Short term recovery of periphyton photosynthesis after pulse exposition to the photosystem II inhibitors atrazine and isoproturon

Indole-3-acetic acid improves periphyton's resistance to ultraviolet-B: From physiological-biochemical properties and bacteria community to livestock-polluted water purification

Livestock-polluted water is a pressing water environmental issue in plateau pastoral regions, necessitating the adoption of eco-friendly solutions. Despite periphyton being a promising alternative, its efficacy is limited by the prevalence of intense ultraviolet radiation, particularly ultraviolet-B (UVB), in these regions. Therefore, this study employs molecular tools and small-scale trials to explore the crucial role of indole-3-acetic acid (IAA) in modulating periphyton characteristics and mediating nutrient removal from livestock-polluted water under UVB exposure. The results revealed that IAA augments periphyton's resilience to UVB stress through several pathways, including increasing periphyton's biomass, producing more extracellular polymeric substances (EPS), and enhancing antioxidant enzyme activities and photosynthetic activity of periphyton. Moreover, IAA addition increased periphyton's bacterial diversity, reshaped bacterial community structure, enhanced community stability, and elevated the R2 value of neutral processes in bacterial assembly from 0.257 to 0.651 under UVB. Practically, an IAA concentration of 50 mg/L was recommended. Small-scale trials confirmed the effectiveness of IAA in assisting UVB-stressed periphyton to remove nitrogen and phosphorus from livestock-polluted water, without the risk of nitrogen accumulation. These findings offer valuable insights into the protection of aquatic ecosystems in plateau pastoral regions based on periphyton property in an eco-friendly manner.

Effects of herbicides and fertilization on biofilms of Pampean lotic systems: A microcosm study

We experimentally assessed the impact of the application of herbicides and fertilizers derived from agricultural activity through the individual and simultaneous addition of glyphosate, atrazine, and nutrients (nitrogen 'N' and phosphorus 'P') on the biofilm community and their resilience when the experimental factors were removed. We hypothesize that i) the presence of agrochemicals negatively affects the biofilm community leading to the simplification of the community structure; ii) the individual or simultaneous addition of herbicides and nutrients produces differential responses in the biofilm; and iii) the degree of biofilm recovery differs according to the treatment applied. Environmentally relevant concentrations of glyphosate (0.7 mgL-1), atrazine (44 μgL-1), phosphorus (1 mg P L-1 [KH2PO4]), and nitrogen (3 mg N L-1[NaNO3]) were used. Chlorophyll a, ash-free dry weight, abundance of main biofilm groups and nutrient contents in biofilm were analyzed. At initial exposure time, all treatments were dominated by Cyanobacteria; through the exposure period, it was observed a progressive replacement by Bacillariophyceae. This replacement occurred on day 3 for the control and was differentially delayed in all herbicides and/or nutrient treatments in which the abundance of cyanobacteria remains significant yet in T5. A significant correlation was observed between the abundance of cyanobacteria and the concentration of atrazine, suggesting that this group is less sensitive than diatoms. The presence of agrochemicals exerted differential effects on the different algal groups. Herbicides contributed to phosphorus and nitrogen inputs. The most frequently observed interactions between experimental factors (nutrients and herbicides) was additivity excepting for species richness (antagonistic effect). In the final recovery time, no significant differences were found between the treatments and the control in most of the evaluated parameters, evincing the resilience of the community.

Effects of atrazine and S-metolachlor on stream periphyton taxonomic and fatty acid compositions

Extensive pesticide use for agriculture can diffusely pollute aquatic ecosystems through leaching and runoff events and has the potential to negatively affect non-target organisms. Atrazine and S-metolachlor are two widely used herbicides often detected in high concentrations in rivers that drain nearby agricultural lands. Previous studies focused on concentration-response exposure of algal monospecific cultures, over a short exposure period, with classical descriptors such as cell density, mortality or photosynthetic efficiency as response variables. In this study, we exposed algal biofilms (periphyton) to a concentration gradient of atrazine and S-metolachlor for 14 days. We focused on fatty acid composition as the main concentration-response descriptor, and we also measured chlorophyll a fluorescence. Results showed that atrazine increased cyanobacteria and diatom chlorophyll a fluorescence. Both herbicides caused dissimilarities in fatty acid profiles between control and high exposure concentrations, but S-metolachlor had a stronger effect than atrazine on the observed increase or reduction in saturated fatty acids (SFAs) and very long-chain fatty acids (VLCFAs), respectively. Our study demonstrates that two commonly used herbicides, atrazine and S-metolachlor, can negatively affect the taxonomic composition and fatty acid profiles of stream periphyton, thereby altering the nutritional quality of this resource for primary consumers.

The response of bacterial community to UVB was significantly different between immature periphyton and mature periphyton, but not for physiological indicators

Periphyton has important ecological functions. It can even exist in environments with strong ultraviolet radiation. However, knowledge of periphyton under ultraviolet is limited, which limits the understanding and application of periphyton in environments with high ultraviolet radiation. In this study, immature periphyton (IMP) and mature periphyton (MP) under ultraviolet B (UVB) irradiation were investigated and compared in terms of physiological characteristics and bacterial community. Analysis of the physiological characteristics showed that the response patterns of IMP and MP to UVB were similar. IMP and MP could adapt to UVB of 1 W/m² well. However, high-intensity UVB (2 and 3 W/m²) reduced the periphyton biomass, inhibited photosynthesis and antioxidant enzyme activity and caused severe lipid peroxidation in both IMP and MP. Integrated Biological Response (IBR) analysis and toxicological model fitting showed that the ED₅₀ values of UVB for IMP and MP were 1.25 and 1.50 W/m², respectively. 16 S rRNA gene analysis showed that in both IMP and MP, bacterial community composition, assembly and function were affected by UVB. In addition, the response of the bacterial community in IMP to UVB was stronger than that in MP. The diversity of the IMP community was inhibited by UVB, but that of the MP community was not. Proteobacteria and Deinococcus-Thermus are key microorganisms responsible for tolerance to UVB stress. Neutral community model fitting showed that both UVB and the development process caused the determinism of bacterial succession. However, UVB may weaken the deterministic process caused by development. Functional prediction showed that many metabolic functions of periphyton were inhibited by UVB in IMP and MP. However, UVB caused different changes (enhancement or inhibition) of some ecological functions in them. This study provides valuable information for understanding periphyton in environments with UVB radiation, which may be used to improve the application of periphyton in these environments.

The sensitivity of aquatic microbial communities to a complex agricultural contaminant depends on previous drought conditions

In intermittent rivers, which represent a prominent part of worldwide rivers, aquatic organisms are exposed to sequential disturbances including flow cessation, potentially associated with water warming, desiccation process and flow resumption. At flow resumption, pollutants stored in soil and washed by rainfalls can reach fresh waters. The interaction between contamination and river intermittency is poorly understood. In this study, we aimed at understanding in what extent the intensity of dry period combined or not to water warming drives the sensitivity of aquatic communities to a complex agricultural run-off (ARO) during rewetting. Phototrophic biofilms, at the basis of freshwater food webs, were chosen as a model of community. Biofilms grown in laboratory were first exposed to a disturbance crossing two temperature conditions (not warmed, 22°C or warmed, 32°C) and three dry periods (no drying, short (3 days), or long (3 months)). Then they were exposed to a chemical mix of nitrates, copper and 3 pesticides at 6 gradual concentrations. Various descriptors associated with biofilm structure and function were assessed one week after ARO addition. When undisturbed biofilms were exposed to ARO, they shifted toward a more heterotrophic state as they lost algal richness and diversity, and gross primary production tended to decrease. Warming alone only slightly modified the sensitivity of biofilms to ARO, with lower effects on algal richness and a trend to increase the effect on gross primary production. In contrast, the association of warming and a dry period strongly modified the sensitivity to ARO, certainly due to the selection of generalist species and/or physiological acclimation inducted by the first disturbance. This study emphasizes the importance of considering water intermittency in the management of the ecological risk of chemicals in aquatic ecosystems.

First evaluation of the periphyton recovery after glyphosate exposure

The potential environmental risk of glyphosate has promoted the need for decontamination of glyphosate-polluted water bodies. These treatments should be accompanied by studies of the recovery potential of aquatic communities and ecosystems. We evaluated the potential of freshwater periphyton to recover from glyphosate exposure using microcosms under laboratory conditions. Periphyton developed on artificial substrates was exposed to 0.4 or 4 mg l-1 monoisopropylamine salt of glyphosate (IPA) for 7 days, followed by translocation to herbicide-free water. We sampled the community 1, 2 and 3 weeks after the transfer. Dry weight, ash-free dry weight, chlorophyll a, and periphyton abundances were analysed. The periphyton impacted with the lowest IPA concentration recovered most of the structural parameters within 7 days in clean water, but the taxonomic structure did not entirely recover towards the control structure. Periphyton exposed to 4 mg IPA l-1 could not recover during 21 days in herbicide-free water, reaching values almost four times higher in % of dead diatoms and four times lower in ash-free dry weight concerning the control at the end of the study. Results suggest a long-lasting effect of the herbicide due to the persistence within the community matrix even after translocating periphyton to decontaminated water. We conclude that the exposure concentration modulates the recovery potential of IPA-impacted periphyton. The current research is the first to study the recovery in glyphosate-free water of periphyton exposed to the most commonly used herbicide in the world. Finally, we highlight the need for more studies focused on the recovery potential of freshwater ecosystems and aquatic communities after glyphosate contamination.

Assessment of risks to listed species from the use of atrazine in the USA: a perspective

Atrazine is a triazine herbicide used predominantly on corn, sorghum, and sugarcane in the US. Its use potentially overlaps with the ranges of listed (threatened and endangered) species. In response to registration review in the context of the Endangered Species Act, we evaluated potential direct and indirect impacts of atrazine on listed species and designated critical habitats. Atrazine has been widely studied, extensive environmental monitoring and toxicity data sets are available, and the spatial and temporal uses on major crops are well characterized. Ranges of listed species are less well-defined, resulting in overly conservative designations of "May Effect". Preferences for habitat and food sources serve to limit exposure among many listed animal species and animals are relatively insensitive. Atrazine does not bioaccumulate, further diminishing exposures among consumers and predators. Because of incomplete exposure pathways, many species can be eliminated from consideration for direct effects. It is toxic to plants, but even sensitive plants tolerate episodic exposures, such as those occurring in flowing waters. Empirical data from long-term monitoring programs and realistic field data on off-target deposition of drift indicate that many other listed species can be removed from consideration because exposures are below conservative toxicity thresholds for direct and indirect effects. Combined with recent mitigation actions by the registrant, this review serves to refine and focus forthcoming listed species assessment efforts for atrazine.Abbreviations: a.i. = Active ingredient (of a pesticide product). AEMP = Atrazine Ecological Monitoring Program. AIMS = Avian Incident Monitoring SystemArach. = Arachnid (spiders and mites). AUC = Area Under the Curve. BE = Biological Evaluation (of potential effects on listed species). BO = Biological Opinion (conclusion of the consultation between USEPA and the Services with respect to potential effects in listed species). CASM = Comprehensive Aquatic System Model. CDL = Crop Data LayerCN = field Curve Number. CRP = Conservation Reserve Program (lands). CTA = Conditioned Taste Avoidance. DAC = Diaminochlorotriazine (a metabolite of atrazine, also known by the acronym DACT). DER = Data Evaluation Record. EC25 = Concentration causing a specified effect in 25% of the tested organisms. EC50 = Concentration causing a specified effect in 50% of the tested organisms. EC50_RGR = Concentration causing a 50% reduction in relative growth rate. ECOS = Environmental Conservation Online System. EDD = Estimated Daily Dose. EEC = Expected Environmental Concentration. EFED = Environmental Fate and Effects Division (of the USEPA). EFSA = European Food Safety Agency. EIIS = Ecological Incident Information System. ERA = Environmental Risk Assessment. ESA = Endangered Species Act. ESU = Evolutionarily Significant UnitsFAR = Field Application RateFIFRA = Federal Insecticide, Fungicide, and Rodenticide Act. FOIA = Freedom of Information Act (request). GSD = Genus Sensitivity Distribution. HC5 = Hazardous Concentration for ≤ 5% of species. HUC = Hydrologic Unit Code. IBM = Individual-Based Model. IDS = Incident Data System. K_OC = Partition coefficient between water and organic matter in soil or sediment. K_OW = Octanol-Water partition coefficient. LC50 = Concentration lethal to 50% of the tested organisms. LC-MS-MS = Liquid Chromatograph with Tandem Mass Spectrometry. LD50 = Dose lethal to 50% of the tested organisms. LAA = Likely to Adversely Affect. LOAEC = Lowest-Observed-Adverse-Effect Concentration. LOC = Level of Concern. MA = May Affect. MATC = Maximum Acceptable Toxicant Concentration. NAS = National Academy of Sciences. NCWQR = National Center of Water Quality Research. NE = No Effect. NLAA = Not Likely to Adversely Affect. NMFS = National Marine Fisheries Service. NOAA = National Oceanic and Atmospheric Administration. NOAEC = No-Observed-Adverse-Effect Concentration. NOAEL = No-Observed-Adverse-Effect Dose-Level. OECD = Organization of Economic Cooperation and Development. PNSP = Pesticide National Synthesis Project. PQ = Plastoquinone. PRZM = Pesticide Root Zone Model. PWC = Pesticide in Water Calculator. QWoE = Quantitative Weight of Evidence. RGR = Relative growth rate (of plants). RQ = Risk Quotient. RUD = Residue Unit Doses. SAP = Science Advisory Panel (of the USEPA). SGR = Specific Growth Rate. SI = Supplemental Information. SSD = Species Sensitivity Distribution. SURLAG = Surface Runoff Lag Coefficient. SWAT = Soil & Water Assessment Tool. SWCC = Surface Water Concentration Calculator. UDL = Use Data Layer (for pesticides). USDA = United States Department of Agriculture. USEPA = United States Environmental Protection Agency. USFWS = United States Fish and Wildlife Service. USGS = United States Geological Survey. WARP = Watershed Regressions for Pesticides.

Karrikinolide alleviates BDE-28, heat and Cd stressors in Brassica alboglabra by correlating and modulating biochemical attributes, antioxidative machinery and osmoregulators

In this study, we have evaluated the role of karrikin (KAR¹) against the absorption and translocation of a persistent organic pollutant (POP), 2,4,4'-Tribromodiphenyl ether (BDE-28) in plants, in the presence of two other stressors, cadmium (Cd) and high temperature. Furthermore, it correlates the physiological damages of Brassica alboglabra with the three stresssors separately. The results revealed that the post-germination application of KAR¹ successfully augmented the growth (200%) and pertinent physiochemical parameters of B. alboglabra. KAR¹ hindered air absorption of BDE-28 in plant tissues, and reduced its translocation coefficient (TF). Moreover, BDE-28 was the most negatively correlated (-0.9) stressor with chlorophyll contents, while the maximum mitigation by KAR¹ was also achieved agaist BDE-28. The effect of temperature was more severe on soluble sugars (0.51), antioxidative machinery (-0.43), and osmoregulators (0.24). Cd exhibited a stronger inverse interrelation with the enzymatic antioxidant cascade. Application of KAR¹ mitigated the deleterious effects of Cd and temperature stress on plant physiological parameters along with reduced aero-concentration factor, TF, and metal tolerance index. The phytohormone reduced lipid peroxidation by decreasing synthesis of ROS and persuading its breakdown. The stability of cellular membranes was perhaps due to the commotion of KAR¹ as a growth-promoting phytohormone. In the same way, KAR¹ supplementation augmented the membrane stability index, antioxidant defense factors, and removal efficiency of the pollutants. Consequently, the exogenously applied KAR¹ can efficiently alleviate Cd stress, heat stress, and POP toxicity.

Growth inhibition and recovery patterns of common duckweed Lemna minor L. after repeated exposure to isoproturon

Aquatic non-targeted organisms are more likely to be exposed to herbicides in multiple pulse events then long continuous exposure. The potential of an organism to recover between exposures has an important role in the overall effects of the toxicant. Common duckweeds show high potential for recovery after a single exposure to isoproturon. To evaluate the growth patterns and recovery potential between multiple exposures, L. minor plants were exposed to isoproturon in three repetitive 7-day treatment cycles in three time-variable exposure scenarios with equivalent time-weighted average concentrations. The growth was significantly inhibited during each exposure phase with significant cumulative effects in every subsequent treatment cycle resulting in a cumulative decrease in biomass production. However, inhibitory effects were reversible upon transferring plants to a herbicide-free nutrient solution. These results indicate that L. minor plants have a high recovery potential even after multiple exposures to isoproturon. Observed cumulative decrease in biomass production, as well as the potential for fast and efficient recovery from repeated herbicide exposure, might affect the competitiveness of L. minor in surface water communities. The observations made during each exposure period, recovery patterns, and the resulting cumulative effects over time may contribute to further development, calibration and validation of mechanistic toxicokinetic/toxicodynamic models for simulating the effects of pesticides on aquatic plants populations in the laboratory and environmental conditions.

Adverse effects of atrazine, DCMU and metolachlor on phytoplankton cultures and communities at environmentally relevant concentrations using Fast Repetition Rate Fluorescence

The widespread and persistent contamination of freshwater environments by low concentrations of pesticides is a growing concern worldwide. In aquatic environments, herbicide pollution is of greatest concern for phytoplankton, due to their similarities to terrestrial plants. Through the use of Fast Repetition Rate Fluorometry (FRRF) during weeklong experiments on 10 phytoplankton cultures from 4 classes and 4 natural communities, we demonstrate that PSII-inhibiting herbicides, notably atrazine that is extensively used in North America, consistently have effects on freshwater phytoplankton photophysiology at concentrations far below concentrations affecting the most sensitive species in previous studies. The parameters specific to FRRF (Ρ, σ, τ₁, τ₂, τ₃) were those most sensitive to PSII inhibitors, compared to the standard fluorescence parameters derived from other fluorescence protocols such as Pulse Amplitude Modulation (PAM) fluorometry (F₀, F_m, F_v/F_m) and extracted chlorophyll a concentrations. Based on these findings, existing national environmental guidelines and standards are insufficient to adequately prevent adverse effects of atrazine and other PSII inhibiting herbicides on algal physiology in aquatic ecosystems.

Periphyton bioconcentrates pesticides downstream of catchment dominated by agricultural land use

Periphyton provides important ecosystem services in aquatic environments, including supporting diverse consumers. We studied pesticide bioconcentration in periphyton in a coastal marsh on Lake Erie. The marsh is within a protected area (Rondeau Provincial Park) but receives discharge from tributaries draining intensively farmed land. Periphyton bioconcentrated 20 pesticide chemicals above levels observed in adjacent water or sediment. Average bioconcentration factors ranged from 12 times for the herbicide dicamba to 6864 times for the fungicide boscalid on a dry-weight basis. Bioconcentration factors were not linearly related to pesticides' log K_ow, log K_oc, or water solubility (simple linear regressions, p > 0.43). The removal of pesticides from ambient water represents another valuable ecosystem service provided by periphyton. However, we caution that bioconcentration of pesticides in periphyton provides a mechanism through which contemporary and legacy pesticides may enter wetland food webs.

Responses of photosynthesis-related parameters and chloroplast ultrastructure to atrazine in alfalfa (Medicago sativa L.) inoculated with arbuscular mycorrhizal fungi

Atrazine is an ingredient in photosynthesis-inhibiting herbicides and has been widely used to combat weeds in farmland. However, most atrazine that is applied fails to degrade in the soil and subsequently affects non-target plants. In this study, we investigated the influence of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae on the photosynthesis-related parameters, chlorophyll content, and chloroplast ultrastructure in alfalfa plants, some of which had been exposed to atrazine. Our results showed that the percentage of AMF hyphal colonization reached 91.23% 35 days after the alfalfa was planted, which suggests a symbiotic relationship between F. mosseae and alfalfa roots. F. mosseae alleviated the inhibition of net photosynthesis and stomatal function significantly in alfalfa exposed to atrazine for 24 h. A chlorophyll fluorescence analysis revealed that F. mosseae prevented a major reduction in the performance of photosystem II (PSII) photochemistry in the presence of atrazine, such as the relative decrease of F_v/F_m between the non-mycorrhizal and F. mosseae mycorrhizal treatments was 4.4% and 5.8% after 24 and 48 h of atrazine exposure time. However, F. mosseae has no significant alleviation on a sharp reduction in the chlorophyll a, chlorophyll b and carotenoid content in alfalfa exposed to atrazine. For the chloroplast ultrastructure in alfalfa exposed to atrazine, the number of both plastoglobules and partial granal stacks was greater in the presence of F. mosseae. In general, our results indicate that the F. mosseae inoculation was beneficial to sustain photosynthesis-related performance, such as net photosynthesis, stomatal conductance, the maximum quantum yield (F_v/F_m) and effective quantum yield (Φ_PSII) of PSII photochemistry in alfalfa after exposure to atrazine, because the mycorrhizal alfalfa had a greater number of plastoglobules and granal stacks in the chloroplast, thereby enhancing its resistance to the oxidative damage induced by atrazine.

Non-destructive Determination of Shikimic Acid Concentration in Transgenic Maize Exhibiting Glyphosate Tolerance Using Chlorophyll Fluorescence and Hyperspectral Imaging

The development of transgenic glyphosate-tolerant crops has revolutionized weed control in crops in many regions of the world. The early, non-destructive identification of superior plant phenotypes is an important stage in plant breeding programs. Here, glyphosate-tolerant transgenic maize and its parental wild-type control were studied at 2, 4, 6, and 8 days after glyphosate treatment. Visible and near-infrared hyperspectral imaging and chlorophyll fluorescence imaging techniques were applied to monitor the performance of plants. In our research, transgenic maize, which was highly tolerant to glyphosate, was phenotyped using these high-throughput non-destructive methods to validate low levels of shikimic acid accumulation and high photochemical efficiency of photosystem II as reflected by maximum quantum yield and non-photochemical quenching in response to glyphosate. For hyperspectral imaging analysis, the combination of spectroscopy and chemometric methods was used to predict shikimic acid concentration. Our results indicated that a partial least-squares regression model, built on optimal wavelengths, effectively predicted shikimic acid concentrations, with a coefficient of determination value of 0.79 for the calibration set, and 0.82 for the prediction set. Moreover, shikimic acid concentration estimates from hyperspectral images were visualized on the prediction maps by spectral features, which could help in developing a simple multispectral imaging instrument for non-destructive phenotyping. Specific physiological effects of glyphosate affected the photochemical processes of maize, which induced substantial changes in chlorophyll fluorescence characteristics. A new data-driven method, combining mean fluorescence parameters and featuring a screening approach, provided a satisfactory relationship between fluorescence parameters and shikimic acid content. The glyphosate-tolerant transgenic plants can be identified with the developed discrimination model established on important wavelengths or sensitive fluorescence parameters 6 days after glyphosate treatment. The overall results indicated that both hyperspectral imaging and chlorophyll fluorescence imaging techniques could provide useful tools for stress phenotyping in maize breeding programs and could enable the detection and evaluation of superior genotypes, such as glyphosate tolerance, with a non-destructive high-throughput technique.

Modelling the effects of PSII inhibitor pulse exposure on two algae in co-culture

A weakness of standard testing procedures is that they do not consider interactions between organisms, and they focus only on single species. Furthermore, these procedures do not take into account pulse exposure. However, pulse exposure is of particular importance because in streams, after crop application and during and after precipitation, herbicide concentrations fluctuate widely and can exceed the Annual Average Environmental Quality Standards (AA-EQS), which aim to protect the aquatic environment. The sensitivity of the algae Scenedesmus vacuolatus and Pseudokirchneriella subcapitata in a co-culture exposed to pulses is thus analysed in this study. As a first step, the growths of the algae in co-culture are investigated. For initial cell densities fixed, respectively, to 100,000 and 50,000 cells/mL, the growth of each alga is exponential over at least 48 h. S. vacuolatus seems to influence the growth of P. subcapitata negatively. Allelopathy is a possible explanation for this growth inhibition. The toxicity of the herbicide isoproturon is later tested on the algae S. vacuolatus and P. subcapitata cultured alone and in the co-culture. Despite the supplementary stress on the algae in the co-culture competing for nutrients, the toxicity of the herbicide is lower for the two algae when they are in the co-culture than when they are in separated culture. A model is adapted and used to predict the cell-density inhibition on the alga S. vacuolatus in the co-culture with the alga P. subcapitata exposed to a pulse concentration of isoproturon. Four laboratory experiments are performed to validate the model. The comparison between the laboratory and the modelled effects shows good agreement. The differences can be considered minor most of time. For future studies, it is important to ensure that the cell count is precise, as it is used to determine the parameters of the model. The differences can be also induced by the fact that the cell number of the alga P. subcapitata re-suspended in a new OECD medium after the centrifugation process cannot be fixed.

Cleaning-up atrazine-polluted soil by using Microbial Electroremediating Cells

Biodegradation of pollutants in soil is greatly limited by the availability of terminal electron acceptors required for supporting microbial respiration. Such limitation can be overcome if soil-buried electrodes accept the electrons released in the microbial metabolism. We propose the term bioelectroventing for such a environmental treatment. The process would be performed in a device so-called Microbial Electroremediating Cell. Indeed, our studies demonstrate that the presence of electrodes as electron acceptors effectively stimulated by 5-fold the biodegradation rate of the herbicide atrazine (2-chloro-4-ethylamino-6-isopropyl amino-1,3,5-triazine) in comparison with soil natural attenuation. Furthermore, a different set of toxicological test using Pseudokirchneriella subcapitata green alga e, Salmonella typhimorium bacteria and Sorghum saccharatum plant seeds respectively, confirm that atrazine-polluted soil can be effectively cleaned-up in short time by the use of MERCs.

Improving Toxicity Assessment of Pesticide Mixtures: The Use of Polar Passive Sampling Devices Extracts in Microalgae Toxicity Tests

Complexity of contaminants exposure needs to be taking in account for an appropriate evaluation of risks related to mixtures of pesticides released in the ecosystems. Toxicity assessment of such mixtures can be made through a variety of toxicity tests reflecting different level of biological complexity. This paper reviews the recent developments of passive sampling techniques for polar compounds, especially Polar Organic Chemical Integrative Samplers (POCIS) and Chemcatcher® and the principal assessment techniques using microalgae in laboratory experiments. The progresses permitted by the coupled use of such passive samplers and ecotoxicology testing as well as their limitations are presented. Case studies combining passive sampling devices (PSD) extracts and toxicity assessment toward microorganisms at different biological scales from single organisms to communities level are presented. These case studies, respectively, aimed (i) at characterizing the "toxic potential" of waters using dose-response curves, and (ii) at performing microcosm experiments with increased environmental realism in the toxicant exposure in term of cocktail composition and concentration. Finally perspectives and limitations of such approaches for future applications in the area of environmental risk assessment are discussed.

Effect of butyl paraben on the development and microbial composition of periphyton

Parabens are extensively used as preservatives and bactericides in personal care and other consumer products, and are commonly found in wastewater and surface water as contaminants. However, few data are currently available on the ecotoxicity of parabens. Periphyton biofilm, a widely distributed microbial aggregate of ecological importance in aquatic environment, is frequently used for water quality monitoring, ecological restoration, and toxicity assessment. In this work, the effects of butyl paraben on the development and microbial composition of periphyton biofilm was studied in a laboratory experiment for 32 days using flow through channels. No effect was observed at the environmental relevant concentration level (0.5 μg L(-1)) during the experiment. At the highest tested concentration level (5000 μg L(-1)), following effects were noted: (1) inhibition on algae growth at the end of the experiment as indicated by the chlorophyll a and total biovolume; (2) inhibition of photosynthetic efficiency on day 24 as suggested by the maximal Photosystem II quantum yield (Fv/Fm); (3) decrease of the algal diversity on day 24 and 32 as reflected by the Pielou and Shannon-Weiner indices. Bacteria were less sensitive than algae in the periphyton biofilm, which showed no difference at all tested concentration levels as illustrated by the Biolog EcoPlates™ analysis. Therefore, we conclude that environmental residues of butyl paraben have a very low risk to periphyton in aquatic ecosystems.

Modelling the effects of pulse exposure of several PSII inhibitors on two algae

Subsequent to crop application and during precipitation events, herbicides can reach surface waters in pulses of high concentrations. These pulses can exceed the Annual Average Environmental Quality Standards (AA-EQS), defined in the EU Water Framework Directive, which aims to protect the aquatic environment. A model was developed in a previous study to evaluate the effects of pulse exposure for the herbicide isoproturon on the alga Scenedesmus vacuolatus. In this study, the model was extended to other substances acting as photosystem II inhibitors and to other algae. The measured and predicted effects were equivalent when pulse exposure of atrazine and diuron were tested on S. vacuolatus. The results were consistent for isoproturon on the alga Pseudokirchneriella subcapitata. The model is thus suitable for the effect prediction of phenylureas and triazines and for the algae used: S. vacuolatus and P. subcapitata. The toxicity classification obtained from the dose-response curves (diuron>atrazine>isoproturon) was conserved for the pulse exposure scenarios modelled for S. vacuolatus. Toxicity was identical for isoproturon on the two algae when the dose-response curves were compared and also for the pulse exposure scenarios. Modelling the effects of any pulse scenario of photosystem II inhibitors on algae is therefore feasible and only requires the determination of the dose-response curves of the substance and growth rate of unexposed algae. It is crucial to detect the longest pulses when measurements of herbicide concentrations are performed in streams because the model showed that they principally affect the cell density inhibition of algae.

Cumulative Stressors Trigger Increased Vulnerability of Diatom Communities to Additional Disturbances

Chronic, non-lethal stressors occurring gradually (in space or time) can result in cumulative impacts that are more dramatic than higher intensities or occasional critical levels of any single one of these stressors. The negative effects of the chronic stressors trigger lasting impacts that may grow in intensity and become problematic over time and/or to higher trophic levels. In rivers, aquatic organisms experience this type of cumulative stress along the up- to downstream gradient in natural and anthropogenic contaminants generally observed in inhabited watersheds. Diatoms are a major component of the periphyton in rivers; their richness and diversity in natural communities are directly related to their varied ecological preferences and sensitivity to disturbance. In this study, we monitored from 2003 to 2008 the changes in the diversity of taxonomic and non-taxonomic features along a small river (Riou-Mort, South West France), at three sites: one site upstream considered as a reference for this watershed, one intermediate site with high nutrient load, and one downstream site exposed to both nutrient and metal pollution. The cumulative impacts of nutrients plus metals led to a gradual decrease in species richness and diversity, and in a potential capacity to cope with additional stresses, e.g., climate change-related ones. This is reflected by a decrease in species richness downstream, more dramatic in the hot summer of 2003 than in cooler summers. With the increasingly protective environmental regulations (e.g., Water Framework Directive in Europe), accumulation of stresses on aquatic resources are recommended to receive increasing attention, in particular considering the expected changes in climate.

Assessing temporal and spatial variation in sensitivity of communities of periphyton sampled from agroecosystem to, and ability to recover from, atrazine exposure

Lotic systems in agriculturally intensive watersheds can experience short-term pulsed exposures of pesticides as a result of runoff associated with rainfall events following field applications. Of special interest are herbicides that could potentially impair communities of primary producers, such as those associated with periphyton. Therefore, this study examined agroecosystem-derived lotic periphyton to assess (1) variation in community sensitivity to, and ability to recover from, acute (48h) exposure to the photosystem II (PSII)-inhibiting herbicide atrazine across sites and time, and (2) attempt to determine the variables (e.g., community structure, hydrology, water quality measures) that were predictive for observed differences in sensitivity and recovery. Periphyton were sampled from six streams in the Midwestern U.S. on four different dates in 2012 (April to August). Field-derived periphyton were exposed in the laboratory to concentrations of atrazine ranging from 10 to 320μg/L for 48h, followed by untreated media for evaluation of recovery for 48h. Effective quantum yield of PSII was measured after 24h and 48h exposure and 24h and 48h after replacement of media. Inhibition of PSII EC50 values ranged from 53 to >320µg/L. The majority of periphyton samples (16 out of 22) exposed to atrazine up to 320µg/L recovered completely by 48h after replacement of media. Percent inhibition of effective quantum yield of PSII in periphyton (6 of 22 samples) exposed to 320µg/L atrazine that were significantly lower than controls after 48h ranged from 2% to 24%. No distinct spatial or temporal trends in sensitivity and recovery potential were observed over the course of the study. Conditional inference forest analysis and variation partitioning were used to investigate potential associations between periphyton sensitivity to and ability to recover from exposure to atrazine. Although certain environmental variables (i.e., proximity of high flow/velocity events and dissolved solutes) were significantly associated with sensitivity to atrazine, recovery was not significantly associated with any variables, which is predicted by the rapid reversible binding at PSII. Consistent and rapid recovery of effective quantum yield of PSII across sites and sampling dates indicates that acute exposure to atrazine is unlikely to adversely affect function of these communities in their current state in intensive agroecosystems.

Herbicide toxicity on river biofilms assessed by pulse amplitude modulated (PAM) fluorometry

The use of Rapid light curves (RLCs) as a toxicity endpoint for river biofilms was examined in this study and compared to "classical fluorescence parameters" i.e. minimal fluorescence (F0), optimal and effective quantum yields of photosystem II (Fv/Fm and ФPSII). Measurements were performed after exposure to five concentrations of diuron (from 0.3 to 33.4μgL(-1)), its main degradation product (DCPMU) (from 1.0 to 1014μgL(-1)) and norflurazon (from 0.6 to 585μgL(-1)) with the lowest exposure concentrations corresponding to levels regularly encountered in chronically contaminated sites. Biofilm responses were evaluated after 1, 5, 7 and 14 days of exposure to the different toxicants. Overall, the responses of both "classical fluorescence parameters" and RLC endpoints were highly time dependent and related to the mode of action of the different compounds. Interestingly, parameters calculated from RLCs (α, ETRmax and Ik) were useful early markers of pesticide exposure since they revealed significant effects of all the tested toxicants from the first day of exposure. In comparison, classical fluorescence endpoints (F0 and Fv/Fm) measured at day 1 were only affected in the DCPMU treatment. Our results demonstrated the interest of RLCs as early markers of toxicant exposure particularly when working with toxicants with less specific mode of action than PSII inhibitors.

Environmental risk of combined emerging pollutants in terrestrial environments: chlorophyll a fluorescence analysis

The risk assessment in terrestrial environments has been scarcely studied for mixtures of organic contaminants. To estimate toxicity due to these compounds, an ecotoxicological test may be done with the appropriate organism and biomarker. Photosynthesis is principally performed at photosystem II, and its efficiency is affected by any environmental stress. Consequently, the measure of this efficiency may be a good indicator of toxicity if different parameters are employed, e.g., the quantum efficiency of photosystem II and the photochemical quenching coefficient. We did a series of assays to determine the toxicity of two organic contaminants, ibuprofen and perfluorooctanoic acid, using a higher plant (Sorghum bicolor). The results showed more toxicity for the perfluorinated compound and greater sensibility for the quantum efficiency of photosystem II. Regarding the binary combination, three methods were applied to calculate EC50: combination index, concentration addition, and independent action. Synergistic behavior is the principal toxicological profile for this mix. Therefore, the combination index, which considers interactions among chemicals, gave the best estimation to determine risk indices. We conclude that the inhibition of photosynthesis efficiency can be a useful tool to determine the toxicity of the mixtures of organic pollutants and to estimate ecological risks in terrestrial environments.

Modelling the effect of fluctuating herbicide concentrations on algae growth

Herbicide concentrations fluctuate widely in watercourses after crop applications and rain events. The level of concentrations in pulses can exceed the water chronic quality criteria. In the present study, we proposed modelling the effects of successive pulse exposure on algae. The deterministic model proposed is based on two parameters: (i) the typical growth rate of the algae, obtained by monitoring growth rates of several successive batch cultures in growth media, characterizing both the growth of the control and during the recovery periods; (ii) the growth rate of the algae exposed to pulses, determined from a dose-response curve obtained with a standard toxicity test. We focused on the herbicide isoproturon and on the freshwater alga Scenedesmus vacuolatus, and we validated the model prediction based on effect measured during five sequential pulse exposures in laboratory. The comparison between the laboratory and the modelled effects illustrated that the results yielded were consistent, making the model suitable for effect prediction of the herbicide photosystem II inhibitor isoproturon on the alga S. vacuolatus. More generally, modelling showed that both pulse duration and level of concentration play a crucial role. The application of the model to a real case demonstrated that both the highest peaks and the low peaks with a long duration affect principally the cell density inhibition of the alga S. vacuolatus. It is therefore essential to detect these characteristic pulses when monitoring of herbicide concentrations are conducted in rivers.

Spatial and temporal variation of algal assemblages in six Midwest agricultural streams having varying levels of atrazine and other physicochemical attributes

Potential effects of pesticides on stream algae occur alongside complex environmental influences; in situ studies examining these effects together are few, and have not typically controlled for collinearity of variables. We monitored the dynamics of periphyton, phytoplankton, and environmental factors including atrazine, and other water chemistry variables at 6 agricultural streams in the Midwest US from spring to summer of 2011 and 2012, and used variation partitioning of community models to determine the community inertia that is explained uniquely and/or jointly by atrazine and other environmental factors or groups of factors. Periphyton and phytoplankton assemblages were significantly structured by year, day of year, and site, and exhibited dynamic synchrony both between site-years and between periphyton and phytoplankton in the same site-year. The majority of inertia in the models (55.4% for periphyton, 68.4% for phytoplankton) was unexplained. The explained inertia in the models was predominantly shared (confounded) between variables and variable groups (13.3, 30.9%); the magnitude of inertia that was explained uniquely by variable groups (15.1, 18.3%) was of the order hydroclimate>chemistry>geography>atrazine for periphyton, and chemistry>hydroclimate>geography>atrazine for phytoplankton. The variables most influential to the assemblage structure included flow and velocity variables, and time since pulses above certain thresholds of nitrate+nitrite, total phosphorus, total suspended solids, and atrazine. Time since a ≥30 μg/L atrazine pulse uniquely explained more inertia than time since pulses ≥ 10 μg/L or daily or historic atrazine concentrations; this result is consistent with studies concluding that the effects of atrazine on algae typically only occur at ≥30 μg/L and are recovered from.

Determining the relative sensitivity of benthic diatoms to atrazine using rapid toxicity testing: a novel method

Herbicides pose a potential threat to aquatic ecosystems, especially to phototrophic organisms such as benthic diatoms. Benthic diatoms may be a valuable indicator of the toxic impacts of herbicides in aquatic systems. However, this requires information on the herbicide sensitivity of a wide range of freshwater benthic diatom taxa. Unfortunately this information is only available for a limited number of species as current methods of developing new algae toxicity tests on individual taxa are lengthy and costly. To address this issue, we developed a new rapid toxicity test method to test natural benthic communities, from which the relative herbicide sensitivity of many individual taxa can be derived. This involved the collection of natural benthic communities from rocks in situ, which were placed directly into laboratory toxicity tests. Sensitivity data for several diatom genera in a 48 hour exposure toxicity test were produced, without the need for cultures or multiple site visits. After exposure to the highest treatment of atrazine (500 μg L(-1)) there were significant declines of healthy cells in the most sensitive genera: Gomphonema declined by 74%, Amphora by 62%, Cymbella by 54% and Ulnaria by 34% compared to control levels. In contrast, the genera, Eunotia, Achnanthidium and Navicula, had no statistically significant decline in cell health. This method can identify the diatom taxa most at risk of herbicide toxicity within the natural benthic diatom community. The rapid toxicity testing method presented is a simple and effective method to obtain sensitivity data for multiple taxa within a natural benthic diatom community in a relatively short period of time.

Single and mixture effects of pesticides and a degradation product on fluvial biofilms

The Morcille River located in the Beaujolais vineyard area (Eastern France) is subjected to strong vine-growing pressure leading to the contamination by a range of herbicides and fungicides of the surrounding freshwater environment. Particularly high concentrations of norflurazon, desmethyl norflurazon and tebuconazole were recorded in spring 2010 at the downstream site of the river. Despite their occurrence in rivers, scarce toxicity data are available for these products, in particular in the case of desmethyl norflurazon (main norflurazon degradation product). Furthermore, the toxicity data are generally available only for single compounds and are issued from single species toxicity tests, leading to a lack of ecological relevance. Consequently, this study was undertaken to evaluate the toxic effects of norflurazon, desmethyl norflurazon and tebuconazole singly and in a ternary mixture on fluvial biofilm. Toxicity tests were performed in microplates for 48 h. Photosynthetic endpoints were measured using pulse amplitude-modulated fluorometry; diatom densities and taxonomic composition were determined. After 48 h of exposure, significant effects on optimal quantum yield (F v/F m) for desmethyl norflurazon and mixture were observed.

Environmental effects of realistic pesticide mixtures on natural biofilm communities with different exposure histories

This study deals with the use of Polar Organic Chemical Integrative Sampler (POCIS) extracts to assess the impact of low-dose pesticide mixtures on natural biofilm communities originating from either a chronically contaminated or a reference field site. To investigate how natural biofilm communities, pre-exposed to pesticides in situ or not might respond to environmentally realistic changes in pesticide pressure, they were exposed to either clean water or to POCIS extracts (PE) in order to represent toxic pressure with a realistic pesticide mixture directly isolated from the field. The impacts of PE were assessed on structure, physiology and growth of biofilms. Initial levels of tolerance of phototrophic communities to PE were also estimated at day 0. PE exposure led to negative effects on diatom growth kinetics independently of in-field biofilm exposure history. In contrast, the impacts observed on dry weight, ash-free dry mass and algal fluorescence-related parameters followed different trends depending on biofilm origin. Exposure to PE induced changes in diatom assemblages for the biofilm originating from the reference field site with higher relative abundance of Eolimna minima and Nitzschia palea with PE exposure. Initial tolerance of phototrophic communities to PE was 8-fold higher for the biofilm originating from the chronically contaminated site compared to the reference field site. The use of POCIS extracts allowed us to highlight both chronic impacts of low doses of a mixture of pesticides on natural communities with regard to biofilm exposure history as well as initial levels of tolerance of phototrophic communities.

Assessing sensitivity and recovery of field-collected periphyton acutely exposed to atrazine using PSII inhibition under laboratory conditions

Periphyton communities are an integral component of freshwater ecosystems and the desire to include data from toxicity testing with these organisms for ecological risk assessment is growing. This study developed sampling, storage, and exposure methods for the consistent and effective characterization of acute response and recovery of field-derived periphyton to photosystem II (PSII) inhibiting herbicides, particularly atrazine. Pulse amplitude modulated fluorometry was used to assess PSII quantum yield. For the method development phase, periphyton samples were collected from lotic and lentic systems in the Guelph, Ontario, Canada area during the summer of 2011. Following method development, native periphyton communities from three agricultural streams from the midwestern U.S. were sampled and exposed to atrazine (10-320 μg/L) and assessed for inhibition of PSII quantum yield (from 2 up to 24 h) and subsequent recovery upon cessation of exposure (up to 48 h post-exposure). Sensitivity to atrazine (EC10 and EC50 values) varied slightly (typically less than twofold difference) by site, date of sampling, and exposure interval. Only the highest initial test concentrations (160 or 320 μg/L) demonstrated greater than ~5% inhibition at 48 h post-exposure; however all other test concentrations recovered to within 5% of control levels, typically within 24 h. The rapid physiological recovery of periphyton communities upon atrazine removal supports the conclusion that acute exposure will not likely result in significant or sustained impacts on either structure or function of periphyton in lotic ecosystems. For ecological risk assessment, this suggests the current approach of relying on direct effects data for the most sensitive single species alone may result in overly conservative estimates of potential effects, especially for complex communities of primary producers.

Use of polar organic chemical integrative samplers to assess the effects of chronic pesticide exposure on biofilms

The responses of aquatic organisms to chronic exposure to environmental concentrations of toxicants, often found in mixtures, are poorly documented. Here passive sampler extracts were used in experimental contamination of laboratory channels, to investigate their effects on natural biofilm communities. A realistic mixture of pesticides extracted from Polar Organic Chemical Integrative Samplers was used to expose biofilms in laboratory channels to total pesticide concentrations averaging 0.5 ± 0.1 μg l⁻¹. The level of exposure was representative of field conditions in terms of relative proportions of the substances but the exposure concentration was not maintained (decreasing concentrations between contamination occasions). The impact on the structural as well as the functional characteristics of the autotrophic and heterotrophic components was determined, using biofilm grown in uncontaminated conditions (reference site) and in sites exposed to pesticides (contaminated site). The exposure imposed did not significantly modify the structure or functions of reference biofilms, nor did it modify tolerance as measured by mixture EC₅₀ (EC₅₀ mix). In contrast, the communities from the more contaminated downstream section lost tolerance following decreased dose exposure, but community composition remained fairly stable. Overall, these results indicate that low levels of contamination did not lead to strong changes in community structure, and 14-day changes in tolerance seemed to depend mainly on physiological adaptation, suggesting that other environmental factors or longer-lasting processes prevailed. This study reports the first attempt to use passive sampler extracts as a realistic composite contaminant for experimental exposure of biofilms, with promising perspectives in further ecotoxicology studies.