Antioxidant enzyme activities as biomarkers of Zn pollution in fluvial biofilms

Exploring the Toxicity of Oxytetracycline in Earthworms (Eisenia fetida) Based on the Integrated Biomarker Response Method

Antibiotic contamination has become a global environmental issue of widespread concern, among which oxytetracycline contamination is very severe. In this study, earthworm (Eisenia fetida) was exposed to oxytetracycline to study its impact on the soil environment. The total protein (TP), catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), glutathione S-transferase (GST), and glutathione peroxidase (GPX) oxidative stress indicators in earthworms were measured, and the integrated biomarker response (IBR) approach was used to evaluate the toxic effect of oxytetracycline on earthworms. A Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) and a path analysis model were used to explore the physiological and metabolic processes of earthworms after stress occurs. The results showed that SOD, GPX, and GST play important roles in resisting oxytetracycline stress. In addition, stress injury showed a good dose-effect relationship, and long-term stress from pollutants resulted in the most serious damage to the head tissue of earthworms. These results provide a theoretical basis for understanding the toxic effect of oxytetracycline on soil animals, monitoring the pollution status of oxytetracycline in soil, and conducting ecological security risk assessment.

Ecotoxicity of tire wear particles to antioxidant enzyme system and metabolic functional activity of river biofilms: The strengthening role after incubation-aging in migrating water phases

Tire wear particles (TWPs) are commonly studied for their exudation toxicity, yet a critical knowledge gap exists regarding the source nature and migration of these particulate pollutants, hindering comprehensive environmental risk assessments. This study explores the pristine properties of three typical TWPs (rolling friction (R-TWPs), sliding friction (S-TWPs), and cryogenically milled tire treads (C-TWPs)) and their aging characteristics after incubation in runoff (primary aging) and sewage (further aging). Our investigation aims to unveil the intrinsic mechanisms of TWPs ecotoxicity towards freshwater biofilms. Results reveal that the generation modes significantly impact pristine physicochemical properties, including surface structure, particle size, and EPFR abundance. These factors, in turn, influence acute ecotoxicity, as evidenced by cell mortality, antioxidant enzyme activity responses, and metabolic changes in freshwater biofilms. The ecological toxicity ranking of pristine exposure groups is S-TWPs, R-TWPs, and C-TWPs, attributed to variations in surface properties and particle size. Following incubation and aging, especially in sewage, differences in physicochemical properties among TWPs types diminish. Alarmingly, ecotoxicity intensifies and becomes consistent across TWPs types, driven by the screening of small particles during water incubation aging and the formation of EPFRs on TWPs surfaces stimulated by photosensitive organic matter or groups. This study underscores the aquatic ecological risks associated with TWP surface properties, highlighting the significant influence of environmental aging conditions on these risks.

Rapid transcriptomic and physiological changes in the freshwater pennate diatom Mayamaea pseudoterrestris in response to copper exposure

Diatoms function as major primary producers, accumulating large amounts of biomass in most aquatic environments. Given their rapid responses to changes in environmental conditions, diatoms are used for the biological monitoring of water quality and for performing ecotoxicological tests in aquatic ecosystems. However, the molecular basis for their toxicity to chemical compounds remains largely unknown. Here, we sequenced the genome of a freshwater diatom, Mayamaea pseudoterrestris NIES-4280, which has been proposed as an alternative strain of Navicula pelliculosa UTEX 664 for performing the Organisation for Economic Co-operation and Development ecotoxicological test. This study shows that M. pseudoterrestris has a small genome and carries the lowest number of genes among freshwater diatoms. The gene content of M. pseudoterrestris is similar to that of the model marine diatom, Phaeodactylum tricornutum. Genes related to cell motility, polysaccharide metabolism, oxidative stress alleviation, intracellular calcium signalling, and reactive compound detoxification showed rapid changes in their expression patterns in response to copper exposure. Active gliding motility was observed in response to copper addition, and copper exposure decreased intracellular calcium concentration. These findings enhance our understanding of the environmental adaptation of diatoms, and elucidate the molecular basis of toxicity of chemical compounds in algae.

Evaluation of the acute toxic effects of crude oil on intertidal mudskipper (Boleophthalmus pectinirostris) based on antioxidant enzyme activity and the integrated biomarker response

With the development of marine oil industry, oil spill accidents will inevitably occur, further polluting the intertidal zone and causing biological poisoning. The muddy intertidal zone and Boleophthalmus pectinirostris were selected as the research objects to conduct indoor acute exposure experiments within 48 h of crude oil pollution. Statistical analysis was used to reveal the activity changes of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) in the gills and liver of mudskipper. Then, integrated biomarker response (IBR) indicators were established to comprehensively evaluate the biological toxicity. The results showed that the activities of SOD, CAT and GST in livers were higher than those in gills, and the maximum induction multipliers of SOD, CAT and GPx in livers appeared earlier than those in gills. Both SOD and GPx activities were induced at low pollutant concentrations and inhibited at high pollutant concentrations. For the dose-effect, the change trends of CAT and SOD were roughly inversed. There was substrate competition between GPx and CAT, with opposite trends over time. The activating mechanism of GST was similar to that of GPx, and the activation time was earlier than that of GPx. In terms of dose-effect trends, the IBR showed that the antioxidant enzymes activities in biological tissues were induced by low and inhibited by high pollutant concentrations. Overall, SOD and GPx in gills and CAT and GST in livers of the mudskippers were suitable as representative markers to comprehensively analyze and evaluate the biotoxicity effects of oil pollution in the intertidal zone. The star plots and IBR values obtained after data standardization were consistent with the enzyme activity differences, which can be used as valid supplementary indexes for biotoxicity evaluation. These research findings provide theoretical support for early indicators of biological toxicity after crude oil pollution in intertidal zones.

Antioxidant system status in threatened native fish Barbus meridionalis from the Osor River (Iberian Peninsula): I. Characterization and II. In vitro Zn assays

The evaluation of antioxidant system capacity is important in aquatic toxicology. It was aimed to characterize the liver antioxidant enzymes (SOD, CAT, GPX, GR, and GST) and to test the in vitro Zn effect (200 and 400 ZnSO₄ μg/L) in native fish Barbus meridionalis obtained from the Osor River (NE, Spain) influenced by Zn contamination. The maximal enzyme activities were at pH 7.0-7.5 and 100 mM phosphate buffer. Barbel showed high catalytic activity (high Vmax and low Km) indicating the efficient antioxidant detoxification ability. Direct Zn effect caused an antioxidant system imbalance. Mostly upon lower Zn concentration, GPX activity decreased (95-100 %) though CAT, GR, and GST increased (36-1543 %). GSH values either stimulated (290 %) or inhibited (85-93 %) due to tissue differences. The first record of barbel antioxidant enzyme characterization and in vitro data presenting an unbalanced antioxidant pattern could be significant to evaluate the metal pollution in the Osor River for further in vivo studies.

Influence of Temperature and Nickel on Algal Biofilm Fatty Acid Composition

Freshwater biofilms play an important role in aquatic ecosystems and are widely used to evaluate environmental conditions. Little is known about the effects of temperature and metals on biofilm fatty acid composition. In the present study, we exposed a natural biofilm cultured in mesocosms to a gradient of nickel (Ni) concentrations at 15 and 21 °C for 28 d. Metal bioaccumulation, algal taxonomic composition, and biofilm fatty acid profiles were determined. At both temperatures, bioaccumulated Ni increased with Ni exposure concentration and reached the highest values at 25 µM Ni, followed by a decrease at 55 and 105 µM Ni. In control biofilms, palmitic acid (16:0), palmitoleic acid (16:1n7), oleic acid (18:1n9), linoleic acid (18:2n6), and linolenic acid (18:3n3) were the dominant fatty acids at 15 and 21 °C. This composition suggests a dominance of cyanobacteria and green algae, which was subsequently confirmed by microscopic observations. The increase in temperature resulted in a decrease in the ratio of unsaturated to saturated fatty acids, which is considered to be an adaptive response to temperature variation. Polyunsaturated fatty acids (PUFAs) tended to decrease along the Ni gradient, as opposed to saturated fatty acids which increased with Ni concentrations. Temperature and Ni affected differently the estimated desaturase and elongase activities (product/precursor ratios). The increase in PUFAs at 15 °C was concomitant to an increase in Δ9-desaturase (D9D). The estimated activities of D9D, Δ12-desaturase, and Δ15-desaturase decreased along the Ni gradient and reflected a decline in PUFAs. The elevated estimated elongase activity reflected the observed increase in saturated fatty acids at the highest Ni exposure concentration (105 µM). Our results suggest that fatty acids could be used as an endpoint to evaluate environmental perturbations. Environ Toxicol Chem 2020;39:1566-1577. © 2020 SETAC.

Effects of titanium dioxide nanoparticles on algal and bacterial communities in periphytic biofilms

The widespread application of commercial TiO₂ NPs inevitably leads to their release into environmental waters through various ways. TiO₂ NPs released into water might be absorbed by and react with periphytic biofilms, which are a kind of aquatic environmental media of important ecological significance, and influence the physiological activity and ecological function of periphytic biofilms. This study investigated the effects of exposure to 1 mg/L and 5 mg/L of TiO₂ NPs on periphytic biofilms cultured indoors. After a 10-day exposure to TiO₂ NPs, the growth (measured by chlorophyll-a content) of microalgal community was inhibited greatly (more than 60%); however, the primary production (indicated by quantum yield) of periphytic biofilms maintained changeless. As for bacteria, TiO₂ NP-exposure increased the bacterial diversity and altered the composition structure. Significant changes were observed in the bacterial communities at the class level, mainly including Alphaproteobacteria, Gammaproteobacteria, Cytophagia, Flavobacteriia, Sphingobacteriia, Synechococcophycideae and Oscillatoriophycideae. The enhancement of metabolic activities (the production of extracellular polymeric substances, especially proteins content increased by 48.51%) of periphytic biofilms was a resistance mechanism to toxicity of NPs. As for extracellular enzyme activities of periphytic biofilms, alkaline phosphatase activity was inhibited (22.43%) after exposed to 5 mg/L of TiO₂ NPs, which posed a threat to phosphorus metabolism of periphytic biofilms. Overall, this study demonstrated that 1 mg/L and 5 mg/L of TiO₂ NPs negatively influenced physiological activities and ecological functions of periphytic biofilms, highlighting that the ecological risks of TiO₂ NPs should be paid attention to.

Factors impacting the interactions of engineered nanoparticles with bacterial cells and biofilms: Mechanistic insights and state of knowledge

Since their advent a few decades ago, engineered nanoparticles (ENPs) have been extensively used in consumer products and industrial applications and their use is expected to continue at the rate of thousands of tons per year in the next decade. The widespread use of ENPs poses a potential risk of large scale environmental proliferation of ENPs which can impact and endanger environmental health and safety. Recent studies have shown that microbial biofilms can serve as an important biotic component for partitioning and perhaps storage of ENPs released into aqueous systems. Considering that biofilms can be one of the major sinks for ENPs in the environment, and that the field of biofilms itself is only three to four decades old, there is a recent and growing body of literature investigating the ENP-biofilm interactions. While looking at biofilms, it is imperative to consider the interactions of ENPs with the planktonic microbial cells inhabiting the bulk systems in the vicinity of surface-attached biofilms. In this review article, we attempt to establish the state of current knowledge regarding the interactions of ENPs with bacterial cells and biofilms, identifying key governing factors and interaction mechanisms, as well as prominent knowledge gaps. Since the context of ENP-biofilm interactions can be multifarious-ranging from ecological systems to water and wastewater treatment to dental/medically relevant biofilms- and includes devising novel strategies for biofilm control, we believe this review will serve an interdisciplinary audience. Finally, the article also touches upon the future directions that the research in the ENP-microbial cells/biofilm interactions could take. Continued research in this area is important to not only enhance our scientific knowledge and arsenal for biofilm control, but to also support environmental health while reaping the benefits of the 'nanomaterial revolution'.

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.

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

Metals are a recognised threat to aquatic organisms but the impact of metals such as copper (Cu) on benthic freshwater diatoms is poorly understood, even if diatoms are commonly used as water quality indicators. Our study aimed to elucidate the cellular targets of Cu toxicity and the mechanisms cells resort to counteract toxicity and to increase tolerance to Cu. A concerted approach analysing the biochemical, physiological and metabolome alterations in diatom cells was conducted by exposing the freshwater diatom Tabellaria flocculosa to 0, 0.3, 6 and 10μgCu/L. Cu was already toxic to T. flocculosa at concentrations common in environments and which are not usually considered to be contaminated (0.3μgCu/L). Under Cu impact, the metabolome of T. flocculosa changed significantly, especially at high concentrations (6 and 10μgCu/L). Cu toxicity was counteracted by increasing extracellular immobilization (EPS, frustulins), antioxidant (SOD, CAT) and detoxifying (GSTs) enzymes activity and low molecular weight antioxidants (GSH). These mechanisms were fuelled by higher energy production (increased ETS activity). At the highest Cu concentration (10μg/L), these processes were specially enhanced in an attempt to restrain the oxidative stress generated by high intracellular Cu concentrations. However, these mechanisms were not able to fully protect cells, and damage in membranes and proteins increased. Moreover, the decrease of hydroxylamine and unsaturated fatty acids and the increase of saturated fatty acids, 2-palmitoylglycerol, glycerol and diterpenoid compounds should be tested as new specific markers of Cu toxicity in future studies. This information can support the prediction of diatom behaviour in different Cu contamination levels, including highly impacted environments, such as mining scenarios, and may assist in environmental risk assessment policies and restoration programs.

Antioxidant enzyme activities as biomarkers of fluvial biofilm to ZnO NPs ecotoxicity and the Integrated Biomarker Responses (IBR) assessment

The presence of ZnO nanoparticles (ZnO NPs) in natural waters has raised concerns about their environmental impacts, but the potential influences of ZnO NPs on fluvial biofilm have not been reported. In this study, the utility of antioxidant enzyme activities (AEA) as biomarkers of fluvial biofilm to ZnO NPs toxicity and a method that combines AEA into an index of "Integrated Biomarker Responses (IBR)" were studied. Compared with the absence of ZnO NPs, scanning electron microscopy (SEM) images revealed that a large amount of ZnO NPs were adsorbed onto biofilm and these NPs exerted adverse effects on the viability of bacteria in biofilm. The production of reactive oxygen species (ROS) with high concentrations (30 and 100mg/L) of ZnO NPs exposure reached to 184% and 244% of the control, while no cell leakage and membrane damage were observed. After exposure to ZnO NPs for 0.25 and 3 days, the activities of catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR), glutathione peroxidase (GSH-Px) were significantly increased, respectively. At the end of exposure period (21 days), the AEA with the presence of 1mg/L ZnO NPs exposure were comparable to the control, while most of those in high concentrations of ZnO NPs were decreased. The results of IBR showed that the biofilm can adapt to 1mg/L ZnO NPs exposure, while be seriously damaged by 30 and 100mg/L ZnO NPs after 3 and 0.25 days. IBR can be used as an appropriate evaluation system of the toxicity effects of ZnO NPs on fluvial biofim.

Effects of ZnO nanoparticles and Zn(2+) on fluvial biofilms and the related toxicity mechanisms

Zinc oxide nanoparticles (ZnO NPs) used in consumer products are largely released into the environment through the wastewater stream. The health hazard of ZnO NPs and the contribution of dissolved Zn(2+) in toxicity of ZnO NPs has attracted extensive worldwide attention. In this study, the toxic effects of ZnO nanoparticles (ZnO NPs) and the effects of dissolved Zn(2+) on fluvial biofilms were investigated. At the end of the exposure time (21 days), scanning electron microscopy (SEM) images and bioaccumulation experiments revealed that large quantities of ZnO NPs were adsorbed on the biofilm. The algal biomasses were significantly decreased by six- and eleven-fold compared with the control (1.43 μg/L) by exposure to concentrations of 100mg/L ZnO NPs and 7.85 mg/L Zn(2+), respectively. Moreover, under the same exposure conditions, the quantum yields presented contents of 53.33 and 33.33% relative to the control, and a shift in the community composition that manifested as a strong reduction in diatoms was observed from 7 days and reached 15.63 and 6.25% of the control after 21 days of exposure, respectively. The reductions in bacteria viability and reactive oxygen species (ROS) production were noticeably enhanced following exposure to 100mg/L ZnO NPs and 7.85 mg/L Zn(2+), respectively. Additionally, the acute and rapid toxicity of Zn(2+) and the increasing toxicity of the ZnO NPs with increased bioaccumulation were noted in the exposure experiment.

Effects of low arsenic concentration exposure on freshwater fish in the presence of fluvial biofilms

Arsenic (As) is a highly toxic element and its carcinogenic effect on living organisms is well known. However, predicting real effects in the environment requires an ecological approach since toxicity is influenced by many environmental and biological factors. The purpose of this paper was to evaluate if environmentally-realistic arsenic exposure causes toxicity to fish. An experiment with four different treatments (control (C), biofilm (B), arsenic (+As) and biofilm with arsenic (B+As)) was conducted and each one included sediment to enhance environmental realism, allowing the testing of the interactive effects of biofilm and arsenic on the toxicity to fish. Average arsenic exposure to Eastern mosquitofish (Gambusia holbrooki) was 40.5 ± 7.5 μg/L for +As treatment and 34.4 ± 1.4 μg/L for B+As treatment for 56 days. Fish were affected directly and indirectly by this low arsenic concentration since exposure did not only affect fish but also the function of periphytic biofilms. Arsenic effects on the superoxide dismutase (SOD) and glutathione reductase (GR) activities in the liver of mosquitofish were ameliorated in the presence of biofilms at the beginning of exposure (day 9). Moreover, fish weight gaining was only affected in the treatment without biofilm. After longer exposure (56 days), effects of exposure were clearly seen. Fish showed a marked increase in the catalase (CAT) activity in the liver but the interactive influence of biofilms was not further observed since the arsenic-affected biofilm had lost its role in water purification. Our results highlight the interest and application of incorporating some of the complexity of natural systems in ecotoxicology and support the use of criterion continuous concentration (CCC) for arsenic lower than 150 μg/L and closer to the water quality criteria to protect aquatic life recommended by the Canadian government which is 5 μg As/L.

Arsenic toxicity effects on microbial communities and nutrient cycling in indoor experimental channels mimicking a fluvial system

The toxicity of chemicals in the environment is influenced by many factors, such as the adsorption to mineral particles, active biological surfaces, biotransformation and/or nutrient concentration. In the present study, a simplified fluvial system including fish, periphyton and sediment was used to investigate the fate and effects of environmentally realistic concentration of arsenic (As) on biofilm growth and nutrient cycling. Total dissolved arsenic concentration decreased exponentially from 120μg/L to 28.0±1.5μg/L during the experiment (60 days), mostly sinking to the sediment and a smaller percentage accumulated in the periphytic biofilm. Most P and N, which was provided by fish, was also retained in the epipsammic biofilm (growing on sediment grains). We conclude that exposure to this concentration of arsenic under oligotrophic conditions is changing the quality and quantity of the base of the aquatic food chain and its respective contribution to nutrient cycling, and normal functioning of the ecosystem. The effects include lowering the total biomass of biofilm and its potential ability to use organic P (i.e., phosphatase activity), inhibiting algal growth, especially that of diatoms, decreasing nitrogen content, and making the epipsammic biofilm more heterotrophic, thus reducing its ability to oxygenate the aquatic environment.

Is the toxicity of pesticide mixtures on river biofilm accounted for solely by the major compounds identified?

Comparative effects of long-term exposure to Polar Organic Chemical Integrative Sampler (POCIS) extracts (PE) and to a reconstituted mixture based on the major compounds quantified in the PE were evaluated on river biofilm communities. The study aimed to characterize the effects of long-term and low-dose exposure to pesticides on natural biofilm communities and to evaluate if the effects due to PE exposure could be explained solely by the major compounds identified in the extracts. Biofilms from an uncontaminated site were exposed in artificial channels to realistic environmental concentrations using diluted PE, with the 12 major compounds quantified in the extracts (Mix) or with water not containing pesticides (Ctr). Significant differences between biofilms exposed to pesticides or not were observed with regard to diatom density, biomass (dry weight and ash-free dry mass), photosynthetic efficiency (ΦpsII) and antioxidant enzyme activities. After 14 days of exposure to the different treatments, the observed trend towards a decrease of mean diatom cell biovolumes in samples exposed to pesticides was related to the control biofilms' higher relative abundance of large species like Cocconeis placentula or Amphora copulata and lower relative abundance of small species like Eolimna minima compared to the contaminated ones. Principal component analyses clearly separated contaminated (PE and Mix) from non-contaminated (Ctr) biofilms; on the contrary, the analyses did not reveal separation between biofilms exposed to PE or to the 12 major compounds identified in the extract.

Involvement of an antioxidant defense system in the adaptive response to cadmium in maize seedlings (Zea mays L.)

Chemical and biological analyses were used to investigate the growth response and antioxidant defense mechanism of maize seedlings (Zea mays L.) grown in soils with 0-100 mg kg(-1) Cd. Results showed that maize seedlings have strong abilities to accumulate and tolerate high concentrations of Cd. For soil with 50 mg kg(-1) Cd, the Cd contents in roots and shoots of maize seedlings are as large as 295.6 and 153.0 mg kg(-1) DW, respectively, without visible symptoms of toxicity. Lower soil Cd concentrations lead to a decrease in reduced glutathione (GSH) content in leaves of maize seedlings, whereas higher soil Cd concentrations resulted in an increase in the activities of superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase. Maize seedlings have strong capacities to adapt to low concentrations of Cd by consuming GSH and to develop an antioxidative enzyme system to defend against high-Cd stress.

Antioxidant enzyme activities in biofilms as biomarker of Zn pollution in a natural system: an active bio-monitoring study

This study aimed to explore the use of antioxidant enzyme activities (AEA) and biofilm metal accumulation capacity in natural communities as effect-based indicator of metal exposure in fluvial systems. To achieve these objectives, an active biomonitoring using fluvial biofilm communities was performed during 5 weeks. Biofilm was colonized over artificial substrata in a non-polluted site. After 5 weeks, biofilms were translocated to four different sites with different metal pollution in the same stream. The evolution of environmental parameters as well as biofilm responses was analysed over time. Physicochemical parameters were different between sampling times as well as between the most polluted site and the less polluted ones, mainly due to Zn pollution. In contrast, AEA and metal accumulation in biofilms allowed us to discriminate the high and moderate metal pollution sites from the rest. Zn, the metal with the highest contribution to potential toxicity, presented a fast and high accumulation capacity in biofilms. According to the multivariate analysis, AEA showed different responses. While catalase (CAT) and ascorbate peroxidase (APX) variability was mainly attributed to environmental stress (pH, temperature and phosphate concentration), glutathione-S-transferase (GST) changes were related to metal pollution. Glutathione reductase (GR) and superoxide dismutase (SOD) responses were related to both stress factors. AEA and metal accumulation are proposed as sensitive effect-based field methods, to evaluate biofilm responses after acute metal exposure (e.g. an accidental spill) due to their capacity to respond after few hours, but also in routinely monitoring due to their persistent changes after few weeks of exposure. These tools could improve the Common Implementation Strategy (CIS) of the Water Framework Directive (WFD) as expert group request.

Seasonal changes in antioxidant enzyme activities of freshwater biofilms in a metal polluted Mediterranean stream

While seasonal variations in fluvial communities have been extensively investigated, effects of seasonality on community responses to environmental and/or chemical stress are poorly documented. The aim of this study was to describe antioxidant enzyme activity (AEA) variability in fluvial biofilms over an annual cycle, under multi-stress scenarios due to environmental variability (e.g., light intensity, water flow, and temperature) and metal pollution (Zn, Mn and Fe). The annual monitoring study was performed at three sites according to their water and biofilm metal concentrations. Metal concentration was affected by water flow due to dilution. Low flow led to higher dissolved Zn concentrations, and thus to higher Zn accumulation in the biofilm. Water temperature, light intensity and phosphate concentration were the environmental factors which determined the seasonality of biofilm responses, whereas dissolved Zn and Zn accumulation in biofilms were the parameters linked to sites and periods of highest metal pollution. Community algal succession, from diatoms in cold conditions to green algae in warm conditions, was clearer in the non metal-polluted site than in those metal-polluted, presumably due to the selection pressure exerted by metals. Most AEA were related with seasonal environmental variability at the sites with low or no-metal pollution, except glutathione-S-transferase (GST) which was related with Zn (dissolved and accumulated in biofilm) pollution occurring at the most polluted site. We can conclude that seasonal variations of community composition and function are masked by metal pollution. From this study we suggest the use of a multi-biomarker approach, including AEA and a set of biological and physicochemical parameters as an effect-based field tool to assess metal pollution.