</td><td>&lt;LOQ-3.31</td><td>0.716-25.92</td><td>&lt;LOQ-0.171</td><td>&lt;LOQ-0.126</td><td>&lt;LOQ-0.874</td><td>&lt;LOQ-0.965</td></tr><tr><td>71 ± 8</td><td>0.135 ± 0.127</td><td>0.107 ± 0.090</td><td>4.06 ± 5.12</td><td>0.432 ± 0.673</td><td>4.60 ± 5.86</td><td>0.034 ± 0.034</td><td>0.039 ± 0.032</td><td>0.212 ± 0.172</td><td>0.183 ± 0.201</td></tr><tr><td>Quantification frequency</td><td>--</td><td>64</td><td>58</td><td>100</td><td>91</td><td>--</td><td>80</td><td>31</td><td>96</td><td>78</td></tr></tbody></table>
<table><caption>Table 2. (cont.)</caption><thead><tr><th>Sampling time</th><th>TBA</th><th>MeO-BDE-47</th><th>MeO-BDE-68</th></tr></thead><tbody><tr><td>2000<br>(n=3)</td><td>0.447-1.22<br>0.759 ± 0.404</td><td>51.4-156<br>102 ± 52</td><td>13.5-33.2<br>22.3 ± 10.0</td></tr><tr><td>2005-2009<br>(n=18)</td><td>0.260-3.47<br>1.19 ± 0.89</td><td>88.9-370<br>181 ± 81</td><td>19.1-209<br>56.7 ± 45.7</td></tr><tr><td>2020-2023<br>(n=24)</td><td>0.133-4.01<br>1.92 ± 1.07</td><td>123-1000<br>328 ± 204</td><td>23.9-180<br>82.0 ± 42.2</td></tr><tr><td>All periods<br>(n=45)</td><td>0.133-4.01<br>1.55 ± 1.04</td><td>51.4-1000<br>254 ± 176</td><td>13.5-209<br>67.9 ± 45.2</td></tr><tr><td>Quantification<br>frequency</td><td>100</td><td>100</td><td>100</td></tr></tbody></table>
<table><caption>Table 3. Total lipid content (% ww), CEC and HNP concentrations (ng g⁻¹ lw), and quantification frequency (%), in whole bodies of small pelagic fishes collected from the Bay of Biscay in February 2023. na : not analysed. The fish standard length (in cm) minimum (min), maximum (max), mean and standard deviation (sd) are given.</caption><thead><tr><th></th><th>Standard length<br>min-max / mean ± sd</th><th>Total lipid<br>content</th><th>anti-DP</th><th>syn-DP</th><th>DEC-602</th><th>DEC-603</th><th>ΣDECs</th><th>anti-Cl<sub>11</sub>-DP</th><th>methyl-triclosan</th></tr></thead><tbody><tr><td rowspan="3">Engraulis encrasicolus</td><td>7.0-8.1 / 7.4 ± 0.4</td><td>1.53</td><td>0.189</td><td>0.249</td><td>0.226</td><td>0.399</td><td>1.06</td><td>0.011</td><td>0.053</td></tr><tr><td>8-9.6 / 9.0 ± 0.5</td><td>2.20</td><td>0.091</td><td>0.136</td><td>0.116</td><td>0.197</td><td>0.541</td><td>0.006</td><td>0.124</td></tr><tr><td>10.0-10.5 / 10.2 ± 0.3</td><td>1.67</td><td>0.137</td><td>0.185</td><td>0.230</td><td>0.320</td><td>0.871</td><td>0.009</td><td>0.145</td></tr><tr><td rowspan="2">Sardina pilchardus</td><td>8.4-9.06 / 9.1 ± 0.5</td><td>0.99</td><td>0.265</td><td>0.610</td><td>0.737</td><td>0.743</td><td>2.36</td><td>0.021</td><td>0.024</td></tr><tr><td>14.2-16.5 / 15.4 ± 1.1</td><td>1.84</td><td>0.119</td><td>0.123</td><td>0.402</td><td>0.343</td><td>0.987</td><td>0.011</td><td>0.120</td></tr><tr><td>Sprattus sprattus</td><td>8.5-10.3 / 9.0 ± 0.6</td><td>1.26</td><td>0.197</td><td>0.370</td><td>0.775</td><td>0.760</td><td>2.10</td><td>0.012</td><td>0.012</td></tr><tr><td>Quantification frequency</td><td>--</td><td>--</td><td>100</td><td>100</td><td>100</td><td>100</td><td>--</td><td>100</td><td>100</td></tr></tbody></table>

<table><caption>Table 3. (cont.)</caption><thead><tr><th></th><th>3-CCZ</th><th>3,6-CCZ</th><th>1,3,6,8-CCZ</th><th>1,3,6,8-BCZ</th><th>TBA</th><th>TBP</th><th>DBP</th><th>MeO-BDE-47</th><th>MeO-BDE-68</th></tr></thead><tbody><tr><td rowspan="3">Engraulis encrasicolus</td><td>&lt;LOQ</td><td>0.156</td><td>0.075</td><td>0.124</td><td>1.49</td><td>10.06</td><td>23.69</td><td>45.7</td><td>5.56</td></tr><tr><td>0.026</td><td>0.105</td><td>0.035</td><td>0.178</td><td>2.97</td><td>9.41</td><td>45.86</td><td>57.8</td><td>6.93</td></tr><tr><td>0.032</td><td>0.174</td><td>0.044</td><td>0.197</td><td>2.75</td><td>10.44</td><td>47.05</td><td>78.5</td><td>11.03</td></tr><tr><td rowspan="2">Sardina pilchardus</td><td>0.097</td><td>0.377</td><td>0.071</td><td>0.253</td><td>0.811</td><td>50.59</td><td>80.58</td><td>23.7</td><td>9.86</td></tr><tr><td>0.039</td><td>0.196</td><td>0.063</td><td>0.436</td><td>1.92</td><td>26.59</td><td>25.34</td><td>29.6</td><td>27.87</td></tr><tr><td>Sprattus sprattus</td><td>0.057</td><td>0.254</td><td>0.024</td><td>0.193</td><td>1.62</td><td>14.68</td><td>8.47</td><td>187</td><td>139</td></tr><tr><td>Quantification frequency</td><td>83</td><td>100</td><td>100</td><td>100</td><td>100</td><td>na</td><td>na</td><td>100</td><td>100</td></tr></tbody></table>
<figure><img src="image_5.png" /><figcaption>Figure 1.</figcaption></figure>

<figure><img src="image_6.png" /></figure>
<figure><img src="image_7.png" /><figcaption>Figure 2.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Figure 3.</figcaption></figure>
## Highlights

- DEC-602 was the major dechlorane-related compound in dolphins' blubber.

- Alternative brominated flame retardants were not detected in dolphins' blubber.

- DEC-602 and *anti*-Cl₁₁-DP were the only biomagnified contaminants.

- Stable levels of most contaminants of emerging concern over the last two decades.

- Halogenated natural products exhibited increasing concentrations from 2000 to 2023.
**Declaration of interests**

[x] The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

[ ] The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

<figure><img src="image_9.png" /></figure>