Alga Scenedesmus Obliquus Research Articles

Salt response of the freshwater microalga Scenedesmus obliquus (Turp.) Kutz is modulated by the algal growth phase

Growth and biochemical responses of the coenobial green alga Scenedesmus obliquus to salinity stress were monitored across different phases of growth. The alga was cultured on BG11 growth medium and subjected to 0, 30, 100, and 200 mmol/L NaCl for a period of 20 d, during which algal cultures were harvested at 4-d intervals. The salinity-induced inhibition of algal growth was accompanied with prolongation of timing of the different growth phases. The sharp and progressive salinity-induced inhibition of algal growth rate during the early phase of growth points to salt shock but moderation of inhibition at the subsequent stages of growth means algal acclimation to salinity. The concentrations of chlorophylls a and b, soluble sugars, proteins as well as those of K+ and Na+ in the alga exhibited peaks at the initiation of the exponential phase of growth, with increasing magnitude in proportion to the increase in the level of salinity. Nevertheless, whereas soluble sugars of the alga peaked at initiation of the exponential phase, starch concentration progressively increased with culture age, reaching saturation towards the stationary phase. Whereas the salinity-induced increase in soluble sugars was most evident at the early stages of growth the reverse was true for starch. The present results point to fast acclimation of S. obliquus to salt stress post a brief salt shock, utilizing soluble sugars, K+ and Na+ for osmotic adjustment. Increasing salinity from 0 to 200 mmol/L NaCl led to progressive increase in soluble sugars, proteins, K + and Na + concentrations of the algal cells, particularly at the early stages of growth. However, the salinity-induced increase in chlorophyll concentration approached a limit at 100 mmol/L NaCl whereas that in starch concentration was more evident at the later stages of growth.

Effect of Electrode Properties on the Performance of a Photosynthetic Microbial Fuel Cell for Atrazine Detection

The growing use of herbicides in agriculture poses increasing concerns on the pollution of water systems worldwide. To be able to assess the presence of these compounds in waters and limit their impact on human health and ecosystems, the development of effective in-situ monitoring tools is key. Yet, many existing sensing technologies are not suitable for in-situ and remote applications, due to challenges in portability, durability, cost and power requirements. In this study, we explore for the first time the use of an algal-assisted cathode in a photosynthetic microbial fuel cell (p-MFC) as a self-powered dissolved oxygen probe for herbicides detection in water. The cathode is enriched with the alga Scenedesmus obliquus and two different electrode materials are tested, graphite felt and indium tin oxide, which mainly differ in porosity, surface roughness and transparency. Despite the much larger specific surface area of graphite felt compared to indium tin oxide, the current generated under light was only 10 times larger (109 ± 2µA vs. 10.5 ± 0.6 µA) and 8 times larger in the dark (37 ± 5 µA vs. 4.2 ± 0.6 µA). By generating a current output that correlates with the dissolved oxygen in the catholyte, the resulting p-MFCs could detect the EU legal atrazine concentration limit of 0.1 µg L-1. The use of graphite felt led to shorter response times and better sensitivity, as a result of the greater current baseline. In both cases, the current baseline was recovered after exposure of the sensor to frequent toxic events, thus showing the resilience of the cathodic biofilm and the potential of the p-MFCs for early warnings of herbicides pollution in water.

Testing The Activities of Some of The Inside and Outside Cellular Compounds Produced by The Algae Chlorococcum infusionum and Scenedesmus obliquus Against Some Bacteria

Testing The Activities of Some of The Inside and Outside Cellular Compounds Produced by The Algae Chlorococcum infusionum and Scenedesmus obliquus Against Some Bacteria

Cultivation of oleaginous microalga Scenedesmus obliquus coupled with wastewater treatment for enhanced biomass and lipid production

Coupling microalgae cultivation with wastewater treatment is a promising strategy to purify the waste streams and harvest the enhanced biomass production. In this study, an oleaginous alga Scenedesmus obliquus that was isolated from the dairy wastewater was examined for its bioremediation of municipal wastewater. Water samples, including raw and treated ones, were collected from three wastewater treatment plants at different scales. Under indoor conditions, S. obliquus showed strong nutrient removal efficiency, with nitrogen and phosphorus removal rates being over 99%. The alga grew faster in the raw wastewater (specific growth rates: 0.37−0.45 d−1), whereas more lipids accumulated in the treated wastewater (31.45–35.74%of dry weight). The raw wastewater-based culture was subsequently enlarged by using panel photo-bioreactors (PBRs) in semi-continuous mode. Such outdoor cultivations were conducted twice in different seasons, reflecting the impacts of environmental fluctuation. Results showed that under the natural condition, the hydraulic retention time (HRT)-based culture was significantly impacted by the changeable temperatures and illumination; instead, replacing the medium (i.e. raw wastewater) following biomass concentration rather than HRT made the culture system more stable. An average biomass productivity of 0.22 g L−1 d−1 was obtained, regardless of the changing environmental conditions. These findings may advance the knowledge of employing S. obliquus for raw wastewater treatment at the industrial scale.

Comparative biodegradation of all chlorinated phenols by the microalga Scenedesmus obliquus — The biodegradation strategy of microalgae

This work presents the comparative biodegradation of all chlorinated phenolic compounds by the green alga Scenedesmus obliquus and determines the microalgal bioenergetic strategy. The microalga manages its energy reserves rationally by investing them, either on growth or on the biodegradation of the toxic compound. The microalga seems to follow two distinct detoxification strategies. In the first one, when microalgae are surrounded by relatively low toxic phenolic compounds (phenol, monochlorophenols, 2,4-dichlorophenol and 2,6-dichlorophenol), they use all, or at least more of their energy reserves to increase the biomass production and not the biodegradation. In the second one, when surrounded by higher toxic chlorophenols (meta-substituted dichlorophenols, trichlorophenols, tetrachlorophenols and pentachlorophenol) the microalgae invest more, or all of their energy reserves directly in the biodegradation of the toxic compounds, while less or no energy is invested in biomass increase. The microalga biodegraded in five days approximately 9% of the lower toxic phenol and 90% of the higher toxic pentachlorophenol. Considering our ability to interfere with microalgae energy reserves, which define their stress tolerance in the toxic environment, and knowing the microalgal bioenergetic strategy, we could easily use microalgae to biodegrade toxic wastes in the frame of a rational biotechnological approach in the near future.

Influence of humic substances on the toxic effects of cadmium and SDBS to the green alga Scenedesmus obliquus

The joint toxicity of chemicals mixture in the aquatic environment was still not well clear. To clarify the joint toxicity of the mixtures of metals and organic pollutants, as well as the influence of dissolved organic matter (DOM) in field water-body on their toxic effects, we conducted the toxicity tests with cadmium (Cd) and sodium dodecyl benzene sulfonate (SDBS) on Scenedesmus obliquus (S. obliquus) with or without the presence of fulvic acid (FA), a typical of DOM. Our results showed Cd was more toxic to S. obliquus than SDBS, and the effects of fulvic acid on SDBS were greater than Cd. The joint toxicity of Cd and SDBS expressed a synergistic effect on S. obliquus, which was observed to be increased with the presence of FA. Our results gave an example for the joint toxicity investigations of organics and metals, aiding to understanding the toxicity of pollutant mixtures in field water bodies containing DOM.

Dissolved organic matter and aluminum oxide nanoparticles synergistically cause cellular responses in freshwater microalgae

ABSTRACTThis study investigated the impact of dissolved organic matters (DOM) on the ecological toxicity of aluminum oxide nanoparticles (Al2O3NPs) at a relatively low exposure concentration (1 mg L−1). The unicellular green alga Scenedesmus obliquus was exposed to Al2O3NP suspensions in the presence of DOM (fulvic acid) at various concentrations (1, 10, and 40 mg L−1). The results show that the presence of DOM elevated the growth inhibition toxicity of Al2O3NPs towards S. obliquus in a dose-dependent manner. Moreover, the combination of DOM at 40 mg L−1 and Al2O3NPs resulted in a synergistic effect. The relative contribution of Al-ions released from Al2O3NPs to toxicity was lower than 5%, indicating that the presence of the particles instead of the dissolved ions in the suspensions was the major toxicity sources, regardless of the presence of DOM. Furthermore, DOM at 10 and 40 mg L−1 and Al2O3NPs synergistically induced the upregulation of intercellular reactive oxygen species levels and superoxide dismutase activities. Analysis of the plasma malondialdehyde concentrations and the observation of superficial structures of S. obliquus indicated that the mixtures of DOM and Al2O3NPs showed no significant effect on membrane lipid peroxidation damage. In addition, the presence of both DOM and Al2O3NPs contributed to an enhancement in both the mitochondrial membrane potential and the cell membrane permeability (CMP) in S. obliquus. In particular, Al2O3NPs in the presence of 10 and 40 mg L−1 DOM caused a greater increase in CMP compared to Al2O3NPs and DOM alone treatments. In conclusion, these findings suggest that DOM at high concentrations and Al2O3NPs synergistically interrupted cell membrane functions and triggered subsequent growth inhibition toxicity.

Removal of pharmaceutical pollutants from synthetic wastewater using chemically modified biomass of green alga Scenedesmus obliquus

Pharmaceutical compounds are considered emerging environmental pollutants that have a potential harmful impact on environment and human health. In this study, the biomass of alga (Scenedesmus obliquus) was modified using alkaline solution, and used for the biosorption of tramadol (TRAM) and other pharmaceuticals. The adsorption kinetics and isotherms were investigated. The obtained results reveal high adsorption capacity of tramadol over modified algal biomass (MAB) after 45min with removal percentage of 91%. Pseudo-second order model was well fitted with the experimental data with correlation coefficient (0.999). Biosorption of tramadol on modified algal biomass proceeds with Freundlich isotherm model with correlation coefficient (0.942) that emphasized uptake of TRAM by MAB is driven by chemisorption. FTIR spectra of MAB before and after the adsorption were analyzed; some IR bands were detected with slight shift and low intensity suggesting their involving in adsorption. The tramadol biosorption by MAB is a chemical process as confirmed by Dubinin-Radushkevich. The adsorption of pharmaceutical over MAB is mainly preceded by hydrophilic interactions between amino and carbonyl groups in pharmaceutical molecules and hydroxyl and carbonyl functional groups on surface of biosorbent. It was emphasized by disappearance O-H and C-O from biomass IR spectra after adsorption. In matrix of pharmaceutical, the recorded adsorption capacities for CEFA, PARA, IBU, TRAM and CIP are 68, 58, 42, 42 and 39mg/g over MAB at natural pH and MAB dose of 0.5g/L. Furthermore, oxygen uptake by bacteria was applied for estimate the toxicity of pharmaceutical. The recorded result concluded the efficient reusability of modified algal biomass for biosorption of pharmaceuticals, as well only the adsorption efficiency decreased by 4.5% after three runs. Subsequently, the modified algal biomass is a promising reusable adsorbent for decontamination of wastewater from pharmaceuticals.

Bioenergetic reprogramming plasticity under nitrogen depletion by the unicellular green alga Scenedesmus obliquus.

Simultaneous nitrogen depletion and 3,4-dichlorophenol addition induce a bioenergetic microalgal reprogramming, through strong Cyt b 6 f synthesis, that quench excess electrons from dichlorophenol's biodegradation to an overactivated photosynthetic electron flow and H 2 -productivity. Cellular energy management includes "rational" planning and operation of energy production and energy consumption units. Microalgae seem to have the ability to calculate their energy reserves and select the most profitable bioenergetic pathways. Under oxygenic mixotrophic conditions, microalgae invest the exogenously supplied carbon source (glucose) to biomass increase. If 3,4-dichlorophenol is added in the culture medium, then glucose is invested more to biodegradation rather than to growth. The biodegradation yield is enhanced in nitrogen-depleted conditions, because of an increase in the starch accumulation and a delay in the establishment of oxygen-depleted conditions in a closed system. In nitrogen-depleted conditions, starch cannot be invested in PSII-dependent and PSII-independent pathways for H2-production, mainly because of a strong decrease of the cytochrome b 6 f complex of the photosynthetic electron flow. For this reason, it seems more profitable for the microalga under these conditions to direct the metabolism to the synthesis of lipids as cellular energy reserves. Nitrogen-depleted conditions with exogenously supplied 3,4-dichlorophenol induce reprogramming of the microalgal bioenergetic strategy. Cytochrome b 6 f is strongly synthesized (mainly through catabolism of polyamines) to manage the electron bypass from the dichlorophenol biodegradation procedure to the photosynthetic electron flow (at the level of PQ pool) and consequently through cytochrome b 6 f and PSI to hydrogenase and H2-production. All the above showed that the selection of the appropriate cultivation conditions is the key for the manipulation of microalgal bioenergetic strategy that leads to different metabolic products and paves the way for a future microalgal "smart" biotechnology.

The toxicity of ionic liquid 1-decylpyridinium bromide to the algae Scenedesmus obliquus: Growth inhibition, phototoxicity, and oxidative stress

Although ionic liquids (ILs) are unlikely to act as air contaminants, their high solubility and slow degradation make them a potential threat to the aquatic environment. The IL 1-decylpyridinium bromide ([DPy]Br) is a common type of pyridine IL, which has varied applications such as in extraction, separation, and catalytic synthesis. Herein, the toxicity of [DPy]Br to S. obliquus is determined. Growth was inhibited by high-concentration [DPy]Br, whereas it had a hormetic effect at low concentrations. The IC50–96h was approximately 0.06mg/L. The cell membrane permeability of S. obliquus increased with [DPy]Br concentration, indicating that [DPy]Br can cause damage to the algae cell structure. Chlorophyll content decreased at high [DPy]Br concentration; chlorophyll fluorescence parameters, such as the maximum effective quantum yield of PSII (Fv/Fm), potential activity of PSII (Fv/F0), yield of the photochemical quantum [Y(II)], and the non-photochemical quenching coefficient (NPQ) were affected, suggesting that [DPy]Br can damage PSII. The ROS fluorescent images revealed that the morphology of cells changed gradually from fusiform to round. High ROS levels were observed with high concentrations of [DPy]Br, indicating that [DPy]Br induced oxidative stress on S. obliquus. The SOD and CAT activities increased when the concentration was lower than IC50, whereas they decreased when the concentration was higher than IC50. The relative ROS content was significantly correlated with growth inhibition rate, cell membrane permeability, chlorophyll content, and SOD and CAT activities. The increase of ROS content in algal cells is an important toxicological mechanism of [DPy]Br to S. obliquus.

Bioaccumulation and effects of novel chlorinated polyfluorinated ether sulfonate in freshwater alga Scenedesmus obliquus.

Chlorinated polyfluorinated ether sulfonate (Cl-PFESA) is a novel alternative compound for perfluorooctane sulfonate (PFOS), with its environmental risk not well known. The bioaccumulation and toxic effects of Cl-PFESA in the freshwater alga is crucial for the understanding of its potential hazards to the aquatic environment. Scenedesmus obliquus was exposed to Cl-PFESA at ng L-1 to mg L-1, with the exposure regime beginning at the environmentally relevant level. The total log BAF of Cl-PFESA in S.obliquus was 4.66, higher than the reported log BAF of PFOS in the freshwater plankton (2.2-3.2). Cl-PFESA adsorbed to the cell surface accounted for 33.5-68.3% of the total concentrations. The IC50 of Cl-PFESA to algal growth was estimated to be 40.3mgL-1. Significant changes in algal growth rate and chlorophyll a/b contents were observed at 11.6mgL-1 and 13.4mgL-1 of Cl-PFESA, respectively. The sample cell membrane permeability, measured by the fluorescein diacetate hydrolyzation, was increased by Cl-PFESA at 5.42mgL-1. The mitochondrial membrane potential, measured by Rh123 staining, was also increased, indicating the hyperpolarization induced by Cl-PFESA. The increasing ROS and MDA contents, along with the enhanced SOD, CAT activity, and GSH contents, suggested that Cl-PFESA caused oxidative damage in the algal cells. It is less possible that current Cl-PFESA pollution in surface water posed obvious toxic effects on the green algae. However, the bioaccumulation of Cl-PFESA in algae would contribute to its biomagnification in the aquatic food chain and its effects on membrane property could potentially increase the accessibility and toxicity of other coexisting pollutants.

Electro-oxidation of tetracycline by a Magnéli phase Ti4O7 porous anode: Kinetics, products, and toxicity

The goal of this study is to evaluate Magnéli phase titanium oxide (Ti4O7) as an anode material for potential application in electrochemical oxidation of organic pollutants in water. The removal of tetracycline (TC) was systematically investigated in terms of kinetics, reaction mechanisms and pathways, and multi-species toxicity. Application of 0.5–3mAcm−2 current densities resulted in >90% total removal of TC over a wide range of initial concentrations from 1ppm to 50ppm with half-lives between 28mins and 75mins. The oxidation mechanisms were further elucidated using salicylic acid (SA) as a hydroxyl free radical trap. At least 40% of total TC removal was attributable to reactions mediated by hydroxyl radicals, which were generated on Magnéli phase Ti4O7 at a rate of 2×10−9molcm−2min−1 under 0.5mAcm−2 applied current density. Tests on Escherichia coli culture indicated that electro-oxidation of TC by Magnéli phase Ti4O7 anode successfully reduced the original antimicrobial activity to a level below detection limit. However, for freshwater micro algae Scenedesmus obliquus, inhibitory effects persisted in the first couple of hours and then dramatically reduced during the last stage of treatment, likely due to intermediate products that later mineralized and detoxified. Reaction pathways were proposed based on the data of high-resolution mass spectrometry, and oxidation products with antibiotic potency similar to or greater than TC were identified in 1h treatment sample, but not detectable in the end-of-treatment solution.

Co-exposure of Freshwater Microalgae to Tetrabromobisphenol A and Sulfadiazine: Oxidative Stress Biomarker Responses and Joint Toxicity Prediction.

Combined toxicity and oxidative stress biomarker responses were determined for tetrabromobisphenol A (TBBPA) and sulfadiazine (SDZ) to the unicellular green alga Scenedesmus obliquus. Concentration-response analyses were performed for single toxicants and for mixtures containing TBBPA and SDZ with two different mixture ratios. The effect concentrations and the observed effects of the mixtures were compared to the predictions of the joint toxicity by the concentration addition (CA) model and independent action (IA) model. Results showed that the observed joint toxicity was within the scope of the highest (TBBPA) and lowest (SDZ) toxicity observed for the individual components. Furthermore, co-exposure of S. obliquus to TBBPA and SDZ provided preliminary evidence that the mixtures induced oxidative stress leading to cell damage. The CA and IA models proved to be valid for the prediction of the joint toxicity of TBBPA and SDZ. This study highlights a combined environmental risk assessment for two emerging pollutants.

Assessment and prediction of joint algal toxicity of binary mixtures of graphene and ionic liquids

Graphene and ionic liquids (ILs) released into the environment will interact with each other. So far however, the risks associated with the concurrent exposure of biota to graphene and ILs in the environment have received little attention. The research reported here focused on observing and predicting the joint toxicity effects in the green alga Scenedesmus obliquus exposed to binary mixtures of intrinsic graphene (iG)/graphene oxide (GO) and five ILs of varying anionic and cationic types. The isolated ILs in the binary mixtures were the main contributors to toxicity. The binary GO-IL mixtures resulted in more severe joint toxicity than the binary iG-IL mixtures, irrespective of mixture ratios. The mechanism of the joint toxicity may be associated with the adsorption capability of the graphenes for the ILs, the dispersion stability of the graphenes in aquatic media, and modulation of the binary mixtures-induced oxidative stress. A toxic unit assessment showed that the graphene and IL toxicities were additive at low concentration of the mixtures but antagonistic at high concentration of the mixtures. Predictions made using the concentration addition and independent action models were close to the observed joint toxicities regardless of mixture types and mixture ratios. These findings provide new insights that are of use in the risk assessment of mixtures of engineered nanoparticles and other environmentally relevant contaminants.

Production and characterization of biodiesel from the unicellular green alga Scenedesmus obliquus

ABSTRACTRegardless of whether biodiesel is represented in the form of oil from grains, agricultural crops, or microorganisms, it is a clean fuel depends mainly on biomass conversion. The present work indicates that the green microalga Scenedesmus obliquus showed higher biomass productivity of 0.15 g (CDW) L−1 d−1. The increase in NaCl concentration up to +100% caused an increase in growth, esterified fatty acid (EFA) content, and EFA productivity of S. obliquus. The decrease or increase of pH values reduced the growth, EFA content, and productivity. Biomass productivity increased from 0.06 g L−1d−1 under a light intensity of 80 μmol m−2s−1 to 0.1 g L−1d−1 at 160 μmol m−2 s−1. Biodiesel characterization showed that the iodine value of biodiesel of S. obliquus was 70 g iodine/100 g oil. Except viscosity, all biodiesel characteristics are in accordance with the European standards for fuel diesel (EN 590:1999). These results nominate S. obliquus as a promising candidate for biodiesel production by outdoor cultivation.

Modulatory effects of Zn2+ ions on the toxicity of citrate- and PVP-capped gold nanoparticles towards freshwater algae, Scenedesmus obliquus.

Gold nanoparticles (GNPs) are widely used for medical purposes, both in diagnostics as well as drug delivery, and hence are prone to release and distribution in the environment. Thus, we have explored the effects of GNPs with two distinct surface capping (citrate and PVP), and three different sizes (16, 27, and 37nm) at 0.01-, 0.1-, and 1-mgL-1 concentrations on a predominant freshwater alga Scenedesmus obliquus in the sterile freshwater matrix. We have also investigated how an abundant metal ion from freshwater, i.e., Zn2+ ions may modulate the effects of the selected GNPs (40nm, citrate, and PVP capped). Preliminary toxicity results revealed that gold nanoparticles were highly toxic in comparison to zinc ions alone. A significant modulation in the toxicity of Zn ions was not noticed in the presence of GNPs. In contrast, zinc ions minimized the toxicity produced by GNPs (both CIT-37 and PVP-37), despite its individual toxicity. Approximately, about 42, 33, and 25% toxicity reduction was noted at 0.05-, 0.5-, and 5-mgL-1 Zn ions, respectively, for CIT-37 GNPs, while 31% (0.05mgL-1), 24% (0.5mgL-1), and 9% (5mgL-1) of toxicity reduction were noted for PVP-37 GNPs. Maximum toxicity reduction was seen at 0.05mgL-1 of Zn ions. Abbott modeling substantiated antagonistic effects offered by Zn2+ ions on GNPs. Stability and sedimentation data revealed that the addition of zinc ions gradually induced the aggregation of NPs and in turn significantly reduced the toxicity of GNPs. Thus, the naturally existing ions like Zn2+ have an ability to modulate the toxicity of GNPs in a real-world environment scenario.

Reduced graphene oxide induces cytotoxicity and inhibits photosynthetic performance of the green alga Scenedesmus obliquus

Increased use of graphene materials might ultimately lead to their release into the environment. However, only a few studies have investigated the impact of graphene-based materials on green plants. In this study, the impact of reduced graphene oxide (RGO) on the microalgae Scenedesmus obliquus was evaluated to determine its phytotoxicity. Treatment with RGO suppressed the growth of the microalgae. The 72-h IC50 values of RGO evaluated using the logistic and Gompertz models were 148 and 151 mg L−1, respectively. RGO significantly inhibited Chl a and Chl a/b levels in the algal cells. Chlorophyll a fluorescence analysis showed that RGO significantly down-regulated photosystem II activity. The mechanism of how RGO inhibited algal growth and photosynthetic performance was determined by analyzing the alterations in ultrastructural morphology. RGO adhered to the algal cell surface as a semitranslucent coating. Cell wall damage and membrane integrity loss occurred in the treated cells. Moreover, nuclear chromatin clumping and starch grain number increase were noted. These changes might be attributed to the increase in malondialdehyde and reactive oxygen species levels, which might have exceeded the scavenging ability of antioxidant enzymes (including peroxidase and superoxide dismutase). RGO impaired the extra- and intra-cellular morphology and increased oxidative stress and thus inhibited algal growth and photosynthesis.

Herbicides interfere with antigrazer defenses in Scenedesmus obliquus

The extensive application of herbicides has led to a serious threat of herbicide contamination to aquatic ecosystem. Herbicide exposure affects aquatic communities not only by exerting toxicity on single species but also by changing interspecific interactions. This study investigated the antigrazer defenses of the common green alga Scenedesmus obliquus against different herbicides [glyphosate, 2,4-dichlorophenoxyacetic acid (2,4-D), and atrazine] at various concentrations (0–2.0 mg L−1). In the presence of grazer (Daphnia)-derived cues, S. obliquus populations without herbicides formed high proportions of multicelled (e.g., four- and eight-celled) colonies. This result confirms that S. obliquus exhibits a morphological defense against grazing risk. At the low concentration range of 0.002–0.02 mg L−1, the three herbicides exerted no influence on the growth and photosynthetic efficiency of S. obliquus, and multicelled colonies showed constant proportions. At the high concentration range of 0.20–2.0 mg L−1, atrazine significantly inhibited the algal growth and photosynthesis whereas glyphosate or 2,4-D did not. Nonetheless, these levels of glyphosate or 2,4-D remarkably decreased the proportion of multicelled colonies, with reduced numbers of cells per particle in Daphnia filtrate-treated population. No eight-celled colony was formed after treatment with atrazine at 0.20–2.0 mg L−1 despite the addition of Daphnia filtrate. These results suggest that herbicide exposure impairs antigrazer colonial morphs in phytoplankton although it is not sufficient to hamper algal growth. This phenomenon can increase the risk of predation by herbivores, thereby disrupting the inducible phytoplankton community. Furthermore, the predator-prey interactions between herbivores and phytoplankton can be potentially changed more seriously than previously considered.

Bicarbonate enhanced removal of triclosan by copper(II) catalyzed Fenton-like reaction in aqueous solution

The antimicrobial and preservative agent triclosan (TCS) is an emerging and persistent pollutant, and is ubiquitous in the environment. Low cost and efficient removing technology for TCS in water has been the target of many researches. In this study, effective removal of TCS from water was achieved by Cu2+/H2O2 system in the presence of environmental relevant concentration of bicarbonate (HCO3−). The removal efficiency of TCS increased with the increase of HCO3− concentration from 0 to 2.0mM, while further increase of the HCO3− concentration caused the decrease of removal efficiency. TCS (0.01mM) could be totally removed over 120min when HCO3− was 2.0mM (pH 8.72) in the presence of 0.01mM Cu2+ ions at 25.0°C. In order to explore the reaction mechanism, radical scavenging technologies, molecular probe compound p-Chlorobenzoic acid (PCBA) and cyclovoltammetric (CV) experiments were employed to determine the reactive oxygen species (ROS), the steady-state concentrations of OH and Cu2+-complex, respectively. The results suggested that the Cu2+-complex formed between Cu2+ and HCO3− could catalyze H2O2 to produce O2−· and OH, which were responsible for the removal of TCS. Based on the reaction mechanism and identified intermediates of the oxidation process using TOF–LC–MS techniques, the reaction pathways for the oxidation of TCS were proposed including the cleavage of the ether bond, hydroxylation and polymerization. Finally, evaluation on the toxicity change of TCS reaction solution mediated by Cu2+/H2O2-HCO3− system with the freshwater green alga Scenedesmus obliquus showed significant detoxification of TCS.

A quantitative structure–activity relationship approach for assessing toxicity of mixture of organic compounds

Four types of reactivity indices were employed to construct quantitative structure–activity relationships for the assessment of toxicity of organic chemical mixtures. Results of analysis indicated that the maximum positive charge of the hydrogen atom and the inverse of the apolar surface area are the most important descriptors for the toxicity of mixture of benzene and its derivatives to Vibrio fischeri. The toxicity of mixture of aromatic compounds to green alga Scenedesmus obliquus is mainly affected by the electron flow and electrostatic interactions. The electron-acceptance chemical potential and the maximum positive charge of the hydrogen atom are found to be the most important descriptors for the joint toxicity of aromatic compounds.