Microalgal whole-cell biomarkers as sensitive tools for fast toxicity and pollution monitoring of urban wet weather discharges

Characterization of microalgal toxicants in the sediments from an industrial area: Application of advanced effect-directed analysis with multiple endpoint bioassays

Microalgal toxicants in sediments from an industrialized area (Ulsan Bay) in South Korea were identified using effect-directed analysis (EDA) with full-scan screening analysis (FSA) and microalgal bioassays with multiple endpoints. The growth rate and cell viability of three microalgae (Isochrysis galbana, Dunaliella tertiolecta, and Phaeodactylum tricornutum) were strongly inhibited following exposure to raw organic extracts of sediments from Site D5 (Woehang River). The polar fraction separated using a silica gel column significantly inhibited growth rate, esterase activity, cell membrane intensity, and chlorophyll a autofluorescence. In comparison, non- and mid-polar fractions induced non-toxic or esterase inhibition. Target toxicants, such as polycyclic aromatic hydrocarbons, styrene oligomers, and alkylphenols, were detected at low concentrations (450, 79, and 98 ng g^-1 dw, respectively) in the sediment of D5, indicating the presence of unmonitored toxicants. FSA was performed for the polar fraction using LC-QTOFMS, and 31 candidates of toxicants were selected. Toxicological confirmation was conducted for 7 candidates for which standards are available. Out of these, 2-nitrophenol, 3-nitrophenol, and 4-nitrophenol showed significant microalgal toxicity; however, these compounds did not fully explain the induced toxicity. Overall, combining EDA and FSA with multiple endpoint bioassays demonstrated the benefits of characterizing the microalgal toxicants in the environments.

Methodological advances and future directions of microalgal bioassays for evaluation of potential toxicity in environmental samples: A review

Microalgal bioassays are widely applied to evaluate the potential toxicity of various persistent toxic substances in environmental samples due to multiple advantages, including high sensitivity, short test duration, and cost-effectiveness. Microalgal bioassay is gradually developing in method, and the scope of application to environmental samples is also expanding. Here, we reviewed the published literature on microalgal bioassays for environmental assessments, focusing on types of samples, sample preparation methods, and endpoints, and highlighted key scientific advancements. Bibliographic analysis was performed with the keywords 'microalgae' and 'toxicity' or 'bioassay', and 'microalgal toxicity'; 89 research articles were selected and reviewed. Traditionally, most studies implementing microalgal bioassays focused on water samples (44%) with passive samplers (38%). Studies using the direct exposure method (41%) of injecting microalgae into sampled water mainly evaluated toxic effects by growth inhibition (63%). Recently, various automated sampling techniques, in situ bioanalytical methods with multiple endpoints, and targeted and non-targeted chemical analyses have been applied. More research is needed to identify causative toxicants affecting microalgae and to quantify the cause-effect relationships. This study provides the first comprehensive overview of recent advances in microalgal bioassays performed with environmental samples, suggesting future research directions based on current understanding and limitations.

Humic acids alleviate the toxicity of reduced graphene oxide modified by nanosized palladium in microalgae

The use of graphene-family materials modified by nanosized palladium (Pd/GFMs) has intensified rapidly in various fields; however, the effects of environmental factors (e.g., natural organic matter (NOM)) on the transformation and ecotoxicity of Pd/GFMs remain largely unknown. In this study, reduced graphene oxide modified by nanosized Pd (Pd/rGO) was incubated with humic acid (HA) under light irradiation for 56 d to explore the effects of NOM on the physicochemical transformations (e.g., defects, surface charges and dispersity) and biological toxicity (e.g., growth inhibition, oxidative stress and ultrastructural damage on algae cells) of Pd/GFMs. The results revealed that HA increased the defects and dispersity of Pd/rGO. Growth inhibition, damage to cellular ultrastructures, and oxidative stress in microalgae cells were induced by Pd/rGO, and corresponding defense responses (e.g., superoxide dismutase, peroxidase and glutathione) were activated. HA diminished the above defense responses in microalgae triggered by Pd/rGO by regulating GSH metabolism and the alanine biosynthesis pathway. In the presence of HA, cell wall damage (i.e., hole formation) caused by exposure to Pd/rGO was restored, and the plasmolysis area was reduced by 28.6 %. In addition, growth inhibition, lipid peroxidation, loss of mitochondrial membrane potential and ROS formation induced by 1.0 mg/L MoS₂NPs were decreased by 1.4-65.6 %, 13.9-26.1 %, 21.8-58.3 % and 9.6-16.1 %, respectively. These findings highlight the need to consider the effects of HA on the environmental transformation and biological toxicity of Pd/GFMs, which presents significant implications for the management of Pd/GFMs.

Microtoxicology by microfluidic instrumentation: a review

Microtoxicology is concerned with the toxic effects of small amounts of substances. This review paper discusses the application of small amounts of noxious substances for toxicological investigation in small volumes. The vigorous development of miniaturized methods in microfluidics over the last two decades involves chip-based devices, micro droplet-based procedures, and the use of micro-segmented flow for microtoxicological studies. The studies have shown that the microfluidic approach is particularly valuable for highly parallelized and combinatorial dose-response screenings. Accurate dosing and mixing of effector substances in large numbers of microcompartments supplies detailed data of dose-response functions by highly concentration-resolved assays and allows evaluation of stochastic responses in case of small separated cell ensembles and single cell experiments. The investigations demonstrate that very different biological targets can be studied using miniaturized approaches, among them bacteria, eukaryotic microorganisms, cell cultures from tissues of multicellular organisms, stem cells, and early embryonic states. Cultivation and effector exposure tests can be performed in small volumes over weeks and months, confirming that the microfluicial strategy is also applicable for slow-growing organisms. Here, the state of the art of miniaturized toxicology, particularly for studying antibiotic susceptibility, drug toxicity testing in the miniaturized system like organ-on-chip, environmental toxicology, and the characterization of combinatorial effects by two and multi-dimensional screenings, is discussed. Additionally, this review points out the practical limitations of the microtoxicology platform and discusses perspectives on future opportunities and challenges.

Synchrotron Radiation-Fourier Transformed Infrared microspectroscopy (μSR-FTIR) reveals multiple metabolism alterations in microalgae induced by cadmium and mercury

Toxic metals such as cadmium (Cd) and mercury (Hg) represent a threat to photosynthetic organisms of polluted aquatic ecosystems, and knowledge about mechanisms of toxicity is essential for appropriate assessment of environmental risks. We used Synchrotron Radiation-Fourier Transformed Infrared microspectroscopy (μSR-FTIR) to characterise major changes of biomolecules caused by Cd and Hg in the model green microalga Chlamydomonas reinhardtii. μSR-FTIR showed several metabolic alterations in different biochemical groups such as carbohydrates, proteins, and lipids in a time-dose dependent manner, with the strongest changes occurring at concentrations above 10 μM Cd and 15 μM Hg after short-term (24 h) treatments. This occurred in a context where metals triggered intracellular oxidative stress and chloroplast damage, along with autophagy induction by overexpressing AUTOPHAGY-RELATED PROTEIN 8 (ATG8). Thin layer chromatography analysis confirmed that toxic metals promoted remarkable changes in lipid profile, with higher degree of esterified fatty acid unsaturation as detected by gas chromatography coupled with mass spectrometry. Under Cd stress, there was specifically higher unsaturation of free fatty acids, while Hg led to stronger unsaturation in monogalactosyldiacylglycerol. μSR-FTIR spectroscopy proved as a valuable tool to identify biochemical alterations in microalgae, information that could be exploited to optimise approaches for metal decontamination.

Identification of potential toxicants in sediments from an industrialized area in Pohang, South Korea: Application of a cell viability assay of microalgae using flow cytometry

Potential toxicants in sediments collected from an industrialized bay of Korea were identified by use of effect-directed analysis (EDA). Three marine microalgal bioassays (Dunaliella tertiolecta, Isochrysis galbana, and Phaeodactylum tricornutum) with diverse endpoints were employed. Initial screening of raw organic extracts of sediments indicated large variations among locations and species in a traditional endpoint "inhibition of growth". After fractionation, inhibition of growths increased significantly, particularly in some fractions containing aromatics with log K_OW 5-6 (F2.6). While viabilities of cells were adversely affected in more fractions, including F2.6-F2.7 (log K_OW 5-7) and F3.5-F3.6 (log K_OW 4-6). Among the several endpoints of viability, esterase activity seemed to be more sensitive, followed by integrity of cell membranes, chlorophyll a, cell size, and intracellular complexity. Instrumental analyses indicated that toxicities to microalgae observed in F2.7 could not be fully explained by target PAHs. Full-scan screening analysis using GC-QTOFMS identified 58 compounds in F2.7 with matching scores ≥90%. Based on toxic potencies for these compounds predicted by ECOSAR, several causative agents, including 1-phenylpyrene, dibenz[a,c]anthracene, and picene were suggested. Overall, viability of microalgae provided sensitive and high-resolution toxicity screening of samples into integrative assessment of sediment.

Effects of erythromycin and sulfamethoxazole on Microcystis aeruginosa: Cytotoxic endpoints, production and release of microcystin-LR

Antibiotics can cause severe ecological problems for aquatic ecosystems due to their wide use and incomplete removal. Microcystis aeruginosa was exposed to different levels of erythromycin (ERY) and sulfamethoxazole (SMX) separately to assess their cytotoxic effects on harmful cyanobacteria. The production and release of the toxin MC-LR was measured, and several endpoints were investigated using flow cytometry (FCM) for 7 d. ERY resulted in cell membrane hyperpolarization and a hormesis effect on growth rate and chlorophyll a fluorescence at environmentally relevant concentrations (0.5 and 5 μg/L). Microcystis exhibited elevated photosynthesis and hyperpolarization at 50 and 125 μg/L of SMX. An increase of metabolically non-active cells was observed in either ERY or SMX cultures while stimulation of esterase activity was also found at 7 d. ERY and SMX caused damage of membrane integrity due to the overproduction of ROS, which led to increased release of MC-LR. MC-LR production apparently was induced by ERY (0.5-500 μg/L) and SMX (50 and 125 μg/L). In conclusion, ERY and SMX can disrupt the physiological status of Microcystis cells and stimulate the production and release of MC-LR, which can exacerbate potential risks to water systems.

From Laboratory Tests to the Ecoremedial System: The Importance of Microorganisms in the Recovery of PPCPs-Disturbed Ecosystems

The presence of a wide variety of emerging pollutants in natural water resources is an important global water quality challenge. Pharmaceuticals and personal care products (PPCPs) are known as emerging contaminants, widely used by modern society. This objective ensures availability and sustainable management of water and sanitation for all, according to the 2030 Agenda. Wastewater treatment plants (WWTP) do not always mitigate the presence of these emerging contaminants in effluents discharged into the environment, although the removal efficiency of WWTP varies based on the techniques used. This main subject is framed within a broader environmental paradigm, such as the transition to a circular economy. The research and innovation within the WWTP will play a key role in improving the water resource management and its surrounding industrial and natural ecosystems. Even though bioremediation is a green technology, its integration into the bio-economy strategy, which improves the quality of the environment, is surprisingly rare if we compare to other corrective techniques (physical and chemical). This work carries out a bibliographic review, since the beginning of the 21st century, on the biological remediation of some PPCPs, focusing on organisms (or their by-products) used at the scale of laboratory or scale-up. PPCPs have been selected on the basics of their occurrence in water resources. The data reveal that, despite the advantages that are associated with bioremediation, it is not the first option in the case of the recovery of systems contaminated with PPCPs. The results also show that fungi and bacteria are the most frequently studied microorganisms, with the latter being more easily implanted in complex biotechnological systems (78% of bacterial manuscripts vs. 40% fungi). A total of 52 works has been published while using microalgae and only in 7% of them, these organisms were used on a large scale. Special emphasis is made on the advantages that are provided by biotechnological systems in series, as well as on the need for eco-toxicological control that is associated with any process of recovery of contaminated systems.

Investigating toxicity of urban road deposited sediments using Chinese hamster ovary cells and Chlorella Pyrenoidosa

Road deposited sediments (RDS) is the key carrier of pollutants in the urban road stormwater processes and hence has been seen as an important pollutant source of urban road stormwater. Although many research studies have focused on RDS and pollutants attached to RDS, the investigation on RDS toxicity is very limited. Toxicity test can permit an overall assessment on whether the RDS polluted stormwater can be safely reused. This paper used two living organisms, namely Chinese hamster ovary (CHO) cells, (mammalian cells to indicate human health related toxicity) and Chlorella Pyrenoidosa (algae to indicate ecological health related toxicity) to test RDS toxicity by using an innovative "equivalent toxicity area (ETA)" approach. The outcomes showed that mammalian cells are more sensitive than algae in terms of RDS toxicity. Pb, Cd and Cr primarily contributed to mammalian cell-based toxicity while Zn, Ni, Cu and TOC are primarily toxic to algae. It is also found that road site characteristics such as land uses exerted an important influence on RDS toxicity. Commercial areas tended to generate RDS with higher human health risk related toxicity while industrial areas had a potential to produce RDS with high ecological health risk related toxicity. The research outcomes also showed that solely focusing on pollutant themselves on RDS can not accurately indicate RDS pollution. An approach to considering both pollutant loads and toxicity is preferred. These results were expected to provide a useful insight to enhancing effectiveness of RDS polluted urban road stormwater management and ensuring their reuse safety.