Ecotoxicological assessment of biomass-derived furan platform chemicals using aquatic and terrestrial bioassays.

An environmental toxicological assessment of fourteen furanic compounds serving as valuable building blocks produced from biomass was performed. The molecules selected included well studied compounds serving as control examples to compare the toxicity exerted against a variety of highly novel furans which have been additionally targeted as potential or current alternatives to biofuels, building blocks and polymer monomers. The impact of the furan platform chemicals targeted on widely applied ecotoxicity model organisms was determined employing the marine bioluminescent bacterium Aliivibrio fischeri and the freshwater green microalgae Raphidocelis subcapitata, while their ecotoxicity effects on plants were assessed using dicotyledonous plants Sinapis alba and Lepidium sativum. Regarding the specific endpoints evaluated, the furans tested were slightly toxic or practically nontoxic for A. fischeri following 5 and 15 min of exposure. Moreover, most of the building blocks did not affect the growth of L. sativum and S. alba at 150 mg L-1 for 72 h of exposure. Specifically, 9 and 11 out of the 14 furan platform chemicals tested were non-effective or stimulant for L. sativum and S. alba respectively. Given that furans comprise common inhibitors in biorefinery fermentations, the growth inhibition of the specific building blocks was studied using the industrial workhorse yeast Saccharomyces cerevisiae, demonstrating insignificant inhibition on eukaryotic cell growth following 6, 12 and 16 h of exposure at a concentration of 500 mg L-1. The study provides baseline information to unravel the ecotoxic effects and to confirm the green aspects of a range of versatile biobased platform molecules.

Acute toxic effect of typical chemicals and ecological risk assessment based on two marine microalgae, Phaeodactylum tricornutum and Platymonas subcordiformis.

With the increasing demand for typical hazardous and noxious substances (HNS) in chemical industry, there is an increased leakage risk of these HNS during transportation by vessel and storage nearby seashore. In this study, the acute toxicity of nonylphenol, butyl acrylate and 1, 2-dichloroethane to Phaeodactylum tricornutum (P. tricornutum) and Platymonas subcordiformis (P. subcordiformis), was investigated to assess their ecological risk. The results showed that the three kinds of HNS showed significant time- and dose-dependent patterns on the growth inhibition of two marine microalgae. The 96 h-EC50 of nonylphenol, butyl acrylate and 1, 2-dichloroethane on P. tricornutum was 1.088, 45.908 and 396 mg L-1, respectively, and the 96 h-EC50 of that on P. subcordiformis was 0.851, 52.621 and 389 mg L-1, respectively. It was a common method to evaluate the harm of pollutants to organisms by calculating HC5 value (the minimum pollutant concentration value harmful to 95 % of the studied species, which was no-effect concentration) with Species Sensitivity Distribution (SSD). On the basis of EC50, the ecological risk assessment was further carried out, and HC5 value of nonylphenol and 1, 2-dichloroethane to aquatic organism was 0.079 and 44 mg L-1, respectively.

Assessment of cytotoxicity biomarkers on the microalga Chlamydomonas reinhardtii exposed to emerging and priority pollutants.

Contamination of aquatic ecosystems linked to anthropogenic activity is currently a major concern; therefore, ecotoxicological studies are needed to assess its effect on organisms. The main objective of this study was to investigate the effects of different pollutants on microalgae in search of sensitive biomarkers that can promote a common cytotoxic response regardless of the contaminant. Cultures of the freshwater microalga Chlamydomonas reinhardtii were exposed for 24 h to four chemicals, three emerging pollutants (benzophenone-3, bisphenol A and oxytetracycline) and one priority substance (atrazine). A cytometric panel was carried out to assess toxicity biomarkers including cellular growth, inherent cell properties, viability, vitality, cytoplasmic membrane potential and ROS levels. Lipid peroxidation, photosynthetic efficiency and transcriptional responses of photosynthesis- and oxidative stress-related genes using RT-qPCR were also studied. Some toxicity responses showed a similar pattern; a decrease in growth rate, vitality and photosynthetic efficiency and an increase in autofluorescence and in the number of cells with depolarised cytoplasmic membrane and were found for all chemicals tested. However, ATZ and OTC provoked a decrease in cell size, whereas BP-3 and BPA caused an increase in cell size, intracellular complexity and ROS levels and a decrease in cell viability. Assayed pollutants generally promoted an overexpression of genes related to cellular antioxidant defence system and a subexpression of photosynthesis-related genes. In addition to the traditional growth endpoint, cell vitality, autofluorescence and gene expression of catalase, glutathione peroxidase and Fe-superoxide dismutase were significantly affected for all chemicals tested, showing a common cytotoxic response. Among the tested substances, BP-3 provoked the strongest cytotoxic alterations on this microalga, pointing out that some emerging contaminants could be more harmful to organisms than priority pollutants.

Modelling quantitative structure activity-activity relationships (QSAARs): auto-pass-pass, a new approach to fill data gaps in environmental risk assessment under the REACH regulation.

Reviewing the toxicological literature for over the past decades, the key elements of QSAR modelling have been the mechanisms of toxic action and chemical classes. As a result, it is often hard to design an acceptable single model for a particular endpoint without clustering compounds. The main aim here was to develop a Pass-Pass Quantitative Structure-Activity-Activity Relationship (PP QSAAR) model for direct prediction of the toxicity of a larger set of compounds, combing the application of an already predicted model for another species, and molecular descriptors. We investigated a large acute toxicity data set of five aquatic organisms, fish, Daphnia magna, and algae from the VEGA-Hub, as well as Tetrahymena pyriformis and Vibrio fischeri. The statistical quality of the models encouraged us to consider this alternative for the prediction of toxicity using interspecies extrapolation QSAAR models without regard to the toxicity mechanism or chemical class. In the case of algae, the use of activity values from a second species did not improve the models. This can be attributed to the weak interspecies relationships, due to different aquatic toxicity mechanisms in species.

Comparing in vivo data and in silico predictions for acute effects assessment of biocidal active substances and metabolites for aquatic organisms.

The purpose of this study was to determine the acute toxicity in aquatic organisms of one biocidal active substance and six metabolites derived from biocidal active substances and to assess the suitability of available QSAR models to predict the obtained values. We have reported the acute toxicity in sewage treatment plant (STP) microorganisms, in the freshwater microalgae Pseudokirchneriella subcapitata and in Daphnia magna following OECD test methods. We have also identified in silico models for acute toxicity of these trophic levels currently available in widely recognized platforms such as VEGA and the OECD QSAR ToolBox. A total of six, four and two models have been selected for Daphnia, algae and microorganisms, respectively. Finally, we have compared the in silico and in vivo data for the seven compounds plus two previously assayed biocidal substances. None of the compounds tested were toxic for Daphnia and STP microorganisms. For microalgae, CGA71019 (1,2,4 triazole) presented an ErC50 value of 38.3 mg/L. The selected in silico models have provided lower EC50 values and are therefore more conservative. Models from the OECD QSAR ToolBox predicted values for 7 out of 9 and for 4 out of 9 chemicals for Daphnia and P. subcapitata, respectively. No predictive models were identified in such platform for STP microorganism's acute effects. In terms of models's specificity, biocide-specific models, developed from curated datasets integrated by biocidal active substances and implemented in VEGA, perform better in the case of microalgae but for Daphnia an alternative, non biocide-specific has revealed a better performance. For STP microorganisms only biocide-specific models have been identified.

Toxicity assessment of particulate matter emitted from different types of vehicles on marine microalgae.

Air pollution caused by vehicle emissions remains a serious environmental threat in urban areas. Sedimentation of atmospheric aerosols, surface wash, drainage water, and urbane wastewater can bring vehicle particle emissions into the aquatic environment. However, the level of toxicity and mode of toxic action for this kind of particles are not fully understood. Here we explored the aquatic toxic effects of particulate matter emitted from different types of vehicles on marine microalgae Porphyridium purpureum and Heterosigma akashiwo. We used flow cytometry to evaluate growth rate inhibition, changes in the level of esterase activity, changes in membrane potential and size changes of microalgae cells under the influence of particulate matter emitted by motorcycles, cars and specialized vehicles with different types of engines and powered by different types of fuel. Both microalgae species were highly influenced by the particles emitted by diesel-powered vehicles. These particle samples had the highest impact on survival, esterase activity, and membrane potential of microalgae and caused the most significant increase in microalgae cell size compared to the particles produced by gasoline-powered vehicles. The results of the algae-bioassay strongly correlate with the data of laser granulometry analyses, which indicate that the most toxic samples had a significantly higher percentage of particles in the size range less than 1 µm. Visual observation with an optical microscope showed intensive agglomeration of the particles emitted by diesel-powered vehicles with microalgae cells. Moreover, within the scope of this research, we did not observe the direct influence of metal content in the particles to the level of their aquatic toxicity, and we can conclude that physical damage is the most probable mechanism of toxicity for vehicle emitted particles.

Ecotoxicological assessment of bauxite residue (red mud) overflow treated by dissolved air flotation (DAF).

In this study, the effluent from the Bayer process of transforming bauxite into alumina, followed by dissolved air flotation (DAF) treatment, was evaluated to identify the best experimental conditions that generate less toxic or nontoxic effluent for discharge. Two freshwater organisms, the Chlorophyceae microalga Raphidocelis subcapitata (96-h algal growth inhibition test), and the microcrustacean Daphnia similis (48-h acute immobility test), were used to analyze the efficiency of effluent treatment by detecting and comparing the toxicity of the treated effluent. Experimental factorial planning used different concentrations of the coagulant ferric chloride and the flocculant Nalco® N-99-005B, and different recycle ratios. The highest recycle ratio (30%) and highest flocculant concentration (150 mg/L) had the best solids removal efficiency, above 90%. Probably the higher concentration of flocculant led to the formation of a more stable froth, promoting an increase in the hydrophobic characteristics of the flocs. Two operating conditions were satisfactory according to acute and chronic bioassays, with removal efficiencies of total suspended solids and turbidity higher than 98%, for both variables. Producers, R. subcapitata microalga, were more sensitive than the primary consumers, D. similis microcrustaceans, indicating the importance of performing tests with different bioindicators.

Toxicity assessment of ZnO nanoparticles to freshwater microalgae Coelastrella terrestris.

Commercial usage of ZnO nanoparticles has increased recently due to its versatile applications, raising serious environmental concern because of its ultimate release of nanoparticles in aquatic ecosystem. Therefore, it is important to understand the impact of ZnO nanoparticle toxicity especially on algal flora, which is the primary producer in the aquatic food chain. In the current study, algal growth kinetics was assessed after the exposure of zinc oxide nanoparticles and its bulk counterpart to Coelastrella terrestris (Chlorophyceae). Zinc oxide nanoparticles were found to be more toxic (y = 34.673x, R2 = - 0.101, 1 mg L-1 nanoparticle (NP)) than bulk (y = 50.635x, R2 = 0.173, 1 mg L-1 bulk) by entrapping the algal cell surface. Higher toxicity may be due to oxidative stress within the algal cell as confirmed through biochemical analysis. Biochemical parameters revealed stressful physiological condition in the alga under nanoparticle exposure, as lactate dehydrogenase release (18.89 ± 0.2 NP; 13.67 ± 0.2 bulk), lipid peroxidation (0.9147 ± 1.2 NP; 0.7480 ± 0.8 bulk), and catalase activity (4.77 ± 0.1 NP; 3.32 ± 0.1 bulk) were found higher at 1 mg L-1 in the case of nano-form. Surface adsorptions of nanoparticles were observed by SEM. Cell organelle damage, cell wall breakage, and cytoplasm shrinkage were found as responses under toxic condition through SEM and TEM. Toxicity was found to be influenced by dose concentration and exposure period. This study indicates that nano-form of ZnO is found to be more toxic than bulk form to freshwater alga.

Toxicological Assessment of Intermediates in Natural Attenuation of p-Xylene to Marine Microalgae.

The toxic effects of p-xylene, 4-methylbenzyl alcohol, p-methyl benzaldehyde, and p-toluic acid on two marine microalgae (Phaeodactylum tricornutum Bohlin, and Skeletonema costatum) were investigated. p-Xylene was the most toxic to Pha. tricornutum with a 96 h EC50 value of 6.76 mg L-1. Based on the 96 h EC50 values for two microalgae, the toxicity of the four chemicals, in descending order, was: p-xylene, p-methyl benzaldehyde, 4-methylbenzyl alcohol, then p-toluic acid. The results showed that the toxicity of the transformed products of p-xylene was lower than that of p-xylene.

Toxicity of 10 organic micropollutants and their mixture: Implications for aquatic risk assessment.

Micropollutants, as a serious water pollution issue, raise considerable toxicological concerns, particularly when present as components of complex mixtures. Due to the interactions of environmental pollution components (contaminant), the micropollutant problem is increasingly complex, thus, water quality of organic chemical contamination assessed substance-by-substance might lead to underestimation in aquatic environmental risk assessment. To assess the aquatic environmental risk of micropollutants mixture, a total of 10 organic micropollutants were selected and analysed by an approach of integration of literature data, laboratory experiments and prediction techniques. The experiment results showed that all 10 micropollutants were capable of causing toxicity in zebrafish embryos, aquatic invertebrates and algae with the LC50 (50% lethal concentration) values from 1.14 mg/L to 14.37 mg/L. Triclosan, carbamazepine, diazinon and diuron were the most hazardous compounds in the Danube River and the Rhine River. The artificial mixture presented a strong antagonistic relationship, which demonstrated an independent action (IA) model of the mixture. Based on the observed toxicity data, the risk quotients (RQs) of environmental mixtures of the Danube River and the Rhine River were extrapolated. It can be concluded that the micropollutant mixture may pose a potential risk for aquatic ecosystems with the present environmentally measured concentrations in the Danube River and Rhine River. Mixture risk assessment results suggested that the toxicity of studied chemicals might be induced by dissimilar actions, which is in agreement with the mixture toxicity prediction of the IA model. The observed findings could be useful to establish an overview of the pressures, vision, measures and expectations for hazardous substances pollution, which can help in making to informed decisions to reduce the concentration and bioactive fraction of pollutants.

Natural plant extracts as an economical and ecofriendly alternative for harvesting microalgae.

The study investigated the ability of plant based natural coagulants from Azadirachta indica; Ficus indica; Moringa oleifera; Citrus sinensis; Punica granatum and Musa acuminata to harvest the microalgal biomass. Influence of eluent type (water and NaCl) and concentration (1-5 N) on coagulant extraction; coagulant dosage (1-5 g) and volume (20-100 ml); pH (6-12) and algal concentration (0.1-1 g l-1) on harvesting were analyzed. The results obtained were compared with alum and chitosan. FTIR and biochemical analysis confirmed the presence of bioactive compounds to aid coagulation. Biomass removal efficiency of 75.50% was obtained with M. oleifera extracts (8 mg ml-1) at pH 7.5-7.8, within 100 min. The harvesting efficiency increased to 95.76% when 4 mg ml-1M. oleifera extracts was combined with 0.75 mg ml-1 chitosan. The life cycle and cost analysis acknowledged the eco-friendly coagulants as strong alternative for conventional coagulants used in microalgal harvesting, thereby improvising the overall bioprocess.

Identification of contaminants of concern in the upper Tagus river basin (central Spain). Part 2: Spatio-temporal analysis and ecological risk assessment.

This study provides a description of the water quality status in the tributaries of the upper Tagus River and a preliminary risk assessment for freshwater organisms. A wide range of physico-chemical parameters, nutrients, metals and organic contaminants (20 pesticides, and 32 point source chemicals, mainly pharmaceuticals) were monitored during spring, summer and autumn of 2016. Monitoring of organic contaminants was performed using conventional grab sampling and passive samples (POCIS). The variation of the different groups of parameters as regards to land use and sampling season was investigated. The prioritization of organic and inorganic contaminants was based on the toxic unit (TU) approach, using toxicity data for algae, invertebrates and fish. Finally, the compliance with the Environmental Quality Standards (EQS) set as part of the Water Framework Directive (WFD) was evaluated for the listed substances. This study shows that the land use characteristics had a large influence on the spatial distribution of the contaminants and other water quality parameters, while temporal trends were only significant for physico-chemical parameters, and marginally significant for insecticides. Acute toxicity is likely to occur for some metals (copper and zinc) in the most impacted sites (TU values close to or above 1). Low acute toxicity was determined for organic contaminants (individual compounds and mixtures) on the basis of grab samples. However, the assessment performed with POCIS samples identified diuron, chlorpyrifos and imidacloprid as potentially hazardous compounds. Several contaminant mixtures that may cause chronic toxicity and that should be considered in future regional chemical monitoring plans were identified. Our study also shows that some metals and pesticides exceeded the WFD regulatory thresholds and that only 30% of the sampled sites had a good chemical status. Further research is needed to identify chemical emission sources and to design proper abatement options in the Tagus river basin.

Toxicity of BDE-47, BDE-99 and BDE-153 on swimming behavior of the unicellular marine microalgae Platymonas subcordiformis and implications for seawater quality assessment.

Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardants, have been extensively applied and eventually leached into the surrounding environment. Marine microalgae are not only the dominant primary producers of marine ecosystem, but also food source for aquaculture. PBDEs have been found to remarkably inhibit growth, photosynthesis and metabolism of marine microalgae. However, whether they also affect swimming behavior of marine motile microalgae remains unknown. We chose BDE-47, BDE-99 and BDE-153 as model PBDEs, and the unicellular marine green flagellate, Platymonas subcordiformis, as test organism to figure out this issue. After two-hour exposure, motile cells proportion (MOT), swimming velocity (VCL, VAP and VSL), and swimming pattern (LIN and STR) of P. subcordiformis were measured via computer assisted cell movement tracking. Results suggest that the three PBDEs not only reduced motile cells proportion and swimming velocity, but also altered swimming pattern. BDE-47 was more toxic than BDE-99, followed by BDE-153, indicating their toxicity decreased as bromination degree increases. Swimming ability of P. subcordiformis was even completely arrested when BDE-47 and BDE-99 at 32 µg/L. The impairment of swimming ability by PBDEs might thereby hinder growth and survival of marine microalgae, and subsequently threaten marine ecosystem and aquaculture industry. More importantly, this study implies that marine microalgae swimming behavior test is more efficiency and sensitive than traditional marine microalgal bioassays, like growth and photosynthesis tests. We suggest that although future work is needed, swimming behavior analysis of P. subcordiformis with MOT, VCL and VAP as endpoints can be developed as a low-cost, convenient, fast, reliable and sensitive method for seawater quality assessment.

Environmental safety data on CuO and TiO2 nanoparticles for multiple algal species in natural water: Filling the data gaps for risk assessment.

Most research on nanoparticle (NP) ecotoxicological effects has been conducted on single species in laboratory conditions that are not environmentally representative. We compared the effects of CuO NPs, CuSO4 (ionic control) and TiO2 NPs in nutrient-adjusted natural water (ANW) and in the OECD201 standard medium to four different algal species: green algae Raphidocelis subcapitata and Chlamydomonas reinhardtii, a diatom Fistulifera pelliculosa, and a cyanobacterium Synechocystis sp. Biomass and the effective quantum yield of photosystem II (Fv/Fm) were used as toxicity endpoints. CuO NPs were very toxic across taxa in the OECD201 assay (biomass-based 72 h EC50 0.2-0.9 mg l-1). Toxicity of CuO NPs was explained by shedding of ions from particles as Cu2+ is highly toxic: 72 h EC50 in the OECD201 medium was 0.01-0.03 mg l-1 in three species and 0.003 mg l-1 in the case of the cyanobacterium. Toxicity of copper compounds was overall reduced in ANW, presumably because of reduced bioavailability due to metal ions binding to natural organic matter. Copper compounds were more toxic to the cyanobacterium than to other algae and this effect was not amended in ANW. TiO2 NPs did not inhibit the biomass production and photosynthesis of the diatom or the cyanobacterium up to 100 mg l-1, but inhibited biomass production of green algae in the OECD201 medium (EC50 14-15 mg l-1). TiO2 NPs also did not significantly inhibit Fv/Fm up to 100 mg l-1, suggesting a general lack of effect on photosynthesis. Adverse effects of TiO2 NPs were at least in part due to cell-NP heteroagglomeration. Our data are informative for the complete risk assessment of engineered NPs by filling data gaps about NP effects in environmentally realistic conditions.

Marine environmental risk assessment and acute water quality criterion for pentachlorophenol in coastal waters.

Pentachlorophenol (PCP) is a organochlorine biocide that, unlike most other organochlorines, is still in use as timber preservative. Its water solubility, high toxicity, bioaccumulation potential, and the concentrations reported in estuarine waters (up to 0.1 µg L-1) indicate it may pose a risk in coastal environments. Aquatic environrmental regulations are commonly based on standard freshwater organisms that may not represent the sensitivity of marine species. The present study consists of a water quality criteira reevalutation of PCP in coastal waters based on toxicity tests conducted recording sensitive endpoints of marine species representative of coastal ecosystems, following QA/QC standard procedures. The toxicity thresholds (EC10) found were 4.69 µg L-1 for Paracentrotus lividus sea-urchin embryos, 6.47 µg L-1 for Mytilus galloprovincialis mussel larvae, and 78.4 µg L-1 for Isochrysis galbana cells. Therefore, there is only one order of magnitude between the predicted no-effect concentration (PNEC) for early life stages of bivalves and echinoderms and the maximum concentrations actually recorded in coastal water, which yields a remarkable risk quotient for PCP in these highly productive marine habitats. In addition, we have reviewed the ecotoxicological data on PCP toxicity on marine species representative of the main systematic groups, from algae to chordates, and derived a probabilistic acute saltwater quality criterion of 2.66 µg L-1, intended to protect 95% of the marine species. Lack of adequate protection for marine ecosystems in some current PCP national guidelines has been identified.

Toxicity assessment of pesticide triclosan by aquatic organisms and degradation studies.

Triclosan is considered as an important contaminant and is widely used in personal care products as an antimicrobial agent. This study demonstrates the biodegradation of triclosan by two freshwater microalgae and the acute toxicity of triclosan and 2,4-dichlorophenol. The effects of culture media and light on biodegradation of triclosan and the changing morphology of microalgae were systematically studied. Geitlerinema sp. and Chlorella sp. degraded 82.10% and 92.83% of 3.99 mg/L of triclosan at 10 days, respectively. The microalgal growth inhibition assay confirmed absence of toxic effects of triclosan on Chlorella sp., even at higher concentration (50 mg/L) after 72 h exposure. HPLC analysis showed that 2,4-dichlorophenol was produced as degradation product of triclosan by Geitlerinema sp. and Chlorella sp. This study proved to be beneficial to understand biodegradation and acute toxicity of triclosan by microalgae in order to provide aquatic environmental protection.

Effects of TiO2 nanoparticles and sunscreens on coastal marine microalgae: Ultraviolet radiation is key variable for toxicity assessment.

Given the large numbers of sunbathers on beaches, sunscreen compounds are being released into the coastal aquatic environment in significant amounts. Until now the effect of these potential pollutants on microbiota has been not well-known. Phytoplankton is a key component of the microbiota community. It forms the basis of the aquatic trophic networks, and any change in the natural population of phytoplankton can affect the structure of aquatic biota. This paper describes an experiment performed outdoors (in natural sunlight conditions including ultraviolet radiation (UVR) and with UVR blocked) on mixed microalgae populations (four species from different key marine taxonomic groups, Nannochloropsis gaditana, Chaetoceros gracilis, Pleurochrysis roscoffensis and Amphidinium carterae), for three days, exposed to a range of concentrations of three commercial sunscreens (with variable TiO2 concentrations: highest concentration for sunscreen C, followed by sunscreen A; and sunscreen B did not contain TiO2 in its composition). With regard to UVR effect, in the absence of sunscreens, the most sensitive species is the centric diatom, Chaetoceros gracilis, and the least is Nannochloropsis gaditana; this last species presented the same behavior in the absence of UVR and with high sunscreen concentrations. The toxicity gradient obtained for sunscreens and nanoparticles under UVR is: TiO2 NPs>Sunscreen C>Sunscreen A>Sunscreen B. The differential sensitivity of microalgae to sunscreens and TiO2 NPs can produce a change in the dynamics of phytoplankton populations and provoke undesirable ecological effects (such as giving dinoflagellates more prominence). The effects of UVR, commonly neglected in bioassays, could alter the results in important ways and should be considered when performing environmentally-relevant bioassays. The toxicity mediated by hydrogen peroxide production associated with the concentration of TiO2 NPs cannot be considered the only factor responsible for the toxicity: the organic compounds in the sunscreens must also be taken into account.

Energy cost of intracellular metal and metalloid detoxification in wild-type eukaryotic phytoplankton.

Microalgae use various cellular mechanisms to detoxify both non-essential and excess essential metals or metalloids. There exists however, a threshold in intracellular metal(loid) concentrations beyond which detoxification mechanisms are no longer effective and inhibition of cell division inevitably occurs. It is therefore important to determine whether the availability of energy in the cell could constrain metal(loid) detoxification capacity and to better define the thresholds beyond which a metal(loid) becomes toxic. To do this we performed the first extensive bioenergetics analysis of intracellular metal(loid) detoxification mechanisms (e.g., metal-binding peptides, polyphosphate granules, metal efflux, metal and metalloid reduction, metalloid methylation, enzymatic and non-enzymatic antioxidants) in wild-type eukaryotic phytoplankton based on the biochemical mechanisms of each detoxification strategy and on experimental measurements of detoxifying biomolecules in the literature. The results show that at the onset of metal(loid) toxicity to growth, all the detoxification strategies considered required only a small fraction of the total cellular energy available for growth indicating that intracellular detoxification ability in wild-type eukaryotic phytoplankton species is not constrained by the availability of cellular energy. The present study brings new insights into metal(loid) toxicity mechanisms and detoxification strategies in wild-type eukaryotic phytoplankton.

Comparison of specific versus literature species sensitivity distributions for herbicides risk assessment.

Species sensitivity distributions (SSDs) are an important predictive tool in risk assessment. Usually, literature data are used to build SSDs that are mostly based on planktonic species. But, to get adequate protective thresholds for environmental communities, one could argue that SSD should be built on ecotoxicological data obtained from species found in the ecosystem that should be protected. This is particularly true when benthic algae are of concern. Due to the lack of literature data, building SSD on benthic microalgae is difficult. This paper aims in comparing SSDs, and thus protective thresholds (hazardous concentration that affects 5% of the species of a community, HC5), built on ecotoxicological data obtained (1) from literature and (2) with specific bioassays on benthic diatoms from a lake. Thresholds were derived for protection against four herbicides separately and for a mixture of them. Sensitivity data obtained from literature were statistically lower than the specific data for all herbicides: Species tested in the literature were usually more sensitive (mainly chlorophytes), leading to more protective lower HC5. The HC5 thresholds (literature or specific) derived for protection against the mixture were also compared to the observed sensitivity of an assemblage of benthic diatom species exposed to an increasing range of herbicide mixture concentrations. We observed that one species within the assemblage (Fragilaria rumpens) was affected at a concentration below both the literature and the specific HC5 thresholds.

Evaluation of several flocculants for flocculating microalgae.

Flocculation of microalgae with chitosan, polyacrylamide, Al2(SO4)3, NaOH and HNO3 was evaluated. Their flocculation efficiencies and optimal dosages were discussed. The effects of the flocculants on cells viability were also investigated and the cells were found to be intact during the flocculation process. Moreover, the effects of flocculants on the extractions were evaluated. Lipid content after flocculants treatments showed no significant differences. Carbohydrate content was lower but protein content was higher after NaOH treatment than those after other treatments. Furthermore, the five flocculated media maintained approximate growth yields to that of the fresh medium in microalgal cultivation, indicating the five flocculated media could be recycled, thereby reducing the cost of biodiesel production from microalgae. Finally, economic comparison of the flocculants was made and the cost of using HNO3, including flocculating cells and recycling medium, was found to be the lowest.