Flow conditions influence diuron toxicokinetics and toxicodynamics in freshwater biofilms

Impact of urban pollution on freshwater biofilms: Oxidative stress, photosynthesis and lipid responses

Urban ecosystems are subjected to multiple anthropogenic stresses, which impact aquatic communities. Artificial light at night (ALAN) for instance can significantly alter the composition of algal communities as well as the photosynthetic cycles of autotrophic organisms, possibly leading to cellular oxidative stress. The combined effects of ALAN and chemical contamination could increase oxidative impacts in aquatic primary producers, although such combined effects remain insufficiently explored. To address this knowledge gap, a one-month experimental approach was implemented under controlled conditions to elucidate effects of ALAN and dodecylbenzyldimethylammonium chloride (DDBAC) on aquatic biofilms. DDBAC is a biocide commonly used in virucidal products, and is found in urban aquatic ecosystems. The bioaccumulation of DDBAC in biofilms exposed or not to ALAN was analyzed. The responses of taxonomic composition, photosynthetic activity, and fatty acid composition of biofilms were examined. The results indicate that ALAN negatively affects photosynthetic yield and chlorophyll production of biofilms. Additionally, exposure to DDBAC at environmental concentrations induces lipid peroxidation, with an increase of oxylipins. This experimental study provides first insights on the consequences of ALAN and DDBAC for aquatic ecosystems. It also opens avenues for the identification of new biomarkers that could be used to monitor urban pollution impacts in natural environments.

Experimental testing of two urban stressors on freshwater biofilms

Aquatic ecosystems and their communities are exposed to numerous stressors of various natures (chemical and physical), whose impacts are often poorly documented. In urban areas, the use of biocides such as dodecyldimethylbenzylammonium chloride (DDBAC) and their subsequent release in wastewater result in their transfer to urban aquatic ecosystems. DDBAC is known to be toxic to most aquatic organisms. Artificial light at night (ALAN) is another stressor that is increasing globally, especially in urban areas. ALAN may have a negative impact on photosynthetic cycles of periphytic biofilms, which in turn may result in changes in their metabolic functioning. Moreover, studies suggest that exposure to artificial light could increase the biocidal effect of DDBAC on biofilms. The present study investigates the individual and combined effects of DDBAC and/or ALAN on the functioning and structure of photosynthetic biofilms. We exposed biofilms in artificial channels to a nominal concentration of 30 mg.L-1 of DDBAC and/or ALAN for 10 days. ALAN modified DDBAC exposure, decreasing concentrations in the water but not accumulation in biofilms. DDBAC had negative impacts on biofilm functioning and structure. Photosynthetic activity was inhibited by > 90% after 2 days of exposure, compared to the controls, and did not recover over the duration of the experiment. Biofilm composition was also impacted, with a marked decrease in green algae and the disappearance of microfauna under DDBAC exposure. The integrity of algal cells was compromised where DDBAC exposure altered the chloroplasts and chlorophyll content. Impacts on autotrophs were also observed through a shift in lipid profiles, in particular a strong decrease in glycolipid content was noted. We found no significant interactive effect of ALAN and DDBAC on the studied endpoints.

Urban-use pesticides in stormwater ponds and their accumulation in biofilms

Stormwater ponds frequently receive urban runoff, increasing the likelihood of pesticide contamination. Biofilms growing in surface waters of these ponds are known to accumulate a range of aquatic contaminants, paradoxically providing both water purification services and potentially posing a threat to urban wildlife. Thus, sampling biofilms in stormwater ponds may be a critical and biologically relevant tool for characterizing pesticide contamination and toxicity in urban environments. Here, we aimed to investigate pesticide occurrences at 21 stormwater ponds in Brampton, ON, one of Canada's fastest growing municipalities, and quantify their accumulation in biofilm. Over nine weeks, we collected time-integrated composite water and biofilm samples for analysis of ∼500 current-use and legacy pesticides. Thirty-two pesticide compounds were detected across both matrices, with 2,4-D, MCPA, MCPP, azoxystrobin, bentazon, triclopyr, and diuron having near-ubiquitous occurrences. Several compounds not typically monitored in pesticide suites (e.g., melamine and nicotine) were also detected, but only in biofilms. Overall, 56 % of analytes detected in biofilms were not found in water samples, indicating traditional pesticide monitoring practices fail to capture all exposure routes, as even when pesticides are below detection levels in water, organisms may still be exposed via dietary pathways. Calculated bioconcentration factors ranged from 4.2 to 1275 and were not predicted by standard pesticide physicochemical properties. Monitoring biofilms provides a sensitive and comprehensive supplement to water sampling for pesticide quantification in urban areas, and identifying pesticide occurrences in stormwater could improve source-tracking efforts in the future. Further research is needed to understand the mechanisms driving pesticide accumulation, to investigate toxicity risks associated with pesticide-contaminated biofilm, and to evaluate whether pesticide accumulation in stormwater pond biofilms represents a route through which contaminants are mobilized into the surrounding terrestrial and downstream aquatic environments.

Seasonal variation in structural and functional distribution of periphyton in a macrolide antibiotics-contaminated river

Periphyton, a microbial assemblage of autotrophic and heterotrophic organisms, is vital to aquatic ecosystems. While exposure to macrolide antibiotics has been confirmed to reduce the biodiversity and damage the critical ecological functions in indoor microcosm bioassays, the distribution of periphyton along a macrolide antibiotic pollution gradient in a river has yet to be determined. Herein, we established the spatiotemporal distribution of five major macrolides, i.e., azithromycin (AZI), roxithromycin (ROX), erythromycin (ERY), clarithromycin (CLA), and anhydro erythromycin (ERY-H2O) in water and periphyton of Zao River (Xi'an, China), after which we evaluated the effects on the structures, photosynthetic activity, and carbon utilization capacity of periphyton in March, June, and September 2023. In contrast with the reference sites, the macrolides were identified in all sewage treatment plants (STPs) impacted sites with concentrations ranging from 0.05 to 2.18 μg/L in water and from not detected - 9.67 μg/g in periphyton. Regarding community structure, the occurrence of macrolides was negatively linked to FirmicutesExiguobacterium undae and Exiguobacterium sibiricum, CyanobacteriaOscillatoriales and Vischeria sp., and ChlorophytaMonostroma grevillei, Selenastrum sp. LU21 and Desmodesmus subspicatus. At the functional level, only the metabolism of phenolic acids was significantly decreased in river reach with high antibiotic levels in June, compared to the other five carbon sources that were not altered. The overall photosynthetic activity of periphytic photosystem II remained unchanged in both reference and STPs impacted groups throughout three seasons. Overall, the macrolides released from STPs were correlated with the altered periphytic structures in the river, whereas a similar trend was not detected for the community functions owing to the functional redundancy. A mesocosm experiments warrants further consideration to validate the field results.

New insights into pesticide occurrence and multicompartmental monitoring strategies in stream ecosystems using periphyton and suspended sediment

Streams are susceptible to pesticide pollutants which are transported outside of the intended area of application from surrounding agricultural fields. It is essential to monitor the occurrence and levels of pesticides in aquatic ecosystems to comprehend their effects on the aquatic environment. The common sampling strategy used for monitoring pesticides in stream ecosystems is through the collection and analysis of grab water samples. However, grab water sampling may not effectively monitor pesticides due to its limited ability to capture temporal and spatial variability, potentially missing fluctuations and uneven distribution of pesticides in aquatic environments. Monitoring using periphyton and sediment sampling may offer a more comprehensive approach by accounting for accumulative processes and temporal variations. Periphyton are a collective of microorganisms that grow on hard surfaces in aquatic ecosystems. They are responsive to chemical and biological changes in the environment, and therefore have the potential to act as a cost-effective, integrated sampling tool to monitor pesticide exposures in aquatic ecosystems. The objective of this study was to assess pesticides detected through periphyton, suspended sediment, and conventional grab water sampling methods and identify the matrix that offers a more comprehensive characterization of a stream's pesticide exposure profile. Ten streams across Southern Ontario were sampled in 2021 and 2022. At each stream site, water, sediment and periphyton, colonizing both artificial and natural substrates, were collected and analyzed for the presence of ~500 pesticides. Each of the three matrices detected distinctive pesticide exposure profiles. The frequency of detection in periphyton, sediment and water matrices were related to pesticides' log Kow and log Koc (P < 0.05). In addition, periphyton bioconcentrated 22 pesticides above levels observed in the ambient water. The bioconcentration factors of pesticides in periphyton can be predicted from their log Kow (simple linear regressions, P < 0.05). The results demonstrate that sediment and periphyton accumulate pesticides in stream environments. This highlights the importance of monitoring pesticide exposure using these matrices to ensure a complete and comprehensive characterization of exposure in stream ecosystems.

Identification of polar organic chemicals in the aquatic foodweb: Combining high-resolution mass spectrometry and trend analysis

Environmental risk assessment of chemical contaminants requires prioritizing of substances taken up by biota as it is a starting point for potential adverse effects. Although knowledge about the occurrence of known chemical pollutants in aquatic organisms has significantly improved during the last decade, there is still a poor understanding for a broad range of more polar compounds. To tackle this issue, we proposed an approach that identifies bioaccumulative and biomagnifiable polar chemicals using liquid chromatography coupled with electrospray ionization to high resolution tandem mass spectrometry (LC-HRMS/MS) and combine it with trend analysis using hierarchical clustering. As a proof-of-concept, this approach was implemented on various organisms and compartments (sediment, litter leaves, periphytic biofilm, invertebrates and fish) collected from a small urban river. HRMS/MS data measured via data-independent acquisition mode were retrospectively analysed using two analytical strategies: (1) retrospective target and (2) suspect/non-target screening. In the retrospective target analysis, 56 of 361 substances spanning a broad range of contaminant classes were detected (i.e. 26 in fish, 18 in macroinvertebrates, 28 in leaves, 29 in periphyton and 32 in sediments, with only 7 common to all compartments), among which 49 could be quantified using reference standards. The suspect screening approach based on two suspect lists (in-house, Norman SusDat) led to the confirmation of 5 compounds with standards (three xenobiotics at level 1 and two lipids at level 2) and tentative identification of seven industrial or natural chemicals at level 2 and 3 through a mass spectra library match. Overall, this proof-of-concept study provided a more comprehensive picture of the exposure of biota to emerging contaminants (i.e., the internal chemical exposome) and potential bioaccumulation or biomagnification of polar compounds along the trophic chain.

Regulation and role of extracellular polymeric substances in the defensive responses of Dictyosphaerium sp. to enrofloxacin stress

Algae are susceptible to enrofloxacin (ENR), an antibiotic frequently detected in aquatic environments. However, algal responses, especially the secretion and roles of extracellular polymeric substances (EPS), under ENR exposure remain unknown. This study is the first to elucidate the variation in algal EPS triggered by ENR at both the physiological and molecular levels. The results showed that EPS were significantly (P < 0.05) overproduced along with increased polysaccharide and protein contents in algae exposed to 0.05, 0.5, and 5 mg/L ENR. Secretion of aromatic proteins, especially tryptophan-like substances with more functional groups or aromatic rings, was specifically stimulated. Furthermore, the genes with upregulated expression related to carbon fixation, aromatic protein biosynthesis, and carbohydrate metabolism are direct causes of enhanced EPS secretion. Improved EPS levels increased the cell surface hydrophobicity and provided more adsorption sites for ENR, which strengthened the van der Waals interaction and reduced ENR internalization. The hormesis effects of ENR were alleviated, as illustrated by the less affected cell density, chlorophyll a/b, and carotenoids biosynthesis in algae with EPS. These findings demonstrate the involvement of EPS in algal ENR resistance and promote a deeper understanding of the ecological effects of ENR in aquatic environments.

An Assessment of the Toxicity of Pesticide Mixtures in Periphyton from Agricultural Streams to the Mayfly Neocloeon triangulifer

Residual concentrations of pesticides are commonly found outside the intended area of application in Ontario's surface waters. Periphyton are a vital dietary component for grazing organisms in aquatic ecosystems but can also accumulate substantial levels of pesticides from the surrounding water. Consequently, grazing aquatic organisms are likely subjected to pesticide exposure through the consumption of pesticide-contaminated periphyton. The objectives of the present study were to determine if pesticides partition into periphyton in riverine environments across southern Ontario and, if so, to determine the toxicity of pesticides in periphyton when fed to the grazing mayfly Neocloeon triangulifer. Sites with low, medium, and high pesticide exposure based on historic water quality monitoring data were selected to incorporate a pesticide exposure gradient into the study design. Artificial substrate samplers were utilized to colonize periphyton in situ, which were then analyzed for the presence of approximately 500 pesticides. The results demonstrate that periphyton are capable of accumulating pesticides in agricultural streams. A novel 7-day toxicity test method was created to investigate the effects of pesticides partitioned into periphyton when fed to N. triangulifer. Periphyton collected from the field sites were fed to N. triangulifer and survival and biomass production recorded. Survival and biomass production significantly decreased when fed periphyton colonized in streams with catchments dominated by agricultural land use (p < 0.05). However, the relationship between pesticide concentration and survival or biomass production was not consistent. Using field-colonized periphyton allowed us to assess the dietary toxicity of environmentally relevant concentrations of pesticide mixtures; however, nutrition and taxonomic composition of the periphyton may vary between sites. Environ Toxicol Chem 2023;42:2143-2157. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Twenty Years of Research in Ecosystem Functions in Aquatic Microbial Ecotoxicology

One of the major threats to freshwater biodiversity is water pollution including excessive loads of nutrients, pesticides, industrial chemicals, and/or emerging contaminants. The widespread use of organic pesticides for agricultural and nonagricultural (industry, gardening, etc.) purposes has resulted in the presence of their residues in various environments, including surface waters. However, the contribution of pesticides to the deterioration of freshwater ecosystems (i.e., biodiversity decline and ecosystem functions impairment) remains uncertain. Once in the aquatic environment, pesticides and their metabolites can interact with microbial communities, causing undesirable effects. The existing legislation on ecological quality assessment of water bodies in Europe is based on water chemical quality and biological indicator species (Water Framework Directive, Pesticides Directive), while biological functions are not yet included in monitoring programs. In the present literature review, we analyze 20 years (2000-2020) of research on ecological functions provided by microorganisms in aquatic ecosystems. We describe the set of ecosystem functions investigated in these studies and the range of endpoints used to establish causal relationships between pesticide exposure and microbial responses. We focus on studies addressing the effects of pesticides at environmentally realistic concentrations and at the microbial community level to inform the ecological relevance of the ecotoxicological assessment. Our literature review highlights that most studies were performed using benthic freshwater organisms and that autotrophic and heterotrophic communities are most often studied separately, usually testing the pesticides that target the main microbial component (i.e., herbicides for autotrophs and fungicides for heterotrophs). Overall, most studies demonstrate deleterious impacts on the functions studied, but our review points to the following shortcomings: (1) the nonsystematic analysis of microbial functions supporting aquatic ecosystems functioning, (2) the study of ecosystem functions (i.e., nutrient cycling) via proxies (i.e., potential extracellular enzymatic activity measurements) which are sometimes disconnected from the current ecosystem functions, and (3) the lack of consideration of chronic exposures to assess the impact of, adaptations to, or recovery of aquatic microbial communities from pesticides. Environ Toxicol Chem 2023;42:1867-1888. © 2023 SETAC.

Dissipation of pesticides by stream biofilms is influenced by hydrological histories

To evaluate the effects of hydrological variability on pesticide dissipation capacity by stream biofilms, we conducted a microcosm study. We exposed biofilms to short and frequent droughts (daily frequency), long and less frequent droughts (weekly frequency) and permanently immersed controls, prior to test their capacities to dissipate a cocktail of pesticides composed of tebuconazole, terbuthylazine, imidacloprid, glyphosate and its metabolite aminomethylphosphonic acid. A range of structural and functional descriptors of biofilms (algal and bacterial biomass, extracellular polymeric matrix (EPS) concentration, microbial respiration, phosphorus uptake and community-level physiological profiles) were measured to assess drought effects. In addition, various parameters were measured to characterise the dynamics of pesticide dissipation by biofilms in the different hydrological treatments (% dissipation, peak asymmetry, bioconcentration factor, among others). Results showed higher pesticide dissipation rates in biofilms exposed to short and frequent droughts, despite of their lower biomass and EPS concentration, compared to biofilms in immersed controls or exposed to long and less frequent droughts. High accumulation of hydrophobic pesticides (tebuconazole and terbuthylazine) was measured in biofilms despite the short exposure time (few minutes) in our open-flow microcosm approach. This research demonstrated the stream biofilms capacity to adsorb hydrophobic pesticides even in stressed drought environments.

Vulnerability and tolerance to nickel of periphytic biofilm harvested in summer and winter

Metals are naturally present in freshwater ecosystems but anthropogenic activities like mining operations represent a long-standing concern. Metals released into aquatic environments may affect microbial communities such as periphytic biofilm, which plays a key role as a primary producer in stream ecosystems. Using two 28-day microcosm studies involving two different photoperiods (light/dark cycle of 16/8 vs 8/16), the present study assessed the effects of four increasing nickel (Ni) concentrations (0-6 μM) on two natural biofilm communities collected at different seasons (summer and winter). The two communities were characterized by different structural profiles and showed significant differences in Ni accumulated content for each treatment. For instance, the biofilm metal content was four times higher in the case of summer biofilm at the highest Ni treatment and after 28 days of exposure. Biomarkers examined targeted both heterotrophic and autotrophic organisms. For heterotrophs, the β-glucosidase and β-glucosaminidase showed no marked effects of Ni exposure and were globally similar between the two communities suggesting low toxicity. However, the photosynthetic yield confirmed the toxicity of Ni on autotrophs with maximum inhibition of 81 ± 7% and 60 ± 1% respectively for the summer and winter biofilms. Furthermore, biofilms previously exposed to the highest long-term Ni concentration ([Ni²⁺] = 6 μM) revealed no acute effects in subsequent toxicity based on the PSII yield, suggesting a tolerance acquisition by the phototrophic community. Taken together, the results suggest that the biofilm response to Ni exposure was dependent of the function considered and that descriptors such as biofilm metal content could be seasonally dependent, information of great importance in a context of biomonitoring.

Synthetic periphyton as a model system to understand species dynamics in complex microbial freshwater communities

Phototrophic biofilms, also known as periphyton, are microbial freshwater communities that drive crucial ecological processes in streams and lakes. Gaining a deep mechanistic understanding of the biological processes occurring in natural periphyton remains challenging due to the high complexity and variability of such communities. To address this challenge, we rationally developed a workflow to construct a synthetic community by co-culturing 26 phototrophic species (i.e., diatoms, green algae, and cyanobacteria) that were inoculated in a successional sequence to create a periphytic biofilm on glass slides. We show that this community is diverse, stable, and highly reproducible in terms of microbial composition, function, and 3D spatial structure of the biofilm. We also demonstrate the ability to monitor microbial dynamics at the single species level during periphyton development and how their abundances are impacted by stressors such as increased temperature and a herbicide, singly and in combination. Overall, such a synthetic periphyton, grown under controlled conditions, can be used as a model system for theory testing through targeted manipulation.

Temperature and Photoperiod Affect the Sensitivity of Biofilms to Nickel and its Accumulation

Whereas metal impacts on fluvial communities have been extensively investigated, effects of abiotic parameters on community responses to contaminants are poorly documented. Variations in photoperiod and temperature commonly occur over the course of a season and could affect aquatic biofilm communities and their responses to contaminants. Our objective was to characterize the influence of environmental conditions (photoperiod and temperature) on nickel (Ni) bioaccumulation and toxicity using a laboratory-grown biofilm. Environmental parameters were chosen to represent variations that can occur over the summer season. Biofilms were exposed for 7 days to six dissolved Ni treatments (ranging from 6 to 115 µM) at two temperatures (14 and 20 °C) using two photoperiods (16:8 and 12:12-h light:dark cycle). Under these different scenarios, structural (dry weight biomass and chlorophyll-a) and functional biomarkers (photosynthetic yield and Ni content) were analyzed at four sampling dates, allowing us to evaluate Ni sensitivity of biofilms over time. The results highlight the effects of temperature on Ni accumulation and tolerance of biofilms. Indeed, biofilms exposed at 20 °C accumulated 1.6-4.2-fold higher concentrations of Ni and were characterized by a lower median effect concentration value using photosynthetic yield compared with those exposed at 14 °C. In terms of photoperiod, significantly greater rates of Ni accumulation were observed at the highest tested Ni concentration for biofilms exposed to a 12:12-h compared with a 16:8-h light:dark cycle. Our study demonstrates the influence of temperature on biofilm metabolism and illustrates that environmental factors may influence Ni accumulation response and thus Ni responses of phototrophic biofilms. Environ Toxicol Chem 2022;41:1649-1662. © 2022 SETAC.

A critical review of effect modeling for ecological risk assessment of plant protection products

A wide diversity of plant protection products (PPP) is used for crop protection leading to the contamination of soil, water, and air, which can have ecotoxicological impacts on living organisms. It is inconceivable to study the effects of each compound on each species from each compartment, experimental studies being time consuming and cost prohibitive, and animal testing having to be avoided. Therefore, numerous models are developed to assess PPP ecotoxicological effects. Our objective was to provide an overview of the modeling approaches enabling the assessment of PPP effects (including biopesticides) on the biota. Six categories of models were inventoried: (Q)SAR, DR and TKTD, population, multi-species, landscape, and mixture models. They were developed for various species (terrestrial and aquatic vertebrates and invertebrates, primary producers, micro-organisms) belonging to diverse environmental compartments, to address different goals (e.g., species sensitivity or PPP bioaccumulation assessment, ecosystem services protection). Among them, mechanistic models are increasingly recognized by EFSA for PPP regulatory risk assessment but, to date, remain not considered in notified guidance documents. The strengths and limits of the reviewed models are discussed together with improvement avenues (multigenerational effects, multiple biotic and abiotic stressors). This review also underlines a lack of model testing by means of field data and of sensitivity and uncertainty analyses. Accurate and robust modeling of PPP effects and other stressors on living organisms, from their application in the field to their functional consequences on the ecosystems at different scales of time and space, would help going toward a more sustainable management of the environment. Graphical Abstract Combination of the keyword lists composing the first bibliographic query. Columns were joined together with the logical operator AND. All keyword lists are available in Supplementary Information at https://doi.org/10.5281/zenodo.5775038 (Larras et al. 2021).

Metabolomics insight into the influence of environmental factors in responses of freshwater biofilms to the model herbicide diuron

Freshwater biofilms have been increasingly used during the last decade in ecotoxicology due to their ecological relevance to assess the effect(s) of environmental stress at the community level. Despite growing knowledge about the effect of various stressors on the structure and the function of these microbial communities, a strong research effort is still required to better understand their response to chemical stress and the influence of environmental stressors in this response. To tackle this challenge, untargeted metabolomics is an approach of choice because of its capacity to give an integrative picture of the exposure to multiple stress and associated effect as well as identifying the molecular pathways involved in these responses. In this context, the present study aimed to explore the use of an untargeted metabolomics approach to unravel at the molecular/biochemical level the response of the whole biofilm to chemical stress and the influence of various environmental factors in this response. To this end, archived high-resolution mass spectrometry data from previous experiments at our laboratory on the effect of the model photosynthesis inhibitor diuron on freshwater biofilm were investigated by using innovative solutions for OMICs data (e.g., DRomics) and more usual chemometric approaches (multivariate and univariate statistical analyses). The results showed a faster (1 min) and more sensitive response of the metabolome to diuron than usual functional descriptors, including photosynthesis. Also, the metabolomics response to diuron resulted from metabolites following various trends (increasing, decreasing, U/bell shape) along increasing concentration and time. This metabolomics response was influenced by the temperature, photoperiod, and flow. A focus on a plant-specific omega-3 (eicosapentaenoic acid) playing a key role in the trophic chain highlighted the potential relevance of metabolomics approach to establish the link between molecular alteration and ecosystem structure/functioning impairment but also how complex is the response and the influence of all the tested factors on this response at the metabolomics level. Altogether, our results underline that more fundamental researches are needed to decipher the metabolomics response of freshwater biofilm to chemical stress and its link with physiological, structural, and functional responses toward the unraveling of adverse outcome pathways (AOP) for key ecosystem functions (e.g., primary production).

Microalgae-Based Fluorimetric Bioassays for Studying Interferences on Photosynthesis Induced by Environmentally Relevant Concentrations of the Herbicide Diuron

The widespread agricultural use of the phenylurea herbicide Diuron (DCMU) requires the investigation of ecotoxicological risk in freshwater and soil ecosystems in light of potential effects on non-target primary producers and a heavier effect on higher trophic levels. We used microalgae-based fluorimetric bioassays for studying the interferences on the photosynthesis of a freshwater and soil model green microalga (Chlamydomonas reinhardtii) induced by environmentally relevant concentrations of the herbicide DCMU. Measurements of steady-state chlorophyll a (Chl-a) fluorescence emission spectra were performed; as well, the kinetics of the Chl-a fluorescence transient were recorded. Percentage indexes of interference on photosynthesis were calculated after comparison of steady-state and kinetic Chl-a fluorescence measurements of DCMU-exposed and control C. reinhardtii cell suspensions. The results obtained after 30 min exposure to the herbicide DCMU confirmed a significant inhibitory effect of DCMU 2 μg/L, and no significant differences between %ι values for DCMU 0.2 μg/L and 0.02 μg/L exposures. Positive %ε values from kinetic measurements of the Chl-a fluorescence transient confirmed the same interfering effect of 2 μg/L DCMU on PSII photochemistry in the exposed C. reinhardtii cell suspensions. Negative values of %ε observed for 0.2 and 0.02 μg/L DCMU exposures could be attributable to a presumptive ‘stimulatory-like’ effect in the photochemistry of photosynthesis. Short-term exposure to sub-μg/L DCMU concentration (≤0.2 μg/L) affects the photosynthetic process of the model microalga C. reinhardtii. Similar environmental exposures could affect natural communities of unicellular autotrophs, with hardly predictable cascading secondary effects on higher trophic levels.

Fish eDNA metabarcoding from aquatic biofilm samples: Methodological aspects

Fish eDNA metabarcoding is usually performed from filtered water samples. The volume of filtered water depends on the study scope and can rapidly become time consuming according to the number of samples that have to be processed. To avoid time allocated to filtration, passive DNA samplers have been used to recover fish eDNA from marine environments faster. In freshwater ecosystems, aquatic biofilms were used to catch eDNA from macroinvertebrates. Here, we test the capacity of aquatic biofilms to entrap fish eDNA in a large lake and, therefore, the possibility to perform fish eDNA metabarcoding from this matrix compared to the traditional fish eDNA approach from filtered water samples. Methodological aspects of the use of aquatic biofilms for fish eDNA metabarcoding (e.g. PCR replicates, biological replicates, bioinformatics pipeline, reference database and taxonomic assignment) were validated against a mock community. When using biofilms from habitats sheltered from wind and waves, biofilm and water approach provided similar inventories. Richness and diversity were comparable between both approaches. Approaches differed only for rare taxa. Our results illustrate the capacity of aquatic biofilms to act as passive eDNA samplers of fish eDNA and, therefore, the possibility to use biofilms to monitor fish communities efficiently from biofilms. Furthermore, our results open up avenues of research to study a diversity of biological groups (among which bioindicators as diatoms, macroinvertebrates and fish) from eDNA isolated from a single environmental matrix reducing sampling efforts, analysis time and costs.

Assessing the effect of herbicide diuron on river biofilm: A statistical model

River biofilm communities are the first ones to be exposed to all toxic discharges received via run off from agricultural fields. Hence, changes in river biofilm community structure and growth pattern are considered as indicator of overall health of lotic ecosystem. Toxicants have effect on biofilm biomass, photosynthetic efficiency and chlorophyll a concentrations. Mathematical models may be applied to estimate the overall vigor of riverine ecosystems considering biofilms as indicators. Herein, previous empirical data of Ricart et al. (2009) on long term effects of environmentally relevant concentrations of diuron on biofilm communities of the River Llobregat, Spain was considered as our model inputs. Our objective is to understand the influence of diuron, chlorophyll a concentrations and photosynthetic efficiency on biovolume using a statistical model. The non-linear relationships between biovolume (dependent variable) and diuron, chlorophyll a concentrations and photosynthetic efficiency (independent variables) were represented by constructing three separate basis functions based on day 8 empirical data. Biovolume, due to nonlinear influence as yielded by the basis functions were used in a multiple linear regression model to estimate the net biovolume. Model validation was done based on day 29 empirical data. The experimentally determined biovolume and our model estimated biovolume showed similar trends. Also, diuron and photosynthetic efficiency had significant (p < 0.05) influence on biovolume. Since, the predominance of diatoms as biofilms within periphytic layers is very common in lotic systems, estimation of changes in diatom biovolume will be significant to assess the effect of herbicides. Diatom biovolume of any day (for example day 22) mentioned in the experimental study may be determined by this model, without the requirement of tedious manual biovolume calculation. Our model will be useful in numerous other studies undertaken on the toxic effect of pollutants on biofilms to quickly and accurately estimate the biofilm biovolume.

Exploring the role of water chemistry on metal accumulation in biofilms from streams in mining areas

Biofilms play a key role in aquatic ecosystems. They are ubiquitous, even in the most contaminated ecosystems, and have great potential as biomonitors of exposure to contaminants such as metals. Freshwater biofilms and surface waters were sampled in two active mining areas of Canada: in the northern part of Nunavik (Quebec) and in the Greater Sudbury area (Ontario). Significant linear relationships were found between both total dissolved and free metal ion concentrations with biofilm metal contents for Cu and Ni, but not for Cd. When pH was below 6, biofilms accumulated less metals than at higher pHs. These results confirm that protons have a protective effect, leading to lower internalized metal concentrations. When considering only the sites where pH was above 6, the linear relationships between metal concentrations in water and in biofilms were improved for all three studied metals. The presence of metal ions could also modify the internalization of a given metal. To further study the role of cations as competitors to Cu, Ni and Cd uptake, relationships between the ratio of biofilm metal contents (Cu, Ni and Cd) on the ambient free metal ion concentrations were built as a function of potential cation competitors, such as major cations and metals. Surprisingly, our data suggest that calcium plays a minor role in preventing metal accumulation as compared to magnesium and possibly other metals. At a global scale, metal accumulation remained highly consistent between the two studied regions and over the sampling period, despite differences in ambient physicochemical water characteristics, climate or types of ecosystems. Metal bioaccumulation is thus a promising biomarker to assess metal bioavailability in a mining context. Nevertheless, more data are still required to further highlight the contribution of each competitor in metal accumulation by biofilms and to be able to build a unifying predictive model.

Effects of the insecticide fipronil in freshwater model organisms and microbial and periphyton communities

Fipronil is a broad-spectrum insecticide whose release in the environment damages many non-target organisms. This study evaluated the toxicity of fipronil at two biological levels using in vivo conditions and environmentally relevant concentrations: the first based on two model organisms (aquatic invertebrate Daphnia magna and the unicellular freshwater alga Chlamydomonas reinhardtii) and a second based on three natural communities (river periphyton and freshwater and soil microbial communities). The physicochemical properties of fipronil make it apparently unstable in the environment, so its behaviour was followed with high performance liquid chromatography (HPLC) under the different test conditions. The most sensitive organism to fipronil was D. magna, with median lethal dose (LC₅₀) values from 0.07 to 0.38 mg/L (immobilisation test). Toxicity was not affected by the media used (MOPS or river water), but it increased with temperature. Fipronil produced effects on the photosynthetic activity of C. reinhardtii at 20 °C in MOPS (EC₅₀ = 2.44 mg/L). The freshwater periphyton presented higher sensitivity to fipronil (photosynthetic yield EC₅₀ of 0.74 mg/L) in MOPS and there was a time-dependent effect (toxicity increased with time). Toxicity was less evident when periphyton and C. reinhardtii tests were performed in river water, where the solubility of fipronil is poor. Finally, the assessment of the metabolic profiles using Biolog EcoPlates showed that bacteria communities were minimally affected by fipronil. The genetic identification of these communities based on 16S rRNA gene sequencing revealed that many of the taxa are specialists in degrading high molecular weight compounds, including pesticides. This work allows us to better understand the impact of fipronil on the environment at different levels of the food chain and in different environmental conditions, a necessary point given its presence in the environment and the complex behaviour of this compound.

Exploring the capacity of aquatic biofilms to act as environmental DNA samplers: Test on macroinvertebrate communities in rivers

Aquatic biofilms are heterogeneous assemblages of microorganisms surrounded by a matrix of extracellular polymeric substances (EPS). Recent studies suggest that aquatic biofilms can physically act as sorptive sponges of DNA. We took the opportunity from already available samples of stone biofilms and macroinvertebrates specimens collected in parallel at the same sites to test the capacity of biofilms to act as DNA samplers of macroinvertebrate communities in streams. Macroinvertebrate communities are usually studied with metabarcoding using the DNA extracted from their bodies bulk samples, which remains a time-consuming approach and involves the destruction of all individual specimens from the samples. The ability of biofilms to capture DNA was explored on 19 rivers sites of a tropical island (Mayotte Island, France). First, macroinvertebrate specimens were identified based on their morphological characteristics. Second, DNA was extracted from biofilms, and macroinvertebrate communities were targeted using a standard COI barcode. The resulting morphological and molecular inventories were compared. They provided comparable structures and diversities for macroinvertebrate communities when one is working with the unassigned OTU data. After taxonomic assignment of the OTU data, diversity and richness were no longer correlated. The ecological assessment derived from morphological bulk samples was conserved by the biofilms samples. We also showed that the biofilm method allows to detect a higher diversity for some organisms (Cnidaria), that is hardly accessible with the morphological method. The results of this study exploring the DNA signal captured by natural biofilms are encouraging. However, a more detailed study integrating more replicates and comparing the biodiversity signal based on both morphological and molecular bulk macroinvertebrate samples to the one captured by biofilms will be necessary. Better understanding how the DNA signal captured by natural biofilms represents the biodiversity of a given sampling site is necessary before considering its use for bioassessment applications.

Bioconcentration of glyphosate in wetland biofilms

Wetland biofilms were exposed to the herbicide glyphosate via in situ field exposures and controlled microcosm experiments to measure bioconcentration and metabolism of glyphosate by biofilm organisms. Concentrations of glyphosate in biofilms were two to four orders of magnitude higher than the surrounding water, bioconcentration factors averaged 835 and 199 L·kg-1 in field- and lab-exposed biofilms, respectively. Glyphosate in water where it had been detected in biofilms at field-exposed sites ranged from below detection (<1 μg·L-1) up to 130 μg·L-1. Bioconcentration of glyphosate in biofilms was inversely proportional to concentrations in the surrounding water, and the retention kinetics were similar to both adsorption and enzymatic models. Microorganisms present in both the water and biofilms metabolized glyphosate to its primary breakdown product aminomethyl phosphonic acid (AMPA), with increased rates of breakdown in and around the biofilms. Photosynthetic efficiency of the algae within the biofilms was not affected by 24 h controlled glyphosate exposures. Our results demonstrate the role of biofilms in improving wetland water quality by removing contaminants like glyphosate, but also as a potential exposure route to higher trophic levels via consumption. Due to bioconcentration of pesticides, exposure risk to organisms consuming or living in biofilms may be much higher than indicated by concentrations in ambient water samples.

Role of Biofilms in Contaminant Bioaccumulation and Trophic Transfer in Aquatic Ecosystems: Current State of Knowledge and Future Challenges

In freshwater environments, microbial assemblages attached to submerged substrates play an essential role in ecosystem processes such as primary production, supported by periphyton, or organic matter decomposition, supported by microbial communities attached to leaf litter or sediments. These microbial assemblages, also called biofilms, are not only involved in nutrients fluxes but also in contaminants dynamics. Biofilms can accumulate metals and organic contaminants transported by the water flow and/or adsorbed onto substrates. Furthermore, due to their high metabolic activity and their role in aquatic food webs, microbial biofilms are also likely to influence contaminant fate in aquatic ecosystems. In this review, we provide (1) a critical overview of the analytical methods currently in use for detecting and quantifying metals and organic micropollutants in microbial biofilms attached to benthic substrata (rocks, sediments, leaf litter); (2) a review of the distribution of those contaminants within aquatic biofilms and the role of these benthic microbial communities in contaminant fate; (3) a set of future challenges concerning the role of biofilms in contaminant accumulation and trophic transfers in the aquatic food web. This literature review highlighted that most knowledge on the interaction between biofilm and contaminants is focused on contaminants dynamics in periphyton while technical limitations are still preventing a thorough estimation of contaminants accumulation in biofilms attached to leaf litter or sediments. In addition, microbial biofilms represent an important food resource in freshwater ecosystems, yet their role in dietary contaminant exposure has been neglected for a long time, and the importance of biofilms in trophic transfer of contaminants is still understudied.

The use of epilithic biofilms as bioaccumulators of pesticides and pharmaceuticals in aquatic environments

Biofilms are a consortium of communities of organisms that live in syntrophic relationships and present a higher organization level than that of individual cells. Biofilms dominate microbial life in streams and rivers, enable crucial ecosystem processes, contribute to global biogeochemical flows and represent the main active bacterial life form. Epilithic biofilms are the main biomass found in rivers; their exposure to contaminants can lead to changes in their structure and composition. The composition of these communities is influenced by physicochemical factors, temperature, light and prior exposure to pollutants, among other factors, and it can be used for water quality monitoring purposes. The heterogenous composition of biofilms enables them to accumulate compounds in an integrative manner. Moreover, the availability of several sorption sites and their likely saturation can contribute to bioaccumulation. In aquatic environments, biofilms are also susceptible to the acquisition of antibiotic resistance genes and participate in their dissemination. Anthropic pressure intensification processes continuously expose water resources and, consequently, biofilm communities to different contamination sources. Therefore, the use of biofilms to indicate environmental pollution is reinforced by the progress of studies on the subject. Biofilm communities' response to pollutants in aquatic environments can be mainly influenced by the presence of different organisms, which may change due to community development or age. The current research aims to review studies about biofilm contamination and highlight the importance of biofilm use to better evaluate and maintain the quality of water bodies.

Enhanced excretion of extracellular polymeric substances associated with nonylphenol tolerance in Dictyosphaerium sp

Dictyosphaerium sp. is tolerant to nonylphenol (NP); however, knowledge regarding the mechanisms involved in NP tolerance is limited. In this study, a batch of algal culture experiments were carried out to elucidate the underlying mechanisms by investigating the production and composition of extracellular polymeric substances (EPS) in algae exposed to NP. The excretion of EPS was significantly enhanced (P < 0.001) in algae exposed to 4 and 8 mg/L of NP. The polysaccharides in soluble EPS and the proteins in bound EPS were specifically overproduced. The three-dimensional excitation and emission matrix fluorescence spectra analyses indicated that tyrosine- and tryptophan-like substances were the main functional compositions in the proteins of EPS. In addition, enhanced EPS secretion significantly alleviated the toxicity of NP to the algae by the reduction of cell internalization, as indicated by the higher IC₅₀, biomass, and cell growth rate in the algae with EPS. These discoveries along with the characterizations by algal cell surface hydrophobicity analysis, scanning electron microscopy, and Fourier transform infrared spectra spectroscopy demonstrated the vital role of EPS in the algal resistance to NP.

Pesticide bioaccumulation in epilithic biofilms as a biomarker of agricultural activities in a representative watershed

Brazil is one of the largest consumers of pesticides in the world. The high rainfall rate and inadequate soil use and management promote the transfer of these compounds to the aquatic system. The aim of this study was to identify and quantify pesticides present in epilithic biofilms in order to evaluate the effectiveness of this matrix as a bioindicator able to discriminate areas and periods with different inputs of pesticides. Among the 25 pesticides analyzed in the biofilms, 20 compounds were detected. The epilithic biofilms picked up pesticides independent of their polarities, even in the period of lower use. The frequency and median concentration of five herbicides (2,4-D, atrazine, desethyl-atrazine, simazine, nicosulfuron), three fungicides (carbendazim, epoxiconazole, tebuconazole), and one insecticide (imidacloprid) were highest in biofilms sampled in summer crops during the growing period. Biofilms collected in the upper region of the catchment, where genetically modified soybean and corn cultivated in a no-tillage system prevail, the highest frequency and median concentration of three herbicides (2,4-D, thifensulfuron, isoproturon), four fungicides (carbendazim, epoxiconazole, tebuconazole, metconazole), and one insecticide (imidacloprid) were observed. Despite the excessive amounts of pesticides used in the catchment, the median values of all pesticides in the epilithic biofilm were considered low. The lower diversity and concentration of pesticides observed in the autumn/winter season is representative of lower use of pesticides, barriers to pesticide transfer from soil to water, and the biofilm's resilience capacity to decompose pesticides.

Biofilms Provide New Insight into Pesticide Occurrence in Streams and Links to Aquatic Ecological Communities

Streambed sediment is commonly analyzed to assess occurrence of hydrophobic pesticides and risks to aquatic communities. However, stream biofilms also have the potential to accumulate pesticides and may be consumed by aquatic organisms. To better characterize risks to aquatic life, the U.S. Geological Survey Regional Stream Quality Assessment measured 93 current-use and 3 legacy pesticides in bed sediment and biofilm from 54 small streams in California across a range of land-use settings. On average, 4 times as many current-use pesticides were detected in biofilm at a site (median of 2) as in sediment (median of 0.5). Of 31 current-use pesticides detected, 20 were detected more frequently in biofilm than in sediment and 10 with equal frequency. Pyrethroids as a class were the most potentially toxic to benthic invertebrates, and of the 9 pyrethroids detected, 7 occurred more frequently in biofilm than sediment. We constructed general additive models to investigate relations between pesticides and 6 metrics of benthic community structure. Pesticides in biofilm improved fit in 4 of the 6 models, and pesticides in sediment improved fit in 2. The results indicate that the sampling of stream biofilms can complement bed-sediment sampling by identification of more current-use pesticides present and better estimation of ecological risks.

Light and temperature influence on diuron bioaccumulation and toxicity in biofilms

Variations of temperature and photoperiod throughout different seasons can affect aquatic communities such as biofilms. Biofilms, generally present at the base of trophic chains in freshwaters, are also subject to organic contamination, and are especially affected by herbicides. Many studies have investigated the effect and interactions of herbicides and environmental factors on biofilms, but never with a toxicokinetic point of view. The objective of this study was to assess structural and functional changes in biofilms exposed to diuron, and to link them with contaminant accumulation, under the influence of temperature and light variations. To this aim, biofilms were exposed to all possible combinations of three concentrations (0, 5 and 50 µg L^-1) of diuron, two temperatures (10 and 26 °C), and two light/dark photoperiods (16/8, 10/14), for durations of 0, 1 and 3 days. Diuron accumulation in biofilms was quantified and structural descriptors (protein and polysaccharide contents, dry weight) and functional endpoints (photosynthetic and enzymatic activities) were analyzed. The results obtained mainly highlighted the influence of temperature on diuron bioaccumulation and the associated toxic impact on biofilms. Bioaccumulation in biofilms exposed during three days at 10 °C, at the highest diuron concentration, was in average 1.4 times higher than bioaccumulation on biofilms exposed to 26 °C. Accordingly, the photosynthetic yield was more inhibited at lower than at higher temperatures. Temperature was also the highest impacting factor for metabolism regulation; for example, at 26 °C after three days of exposure, polysaccharide production was boosted under both photoperiods tested.

Potential impact of hydrodynamic shear force in aquifer thermal energy storage on dissolved organic matter releasement: A vigorous shaking batch study

The combination of bioremediation and aquifer thermal energy storage (ATES) has become attractive because of the possibility of solving environmental and energy problems simultaneously. While the impact of ATES on groundwater quality due to temperature change has received ample attention in literature, the effect of the greatly enhanced groundwater flow velocity on groundwater quality has not yet received sufficient scientific attention. To fill this gap in understanding, we conducted a simple yet straightforward experiment to illustrate the impact of hydrodynamic shear force due to the water flow by ATES on the release of dissolved organic matter, which can potentially be advantageous to bioremediation. Vigorous shaking conditions were applied to simulate the enhanced dynamics at the ATES well center and nearby. As the indicators of dissolved organic matter, COD and TOC concentrations were significantly impacted by shaking. COD increased from 5.4 mgO₂/L to 36.3 mgO₂/L during horizontal shaking. The maximum COD level was determined as 33.8 mgO₂/L during orbital shaking, while the TOC level was growing from 6.7 to 28.7 mg C/L. Meanwhile, redox potential (with initial level -100 mV) was decreasing to -450 mV synchronously with the elevating COD and TOC level. Temperature was also revealed as a significant factor in the organic matter releasement. Microbial iron reduction was deemed to occur, yet sulfate reduction was not initiated during the whole experiment. Eventually, the structure of the soil-water matrix has been changed due to the extensive hydraulic and particle collisions, resulting in blackish appearance and thicker layer of fine particles. Overall, the findings advance our understanding of the role of the ATES-induced water flow in the subsurface biogeochemistry and give insight into the perspective of the combination of bioremediation and ATES. In general, an increase in dissolved organic matter can be expected due to the increased shear force at high flow conditions in the ATES system.