Algal Toxicity Research Articles

Applicability Evaluation of Soil Algae Pipe Assay in Silver Nanoparticle-Contaminated Soils

Due to pervasive and resilient soil contaminants, heterogeneously contaminated soil poses unpredictable potential threats to ecosystems. In this study, the extension of a previously developed soil algae pipe assay for evaluating heterogeneously contaminated soil under an open system is described. The assay can be used in soil that is heterogeneously contaminated with silver nanoparticles in combination with the examination of morphological changes (e.g., in vivo chlorophyll a, cell granularity, cell size, and mucilaginous sheath) and lipid contents. In addition, we attempted to extend the exposure duration under an open system. We evaluated the applicability of this soil algae pipe assay using green alga Chlamydomonas reinhardtii exposed to heterogeneous and homogeneous polyvinylpyrrolidone capping silver nanoparticles in contaminated soils. The results demonstrated that this method is an applicable bioassay that can be employed to better evaluate soil algal toxicity under an open system, with significant changes in the measured endpoints. The developed assay showed decent predictivity, which can be a useful tool when evaluating heterogeneous soil algae contamination.

Effects of leachates from UV-weathered microplastic on the microalgae Scenedesmus vacuolatus

Plastics undergo successive fragmentation and chemical leaching steps in the environment due to weathering processes such as photo-oxidation. Here, we report the effects of leachates from UV-irradiated microplastics towards the chlorophyte Scenedesmus vacuolatus. The microplastics tested were derived from an additive-containing electronic waste (EW) and a computer keyboard (KB) as well as commercial virgin polymers with low additive content, including polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS). Whereas leachates from additive-containing EW and KB induced severe effects, the leachates from virgin PET, PP, and PS did not show substantial adverse effects in our autotrophic test system. Leachates from PE reduced algae biomass, cell growth, and photosynthetic activity. Experimental data were consistent with predicted effect concentrations based on the ionization-corrected liposome/water distribution ratios (Dlip/w) of polymer degradation products of PE (mono- and dicarboxylic acids), indicating that leachates from weathering PE were mainly baseline toxic. This study provides insight into algae toxicity elicited by leachates from UV-weathered microplastics of different origin, complementing the current particle- vs. chemical-focused research towards the toxicity of plastics and their leachates.Graphical abstract

Drinking water quality evaluation of hand pumping wells using water quality index and standard algal toxicity testing in Mansoura and Talkha cities, Egypt

Six house-hold Abyssinian pumps distributed in different villages of Mansoura (Mans-I, Mans-II and Mans-III) and Talkha (Talk-I, Talk-II and Talk-III) cities, Egypt, have been selected for regular seasonal water quality assessment during 2017. Water samples have been collected within the mid-periods of four seasons Standard assessment tools were employed for the integrated water quality assessment including Water Quality Index (WQI) and ISO standard algal toxicity test. WQI displayed remarkable local and seasonal variations with excellent (≥ 90) and good (70 - 89) only recorded for water samples collected from Mans-I pump located in sparsely populated area and far 50 meters only from the eastern (Damietta) branch of Nile River. WQI of other pumps located in densely populated areas and far kilometers from the Nile branch indicated either medium (50-69) or bad (25-49) quality depending on sampling season and sampling site location. All water samples collected from the pump Mans-I were non toxic without any inhibitory effects on the growth of the standard test alga Pseudokirchneriella subcapitata. Water samples from all other pumps, however, showed obvious toxic effects on test algae growth with varying EC50 values ranged between15.8% and 83%, depending on water sample and the sampling season. Concisely, all water samples collected from Mans-I pump were health safe with acceptable drinking water guidelines while samples collected from other pumps can impose great human health risks if used for drinking

Toxicity of selenium nanoparticles on Poterioochromonas malhamensis algae in Waris-H culture medium and Lake Geneva water: Effect of nanoparticle coating, dissolution, and aggregation

Understanding the algal toxicity of selenium nanoparticles (SeNPs) in aquatic systems by considering SeNPs physicochemical properties and environmental media characteristics is a concern of high importance for the evaluation and prediction of risk assessment. In this study, chitosan (CS) and sodium carboxymethyl cellulose (CMC) coated SeNPs are considered using Lake Geneva water and a Waris-H cell culture medium to investigate the effect of SeNPs on the toxicity of algae Poterioochromonas malhamensis, a widespread mixotrophic flagellate. The influence of surface coating, z-average diameters, ζ-potentials, aggregation behavior, ions release, and medium properties on the toxicity of SeNPs to algae P. malhamensi was investigated. It is found that SeNPs are 5–10 times more toxic in Lake Geneva water compared to the culture medium, suggesting that the traditional algal tests in Waris-H culture medium currently underestimate the toxicity of NPs in a natural water environment. Despite significant dissolution, it is also found that SeNPs themselves are the toxicity driver, and dissolved ions have only a marginal influence on toxicity. SeNPs diameter is found a minor factor in toxicity. Based on a principal component analysis (PCA) it is found that in Lake Geneva water, the nature of the surface coating (CMC versus CS) is the most influential factor controlling the toxicity of SeNPs. In the culture medium, surface coating, ζ-potential, and aggregation are found to contribute at the same level. These results highlight the importance of considering in details both NPs intrinsic and media properties in the evaluation of NPs biological effects.

Dissipation behaviour and safety risk assessment of a ready-mix formulation of clomazone and 2,4-D in rice field under tropical agro-climatic conditions of India

ABSTRACT This study portrays the dissipation behaviour of the herbicide mixture of clomazone and 2,4-D (clomazone 20% + 2,4-D ethyl ester 30% EC) in a rice field system. The combined formulation is widely used in India as it controls a broad spectrum of weeds, but its fate in tropical environment and the risks involved to the consumer as well as to the environment are still unexplored. Therefore, a supervised field trial was conducted following the post-emergence application of clomazone 20% + 2,4-D ethyl ester 30% EC at recommended (625 g a.i./ha) and double the recommended dose (1250 g a.i./ha) in rice in two consecutive seasons (Kharif and Rabi). The analytical methods for both clomazone and 2,4-D validated as per the SANTE guideline. The residues of clomazone were extracted by the modified QuEChERS method and analysed by GC-MS/MS, whereas the residues 2,4-D were extracted by classical partitioning method and analysed by LC-MS/MS. The recovery percentage of both the compounds ranged between 86–95% with LOQ 0.01 mg/kg for all matrices (rice grain, straw, husk, and field soil). The dissipation of both the compounds followed first-order kinetics. The half-life of clomazone and 2,4-D in soil ranged between 1.06–1.27 days and 4.74–6.24 days, respectively. The residues of clomazone and 2,4-D were below quantification level (BLOQ) in the harvested rice co-products (rice grain, husk and straw) and soil samples. Therefore, it can be summarised that the application of this herbicide mixture in rice cultivation will not pose any residual toxicity and the rice grains are safe for human consumption. Besides, the soil ecological risk assessment indicated that both the compounds possess low risk towards earthworm and soil arthropods. However, there was a concern about soil algal toxicity, which needs to be reconfirmed by further studies to establish a conclusive inference.

Toxicity assessment and underlying mechanisms of multiple metal organic frameworks using the green algae Chlamydomonas reinhardtii model

Metal-organic frameworks (MOFs) are an emerging class of materials which have garnered increasing attention for their utility as adsorbents and photocatalysts in water treatment. Nevertheless, the environmental risks of MOFs, especially their underlying impacts on aquatic organisms, are not fully explored. Herein, the toxicity of multiple representative MOFs was systematically assessed using a freshwater green alga (Chlamydomonas reinhardtii) model. Six typical MOFs with different metal nodes or organic linkers, including four transition metal incorporated aluminum-based porphyrin MOFs [pristine Al-PMOF, Al-PMOF (Cu), Al-PMOF (Ni), and Al-PMOF (Co)], one amine-functionalized MOF NH2-MIL-125 (Ti), and one bimetallic Hofmann MOF (NiCo-PYZ), were successfully synthesized and characterized. All the tested MOFs significantly reduced the chlorophyll content and inhibited the algal growth, with the most toxic materials being NiCo-PYZ and Al-PMOF (Cu). Distinct toxic mechanisms were observed for the tested MOFs. Metal ion release was the primary cause for algal toxicity induced by NiCo-PYZ. The algal toxicity induced by porphyrin MOFs could be explained by the combined effects of metal ion release and nutrient adsorption, agglomeration and physical interactions, and reactive oxygen species generation. NH2-MIL-125 (Ti) showed higher stability and more biocompatibility than the other tested MOFs. MOFs concentrations with no harmful effects to algae can be taken as the threshold values for safe use and discharge of MOFs. The ecotoxicological risks of MOFs should be considered as the applied concentrations of MOFs at mg/mL levels in environmental remediation were much higher than the no harmful effect thresholds.

Transcriptional Responses of Flavin-Containing Monooxygenase Genes in Scallops Exposed to PST-Producing Dinoflagellates Implying Their Involvements in Detoxification

Flavin-containing monooxygenase (FMO) is one of the most prominent xenobiotic metabolic enzymes. It can catalyze the conversion of heteroatom-containing chemicals to polar, readily excretable metabolites and is considered an efficient detoxification system for xenobiotics. Bivalves can accumulate paralytic shellfish toxins (PSTs) produced by dinoflagellates, especially during outbreaks of harmful algal blooms. Exploring FMO genes in bivalves may contribute to a better understanding of the adaptation of these species and the mechanisms of PSTs bioavailability. Therefore, through genome screening, we examined the expansion of FMO genes in two scallops (Patinopecten yessoensis and Chlamys farreri) and found a new subfamily (FMO_like). Our expression analyses revealed that, in both scallops, members of the FMO_N-oxide and FMO_like subfamilies were mainly expressed from the D-stage larvae to juveniles, whereas the FMO_GS-OX subfamily genes were mainly expressed at and prior to the trochophore stage. In adult organs, higher expressions of FMOs were observed in the kidney and hepatopancreas than in other organs. After exposure to PST-producing algae, expression changes in FMOs occurred in hepatopancreas and kidney of both scallops, with more members being up-regulated in hepatopancreas than in kidney for Alexandrium catenella exposure, while more up-regulated FMOs were found in kidney than in hepatopancreas of C. farreri exposed to A. minutum. Our findings suggest the adaptive functional diversity of scallop FMO genes in coping with the toxicity of PST-producing algae.

New insights into mechanisms of copper nanoparticle toxicity in freshwater algae Chlamydomonas reinhardtii: Effects on the pathways of secondary metabolites

The effects of copper nanoparticles (Cu-NPs), including their stability in the medium, were studied with the green unicellular algae Chlamydomonas reinhardtii (CC-125). Cu-NPs were synthesized and characterized. Cu-NP particles were uniform, regular, and largely spherical, and they had smooth surfaces; the average size was estimated to be 137.4 ± 2.1 nm. Chlamydomonas cells were cultivated for 96 h under controlled conditions in the presence of Cu-NPs, according to OECD guidelines, and then subjected to toxicological bioassays. Based on scanning electron microscopy (SEM) observations, the effects of Cu-NPs resulted in part from the dissolution of nanoparticles (NPs) and the action of copper itself, which shows the importance of studying NP stability in the testing environment. In this assay, deleterious effects were enhanced by increasing Cu-NP concentrations (5, 10, 25, 50, and 100 mg/L). Concentrations higher than 25 mg/L exhibited extreme toxicity. We confirmed the known toxic effects of metal NPs, namely, growth inhibition, reduction of chlorophyll levels in cells, cell penetration and increased ROS production. Attention was also paid to select underexplored metabolites, which were studied with a LC-MS/MS system. Treatments caused changes in metabolites profiles, and levels of p-hydroxybenzaldehyde and protocatechuic acid were especially enhanced, suggesting their positive roles in the antioxidant defence response. Furthermore, a repeatable increase in suberic acid levels was observed for various stress conditions tested, and we expect that this was the result of lipid peroxidation.

Relative sensitivity of duckweed Lemna minor and six algae to seven herbicides.

We investigated the relative sensitivity of duckweed Lemna minor and six species of algae to seven herbicides, using an efficient high-throughput microplate-based toxicity assay. First, we assessed the sensitivity of L. minor to the seven herbicides, and then we compared its sensitivity to that of previously published data for six algal species based on EC50 values. For five herbicides, the most sensitive species differed: L. minor was most sensitive to cyclosulfamuron: Raphidocelis subcapitata was most sensitive to pretilachlor and esprocarb: Desmodesmus subspicatus was most sensitive to pyraclonil; and Navicula pelliculosa was most sensitive to pyrazoxyfen. Simetryn was evenly toxic to all species, whereas 2,4-D was evenly less toxic, with only small differences in species sensitivity. These results suggested that a single algal species cannot represent the sensitivity of the primary producer assemblage to a given herbicide. Therefore, to assess the ecological effects of herbicides, aquatic plant and multispecies algal toxicity data sets are essential.

QSTR and interspecies-QSTR modelling for aquatic toxicity data gap filling of cationic polymers

Polymers are extensively used in several fields representing a growing multi-billion dollar industry covering several thousands of materials and billions of kilos used globally every year. The widespread use of cationic polymers may significantly discharge such compounds into the aquatic environment, which may cause potential toxic effects on aquatic organisms. The amount of publicly available, high-quality environmental toxicity data for industrial polymers such as cationic polyquaterniums is low. We have developed here individual quantitative structure–toxicity relationship (QSTR) models for toxicity prediction against fish and algae. These models against fish and algae showed optimistic statistical quality in terms of several internal and external quality and validation metrics such as determination coefficient R2 (0.703 and 0.676), cross-validated leave-one-out Q2 (0.638 and 0.516) and predictive R2pred or Q2ext (0.776 and 0.703) for fish (Ntrain = 72, Ntest = 23) and algae (Ntrain = 40, Ntest = 14) toxicity datasets, respectively. The study revealed that higher charge density increases the toxicity against both the response endpoints. However, a higher percentage of oligomers with a molecular mass of lower than 1000 Daltons results in a decreased toxicity towards both the studied endpoints. Similarly, primary amines in the molecular building block result in a reduction in the toxicity against the algal species. However, acceptable individual QSTR models against D. magna could not be generated with the limited feature information obtained from the United States Environmental Protection Agency and additional data provided by Environmental Climate Change Canada (ECCC). Therefore, we have also proposed interspecies quantitative structure–toxicity relationship (i-QSTR) models among three species (D. magna, fish and algae species) to bridge the toxicity data gap for cationic polymers. The mechanistic interpretation of i-QSTR models revealed several important characteristic features of polymers along with the experimental response of one species which are also helpful for toxicity prediction of other species, ultimately helping to reduce the experimental testing for toxicity prediction. Finally, the proposed QSTR and i-QSTR models can be helpful to compute the toxicity of polymers in the early stages of screening for regulatory purposes and data gap filling for new or untested polymers falling within the applicability domain of the models.

Biodegradable and re-usable sponge materials made from chitin for efficient removal of microplastics

Microplastics have attracted widespread attention due to their detrimental effects on organisms, and their efficient removal poses great challenges, especially those smaller than 3 µm that are more harmful for aquatic biota. Herein, the chitin based sponges with interconnected pores, excellent elasticity and mechanical durability were fabricated and composed with graphene oxide (GO) and oxygen-doped carbon nitride (O-C3N4). The chitin based sponges could effectively remove different functionalized microplastics (~1 µm) at pH 6–8, including carboxylate-modified polystyrene (PS-COOH), amine-modified polystyrene (PS-NH2), and polystyrene (PS). Notably, the removal efficiency of three microplastics by the chitin based sponges reached up to 71.6–92.1% at an environmentally relevant concentration of 1 mg L−1 in water system. The potential driving forces of the adsorption were electrostatic interactions, hydrogen bond interactions, and π-π interactions. In addition, the chitin based sponges are reusable and after re-used for 3 cycles due to their excellent compressibility. The algae toxicity test demonstrated good biocompatibility of the chitin based sponges and they are also biodegradable in a natural soil. This study provides a green and promising method for fabricating environmentally friendly adsorbents for small-size microplastics removal, and expands the insights into the mechanisms of microplastic adsorption onto the sponge materials.

Evidence for antifouling biocides as one of the limiting factors for the recovery of macrophyte communities in lakes of Schleswig-Holstein

BackgroundThe European Water Framework Directive (WFD) has been implemented to achieve a good ecological status in European water bodies requiring macrophyte community assessment as one of the biological quality elements (BQEs). While in several lakes in Schleswig-Holstein (Germany) different BQEs improved within recent years, no recovery of macrophyte communities in some lakes could be achieved, despite the reduction of nutrient input and eutrophication. Due to the fact that no impairment of phytoplankton could be observed, toxic stress due to sediment contamination was hypothesized as a possible limiting factor of macrophyte community recovery.ResultsSediment toxicity was investigated by performing an extensive chemical screening of sediment contamination and a risk assessment based on toxic unit (TU) summation, using equilibrium water concentrations and algal toxicity as surrogates for lacking data on macrophyte toxicity. Possible indirect risks via toxic pressure on grazer were assessed via TUs based on crustaceans. The study revealed algal TUs of more than one order of magnitude below chronic toxicity thresholds in lakes with high and good status of the macrophyte community and increasing concentrations and frequency of exceedance of toxicity thresholds for lakes with moderate-to-bad status. The antifouling biocides irgarol and diuron were identified as major risk drivers. In addition, PAHs and glyphosate could not be ruled out to contribute to toxic pressure on macrophytes. Despite exceedance of toxicity thresholds for crustaceans, no connection of the ecological status of the macrophyte communities with toxic risks to grazers could be observed.ConclusionsOur study suggests that in a multiple pressure situation the toxic pressure created due to the contamination of sediments with antifouling biocides is one of the limiting factors for the recovery of macrophyte communities in impaired lakes of Schleswig-Holstein. This finding is in agreement with a Europe-wide survey on almost 47,000 sites suggesting that no good ecological status can be observed at sites with contamination exceeding toxicity thresholds. Similar to the survey, our study indicates additional stressors preventing the achievement of a good quality status of the lake ecosystems.

Acute toxicity of piggery effluent and veterinary pharmaceutical cocktail on freshwater organisms.

Intensive livestock farming has increased the use of veterinary pharmaceuticals in many developing countries, and this is considered a significant concern to the freshwater ecosystem. However, the information on the potential acute toxicity of piggery effluent waste and the veterinary pharmaceutical effluent discharged into the aquatic environment is limited. This study assessed the adverse effect of a piggery effluent and the cocktail mixtures of high- and low-level doses of three frequently occurring veterinary pharmaceuticals (tetracycline (TETR), ivermectin (IVER), and salicylic acid (SALA)) on freshwater organisms using three representative freshwater biotests organisms: Pseudokirchneriella subcapitata (P. subcapitata), Daphnia magna (D. magna), and Tetrahymena thermophila (T. thermophila). The freshwater organism test results showed that the 24-h and 48-h EC50 algal toxicity to P. subcapitata exposed to 10% unfiltered piggery effluent were 25.6 and 49.3% respectively while the 24-h LC50 value to Cladocera, D. magna exposed to unfiltered piggery effluent was 23.2 (17.7-30.4)%. The 24-h EC50 protozoan toxicity to T. thermophila exposed to 1% HLD veterinary pharmaceuticals was 0.014μg/L. Thus, the study established the different sensitivities of freshwater organisms to various percentage levels of piggery effluent and high- and low-level doses of veterinary pharmaceutical. The piggery effluent and the pharmaceutical cocktail mixtures have potential toxicological effects on the freshwater ecosystem.

Enhanced treatment of shale gas fracturing waste fluid through plant-microbial synergism.

Cost-efficient and environmentally friendly treatment of hydraulic fracturing effluents is of great significance for the sustainable development of shale gas exploration. We investigated the synergistic effects of plant-microbial treatment of shale gas fracturing waste fluid. The results showed that illumination wavelength and temperature are direct drivers for microbial treatment effects of CODCr and BOD5, while exhibit little effects on nitrogen compounds, TDS, EC, and SS removals as well as microbial species and composition. Plant-microbial synergism could significantly enhance the removal of pollutants compared with removal efficiency without plant enhancement. Additionally, the relative abundance and structure of microorganisms in the hydraulic fracturing effluents greatly varied with the illumination wavelength and temperature under plant-microbial synergism. 201.24 g water dropwort and 435 mg/L activated sludge with illumination of 450-495 nm (blue) at 25 °C was proved as the best treatment condition for shale gas fracturing waste fluid samples, which showed the highest removal efficiency of pollutants and the lowest algal toxicity in treated hydraulic fracturing effluents. The microbial community composition (36.73%Flavobacteriia, 25.01% Gammaproteobacteria, 18.55%Bacteroidia, 9.3% Alphaproteobacteria, 4.1% Cytophagia, and 2.83% Clostridia) was also significantly different from other treatments. The results provide a potential technical solution for improved treatment of shale gas hydraulic fracturing effluents.

Plant and algal toxicity of persistent free radicals and reactive oxygen species generated by heating anthracene-contaminated soils from 100 to 600 °C

Persistent free radicals (PFRs) are emerging contaminants of increasing concern, yet their formation, fate, toxicity and health risk are poorly known. Thermal treatment, a common remediation technique to clean industrial soils, induces the formation of PFRs, which could paradoxically increase soil toxicity, contrary to the original objective of remediation. Actually, there is little knowledge on the formation and toxicity of PFRs in soils contaminated by polycyclic aromatic hydrocarbons (PAHs). Here we studied the generation of PFRs of soils spiked with anthracene and heated 1 h from 100 to 600 °C, using electron paramagnetic resonance. We also investigated the formation of reactive oxygen species (ROS), e.g. superoxide radical (O2·−), hydrogen peroxide (H2O2) and hydroxyl radical (·OH), in the aqueous phase of thermal-treated soil, and the impact of heating on soil oxidative potential, wheat growth and green algae activity. Results showed that PFRs, ROS, soil oxidative potential, plant toxicity and algal toxicity show a similar trend with an increase from 100 to 300 °C, followed by a decrease to 600 °C. Scavenger trapping tests reveal that algal toxicity is mainly due to the generation of O2·−, ·OH and H2O2 induced by anthracene-PFRs and that anthracene and anthracene-PFRs have negligible direct algal toxicity. Overall, our findings reveal the unintended formation of toxic compounds peaking at 300 °C during the thermal remediation of PAH-contaminated soils. These results should help to assess the environmental risk of thermally treated PAH-contaminated soils.

Development of multifunctional polyester using disperse dyes based through a combination of mosquito repellents

Advancement of new protection methodologies to counter mosquito-borne diseases always remains a public intrigue. Among all reported and researched methods, mosquito repellent textiles may prove an effective product, as textiles being the basic need, cover most parts of the human body. This investigation focuses on the synthesis of novel mosquito repellent dyes from a combination of mosquito repellents like N, N‑diethyl-3-methyl benzamide (DEET) derivative, ethyl anthranilate, and 4‑hydroxy coumarin. Resultant dyes were analysed by FTIR, 1HNMR, UV spectroscopy, mass spectroscopy, and elemental analysis. The synthesized dyes were utilized for the dyeing of polyester. Dyed polyester demonstrated 100% mosquito repellency along with other functional properties such as antibacterial activity (>93%) and UV protection (UPF>124). The mosquito repellency was retained to a significant extent even after 20 washes. The synthesized dyes also displayed an efficient antioxidant activity and low algal toxicity. As most of the textiles are coloured, the synthesized novel disperse dyes can act as a tool for the multifunctional modification of polyester-based textile substrates.

Quantitative structure-activity relationship and a category approach to support algal toxicity assessment of human pharmaceuticals

Quantitative structure-activity relationship and a category approach to support algal toxicity assessment of human pharmaceuticals

Biological toxicity of fresh and rotten algae on freshwater fish: LC50, organ damage and antioxidant response

In recent decades, harmful algal blooms (HABs) induced by eutrophication have caused organisms in freshwater ecosystems to become surrounded by toxic cells and dissolved toxins. In this study, the toxic effects of fresh algae solution (FAS) and rotten algae solution (RAS) were investigated. The results showed that the composition of RAS was predominantly organic acids, ketones, polypeptides, esters, phenols, amino acids and intermediate metabolic products. The safety concentrations (SCs) of FAS to Carassius auratus, Ctenopharyngodon idellus and Hypophthalmichthys molitrix were 1.92 × 1010 cells/L, 1.58 × 1011 cells/L and 1.30 × 1011 cells/L, respectively. The SCs of the RAS were significantly lower than those of the FAS (p < 0.05), with the values of 1.25 × 109 cells/L, 8.8 × 109 cells/L and 9.7 × 109 cells/L, for each species, respectively. The toxic algae solutions caused congestion inside the gills, intestinal lesions and high infection rates in the tested fish. FAS and RAS exposure also activated the antioxidant defense system and changed the intestinal microbial structure, resulting in the damage to the microbial balance in the body, and eventually the death of the fish. By studying the acute toxicity to fish, the harm of HABs to aquatic organisms can be predicted.

A simple and rapid algal assay kit to assess toxicity of heavy metal-contaminated water.

This study presents a novel algal-based toxicity test suitable for simple and rapid assessment of heavy metal (Hg2+, Cr6+, Cd2+, Pb2+, or As3+)-contaminated water. A closed-system kit-type algal assay was developed using Chlorella vulgaris. Toxicity was assessed by oxygen evolution in the gaseous phase of the assay kits, which was measured via a needle-type oxygen sensor. Initial cell density, light intensity, and exposure time that enabled favorable test performance for the algal assay kits were 103cells/mL, 250μmolm-2s-1, and 18h, respectively. Results from the heavy metal toxicity tests demonstrate that Hg2+, Cr6+, Cd2+, and Pb2+ are more toxic in inhibiting algal photosynthetic activity than As3+. The 18h half-maximum effective concentrations (EC50) for Hg2+, Cr6+, Cd2+, Pb2+, and As3+ were determined to be 31.3±0.5, 179.6±7.5, 301.3±6.1, 476.1±10.5, and 2184.1±31.1μg/L, respectively. A strong correlation between oxygen concentrations in the headspace of the assay kits and chlorophyll a production indicates that oxygen evolution in the gaseous phase is able to represent algal photosynthetic activity and serve as the end-point in algal toxicity tests. High test sensitivity and reproducibility as well as an easy test protocol and rapid processing time make the algal assay kit a suitable tool for simple and rapid toxicity testing of heavy metal-contaminated water.

Rapid assessment of heavy metal-induced toxicity in water using micro-algal bioassay based on photosynthetic oxygen evolution

Toxicity assessment using microalgae adopted various endpoint measurements like mortality rate, photosynthetic activity, chlorophyll content, enzymatic activity, cell density, &lt;sup&gt;14&lt;/sup&gt;C assimilation, and phosphate uptake. These algal toxicity tests usually require 3-4 days of exposure time and laborious work to measure these endpoints parameters. In the present study, we described a simple and rapid toxicity assessment procedure using photosynthetic oxygen evolution as an endpoint measurement to determine heavy metal-induced toxicity. Oxygen evolution in gaseous phase was measured over a 12 h exposure time. The toxicity of six selected heavy metals was assessed. Concentrations of 1.02, 1.91, 0.46, 3.2, 7.5, and 65.6 mg/L were obtained as EC50 values for mercury, silver, cyanide, copper, cadmium, and hexavalent chromium, respectively, for microalgae (Chlorella vulgaris). Our results demonstrated that hexavalent chromium is less sensitive depending on the conditions (low exposure time, pH 6, and high initial biomass). Toxicities in decreasing order of strength were cyanide &gt; mercury &gt; silver &gt; copper &gt; cadmium &gt; hexavalent chromium. Results obtained in the current and earlier studies demonstrate that photosynthetic oxygen evolution offers an alternative endpoint measurement to assess toxicity since it allows sensitive and rapid detection of heavy metal-induced toxicity in water.