Assessing Cu impacts on freshwater diatoms: biochemical and metabolomic responses of Tabellaria flocculosa (Roth) Kützing

Viscoelastic Fluid Focusing Chip-ICP-MS Single-Cell Analysis Enables Elucidating the Effect of Extracellular Polymeric Substances on Bioaccumulation of Hg2+/HgS in Microcystis aeruginosa Cell

Understanding the interactions between mercury and microalgae, especially the interactions between inorganic mercury (IHg) and extracellular polymeric substances (EPS, a protective barrier between cells and their external environment), is essential for elucidating mercury's toxicological mechanisms. Given the inherent cell heterogeneity, a novel analysis system of an online viscoelastic fluid focusing chip-time-resolved analysis inductively coupled plasma mass spectrometry has been developed to investigate the bioaccumulation of HgS nanoparticles and Hg2+ in single Microcystis aeruginosa (M. aeruginosa) cells, exploring the interaction mechanisms between HgS/Hg2+ accumulation in algal cells and EPS. The single-cell analysis results reveal minimal bioavailability of HgS within algal cells, with mercury's toxicity to M. aeruginosa being species-dependent. Notably, algal cells exhibited more heterogeneity in HgS uptake than in Hg2+ uptake. Under Hg2+/HgS stress, M. aeruginosa cells with EPS removed (EPS-R algal cells) showed an increased level of bioaccumulation of mercury compared to those with EPS (EPS-C algal cells), highlighting the critical role of EPS in mercury bioaccumulation. Overall, the designed viscoelastic fluid microfluidic focusing chip integrates focusing and cleaning functions, featuring easy fabrication, simple operation, low sample loss, and relatively high throughput. Under the optimal conditions, the sample throughput is 1195 min-1 and the cell recovery is 90%. Besides, this research offers novel insights into the interaction mechanisms between Hg2+/HgS and EPS in microalgal cells and unveils the specific toxic effects of Hg2+/HgS on M. aeruginosa at the single-cell level, contributing to a deeper understanding of mercury's ecological and toxicological impact in aquatic environments.

Potential effects of the discharge of wastewater treatment plant (WWTP) effluents in benthic communities: evidence from three distinct WWTP systems

Wastewater treatment plant (WWTP) effluents can be sources of environmental contamination. In this study, we aimed to understand whether effluents of three different WWTPs may have ecological effects in riverine recipient ecosystems. To achieve this, we assessed benthic phytobenthos and macroinvertebrate communities at three different locations relative to the effluent discharge: immediately upstream, immediately downstream and 500-m downstream the effluent discharge. Two approaches were employed: the ecological status classification as defined in the Water Framework Directive (WFD) based on biological indicators; constrained multivariate analysis to disentangle the environmental drivers (physicochemical variables and contaminants, namely metals, polycyclic aromatic hydrocarbons, pharmaceuticals, and personal care products) of ecological changes across the study sites. The results showed inconsistencies between the WFD approach and the multivariate approach, as well as between the responses of macroinvertebrates and diatoms. The WWTP effluents impacted benthic communities in a single case: macroinvertebrates were negatively affected by one of the WWTP effluents, likely by the transported pharmaceuticals (other stressors are essentially homogeneous among sites). Given the findings and the scarcity of consistent evidence on ecological impacts that WWTP effluents may have in recipient ecosystems, further research is needed towards more sustainable regulation and linked environmental protection measures.

Mercury species induce metabolic reprogramming in freshwater diatom Cyclotella meneghiniana

Mercury is a hazardous pollutant of global concern. While advances have been made in identifying the detrimental effects caused by Hg species in phytoplankton, knowledge gaps remain regarding the metabolomic perturbations induced by inorganic mercury (Hg(II)) and monomethylmercury (MeHg) in these organisms. Diatoms represent a major phytoplankton group essential in various global biogeochemical cycles. The current study combined targeted metabolomics, bioaccumulation, and physiological response assays to investigate metabolic perturbations in diatom Cyclotella meneghiniana exposed for 2 h to nanomolar concentrations of Hg(II) and MeHg. Our findings highlight that such exposures induce reprogramming of the metabolism of amino acids, nucleotides, fatty acids, carboxylic acids and antioxidants. These alterations were primarily mercury-species dependent. MeHg exposure induced more pronounced reprogramming of the metabolism of diatoms than Hg(II), which led to less pronounced effects on ROS generation, membrane permeability and chlorophyll concentrations. Hg(II) treatments presented distinct physiological responses, with more robust metabolic perturbations at higher exposures. The present study provides first-time insights into the main metabolic alterations in diatom C. meneghiniana during short-term exposure to Hg species, deepening our understanding of the molecular basis of these perturbations.

Ecological Effect of Differently Treated Wooden Materials on Microalgal Biofilm Formation in the Grado Lagoon (Northern Adriatic Sea)

Within the framework of the Interreg Italy-Slovenia programme, the project DuraSoft aimed at testing innovative technologies to improve the durability of traditional wooden structures in socio-ecologically sensitive environments. We focused on the impact of different wood treatments (i.e., copper-based coatings and thermal modification) on microbial biofilm formation in the Grado Lagoon. Wooden samples were placed in 2 areas with diverse hydrodynamic conditions and retrieved after 6, 20, and 40 days. Light, confocal and scanning electron microscopy were employed to assess the treatment effects on the microalgal community abundance and composition. Lower hydrodynamics accelerated the colonisation, leading to higher algal biofilm abundances, regardless of the treatment. The Cu-based agents induced modifications to the microalgal community, leading to lower densities, small-sized diatoms and frequent deformities (e.g., bent apices, frustule malformation) in the genera Cylindrotheca and Cocconeis. After 20 days, taxa forming 3D mucilaginous structures, such as Licmophora and Synedra, were present on chemically treated panels compared to natural ones. While in the short term, the treatments were effective as antifouling agents, in the long term, neither the copper-based coatings nor the thermal modification successfully slowed down the biofouling colonisation, likely due to the stimulating effect of nutrients and other substances released from these solutions. The need to develop more ecosystem friendly technologies to preserve wooden structures remains urgent.

Current Status of Omics in Biological Quality Elements for Freshwater Biomonitoring

Freshwater ecosystems have been experiencing various forms of threats, mainly since the last century. The severity of this adverse scenario presents unprecedented challenges to human health, water supply, agriculture, forestry, ecological systems, and biodiversity, among other areas. Despite the progress made in various biomonitoring techniques tailored to specific countries and biotic communities, significant constraints exist, particularly in assessing and quantifying biodiversity and its interplay with detrimental factors. Incorporating modern techniques into biomonitoring methodologies presents a challenging topic with multiple perspectives and assertions. This review aims to present a comprehensive overview of the contemporary advancements in freshwater biomonitoring, specifically by utilizing omics methodologies such as genomics, metagenomics, transcriptomics, proteomics, metabolomics, and multi-omics. The present study aims to elucidate the rationale behind the imperative need for modernization in this field. This will be achieved by presenting case studies, examining the diverse range of organisms that have been studied, and evaluating the potential benefits and drawbacks associated with the utilization of these methodologies. The utilization of advanced high-throughput bioinformatics techniques represents a sophisticated approach that necessitates a significant departure from the conventional practices of contemporary freshwater biomonitoring. The significant contributions of omics techniques in the context of biological quality elements (BQEs) and their interpretations in ecological problems are crucial for biomonitoring programs. Such contributions are primarily attributed to the previously overlooked identification of interactions between different levels of biological organization and their responses, isolated and combined, to specific critical conditions.

A comparative study of the accumulation and detoxification of copper and zinc in Chlamydomonas reinhardtii: The role of extracellular polymeric substances

Extracellular polymeric substances (EPS) form an interface between microalgae and the surrounding water environment. Copper (Cu) and zinc (Zn) are essential micronutrients but may negatively affect microbial growth when their concentrations reach toxic thresholds. However, how EPS affect the accumulation and resistance of Cu and Zn in microalgae remains largely unknown. Here, we investigated EPS production upon Cu/Zn exposure and compared the tolerance strategies to the two metals by Chlamydomonas reinhardtii with and without EPS. Microalgal EPS synthesis was induced by Cu/Zn treatments, and the functional groups of polysaccharides and proteins were involved in complexation with metal ions. The extraction of EPS aggravated the toxicity and reduced the removal of metals from solution, but the effect was more pronounced for Cu than for Zn. Copper bound on the cell surface accounted for 54.6 ± 2.0 % of the Cu accumulated by C. reinhardtii, whose EPS components strongly correlated with Cu adsorption. In contrast, 74.3 ± 3.0 % of accumulated Zn was absorbed in cells, and glutathione synthesis was significantly induced. Redundancy and linear correlation analyses showed that the polysaccharide, protein and DNA contents in EPS were significantly correlated with Cu accumulation, absorption and adsorption but not with Zn. Data fitted to a Michaelis-Menten model further showed that the EPS-intact cells had higher binding capacity for Cu²⁺ but not for Zn²⁺. These differential impacts of EPS on Cu/Zn sorption and detoxification contribute to a more comprehensive understanding of the roles of microalgal EPS in the biogeochemical cycle of metals.

Bioactive Molecules from Marine Diatoms and Their Value for the Nutraceutical Industry

The search for novel sources of nutrients is among the basic goals for achievement of sustainable progress. In this context, microalgae are relevant organisms, being rich in high-value compounds and able to grow in open ponds or photobioreactors, thus enabling profitable exploitation of aquatic resources. Microalgae, a huge taxon containing photosynthetic microorganisms living in freshwater, as well as in brackish and marine waters, typically unicellular and eukaryotic, include green algae (Chlorophyceae), red algae (Rhodophyceae), brown algae (Phaeophyceae) and diatoms (Bacillariophyceae). In recent decades, diatoms have been considered the most sustainable sources of nutrients for humans with respect to other microalgae. This review focuses on studies exploring their bio-pharmacological activities when relevant for human disease prevention and/or treatment. In addition, we considered diatoms and their extracts (or purified compounds) when relevant for specific nutraceutical applications.

Assessment of metal exposure (uranium and copper) in fatty acids and carbohydrate profiles of Calamoceras marsupus larvae (Trichoptera) and Alnus glutinosa leaf litter

Physiological changes were explored in fatty acids (FA) and carbohydrate (CHO) composition in the shredder Calamoceras marsupus larvae (Trichoptera) and leaf litter (C. marsupus food) exposed to copper and uranium under natural and experimental conditions. We measured FA and CHO content in leaf litter and larvae specimens from reference and impacted streams, and exposed for 5 weeks to four realistic environmental concentrations of copper (35 μg L^-1 and 70 μg L^-1) and uranium (25 μg L^-1 and 50 μg L^-1). Regarding FA, (1) leaf litter had a reduced polyunsaturated FA (PUFA) content in metal treatments, s (14 to 33% of total FA), compared to natural conditions (≥39% of total FA). Leaf litter exposed to uranium also differed in saturated FA (SFA) composition, with lower values in natural conditions and higher values under low uranium concentrations. (2) C. marsupus had/showed low PUFA content under Cu and U exposure, particularly in high uranium concentrations. Detritivores also decreased in PUFA under exposure to both metals, particularly in high uranium concentrations. On the other hand, (1) microorganisms of the biofilm colonizing leaf litter differed in CHO composition between natural (impacted and reference) and experimental conditions, with glucose and galactose being consistently the most abundant sugars, found in different amounts under copper or uranium exposure; (2) CHO of detritivores showed similar high galactose and fucose concentrations in contaminated streams and high copper treatments, whereas low copper treatment showed distinct CHO profiles, with higher mannose, glucose, arabinose, and fucose concentrations. Our study provides evidence of metal exposure effects on FA and CHO contents at different trophic levels, which might alter the quality of food flow in trophic webs.

Metabolic alterations in alga Chlamydomonas reinhardtii exposed to nTiO2 materials

Nano-sized titanium dioxide (nTiO2) is one of the most commonly used materials, however the knowledge about the molecular basis for metabolic and physiological changes in phytoplankton is yet to be explored. In the present study we use a combination of targeted metabolomics, transcriptomics and physiological response studies to decipher the metabolic perturbation in green alga Chlamydomonas reinhardtii exposed for 72 h to increasing concentrations (2, 20, 100 and 200 mg L-1) of nTiO2 with primary sizes of 5, 15 and 20 nm. Results show that the exposure to all three nTiO2 materials induced perturbation of the metabolism of amino acids, nucleotides, fatty acids, tricarboxylic acids, antioxidants but not in the photosynthesis. The alterations of the most responsive metabolites were concentration and primary size-dependent despite the significant formation of micrometer-size aggregates and their sedimentation. The metabolic perturbations corroborate the observed physiological responses and transcriptomic results and confirmed the importance of oxidative stress as a major toxicity mechanism for nTiO2. Transcriptomics revealed also an important influence of nTiO2 treatments on the transport, adenosine triphosphate binding cassette transporters, and metal transporters, suggesting a perturbation in a global nutrition of the microalgal cell, which was most pronounced for exposure to 5 nm nTiO2. The present study provides for the first-time evidence for the main metabolic perturbations in green alga C. reinhardtii exposed to nTiO2 and helps to improve biological understanding of the molecular basis of these perturbations.

Thorium Exposure Drives Fatty Acid and Metal Transfer from Biofilms to the Grazer Lymnaea sp

Aquatic ecotoxicological risks associated with tetravalent metallic elements such as thorium (Th) are still poorly understood. Periphytic biofilm represents an important food source in aquatic environments; thus, such risks could severely affect nutrient and energy cycling in these ecosystems. The present study investigated the potential for Th to change the fatty acid composition of biofilm communities. Bioaccumulation of Th and fatty acids were measured after 4 wk to 2 exposure conditions: a control (C0) and Th exposure (C10). Some major fatty acids such as C16:1n-7 and docosahexaenoic acid C22:6n-3 differed significantly between control and C10 conditions. To determine if Th can be trophically transferred and to investigate the impacts of nutritional quality changes on primary consumers, common pond snails (Lymnaea sp.) were fed for 4 wk with control and Th-exposed biofilm. Thorium appeared to be trophically transferable to the grazers, although we cannot exclude that part of the Th accumulated by the snails may have been taken from the water through release from the biofilms. The composition of major fatty acids observed in the grazers was also significantly affected, notably by a decrease of total polyunsaturated fatty acids. These results indicate that very low Th concentrations can decrease the nutritional quality of organisms at the base of the food chain. Environ Toxicol Chem 2021;40:2220-2228. © 2021 SETAC.

Metabolomic Responses of Green Alga Chlamydomonas reinhardtii Exposed to Sublethal Concentrations of Inorganic and Methylmercury

Metabolomics characterizes low-molecular-weight molecules involved in different biochemical reactions and provides an integrated assessment of the physiological state of an organism. By using liquid chromatography-mass spectrometry targeted metabolomics, we examined the response of green alga Chlamydomonas reinhardtii to sublethal concentrations of inorganic mercury (IHg) and monomethylmercury (MeHg). We quantified the changes in the levels of 93 metabolites preselected based on the disturbed metabolic pathways obtained in a previous transcriptomics study. Metabolites are downstream products of the gene transcription; hence, metabolite quantification provided information about the biochemical status of the algal cells exposed to Hg compounds. The results showed that the alga adjusts its metabolism during 2 h exposure to 5 × 10^-9 and 5 × 10^-8 mol L^-1 IHg and MeHg by increasing the level of various metabolites involved in amino acid and nucleotide metabolism, photorespiration, and tricarboxylic acid (TCA) cycle, as well as the metabolism of fatty acids, carbohydrates, and antioxidants. Most of the metabolic perturbations in the alga were common for IHg and MeHg treatments. However, the exposure to IHg resulted in more pronounced perturbations in the fatty acid and TCA metabolism as compared with the exposure to MeHg. The observed metabolic perturbations were generally consistent with our previously published transcriptomics results for C. reinhardtii exposed to the comparable level of IHg and MeHg. The results highlight the potential of metabolomics for toxicity evaluation, especially to detect effects at an early stage of exposure prior to their physiological appearance.

Characterization of river biofilm responses to the exposure with heavy metals using a novel micro fluorometer biosensor

River biofilms are a suitable indicator of toxic stress in aquatic ecosystems commonly exposed to various anthropogenic pollutants from industrial, domestic, and agricultural sources. Among these pollutants, heavy metals are of particular concern as they are known to interfere with various physiological processes of river biofilm, directly or indirectly related to photosynthetic performance. Nevertheless, only limited toxicological data are available on the mechanisms and toxicodynamics of heavy metals in biofilms. Pulse Amplitude Modulated (PAM) fluorometry is a rapid, non-disruptive, well-established technique to monitor toxic responses on photosynthetic performance, fluorescence-kinetics, and changes in yield in other non-photochemical processes. In this study, a new micro-PAM-sensor was tested to assess potential acute and chronic effects of heavy metals in river biofilm. Toxicity values across the three parameters considered in this study (photosynthetic yield YII, non-photochemical quenching NPQ, and basal fluorescence F₀) were comparable, as determined EC50 were within one order of magnitude (EC50 ∼1-10 mg L^-1). However, the stimulation of NPQ was more clearly associated with early acute effects, especially in illuminated samples, while depression of YII and F₀ were more prevalent in chronic tests. These results have implications for the development of functional indicators for the biomonitoring of aquatic health, in particular for the use of river biofilm as a bioindicator of water quality. In conclusion, the approach proposed seems promising to characterize and monitor the exposure and impact of heavy metals on river periphyton communities. Furthermore, this study provides a fast, highly sensitive, inexpensive, and accurate laboratory method to test effects of pollutants on complex periphyton communities that can also give insights regarding the probable toxicological mechanisms of heavy metals on photosynthetic performance in the river biofilm.

Ecological and toxicological assessments of anthropogenic contaminants based on environmental metabolomics

There has long been a great concern with growing anthropogenic contaminants and their ecological and toxicological effects on living organisms and the surrounding environment for decades. Metabolomics, a functional readout of cellular activity, can capture organismal responses to various contaminant-related stressors, acquiring direct signatures to illustrate the environmental behaviours of anthropogenic contaminants better. This review entails the application of metabolomics to profile metabolic responses of environmental organisms, e.g. animals (rodents, fish, crustacean and earthworms) and microorganisms (bacteria, yeast and microalgae) to different anthropogenic contaminants, including heavy metals, nanomaterials, pesticides, pharmaceutical and personal products, persistent organic pollutants, and assesses their ecotoxicological impacts with regard to literature published in the recent five years. Contaminant-induced metabolism alteration and up/down-regulation of metabolic pathways are revealed in typical organisms. The obtained insights of variations in global metabolism provide a distinct understanding of how anthropogenic contaminants exert influences on specific metabolic pathways on living organisms. Thus with a novel ecotechnique of environmental metabolomics, risk assessments of anthropogenic contaminants are profoundly demonstrated.

Marine Antibiofouling Properties of TiO2 and Ti-Cu-O Films Deposited by Aerosol-Assisted Chemical Vapor Deposition

The actual interest in developing light-induced catalytic coatings to act as an antibiofouling alternative has recently prompted interest in the incorporation of Cu into TiO2 films, working as a visible light sensitizer catalyst. TiO2 and new Ti-Cu-O films with Cu contents ranging between 16% and 75% Cu/(Cu + Ti) are deposited by aerosol-assisted metalorganic chemical vapor deposition at a substrate temperature of 550 °C. The films are composed of TiO2 anatase phase, mixed with Cu2O when including Cu in the composition. Pure TiO2 films’ morphologies are characterized by the formation of microflower-like structures with nanometric petals, which induce a high specific surface. These features are not present in Ti-Cu-O films. A UV-Visible study revealed that the optical band gap energy decreases with increasing Cu content. Interestingly, Ti-Cu-O films presented a highly photo-catalytic activity in the orange-G degradation. Marine biofouling field tests in Lorient’s Harbor in France and in vitro tests were carried out in order to evaluate the antifouling performance of the films, revealing that topography and chemical composition can act differently on different species. Field tests revealed that TiO2 microflowers reduced the fouling coverage. Besides, Ti-Cu-O films with 16 at.% Cu presented lower fouling coverage than films containing 58 at.% Cu. In vitro tests using two diatoms (P. tricornutum and N. perminuta) showed that the spaces between microflowers play a significant role in the adhesion of diatoms: microalgae adhere less when spaces are bigger than their cells, compared to when spaces are of the same size as cells. Films containing Cu did not alter N. perminuta growth nor adhesion, while they affected P. tricornutum by lowering its growth rate and adhesion without noticeable toxicity. Indeed, Cu-Ti-O is a very promising non-toxic fouling release film for marine and industrial applications.

The impacts of century-old, arsenic-rich mine tailings on multi-trophic level biological assemblages in lakes from Cobalt (Ontario, Canada)

Silver mining in the early-1900s has left a legacy of arsenic-rich mine tailings around the town of Cobalt, in northeastern Ontario, Canada. Due to a lack of environmental control and regulations at that time, it was common for mines to dispose of their waste into adjacent lakes and land depressions, concentrating metals and metalloids in sensitive aquatic ecosystems. In order to examine what impacts, if any, these century-old, arsenic-rich mine tailings are having on present-day aquatic ecosystems, we sampled diatom assemblages in lake surface sediment in 24 lakes along a gradient of surface water arsenic contamination (0.4-972 μg/L). In addition, we examined sedimentary Cladocera and chironomid abundances and community composition, as well as open-water zooplankton communities and chlorophyll-a concentrations in10 of these study lakes along a gradient of arsenic contamination (0.9-1113 μg/L). Our results show that present-day arsenic concentration is not a significant driver of biotic community composition of the organisms we studied, but instead, that other variables such as lake depth and pH were more important in structuring assemblages. These results suggest that, while legacy contamination has greatly increased metal concentration beyond historical conditions, variability in lake-specific controls among the study lakes appear to be more important in the structuring of diatom, Cladocera, chironomidae, and zooplankton in these lakes.

Metabolome response to anthropogenic contamination on microalgae: a review

BACKGROUND

Microalgae play a key role in ecosystems and are widely used in ecological status assessment. Research focusing on such organisms is then well developed and essential. Anyway, approaches for a better comprehension of their metabolome's response towards anthropogenic stressors are only emerging.

AIM OF REVIEW

This review presents the biochemical responses of various microalgae species towards several contaminants including metals and chemicals as pesticides or industrial compounds. We aim to provide a comprehensive and up-to-date overview of analytical approaches deciphering anthropogenic contaminants impact on microalgae metabolome dynamics, in order to bring out relevant biochemical markers that could be used for risk assessment.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Studies to date on ecotoxicological metabolomics on microalgae are highly heterogeneous in both analytical techniques and resulting metabolite identification. There is a real need for studies using complementary approaches to determine biomarkers usable for ecological risk assessment.

Impact of diuron and S-metolachlor on the freshwater diatom Gomphonema gracile: Complementarity between fatty acid profiles and different kinds of ecotoxicological impact-endpoints

Fatty acids (FA) are crucial for the maintenance of membrane fluidity and play a central role in metabolic energy storage. Polyunsaturated fatty acids play an essential ecological role since they are key parameters in the nutritional value of algae. Pesticide impacts on fatty acid profiles have been documented in marine microalgae, but remain understudied in freshwater diatoms. The aims of this study were to: 1) investigate the impact of diuron and S-metolachlor on "classical descriptors" (photosynthesis, growth rate, pigment contents, and on the expression levels of target genes in freshwater diatoms), 2) examine the impact of these pesticides on diatom fatty acid profiles and finally, 3) compare fatty acid profiles and "classical descriptor" responses in order to evaluate their complementarity and ecological role. To address this issue, the model freshwater diatom Gomphonema gracile was exposed during seven days to diuron and S-metolachlor at 10 μg.L^-1. G. gracile was mostly composed of the following fatty acids: 20:5n3; 16:1; 16:0; 16:3n4; 14:0 and 20:4n6 and highly unsaturated fatty acids were overall the best represented fatty acid class. S-metolachlor decreased the growth rate and chlorophyll a content of G. gracile and induced the expression of cox1, nad5, d1 and cat genes, while no significant impacts were observed on photosynthesis and carotenoid content. In a more global way, S-metolachlor did not impact the fatty acid profiles of G. gracile. Diuron inhibited photosynthesis, growth rate, chlorophyll a content and induced cat and d1 gene expressions but no significant effect was observed on carotenoid content. Diuron decreased the percentage of highly unsaturated fatty acids but increased the percentage of monounsaturated fatty acids. These results demonstrated that fatty acids responded to diuron conversely to pigment content, suggesting that fatty acids can inform on energy content variation in diatoms subjected to herbicide stress.

Effects of pollution on freshwater aquatic organisms

This paper presents the reviews of scientific papers published in 2018 issues on the effects of anthropogenic pollution on the aquatic organisms dwelling in freshwater ecosystem at global scale. The first part of the study provides the summary of relevant literature reviews followed by field and survey based studies. The second part is based on categories of different classes/sources of pollutants which affect freshwater organism. This is composed of several sections including metals and metalloids, wastewater and effluents, sediments, nutrients, pharmaceuticals, polycyclic aromatic hydrocarbons, flame retardants, persistent organic pollutants, pharmaceuticals and illicit drugs, emerging contaminants, pesticides, herbicides, and endocrine disruptors. The final part of the study highlights the reviews of published research work on new pollutants such as microplastics and engineered nanoparticles which affect the freshwater organisms. PRACTITIONER POINTS: Heavy metals concentrations should be assessed at nano-scale in aquatic environment. Air pollutants could have long-term effects on freshwater ecosystem. Future studies should focus on bioremediations of freshwater pollution.

Assessing the quality of potentially reclaimed mine soils: Environmental implications for the construction of a nearby water reservoir

The cementation complex of Las Viñas (SW Spain) is a partially reclaimed abandoned mine site located in the drainage basin of a water reservoir currently under construction. The aim of this investigation was to analyze these mine soils to evaluate their potential environmental impact, especially on the final reservoir water quality. Results evidence the extremely high acidity of soils (pH of 3.4 and maximum potential acidity of 47 kg CaCO₃/ton), with high concentrations of trace elements, especially As, Pb and Cu. Sequential extraction data reveal the potential release of significant quantities of Mn, Cd, Cu and other easily-soluble trace elements by rainfalls. The weathering and transport of soils to the bottom sediments of the planned reservoir could lead to the release of significant quantities of toxic trace elements to the water column if anoxic (mainly As, Sb, Cr, Ni, Cu and Pb) or oxic (mainly Hg, Pb, V, Cu and As) conditions are found in the sediments. The acidity and metals released from these soils could jeopardize the quality of the reservoir waters. Remediation measures must be therefore adopted, focused on the cleanup and liming of soils in order to promote colonization and vegetation succession, thus avoiding soil erosion and limiting metal release to the hydrosphere. This study proposes the use of different low-cost materials to improve the soil quality, limiting the metal transfer to the planned reservoir water. The information contained in this study could be of great importance in other watersheds affected by abandoned mine sites.

Copper Affects Composition and Functioning of Microbial Communities in Marine Biofilms at Environmentally Relevant Concentrations

Copper (Cu) pollution in coastal areas is a worldwide threat for aquatic communities. This study aims to demonstrate the usefulness of the DNA metabarcoding analysis in order to describe the ecotoxicological effect of Cu at environmental concentrations on marine periphyton. Additionally, the study investigates if Cu-induced changes in community structure co-occurs with changes in community functioning (i.e., photosynthesis and community tolerance to Cu). Periphyton was exposed for 18 days to five Cu concentrations, between 0.01 and 10 μM, in a semi-static test. Diversity and community structure of prokaryotic and eukaryotic organisms were assessed by 16S and 18S amplicon sequencing, respectively. Community function was studied as impacts on algal biomass and photosynthetic activity. Additionally, we studied Pollution-Induced Community Tolerance (PICT) using photosynthesis as the endpoint. Sequencing results detected an average of 9,504 and 1,242 OTUs for 16S and 18S, respectively, reflecting the high biodiversity of marine periphytic biofilms. Eukaryotes represent the most Cu-sensitive kingdom, where effects were seen already at concentrations as low as 0.01 μM. The structure of the prokaryotic part of the community was impacted at slightly higher concentrations (0.06 μM), which is still in the range of the Cu concentrations observed in the area (0.08 μM). The current environmental quality standard for Cu of 0.07 μM therefore does not seem to be sufficiently protective for periphyton. Cu exposure resulted in a more Cu-tolerant community, which was accompanied by a reduced total algal biomass, increased relative abundance of diatoms and a reduction of photosynthetic activity. Cu exposure changed the network of associations between taxa in the communities. A total of 23 taxa, including taxa within Proteobacteria, Bacteroidetes, Stramenopiles, and Hacrobia, were identified as being particularly sensitive to Cu. DNA metabarcoding is presented as a sensitive tool for community-level ecotoxicological studies that allows to observe impacts simultaneously on a multitude of pro- and eukaryotic taxa, and therefore to identify particularly sensitive, non-cultivable taxa.

Blinded by the light: Increased chlorophyll fluorescence of herbicide-exposed periphyton masks unfavorable structural responses during exposure and recovery

In surface waters within agricultural catchments, periphyton - i.e., biofilms containing algae, heterotrophs, and associated detritus - is subjected to multiple stressors including herbicides. Although herbicide effects on periphyton are frequently studied, the focus has been on photosynthesis-inhibiting herbicides while other modes of toxic action have received little attention. Against this background, a 21-days-lasting bioassay was conducted, during which mature periphytic communities were exposed to the carotenoid-biosynthesis-inhibiting herbicide diflufenican for 12 days (up to 10 μg/L; n = 4), followed by a 9-days-lasting recovery phase in herbicide-free medium. Variables related to periphytic functioning (photosynthetic efficiency and non-photochemical quenching) and structure (pigment concentrations, biomass, and algal community structure) were quantified every third day during both experimental phases. Exposure to ≥ 0.2 μg diflufenican/L resulted in 20-25% and 25-30% lowered carotenoid and chlorophyll a concentrations, respectively, likely explained by a reduced algal biovolume as well as diflufenican's mode of toxic action and thus a shift towards a higher heterotrophy of the communities. Despite these adverse effects on the photosynthetic apparatus, the photosynthetic efficiency increased by up to ∼15% under diflufenican exposure judged on higher chlorophyll fluorescence. This may be explained by an up to ∼60% reduced non-photochemical quenching as well as binding of diflufenican to the pigment-protein membrane complex of the photosystem II, two processes causing higher chlorophyll fluorescence. Additionally, phototrophs may have actively increased energy assimilation to cope with higher energy demands under chemical stress. Although periphyton showed some recovery potential following the exposure phase, observed as increasing chlorophyll a concentrations and non-photochemical quenching, periphyton may not be able to quickly recover from stress given the persistent increase in the photosynthetic efficiency. While the processes underlying the observed effects yet remain speculative, the results suggest a shift towards a higher degree of heterotrophy in periphytic communities ultimately increasing the importance of heterotrophic ecosystem functions at impacted sites over the long term.

A freshwater diatom challenged by Zn: Biochemical, physiological and metabolomic responses of Tabellaria flocculosa(Roth) Kützing

Freshwater ecosystems are under threatening anthropogenic pressures worldwide, namely by metals. Diatoms are used as water quality indicators, but the influence of micronutrients such as Zn and its impacts are poorly understood. Thus, our study aimed to elucidate the tolerance level, the cellular targets and the responses to counteract Zn toxicity of freshwater diatoms by exposing Tabellaria flocculosa, isolated from a Zn contaminated stream. Biochemical, physiological and metabolomic approaches were used. It was demonstrated that Zn is toxic to T. flocculosa at concentrations occurring in contaminated environments. At low stress (30 μg Zn/L) few alterations in the metabolome were observed, but the enzymatic (SOD, CAT) and molecular (GSH, GSSG) antioxidant systems were induced, protecting cells from oxidative stress. At moderate stress (500 μg Zn/L) the main changes occurred in the metabolome (increases in fatty acids, amino acids, terpenoids, glycerol and phosphate, decreases in sucrose and lumichrome) with a moderate increase in cell damage (LPO and PC). The concerted action of all these mechanisms resulted in a non-significant decrease of growth, explaining the survival of this T. flocculosa strain in an environment with this Zn concentration. At the highest stress level (1000 μg Zn/L) the metabolome was identical to 500 μg Zn/L, and the induction of antioxidant systems and extracellular ion chelation (exopolysaccharides, frustulins) were the main responses to the increase of Zn toxicity. However, these mechanisms were unable to effectively abrogate cellular damage and growth reduction was observed. Moreover, the decrease in sucrose and especially in lumichrome should be tested as new specific markers of Zn toxicity. The information obtained in this study can assist in environmental risk assessment policies, support the prediction of diatom behaviour in highly impacted Zn environments, such as mining scenarios, and may help develop new indices, which include alterations induced by metals.

Distribution of Microplastics and Nanoplastics in Aquatic Ecosystems and Their Impacts on Aquatic Organisms, with Emphasis on Microalgae

Plastics, with their many useful physical and chemical properties, are widely used in various industries and activities of daily living. Yet, the insidious effects of plastics, particularly long-term effects on aquatic organisms, are not properly understood. Plastics have been shown to degrade to micro- and nanosize particles known as microplastics and nanoplastics, respectively. These minute particles have been shown to cause various adverse effects on aquatic organisms, ranging from growth inhibition, developmental delay and altered feeding behaviour in aquatic animals to decrease of photosynthetic efficiency and induction of oxidative stress in microalgae. This review paper covers the distribution of microplastics and nanoplastics in aquatic ecosystems, focusing on their effects on microalgae as well as co-toxicity of microplastics and nanoplastics with other pollutants. Besides that, this review paper also discusses future research directions which could be taken to gain a better understanding of the impacts of microplastics and nanoplastics on aquatic ecosystems.