Toxic cyanobacteria and drinking water: Impacts, detection, and treatment

Role of surface functional groups in the adsorption behavior of microcystin-LR on graphene surfaces

Biochars are good adsorbents for removing microcystin from water but the molecular interactions responsible for microcystin adsorption are not understood. In this work, adsorption behavior of microcystin-LR (MC-LR) on three model surfaces that mimic biochar (bare graphene, graphene with ammonium, and with phosphate functional groups) is studied using well-tempered metadynamics in atomistic simulations. MC-LR is found to strongly adsorb on all the three surfaces. The adsorption free energy is most favorable for the bare graphene surface. On both bare graphene and the surface with phosphate groups, MC-LR adsorbs with its ring parallel to the surface. On the surface with ammonium groups, MC-LR adsorbs with its ring tilted with respect to the surface because of favorable Coulombic interactions between the ammonium groups and the glutamic acid in the MC-LR ring. On the bare graphene surface, the phenyl ring of the pendant Adda group shows a bimodal distribution with peaks at 0° and 40° with the surface normal, indicating that the phenyl ring forms π-π interactions with graphene in some adsorbed configurations. Such π-π interactions are not observed on the surfaces with ammonium and phosphate groups. Favorable adsorption free energy of MC-LR on the charge-neutral (bare graphene), positively charged (ammonium) and negatively charged (phosphate) surfaces suggest that the adsorption is dominated by van der Waals and hydrophobic interactions. Coulombic and π-π interactions affect the orientation of MC-LR in the adsorbed state.

Simultaneous removal of Microcystis aeruginosa and microplastics by oxidation enhanced coagulation

The composite pollution is an increasingly severe challenge in the field of water treatment. Especially, microplastics (MPs) contamination and Microcystis aeruginosa (M. aeruginosa) were verified that they could synergistically pose a serious threat to safety of drinking water. Therefore, developing effective removal technology is an urgent task. In this study, the simultaneous removal of M. aeruginosa and polystyrene (PS, a typical plastic matter) was investigated by H2O2 enhanced Fe(II) coagulation. The results demonstrated that the removal rate of both algae and PS can reach over 90%. It was also demonstrated that the PS removal efficiency increased from 23.3% to 97.3% with the increase of M. aeruginosa biomass from 0 cells/mL to 0.5 × 106 cells/mL. The possible reason might be that the addition of algal cells raises the number of contaminant particles, which greatly increases the floc size during the coagulation process. It makes MPs easier to be trapped by sweep flocculation in this process. Additionally, naturally weathered polystyrene (NWPS) exhibited higher removal rate than virgin PS, due to more original functional groups, larger particle size (d50 9.75 μm-11.25 μm), and a lower absolute zeta potential (-34.15 mV to -30.1 mV). Furthermore, low Fe residue level and AOM (algal organic matter) control was simultaneously achieved in this process (TOC <1 mg/L, MCs <1 μg/L). Therefore, this study suggests that the H2O2-Fe(II) process is an efficient and green technology for the removal of M. aeruginosa and PS composite pollutants without secondary pollution, which is promising technology in drinking water treatment plant.

Investigation of adsorption parameters of saxitoxin onto loblolly pine-derived biochar synthesized at various pyrolysis temperature

This study highlights the use of loblolly pine derived biochar for the removal of harmful algal bloom toxin, Saxitoxin (STX), from water. Biochar samples were prepared at varying pyrolysis temperatures (400, 600 and 800 °C) for 60 min. As pyrolysis temperature increases, enhancement in surface porosity was observed (SBET = 7.26 ± 0.2 m2/g to 408.15 ± 6.19 m2/g) while a decline in oxygen-containing functional groups was observed (1517.80 ± 14.98 μmol/g to 823.01 ± 7.72 μmol/g). This study aimed to discover the effects of adsorption parameters such as biochar dosage amount, contact time, initial concentration and initial pH on Saxitoxin adsorption. These studies revealed impressive results with >90 % toxin removal with dosage rate of 0.01 g/L, contact time of 30 min, and increasing percent removal with increasing initial STX concentration and initial pH in water. Maximum uptake was calculated for P400 with adsorption capacity of 314.37 μg/g. This showed that surface functionality showed higher affinity for STX uptake, which may be possible due to hydrogen bonding, electrostatic interactions, ion-exchange, and π-π interactions. Applied kinetic models indicated both physisorption and chemisorption interactions with best fit supporting the Elovich models. Complementary, adsorption isotherm analysis confirmed the multilayer adsorption behavior of the Freundlich model. Therefore, these findings support the viable use of biochar material for the remediation of STX waters.

Guarding Drinking Water Safety against Harmful Algal Blooms: Could UV/Cl2 Treatment Be the Answer?

Frequent and severe occurrences of harmful algal blooms increasingly threaten human health by the release of microcystins (MCs). Urgent attention is directed toward managing MCs, as evidenced by rising HAB-related do not drink/do not boil advisories due to unsafe MC levels in drinking water. UV/chlorine treatment, in which UV light is applied simultaneously with chlorine, showed early promise for effectively degrading MC-LR to values below the World Health Organization's guideline limits. Still, much is unknown regarding potential disinfection byproduct formation and associated toxicity, which can occur from the reaction of chlorine and other reactive species with MCs and algal and natural organic matter. To ensure UV/chlorine guarding drinking water for human consumption, the degradation and detoxification of four of the most problematic MC variants, namely, MC-LR, -RR, -YR, and -LA, which differ in amino acid substituents, were evaluated using UV/chlorine and compared to results from chlorination. Overall, UV/chlorine effectively enhanced MC degradation kinetics and generated less halogenated disinfection byproducts in the target analysis of 11 types of DBPs_C1-3 from 7 classes, total organic chlorine, and nontarget analysis revealing 35 higher molecular weight DBPs_C46-52, which maintained the MC structures. Reactivity and cytotoxicity changes varied based on the individual amino acid moieties within the cyclic heptapeptide structure common to all MCs. Analogous trends in MC reactivity were observed in degradation kinetics and mixed MC competition reactions, aligning with individual amino acid structure-reactivity. Cytotoxicity results indicated no significant unintended toxic consequences from MC_DBPs. Our results suggest that UV/chlorine treatment offers an efficient strategy for treating MCs in drinking water.

Adsorption adaptive response exposed to algal organic matter: correlation to the characteristics of granular activated carbon

The release of algal organic matter (AOM) during seasonal algal blooms increases the complexity and heterogeneity of natural organic matter (NOM) in water sources, altering its hydrophilic-hydrophobic balance and posing significant challenges to conventional water treatment processes. This study aims to verify whether the (Granular activated carbon) GAC selected for the adsorption of NOM in sand filtration effluent can adapt to water quality fluctuations caused by AOM release, and identify the criteria influencing GAC adsorption performance. Results indicated that external surface area, mesopore volume, pore size and surface functional groups were key indicators of GAC adsorption performance. AOM exposure increased the soluble microbial byproducts (SMP) and humic acid components in sand filter effluent, and induced the presence of high molecular weight biopolymers. The removal characteristics of sand filtration effluent spiked with AOM indicated that GAC preferentially adsorbed unsaturated bonds and aromatic compounds, as well as organic acids like fulvic and humic acids. Its adsorption primarily involved physical and chemical processes such as pore filling, hydrophobic interactions, and reactions between chemical functional groups. AOM exposure led to an increase in hydrophilic macromolecules such as polysaccharides and proteins, causing competitive adsorption and pore blockage. This study provided a theoretical basis for the efficient and rapid selection of GAC during outbreaks of AOM pollution.

Cyanobacteria hot spot detection integrating remote sensing data with convolutional and Kolmogorov-Arnold networks

Prompt and accurate monitoring of cyanobacterial blooms is essential for public health management and understanding aquatic ecosystem dynamics. Remote sensing, in particular satellite observations, presents a good alternative for continuous monitoring. This study employs multispectral images from the Sentinel-2 constellation alongside ERA5-Land to enable broad-scale data acquisition. A simple deep convolutional neural network (CNN) architecture was proposed to analyze cyanobacteria (CB) concentration dynamics in Pigeon Lake, Canada, over five years. The model achieved an R2 value of 0.81 and an RMSE score of 0.03 for the training set and 0.15 for the testing set, demonstrating high predictive accuracy. Using the Local Getis-Ord statistic, we identified and analyzed trends in hot and cold spots under the null hypothesis that such spots are randomly distributed, observing changes in their distribution and the median CB concentration in hot spots over time. Additionally, a Kolmogorov-Arnold Network (KAN) and dense neural networks (NN) with a single hidden layer were trained to classify sections of the lake shoreline into hot and no hot spots using the Dynamic World dataset within a 500m radius of the lake. The KAN achieved a recall metric of 0.83 for detecting hot spots.

Current Trends in Development and Use of Polymeric Ion-Exchange Resins in Wastewater Treatment

Drinking and wastewater are to be treated for safe human consumption and for keeping surface waters clean. There are multiple water purification procedures, but the use of ion-exchange resins significantly enhances water purification efficiency. This review was targeted on highlighting the concept and classification of polymeric ion-exchange resins as well as pointing out their real-world applications. Their successful use for purification purposes has been linked to their chemical structure, simplicity of operation, accessibility, and reusability. Therefore, polymeric ion-exchange resins have been used for the removal of a wide range of organic and inorganic pollutants such as pharmaceutical compounds, dyes, organic matter, metals, and many others. Ion-exchange resins are obtained directly by synthesis methods or grafting ionizable groups on polymer matrix in order to ensure continuous improvement. Furthermore, the newly designed ion-exchange resins take into consideration biodegradability potential towards obtaining ecofriendly compounds.

Mitigating harmful cyanobacterial blooms in drinking water reservoirs through in-situ sediment resuspension

Mitigating harmful cyanobacterial blooms is a global challenge, particularly crucial for safeguarding source water. Given the limitations of current technologies for application in drinking water reservoirs, we propose an innovative strategy based on in-situ sediment resuspension (SR). This method's effectiveness in cyanobacterial control and its potential impacts on water quality were assessed through laboratory culture experiments and further validated via field applications in five drinking water reservoirs. The results revealed that SR could significantly mitigate cyanobacterial growth, evidenced by the treated sets (removal rate: 3.82×106 cells L-1d-1) compared to the control set (growth rate: 2.22×107 cells L-1d-1) according to the laboratory experiments. The underlying mechanisms identified included underwater light reduction (2.38× increase in extinction coefficient) and flocculation and entrainment of cells by resuspended particles (30 % reduction per operation). Additional contributions were noted in the reduction of bioavailable phosphate and remediation of anaerobic sediment characterized by increased redox potential. This facilitated the oxidation of iron, which in turn promoted the co-precipitation of phosphate (removal rate: 46 μg L-1d-1) and inhibited its release from the sediment. The SR operation, devoid of importing extra substances, represents a safe and economical technology for controlling harmful cyanobacteria in drinking water reservoirs.

Early Detection Methods for Toxic Cyanobacteria Blooms

Harmful cyanobacterial blooms produce cyanotoxins which can adversely affect humans and animals. Without proper monitoring and detection programs, tragedies such as the loss of pets or worse are possible. Multiple factors including rising temperatures and human influence contribute to the increased likelihood of harmful cyanobacteria blooms. Current approaches to monitoring cyanobacteria and their toxins include microscopic methods, immunoassays, liquid chromatography coupled with mass spectrometry (LCMS), molecular methods such as qPCR, satellite monitoring, and, more recently, machine learning models. This review highlights current research into early detection methods for harmful cyanobacterial blooms and the pros and cons of these methods.

Defining algal bloom phenology in Lake Erie

Elucidating the impact of global climate change on aquatic ecosystems, particularly through phenological shifts in primary producers, is critical for understanding ecological resilience. Here, we focus on the phenological shifts in chlorophyll as a proxy for algae biomass and primary production in aquatic ecosystems, specifically in Lake Erie as well as concentrations of the toxin microcystin. By tracking temporal changes in each, we identified key phenological phases important to estimate duration, magnitude, and intensity of harmful algal blooms (HABs). Determining which influential biotic and abiotic factors such as temperature, wind speed, nutrient availability, and climate change is most important, is a long-term management need for Lake Erie, which can be explored using our methodology. Our novel statistical framework employing Bayesian generalized additive mixed models described seasonal chlorophyll and particulate microcystin concentration from Lake Erie and our simple geometric method identified the start, peak, and end of algal blooms. This research enhances our understanding of the ecological effects of nutrient pollution on aquatic ecosystems and provides a repeatable method for determining phenological events without the need for user defined cutoffs which aids in the management and mitigation of HABs, safeguarding water quality in regions dependent on lakes for drinking water.

Microcystis abundance is predictable through ambient bacterial communities: A data-oriented approach

The number of cyanobacterial harmful algal blooms (cyanoHABs) has increased, leading to the widespread development of prediction models for cyanoHABs. Although bacteria interact closely with cyanobacteria and directly affect cyanoHABs occurrence, related modeling studies have rarely utilized microbial community data compared to environmental data such as water quality. In this study, we built a machine learning model, the multilayer perceptron (MLP), for the prediction of Microcystis dynamics using both bacterial community and weekly water quality data from the Daechung Reservoir and Nakdong River, South Korea. The modeling performance, indicated by the R2 value, improved to 0.97 in the model combining bacterial community data with environmental factors, compared to 0.78 in the model using only environmental factors. This underscores the importance of microbial communities in cyanoHABs prediction. Through the post-hoc analysis of the MLP models, we revealed that nitrogen sources played a more critical role than phosphorus sources in Microcystis blooms, whereas the bacterial amplicon sequence variants did not have significant differences in their contribution to each other. Similar to the MLP model results, bacterial data also had higher predictability in multiple linear regression (MLR) than environmental data. In both the MLP and MLR models, Microscillaceae showed the strongest association with Microcystis. This modeling approach provides a better understanding of the interactions between bacteria and cyanoHABs, facilitating the development of more accurate and reliable models for cyanoHABs prediction using ambient bacterial data.

Kinetics and Mechanism of Cyanobacteria Cell Removal Using Biowaste-Derived Activated Carbons with Assessment of Potential Human Health Impacts

Harmful cyanobacteria blooms and the escalating impact of cyanotoxins necessitates the effective removal of cyanobacteria from water ecosystems before they release cyanotoxins. In this study, cyanobacteria removal from water samples taken from the eutrophic Aleksandrovac Lake (southern Serbia) was investigated. For that purpose, novel activated carbons derived from waste biomass-date palm leaf stalk (P_AC), black alder cone-like flowers (A_AC), and commercial activated carbon from coconut shell (C_AC) as a reference were used. To define the best adsorption conditions and explain the adsorption mechanism, the influence of contact time, reaction volume, and adsorbent mass, as well as FTIR analysis of the adsorbents before and after cyanobacteria removal, were studied. The removal efficiency of P_AC and A_AC achieved for the applied concentration of 10 mg/mL after 15 min was ~99%, while for C_AC after 24 h was only ~92% for the same concentration. To check the safety of the applied materials for human health and the environment, the concentrations of potentially toxic elements (PTEs), the health impact (HI) after water purification, and the toxicity (MTT and Comet assay) of the materials were evaluated. Although the P_AC and A_AC achieved much better removal properties in comparison with the C_AC, considering the demonstrated genotoxicity and cytotoxicity of the P_AC and the higher HI value for the C_AC, only the A_AC was further investigated. Results of the kinetics, FTIR analysis, and examination of the A_AC mass influence on removal efficiency indicated dominance of the physisorption mechanism. Initially, the findings highlighted the superior performance of A_AC, with great potential to be globally commercialized as an effective cyanobacteria cell adsorbent.

Reactivity of Cyanobacteria Metabolites with Ozone: Multicompound Competition Kinetics

Cyanobacterial blooms occur at increasing frequency and intensity, notably in freshwater. This leads to the introduction of complex mixtures of their products, i.e., cyano-metabolites, to drinking water treatment plants. To assess the fate of cyano-metabolite mixtures during ozonation, a novel multicompound ozone (O3) competition kinetics method was developed. Sixteen competitors with known second-order rate constants for their reaction with O3 ranging between 1 and 108 M-1 s-1 were applied to cover a wide range of the O3 reactivity. The apparent second-order rate constants (kapp,O3) at pH 7 were simultaneously determined for 31 cyano-metabolites. kapp,O3 for olefin- and phenol-containing cyano-metabolites were consistent with their expected reactivity (0.4-1.7 × 106 M-1 s-1) while kapp,O3 for tryptophan- and thioether-containing cyano-metabolites were significantly higher than expected (3.4-7.3 × 107 M-1 s-1). Cyano-metabolites containing these moieties are predicted to be well abated during ozonation. For cyano-metabolites containing heterocycles, kapp,O3 varied from <102 to 5.0 × 103 M-1 s-1, giving first insights into the O3 reactivity of this class of compounds. Due to lower O3 reactivities, heterocycle- and aliphatic amine-containing cyano-metabolites may be only partially degraded by a direct O3 reaction near circumneutral pH. Hydroxyl radicals, which are formed during ozonation, may be more important for their abatement. This novel multicompound kinetic method allows a high-throughput screening of ozonation kinetics.

Advances and challenges in the technologies for cyanobacterial cells removal in drinking water treatment

Harmful cyanobacteria in reservoirs pose a serious threat to drinking water safety due to the intracellular metabolites, such as toxins and unpleasant tastes & odours. Effective removal of harmful cyanobacteria with little to no cell damage is very important to ensure the safety of drinking water. This review first introduced development history of cyanobacterial removal technologies in drinking water treatment. Then, impacts of oxidation, coagulation and pre-oxidation enhanced coagulation processes on cyanobacterial removal and integrity of the cells were comprehensively evaluated and discussed. Oxidation can remove cyanobacteria, but high doses of oxidants can result in significant cell lysis and release of intracellular metabolites, especially when using chlorine or ozone. Although there is practically no cell damage during coagulation, the removal efficiency is low in many cases. Pre-oxidation may improve cyanobacterial removal by the subsequent solid-liquid separation processes, and moderate pre-oxidation with little to no cell lysis is very important. Mechanisms of interface interaction between pre-oxidants and cyanobacteria should be defined in future to ensure moderate pre-oxidation of algal cells. Fate of cyanobacterial cells in sludge is also reviewed because more and more waterworks return sludge supernatant to the inlet of plant. Damage to cyanobacterial cells in sludge depends mainly upon coagulant type and dosage, algal species, and cyanobacteria-containing sludge should be treated before cell lysis. Efficient techniques for harmless disposal of cyanobacteria-containing sludge should be developed in future. This paper will help to better understand the cyanobacterial removal processes and provide improved perspectives for future research in this field.

Effect of rainfall in shaping microbial community during Microcystis bloom in Nakdong River, Korea

Various environmental factors play a role in the formation and collapse of Microcystis blooms. This study investigates the impact of heavy rainfall on cyanobacterial abundance, microbial community composition, and functional dynamics in the Nakdong River, South Korea, during typical and exceptionally rainy years. The results reveal distinct responses to rainfall variations, particularly in cyanobacterial dominance and physicochemical characteristics. In 2020, characterized by unprecedented rainfall from mid-July to August, Microcystis blooms were interrupted significantly, exhibiting lower cell densities and decreased water temperature, compared to normal bloom patterns in 2019. Moreover, microbial community composition varied, with increases in Gammaproteobacteria and notably in genera of Limnohabitans and Fluviicola. These alterations in environmental conditions and bacterial community were similar to those of the post-bloom period in late September 2019. It shows that heavy rainfall during summer leads to changes in environmental factors, consequently causing shifts in bacterial communities akin to those observed during the autumn-specific post-bloom period in typical years. These changes also accompany shifts in bacterial functions, primarily involved in the degradation of organic matter such as amino acids, fatty acids, and terpenoids, which are assumed to have been released due to the significant collapse of cyanobacteria. Our results demonstrate that heavy rainfall in early summer induces changes in the environmental factors and subsequently microbial communities and their functions, similar to those of the post-bloom period in autumn, leading to the earlier breakdown of Microcystis blooms.

Summer heatwaves promote harmful algal blooms in the Fuchunjiang Reservoir, an important drinking water source

Extensive outbreaks of harmful algal blooms (HABs) occurred in the Fuchunjiang Reservoir in 2022, a crucial urban drinking water source, coinciding with extreme summer heatwaves. We hypothesize that these heatwaves contributed to HABs formation and expansion. Leveraging Landsat 8 and Sentinel-2 data, we employed clustering and machine learning methods to quantify the HABs distribution and area. Concurrent meteorological and water quality data aided in uncovering the effects of heatwave on HABs. When applying different methods to extract HABs from remote sensing images, random forest (RF) analyses indicated accuracies of 99.3% and 99.8% for Landsat 8 and Sentinel-2 data, respectively, while classification and regression tree (CART) analyses indicated 99.1% and 99.7% accuracies, respectively. Support vector machine (SVM) exhibited lower accuracies (83.5% and 97.4%). Thus RF, given its smaller differences between satellites and high accuracy, was selected for further analysis. Both satellites detected extensive HABs in 2022, with Sentinel-2 recording a peak area of 24.13 km2 (44.6% of cloud-free water area) on August 11, 2022. Increasing trends with amplified durations were observed for summer heatwaves in Jiande and Tonglu around the Fuchunjiang Reservoir. Notably, these areas experienced extreme heatwaves for 63 and 58 days in 2022, respectively, more than double the 1980-2022 average. From June 1 to October 8, 2022, water temperature peaks significantly coincided with expansive HABs and elevated chlorophyll a (Chl-a) concentration from 4.8 μg/L to 119.2 μg/L during the summer heatwaves. Our findings indicated that the reservoir became more HAB-prone during heatwave events, escalating the drinking water safety risk. These results emphasize the challenges faced by reservoir managers in dealing with climate-induced extreme heatwaves and underscore the urgency for heightened attention from water source management departments.

An assessment of a biosensor system for the quantification of microcystins in freshwater cyanobacterial blooms

Microcystin-producing cyanobacterial blooms are a global issue threatening drinking water supplies and recreation on lakes and beaches. Direct measurement of microcystins is the only way to ensure waters have concentrations below guideline concentrations; however, analyzing water for microcystins takes several hours to days to obtain data. We tested LightDeck Diagnostics' bead beater cell lysis and two versions of the quantification system designed to give microcystin concentrations within 20 min and compared it to the standard freeze-thaw cycle lysis method and ELISA quantification. The bead beater lyser was only 30 % effective at extracting microcystins compared to freeze-thaw. When considering freeze-thaw samples analyzed in 2021, there was good agreement between ELISA and LightDeck version 2 (n = 152; R2 = 0.868), but the LightDeck slightly underestimated microcystins (slope of 0.862). However, we found poor relationships between LightDeck version 2 and ELISA in 2022 (n = 49, slopes 0.60 to 1.6; R2 < 0.6) and LightDeck version 1 (slope = 1.77 but also a high number of less than quantifiable concentrations). After the quantification issues are resolved, combining the LightDeck system with an already-proven rapid lysis method (such as microwaving) will allow beach managers and water treatment operators to make quicker, well-informed decisions.

Pulse Feature-Enhanced Classification of Microalgae and Cyanobacteria Using Polarized Light Scattering and Fluorescence Signals

Harmful algal blooms (HABs) pose a global threat to the biodiversity and stability of local aquatic ecosystems. Rapid and accurate classification of microalgae and cyanobacteria in water is increasingly desired for monitoring complex water environments. In this paper, we propose a pulse feature-enhanced classification (PFEC) method as a potential solution. Equipped with a rapid measurement prototype that simultaneously detects polarized light scattering and fluorescence signals of individual particles, PFEC allows for the extraction of 38 pulse features to improve the classification accuracy of microalgae, cyanobacteria, and other suspended particulate matter (SPM) to 89.03%. Compared with microscopic observation, PFEC reveals three phyla proportions in aquaculture samples with an average error of less than 14%. In this paper, PFEC is found to be more accurate than the pulse-average classification method, which is interpreted as pulse features carrying more detailed information about particles. The high consistency of the dominant and common species between PFEC and microscopy in all field samples also demonstrates the flexibility and robustness of the former. Moreover, the high Pearson correlation coefficient accounting for 0.958 between the cyanobacterial proportion obtained by PFEC and the cyanobacterial density given by microscopy implies that PFEC serves as a promising early warning tool for cyanobacterial blooms. The results of this work suggest that PFEC holds great potential for the rapid and accurate classification of microalgae and cyanobacteria in aquatic environment monitoring.

The dependence in microcystin removal with powdered activated carbon on variant properties, carbon properties, and dissolved organic matter

Powdered activated carbon (PAC) is commonly used by water treatment plants to remove harmful cyanotoxins such as microcystins (MCs) produced during seasonal harmful algal blooms. MC removal by PAC depends upon the properties of the PAC, the properties of the MC variant, and the presence and properties of dissolved organic matter (DOM). To identify which of these factors has the greatest impact on the removal of MC by PAC, we evaluated the removal of four different MC variants (MC-LR, MC-LA, MC-RR and desmethylated MC-RR) by three different PAC types (wood-based, coal-blend and coal-based). The role of DOM properties was evaluated using DOM isolated from two different sources, a terrestrial source (Suwannee River Fulvic Acid, SRFA) and a microbial source (Grand Lake St Marys DOM, GLSM). The results of adsorption experiments conducted over a period of 72 h demonstrated the wood-based PAC, which had the highest surface area and mesopore volume of the PAC tested, had the highest adsorption rate and capacity for all four MC variants. Of the variants studied, neutrally charged MC-RR was adsorbed more rapidly and to a greater extent on all of the PAC types than were the other variants. Although MC-LA and MC-LR had the greatest hydrophobicity, their negative charges resulted in their being adsorbed the least. As expected, DOM inhibited microcystin adsorption to PAC. The degree of inhibition, however, did not significantly vary for the two DOM types evaluated, indicating the properties of the DOM on MC adsorption to PAC was less important than the PAC properties or MC variant properties. Overall, PAC properties were a more important factor in MC removal than were the MC properties or DOM conditions.

Is monochloramine pre-oxidation a viable strategy for enhancing the treatment efficiency of algae-laden water with conventional drinking water treatment process?

Algal blooms worldwide pose many challenges to drinking water production. Pre-oxidation with NaClO, KMnO4, or ozone is commonly used to enhance algal removal in conventional drinking water treatment processes. However, these currently utilized oxidation methods often result in significant algal cell lysis or impede the operation of the subsequent units. Higher algal removal with pre-chlorination in algal solutions prepared with natural water, compared to those prepared with ultrapure water, has been observed. In the present studies, preliminary findings indicate that ammonium in natural water alters chlorine species to NH2Cl, leading to improved treatment efficiency. NH2Cl with 1.5-3.0 mg∙L-1 as Cl2 with an oxidation time of 3-7 h significantly enhancing algal removal by coagulation. The selective oxidation of surface-absorbed organic matter (S-AOM) by NH2Cl, followed by the subsequent peeling off of this material from the algal surface, leading to an increase in zeta potential from -20.2 mV to -3.8 mV, constitutes the primary mechanism of enhanced algal removal through coagulation. These peeled S-AOM retained their large molecular weight and acted as polymer aids. Compared with NaClO and KMnO4, NH2Cl displays the best performance in improving algal removal, avoiding cell lysis, and decreasing the potential for nitrogenous disinfection byproducts formation under the reaction conditions used in this study. Notably, in major Chinese cities, water purification plants commonly rely on suburban lakes or reservoirs as water sources, necessitating the transportation of raw water over long distances for times up to several hours. These conditions favor the implementation of NH2Cl pre-oxidation. The collective results indicate the potential of NH2Cl oxidation as a viable pretreatment strategy for algal contamination during water treatment processes.

Performance evaluation of Moringa oleifera seeds aqueous extract for removing Microcystis aeruginosa and microcystins from municipal treated-water

Introduction: Toxic microcystins (MCs) produced by cyanoprokaryotes -particularly by the cosmopolitan cyanobacterium Microcystis aeruginosa- pose adverse effects on aquatic organisms and their ecosystem and may also cause serious impacts on human health. These harmful monocyclic heptapeptides are the most prevalent cyanotoxins reported in freshwaters and must be eliminated for avoiding MCs release in receiving water bodies. Hence, this work aimed to test the efficacy of Moringa oleifera seeds water-based extract (MO) as a natural coagulant for removing cyanobacteria (especially M. aeruginosa), microalgae, and its associated MCs from pre-treated municipal wastewaters. Methodology: Four different MO coagulant doses (25, 50, 75 and 100 mg L-1) were investigated for cyanobacteria and microalgae removal by conventional coagulation assays and morphology-based taxonomy studies. Additionally, water turbidity and chlorophyll a (Chl a) content were also determined. Further, the presence and concentration of MCs soluble in water, remaining in the particulate fraction, and flocculated within the residual sludge were assessed using high-performance liquid chromatography coupled with diode array detection (HPLC-DAD). Results: The treatment with MO at 100 mg L-1 substantially reduced the number of cyanobacterial and microalgal species in the treated samples (average removal rate of 93.8% and 86.9%, respectively). These results agreed with a ∼44% concomitant reduction in Chl a and ∼97% reduction in water turbidity (a surrogate marker for suspended solids content). Notably, MCs concentrations in the treated water were significantly lowered to 0.6 ± 0.1 µg L-1 after addition of 100 mg L-1 MO. This value is below the WHO recommended limits for MCs presence in drinking water (<1.0 µg L-1). Discussion: The present study provides promising insights into the applicability of MO as a cost-effective, reliable, and sustainable natural coagulant, particularly for using in developing countries, to eliminate harmful cyanobacteria and cyanotoxins in municipal water treatment facilities.

UV radiation and temperature increase alter the PSII function and defense mechanisms in a bloom-forming cyanobacterium Microcystis aeruginosa

The aim was to determine the response of a bloom-forming Microcystis aeruginosa to climatic changes. Cultures of M. aeruginosa FACHB 905 were grown at two temperatures (25°C, 30°C) and exposed to high photosynthetically active radiation (PAR: 400-700 nm) alone or combined with UVR (PAR + UVR: 295-700 nm) for specified times. It was found that increased temperature enhanced M. aeruginosa sensitivity to both PAR and PAR + UVR as shown by reduced PSII quantum yields (Fv/Fm) in comparison with that at growth temperature (25°C), the presence of UVR significantly exacerbated the photoinhibition. M. aeruginosa cells grown at high temperature exhibited lower PSII repair rate (Krec) and sustained nonphotochemical quenching (NPQs) induction during the radiation exposure, particularly for PAR + UVR. Although high temperature alone or worked with UVR induced higher SOD and CAT activity and promoted the removal rate of PsbA, it seemed not enough to prevent the damage effect from them showing by the increased value of photoinactivation rate constant (Kpi). In addition, the energetic cost of microcystin synthesis at high temperature probably led to reduced materials and energy available for PsbA turnover, thus may partly account for the lower Krec and the declination of photosynthetic activity in cells following PAR and PAR + UVR exposure. Our findings suggest that increased temperature modulates the sensitivity of M. aeruginosa to UVR by affecting the PSII repair and defense capacity, thus influencing competitiveness and abundance in the future water environment.

Forecasting freshwater cyanobacterial harmful algal blooms for Sentinel-3 satellite resolved U.S. lakes and reservoirs

This forecasting approach may be useful for water managers and associated public health managers to predict near-term future high-risk cyanobacterial harmful algal blooms (cyanoHAB) occurrence. Freshwater cyanoHABs may grow to excessive concentrations and cause human, animal, and environmental health concerns in lakes and reservoirs. Knowledge of the timing and location of cyanoHAB events is important for water quality management of recreational and drinking water systems. No quantitative tool exists to forecast cyanoHABs across broad geographic scales and at regular intervals. Publicly available satellite monitoring has proven effective in detecting cyanobacteria biomass near-real time within the United States. Weekly cyanobacteria abundance was quantified from the Ocean and Land Colour Instrument (OLCI) onboard the Sentinel-3 satellite as the response variable. An Integrated Nested Laplace Approximation (INLA) hierarchical Bayesian spatiotemporal model was applied to forecast World Health Organization (WHO) recreation Alert Level 1 exceedance >12 μg L-1 chlorophyll-a with cyanobacteria dominance for 2192 satellite resolved lakes in the United States across nine climate zones. The INLA model was compared against support vector classifier and random forest machine learning models; and Dense Neural Network, Long Short-Term Memory (LSTM), Recurrent Neural Network (RNN), and Gneural Network (GNU) neural network models. Predictors were limited to data sources relevant to cyanobacterial growth, readily available on a weekly basis, and at the national scale for operational forecasting. Relevant predictors included water surface temperature, precipitation, and lake geomorphology. Overall, the INLA model outperformed the machine learning and neural network models with prediction accuracy of 90% with 88% sensitivity, 91% specificity, and 49% precision as demonstrated by training the model with data from 2017 through 2020 and independently assessing predictions with data from the 2021 calendar year. The probability of true positive responses was greater than false positive responses and the probability of true negative responses was less than false negative responses. This indicated the model correctly assigned lower probabilities of events when they didn't exceed the WHO Alert Level 1 threshold and assigned higher probabilities when events did exceed the threshold. The INLA model was robust to missing data and unbalanced sampling between waterbodies.

Comparative study about ozonation to treat Microcystis-laden source water at the development and maintenance stage

The outbreak of toxic cyanobacteria blooms is hazardous to water safety. Ozonation has been used to treat cyanobacteria-laden source water. Generally, cyanobacterial blooms enter into a long-term maintenance stage from the bloom development, but how the changed bloom stage affects ozonation is still unknow. Herein, influences of ozonation on cell inactivation and microcystin removal of Microcystis at the development and maintenance stage, were investigated. Then, ozonation-assisted coagulation for Microcystis removal at the two stages was compared. Results showed no significant difference in the photosynthetic inactivation of Microcystis at both stages. Microcystis at the maintenance stage exhibited a lower loss of membrane integrity (268-480 M-1 s-1) than that at the development stage (413-596 M-1 s-1). However, the extracellular microcystin increased by 30-410% at the maintenance stage at a lower ratio of [O3: DOC] (0.10-0.80) compared to the development stage (0.21-1.68), mainly ascribed to a decrease in the ozonation efficiency for microcystin removal. This finding might result from the elevated biomass and N-containing organics as competitors to reduce microcystin ozonation. Meanwhile, it was possible to generate fewer hydroxyl radicals to oxidize microcystin at the maintenance stage than that at the development stage. Besides, the removal ratio of Microcystis after ozonation-assisted coagulation, was reduced by 46-230% at the maintenance stage, due to the insufficient modification of cellular surface or elevated organics of 3-30 kDa. This work indicated that ozonation is effective to treat Microcystis at the development stage of a bloom whist pre-ozonation might be an inappropriate choice at the long-term maintenance stage.

A review on aquatic toxins - Do we really know it all regarding the environmental risk posed by phytoplankton neurotoxins?

Aquatic toxins are potent natural toxins produced by certain cyanobacteria and marine algae species during harmful cyanobacterial and algal blooms (CyanoHABs and HABs, respectively). These harmful bloom events and the toxins produced during these events are a human and environmental health concern worldwide, with occurrence, frequency and severity of CyanoHABs and HABs being predicted to keep increasing due to ongoing climate change scenarios. These contexts, as well as human health consequences of some toxins produced during bloom events have been thoroughly reviewed before. Conversely, the wider picture that includes the non-human biota in the assessment of noxious effects of toxins is much less covered in the literature and barely covered by review works. Despite direct human exposure to aquatic toxins and related deleterious effects being responsible for the majority of the public attention to the blooms' problematic, it constitutes a very limited fraction of the real environmental risk posed by these toxins. The disruption of ecological and trophic interactions caused by these toxins in the aquatic biota building on deleterious effects they may induce in different species is paramount as a modulator of the overall magnitude of the environmental risk potentially involved, thus necessarily constraining the quality and efficiency of the management strategies that should be placed. In this way, this review aims at updating and consolidating current knowledge regarding the adverse effects of aquatic toxins, attempting to going beyond their main toxicity pathways in human and related models' health, i.e., also focusing on ecologically relevant model organisms. For conciseness and considering the severity in terms of documented human health risks as a reference, we restricted the detailed revision work to neurotoxic cyanotoxins and marine toxins. This comprehensive revision of the systemic effects of aquatic neurotoxins provides a broad overview of the exposure and the hazard that these compounds pose to human and environmental health. Regulatory approaches they are given worldwide, as well as (eco)toxicity data available were hence thoroughly reviewed. Critical research gaps were identified particularly regarding (i) the toxic effects other than those typical of the recognized disease/disorder each toxin causes following acute exposure in humans and also in other biota; and (ii) alternative detection tools capable of being early-warning signals for aquatic toxins occurrence and therefore provide better human and environmental safety insurance. Future directions on aquatic toxins research are discussed in face of the existent knowledge, with particular emphasis on the much-needed development and implementation of effective alternative (eco)toxicological biomarkers for these toxins. The wide-spanning approach followed herein will hopefully stimulate future research more broadly addressing the environmental hazardous potential of aquatic toxins.

Understanding the Risks of Diffusion of Cyanobacteria Toxins in Rivers, Lakes, and Potable Water

Blue-green algae, or cyanobacteria, may be prevalent in our rivers and tap water. These minuscule bacteria can grow swiftly and form blooms in warm, nutrient-rich water. Toxins produced by cyanobacteria can pollute rivers and streams and harm the liver and nervous system in humans. This review highlights the properties of 25 toxin types produced by 12 different cyanobacteria genera. The review also covered strategies for reducing and controlling cyanobacteria issues. These include using physical or chemical treatments, cutting back on fertilizer input, algal lawn scrubbers, and antagonistic microorganisms for biocontrol. Micro-, nano- and ultrafiltration techniques could be used for the removal of internal and extracellular cyanotoxins, in addition to powdered or granular activated carbon, ozonation, sedimentation, ultraviolet radiation, potassium permanganate, free chlorine, and pre-treatment oxidation techniques. The efficiency of treatment techniques for removing intracellular and extracellular cyanotoxins is also demonstrated. These approaches aim to lessen the risks of cyanobacterial blooms and associated toxins. Effective management of cyanobacteria in water systems depends on early detection and quick action. Cyanobacteria cells and their toxins can be detected using microscopy, molecular methods, chromatography, and spectroscopy. Understanding the causes of blooms and the many ways for their detection and elimination will help the management of this crucial environmental issue.

A Perspective on Removal of Cyanotoxins from Water Through Advanced Oxidation Processes

This perspective discusses the challenges associated with the removal of cyanotoxins from raw water sources for drinking water treatment and the emergence of sulfate radical-based advanced oxidation processes (SR-AOPs) as an effective treatment technique. The advantage of SR-AOPs is that they can be activated using a variety of methods, including heat, UV radiation, and transition metal catalysts, allowing for greater flexibility in treatment design and optimization. In addition, the byproducts of SR-AOPs are less harmful than those generated by •OH-AOPs, which reduces the risk of secondary contamination. SR-AOPs generate sulfate radicals (SO4 •-) that are highly selective to certain organic contaminants and have lower reactivity to background water constituents, resulting in higher efficiency and selectivity of the process. The presence of natural organic matter and transition metals in the natural water body increases the degradation efficiency of SR-AOPs for the cyanotoxins. The bromate formation is also suppressed when the water contaminated with cyanotoxins is treated with SR-AOPs.

Effects of cyanobacterial metabolites: Aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin in binary and quadruple mixtures on the survival and oxidative stress biomarkers of Daphnia magna

The aim of our study was to determine the effects of aeruginosin 98 A (ARE-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A) cylindrospermopsin (CYL) and their binary and quadruple mixtures on the survival and the levels of oxidative stress biomarkers in Daphnia magna: total glutathione (GSH), catalase (CAT), dismutase (SOD) and malondialdehyde (MDA). The biochemical indicators were measured with ELISA kits and the interactive effects were determined by isobole and polygonal analysis with Compusyn® computer software. The study revealed that oligopeptides did not decrease daphnid survival, only CYL inhibited this parameter, with synergistic effects when it was used as a component. The single metabolites at the two highest concentrations and all the binary and quadruple mixtures at all concentrations diminished GSH level, however both in the binary and in the quadruple mixtures most of the interactions between the metabolites were antagonistic. Nearly additive effects were found only in AER-A + CYL and MG-FR1+CYL. On the other hand, CAT activity was slightly increased in daphnids exposed to the binary mixtures with antagonistic interactions, however nearly addivive effects were found in animals exposed to the mixture of AER-A + ANA-A and synergistic in the quadruple mixture. SOD was elevated in daphnids exposed to single AER-A and MG-FR1, however it was diminished in the animals exposed to ANA-A and CYL. Binary mixtures in which CYL was present as a component decreased the level of this enzyme with nearly additive interactions in ANA-A + CYL. The quadruple mixture increased SOD level, with antagonistic interactions. Both single cyanobacterial metabolites, their binary and quadruple mixtures induced lipid peroxidation measured by MDA level and most of interactions in the binary mixtures were synergistic. The study suggested that antioxidative system of Daphnia magna responded to the tested metabolites and the real exposure to mixtures of these products may lead to various interactive effects with varied total toxicity.

Global Discovery and Temporal Changes of Human Albumin Modifications by Pan-Protein Adductomics: Initial Application to Air Pollution Exposure

Assessing personal exposure to environmental toxicants is a critical challenge for predicting disease risk. Previously, using human serum albumin (HSA)-based biomonitoring, we reported dosimetric relationships between adducts at HSA Cys³⁴ and ambient air pollutant levels (Smith et al., Chem. Res. Toxicol. 2021, 34, 1183). These results provided the foundation to explore modifications at other sites in HSA to reveal novel adducts of complex exposures. Thus, the Pan-Protein Adductomics (PPA) technology reported here is the next step toward an unbiased, comprehensive characterization of the HSA adductome. The PPA workflow requires <2 μL serum/plasma and uses nanoflow-liquid chromatography, gas-phase fractionation, and overlapping-window data-independent acquisition high-resolution tandem mass spectrometry. PPA analysis of albumin from nonsmoking women exposed to high levels of air pollution uncovered 68 unique location-specific modifications (LSMs) across 21 HSA residues. While nearly half were located at Cys³⁴ (33 LSMs), 35 were detected on other residues, including Lys, His, Tyr, Ser, Met, and Arg. HSA adduct relative abundances spanned a ∼400 000-fold range and included putative products of exogenous (SO₂, benzene, phycoerythrobilin) and endogenous (oxidation, lipid peroxidation, glycation, carbamylation) origin, as well as 24 modifications without annotations. PPA quantification revealed statistically significant changes in LSM levels across the 84 days of monitoring (∼3 HSA lifetimes) in the following putative adducts: Cys³⁴ trioxidation, β-methylthiolation, benzaldehyde, and benzene diol epoxide; Met³²⁹ oxidation; Arg¹⁴⁵ dioxidation; and unannotated Cys³⁴ and His¹⁴⁶ adducts. Notably, the PPA workflow can be extended to any protein. Pan-Protein Adductomics is a novel and powerful strategy for untargeted global exploration of protein modifications.

Modeling future land cover and water quality change in Minneapolis, MN, USA to support drinking water source protection decisions

Continued alteration of the nitrogen cycle exposes receiving waters to elevated nitrogen concentrations and forces drinking water treatment services to plan for such increases in the future. We developed four 2011-2050 land cover change scenarios and modeled the impact of projected land cover change on influent water quality to support long-term planning for the Minneapolis Water Treatment Distribution Service (MWTDS) using Soil Water and Assessment Tool. Projected land cover changes based on relatively unconstrained economic growth led to substantial increases in total nitrogen (TN) loads and modest increases in total phosphorus (TP) loads in spring. Changes in sediment, TN, and TP under two "constrained" growth scenarios were near zero or declined modestly. Longitudinal analysis suggested that the extant vegetation along the Mississippi River corridor upstream of the MWTDS may be a sediment (and phosphorus) trap. Autoregressive analysis of current (2008-2017) chemical treatment application rates (mass per water volume processed) and extant (2001-2011) land cover change revealed that statistically significant increases in chemical treatment rates were temporally congruent with urbanization and conversion of pasture to cropland. Using the current trend in chemical treatment application rates and their inferred relationship to extant land cover change as a bellwether, the unconstrained growth scenarios suggest that future land cover may present challenges to the production of potable water for MWTDS.

Effect of three commercial algaecides on cyanobacteria and microcystin-LR: implications for drinking water treatment using activated carbon

Toxic cyanobacterial blooms in aquatic ecosystems are associated to both public health and environmental concerns worldwide. Depending on the treatment technologies used, the removal capacity of cyanotoxins by drinking water treatment plants (DWTPs) is not sufficient to reach safe levels in drinking water. Likewise, controlling these blooms with algaecide may impair the efficiency of DWTPs due to the possible lysis of cyanobacterial cells and consequent release of cyanotoxins. We investigated the effects of three commercial algaecides (cationic polymer, copper sulfate, and hydrogen peroxide) on the growth parameters of the cyanobacterium Microcystis aeruginosa and the release of microcystin-LR (MC-LR). The potential interference of each algaecide on the MC-LR removal by adsorption on activated carbon (AC) was also tested through adsorption isotherms and kinetics experiments. Most algaecides significantly decreased the cell density and biovolume of M. aeruginosa, as well as increased the release of MC-LR. Interestingly, the presence of the algaecides in binary mixtures with MC-LR affected the adsorption of the cyanotoxin. Relevant adsorption parameters (e.g., maximum adsorption capacity, adsorption intensity, and affinity between MC-LR and AC) were altered when the algaecides were present, especially in the case of the cationic polymer. Also, the algaecides influenced the kinetics (e.g., by shifting the initial adsorption and the desorption constant), which may directly affect the design and operation of DWTPs. Our study indicated that algaecides can significantly impact the fate and the removal of MC-LR in DWTPs when the adsorption process is employed, with important implications for the management and performance of such facilities.

A comprehensive review on the photocatalytic inactivation of Microcystis aeruginosa: Performance, development, and mechanisms

Harmful algae blooms (HABs), caused by severe eutrophication and extreme weather, have spread all over the world, posing adverse effects on eco-environment and human health. Microcystis aeruginosa is the dominant harmful cyanobacterial species when HABs occur, and the toxic metabolites produced by it, microcystins, are even fatal to humans. Photocatalytic technology has received wide attention from researchers for its clean and energy-efficient features, while the basic mechanisms and modification methods of photocatalysts have also been widely reported. In recent years, photocatalytic technology has shown great promise in the inhibition of HABs. In this article, we systematically reviewed the progress in photocatalytic performance and algae removal efficiency, discuss the damage mechanisms of photocatalysts for algae removal, including physical damage and various oxidative stresses, and also explore the degradation rates and possible pathways of microcystins. It can be concluded that during the photocatalytic process, the cytoarchitectural integrity of algae cells was damaged, a variety of important protein and enzyme systems were disrupted, and the antioxidant systems collapsed due to the continuous attack of ROS, which adversely affected the normal physiological activities and growth, resulting in the inactivation of algae cells. Moreover, photocatalysts have a degrading effect on microcystins, thus reducing the adverse effects of HAB. Finally, a brief summary of future research priorities regarding the photocatalytic degradation of algae cells is presented. This study helps to enhance the understanding of the destruction mechanism of Microcystis aeruginosa during the photocatalytic process, and provides a reference for the photodegradation of HAB in water bodies.

Untargeted and targeted LC-MS and data processing workflow for the comprehensive analysis of oligopeptides from cyanobacteria

Cyanobacteria produce a plethora of structurally diverse bioactive secondary metabolites, including cyanotoxins which pose a serious threat to humans and other living organisms worldwide. Currently, a wide variety of mass spectrometry-based methods for determination of microcystins (MCs), the most commonly occurring and studied class of cyanotoxins, have been developed and employed for research and monitoring purposes. The scarcity of commercially available reference materials, together with the ever-growing range of mass spectrometers and analytical approaches, make the accuracy of quantitative analyses a critical point to be carefully investigated in view of a reliable risk evaluation. This study reports, a comparative investigation of the qualitative and quantitative MCs profile obtained using targeted and untargeted liquid chromatography-mass spectrometry approaches for the analyses of cyanobacterial biomass from Lake Kastoria, Greece. Comparison of the total MCs content measured by the two approaches showed good correlation, with variations in the range of 3.8-13.2%. In addition, the implementation of an analytical workflow on a hybrid linear ion trap/orbitrap mass spectrometer is described, based on combining data-dependent acquisition and a powerful database of cyanobacterial metabolites (CyanoMetDB) for the annotation of known and discovery of new cyanopeptides. This untargeted strategy proved highly effective for the identification of MCs, microginins, anabaenopeptins, and micropeptins. The systematic interpretation of the acquired fragmentation patterns allowed the elucidation of two new MC structural variants, MC-PrhcysR and MC-Prhcys(O)R, and proposal of structures for two new microginins, isomeric cyanostatin B and MG 821A, and three isomeric micropeptins at m/z 846.4715, 846.4711 and 846.4723.

Remote sensing to detect harmful algal blooms in inland waterbodies

Harmful algal blooms (HABs) are an issue of concern for water management worldwide. As such, effective monitoring strategies of HAB spatio-temporal variability in waterbodies are needed. Remote sensing has become an increasingly important tool for HAB detection and monitoring in large lakes. However, accurate HAB detection in small-medium waterbodies via satellite data remains a challenge. Current barriers include the waterbody size, the limited freely available high resolution satellite data, and the lack of field calibration data. To test the applicability of remote sensing for detecting HABs in small-medium waterbodies, three satellites (Planetscope, Sentinel-2 and Landsat-8) were used to understand how spatial resolution, the availability of spectral bands, and the waterbody size itself effect HAB detection skill. Different algorithms and a non-parametric method, Self-Organizing Map (SOM), were tested. Curvature Around Red and NIR minus Red had the best HAB detection skill of the 20 existing algorithms that were tested. Landsat 8 and Sentinel 2 were the best satellites for HAB detection in small to medium waterbodies. The most critical attribute for detecting HABs were the available satellite bands, which determine the detection algorithms that can be used. Importantly, algorithm performance was mostly unrelated to waterbody size. However, there remain some barriers in utilizing satellite data for HAB detection, including algae dynamics, macrophyte cover within the waterbody, weather effects, and the correction models for satellite data. Moreover, it is important to consider the match time between satellite overpass and sampling activities for calibration. Given these challenges, integrating regular sampling activities and remote sensing is recommended for monitoring and managing small-medium waterbodies.

A Promising Use of Trimethyl Chitosan for Removing Microcystis aeruginosa in Water Treatment Processes

The increase in cyanobacterial blooms linked to climate change and the eutrophication of water bodies is a global concern. The harmful cyanobacterium Microcystis aeruginosa is one of the most common bloom-forming species whose removal from fresh water and, in particular, from that used for water treatment processes, remains a crucial goal. Different biodegradable and environmentally friendly coagulants/flocculants have been assayed, with chitosan showing a very good performance. However, chitosan in its original form is of limited applicability since it is only soluble in acid solution. The objective of this work was therefore to test the coagulant/flocculant capacity of trimethylchitosan (TMC), a chitosan derivative produced from residues of the fishing industry. TMC has a constitutively net positive charge enabling it to remain in solution regardless of the pH. Results show that even at alkaline pHs, common during cyanobacterial blooms, TMC is effective in removing buoyant cyanobacteria from the water column, both in test tube and Jar-Test experiments. Cell integrity was confirmed by fluorescent stain and electron microscopy. Our findings lead us to conclude that the use of TMC to remove bloom cells early in the treatment of drinking water is both feasible and promising.

Shotgun Metagenomic Sequencing to Assess Cyanobacterial Community Composition following Coagulation of Cyanobacterial Blooms

The excessive proliferation of cyanobacteria in surface waters is a widespread problem worldwide, leading to the contamination of drinking water sources. Short- and long-term solutions for managing cyanobacterial blooms are needed for drinking water supplies. The goal of this research was to investigate the cyanobacteria community composition using shotgun metagenomics in a short term, in situ mesocosm experiment of two lakes following their coagulation with ferric sulfate (Fe₂(SO₄)₃) as an option for source water treatment. Among the nutrient paramenters, dissolved nitrogen was related to Microcystis in both Missisquoi Bay and Petit Lac St. François, while the presence of Synechococcus was related to total nitrogen, dissolved nitrogen, dissolved organic carbon, and dissolved phosphorus. Results from the shotgun metagenomic sequencing showed that Dolichospermum and Microcystis were the dominant genera in all of the mesocosms in the beginning of the sampling period in Missisquoi Bay and Petit Lac St. François, respectively. Potentially toxigenic genera such as Microcystis were correlated with intracellular microcystin concentrations. A principal component analysis showed that there was a change of the cyanobacterial composition at the genus level in the mesocosms after two days, which varied across the studied sites and sampling time. The cyanobacterial community richness and diversity did not change significantly after its coagulation by Fe₂(SO₄)₃ in all of the mesocosms at either site. The use of Fe₂(SO₄)₃ for an onsite source water treatment should consider its impact on cyanobacterial community structure and the reduction of toxin concentrations.

Kinetics and mechanism of ozonation to treat Microcystis-laden source waters affected by cell-viability

Toxic cyanobacteria are challenging drinking water safety globally, and their cell-viability declines at decay stage of a succussive bloom. Ozone might be a more effective oxidant to treat both high- and low-viability cyanobacteria than other common oxidants (e.g., chlorine, potassium permanganate). However, previous studies only conducted ozonation experiments using high-viability cyanobacteria, and potential influences of cell-viability on ozonation process, remains unknown. In this study, kinetics of ozone decay, cell inactivation, membrane destruction, and cyanotoxin fate of high- and low-viability Microcystis (the most common genus), was investigated, and associated mechanism was discussed. Results showed that low-viability Microcystis exhibited a higher rate constant of membrane destruction (665-744 M^-1 s^-1) than high-viability Microcystis (364-600 M^-1 s^-1) by equal concentrations of ozone, ascribed to loosely gelatinous sheath comprised with fewer organic matters as oxidant scavengers. Meanwhile, a higher rate constant of photosynthetic inactivation induced by ozonation, was observed for low-viability Microcystis (312-364 M^-1 s^-1) than that for high-viability Microcystis (168-294 M^-1 s^-1). However, elevated aromatic organics competitively inhibited microcystin ozonation for low-viability Microcystis, and hydroxyl radicals for microcystin oxidation could be reduced by elevated organic loads and alkalinity. Moreover, elevated ozone exposure (>51 mg min L^-1) did not totally oxidize microcystin with a residual of 30 μg L^-1 for low-viability Microcystis. These findings suggested that elevated microcystin risk would be the great barrier to limit ozonation application for low-viability Microcystis, even with benefits of higher cell inactivation compared to high-viability Microcystis.

Low Levels of Contaminants Stimulate Harmful Algal Organisms and Enrich Their Toxins

A widespread increase in intense phytoplankton blooms has been noted in lakes worldwide since the 1980s, with the summertime peak intensity amplifying in most lakes. Such blooms cause annual economic losses of multibillion USD and present a major challenge, affecting 11 out of the 17 United Nations Sustainable Development Goals. Here, we evaluate recent scientific evidence for hormetic effects of emerging contaminants and regulated pollutants on Microcystis sp., the most notorious cyanobacteria forming harmful algal blooms and releasing phycotoxins in eutrophic freshwater systems. This new evidence leads to the conclusion that pollution is linked to algal bloom intensification. Concentrations of contaminants that are considerably smaller than the threshold for toxicity enhance the formation of harmful colonies, increase the production of phycotoxins and their release into the environment, and lower the efficacy of algaecides to control algal blooms. The low-dose enhancement of microcystins is attributed to the up-regulation of a protein controlling microcystin release (McyH) and various microcystin synthetases in tandem with the global nitrogen regulator Ycf28, nonribosomal peptide synthetases, and several ATP-binding cassette transport proteins. Given that colony formation and phycotoxin production and release are enhanced by contaminant concentrations smaller than the toxicological threshold and are widely occurring in the environment, the effect of contaminants on harmful algal blooms is more prevalent than previously thought. Climate change and nutrient enrichment, known mechanisms underpinning algal blooms, are thus joined by low-level pollutants as another causal mechanism.

Cyanotoxins and water quality parameters as risk assessment indicators for aquatic life in reservoirs

We assessed the extent of pollution in an essential public water supply reservoir (southeastern Brazil). An environmental monitoring study was performed at the Billings Reservoir (at the water catchment site) to assess the water quality in 2017, 2018, and 2019. Physicochemical parameters were analyzed, quantifying the total cyanobacteria and the cyanotoxins microcystins (MCs) and saxitoxins (SXTs), as well as their possible ecological risk to the aquatic environment. We also determined metals and metalloids (As, Ba, Cd, Pb, Cu, Cr, Fe, Mn, Ni, Zn, and Sb) and fecal bacteria (Escherichia coli). Monthly samplings were performed for 2017, 2018, and 2019 (totaling 36 sampling campaigns). Metals, metalloids, and E. coli values were below the maximum limit allowed by the Brazilian legislation. High concentrations of total cyanobacteria (3.07 × 10⁴ - 3.23 × 10⁵ cells/mL), microcystin variants MC-LR (0.67-23.63 μg/L), MC-LA (0.03-8.66 μg/L), MC-RR (0.56-7.92 μg/L), and MC-YR (0.04-1.24 μg/L), as well as the saxitoxins GTX2 (0.18-5.37 μg/L), GTX3 (0.13-4.40 μg/L), and STX (0.12-2.92 μg/L) were detected. From an ecotoxicological point of view, the estimated values for the risk quotient (RQ) for microcystins and saxitoxins were largely greater than 1, indicating a high risk to aquatic life. Therefore, further efforts need to be made to delay the eutrophication of the reservoir.

Adsorbents Used for Microcystin Removal from Water Sources: Current Knowledge and Future Prospects

The increasing occurrence of toxic cyanobacteria in water sources, driven by climate change and eutrophication, is of great concern worldwide today. Cyanobacterial blooms can negatively affect water bodies and generate harmful secondary metabolites, namely microcystins (MCs), which significantly impair water quality. Various adsorbents used for MC removal from water sources were assessed in this investigation. Activated carbon constitutes the most widely used adsorbent for treating contaminated waters due to its high affinity for adsorbing MCs. Alternative adsorbents have also been proposed and reported to provide higher efficiency, but the studies carried out so far in this regard are still insufficient. The mechanisms implicated in MC adsorption upon different adsorbents should be further detailed for a better optimization of the adsorption process. Certainly, adsorbent characteristics, water pH and temperature are the main factors influencing the adsorption of MCs. In this context, optimization studies must be performed considering the effectiveness, economic aspects associated with each adsorbent. This review provides guidelines for more practical field applications of the adsorption in the treatment of waters actually contaminated with MCs.

Evidence-Based Framework to Manage Cyanobacteria and Cyanotoxins in Water and Sludge from Drinking Water Treatment Plants

Freshwater bodies and, consequently, drinking water treatment plants (DWTPs) sources are increasingly facing toxic cyanobacterial blooms. Even though conventional treatment processes including coagulation, flocculation, sedimentation, and filtration can control cyanobacteria and cell-bound cyanotoxins, these processes may encounter challenges such as inefficient removal of dissolved metabolites and cyanobacterial cell breakthrough. Furthermore, conventional treatment processes may lead to the accumulation of cyanobacteria cells and cyanotoxins in sludge. Pre-oxidation can enhance coagulation efficiency as it provides the first barrier against cyanobacteria and cyanotoxins and it decreases cell accumulation in DWTP sludge. This critical review aims to: (i) evaluate the state of the science of cyanobacteria and cyanotoxin management throughout DWTPs, as well as their associated sludge, and (ii) develop a decision framework to manage cyanobacteria and cyanotoxins in DWTPs and sludge. The review identified that lab-cultured-based pre-oxidation studies may not represent the real bloom pre-oxidation efficacy. Moreover, the application of a common exposure unit CT (residual concentration × contact time) provides a proper understanding of cyanobacteria pre-oxidation efficiency. Recently, reported challenges on cyanobacterial survival and growth in sludge alongside the cell lysis and cyanotoxin release raised health and technical concerns with regards to sludge storage and sludge supernatant recycling to the head of DWTPs. According to the review, oxidation has not been identified as a feasible option to handle cyanobacterial-laden sludge due to low cell and cyanotoxin removal efficacy. Based on the reviewed literature, a decision framework is proposed to manage cyanobacteria and cyanotoxins and their associated sludge in DWTPs.

Natural Cyanobacteria Removers Obtained from Bio-Waste Date-Palm Leaf Stalks and Black Alder Cone-Like Flowers

The impact of urbanization and modern agricultural practice has led to accelerated eutrophication of aquatic ecosystems, which has resulted in the massive development of cyanobacteria. Very often, in response to various environmental influences, cyanobacteria produce potentially carcinogenic cyanotoxins. Long-term human exposure to cyanotoxins, through drinking water as well as recreational water (i.e., rivers or lakes), can cause serious health consequences. In order to overcome this problem, this paper presents the synthesis of completely new activated carbons and their potential application in contaminated water treatment. The synthesis and characterization of new active carbon materials obtained from waste biomass, date-palm leaf stalks (P_AC) and black alder cone-like flowers (A_AC) of reliable physical and chemical characteristics were presented in this article. The commercial activated carbon (C_AC) was also examined for the purpose of comparisons with the obtained materials. The detailed characterization of materials was carried out by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), low-temperature N2 physisorption, and Field emission scanning electron microscopy (FESEM). Preliminary analyzes of the adsorption capacities of all activated carbon materials were conducted on water samples from Aleksandrovac Lake (Southern part of Serbia), as a eutrophic lake, in order to remove Cyanobacteria from water. The results after 24 h showed removal efficiencies for P_AC, A_AC, and C_AC of 99.99%, 99.99% and 89.79%, respectively.

Evaluating the Effectiveness of Screened Lactic Acid Bacteria in Improving Crop Residues Silage: Fermentation Parameter, Nitrogen Fraction, and Bacterial Community

Ensiling characteristics of sweet potato vine (SPV) and peanut straw (PS), as well as the effects of lactic acid bacteria (LAB) strains, Lactococcus Lactis MK524164 (LL) and Lactobacillus farciminis MK524159 (LF), were investigated in this study. Fermentation parameters, nitrogen fractions, and bacterial community of SPV and PS were monitored at intervals during the ensiling process. The results showed that inoculating LAB increased lactate production (2.23 vs. 2.73%; 0.42 vs. 1.67% DM), accelerated pH decline (5.20 vs. 4.47; 6.30 vs. 5.35), and decreased butyrate (0.36% DM vs. not detected), ammonia-N (6.41 vs. 4.18% CP), or nonprotein-N (43.67 vs. 35.82% CP). Meanwhile, it altered the silage bacterial community, where the relative abundance of Lactobacillus was increased (6.67–32.03 vs. 45.27–68.43%; 0.53–10.45 vs. 38.37–68.62%) and that of undesirable bacteria such as Clostridium, Enterobacter, Methylobacterium, or Sphingomonas was much decreased. It is suggested that the screened LAB strains LL and LF can effectively improve the silage quality of SPV and PS silages.

Development, Validation and Application of a Targeted LC-MS Method for Quantification of Microcystins and Nodularin: Towards a Better Characterization of Drinking Water

Cyanotoxins can be produced in surface waters by cyanobacterial blooms, mostly during summer and early autumn. Intoxications would result from consumption of water contaminated with the potent hepatotoxins, microcystins and nodularin. Therefore, the WHO has set a guideline value for drinking water quality concerning one congener of microcystin. Consequently, the design of a validated, public reference method to detect and quantify the hepatotoxins in drinking water is necessary. During this study, a method was developed to quantify cyanotoxins (eight microcystin congeners and nodularin) in water using liquid chromatography coupled with tandem mass spectrometry. Additionally, bottled and tap water samples were tested for the presence of cyanotoxins. No cyanotoxins were detected in any of the collected water samples. However, quality controls and the results of a proficiency test show the validity of the method.

Optimization of Biodegradation Characteristics of Sphingopyxis sp. YF1 against Crude Microcystin-LR Using Response Surface Methodology

Sphingopyxis sp. YF1 has proven to be efficient in biodegrading microcystin (MC)-leucine (L) and arginine (R) (MC-LR); however, the optimal environmental factors to biodegrade the toxin have not been investigated. In this study, the biodegrading characteristics of strain YF1 against MC-LR were assessed under diverse environmental factors, including temperature (20, 30 or 40 °C), pH (5, 7 or 9) and MC-LR concentration (1, 3 or 5 µg/mL). Data obtained from the single-factor experiment indicated that MC-LR biodegradation by strain YF1 was temperature-, pH- and MC-LR-concentration-dependent, and the maximal biodegradation rate occurred at 5 µg/mL/h. Proposing Box-Behnken Design in response surface methodology, the influence of the three environmental factors on the biodegradation efficiency of MC-LR using strain YF1 was determined. A 17-run experiment was generated and carried out, including five replications performed at the center point. The ANOVA analysis demonstrated that the model was significant, and the model prediction of MC-LR biodegradation was also validated with the experimental data. The quadratic statistical model was established to predict the interactive effects of the environmental factors on MC-LR biodegradation efficiency and to optimize the controlling parameters. The optimal conditions for MC-LR biodegradation were observed at 30 °C, pH 7 and 3 µg/mL MC-LR, with a biodegradation efficiency of 100% after 60 min. The determination of the optimal environmental factors will help to unveil the detailed biodegradation mechanism of MC-LR by strain YF1 and to apply it into the practice of eliminating MC-LR from the environment.

Exposure to microcystin-LR in tropical reservoirs for water supply poses high risks for children and adults

While the presence of microcystin-LR (MC-LR) in raw water from eutrophic reservoirs poses human health concerns, the risks associated with the ingestion of MC-LR in drinking water are not fully elucidated. We used a time series of MC-LR in raw water from tropical urban reservoirs in Brazil to estimate the hazard quotients (HQs) for non-carcinogenic health effects and the potential ingestion of MC-LR through drinking water. We considered scenarios of MC-LR removal in the drinking water treatment plants (DWTPs) of two supply systems (Cascata and Guarapiranga). The former uses coagulation/flocculation/sedimentation/filtration/disinfection, while the latter has an additional step of membrane ultrafiltration, with contrasting expected MC-LR removal efficiencies. We considered reference values for infants (0.30 μg L^-1), children/adults (1.60 μg L^-1), or the population in general (1.0 μg L^-1). For most scenarios for Cascata, the 95% upper confidence level of the HQ indicated high risks of exposure for the population (HQ > 1), particularly for infants (HQ = 30.910). The water treatment in Cascata was associated to the potential exposure to MC-LR due to its limited removal capacity, with up to 263 days/year with MC-LR above threshold values. The Guarapiranga system had the lowest MC-LR in the raw water as well as higher expected removal efficiencies in the DWTP, resulting in negligible risks. We reinforce the importance of integrating raw water quality characteristics and treatment technologies to reduce the risks of exposure to MC-LR, especially for vulnerable population groups. Our results can serve as a starting point for risk management strategies to minimize cases of MC-LR intoxication in Brazil and other developing countries.

Comprehensive and functional analyses reveal the genomic diversity and potential toxicity of Microcystis

Microcystis is a cyanobacteria that is widely distributed across the world. It has attracted great attention because it produces the hepatotoxin microcystin (MC) that can inhibit eukaryotic protein phosphatases and pose a great risk to animal and human health. Due to the high diversity of morphospecies and genomes, it is still difficult to classify Microcystis species. In this study, we investigated the pangenome of 23 Microcystis strains to detect the genetic diversity and evolutionary dynamics. Microcystis revealed an open pangenome containing 22,009 gene families and exhibited different functional constraints. The core-genome phylogenetic analysis accurately differentiated the toxic and nontoxic strains and could be used as a taxonomic standard at the genetic level. We also investigated the functions of HGT events, of which were mostly conferred from cyanobacteria and closely related species. In order to detect the potential toxicity of Microcystis, we searched and characterized MC biosynthetic gene clusters and other secondary metabolite gene clusters. Our work provides insights into the genetic diversity, evolutionary dynamics, and potential toxicity of Microcystis, which could benefit the species classification and development of new methods for drinking water quality control and management of bloom formation in the future.