M L Pedrotti

S Petit

B Eyheraguibel

M E Kerros

A Elineau

J F Ghiglione

J F Loret

A Rostan

G Gorsky

S Petit Ae

Pollution by anthropogenic microfibers in North-West Mediterranean Sea and efficiency of microfiber removal by a wastewater treatment plant

Keywords: Microplastic, microfibers, airborne, wastewater treatment plant, urban environment, Mediterranean Sea

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

It is estimated that 8300 million metric tons (Mt) of virgin plastic have been produced since the 1950s and production is expected to increase by 4% per year [START_REF] Geyer | Production, use, and fate of all plastics ever made[END_REF], Plastic Europe 2018). In 2010, poor household or municipal waste management generated 5 to 13 million tons of plastic waste in the oceans [START_REF] Jambeck | Plastic waste inputs from land into the ocean[END_REF]. Dumped or transported by sewage, rivers or tides, or simply by wind or urban surface runoff, about 80% of ocean plastic leakage comes from land-based sources [START_REF] Andrady | Microplastics in the marine environment[END_REF][START_REF] Lebreton | River plastic emissions to the world's oceans[END_REF].

According to the latest estimates, at least 5,000 billion particles of plastic debris weighing 268,940 tons are currently floating in the oceans, with microplastics accounting for 92.4% of the total number of particles (Cozar et al., 2014;[START_REF] Eriksen | Plastic pollution in the world's oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea[END_REF]. However, these estimates, based on currently used sampling methods (using a Manta or Neuston net with a mesh size of 333 mm), underestimate the true concentrations of microplastics because they do not account for the smaller particles and microfibers from synthetic textiles [START_REF] Conkle | Are we underestimating microplastic contamination in aquatic environments?[END_REF]. Recent studies suggest that smaller plastics (<0.3 mm) are 5 to 7 orders of magnitude higher than microplastic concentrations between 0.3 and 5 mm (Brandon et al., 2019). Synthetic MFs can be considered a distinct category of microplastics because of their ubiquitous distribution, commonly found in aquatic and terrestrial environments, in human skin, as well as component of air pollution, occurring mainly as fibrous particles in dust and in the atmosphere [START_REF] Browne | Accumulation of microplastic on shorelines worldwide: sources and sinks[END_REF][START_REF] Dris | Synthetic fibers in atmospheric fallout: A source of microplastics in the environment?[END_REF]. They are suspected to be a major contributor to plastic pollution at sea and are observed in higher concentrations than granules or fragments [START_REF] Gago | Synthetic microfibers in the marine environment: A review on their occurrence in seawater and sediments[END_REF]. The textile industry is of great economic importance, with 65 million tons of plastic used for the production of textile fibers in 2016 with polyester, polyamide, acrylic and polyolefin being the most common (The Fiber Year, 2017). MFs are not exclusively synthetic polymers such as nylon, polyester or polypropylene, but include also natural (cotton, wood, yarn) and artificial fibers (rayon, viscose, cellulose acetate) [START_REF] Houck | Identification of Textile Fibres[END_REF]. Their release into the environment, whether of synthetic or natural materials, has become an emerging pollution concern [START_REF] Barrows | Marine environment microfiber contamination: global patterns and the diversity of microparticle origins[END_REF][START_REF] Suaria | Microfibers in oceanic surface waters: a global characterization[END_REF].

MFs entering the environment through urban runoff or discharged from textiles and transported by wastewater to coastal zones are considered as major sources of microplastics [START_REF] Browne | Accumulation of microplastic on shorelines worldwide: sources and sinks[END_REF][START_REF] Almroth | Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment[END_REF][START_REF] Galafassi | Plastic sources: a survey across scientific and grey literature for their inventory and relative contribution to microplastics pollution in natural environments, with an emphasis on surface water[END_REF]. Wastewater treatment plants (WWTP) are effective waste management infrastructures and a strategic tool to combat marine pollution. However, according to the literature, even in high-income countries, not all MFs are retained by sewage treatment and large quantities are found both near the coasts and in the open sea [START_REF] Van Cauwenberghe | Microplastic pollution in deep-sea sediments[END_REF][START_REF] Thompson | Lost at sea: where is all the plastic?[END_REF][START_REF] Yu | Occurrence and distribution of microplastics at selected coastal sites along the southeastern United States[END_REF]. Also, recent studies show that atmospheric deposition may also play an important role in the delivery of MFs to the marine environment [START_REF] Enyoh | Airborne microplastics: a review study on method for analysis, occurrence, movement and risks[END_REF][START_REF] Windsor | A catchment-scale perspective of plastic pollution[END_REF][START_REF] Allen | Atmospheric transport and deposition of microplastics in a remote mountain catchment[END_REF].

Like other types of microplastics, MFs are vectors for contaminants, absorbing persistent organic pollutants (POPs) such as hydrocarbons and polychlorinated biphenyl PCBs and releasing chemical additives into the environment and/or into the organisms that ingest them with multiple unknown consequences for animal and human health (Teuten et al., 2009, Hüffer and[START_REF] Hüffer | Sorption of non-polar organic compounds by micro-sized plastic particles in aqueous solution[END_REF][START_REF] Baini | First detection of seven phthalate esters (PAEs) as plastic tracers in superficial neustonic/planktonic samples and cetacean blubber[END_REF]. In addition, the ingestion of MFs by marine life leads to physical and chemical damage such as internal abrasions or disruption of the digestive system, reduced growth and reproduction. [START_REF] Derraik | The pollution of the marine environment by plastic debris: a review[END_REF][START_REF] Moore | Synthetic polymers in the marine environment: a rapidly increasing, long-term threat[END_REF][START_REF] Mathalon | Microplastic fibers in the intertidal ecosystem surrounding Halifax Harbor, Nova Scotia[END_REF]Galloway andLewis, 2016, Torre et al., 2016). With respect to human exposure to microplastics, the main routes suggested are ingestion and inhalation [START_REF] Smith | Microplastics in seafood and the implications for human health[END_REF], with ingestion being low compared to exposure via atmospheric deposition of household fibers [START_REF] Catarino | Low levels of microplastics (MP) in wild mussels indicate that MP ingestion by humans is minimal compared to exposure via household fibres fallout during a meal[END_REF].

Due to the high risk of contamination during sampling and laboratory processing, fibers are often excluded from microplastic analyses [START_REF] Foekema | Plastic in North Sea Fish[END_REF], Woodall et al., 2016;[START_REF] Torre | Anthropogenic microfibers pollution in marine biota. A new and simple methodology to minimize airborne contamination[END_REF]. In addition, in the majority of studies, fibers are not sampled due to the difficulty of collecting them or their abundance is underestimated by the use of large mesh size nets [START_REF] Gago | Synthetic microfibers in the marine environment: A review on their occurrence in seawater and sediments[END_REF].

To date, few studies have been conducted on the impact of microfibers in various environments (Driss et al., 2015[START_REF] Gago | Synthetic microfibers in the marine environment: A review on their occurrence in seawater and sediments[END_REF][START_REF] Stanton | Freshwater and airborne textile fibre populations are dominated by 'natural', not microplastic, fibres[END_REF]. Here we report on a comprehensive and systematic survey of the occurrence of synthetic MFs in an urban area and in the surface waters of the northwestern Mediterranean, one of the most polluted seas with highly variable concentrations of plastic [START_REF] Kaandorp | Closing the Mediterranean marine floating plastic mass budget: inverse modeling of sources and sinks[END_REF][START_REF] Llorca | Microplastics in Mediterranean coastal area: toxicity and impact for the environment and human health[END_REF]. We have established methods and quantified synthetic MFs in the air, production by domestic washing machines, at the inlet and outlet of the Haliotis wastewater treatment plant in Nice (Provence Alpes Côte-d'Azur, France) and concentrations in coastal and offshore areas. This research aims to enrich existing knowledge on the sources and transport of these polymers into the marine environment. This is of paramount importance for the application of preventive and corrective solutions for European citizens, communities and industries [START_REF] Carr | Sources and dispersive modes of micro-fibers in the environment[END_REF].

Material and methods

Minimize microfiber contamination

To minimize the amount of contamination in our samples a quality control approach was undertaken according to the protocol previously described by Woodall and colleagues (2015) and Dris and colleagues (2016). First of all, to collect and process the samples, plastic material has been replaced by glass or stainless-steel material except for a 50-liter Nalgene cylinder and a 500-ml Nalgene pressure bottle due to technical constraints or safety at sea. For each in situ sampling site or laboratory experiment, clean material was used, previously washed with alkaline and acidic detergents and rinsed three times before each handling with 0.2 µm (1.8 Ohm, Merck Millipore, Germany) milli-Q microfiltered water. A cotton coat was worn during sampling and further processing. During the automated sampling of waste and treated water, the samples remained in contact with the ambient air for 24 h. To account this potential source of contamination, a control consisting of 2 L of milli-Q water was maintained in the autosamplers for the same period in all experiments and then filtered through a cellulose acetate filter (Whatman®). During sample collection and laboratory analysis an ambient air blank was made by placing wet GF/F glass microfiber filter (Whatman®) in a clean 47 mm glass Petri dish kept open during the whole experiment. Finally, on the laboratory bench, blanks were also used to control all materials and fluids used for microfiber quantification. For this purpose, 300 mL of milli-Q water were passed through the equipment used and filtered through a cellulose acetate filter (Whatman®). The controls were examined using the same procedure as for the experimental samples and the count values were systematically removed from the calculated MFs results.

Sources, Sites and sampling procedures

Production of MFs by domestic washing machines

A Miele Pro WS5425 domestic washing machine was used to quantify the release of synthetic MFs into wastewater. To be as close as possible to actual washing conditions, a commercial detergent was used. The washing program used was a "delicate synthetic" cycle at 30 °C for 40 min with a spin speed of 600/800 rpm. The effluent was recovered at the machine outlet pipe in two 50 L Nalgene jerrycans (Dutscher, France). Seven runs of washes were carried out with different clothing compositions ranging from 100% synthetic to a mixture of natural, artificial and synthetic textiles (Table S1). For each wash, the composition and weight of the garments were recorded and 70 L of wash was collected and sieved through a stainless-steel sieve of porosity 20 μm. In order to minimize MFs contamination remaining from previous washes, five rinse and drain cycles at 600/800 rpm of 15 min each were performed without clothes at the beginning of the experiment and two cycles between washing experiments. This is based on preliminary tests which have shown that from 2 rinses onwards, the number of fibers is reduced by a factor of 10 and that this number remains constant.

These concentrated MFs issue from the washing and rinsing experiments were recovered with 75 to 575 ml of 0.2 μm milli-Q water (Merck Millipore, Germany) and stored in amber glass bottles until analysis. When the results were calculated, the remaining fiber contamination between two runs was subtracted from the next washing experiment. The diversity of natural and synthetic fibers allowed us to build a library of MFs for further analyses.

Air compartment

The number of MFs in aerosols was estimated by collecting atmospheric particles at two sampling sites (Fig. 1): A) at Saint Jean Cap Ferrat (locality with 1645 inhabitants), using the

Atmospheric platform of the French national program MOOSE (Mediterranean Ocean

Observing System for the Environment). Three experiments were conducted in June 2014 with a sampling period ranging from 6 to 11 days depending on prevailing weather conditions. The mean aerosol volume of 393m 3 with the atmospheric particles was filtered through cellulose acetate filters (Sartorius SM 11106, porosity 0.45 μm, diameter 47 mm) using a Central Partisol 2000 air sampler configured for PM10 sampling. In the site B, located on the rooftop of Haliotis treatment plant (Nice, a city of 377,328 inhabitants), two experiments were conducted in May 2016, the atmospheric particles (mean aerosol volume of 109 m 3 ) were filtered with a cellulose acetate filter (Whatman®, porosity 0.45 μm and diameter 47 mm) using a sampling system consisting of a vacuum pump and a filter holder placed 2.5 meters high on the roof of the treatment plant. At the same time, the atmospheric deposition of MFs was measured by recovering all synthetic particles and MFs adhering to the funnel [START_REF] Dris | Synthetic fibers in atmospheric fallout: A source of microplastics in the environment?[END_REF]. For this purpose, a stainless-steel funnel (0.0735 m²) was placed on top of a 15 L stainless steel bucket. Samples were collected during 4-6 days and then filtered through cellulose acetate filters with a porosity of 0.45 μm.

Urban and treated wastewaters

The Nice Haliotis WWTP processes 120,000 m 3 of wastewater per day and discharges its effluent into the Mediterranean Sea, 1.2 km from coast and at 100 meters depth. The treatment includes a pre-treatment unit (screening, removal of gravel and oils), primary treatment (sieving and lamellar settling), biological treatment (activated sludge), sludge treatment, the offshore pumping station and an air treatment unit.

In order to establish the sampling protocol, preliminary tests for the detection and analysis of MFs were conducted from December 2013 to March 2014 at the Haliotis WWTP. Subsequently, seasonal monitoring was carried out from March to November 2014 and six sampling campaigns of 3 days each were conducted. For each campaign, three replicate samples of 2 L of water were taken, with a sampling frequency of 1 hour, using an autosampler that provided a 24-hour average sample. At the inlet of the treatment plant the samples were taken after the pre-treatment unit, at the outlet the treated water was sampled after the clarifier (Fig. S1). A total of 36 samples were collected and sieved through a stainless-steel sieve of porosity 20 μm and stored at + 4 °C in amber bottles until their analysis. In order to evaluate the physical and environmental parameters that may influence the efficiency of microfiber treatment, the concentration of suspended solids (according to the European standard NF EN 872), the flow rates of the treatment plants and precipitation events were recorded.

In situ surface sampling in the Mediterranean Sea

A field survey was conducted from February to October 2014 in the northwestern Mediterranean Sea. A total of 15 sites were sampled and 34 water samples were taken (Fig. 1). Seven sites were seasonally monitored in spring, summer and fall with the RV The Alchemy, an 11m long sailing ship. First, a grid of 5 sampling points was set-up in the vicinity of the Haliotis WWTP, upstream and downstream of the outfall. Second, sampling was undertaken at Point B (permanent stations at the entrance of the Bay of Villefranche-sur-Mer) where surface and 10m depth samples were collected. Third, we sampled the offshore permanent sampling site called Dyfamed (42.6 Km offshore from Villefranche). The two permanent stations are characterized by low anthropogenic contamination (for more details see: https://www.imev-mer.fr/web/). The other 8 sites were sampled with the RV Tara a 36 m long oceanographic schooner in summer in the coastal zones of French Riviera, near Bastia and Calvi (Corsica) and in the Bay of Naples (Italy) during the Tara Mediterranean expedition (https://oceans.taraexpeditions.org/en/tara-mediterranee-expedition/). While sampling the Ligurian Sea, Tara sampled also the Pt. B and Dyfamed stations. Surface samples were collected using a stainless-steel bucket held by a sheathed steel wire.

To minimize contamination, all equipment was rinsed three times at each point with the sampled water. At each station fifty liters of surface seawater were collected. For the 10m depth seasonal samples at Pt. B, a 10 L Niskin bottle was used. On the boat, the samples were filtered through the stainless-steel sieve 20 μm and resuspended in 200 mL of 0.2 μm filtered seawater, stored at + 4 °C in amber bottles until their analysis.

Detection and quantification of synthetic MFs

Sample preparation for analysis

Digestion protocols were either inefficient or damaged the MFs structures at the time of the study ( 2014), therefore we decided to use a dilution protocol. Preliminary tests were performed to evaluate the filtered aliquots used for each experiment to avoid clogging the filters and to ensure that sufficient material was present and that organic material did not affect the Fourier Transform Infrared Spectroscopy analysis (FTIR) analysis. The filtered volumes for the washing experiment were 750 ml, for wastewater (inlet) and treated water (outlet) 125 ml and 500 ml respectively, and for seawater 6.25 L of surface water. All filters showed a considerable amount of fibers. With exception of the inlet, FTIR analysis was performed at all the different steps of water treatment.

In the laboratory, samples were filtered by vacuum filtration in duplicate on a 0.2 μm Anodisc membrane (aluminum oxide, 47 mm). Control and experimental fibers were counted by the same individual under a stereo microscope (Olympus SZX10, X4.725 -X94.5) after filters being placed in a Dollfus cell (with 200 squares of 25 mm²). For the control, aerosol and outlet samples the totality of the filters was counted. For the washing machine experiments, half of the filters (100 squares) were randomly counted (median 3906; min 2000; max 5164). For the inlet and seawater samples at least 100 squares were randomly counted in order to have a minimum of 40 fibers in each filter (median 60; min 40; max 260).

Visual observation, size measurements and FTIR analysis

Visual characterization of the fibers was performed using a stereomicroscope coupled with polarized light to improve the efficiency of fiber identification [START_REF] Santana | Microplastic contamination in natural mussel beds from a Brazilian urbanized coastal region: rapid evaluation through bioassessment[END_REF].

The following criteria were used to classify synthetic fibers: the absence of cellular structures and scales on the surface, a uniform surface, the presence of equal thickness along its entire length, curved shape, coloration and solid strands [START_REF] Hidalgo-Ruz | Microplastics in the marine environment: a review of the methods used for identification and quantification[END_REF][START_REF] Wright | The physical impacts of microplastics on marine organisms: a review[END_REF][START_REF] Barrows | Marine environment microfiber contamination: global patterns and the diversity of microparticle origins[END_REF]. The visual characterization of fibers is still an important tool given the considerable limitation of the use of FTIR spectroscopy for the analysis of textile fibers [START_REF] Stanton | Freshwater and airborne textile fibre populations are dominated by 'natural', not microplastic, fibres[END_REF]. We have taken great care to avoid the overestimation of synthetic microfibers, therefore, we also analyzed images from the different washing experiments to distinguish between synthetic and non-synthetic fibers. All samples and particles that did not matched the above criteria were not considered as microplastics (about 40-60%) and were discarded from data analyzes. Consequently, in this study abundance and size measurement are then given only for the synthetic microfibers (MFs).

Size measurements were carried out in a subset of the samples. For each filter 200 images were made corresponding to the Dollfus cell squares and the synthetic fibers that followed the above criteria were selected and the length was analyzed using ImageJ v.1.5 software (Schneider et al., 2012). A total of 2673 MF was measured.

In order to validate the visual identification of MFs the chemical analysis of a subsample of particles was conducted by FTIR. Analyses were carried out using a Nicolet ™ iN10 MX infrared imaging microscope (ThermoFisher Scientific) to locate MFs on filters and obtain their IR spectrum. To screen the filters within a reasonable time and obtain a representative distribution of chemical nature of fibers, the number of MFs to be analyzed was determined using calculation methods developed by [START_REF] Kedzierski | Microplastics in Mediterranean Sea: a protocol to robustly assess contamination characteristics[END_REF]. Considering the heterogeneity in the total numbers of fibers between samples, the minimum number of fibers to be analyzed for each sample was defined to reach at least 15% of confidence interval. MFs were randomly picked on the filters and analyzed by FTIR.

The analyses were performed with a variable aperture adapted to the size of each fiber, on MFs up to a diameter of 5 μm and on surfaces up to 300 μm 2 (60 μm long). To improve the contact with the fiber and to optimize the acquisition of the FTIR signal, the spectra were collected in ATR (attenuated total reflectance) mode using 16 scans of 4000 cm -1 at 400 cm -1 , with a resolution of 4 cm -1 . Spectra processing and fiber identification was performed using Omnic TM Specta software (ThermoFisher Scientific) to characterize the proportion of synthetic and natural MFs and to assess the predominant polymers. An automated baseline correction was performed on each spectrum and the corrected spectra were compared with 2 different polymer libraries: a commercial database (Hummel polymers library) and an open access polymer database published by [START_REF] Primpke | Reference database design for the automated analysis of microplastic samples based on Fourier transform infrared (FTIR) spectroscopy[END_REF]. The hit quality index for identification of fibers was set at 70%. Indeed, the use of a single commercial polymer database (Hummel polymer and additives) can provide low matching scores or inaccurate identification. The comparison with a second library containing spectra from a wider type of component based on polymers, plant types and animal furs and considering the oxidized nature of environmental samples clearly improved the identification of the nature of the MFs [START_REF] Primpke | Reference database design for the automated analysis of microplastic samples based on Fourier transform infrared (FTIR) spectroscopy[END_REF].

Manual assessment was performed to refine the chemical identification when the spectrum signal lacked intensity and provided a low matching score with the libraries.

Characteristic absorption bands of reference synthetic polymers were sought in the sample spectra. The polymer identification was validated using a minimum of four matching absorption bands [START_REF] Jung | Validation of ATR FT-IR to identify polymers of plastic marine debris, including those ingested by marine organisms[END_REF].

As commonly observed in other studies, the shape, length and positioning of the MFs do not always allow the acquisition of accurate and intense IR spectra (Mintening et al., 2017).

The small diameters of the MFs made it impossible to target a zone of analysis restricted to the fiber, which complicated the acquisition of the spectrum. Indeed, it is difficult to go below a filter surface of 225 square microns (e.g., MFs of 15 x 15 microns) and obtain an easily identifiable spectrum for MFs smaller than 15µm in diameter. In addition, the fiber configuration and 3D positioning on the filter surface did not always allow analysis on the same focal plane, which limited the recorded signal and did not allow the acquisition of spectra by automatic methods. Therefore, the acquisition of spectra was performed individually, fiber by fiber, on subsamples with a total of 104 fibers out of 295 analyzed.

Statistical Analyses

Statistical analysis were performed using the statistical software R-v.2.15.0 (R Development Core Team, 2009). The Kruskal-Wallis (KW) was used to test the significance in MFs concentrations as a function of season and sampling locations. The Spearman correlation test was performed to study the correlation between the amount of MFs by season, between MFs and suspended solids, and between the amount of MFs and distance to land.

One-Way ANOVA was used to verify significant differences in MFs size among samples as data were normal distributed (Shapiro-Wilk normality test; W = 0.99 to 0.98) and the Tukey 14 HSD test analyses were applied. The statistical significance threshold was set at a p-value of 0.05.

Results and discussion

Contamination control

The number of MFs observed in the laboratory blank control ranged from 2 to 14 items per filter analyzed. The average contamination observed in fluids passing through the experimental devices was 6.3 ± 4.6 MFs L -1 . The air checks carried out over 24 hours using automatic samplers placed at the inlet and outlet of the Haliotis plant gave an average contamination of 15.6 ± 9.4 MFs L -1 (Table 1A). These high values compared to laboratory controls are probably due to the fact that the samples are exposed to the air for a longer period of time. The resulted blank data were systematic subtracted from the respective results.

Overall, blank test results indicate that contamination can be a significant source of error (14% median value). This underlines the importance of a correct evaluation of the sources of contamination in order to better take into account this category in routine microplastic analysis. In order to correctly determine the distribution and occurrence of LF, systematic quality control must be performed during sampling and processing and taken into consideration when processing the data.

Microfiber characterization

The FTIR fiber analysis of textile washes considered 100% synthetic showed that 17.4% of the microfibers were natural or derived from the transformation of natural polymers.

Although this percentage is related to the number of fibers identified as synthetic/natural in the set of fibers analyzed, we can conclude that significant contamination by non-synthetic fibers may occur during the analyses. At the end of the treatment process of the Haliotis plant due to the high removal efficiency, we were unable to identify the plastic polymers, probably due to the small number of MFs observed on the filters. A cross-check of airborne contamination suggests that values were below 10 3 MFs per cubic meter and near the detection limit. Nevertheless, we kept the estimates from microscope counts, knowing that this could create a potential underestimate of the non-synthetic microfibers, which were not fully classified in the initial analysis.

In the marine samples, the overall results showed that 14-50% of the raw materials analyzed were synthetic, with the highest rate observed in surface waters at the Haliotis outfall site. The remaining 35-72% are of natural origin (cotton, wool) or made by processing natural polymers (especially cellulose) and the rest are a mixture of different materials or could not be identified (14-21%) as explained above (Table 2; Table S2). This is slightly higher than the results of textile production, where more than half of the world's production is based on plastic polymers with about 49% of the world's clothing is made of polyester [START_REF] Sundt | Sources of Microplastic-pollution to the Marine Environment. Mepex Report M-321 commissioned[END_REF]. The relative high presence of natural fibers is consistent with the results obtained by [START_REF] Suaria | Microfibers in oceanic surface waters: a global characterization[END_REF] who found high proportion of animal-and plant-based fibers throughout world's oceans with values of 6.8% for the Mediterranean Sea. Although, compared to our results this estimate is lower. Among synthetic fibers, polyamide (30%) and polyester (22%) are the most important polymers in urban wastewater and it should be noted that this material is also predominant in offshore sites with polyester reaching 62% at the Dyfamed site where the anthropogenic impact should be reduced. The first observations concerning the characterization of microplastics at the outlet of wastewater treatment plants have shown that polyester fibers are the main source of contamination and contribute to environmental pollution to a larger extent than microplastics resulting from fragmentation of larger plastics [START_REF] Napper | Release of synthetic microplastic plastic fibres from domestic washing machines: Effects of fabric type and washing conditions[END_REF]. This is probably because of its low cost and versatile use. Indeed, polyester are the most widely used and the dominant types of polymer clothing including high-performance outdoor wear but also in-home furnishings, and as a reinforcing fiber in tires, belts, and hoses (IEEE GlobalSpec, 2019). Polyamide density ranges from 1.02 to 1.15 g cm -3 (Hidalgo-Ruz et al., 2012) so we can expect that only less dense PA could float explaining the lower concentration of this polymer in seawater [START_REF] Reisser | Marine plastic pollution in waters around Australia: characteristics, concentrations, and pathways[END_REF], Cozar et al., 2014). However, the higher density of Mediterranean waters (usually > 1.026 g cm -3 ) could also explain the relatively high proportion of polyamide found in its surface waters [START_REF] Pedrotti | Changes in the floating plastic pollution of the Mediterranean Sea in relation to the distance to Land[END_REF]. Polypropylene, polystyrene and polyvinyl chloride were only found at the Haliotis outfall site, while polyvinyl acetate was only found at the Point B station. Polyvinyl acetate is known as a major constituent of fishing nets and nets are widely used in the region.

In our samples, we were able to identify several types of synthetic MFs representing up to fifty percent of total fibers collected. We also showed that un important fraction of fibers is from natural origin (35-72%). The most striking results showed the presence not only of polyester and polyamide, but also of polypropylene and acrylic MFs, albeit in smaller quantity. Further studies should include size and shape for characterization of MFs in air and seawater and improve the spectral intensity and resolution of the analysis down to small size in order to understand their sources, transfers and persistence in the environment.

MFs measurement in the different compartments

The majority of the synthetic fibers collected in this study are sub-millimetric in size.

The overall length distribution is asymmetric with a fiber frequency increase with decreasing length suggesting the presence of shorter fibers (Fig. 2). The lower size limit of MFs analyzed is 25 µm in aerosols samples and washing machine samples and maximum values 7240 µm are detected in washing machine experiments. In the marine compartment, the length of the marine MFs, irrespective of the location (coastal stations, Pt. B and offshore Dyfamed), was not significantly different (F 0.25; p > 0.8) and were pooled together for further analyses. Comparison of MFs length revealed significant differences between different environments sampled (air, washing machine, WWTP outlet and marine, ANOVA; p = 0.0001) (Table S3). The smaller size length was observed in aerosols (median 83µm) with predominant fibers lengths of 50-200 µm (75%) suggesting different sources than the other compartments (Fig. 2). A similar distribution was found for total atmospheric deposition fibers [START_REF] Dris | Synthetic fibers in atmospheric fallout: A source of microplastics in the environment?[END_REF][START_REF] Dris | A first overview of textile fibers, including microplastics, in indoor and outdoor environments[END_REF]. This suggests that smaller microplastics may persist and be transported in the atmosphere, deposited or inhaled continuously, with potential long-term threats to ecosystems and human health [START_REF] Gasperi | Microplastics in air: are we breathing it in?[END_REF][START_REF] Allen | Atmospheric transport and deposition of microplastics in a remote mountain catchment[END_REF], Lui et. al., 2019). The median length of MFs collected in the washing machine and in the outlet of the WWTP are respectively 287 and 364 µm. The length of synthetic fibers released during washing experiments depends on the fiber type and fabric characteristics, in the washing experiments [START_REF] Napper | Release of synthetic microplastic plastic fibres from domestic washing machines: Effects of fabric type and washing conditions[END_REF] found longer lengths for polyester, polyester/cotton blend and acrylic 5.0 to 7.8 mm suggesting differentiated retention in WWTP. This could explain the significant difference between size of MFs transiting in the Haliotis WWTPs. MFs in the marine compartment have median length values of 589 µm and the largest range of size from 56 to 5,263 µm. The predominant fiber length is between 150 and 550 µm (48%). The upper class of MFs (>1000 µm), which is rare in aerosols, in washing machine effluents or at the outlet of sewage treatment plants, indicates a source other than wastewater treatment.

Air compartment

In the aerosol experiments, only fibers dominate the shape of the microplastics (Table 1B).

The aerosol fibers could not be analyzed by FTIR, the results come from visual observations. Their average concentration in the area of Nice was 0.043 ± 0.026 MFs m -3 , while the average concentration in Cap Ferrat, 25 km away, was three times higher (0.140 ± 0.120 MFs m -3 ) although not significantly different. These urban areas are not industrialized nor densely populated and the concentration values obtained are an order of magnitude lower (0.3 and 1.5 fibers m -3 ) than those found in an outdoor area outside from Paris [START_REF] Dris | A first overview of textile fibers, including microplastics, in indoor and outdoor environments[END_REF]. On the other hand, the average atmospheric deposition rate of MFs in Nice (average 392 ± 141 particles m -² day -1 ) is higher than that reported in a densely populated urban area of Paris ( 118and 110 ± 96 m -² day -1 , [START_REF] Dris | Microplastic contamination in an urban area: a case study in Greater Paris[END_REF][START_REF] Dris | Synthetic fibers in atmospheric fallout: A source of microplastics in the environment?[END_REF] and in Dongguan, China (36 ± 7 m -² day -1 , [START_REF] Cai | Characteristic of microplastics in the atmospheric fallout from Dongguan city, China: preliminary research and first evidence[END_REF] and a slightly lower than in the megacity of London (712 ± 162 microplastics m -² day -1 , [START_REF] Wright | Atmospheric microplastic deposition in an urban environment and an evaluation of transport[END_REF]. As in our survey, in all the above-mentioned sites, the fibrous form accounted for the vast majority of microplastics.

Results similar to ours were found in a pristine mountain catchment (French Pyrenees) (365 m ² day -1 , [START_REF] Allen | Atmospheric transport and deposition of microplastics in a remote mountain catchment[END_REF] and in Hambourg metropolitan region (275 microplastics m -² day - 1 ; Klein and Fischer 2019) with the dominant shape of microplastics identified as fragments.

Air mass trajectories and winds were suggested as a possible transport route for microplastics to these sparsely inhabited areas [START_REF] Allen | Atmospheric transport and deposition of microplastics in a remote mountain catchment[END_REF]. The different methodologies used in the previous work as well as the detection of different shapes of particles at different thresholds make comparisons difficult. However, these results suggest that although cities are a source of airborne microplastics, higher population density alone does not seem to explain their abundance of and that factors other than proximity to cities, such as weather and precipitation rates and climate, also play an important role in the transport, dispersion and deposition of MFs in the wider environment [START_REF] Dris | Synthetic fibers in atmospheric fallout: A source of microplastics in the environment?[END_REF][START_REF] Allen | Atmospheric transport and deposition of microplastics in a remote mountain catchment[END_REF].

Data presented here, while corroborating other studies, should be interpreted with caution as only a few experiments were conducted and because fiber identification was based solely on visual inspection giving place to a possible overestimation of synthetic fibers. The transport of urban atmospheric microplastics can be an important pathway for contamination of the marine environment and future research should include this compartment in monitoring activities.

Microfiber release from domestic washing machines

The MFs observed after cleaning the washing machine with two wash cycles before each run represented only 0.3% of the MFs collected from the samples. We can therefore conclude that there is no contamination from the empty machine. Our results showed that during conventional washing, from 3.2 x 10 6 to more than 3.9 x 10 7 MFs per cubic meter (average of 12.8 x 10 6 MFs m -3 ) could be released (Table 3). This corresponds to 3 to 99 fibers per gram of the garments released during washing (Table S1). This clearly indicate that the shedding of fibers from clothing during washing is an important emitter of microplastics. The design of garments, including the type of fabric used, and the washing treatment can significantly affect the amount of fibers released [START_REF] Napper | Release of synthetic microplastic plastic fibres from domestic washing machines: Effects of fabric type and washing conditions[END_REF]De Falco et al., (2019). In addition, the age of the textile can be another factor to consider [START_REF] Hartline | Microfiber masses recovered from conventional machine washing of new or aged garments[END_REF]. Given this diversity, a daily wash was simulated with different types of garments and different load sizes to assess the number of MFs shed in a conventional wash. Our results corroborate reported levels of shedding from fabrics found by [START_REF] Pirc | Emissions of microplastic fibers from microfiber fleece during domestic washing[END_REF] and [START_REF] Almroth | Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment[END_REF] and are higher than those observed by [START_REF] Napper | Release of synthetic microplastic plastic fibres from domestic washing machines: Effects of fabric type and washing conditions[END_REF] who estimate that over 7.0 x 10 5 MFs fibers could be released from an average 6 kg wash load of acrylic fabric. As garments are mixed during most washing experiments, we cannot evaluate the relationship between the type of fabric and the number of MFs released but according to [START_REF] Almroth | Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment[END_REF] no significant difference was found between nylon, acrylic, and polyester knits however these authors found that polyester fleece fabrics release a significantly greater number of fibers than other knits. This corroborates our finding of the two washing experiments using 100% polyester (Table S1); there is an order of magnitude difference between polyester fleece fabrics (R1) compared to the smarter polyester (R2) used for ski jackets and pants.

Our results allow us to estimate the expected concentration of textile microfibers resulting from the washing of clothing conveyed in sewage to and treated in the Haliotis plant in Nice. If we consider a population of 358,000 inhabitants connected to the WWTP and waste water from an average of 0.3 laundries per inhabitant per day (statistics published on www.planetoscope.com) with an average volume of 75 liters of effluent discharged by each machine, the average flow treated by the Haliotis plant per day from the washing machines is approximately 8.1 x 10 3 m 3 . This effluent corresponds to 6% of the average flow treated daily by the Haliotis plant. An average of 1.03 x 10 11 MFs textiles enter the treatment plant daily (min 2.62 x 10 10 ; max 3.19 x 10 11 ). With a daily flow of 120,000 m 3 , we therefore expect an average of 8.58 x 10 5 MF textiles m -3 (min 2.17 x 10 5 ; max 2.66 x 10 6 ) of wastewater entering the Haliotis treatment plant daily (Table 3). MFs disseminated by domestic washing constitute an important part of microplastics in the environment; given the increase in the production and consumption of synthetic textiles, this pollution has become an urgent issue [START_REF] Cesa | Synthetic fibers as microplastics in the marine environment: a review from textile perspective with a focus on domestic washings[END_REF].

Efficiency of the WWTP and estimated discharge of synthetic MFs in the marine environment

Large quantities of MFs were detected at the treatment plant inlet with an average of 5.31

x 10 5 items m -3 . These concentrations are consistent with those estimated from the domestic washing experiments (8.56 x 10 5 MFs m -3 ) validating the consistency of the methodology used (Table 3). At the outlet of the WWTP Haliotis an average concentration of 3.6 x 10 4 synthetic MFs per cubic meter was counted (Min 6 x 10 3 ; Max 6.9 x 10 4 ), (Table 3). The concentration of suspended solids at the inlet of the treatment plant varies from 212 to 293 µg m -3 (average 257.14 ± 24.47 µg m -3 ) and at the outlet from 8 to 30 µg m -3 (17.5 ± 6.8 µg m -3 ), (Table S4). MFs concentrations varies significantly with the amounts of suspended solids in the inlet of the treatment plant (rs = -0.84, p = 0.006) while in the outlet no correlation was observed probably because of the small number of particles. This large variation highlighted that sediments and large particles in wastewater could efficiently aggregate with synthetic MFs and act as a pre-filter in the sewer system. It is assumed that, in rainy weather, this natural elimination of MFs will not occur.

Wastewater treatment plants are thus very effective in removing microplastic particles from the wastewater stream and the Nice Haliotis treatment plant has a significant removal percentage ranging from 87.5%, to 98.5% (average 91.87 ± 5.52%) (Fig. 3). These abatements are in the same range as the WWTP found at the Detroit WWTP (95.6%) [START_REF] Michielssen | Fate of microplastics and other small anthropogenic litter in wastewater treatment plants depends on unit processes employed[END_REF] and at the Glasgow (98.41%) [START_REF] Murphy | Wastewater treatment works as a source of microplastics in the aquatic environment[END_REF] using activated sludge as secondary treatment. We observed a significant seasonal effect (p = 0.003) in the concentration of MFs collected at the inlet of the Haliotis with higher concentrations in early spring (Fig. S2.A). This result is consistent with clothing customs since technical and warmer clothing is mainly made of synthetic and plastic MFs. However, no seasonal differences were detected in the number of synthetic MFs leaving the treatment plant (Fig. S2.B), highlighting the efficiency of treatment and the sensitivity of detection.

Despite the high removal efficiency of the Haliotis plant, based on the large volume of treated wastewater and effluent discharged into surface waters (120,000 m 3 per day), we have estimated that 4.3 billion fibers enter daily the marine environment from the treatment plant. This value is in line with values reported by Michielssen and his colleagues (2016) where 8.9 billion MFs seem to be discharged daily from the Detroit plant. WWTPs are also known sources of microplastics in the freshwater environment, given their incomplete removal during treatment [START_REF] Estahbanati | Influence of wastewater treatment plant discharges on microplastic concentrations in surface water[END_REF]. As machine filters and WWTPs are not specifically designed to retain all fibers, this means that the washing of synthetic garments is likely to be a significant source of fiber to the environment.

Although wastewater treatment plants are effective at removing microfiber particles from the wastewater stream, effluent discharges often contain high concentrations of MFs. These fibers are found in the environment at concentrations of up to thousands of particles per cubic meter, being available to be ingested by a broad range of species. Other problems remain unanswered, as a large proportion of these particles will settle in the sludge, they may become an environmental polluter that should be monitored.

Spatial-temporal patterns of microfiber contamination in surface waters of the

Mediterranean Sea

During the two campaigns from February to October 2014, MFs were found in all samples collected with an overall mean concentration of 1.06 x 10 4 ± 6.77 x 10 3 MFs m -3 (median 1.07 x10 4 MFs m -3 ). Maximum MFs concentration was found offshore at Dyfamed station and in the Bay of Naples (respectively 2.54 and 3.70 x 10 4 MFs m -3 ) while lowest concentration was found in Bastia station (3.31 x 10 3 MFs m -3 ), (Fig. 1). Results of seasonal monitoring in front of the Haliotis WWTP (outfall, upstream and downstream the outfall, east and west of the outfall), showed comparable mean concentrations of MFs (1.32 x 10 4 ± 1.35 x 10 3 m -3 ; Fig. 1), and no significant differences were observed between Haliotis WWTP, Point B and Dyfamed during the year (Fig. 4). In addition, we found no geographical differences in MFs abundance along the sampling sites in NW Mediterranean Sea characterized by different levels of anthropisation, nor at a depth of 10 m at point B (1.63 x 10 4 ± 1.0 5 x 10 4 MFs m -3 ).

Finally, no relationship was found between MFs concentrations and distance to land (rs = -0.0853), probably due to their rapid dilution and transport.

Our values are several orders of magnitude higher than those reported in previous studies where a wide range of concentrations ranging from 0 to more than 450 MFs m -3 was found [START_REF] Gago | Synthetic microfibers in the marine environment: A review on their occurrence in seawater and sediments[END_REF]. These studies are however difficult to compare because of the heterogeneity of approaches used. The majority of studies focus on the surface layer and most of them use 333 µm manta nets where most fibers are not sampled and even the larger size are underestimated due to the difficulty of collecting and identify them properly [START_REF] Gago | Synthetic microfibers in the marine environment: A review on their occurrence in seawater and sediments[END_REF].

Few studies have used a mesh size of 20 µm to study marine MFs. Our study, with that of [START_REF] Suaria | Microfibers in oceanic surface waters: a global characterization[END_REF], are the only ones available for the Mediterranean Sea. By compiling a global dataset of fibers collected in six ocean basins, [START_REF] Suaria | Microfibers in oceanic surface waters: a global characterization[END_REF] showed that the highest concentration of fibers is found in Mediterranean Sea with a median of 4.2 fibers L -1 .

Although the proportion of synthetic and non-synthetic products differs between the two studies, the abundance values obtained in this study are higher than those obtained in the previous one. Microfiber pollution is a complex and worrisome threat [START_REF] Carr | Sources and dispersive modes of micro-fibers in the environment[END_REF] as it is present in the majority of samples collected from the sea surface, from filter-feeders' gut contents [START_REF] Lusher | Occurrence of microplastics in the gastrointestinal tract of pelagic and demersal fish from the English Channel[END_REF][START_REF] Devriese | Microplastic contamination in brown shrimp from coastal waters of the Southern North Sea and Channel area[END_REF], from the deep sea and the sediments [START_REF] Sanchez-Vidal | The imprint of microfibres in southern European deep seas[END_REF]. It is likely that fibers collected in the vicinity of Haliotis are mainly from urban sources, the size categories of fibers that WWTP Haliotis send to the ocean is within 25-600 µm (73%). Smaller fibers observed in situ are likely to come from airborne fibers and their continuous atmospheric deposition may contribute to maintaining the large reservoir observed. The larger fibers (>1000 µm) found mainly in this environment most likely come from marine activities such as fishing, aquaculture and shipping. Almost the whole global fishing activities use synthetic materials as polyamide and polyolefin, where some of the most common lost or discarded objects, constituted of textile fibers, comprise ropes, lines and fishing nets [START_REF] Cole | Microplastics as contaminants in the marine environment: a review[END_REF][START_REF] Sundt | Sources of Microplastic-pollution to the Marine Environment. Mepex Report M-321 commissioned[END_REF]. As revealed in a study in the Great Lakes [START_REF] Baldwin | Plastic debris in 29 great lakes tributaries: relations to watershed attributes and hydrology[END_REF], the estimation of microfiber concentrations in aquatic environments is higher than expected from sanitation systems only. These results underscore that the release of laundry fibers, as previously assumed [START_REF] Browne | Accumulation of microplastic on shorelines worldwide: sources and sinks[END_REF][START_REF] Eriksen | Microplastic pollution in the surface waters of the Laurentian Great Lakes[END_REF][START_REF] Mason | Microplastic pollution is widely detected in US municipal wastewater treatment plant effluent[END_REF], is not the only route of dissemination of synthetic MF in the aquatic environment [START_REF] Raju | Transport and fate of microplastics in wastewater treatment plants: implications to environmental health[END_REF]. A significant fraction of this leakage originates also from rivers that transport plastic waste from further inland and concentrate the litter following extreme rainfall rains and floods events [START_REF] Axelsson | Prevention through policy: Urban macroplastic leakages to the marine environment during extreme rainfall events[END_REF]. Our results showed that MFs seem to be ubiquitous and widespread found in concentrations of the same order of magnitude in urban areas as in offshore surface waters of the northwestern Mediterranean.

The sources of MFs in the marine environment are multiple, with laundry fibers discharges from WWTP and atmospheric transport of urban fibers being among the important pathways.

Final remarks

We implemented a relevant methodology to study the transport dynamics of synthetic MFs from urbanized areas to the open sea. We analyzed and quantified atmospheric contribution, so far, only a few studies have investigated atmospheric microplastics. Our study contributes to the construction of a global assessment of MPs across different environmental compartments.

Figure 5 summarizes the flow of synthetic MFs from the atmosphere to the surface of the western Mediterranean Sea. The MFs from washing machines represent an important part (average of 12.8 x 10 6 MFs m 3 ) of microplastics entering the WWTP with large quantities detected in the inlet (5.31 x 10 5 MFs m -3 ). Although Haliotis is very effective (up to 98.5%) in removing microfibers, large concentrations (2.6 x 10 3 to 3.70 x 10 4 m -3 ) are found in nearshore and offshore marine areas.

Understanding the sources and dispersion of MFs is a major issue for policy development and prevention of this emerging pollution. Coastal urban areas have sanitation systems whose efficiency varies greatly according to the types of pollution. Hydraulic regimes (rainfall, floods) may cause massive discharges into the sea (Fisher et al., 2015).

Once removed from wastewater, fibers end up as biosolids a nutrient-rich waste used as a fertilizer for soils that can persist for decades [START_REF] Bayo | Microplastics and microfibers in the sludge of a municipal wastewater treatment plant[END_REF][START_REF] Dris | Microplastic contamination in an urban area: a case study in Greater Paris[END_REF]. The application of biosolids to soils likely results in the particles ending up in rivers and lakes and being exported to the aquatic environment [START_REF] Crossman | Transfer and transport of microplastics from biosolids to agricultural soils and the wider environment[END_REF].

Preventive solutions are needed to deal with the impact of man-made MFs on marine life and human health. In order to reduce fiber contamination in the environment, future research should be directed towards upstream techniques using strategies that can mitigate this problem. As suggested by [START_REF] Almroth | Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment[END_REF], making textiles smarter, reducing fiber losses in manufacturing or using more efficient filters in domestic washing machines are possible solutions.

However, the ultimate solution to curb this pollution, which is entirely of human origin, can only be achieved through a collective effort to modify use of plastics.

Tables and figure legends

Table 1. Summary of the concentration of synthetic microfibers counted. A-In the laboratory control experiments and in the controls of the autosampler of the Haliotis WWTP (MFs L -1 ).

B-In atmospheric samples in St-Jean Cap-Ferrat and in Nice-Haliotis site (MFs m -3 ) and in the atmospheric fallout in Nice-Haliotis site (MFs m -2 day -1 ). N: number of experiments.

Table 2. ATR-FTIR analysis of microfibers collected in urban and marine waters with the respective polymer composition of synthetic fibers (%). 2.17 x 10 5 1.57 x 10 5 6 x 10 3 Mean 12.8 x 10 6 8.56 x 10 5 5.31 x 10 5 3.6 x 10 4 Max 3.9 x 10 7 2.66 x 10 6 1.02 x 10 6 6.9 x 10 4

Table 3 .

 3 Synthetic microfibers concentrations (MFs m -3 ) released during a conventional machine washing, estimation of washing input in WWTP and concentrations observed at the inlet and outlet of the Haliotis WWTP.

Figure 1 .

 1 Figure 1. Concentrations of synthetic microfibers (MFs m -3 ) in surface waters of the northwestern Mediterranean Sea in the study conducted from February to October 2014. The 15 sampling sites are highlighted with the zoomed white square in the upper right corner corresponding to the grid of 5 sampling sites in front of the Nice-Haliotis wastewater treatment plant, the coastal station off Nice, Point B and the station off Villeneuve Loubet. The points with the yellow crosses are the two inland stations at Cap Ferrat and Haliotis, where atmospheric fallout was studied. The colored circles represent the concentrations of MFs (m -3 ) in marine samples: Blue 3.3 -9.1 10 3 MFs m 3 ; Orange 1.2 -1.5 10 4 MFs m -3 and Red 2.3 -2.5 10 4 MFs m -3 respectively.

Figure 2 .

 2 Figure 2. The frequency distribution of synthetic microfiber lengths. A-In atmospheric fallout (n = 351). B-In washing machine effluents with 100% synthetic textiles (n = 1898). C-At the outlet of the Haliotis treatment plant (n = 14) and D-In the in situ samples (380). The initial bins are 25 µm and 50µm, then they are grouped together by 100µm bins.

Figure 3 .

 3 Figure 3. Seasonal concentrations of synthetic microfibers (MFs m -3 ) at the inlet (dark grey) and outlet (light grey) of the Haliotis WWTP. The percentage (%) corresponds to the disposal efficiency of the WWTP Haliotis.

Figure 4 .

 4 Figure 4. Concentrations of synthetic microfibers (MFs m -3 ) recovered from surface samples from February to October 2014 in front of the Haliotis WWTP, at Point B station, and in Dyfamed station. Boxes show the 25-75 percentiles, with median value as a central line; whiskers denote upper and lower inner fences values.

Figure 5 .

 5 Figure 5. Pathway of synthetic microfibers (MFs) from atmospheric fallout and domestic wash to the WWTP and to the Mediterranean Sea. The arrows symbolize the flow of MFs. The figures are average densities values for each compartment. Boxes are concentrations of MFs (m -3 ) from domestic washing, wastewater treatment plant outlet and the Mediterranean Sea surface, it shows the 25-75 percentiles, with median value as a central line; whiskers indicated upper and lower inner interval values, and the outer values are indicated by crosses.

Table 2 .

 2 ATR-FTIR analysis of microfibers collected in urban and marine waters with the respective polymer composition of synthetic fibers (%).

		Total	Analyzed	Analyzed	Unknown	Natural	Synthetic
		Fibers (nb)	fibers (nb)	%	%		%	%
	Haliotis Outfall	65	27		41	15		35	50
	Point B	23	15		65	14		72	14
	Bastia	32	24		75	21		58	21
	Dyfamed	178	38		21	18		47	34
		PA	PAN	PES	PP	PS	PVA PVC
	Haliotis Outfall	30	13	22	9	17		9
	Point B	17	17	33			33
	Bastia	60		40
	Dyfamed	38		62
	PA Polyamide; PAN Acrylic; PES Polyester; PP Polypropylene; PS Polystyrene; PVA
	Polyvynil acetate; VA Vinyl acetate

Table 3 .

 3 Synthetic microfibers concentrations (MFs m -3 ) released during a conventional machine washing, estimation of washing input in WWTP and concentrations observed at the inlet and outlet of the Haliotis WWTP.

		Conventional	Estimated	Inlet Haliotis	Outlet Haliotis
		washing	washing input	WWTP	WWTP
			in WWTP
	Min	3.2 x 10 6

Acknowledgments 26

The authors thank the commitment of the following institutions, people and sponsors: CNRS, UPMC, LOV, Genoscope/CEA, the Tara Ocean Foundation and its funders: Agnès b., Etienne Bourgeois, Romain Troublé, the Tara schooner and crew teams. We are also grateful to the French Ministry of Foreign Affairs for supporting the expedition and to the countries that graciously granted sampling permissions. We also thank Thierry Astruc from the INRA Unit "Quality of animals products" for the access to FTIR instrumentation and David Bourgogne from the Institute of chemistry of Clermont-Ferrand for the help with FTIR database management. We thank the reviewers for their comments that helped improve the manuscript and J. Dolan for his help with English. This work was supported by Degrémont-SUEZ Environment and the French Ministry of Research (CNRS).