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International audience; Since the early 1920’s, pharmaceuticals, including antibiotics, have been massively producedand consumed for the benefit of both human and animal health. Pharmaceuticals residues havethen reached the aquatic environment through diffuse and point (wastewater) sources. Amongthe pharmaceutical residues, the ubiquitous presence of antibiotics could exert a selectivepressure on microbial communities leading to the acquisition and dissemination of antibioticresistance in the environment.We present here the synthesis of recent research projects (e.g. PANDORE, Antibio-tools,Antibiotox, PharmaTox...) investigating the dissemination of pharmaceuticals, includingantibiotics, in the different aquatic compartments (surface water, periphyton, sediment) and itsimpact on periphyton and sediment microbial communities. These projects mainly focused onantibiotic resistance genes (ARG), community tolerance to pharmaceuticals (PICT) and antibioticbiodegradation capacity by combining field studies on different lake and lotic ecosystem (e.g.rivers Arve, Tillet and Le Clain; lake Geneva) and experimental approaches in microcosms. Ourresults highlight the ubiquitous presence of pharmaceuticals in the studied ecosystems and thespecific distribution of pharmaceuticals in the different investigated compartments. The fieldsurveys generated an important antibiotic resistance database including relative abundance ofARG and genetic mobile elements as well as functional measurements of microbial tolerance(PICT approach) to selected pharmaceuticals and biodegradation potential of sulfonamideantibiotics. Antibiotic resistance was found to be positively correlated with the presence ofwastewater treatment plant effluents, but we confirm that the links between exposure levels,i.e. antibiotics concentrations, and antibiotic resistance must be considered in all ecosystemcomplexity. Further analyses are currently on-going to better take into account potentialconfounding factors.These research projects generated advances in our knowledge on pharmaceuticals andantibiotic resistance dissemination within the aquatic environment but also reveal the currentchallenges to better understand the drivers of antibiotic resistance in such complexenvironments.

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International audience; Lake sediments are natural receptors for a wide range of anthropogenic contaminants including organic matter and toxicants such as trace metals, polycyclic aromatic hydrocarbons, polychlorinated biphenyls that accumulate over time. This contamination can impact benthic communities, including microorganisms which play a crucial role in biogeochemical cycling and food-webs. The present survey aimed at exploring whether anthropogenic contamination, at a large lake scale, can influence the diversity, structure and functions of microbial communities associated to surface sediment, as well as their genetic potential for resistance to metals and antibiotics. Changes in the characteristics of these communities were assessed in surface sediments collected in Lake Geneva from eight sampling sites in October 2017 and May 2018. These sampling sites were characterized by a large concentration range of metal and organic compound contamination. Variation between the two sampling periods were very limited for all sampling sites and measured microbial parameters. In contrast, spatial variations were observed, with two sites being distinct from each other, and from the other six sites. Benthic communities from the most contaminated sampling site (Vidy Bay, near the city of Lausanne) were characterized by the lowest bacterial and archaeal diversity, a distinct community composition, the highest abundance of antibiotic resistance genes and functional (respiration, denitrification, methanogenesis, phosphatase, and beta-glucosidase) activity levels. The second sampling site which is highly influenced by inputs from the Rhône River, exhibited low levels of diversity, a distinct community composition, high abundance of antibiotic resistance genes and the highest bacterial abundance. Overall, our results suggest that local anthropogenic contamination, including organic matter and toxicants, is a major driver of the diversity and functioning of sediment-microbial communities in Lake Geneva. This highlights the need to consider benthic microbial communities and a suite of complementary ecotoxicological endpoints for more effective environmental risk assessments of contaminants in lake sediments.

Visioconférence; National audience; Freshwater contamination by pesticide residues is a major and growing threat to aquatic communities, ecosystem functioning and ultimately human health worldwide. Typical pesticide contamination in agricultural landscapes is characterized by a cocktail of a large number of active compounds and their main transformation products, each of them found at very low and temporally fluctuating concentrations. This makes the quantification of pesticide residues in streams highly challenging and costly by means of grab chemical sampling. Accordingly, it makes also difficult to characterize the chronic exposure of aquatic communities in pesticide-contaminated streams and the resultingecological effects on community structure and functions. During the last decade, the development and implementation of pesticide integrative samplers has allowed to improve the monitoring of the chemical quality through the determination of time-weighted average concentrations over an exposure period, leading to a better representativeness of measurements. However, scientists and regulators are still facing the challenge of going beyond the estimation of pesticide concentrations to take into account the ecological effects on exposed aquatic communities in the evaluation of the ecological status in the particular context of pesticide contamination. To overcome these limitations, microbial communities can be viewed as potential bioindicators that may provide a broad array of structural and functional metrics to diagnose the effects of stream contamination by pesticide residues, and constitute an innovative toolbox to monitor the effect of pesticide residues on stream biological quality. In this study, we evaluated 13 structural and functional metrics on microbial communities from 10 streams that belonged to 3 catchments, and repeated themeasurements at 2 seasons in 4 out of the 10 streams. Streams were selected in different agrosystems to be representative of different scenarios of pesticide contamination gradient, as evidenced by pesticide quantification using composite silicone rubber and POCIS integrative chemical samplers (66 molecules targeted). Our metrics were measured on microbial communities associated with sediment (3), periphyton (2) or benthic particulate organic matter (8) and spanned a broad range of microorganism types (bacteria, fungi, algae). They included microbial processes (organic matter decomposition, degradation of targeted pesticides, fungal reproduction rates and enzymatic activities), their resilience to pesticide exposure (Pollution Induced Community Tolerance), as well as community features (fungal, bacterial and algal community structure, fungal biomass, abundance of pesticide degrading micro-organisms). Based on our results and on literature data, we identify and discuss the respective objectives, advantages, disadvantages and knowledge gaps associated with each indicator in the context of estimating the effect of pesticide contamination on the biological quality of streams. Finally, based on a survey of stream and water resource managers, we conclude on their possible applicability and interest for end-users.

International audience; In France, many rivers face complex cocktails of contaminants at concentrations sometimes close to environmental quality standards (EQS). This type of complex pollution is typically encountered in the case of pesticides, and is usually poorly reflected by the bioindicators currently implemented within the European Water Framework Directive (WFD). In fact these indicators are not always able to reveal the subtle effects of this type of pollution, i.e. direct episodic and chronic or indirect (via trophic transfer, etc.) effects. It is therefore essential to develop indicators able to detect early signs of changes in water quality under natural conditions, but also to assess the possible associated indirect effects (e.g. propagation of effects in the food chain, and from upstream to downstream) and their consequences on the functioning of ecosystems. For this purpose, phototrophic biofilms present a wide range of structural and functional descriptors that could be of interest.The contamination that has been observed for several years in the Cleurie River (Eastern France, Vosges) appears to be an ideal case study site for testing such descriptors. Due to industrial activities (textiles), this small headwater forested stream exhibit a complex cocktail of molecules, chronic and episodic (from daily to seasonal basis) but below EQS. This cocktail is characterized by high concentrations of glyphosate and AMPA as well as a high load of dissolved organic matter (OM) dominated by optical brighteners/dyes. The current media coverage of glyphosate associated to frequent changes in the color of the water feed a local environmental controversy, which is part of the more general and old one on the toxicity of pesticides. In this context, an in situ monitoring, solicited by stakeholders, has been recently initiated in order to identify global indicators allowing studying this contamination. Our objectives are to fingerprint the chemical signature of the toxic pressure (e.g. using integrative passive sampling and spectrometry) and to characterize its effects on biofilms, a pivotal ecological player in these ecosystems. This presentation will focus on the first results: traditional biofilm-based descriptors (primary production, biodiversity) will be compared to others currently under development, either structural (the occurrence of deformities displayed by diatoms) or functional (acquisition of tolerance to glyphosate via a PICT-Pollution Induced Community Tolerance approach). These results will be further used within the framework of a broader interdisciplinary approach aiming at studying the circulation of scientific knowledge between the different actors (researchers, end-users, stakeholders…) involved in this controversy.

Xenobiotics such as organochlorine compounds (OCs) and metals have been suggested to play a signif-icant role in the collapse of European eel stocks in the last decades. Several of these pollutants couldaffect functioning of the nervous system. Still, no information is so far available on levels of potentiallyneurotoxic pollutants in eel brain. In present study, carried out on female eels caught in Belgian rivers andcanals, we analyzed brain levels of potentially-neurotoxic trace elements (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Hg,MeHg, Mn, Ni, Pb, Sn, Sb, Zn) and OCs (Polychlorinated biphenyls, PCBs; Hexachlorocyclohexanes, HCHs;Dichlorodiphenyltrichloroethane and its metabolites, DDTs). Data were compared to levels in liver andmuscle tissues. Eel brain contained very high amounts of OCs, superior to those found in the two other tis-sues. Interestingly, the relative abundance of PCB congeners markedly differed between tissues. In brain,a predominance of low chlorinated PCBs was noted, whereas highly chlorinated congeners prevailed inmuscle and liver. HCHs were particularly abundant in brain, which contains the highest amounts of -HCH and ϒ-HCH. p,p’-DDTs concentration was similar between brain and muscle (i.e., about twice that ofliver). A higher proportion of p,p’-DDT was noticed in brain. Except for Cr and inorganic Hg, all potentiallyneurotoxic metals accumulated in brain to levels equal to or lower than hepatic levels. Altogether, resultsindicate that eel brain is an important target for organic and, to a lesser extent, for inorganic neurotoxicpollutants.

In aquatic ecosystems, environmental conditions (e.g. temperature, food quality, water quantity...) are seldom optimal and change overtime. Though these variations may affect organisms' capacity to cope with chemical contamination, they are rarely taken into account in classical ecotoxicological tests and most of the regulation on chemicals is based on single substance test performed under optimal conditions. Nevertheless, different environmental conditions (e.g. food quality) can modify the characteristics of an organism (e.g. nutritional status) and thus can influence both the entrance of chemicals within this organism and its ability to cope with it. In particular, in fish, fatty acid composition can modulate membrane fluidity and thus influence contaminant uptake. Due to their different antioxidant properties, fatty acids are also likely to influence cells' sensibility to oxidative stress induced by contaminants. Fish fatty acid profile is influenced strongly by nutrition and temperature, thus, fish from the same species may present strong differences in their fatty acid profile and may respond differently to contamination. Few studies have been exploring this hypothesis therefore an in vitro approach was set up to better explore the role of a wide range of fatty acids in fish response to contaminants such as metals. Fish hepatocytes from the same cell line (RTL-W1) but with up to 7 different fatty acid profiles were then obtained by enriching the growth medium with 6 different fatty acids of interest. Though these cells were from the same cell line; the modification of their fatty acid profile changed certain of their properties (e.g. membrane fluidity) and modified their response to increasing concentrations of mercury (HgCl2 or CH3HgCl) or cadmium (CdCl2). For instance, cells enriched with the omega-3 fatty acid: alpha-linolenic acid showed a stronger resistance to organic mercury (EC50CH3HgCl = 6.6 µM) than non-enriched cells (EC50CH3HgCl = 2.9 µM) but a similar resistance to cadmium and inorganic mercury. The use of a fish cell line allowed screening the influence of various types of fatty acid profiles on heavy metals' sensitivity of fish. Based on these result, the multiple stress scenarios more likely to present a risk for the environment have been selected for further mechanistic (in vitro) and ecotoxicologic (in vivo) investigation.

Films of biogenic compounds exposed to the atmosphere are ubiquitously found on surfaces of cloud droplets, aerosol particles, buildings, plants, soils, and the ocean. These air/water interfaces host 15 countless amphiphilic compounds concentrated there with respect to bulk water, leading to a unique chemical environment. Here, photochemical processes at the air/water interface of biofilm-containing solutions were studied, demonstrating abiotic VOC production from a mixture of authentic biogenic surfactants under ambient conditions. Using a combination of online-APCI-HRMS and PTR-TOF-MS, unsaturated and functionalized VOCs were identified and quantified, giving fluxes comparable to previous field and laboratory observations. Interestingly, VOC fluxes increased with less living organisms in the samples, indicating that cell lysis due to cell death was the main source for surfactants. In particular, irradiation of samples containing solely biofilm cells and no matrix components exhibited the strongest VOC production upon irradiation. In agreement with previous studies, LC-MS measurements of the liquid phase suggested the presence of fatty acids and known photosensitizers, possibly inducing the observed VOC production via peroxy-radical chemistry. Up to now such VOC emissions were directly accounted to high biological activity in surface waters. However, the obtained results suggest that abiotic photochemistry can lead to similar emissions into the atmosphere, especially in less biologically-active regions. Furthermore, chamber experiments suggested that oxidation (O3/OH-radicals) of the photochemically-produced VOCs leads to aerosol formation and growth, possibly affecting atmospheric chemistry and climate-related processes, such as cloud formation or the Earth’s radiation budget.

Recognizing multiple anthropogenic pressures in marine coastal zones, countries of the Mediterranean region have implemented several directives focused on sustainable management of the Mediterranean Sea coastal zones. One of the essential directives is the Marine Strategy Framework Directive (MSFD), challenging countries, including Croatia, to achieve and maintain Good Environmental Status of their marine environment. The health of the marine environment is undeniably influenced by microorganisms which play a key role in functioning of marine food webs and biogeochemical cycling. The MSFD neglects the importance of microbial communities and possible changes in their function and structure under the anthropogenic influence influencing stability of the whole marine ecosystem. Project MicroLink, funded by the Croatian Science Foundation, aims to highlight the significance of microbial communities in monitoring and consequently preserving the quality of marine environment with the final goal to propose incorporation of the selected microbial attributes among MSFD Quality Descriptors. Sampling of 67 sediments was performed in seven harbors along the eastern Adriatic coast, which were previously identified as pollution “hot spots”. Sediments were comprehensively analyzed and parameters such as metal concentrations, Hg, TP, TN, TC, TBT, toxicity testing etc. were measured. To find the correlation between anthropogenic pollution and changes in the microbial communities, the project MicroLink integrates different approaches: i) multi-domain approach (analyzing changes in Bacteria, Archaea, Protists, and Fungi) and ii) multi-layer approach (changes in structure, microbial networks, abundance of functional genes and biodegradation potential). Due to continuous accumulation of pollutants, sediments and benthic microbial communities could be reliable indicators of the persisting exposure of the marine environment to anthropogenic pressures. Microbial communities should not be neglected in future strategies and measures for conservation of coastal and marine environments.

International audience; Since the early 20's antibiotics have been massively produced and consumed for the benefit of bothhuman and animal health. Nevertheless, antibiotics have also reached the aquatic environmentthrough diffuse sources (e.g. veterinary treatment, contaminated manure application...) and throughwastewater. Consequently, antibiotics concentrations between the ng/L and μg/L range are regularlydetected in surface water and those molecules have also been found in sediments and aquatic biota.The ubiquitous presence of antibiotics exerts a selective pressure on microbial communities leading tothe acquisition and dissemination of antibioresistance in the environment. While both antibiotics andantibioresistance have been found in different aquatic compartments, more investigation is requiredto better understand their distribution and to identify hot spots of accumulation.In this context, we investigated the repartition of antibiotics and antibioresistance in different aquaticcompartments on 4 stations belonging to regional observatories and presenting contrasting levels ofpharmaceuticals: 2 on the Arve river belonging to Sipibel observatory and 2 on Lake Geneva belongingto the Observatory on Lakes. On the Arve river, the 2 stations were located up- and down- stream thedischarge place of a wastewater treatment plant (WWTP) collecting both urban and hospitalwastewaters. On Lake Geneva, one station was located in a relatively pristine area while the secondwas close to the discharge of an urban WWTP. To better identify a potential temporal dynamic ofantibiotics and antibioresistances over seasons, 6 samplings were conducted during 1.5 year. On eachsampling campaign, the following parameters were determined: (i) antibiotics levels in water,sediments and periphyton; (ii) antibioresistance in periphyton and sediments using various techniques:detection of resistance genes, integrons quantification, detection of tolerance acquisition via a PICT(Pollution Induced Community Tolerance) approach; (iii) antibiotics biodegradation potential ofmicrobial community from sediments (by radiorespirometric measurement); (iv) diversity of bacteriaand diatoms in periphyton and sediments; (v) physico-chemical parameters and (vi) metalliccontamination in sediments.While microbial resistance to antibiotics is commonly assessed by quantifying resistance genes orisolating antibiotic resistant bacteria, antibiotic resistance can also be estimated by measuring theacquisition of antibiotics tolerance at community level, following a PICT approach. In our study,periphytic microbial communities from the Arve river were found to have a higher tolerance to thetested antibiotics (ciprofloxacin, ofloxacin, sulfamethazine and erythromycin) than communities fromLake Geneva, in agreement with the expected levels of contamination. In addition, in some cases, ahigher tolerance was also found at stations close to WWTP effluents than in upstream/protectedstations. For example, periphytic microbial communities collected downstream the WWTP on the Arveriver were generally found to have a higher tolerance to ciprofloxacin than the upstream communities.Comparing whole community tolerance to other classical indicators of antibioresistance and toantibiotics levels in the aquatic ecosystems allows us to better understand the interconnectionbetween pharmaceutical exposure, in situ tolerance and genetic potential for antibioresistance.