Lauren Arpin-Pont

Maria Jesus Martinez Bueno

Elena Gomez

Hélène Fenet
email: hfenet@univ-montp1.fr

Occurrence of PPCPs in the marine environment: a review

Keywords: pharmaceuticals, personal care products, marine environment, seawater, sediment, marine organisms 2012

Little research has been conducted on the occurrence of pharmaceuticals and personal care products (PPCPs) in the marine environment despite being increasingly impacted by these contaminants. This article reviews data on the occurrence of PPCPs in seawater, sediment and organisms in the marine environment. Data pertaining to 196 pharmaceuticals and 37 personal care products reported from more than 50 marine sites are analyzed taking into account sampling strategies and analytical methods. A particular attention is given to the most frequently detected substances and at highest concentrations. A snapshot of the most impacted marine sites is provided by comparing the highest concentrations reported for quantified substances. The present review reveals that i) PPCPs are widespread in seawater; particularly at sites impacted by anthropogenic activities and that ii) the most frequently investigated and detected molecules in seawater and sediments were antibiotics, such as erythromycin. Moreover, this review points out other PPCPs of concern such as ultraviolet filters and underlines the scarcity of data on those substances despite recent evidence on their occurrence in marine organisms. Thus, the review discusses the exposure of marine organisms in regard to these insufficient data.

Introduction

The expression 'pharmaceuticals and personal care products' (PPCPs) encompasses many different substances, such as drugs used in human and veterinary medicine, fragrances, sun-screen agents and cosmetics ingredients [START_REF] Daughton | Pharmaceuticals and personal care products in the environment: Agents of subtle change?[END_REF][START_REF] Richardson | Emerging chemicals of concern: Pharmaceuticals and personal care products (PPCPs) in Asia, with particular reference to Southern China[END_REF]. More than 3000 PPCPs are currently marketed and new molecules enter the market yearly. Pharmaceuticals (PPs), after their therapeutic use, and some personal care products (PCPs), after regular use, are released in raw sewage waters and then often inefficiently treated in sewage treatment plants (STPs) and finally discharged in rivers, streams or lakes. These compounds are ubiquitously detected in treated wastewater, which is the main source of surface water contamination [START_REF] Verlicchi | Occurrence of pharmaceutical compounds in urban wastewater: Removal, mass load and environmental risk after a secondary treatment-A review[END_REF]. The PPCPs present in solid waste discharge, sewage sludge and in manure applied as fertilizer may leach from fields and, depending on their mobility in the soils, end up in ground waters [START_REF] Daughton | Pharmaceuticals and personal care products in the environment: Agents of subtle change?[END_REF][START_REF] Diaz-Cruz | Environmental behavior and analysis of veterinary and human drugs in soils, sediments and sludge[END_REF]. Some PCPs are also directly released into water during swimming and bathing activities in lakes or rivers [START_REF] Balmer | Occurrence of some organic UV filters in wastewater, in surface waters, and in fish from Swiss lakes[END_REF]. PPCPs used throughout the world are thus widely detected in freshwater environments. Recent reviews have reported the occurrence of PPCPs in surface water [START_REF] Brausch | A review of personal care products in the aquatic environment: Environmental concentrations and toxicity[END_REF][START_REF] Pal | Impacts of emerging organic contaminants on freshwater resources: Review of recent occurrences, sources, fate and effects[END_REF] and in groundwater [START_REF] Lapworth | Emerging organic contaminants in groundwater: A review of sources, fate and occurrence[END_REF].

Marine ecosystems are also affected by PPCP contamination (Klosterhaus et al., 2013) but little data has been published on PPCPs in seawater. However, coastal zones are subject to growing pressure due to the increase in human activities. PPCPs are released into seawater through submarine or marine STP outfalls [START_REF] Fenet | Reducing PEC uncertainty in coastal zones: A case study on carbamazepine, oxcarbazepine and their metabolites[END_REF] or in runoff via rivers and streams (la [START_REF] Farre | Fate and toxicity of emerging pollutants, their metabolites and transformation products in the aquatic environment[END_REF]. Other sources of PPCPs in the marine environment are fish farming, for antibiotics (Zou et al., 2011) and antiparasitic drugs [START_REF] Rico | Probabilistic risk assessment of veterinary medicines applied to four major aquaculture species produced in Asia[END_REF], and recreational activities, especially regarding sun screen agents, which are washed from the skin into the water [START_REF] Bachelot | Organic UV filter concentrations in marine mussels from French coastal regions[END_REF]Langford and Thomas, 2008). Fewer studies have been conducted in the marine environment because PPCP levels are expected to be low due to dilution and diffusion, and because of the complex hydrodynamics of the marine environment in coastal zones, for instance. Vidal-Dorsch et al. (2012) observed a significant dilution of STP effluent discharge in seawater at submarine outfalls and highlighted the difficulty to determine the environmental relevance of the low level PPCPs observed in seawater. However, several authors reported the occurrence of PPCPs in marine organisms (Klosterhaus et al., 2013;Nakata et al.,

Study design

The sampling strategies deployed were highly dependent on the objectives of the reported studies. When the aim was to evaluate the spatial distribution of PPCPs within a defined area receiving a point source pollution (STP, rivers, etc.), samples were collected at regular distances from the source (Rubinfeld and Luthy, 2008), in different directions (Fang et al., 2012) or at different depths (Liang et al., 2013). Most often, concentrations were generally found to decrease with increasing distance from the pollution source such as an STP outfall [START_REF] Amine | UV filters, ethylhexyl methoxycinnamate, octocrylene and ethylhexyl dimethyl PABA from untreated wastewater in sediment from eastern Mediterranean river transition and coastal zones[END_REF]Minh et al., 2009), a bathing area (Langford and Thomas, 2008) or a more polluted area such as a river or an estuary [START_REF] Andresen | Emerging pollutants in the North Sea in comparison to Lake Ontario, Canada, data[END_REF]Weigel et al., 2002), emphasizing the role of dilution in the marine environment. However, the observed concentration was also largely dependent on the coastal hydrodynamics as shown by Bayen et al. (2013). Indeed, these authors demonstrated that the long residence times created by the hydrodynamic resulted in highest concentrations of pollutants than those in the proximity to the STP reject. Depth was involved differently in the dilution from point sources of pollution. When contaminated fresh water comes from the bottom, as it is the case with submarine outfalls, [START_REF] Fenet | Reducing PEC uncertainty in coastal zones: A case study on carbamazepine, oxcarbazepine and their metabolites[END_REF] showed that a thermocline observed in summer limits the PPCP diffusion from the bottom to the surface. In estuaries, diffusion from fresh water carrying the PPCPs to the salt water was limited with depth, as observed by Liang et al. (2013), which reported that the total concentration of antibiotics of the Pearl River estuary was significantly higher in the surface water than in the bottom water layer during both dry and wet seasons. In marine water, tidal stage could have an influence on dilution and diffusion of a contaminant. However, Fair et al. (2009) have studied the influence of the tidal stage on triclosan concentrations in the Charleston Harbor, and found no significant difference between the low tidal stage and the high tidal stage. The synthesis that can be made from these results is that, even more than in the case of fresh water, the site conformation and hydrodynamics will determine the spatial distribution of concentrations found for PPCPs. The parameters which may influence the temporal variation of concentrations in seawater and sediments are seasons (dry or wet season) and recreational activities (tourism) as indicated by Liang et al. (2013) and (Knee et al., 2010). Beyond the sampling strategy, the method used to sample the different compartments could have an impact on the results. In most of the reviewed articles (43), water was collected by active sampling with pumps or grab sampling. Passive integrative samplers for polar molecules (POCIS) were used by [START_REF] Alvarez | Occurrence of contaminants of emerging concern along the California coast (2009-10) using passive sampling devices[END_REF]), Martinez Bueno et al. (2009) and Munaron et al. (2012). Active sampling is easier to implement than passive sampling and enables direct quantification of PPCPs in water. However, to be representative of the studied area, numerous samples should be collected and more if a temporal variation was researched. Passive sampling allows an estimation of the target analyte concentration during an exposure time, enabling the semi-quantification of some PPs depending on the sampling rate (Rs), predefined in the laboratory. However, harmonizing measurements during laboratory calibration is difficult (Munaron et al., 2012), which explains the low use of this technique at the moment. Sediment depth sampled in the reviewed articles varied from 2-3 cm (Long et al., 2013;Maruya et al., 2012) to 40 cm (Miller et al., 2008) requiring different equipments. Surface sediment was sampled using a stainless steel Van Veen type grab sampler whereas sediment cores were sampled with gravity corers. The sample pre-treatment (freeze drying, homogenization, sieving) may influence the analysis efficiency. [START_REF] Belkessam | Influence of pre-treatment step on PAHs analyses in contaminated soils[END_REF] revealed that the increasing sample homogeneity improved analysis reproducibility and extraction recovery of PAH compounds. This influence observed for persistent contaminants could be studied for PPCPs, which should possibly have a different behavior. The storage may have an influence on the stability of the compounds. [START_REF] Negreira | Study of the stability of 26 cytostatic drugs and metabolites in wastewater under different conditions[END_REF] showed that environmental samples such as wastewater had to be frozen immediately after collection and had to be analyzed as soon as possible in order to minimize the degradation of cytostatic drugs. The influence of freeze on PPCPs in sediments remains to determine. Most of the articles have studied the spatial variation of PPCP contamination in surface sediments whereas some authors have investigated the geochronology of the contamination by sampling sediment cores (Cantwell et al., 2010;Miller et al., 2008). The contaminant distribution in sediments varies in function to the sediment composition, which depends on sedimentation rates, and is variable in line with the characteristics of the studied sites (topography and hydraulic conditions). Beretta et al. (2014) reported the influence of the location in an area of low energy with high sediment rates on the composition of muddy sediments, composed predominantly of clay and silt, prone to become a sink of organic contaminants such as PPCPs. Moreover, transformation processes in sediment such as aerobic and anaerobic degradation are dependent on the location and depth in the sediment [START_REF] Hektoen | Critical review of the application of liquid chromatography/mass spectrometry to the determination of pesticide residues in biological samples[END_REF][START_REF] Robinson | Biodegradation of endocrine disrupting compounds in harbour seawater and sediments[END_REF]. This latter point may affect the rate of degradation and detection of PPCP transformation products (Cantwell et al., 2010). Concerning marine organisms, sampling was performed mainly to assess the status of contamination of studied sites subjected to anthropogenic pressure. Bivalves (mussels, oysters, scallops and clams) were the most frequently studied organisms, by direct sampling [START_REF] Bachelot | Organic UV filter concentrations in marine mussels from French coastal regions[END_REF]Dodder et al., 2014;Klosterhaus et al., 2013;Li et al., 2012;Martinez Bueno et al., 2014;Na et al., 2013;Nakata et al., 2007;Picot Groz et al., 2014) or via caging at sites of interest (Hoenicke et al., 2007;Kookana et al., 2013;McEneff et al., 2014;Wille et al., 2011). Bivalves, such as mussels have often been used as bioindicators for aquatic pollution monitoring [START_REF] Quinete | Specific profiles of perfluorinated compounds in surface and drinking waters and accumulation in mussels, fish, and dolphins from southeastern Brazil[END_REF], and they are representative of the sampling area because of their sedentary behavior [START_REF] De Donno | Mytilus galloprovincialis as a bioindicator of microbiological pollution of coastal waters: A study conducted in the Salento peninsula (Italy)[END_REF], whereas fishes are less representative of a site. Fishes are highly mobile and may have a migratory behavior [START_REF] Ferreira | Vitellogenin gene expression in the intertidal blenny Lipophrys pholis: A new sentinel species for estrogenic chemical pollution monitoring in the European Atlantic coast?[END_REF], thus complicating data interpretation. However marine mammals (dolphins, sea lions, otters, seals) and fishes (sharks, salmons, flatfishs, eelpouts, rays) were also studied in four papers (Kannan et al., 2005;Maruya et al., 2012;Nakata et al., 2007;Rüdel et al., 2006). In fish and marine mammals, liver was often sampled because biotransformation enzymes are mainly distributed in this organ [START_REF] Matsuo | Characterization of Phase I biotransformation enzymes in coho salmon (Oncorhynchus kisutch)[END_REF][START_REF] Teramitsu | Identification of novel cytochrome P450 1A genes from five marine mammal species[END_REF], while in mussels, all the soft tissues were mainly sampled, although xenobiotics are accumulated in the digestive gland, responsible for metabolic activity [START_REF] Fasulo | Metabolomic investigation of Mytilus galloprovincialis (Lamarck 1819) caged in aquatic environments[END_REF].

As a conclusion of this section, although several parameters influence the results of the analysis as well as in freshwater studies, the issue of the sampling site choice is a critical aspect of the study design and appears to depend mostly on the knowledge of hydrodynamic characteristics of the studied site.

Analytical procedures

Beyond the sampling strategies, one of the difficulties in reviewing research in this area is to compare data derived from various analytical procedures. The different analytical steps, such as the extraction process, quantification methods and the addition of an internal standard have consequences on the analytical performances, such as the limit of quantification or repeatability. Multiple residues analyses were often performed in the reviewed articles. As regards the extraction steps for the aqueous samples, in the last 30 years solid phase extraction (SPE) has replaced the traditional liquid-liquid extraction (LLE) and has become the technique most commonly used for sample preparation. At present, hydrophilic-lipophilic-balanced-reversed-phase (HLB) sorbent is best used for the extraction of organic pollutants from water samples, due to its ability to retain analytes in a wide range of polarities and stability throughout the pH range. One of the great advantages of these adsorbents is the possibility of multi-analyte method work at neutral pH [START_REF] Gomez | Determination of pharmaceuticals of various therapeutic classes by solid-phase extraction and liquid chromatography-tandem mass spectrometry analysis in hospital effluent wastewaters[END_REF], which greatly simplifies the treatment of the sample. However, for very polar and water-soluble analytes, such as ranitidine, recoveries may be low if the samples are not adjusted to the appropriate pH [START_REF] Pichon | Solid-phase extraction for multiresidue analysis of organic contaminants in water[END_REF]. For the analyses, liquid chromatography-mass spectrometry (LC-MS or LC-MS/MS) and gas chromatography-spectrometry (GC-MS or GC-MS/MS) were used to quantify concentrations in samples in 32 and 37 articles, respectively. However, matrix effects are widely described in LC-MS analyses of complex matrices [START_REF] Petrović | Liquid chromatography-tandem mass spectrometry for the analysis of pharmaceutical residues in environmental samples: a review[END_REF], and are most frequent than in GC-MS analyses [START_REF] Caban | Matrix effects and recovery calculations in analyses of pharmaceuticals based on the determination of β-blockers and β-agonists in environmental samples[END_REF]. The use of an isotope-labeled standard in isotope dilution-based methods helps correct this issue [START_REF] Hektoen | Critical review of the application of liquid chromatography/mass spectrometry to the determination of pesticide residues in biological samples[END_REF]. More broadly, the use of an internal standard (IS) can correct errors related to extraction processes, injection and ionization such as matrix effects. The use of an IS was reported in more than 80% of the papers reviewed, and a third of these 80% used isotopic dilution. Isotope dilution can significantly reduce systematic errors from several sources, including sample stability prior to analysis, analyte loss during extraction procedures and matrix effects [START_REF] Boden | Development of an isotope-dilution gas chromatographic-mass spectrometric method for the analysis of polycyclic aromatic compounds in environmental matrices[END_REF][START_REF] Vanderford | Analysis of pharmaceuticals in water by isotope dilution liquid chromatography/tandem mass spectrometry[END_REF]. However, limited availability of isotope labeled standards is problematic for broad screening analysis, for some PPCPs and particularly for metabolites. For example, Martinez Bueno et al. (2014) analyzed metabolites of venlafaxine, Ndesmethylvenlafaxine, in mussels by LC-MS/MS with venlafaxine-d6 as a surrogate because no isotope labeled standard is marketed for this venlafaxine metabolite. In the present review, the reported occurrence values in articles were selected when the use of an internal standard was reported. Furthermore, the limits of quantification (LOQ) and limits of detection (LOD) for a molecule varied in the reviewed articles with the overall analytical procedures. For example, for sulfamethoxazole, LODs ranged from 0.084 (Yang et al., 2011) to 300 ng/L (Bayen et al., 2013). Thus, the authors are aware that when a detection frequency was calculated for PPCPs detected at the different sites reviewed in the present work, there was bias due to the difference in LODs at the different studies. As presented above, there are a wide variety of analytical procedures applied to the environmental samples studied in the reviewed articles. A standardization of the analytical procedures, mainly for multi-residue analyses, could allow an accurate comparison of the results.

Data analysis considerations

As the authors are aware of the uncertainties and the limits of the comparison of the results in this review and as previously mentioned, regarding the available articles, for occurrence studies (detection frequencies and concentrations), data were selected only when an internal standard (surrogate or isotopic) was used. Furthermore, as recommended by the European Commission's 'Guidance documents on pesticide residue analytical methods' ("SANCO/825/00," 2010), the data were reported in this occurrence review, when the reported recovery ranged from 70% to 120% and the precision, expressed as the relative standard deviation (RSD), was lowest than 20 %. Furthermore, passive sampling data (POCIS) were not included in the occurrence study as we consider that data are semiquantitative. Based on the selected data, the detection frequencies of studied PPCPs were calculated in aqueous phase by including all sampling sites of each study selected in the present review. The detection frequency for each PPCP expressed in % was calculated with the formula (d/i) ×100, where d is the number of sampling sites where the specific compound was detected and i is the number of sampling sites where the compound was investigated. The frequency was calculated when a compound had been detected in at least ten sampling sites, and at least two distinct geographical areas. For some articles, information on detected but not quantified compounds was missing. In these cases, the reported frequency in the present review work should be considered as underestimated. However, the detection frequencies gave a good overview of the occurrence of PPCPs in the marine environment. For the presentation of the reviewed data, the maximum concentrations were chosen to reflect the occurrence of the studied compounds as these values were the most commonly cited values in the reviewed articles. Moreover, maximum concentrations far from the limit of detection were likely more independent of the variability in the sensitivity of the analytical techniques than the concentrations close to the limit of detection, such as minimal concentrations. The median values would have been the preferred values as they were less impacted by the extreme values chosen, but these data were not available for all the reviewed studies. Thus, the results were expressed as follows: number of sampling sites where the molecule was investigated (s), detection frequency for all sites (f) %, and number of studies (n).

2-Occurrence in seawater

PPCPs were investigated worldwide in seawater in North America (Canada and USA), in northern Europe (United Kingdom (UK)), Ireland, Belgium, Germany, Netherlands, Denmark, Sweden and Norway), in southern Europe (France, Spain, Majorca, Portugal, Italy and Greece) and in Asia (China, Taiwan and Singapore) (Table A -supplementary material). For PPs, different trends between continents and countries could have been expected due to differences in prescription habits, authorized drugs and patient consumption. However the data were too scarce to study any difference between these continents and countries. On the 100 investigated compounds (parents and metabolites) in water meeting the entered criteria, the half was detected. The most frequently investigated and detected compounds were antibiotics with erythromycin (s: 220; f: 77%; n:7), sulfamethoxazole (s: 251, f: 71%; n:9 ) and trimethoprim (s:168, f:80%; n:6), antiepileptics with carbamazepine (s: 85, f: 23%, n:5), caffeine (s:76, f: 86%, n:5), antiinflammatories with ibuprofen (s:79, f:38%, n:5) and analgesics with acetaminophen (s:65, f:81%; n:3). Maximum PP concentrations reported in seawater were in a large range of concentrations from the LOQ (few ng/L) to 230,000 ng/L (Fig. 1 A-F). Antibiotic concentrations ranged from 0.24 to 1900 ng/L (Fig. 1 A). The most frequently detected compounds were erythromycin, sulfamethoxazole and trimethoprim. The highest concentration was quantified for erythromycin, i.e. 1900 ng/L at the site immediately adjacent to the effluent discharge of a STP located in the typhoon shelter situated in Victoria Harbor (Hong Kong, China), where the water exchange to the outside sea is particularly low (Minh et al., 2009). Non-steroidal anti-inflammatory drugs (NSAIDs) (Fig. 1 B) were detected in seawater at maximal concentrations ranging from 0.7 ng/L to 6100 ng/L (Jiang et al., 2014;Togola and Budzinski, 2008;Weigel et al., 2004). Although the highest concentration was found for ketoprofen (s:60, f:68%,n:2), ibuprofen was the most frequently investigated and detected NSAID. For central nervous system drugs (Fig. 1 C), carbamazepine was the most frequently detected compound in water (Jiang et al., 2014;Togola and Budzinski, 2008;Wille et al., 2010). Amitriptyline was less often screened and presented lower concentrations (30 ng/L) (Togola and Budzinski, 2008). Among cardiovascular system drugs (Fig. 1 D), atenolol was detected at the highest level (293 ng/L) although its detection frequency was very low (s:64, f:3%, n:2). Gemfibrozil was the most frequently detected compound (s:68, f:40%, n:3). Other less investigated classes such as analgesics, analeptics and illicit drugs were reported in Fig. 1 (E-F). The most frequently investigated and detected compound was caffeine. The highest levels were reported for acetaminophen (230,000 ng/L) and aspirin (8300 ng/L) in sampling sites close to the pollution source, at less than 500 m from an STP outfall (Marseille, France) without secondary treatment, where the effluent was rejected in a semi enclosed area, poorly submitted to dilution (Togola and Budzinski, 2008). Among PCPs (Fig. 1 G-I), little data was available. Musks and disinfectants are rejected in seawater with STP discharges and were detected at sites influenced by anthropogenic pressures, such as estuaries or harbors. Musks AHTN (Tonalide ® ), HHCB (Galaxolide ® ) were detected at levels up to 28 ng/L for HHCB (Sumner et al., 2010). Triclosan was detected at concentrations up to 99.3 ng/L in Victoria Harbor waters (China) (Wu et al., 2007). Concerning UV filters, most of studies were conducted along the coasts, as recreational activities are the main source of contamination. Highest concentrations were reported for benzophenone 3 (BP-3) and octocrylene (OC) with 2013 ng/L and 1409 ng/L respectively in the most highly frequented beaches sampled by Bratkovics and Sapozhnikova (2011). Tovar-Sanchez et al. ( 2013) studied the intra-day variation in concentrations of sunscreen agents and found the maximum levels in seawater when the sunlight radiation was maximum, when the skin applications are highest. This broad range of concentrations was noted for most of the investigated PPCPs. This could be due to the sampling sites (proximity of the sources of contamination with direct or indirect input) and sampling strategies (depth in the water column, etc.), the hydrodynamics of the investigated sites with various dilution and diffusion processes and probably to variable attenuation processes. Little data is available on these two latter points regarding PPCPs in the marine environment.

Figure 1: Maximum PPCP concentrations in seawater (ng/L). PPs: A-antibiotics/B-NSAIDs/Ccentral nervous system drugs/ D-cardiovascular system drugs /E-analgesics/ F-other drugs; PCPs: G-musks/H-UV filters/I-disinfectants

For the sampling sites, as data concerning the most frequently quantified compounds were available for numerous sites, the results are presented according to the nature of the sampling sites. As to Fig. 2, the sites were classified as sites heavily influenced by STP, harbors, estuaries, bays, coasts, open seas and high seas to study the influence of the distance to a source of pollution on PP concentrations. As one might expect, highest concentrations were detected in zones closely impacted by STP effluents, harbors and bays where urban activities were located and estuaries subject to surface water contamination. In open seas and high seas, concentrations were lower (up to 16.6 ng/L) due to the lower anthropogenic pressure and to higher dilution or advection mechanisms. For example, for erythromycin, the highest reported concentrations were reported at a site directly impacted by STP (Minh et al., 2009), then in a harbor and an estuary, with maximum levels ranging from 121 to 212 ng/L (Liang et al., 2013;Minh et al., 2009), whereas in bays, coasts, open seas and high seas, maximum concentrations ranged from 0.76 to 26.6 ng/L (Zhang et al., 2013a(Zhang et al., , 2013b(Zhang et al., , 2012)). In marine water, as expected, the maximum concentrations of PPCPs reported in the literature were lower than those reported in freshwater. For example, carbamazepine was found at levels ranging from 9 to 2,000 ng/L in surface waters [START_REF] Fent | Ecotoxicology of human pharmaceuticals[END_REF] whereas concentrations reported in marine waters ranged from 3.89 ng/L along the coasts (Jiang et al., 2014) to 185 ng/L in estuaries (Wille et al., 2010). Triclosan was detected with concentrations ranging from 0.1 to 1023 ng/L in freshwater [START_REF] Bu | Pharmaceuticals and personal care products in the aquatic environment in China: A review[END_REF][START_REF] Gorga | Multi-residue analytical method for the determination of endocrine disruptors and related compounds in river and waste water using dual column liquid chromatography switching system coupled to mass spectrometry[END_REF] and from 6.87 to 99.3 ng/L in marine water (Wu et al., 2007;Xie et al., 2008). Similarly, 2-ethyl-hexyl-4-trimethoxycinnamate (EHMC) was detected in seawater at levels of 144-264 ng/L (Benedé et al., 2014;Bratkovics and Sapozhnikova, 2011) whereas in freshwater, the concentrations range was 7-3009 ng/L [START_REF] Balmer | Occurrence of some organic UV filters in wastewater, in surface waters, and in fish from Swiss lakes[END_REF][START_REF] Rodil | Non-porous membrane-assisted liquid-liquid extraction of UV filter compounds from water samples[END_REF]. In the same way, OC was detected in the reviewed studies with the lowest concentrations in seawater, ranging from 187 to 1409 ng/L (Benedé et al., 2014;Bratkovics and Sapozhnikova, 2011) and 5 to 4301 ng/L in freshwater [START_REF] Kameda | Occurrence and profiles of organic sun-blocking agents in surface waters and sediments in Japanese rivers and lakes[END_REF][START_REF] Rodil | Non-porous membrane-assisted liquid-liquid extraction of UV filter compounds from water samples[END_REF].

3-Occurrence in sediment

Most of the studies have been conducted on the aqueous compartment insofar as most of PPCPs are molecules particularly water-soluble. However, some PCPs are more lipophilic compounds, such as OC or EHMC (log K ow close to 6), and may be highly subject to sorption by sediment [START_REF] Amine | UV filters, ethylhexyl methoxycinnamate, octocrylene and ethylhexyl dimethyl PABA from untreated wastewater in sediment from eastern Mediterranean river transition and coastal zones[END_REF]. A relationship between the degree of sorption and organic matter has been shown to some PPCPs. Sorption to sediment is a complex process influenced simultaneously by hydrophobic interactions (Van der Waals forces), ionic interactions (electrostatic interactions, complexation), hydrogen bonding etc., i.e. electrostatic forces are stronger than Van der Waals forces [START_REF] Von Oepen | Sorption of nonpolar and polar compounds to soils: Processes, measurements and experience with the applicability of the modified OECD-Guideline 106[END_REF]. More recently, studies investigated the sorption of PPs pointed out that the degree of ionization of the functional groups is a factor which influences the sorption on sediment. Numerous environmentally relevant PPs contain one or several dissociable functional groups (acidic/basic). Therefore, these compounds are in dissociation equilibrium depending on the seawater pH. Particularly for compounds with pK a within the seawater 7.4-8.35 pH range [START_REF] Byrne | Inorganic speciation of dissolved elements in seawater: the influence of pH on concentration ratios[END_REF], a highly pH-dependent sorption behaviour could be expected [START_REF] Franco | Influence of soil pH on the sorption of ionizable chemicals: modeling advances[END_REF][START_REF] Franco | Estimation of the soil-water partition coefficient normalized to organic carbon for ionizable organic chemicals[END_REF][START_REF] Kah | Prediction of the adsorption of ionizable pesticides in soils[END_REF]. Studies performed on the sorption process of antibiotics by [START_REF] Vasudevan | pH-dependent ciprofloxacin sorption to soils: Interaction mechanisms and soil factors influencing sorption[END_REF] revealed that ciprofloxacin was able to mainly undergo cationic exchange and that its sorption was strongly dependant on the soil CEC at all tested pH values. [START_REF] Yamamoto | Persistence and partitioning of eight selected pharmaceuticals in the aquatic environment: Laboratory photolysis, biodegradation, and sorption experiments[END_REF] reported the existence and dominant role of cation exchange processes for atenolol, positively charged at neutral pH. However, studies on sorption processes of PPs were mainly conducted in freshwater-sediment systems. Few data are available on the sorption of PPs in marine sediments while the degree of salinity is an additional factor that may control the PP sorption onto natural sediment. [START_REF] Wang | Studies on the sorption of tetracycline onto clays and marine sediment from seawater[END_REF], who studied the sorption of antibiotic tetracycline onto clays and marine sediment from seawater, found that sorption decreased with increased salinity. A few studies have focused on PPCPs in marine sediment (15 papers between 2008 and 2014, Table A -supplementary material). PPCPs were investigated in North America in USA, in South America, in northern (UK) and southern Europe (France, Spain), in the Near East in Lebanon, and in Asia in China. These scarce publications showed that the marine sediment is also concerned by the presence of PPCPs. Twenty PPCPs (14 PPs and 6 PCP) were detected among thirty researched compounds, parents and metabolites (Table 1). Detection frequencies could not be estimated due to the lack of data. Among data selected as previously mentioned, the PP quantified at the highest levels was sulfameter (56.65 ng/g dry weight (dw)) in sediments located in the Dalian coastal environment (China) (Na et al., 2013). The reason could be that sulfameter had the highest sorption capacity among antibiotics investigated by Na and al. (2013). Among PCPs, UV filters, musks and antimicrobials were detected and quantified. A general trend is difficult to highlight as it has been performed for aqueous compartment, because of the lack of data for marine sediments, however some studies highlighted, as expected, that the highest concentrations were mostly reported in zones impacted by anthropogenic activities. Cantwell et al. (2010) reported a high concentration of triclosan (400 ng/g dw) in the urbanized estuary of the Narragansett Bay (USA). It is acknowledged that STP effluents are the primary source of triclosan in estuarine sediments. [START_REF] Amine | UV filters, ethylhexyl methoxycinnamate, octocrylene and ethylhexyl dimethyl PABA from untreated wastewater in sediment from eastern Mediterranean river transition and coastal zones[END_REF] studied levels and spatial trends of concentrations of three UV filters in coastal zones impacted by indirect inputs (rivers and STP), highest concentrations of UV filters were reported for OC (78 ng/g dw) in surface sediments receiving STP effluents along El Mina city coastline. Concerning musks, Beretta et al. (2014) detected AHTN and HHCB in sediments in the Todos os Santos Bay (Brazil), at highest levels, i.e. 52.5 ng/g dw for HHCB, at sites with the highest population density and the presence of muddy coastal sediments. Despite the limited results available, it appeared that the concentrations found in marine sediments were lower than those observed in rivers sediments (Zeng et al., 2008). For example, sulfamethazine and triclosan were detected in river sediments in China at concentrations up to 248 ng/g dw (Yang et al., 2010) and 1329 ng/g dw [START_REF] Zhao | Occurrence and risks of triclosan and triclocarban in the Pearl River system, South China: From source to the receiving environment[END_REF] respectively. In contrast, the maximum concentrations reported in this review were 3.24 ng/g dw for sulfamethazine and 400 ng/g dw for triclosan (Liang et al., 2013).

4-What about marine organisms?

Although the presence of PPCPs in organisms sampled in marine environment has been rarely reported in the literature, mostly because of the high polarity of some of them, these compounds (PCPs) were detected at levels up to 7112 ng/g dw [START_REF] Bachelot | Organic UV filter concentrations in marine mussels from French coastal regions[END_REF]. Thus, this aspect of PPCPs contamination in the marine environment has to be considered. Twenty articles were published between 2006 and 2014 and were reported in Table A -supplementary material. The occurrence of PPCPs in organisms has been documented in North America from San Francisco Estuary and Bay, along the California and Florida coasts to Charleston Harbor and South America along the Brazilian coasts, in Europe along the Portuguese, French, Ireland and Belgian coasts, in Asia and in Australia. Ranges of concentrations detected in marine organisms are presented in Table 2A for PPs and 2B for PCPs. As regard to selected data, PPs were detected in bivalves. Antibiotics were the main represented pharmaceutical class with a little more than ten detected molecules. The highest concentrations were 490 ng/g dw for salicylic acid, 115 ng/g dw for acetaminophen in mussels Mytilus edulis of the Oostende marina in Belgium (Wille et al., 2011) and 19.9 ng/g ww for sulfamerazine in bivalves Crassostrea gigas, Patinopecten yessoensis and Chlamys farreri located at the Dalian coastal sites in China (Na et al., 2013). Martinez Bueno et al. (2014) detected the antidepressant venlafaxine and four of its metabolites in mussels Mytilus galloprovincialis sampled in the vicinity of a submarine outfall with industrial and urban discharges in Montpellier (France). Among PCPs, the highest concentrations were found in mussels Mytilus galloprovincialis and Mytilus edulis for OC and for the stabilizer UV-328 at levels up to 7112 ng/g dw at a the Mediterranean coastal site [START_REF] Bachelot | Organic UV filter concentrations in marine mussels from French coastal regions[END_REF] and up to 14,000 ng/g lw in mussels Perna viridis and Mytilus edulis in Kohyongsong Bay in Korea (Nakata et al., 2012), respectively. [START_REF] Bachelot | Organic UV filter concentrations in marine mussels from French coastal regions[END_REF] reported highest levels of sunscreen agents in recreational sites in summer period, in July and August. Picot Groz et al. ( 2014) observed similar seasonal trends of UV filters in mussels Mytilus galloprovincialis sampled along the Portuguese coasts, with highest concentrations in July. As noticed by Tovar-Sanchez et al. (2013), concentrations of UV filters in seawater vary throughout the day, depending on the arrival of bathers. This lead thus to an intra-day variation of organisms exposure which could be investigated through the measurement of concentrations in exposed organisms, helping to a better interpretation of pharmacokinetic studies concerning UV filters. However, for musks, a seasonal trend was not reported and their presence at sampling sites was due to the proximity of a STP (Picot Groz et al., 2014). Concerning marine mammals, Kannan et al. (2005) reported HHCB concentrations of 25 ng/g lw in striped dolphins and of 6.6 ng/g lw in pigmy sperm whales of the Florida coast. Although PPs are found at relatively low levels in the environment, their possible risk for aquatic organisms is mostly related to chronic exposure. The real ecological risk of these compounds is thus difficult to apprehend. The studies show generally effects at concentrations highest than those reported in the environment. As an example, [START_REF] Huggett | Toxicity of select beta adrenergic receptor-blocking pharmaceuticals (β-blockers) on aquatic organisms[END_REF] observed a significant decrease in eggs production of the fish Orizias latipes after a 4-week exposition to propranolol at 500 ng/L which is higher than the maximum concentration observed in seawater of 52 ng/L (Wille et al., 2011). Recently, some studies reported results of toxicity at levels close to the environmental concentrations, which is subject of controversy. Di Poi et al. ( 2013) and [START_REF] Franzellitti | The mode of action (MOA) approach reveals interactive effects of environmental pharmaceuticals on Mytilus galloprovincialis[END_REF] reported behavioral effects of antidepressant fluoxetine on the cuttlefish Sepia officinalis and transcriptional effects on the marine mussel Mytilus galloprovincialis respectively, both at concentrations of 1 ng/L or less. [START_REF] Sumpter | Are some invertebrates exquisitely sensitive to the human pharmaceutical Fluoxetine?[END_REF] have risen to question the relevance and the significance of these results in a commentary paper, and have highlighted the lack of pharmacological and pharmacokinetic data in aquatic organisms exposed to such molecules, helpful to confirm these results. Although pharmacokinetics have been studied concerning some marine species [START_REF] Li | Residual pharmaceutically active compounds (PhAcs) in aquatic environmentstatus, toxicity and kinetics: a review[END_REF], few studies have been published, mainly for invertebrates, for which it is difficult to know the fluid concentrations such as haemolymph in mussels [START_REF] Franzellitti | Response to Commentary on "Are some invertebrates exquisitely sensitive to the human pharmaceutical fluoxetine?[END_REF]. [START_REF] Li | Residual pharmaceutically active compounds (PhAcs) in aquatic environmentstatus, toxicity and kinetics: a review[END_REF] showed that environmental conditions such as water temperature and salinity influence the pharmacokinetics in aquatic organisms. Metabolisation data are currently lacking to assess the loss of parent compounds by metabolite production. [START_REF] Ueno | Pharmacokinetics and metabolism of miloxacin in cultured eel[END_REF] studied the distribution of the antibiotic miloxacin in the fish Anguilla japonica and found the highest concentrations in kidney, in muscle and liver after oral administration. [START_REF] Smith | Cross-species comparison of fluoxetine metabolism with fish liver microsomes[END_REF] studied the hepatic metabolism of fluoxetine in freshwater fishes (rainbow trout, goldfish, killifish, zebrafish) and found that the metabolism was lower than in mammals, with differences noted regarding the metabolite nature and in proportions. Such studies have never been performed in marine organisms. Concerning some PCPs, more lipophilic than PPs, their risk may be predicted by their bioaccumulation or bioconcentration potential. The main property which influences bioaccumulation is the hydrophobicity of the substance, expressed as log K ow . The log K ow values of the PCPs discussed in the present review range from approximately 5.0 to 7.5. Beyond chemical properties, several biological parameters may influence the bioaccumulation. [START_REF] Borga | Biological and chemical factors of importance in the bioaccumulation and trophic transfer of persistent organochlorine contaminants in arctic marine food webs[END_REF] reported the influence of lipids, seasonality, reproduction, body size, age, sex, life cycle, biotransformation, habitat use, migration, and feeding ecology in bioaccumulation of organochlorine contaminants in arctic marine organisms. Although PCPs have different properties, the influence of such parameters should be taken into consideration. A few studies have been conducted on the distribution and bioaccumulation of PCPs in aquatic organisms, especially in marine organisms. Gatidou et al. (2010) and Kookana et al. (2013) studied the bioaccumulation of triclosan in marine mussels and reported a log BCF of 3.23 and 2.81 L/kg dw, at exposition levels in water of 300 and 100 ng/L, respectively. [START_REF] Gomez | Bioconcentration of two pharmaceuticals (benzodiazepines) and two personal care products (UV filters) in marine mussels (Mytilus galloprovincialis) under controlled laboratory conditions[END_REF] studied the accumulation kinetic of OC and EHMC during 48h in Mytilus galloprovincialis exposed by food at 0h and 24h, and observed higher concentrations 24h after the second spiking than the initial concentration. Bioaccumulation can be observed in marine mammals which may particularly accumulate hydrophobic compounds because they are at the top of the food chain [START_REF] Teramitsu | Identification of novel cytochrome P450 1A genes from five marine mammal species[END_REF]. Indeed, Kannan et al. (2005) detected higher concentrations for musks AHTN and HHCB in marine mammals than in fishes sampled in the California seawater. Considering the available data, it appears that the highest levels were reported for UV filters, which are able to bioaccumulate in organisms. However, for the most lipophilic compounds such as sunscreen compounds, it remains to obtain in the same time the concentrations in seawater and in the organisms, to calculate a BCF and assess the exposure of the organisms to these contaminants. The presence of PCPs in marine mammals confirms their bioconcentration potential and their possible risk. Further investigations on temporal trends, regional and global monitoring of PPCPs is needed to understand their environmental profiles and potential risks to wildlife. As little or no information was being gathered on chemicals of emerging concerns (CECs) on a national scale in US coastal ecosystems, the Mussel Watch Program recommended, since 2009, the inclusion of CECs (in particular PPCPs), as pilot study and regular monitoring efforts are done to assess the risk posed by these contaminants to the marine wildlife. The questions of occurrence (frequency of detection, concentration) and its variability were raised and factors as land use, proximity of wastewater treatment plant outflow and stormwater runoff were discussed. To answer these questions, native mussels were collected and analyzed at 68 sampling sites along the California coasts to characterize the spatial extent and temporal trends in contaminant concentrations [START_REF] Bricker | NOAA's Mussel Watch Program: Incorporating contaminants of emerging concern (CECs) into a long-term monitoring program[END_REF]Dodder et al., 2014;Maruya et al., 2014aMaruya et al., , 2014b)). The results showed that 30 out of 88 PPCPs were detected and that frequencies of detection of lomefloxacine and sertraline exceed 60%. Dodder et al. (2014) revealed a widespread occurrence of PPCPs in mussels without discernible trend with land use. Moreover, neither discharge of WTP nor discharge of stormwater runoff dominated the input. Among CECs, lomefloxacine was proposed to be included in future coastal bivalve monitoring efforts because of its relatively high concentrations and detection frequencies. This study demonstrates that PPCPs have to be taken into account in pollution monitoring programs. Such pilot studies should be conducted in other countries to better understand the local specificities of this contamination.

CONCLUSION

Over the last few decades, the characterization of the PPCP contamination in the marine environment and the identification of sources that lead to contamination have been made possible by the widespread availability of sensitive analytical techniques designed to detect environmental traces. However, studies concerning the quantitative analysis of PPCPs in marine ecosystems are still somewhat limited. Reported concentrations were generally lower than those reported in freshwater environments making the assessment of ecological risks caused by this contamination challenging. Despite the scarcity of quantitative data, the contamination of the marine ecosystem is a new reality that leads to the exposure of the marine wildlife species, confirmed by the data of occurrence in marine organisms available in literature. It is essential to acquire more accurate data on the fate of PPCPs in the marine ecosystem and the effects of PPCPs on marine organisms. The main knowledge gaps and research needs highlighted by the present study address the following issues.

1) Through the analysis of reviewed papers, some factors influencing the distribution of the PPCPs concentrations in marine environment were emphasized. The site conformation and hydrodynamic conditions will largely determine the spatial distribution of marine PPCP concentrations. These particular aspects should be considered when designing an occurrence study at a marine site.

2) A need for harmonizing analytical procedures for multi-residue analyses in aquatic environments was highlighted. It would allow more effective data comparisons and make the characterization of the PPCP contamination more accurate. Moreover, there is a lack of specific quality criteria for organic contaminant multi-residue analyses. More specific guidelines should be completed to obtain higher quality occurrence data for PPCPs.

3) Research projects to assess the fate of PPCPs in the marine environment should be conducted. Sorption studies on marine sediments are rare in literature. For some PPCPs, degradation processes need to be better understood. With these data, hydrodynamic models could help predict the behavior of such substances on a local scale, by integrating degradation and sorption parameters.

4) The assessment of any potential risk of PPCP exposure to marine species should be completed with supplemental studies. The ecological significance of ecotoxicity data extrapolated to natural marine systems is difficult to understand. There is thus a need to conduct long-term ecotoxicological tests on sensitive species at environmental levels. The use of sensitive approaches and informative techniques, such as "omics" approaches, already used for other pollutants such as heavy metals or pesticides [START_REF] Kwon | Characterizing the effect of heavy metal contamination on marine mussels using metabolomics[END_REF][START_REF] Milan | Gene transcription and biomarker responses in the clam Ruditapes philippinarum after exposure to ibuprofen[END_REF] could help obtain this information.

5) In the future, marine pollution monitoring programs conducted at local scales should, to the extent feasible, include PPCPs to improve understanding of the local specificities of the PPCP contamination and thus better inform future management decisions concerning the quality of the marine environment. [START_REF] Andresen | Emerging pollutants in the North Sea in comparison to Lake Ontario, Canada, data[END_REF] Emerging pollutants in the North Sea in comparison to Lake Ontario, Canada, data. Environmental Toxicology and Chemistry 26, 1081-1089. doi:10.1897/06-416R. 1 Bachelot, M., Li, Z., Munaron, D., Le Gall, P., Casellas, C., Fenet, H., Gomez, E., 2012. Organic UV filter concentrations in marine mussels from French coastal regions. Science of the Total Environment 420, 273-279. doi:10.1016/j.scitotenv.2011.12.051

Figure 2 :

 2 Figure 2: Concentration ranges of caffeine (CAF), carbamazepine (CBZ), erythromycin (ETM), sulfamethoxazole (SMX), and trimethoprim (TMP) at different sampling sites in seawater: STP, harbor, estuary, bay, coast, open sea and high sea (ng/L)

Table 1 :

 1 Occurrence of PPCPs in marine sediments (highest concentrations in ng/g dw) OD-PABA:octyl-dimethyl-PABA

	Type	Class	Compound	Concentrations ng/g dw	References
		Antibiotics	chloramphenicol	2.31	Na et al., 2013
			doxycycline	1.54	Na et al., 2013
			erythromycin	2.29-14	Beretta et al., 2014 ; Liang et al., 2013
			roxithromycin	13.5	Liang et al., 2013
			sulfacetamide	1.39	Na et al., 2013
	PPs		sulfadiazine sulfamerazine	1.68 3.67	Na et al., 2013 Na et al., 2013
			sulfameter	56.65	Na et al., 2013
			sulfamethazine	1.76-3.24	Liang et al., 2013; Na et al., 2013
			sulfamethoxypyridazine	7.67	Na et al., 2013
			sulfathiazole	1.89	Na et al., 2013
			tetracyclin	1.74-7.13	Liang et al., 2013; Na et al., 2013
		Antiepileptics	carbamazepine	4.81	Beretta et al., 2014
		NSAIDs	diclofenac	1.06	Beretta et al., 2014
			ibuprofen	14.3	Beretta et al., 2014
		Others	caffeine	23.4	Beretta et al., 2014
			diazepam	0.71	Beretta et al., 2014
		Antimicrobials	triclosan	400	Cantwell et al., 2010
		Musks	AHTN	17.3-27.9	Beretta et al., 2014 ; Zeng et al., 2008
	PCPs	UV filters	HHCB EHMC	44.5-52.5 9	Beretta et al., 2014 ; Zeng et al., 2008 Amine et al., 2012
			OC	78	Amine et al., 2012
			OD-PABA	9	Amine et al., 2012

Table 2A :

 2A Highest concentrations of PPs reported in marine organisms in the literature (ng/g, dry weight or wet weight*), NDV: N-desmethylvenlafaxine, NODDV: N,O-didesmethylvenlafaxine, ODV: O-desmethylvenlafaxine Eleven sampling sites in the Tamar Estuary, influenced by agricultural land runoff, discharges from STPs serving the city of Plymouth and commercial and industrial shipping activities in the area. Two samples in Breivika Harbor, one off the Tromso STP, two 300 m north of an STP, two in a marina, three on a sewage plume (upstream, downstream) and two reference points in the open North Atlantic Ocean. Treated STP and untreated effluents are discharged. from the Eastern Schedt placed in the marina of Nieuwpoort, Oostende, Zeebrugge, and in the open sea. the Yangtze River Estuary, two in coastal waters, and three around an STP (upstream, downstream and in the STP outfall).Sixty two samples collected in the Bohai Sea semi-enclosed sea and in the Yellow Sea (open sea) where coasts have dense human populations, developed industries and agriculture, including animal husbandry and aquaculture. samples in Jiaozhou Bay and in Yantai Bay, close to urbanized areas with agriculture, fish farming, and industries.

	Number of	Type of	PP	Germany,	Four samples in Halifax Estuary, three in Pictou Estuary, where both York). pipe of an local STP and the surrounding surface water.
	Reference Alvarez et al., 2014 Amine et al., 2012 Andresen et al., 2007 Bachelot et al., 2012 Bayen et al., 2013 Benedé et al., 2014 Beretta et al., 2014 Bertin et al., 2011 Bratkovics and Sapozhnikova, 2011 Comeau et al., 2008 del Rey et al., 2012 Dodder et al., 2014 Minh et al., 2009 Rüdel et al., 2006 Xie et al., 2008 Montesdeoca-Esponda et al., 2012 Moon et al., 2011 Siegener and Chen, 2002 Singh et al., 2010 Yang et al., 2011 One sample in Zeng et al., 2008 purchased compounds Sampling water sampling and/or PCP Location Site description 5 Water POCIS PP, PCP USA Eleven sampling stations along the California's San Francisco Bay and the Southern California Bight with urban and agricultural activities, stormwater discharges and STPs. 3 Sediment -PCP Lebanon southern France Sampling in coastal zones of three Lebanese rivers with urban and agricultural pressure, along the El-Mina coastline with a commercial harbor, a fishing harbor and four STPs. In France, sampling in coastal lagoons and in the vicinity of a submarine outfall. 7 Water Active PCP North Sea Sampling sites in the German Bight, a region of special concern for fisheries, heavily influenced by shipping, fishing and recreational activities and by the river Elbe estuary. 3 Organism -PCP France Ten sites along the French coast, three in eastern France, seven in southern France, representing different anthropogenic pressures and geomorphologic configurations. 4 Water Active PP, PCP Singapore Twenty four samples from eight sites around Singapore. 8 Water Active PCP Spain Three sampling sites in the Palmira Beach (Majorca Island), the Malvarrosa Beach and the Pinedo Beach (Valencia). 9 Sediment -P,PCP Brazil Seventeen sampling sites in the Todos os Santos Bay, receiving drainage from various watersheds and the main destination for the domestic and hospital sewage from the city of Salvador. 1 Sediment -PP Chile Sampling at nine sites at the discharge locations of nine STPs distributed along the Pacific Ocean coastline of the Biobío region. STPs treat domestic and industrial waste waters with primary treatment mostly. 7 Water Active PCP USA Sampling at four sites along the Folly Beach, South Carolina, differing in access and in usage. Samples collected in four urbanized estuaries situated along the 11 Water Active PP Canada untreated and treated waste waters are released and two sampling points in the Cocagne Estuary, where there is no sewage release, but possibility of septic tank leaching. 1 Water Active PP USA Fourteen samples along the Oregon coast, from Astoria in the North, to Brookings in the South, some with populated areas with pollution threats (STP, rivers) and some with sparsely populated areas with no identifiable pollution threats. 86 Organism -PP, PCP USA Sixty-eight mussel stations along the coast of California. These stations were located in areas submitted to different pressures (receiving STP 16 Water Active PP Twenty samples in Victoria Harbor, mainly near the sewage effluent 8 Organism -PCP North Sea, Baltic Sea 1 Water Active PCP Denmark and Twenty four sampling sites in the German Bight. Samples from Environmental Specimen Bank (ESB) of mussels and Netherlands fishes eelpout. China discharge points. 5 Sediment -PP Spain Sampling close to a submarine outfall located in the southern region of Gran Canaria Island, discharging treated waste waters from an STP 5 Organism -PCP Korea Fifty two samples of bubbler from dolphins entangled in fishing nets 1 Water Active PP USA Boston Harbor and Massachusetts Bay. 5 Water Active PP,PCP USA Eight samples in Kay Largo Harbor, largest island of Florida Keys, with several tank systems and 40 sampling points in Looe Key, a popular reef for scuba diving and snorkelling. 9 Water, Sediment, SPM Active PP China 6 Sediment -PCP Three sampling sites along the Macao coast, a know pollution China deposition zone in the Pearl River Delta. along the Yellow Sea and the South Sea. Munaron et al., 2012 21 Water POCIS PP France Thirteen samples the Mediterranean coast, from the Italian border to the East to the Spanish border to the West. Sumner et al., 2010 6 Water, Active PCP UK Zhang et al., 2012 13 Water Active PP Twenty seven samples in Laizhou Bay (15 in inner bay and 12 in outer China bay). sediment, SPM discharge, agriculture areas, urbanized areas and stormwater receiving areas). Fair et al., 2009 1 Water, organism Active PCP USA Blood sampled from dolphins in Charleston and in Indian River lagoon. Eighteen samples were collected in estuarine surface waters of Charleston. Fang et al., 2012 4 Water Active PP Taiwan Fourteen samples in Danshui Estuary where Bali STP discharges its effluents through an ocean outfall pipe. It receives untreated sewage from several industries and domestically treated and untreated wastewaters. Fernandes et al., 2011 2 Sediment -PCP Australia receiving effluents from the Bolivar STP. Gago-Ferrero et al., 2013 1 Organism -PCP Brazil Gatidou et al., 2010 1 Organism -PCP Greece Eighteen bivalve samples collected in the Thermaikos Gulf and the Giokas et al., 2004 4 Water Active PCP Greece Giokas et al., 2005 5 Water Active PCP Greece Sampling done in a closed gulf located in a popular touristic area. Picot Groz et al., 2014 9 Organism -PCP Portugal recreational and tourist population pressures. Weigel et al., 2004 13 Water Active PP, PCP Norway Four different beaches in the south of Portugal with different site of recreational and bathing activities. coast). Samples collected along the coastal line of North Greece (Epirus), at a Nguyen et al., 2011 6 Water Active PCP Italy collected in Santa Margherita, San Fruttoso and Camogli (Ligurian Netherlands Lesvos Island. Ten samples, one blank at the Surla Beach in Genoa, nine others were Weigel et al., 2002 2 Water Active PP Norway, UK, Fifteen samples in the North Sea. Vietnam wastewaters. Denmark, USA, the southern Brazilian coast (six sampling sites), impacted by domestic Philippines, one from a reference area. Fifty-six samples collected from dolphins found dead on beaches along Nakata et al., 2012 6 Organism -Malaysia, farming, residential areas and open coastal sites. Vidal-Dorsch et al., 2012 20 Water Active PP, PCP USA located near municipal wastewater outfall effluent discharge areas and PCP Japan, Korea, Coastal waters: harbors, fisheries, aquaculture, commercial, industrial, Samples collected at five stations in the Southern California Bight, four Thirty sampling sites near the Barket Inlet mouth in South Australia, Na et al., 2013 20 Water, organism, Active PP China Twenty sampling sites along the Dalian coasts in the Yellow Sea. Thomas and Hilton, 2004 14 Water Active PP UK Twenty two samples in estuaries of the rivers Tyne, Tees, Mersey, and Zhang et al., 2013a 11 Water Active PP China Thames and Belfast Lough. sediment Nakata et al., 2007 5 Organism -PCP Japan Samples in Cortiou rocky inlet (Marseille) in the Mediterranean Sea in Samples from the Ariake Sea, the Chiba coast, Shizuoka coast, Ise Bay, Mikawa bay, Taiji coast, Seto Inland Sea, Fukuoka coast and the Omura Bay. Togola and Budzinski, 2008 17 Water Active PP France the effluent plume of a wastewater treatment plant (no biological treatment). Sampling in two areas corresponding to semi-enclosed and densely Zhang et al., 2013b 11 Water Active PP China Fifty-six Zheng et al., 2012 11 Water Active PP China Thirty-five samples in Beibu Gulf where aquaculture is developed. Cambodia, China, India, Indonesia, Tovar-Sanchez et al., 2013 2 Water Active PCP Majorca populated beaches and a third considered as a control, an open and scarcely used beach. Zou et al., 2011 21 Water Active PP Twenty-eight samples in Bohai Bay, which receives wastewaters and China municipal sewage from the city of Beijing
	Cantwell et al., 2010 Cavalheiro et al., 2013 Gulkowska et al., 2007 Hoenicke et al., 2007 Jiang et al., 2014 Pintado-Herrera et al., 2014 Rocha et al., 2013 Wille et al., 2010 Rubinfeld and Luthy, 2008 Wille et al., 2011 Cages of mussels Wu et al., 2007 1 Sediment -PCP USA Atlantic coast of the United States including Boston Harbor, Narragansett Bay, the Lower Hudson River and Chesapeake Bay. 9 Water Active PCP France, Spain Samples collected in the Gernika estuary (Bay of Biscay) and the Adour estuary (Bayonne). 9 Water Active PP China Eight samples along Hong Kong coasts, one in Victoria Harbor, one farther away near an STP outfall, two as a reference location, and three in waters influenced by an STP outfall. 8 Organism -PCP USA Mollusks deployed at 4 sites: Coyote Creek, Redwood Creek, Napa River, and Yerba Buena Island (San Francisco Estuary). 31 Water Active PP, PCP Taiwan Fifty-three sampling stations in coastal south-western Taiwan, which 2 Water, sediment Active PCP Sampling sites in the province of Cadiz, in the Guadalete River estuary Spain receiving urban, agricultural and industrial effluents discharges. 2 Water Active PP Nine sampling sites in the Ria Formosa Lagoon along the coast 13 Water Active PP Eleven harbors (Ostend, Nieuwpoort and Zeebrugge), six offshore and Belgium two Schedt Estuary samples. Portugal covering urban centers and a protected natural park area. 2 Water, sediment Active PCP USA Sediments collected from 14 sites located in the South San Francisco estuary intertidal zone. Water samples were collected from the outfall 11 Organism -PP Belgium 1 Water Active PCP China Sampling in Victoria Harbor and Tai Po Harbor (Hong Kong).

Table A :

 A Main characteristics of sites where PPCP contamination was reported in the papers reviewed (PP: pharmaceutical, PCP: personal care product, SPM: suspended particulate matter, UK: United Kingdom, USA: United States of America) Alvarez, D.A., Maruya, K.A., Dodder, N.G., Lao, W., Furlong, E.T., Smalling, K.L., 2014. Occurrence of contaminants of emerging concern along the California coast (2009-10) using passive sampling devices. Marine Pollution Bulletin 81, 347-354. doi:10.1016/j.marpolbul.2013.04.022 Amine, H.,[START_REF] Amine | UV filters, ethylhexyl methoxycinnamate, octocrylene and ethylhexyl dimethyl PABA from untreated wastewater in sediment from eastern Mediterranean river transition and coastal zones[END_REF]. UV filters, ethylhexyl methoxycinnamate, octocrylene and ethylhexyl dimethyl PABA from untreated wastewater in sediment from eastern Mediterranean river transition and coastal zones. Marine Pollution Bulletin 64, 2435-2442. doi:10.1016/j.marpolbul.2012.07.051 Andresen, J.A., Muir, D.,

Acknowledgement

Funding support was obtained from the Agence Nationale de la Recherche, France, and the PEPSEA Project is acknowledged. This research benefited from the support of the Chair VEOLIA ENVIRONNEMENT -HydroSciences: Risk analysis relating to emerging contaminants in water bodies. M.J. Martinez Bueno thanks UM1 (University of Montpellier) for the post-doctorate grant.

Class


Jojomon Joseph
email: joseph.jojomon@mitis.be

Michel Delanaye

Danish Rehman

Rabia Nacereddine

Jan G Korvink

Juergen J Brandner

A Marie-Curie-ITN within H2020 ISTEGIM 2019 -282727 NUMERICAL AND EXPERIMENTAL INVESTIGATION OF HEAT EXCHANGER PERFORMANCE FOR A MICRO-CHP APPLICATION

Keywords: Micro channel, CFD methodology, Reduced model, Wire-net perturbators, S-shaped perturbators, Hightemperature heat exchangers

) along the counter-flow passages with an integrated collector.

Microchannel performance

Three-dimensional, ideal gas, steady CHT simulations were carried out to investigate the effect of thermal efficiency and pressure losses for various inlet mass flow rates in ANSYS Fluent. Turbulent K-ω shear stress transport turbulent model was utilized for all the CHT models and collectors simulations. The free microchannel simulations were conducted using laminar models. The K -epsilon model is not accurate in the near-wall region. On the contrary, the K-ω model is appropriate for the

Proceedings of the International Symposium on

Thermal Effects in Gas flows In Microscale October 24-25, 2019 -Ettlingen, Germany

2

A Marie-Curie-ITN within H2020

near-wall turbulent flows. Both conventional models are mixed to take advantage of both models [START_REF] Manceau | Industrial codes for CFD, International masters in turbulence[END_REF].

The microchannel thermal efficiency, ε, % is calculated using the relation,

ε, % = C ) (T ,- ) -T /01 ) )
min(C 6 , C ) ) (T ,- ) -T ,- 6 ) × 100 [START_REF] Joseph | Advanced numerical methodology to analyze high-temperature wire-net compact heat exchangers for a microcombined heat and power system application[END_REF] where Cp 6/) being the hot and cold fluid capacity rates, T ,-//01 ) and T ,-//01 6 are the inlet and outlet temperatures of the counter-flow channels. m <6/<) is the microchannel mass flow rate at hot and cold inlet. The microchannel pressure losses, ∆P, % were calculated using the relation, ΔP, % = P ,--P /01 P ?@ × 100

(3)
Where, P ,-//01 is the inlet and outlet total pressure drop and P ?@ is the absolute pressure at the inlet.

Two types of geometrical symmetry exist in a plane that is parallel to the inlet flow direction (see Fig. 1a). cylindrical collectors with wire-net microchannel is shown in Fig. 1a. The primary symmetrical domain (see Fig. 1b) is along half of the secondary collector diameter. Besides, the secondary symmetrical domain is at the centre of the wire-net compact heat exchanger (see Fig. 1c).

It is computationally expensive to carry out a Conjugate Heat Transfer (CHT) analysis by holding the primary symmetry (see Fig. 1b). Similarly, periodic boundary conditions were implemented in the plane that is perpendicular to the inlet flow direction. A periodicity exists in half of the microchannel foil thickness on every hot and cold side alternatively. Thus, the counter-flow arrangement is simplified into a single hot and cold microchannel with partition foil above it, as shown in Fig. 1c.

Fig. 2a depicts the non-dimensional velocity contours for microchannels with and without wire-net. The non-uniform velocity distribution in the microchannels (without wire-net) adversely affects the compact heat exchanger performance as mentioned by Yang et al. [START_REF] Yang | Experimental and Numerical Analysis of Gas Forced Convection through Microtubes and Micro Heat Exchangers[END_REF] due to the least resistance from the inlet to the outlet. This reduces the benefits of counter-flow passages since the maximum velocity gradients lie at two extreme inlets (see Fig. 2a). However, the microchannels with wire-net have more homogeneous velocity distribution that retains the counter-flow effects (see Fig. 2a). These effects are similar to the conventional grid turbulence theory [START_REF] Gersten | Boundary-Layer Theory[END_REF] where a grid generates turbulence that is nearly homogeneous and isotropic. This is the idealized model assumed in most of the turbulence theory and most of the turbulence models [START_REF]Grid turbulence[END_REF]. Thus the numerical model was further simplified (see Fig. 1c and1e) for detailed CHT analysis.

There is an optimum mass flow rate where the thermal efficiency reaches a maximum [START_REF] Joseph | Advanced numerical methodology to analyze high-temperature wire-net compact heat exchangers for a microcombined heat and power system application[END_REF][START_REF] Joseph | Numerical and experimental investigation of a wire-net compact heat exchanger performance for high-temperature applications[END_REF]. However, a substantial decrease in efficiency at higher mass flow rates has been encountered. The steepness of this efficiency curve pattern is stronger for the S-shape perturbator compared to the wire-net protrusions (see Fig. 2b). This steepness increases the working range and thereby reduces the size and cost of the compact heat exchanger. As the steepness decreases, the microchannels can work at high mass flow rates with higher efficiency and thereby the number of microchannels required will decrease. As the result, heat exchanger becomes more compact and cost-effective. However, for the wire-net (at higher Reynolds numbers) the pressure loss is relatively high. The pressure loss varying pattern (along with an increasing mass flow rate) is quadratic, which is similar to the conventional

C 6 = m <6 Cp 6 ; C ) = m <) Cp ) ( 2
)
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Darcy Forschmiers Law, where the inertial and viscous term are well-balanced. The free microchannels have the least pressure losses as expected. The wire-net introduces higher pressure losses compared to S-shaped fins (see Fig. 2b). CHT analysis was conducted on microchannels with different arrangement of S-shape perturbators.

The number for S-shaped fins of normal, inverted and aligned arrangements were 22, 26 and 26

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respectively. Fig. 3 shows the pressure loss and thermal efficiency of the microchannels with different S-shaped fin arrangement. The quadratic pressure loss curve is plotted along the secondary y-axis, and the thermal efficiency is plotted along the primary y-axis. The microchannel performance is not directly proportional to the number of fins. However, the performance is directly proportional to the flow physics. In general, the pressure losses were lowest for the case in which the S-shaped fins were inverted, which results in lower thermal efficiency as well. A CFD methodology was utilised (presented in paper Joseph et al. [START_REF] Joseph | Advanced numerical methodology to analyze high-temperature wire-net compact heat exchangers for a microcombined heat and power system application[END_REF][START_REF] Joseph | Numerical and experimental investigation of a wire-net compact heat exchanger performance for high-temperature applications[END_REF] for the collector analysis. The primary and secondary collector mesh model is depicted in Fig. 4a and4b, respectively. Half section of the cylindrical collectors that feed 60 microchannels is depicted in Fig. 4a. Trapezoidal primary collectors distributed the flow to 16 secondary collector inlets and illustrated in Fig. 4b. Apparently, a cylindrical channel with porous medium approximation replaces the effects of secondary collector and microchannels. The microchannels of the wire-net/S-shape fins have a complicated structure, which makes the numerically expensive to simulate. The best method is to split the heat exchanger configuration part by part and analyze the performance using Reduced Order Modelling (ROM). An outline of the CFD methodology is shown in Fig. 5a. Secondary collectors mass flow rate is defined as the deviation from the ideal CHT inlet mass calculated using the relation,

m <BCD = E FG g -HI (4)
m <BCD is the microchannel mass flow rate,m 6/ is the collector mass flow rate, n UV is the number of plates/channels and g is the microchannel size reduction coefficient, calculated because of simplification of computational domain (symmetric and periodic BCs). For primary collectors, its defined as the ideal secondary collector mass flow rate calculated using,

m 6/ = E ]G ^-_I (5)
m 6/ is the secondary collector mass flow rate, m 1/ is the total mass flow rate and n @V is the number of blocks/exchangers

The modelling is performed in three different stages: 1. Microchannel Conjugate Heat Transfer model -Estimating the microchannel performance using detailed three-dimensional CHT analysis. 2. Reduced model for secondary collectors-Microchannels are replaced by porous medium models to evaluate the flow maldistribution and thereby the secondary collector performance. Therefore, the microchannels are having a very coarse mesh (10 000 cells per channels), and the secondary collector has a highly refined mesh to capture the secondary effects. 3. Reduced model for primary collectors-Scalability of the ROM is utilized to model both microchannel along with the secondary collectors as a single porous medium. Therefore, the effects of both microchannels and secondary collectors were introduced into a cylindrical duct. The cylindrical duct has a very coarse mesh, and the primary collector has a highly In the first stage of the CFD modelling, a detailed CHT analysis is carried out for a microchannel section with specific boundary conditions. Microchannel performance characteristics are utilized to model the microchannels as porous media with inertial and viscous coefficients as the main parameters. In the second stage of modelling, the microchannels are considered as porous media, and the secondary collector performance is evaluated. Constant Integration Method (CIM) based on Darcy-Forchheimer law was utilized to calculate the porous medium characteristics which replicated the conjugate heat transfer model. The computational domain is sharply reduced since the microchannels are examined as porous media with free-slip boundary condition.

In the third stage of modelling, the microchannels with collectors are considered as porous media, and the scalability of the ROM provides the easiness to create the temperature and pressure jump across different type of cross-sections. Scalability of the ROM is developed to characterize the primary collector performance and thereby the overall heat exchanger performance for the micro CHP system.

Porous medium

The global parameters such as pressure drop, thermal efficiency, and turbulent viscosity are determined from three-dimensional CHT analysis of microchannels. This is utilized to calculate the inertial and viscous coefficients (porous medium model) of the reduced model using CIM. The Darcy-

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Forchheimer law was modified and implemented to account for the large temperature variation (∆𝑇 = 600 𝐾) and localized turbulence effect in the microchannels [START_REF] Joseph | Advanced numerical methodology to analyze high-temperature wire-net compact heat exchangers for a microcombined heat and power system application[END_REF],

(𝑃 ij -𝑃 klm ) 𝐿 = 1 𝛼 𝐿 𝛥𝑇 𝑚 𝐴 𝑅 𝑃 tu𝑇 v ^(3𝑇 ^-5𝑆 v 𝑇 + 15𝑆 v ^) -15𝑆 v z ^arctan { 𝑇 𝑆 v | v ^) + 𝜖 ~𝑃𝑇 𝑅 • € • € ' + 1 2 𝐶 ^𝑚 𝐴 … 𝑇 2 † € • € ' ‡ (6)
Power per unit volume was implemented as a source term along the microchannels (see Eq.( 6)). Joseph et al. [START_REF] Joseph | Advanced numerical methodology to analyze high-temperature wire-net compact heat exchangers for a microcombined heat and power system application[END_REF] implemented the new approach and validated the porous media model (with modified inertial and viscous coefficients) for secondary collectors. Q = m <BCD (T ,- )/6 -T /01 )/6 )Cp )/6 (7) The model is validated numerically and experimentally [START_REF] Joseph | Advanced numerical methodology to analyze high-temperature wire-net compact heat exchangers for a microcombined heat and power system application[END_REF][START_REF] Joseph | Numerical and experimental investigation of a wire-net compact heat exchanger performance for high-temperature applications[END_REF][START_REF] Delanaye | Development of a recuperated flameless combustor for an inverted bryton cycle microturbine used in residential micro-chp[END_REF]. Rehman et al. [START_REF] Rehman | A porous media model for a double-layered gas-to-gas micro heat exchanger operating in laminar flow regime[END_REF] used similar approach for microchannels with large density variations (compressible flows). The collector's flow maldistribution influences the mass flow rate and thereby the heat transfer prediction is biased along with total pressure losses.

Collector performance

Secondary collector

The secondary collectors distribute the flow to 60 microchannels and the flow maldistribution is depicted in Fig. 5b. The collectors with a higher mass flow rate have a maximum deviation from the ideal CHT mass flow rate. Studies made by Thansekhar et al. [START_REF] Thansekhar | Experimental investigation of header shape and inlet configuration on flow maldistribution in microchannel[END_REF] and Teng et al. [START_REF] Liu | Investigation of the flow mald-istribution in microchannels[END_REF] showed that, higher the flow resistance through the channels better is the flow distribution among the channels. From there studies, at higher flow rates, the flow distribution becomes more uniform and also the flow resistance increases with the increased mass flow. As the mass flow rate increases, the microchannel pressure loss also increases. Apparently, the static pressure rise in the secondary collector is not relatively high at higher microchannel mass flow rates. Thus the collectors maintain uniform pressure in the collectors, resulting in a low maldistribution.

Partition foil thickness with 100 and 300 microns was selected for secondary collector performance analysis. An overall thermal efficiency for each collector inlet mass flow rate is calculated as the mass flow rate-weighted average thermal efficiency of all microchannels and plotted in Fig. 5c. The overall pressure losses is extracted directly from the ROM model for specific operating condition and depicted in Fig. 5c. The quadratic increase in pressure loss is evident from the microchannel analysis. The thermal efficiency is higher for the 100 microns configuration. As the partition foil thickness decreases, the thermal efficiency is enhanced for a counter-flow arrangement [START_REF] Yang | Experimental and Numerical Analysis of Gas Forced Convection through Microtubes and Micro Heat Exchangers[END_REF]. Fig. 6a shows the Lambda 2.velocity, vorticity strength of the recirculation zone for three different mass flow rates. The vortices originate at the beginning of the recirculation zone and remain steady enough to dissipate the integral vortex near the collector beds. Due to the intense mixing of the recirculating fluid with the entraining fluid, strong vortices originate along the recirculation zone. The intensity of the recirculation zones of the cylindrical collector is evident from the vorticity contour (see Fig. 6a). Thus the mass flow rate has a strong effect on flow maldistribution. As the resistance inside the microchannel increases, the vorticity strength increases. The mass flow rate distribution near the collector beds become irregular, and deviation from the CHT mass flow rate increases with an increase in collector inlet mass flow rate (see Fig. 5b).

Primary collector

The primary trapezoidal collector inlet distributes the flow to 16 secondary collectors and then to 60 microchannels. Collector flow maldistribution strongly depends on the secondary flows in the primary collectors. Parametric study on different primary collector heights were conducted and the flow maldistribution is depicted in Fig. 6b. As the collector height increases, the maldistribution decreases and the optimum collector height is found to be at 100 mm. The velocity contour of minimum and maximum collector heights is represented in Fig. 6c and6d) respectively. As the height increases, the velocity near the secondary collector inlets decreases, and the recirculation strength also decreases. The highest turbulence production for the maximum height configuration is near the primary collector outlet. The small collector height primary collector configuration has profoundly influenced the flow distribution as well as the turbulence characteristics.

Experimental testing

A mass flow rate controller with an operating range of 0-5000 NmL/min controlled the mass flow rate inlet. The facility is equipped with three flow meters having a different operative range. We switch from one controller to another tank to a three-way valve in order to obtain the desired Reynolds number inside the channel with the best precision. The total pressure drop between the inlet and the

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outlet of the microchannel assembly is measured utilizing a differential pressure transducer (Validyne DP15) with an interchangeable sensing element that allows accurate measurements over the whole range of encountered pressures. Atmospheric pressure is measured using an absolute pressure sensor (Validyne AP42). The pressure sensor calibration is performed using a comparison test pump (Giussani BT 400), which is capable of imposing the desired pressure difference relative to the atmosphere. The analog voltage signal from DP sensors is amplified and is fed to an internal multiplexer board of Agilent 49470A and then read employing the Labview program. To measure the temperature at the entrance of the microchannel a K-type, the calibrated thermocouple is used. Thermocouple voltage and an amplified voltage of pressure sensors are fed to the internal multiplexer board of Agilent 39470A and are read through a PC using a Labview program.

Test bench for microchannels with S-shaped perturbators are depicted in Fig. 7a. The microchannels were tested for a regime of mass flow rates. It was found that the critical Reynolds number has shifted to lower Reynolds number. Deviation of laminar friction factor to turbulent friction factor (from Blasius profile) occurred at Re=180, see Fig. 7b. This is in good agreement with several studies conducted by Shah and Wanniarachchi [START_REF] B. Thonon P. Tochon | Progress in the numerical analysis of compact heat exchanger surfaces[END_REF], Heggs et al. [START_REF] Walton | Local transfer coefficients in corru-gated plate heat exchanger channels[END_REF], Focke et al. [START_REF] Focke | The effect of the corrugation inclination angle on the thermohydraulic performance of plate heat exchangers[END_REF] and Liu and Tsai [START_REF] Tsai | An experimental and numerical investigation of fluid flow in a crosscorrugated channel[END_REF] on corrugated plate heat exchanger microchannel geometries. For Shah, the Reynolds critical was less than 200, while Heggs suggested that the flow is never laminar after Re= 150. The rest authors suggested the Reynolds critical is in between Reynolds number 300 and 400. The length scale (roughness, perturbators size) of the microchannels disturbances determines the turbulent transition.

If the length scale is too small, the turbulent transition occurs at the conventional Reynolds number. When length scale increases, the critical Reynolds number reduces to smaller Reynolds number.

Apart from that, secondary collector together with the microchannel configuration was tested. It was fabricated using 3D printing (plastic). Six pressure taps which were installed for pressure readings (see Fig. 8a). Five pressure taps were installed near the microchannel inlets, and the remaining one was placed at the collector inlet. The size of the pressure tap hole was 60 microns, and it was ensured that the pressure taps were placed precisely at the center of the duct, see Fig. 8a. The test was carried out to investigate the collector pressure losses and compare it with CFD. The results between CFD and microchannel is depicted in Fig. 8b. There is a good agreement between CFD and experiments and the relative error is less than 4 %.

Conclusion

The wire-net microchannels have a better performance in terms of thermal efficiency. On the contrary, S-shape fins have a better performance in terms of pressure losses. The wire-net produced more pressure losses relative to S-shape and plane channels. The wire-net geometry suppresses the separation and reduces the size of flow detachment zones lowering the pressure losses with an enhanced heat transfer.

Collector performance assessed using the ROM showed that the flow maldistribution increases as the microchannel pressure drop decreases. The strength of the recirculation zone near the collector beds was suppressed at higher mass flow rates. Higher the primary collector height, lower the maldistribution, and thereby, thermal efficiency and pressure drop is enhanced. There is an optimum height where the pressure loss is saturated, and the non-uniformity in maldistribution is relatively less (for different primary collector heights). Experimental testing showed that the turbulent transition occurred at very low Reynolds number due to the effect of perturbators. Apart from that, the collector simulation results coincided with the experimental results with good accuracy (< 4%.).

Nomenclature

A -cross-sectional area, m 2 BCs -Boundary conditions CFD -computational fluid dynamics CHP -combined heat and power CHT -conjugate heat transfer CHE -compact heat exchanger Cp 6/) -heat capacity at constant pressure for cold/hot inlet microchannels, -inlet and outlet total temperatures for hot \-cold microchannel inlets and outlets, K ΔT -temperature drop across the microchannel length, K ΔP -pressure drop across the length, Pa Q -thermal source term,

Figure 1 .

 1 Figure 1. (a) Wire net brazed heat exchanger Arrangement, (b) Microchannels with wire-net perturbators, (c) Conjugate Heat Transfer domain, (d) Microchannels with S-shaped perturbators,(e) Conjugate Heat Transfer domain.

Figure 2 .

 2 Figure 2. (a) Non-dimensional velocity contour of microchannels with and without wire-net, (b) Thermal efficiency and pressure drop of free channels, with wire-net and S-shape microchannels for various mass flow rates.

Figure 3 .

 3 Figure 3. Thermal efficiency and pressure losses for three different types of S-shape fin arrangements.

5 AFigure 4 .

 54 Figure 4. (a) Secondary collector model, (b) Primary collector mesh model with 16 porous media which replicates 16 collectors.

6 A

 6 Proceedings of the International Symposium onThermal Effects in Gas flows In Microscale October 24-25, 2019 -Ettlingen, Germany Marie-Curie-ITN within H2020 refined mesh. An overall heat exchanger performance is estimated based on the flow maldistribution and overall pressure losses.

Figure 5 .

 5 Figure 5. (a) Scheme for CFD methodology, (b) Mass flow rate distribution, (c) Secondary collector performance with different microchannel foil thickness

8 A

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Figure 6 .

 6 Figure 6. (a) Secondary collector performance for different heights, (b) velocity contour height= 50 mm, (c) velocity contour height= 160 mm,

Figure 7 . 10 AFigure 8 .

 7108 Figure 7. (a) Experimental test bench for S-shaped microchannels, (b) Friction factor for various Reynolds number

11 A 6 /

 116 Proceedings of the International Symposium onThermal Effects in Gas flows In Microscale October 24-25, 2019 -Ettlingen, Germany length, mm m < , m <6 , m <) -microchannel mass flow for cold/ hot inlet channels, -collector inlet mass flow for cold/hot inlet side, OE• Ž m <BCD microchannel mass flow calculated from CHT model inlet, OE• Žn UV -number of plates PM -porous medium P, P ,-, P /01 , P ?@ -inlet/ outlet total pressure and absolute pressure, Pa ROM -reduced order model R -universal gas constant,

  ,--stream wise mean velocity, inlet velocity, Ž Greek Symbols 1/a -viscous coefficient, m "^ b -inertial coefficients, m "v g -microchannel size reduction coefficient r -density, kg/m 3 e -thermal efficiency, % ϵ E -turbulent viscosity, m ^. s"v

Acknowledgements

This ITN Research Project MIGRATE (www.migrate2015.eu) is supported by European Community H2020 Framework under the Grant Agreement No. 643095. The research of MITIS has been funded by grants Nanocogen+ and Nanocogen+2 from DGO4 and DGO6 directorates of Wallonia.