Impacts of Hydrogen Peroxide and Copper Sulfate on the Control of Microcystis aeruginosa and MC-LR and the Inhibition of MC-LR Degrading Bacterium Bacillus sp

Field and laboratory studies of fluorescence-based technologies for real-time tracking of cyanobacterial cell lysis and potential microcystins release

Elevated levels of dissolved microcystins (MCs) in source water due to rapid cell lysis of harmful cyanobacterial blooms may pose serious challenges for drinking water treatment. Catastrophic cell lysis can result from outbreaks of naturally-occurring cyanophages - as documented in Lake Erie during the Toledo water crisis of 2014 and in 2019, or through the application of algaecides or water treatment chemicals. Real-time detection of cyanobacterial cell lysis in source water would provide a valuable tool for drinking water plant and reservoir managers. In this study we explored two real-time fluorescence-based devices, PhycoSens and PhycoLA, that can detect unbound phycocyanin (uPC) as a potential indication of cell lysis and MCs release. The PhycoSens was deployed at the Low Service pump station of the City of Toledo Lake Erie drinking water treatment plant from July 15 to October 19, 2022 during the annual cyanobacteria bloom season. It measured major algal groups and uPC in incoming lake water at 15-min intervals during cyanobacteria dominant and senescence periods. Intermittent uPC detections from the PhycoSens over a three-month period coincided with periods of increasing proportions of extracellular MCs relative to total (intracellular and extracellular) MCs, indicating potential for uPC use as an indicator of cyanobacterial cell integrity. Following exposures of laboratory-cultured MCs-producing Microcystis aeruginosa NIES-298 (120 μg chlorophyll/L) to cyanophage Ma-LMM01, copper sulfate (0.5 and 1 mg Cu/L), sodium carbonate peroxyhydrate (PAK® 27, 6.7 and 10 mg H2O2/L), and potassium permanganate (2.5 and 4 mg/L), appearance of uPC coincided with elevated fractions of extracellular MCs. The PhycoLA was used to monitor batch samples collected daily from Lake Erie water exposed to algaecides in the laboratory. Concurrence of uPC signal and surge of dissolved MCs was observed following 24-h exposures to copper sulfate and PAK 27. Overall results indicate the appearance of uPC is a useful indicator of the onset of cyanobacterial cell lysis and the release of MCs when MCs are present.

Ecotoxicology and geostatistical techniques employed in subtropical reservoirs sediments after decades of copper sulfate application

Spatial distribution linked to geostatistical techniques contributes to sum up information into an easier-to-comprehend knowledge. This study compares copper spatial distribution in surface sediments and subsequent categorization according to its toxicological potential in two reservoirs, Rio Grande (RG) and Itupararanga (ITU) (São Paulo-Brazil), where copper sulfate is applied and not applied, respectively. Sediments from 47 sites in RG and 52 sites in ITU were collected, and then, copper concentrations were interpolated using geostatistical techniques (kriging). The resulting sediment distributions were classified in categories based on sediment quality guides: threshold effect level and probable effect level; regional reference values (RRVs) and enrichment factor (EF). Copper presented a heterogenic distribution and higher concentrations in RG (2283.00 ± 1308.75 mg/kg) especially on the upstream downstream, associated with algicide application as well as the sediment grain size, contrary to ITU (21.81 ± 8.28 mg/kg) where a no-clear pattern of distribution was observed. Sediments in RG are predominantly categorized as "Very Bad", whereas sediments in ITU are mainly categorized as "Good", showing values higher than RRV. The classification is supported by the EF categorization, which in RG is primarily categorized as "Very High" contrasting to ITU classified as "Absent/Very Low". Copper total stock in superficial sediment estimated for RG is 4515.35 Ton of Cu and for ITU is 27.45 Ton of Cu.

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.

Compounds to mitigate cyanobacterial blooms affect growth and toxicity of Microcystis aeruginosa

Numerous products and techniques are used to combat harmful cyanobacterial blooms in lakes. In this study, we tested nine products, the phosphate binders Phoslock® and Aqual-P^TM, the coagulant chitosan, the phosphorus binder and coagulant aluminum salts (aluminum sulphate and sodium aluminate), the copper-based algicides SeClear, Captain® XTR and CuSO₄·5H₂O, the antibiotic Streptomycin and the oxidant hydrogen peroxide (H₂O₂) on their efficiency to manage the cyanobacterium Microcystis aeruginosa (M. aeruginosa). To this end, 7 days of laboratory experiments were conducted and effects were determined on chlorophyll-a, photosystem II efficiency (PSII), soluble reactive phosphorus (SRP) and intracellular and extracellular microcystin (MC) concentrations. The algicides, chitosan and H₂O₂ were the most powerful in reducing cyanobacteria biomass. Biomass reductions compared to the controls yielded: Chitosan (99.8%) > Hydrogen peroxide (99.6%) > Captain XTR (98.2%) > SeClear (98.1%) > CuSO₄·5H₂O (97.8%) > Streptomycin (86.6%) > Phoslock® (42.6%) > Aqual-P^TM (28.4%) > alum (5.5%). Compounds that caused the largest reductions in biomass also strongly lowered photosystem II efficiency, while the other compounds (Phoslock®, Aqual-P^TM, aluminum salts) had no effect on PSII, but strongly reduced SRP. Intracellular MC concentration followed the biomass patterns, extracellular MC was generally lower at higher doses of algicides, chitosan and H₂O₂ after one week. Recovery of PSII was observed in most algicides and chitosan, but not at the highest doses of SeClear and in all streptomycin treatments. Our results revealed that M. aeruginosa can be killed rapidly using several compounds, that in some treatments already signs of recovery occurred within one week. P fixatives are efficient in reducing SRP, and thus acting via resource suppression, which potentially may provide an addition to fast-acting algicides that kill most of the cells, but allow rapid regrowth as sufficient nutrients remain.

Monitoring and control methods of harmful algal blooms in Chinese freshwater system: a review

Harmful algal blooms (HABs) are a worldwide problem with substantial adverse effects on the aquatic environment as well as human health, which have prompted researchers to study measures to stem and control them. Meanwhile, it is key to research and develop monitoring methods to establish early warning HABs. However, both the current monitoring methods and control methods have some shortcomings, making the field application limited. Thus, we need to improve current approaches for monitoring and controlling HABs efficiently. Based on the freshwater system features in China, we review various monitoring and control methods of HABs, summarize and discuss the problems with these methods, and propose the future development direction of monitoring and control HABs. Finally, we envision that it can combine physical, chemical, and biological methods to inhibit HAB expansion in the future, complementing each other with advantages. Further, we promise to establish a long-term strategy of controlling HABs with various algicidal bacteria co-cultivate for field applications in China. Efforts in studying algicidal bacteria must be increased to better control HABs and mitigate the risks of aquatic ecosystems and human health in China.

Innovative method of utilising hydrogen peroxide for source water management of cyanobacteria

The treatment and control of cyanobacterial blooms using copper-based algaecides in water reservoirs have historically been used; however, due to the adverse impact of copper on the environment, water authorities have been researching and studying new and innovative ways to control cyanobacterial blooms. Hydrogen peroxide has been investigated as an environmentally friendly alternative, and this research aims to determine the impact of water quality on its effectiveness based on the decay characteristics in different water samples. Natural water samples from South Australian reservoirs and river were used to evaluate hydrogen peroxide decomposition and provide a better strategy for water operators in using it as an algaecide. Our experiments show the dependency of hydrogen peroxide decomposition not only on water quality but also on the initial hydrogen peroxide dose. A higher initial hydrogen peroxide dose can trigger the increase of pH, leading to increased consumption of hydrogen peroxide. In addition, the hydrogen peroxide decomposition is significantly accelerated with the rise of copper concentration in water samples. Moreover, it is found that UV light can also affect the decomposition rate of hydrogen peroxide. The hydrogen peroxide decay is more significant under UV light for the samples with lower hydrogen peroxide concentrations. Our study also shows the impact of dissolved organic carbon (DOC) on hydrogen peroxide decomposition is not substantial. The study also presents a modelling method to optimise hydrogen peroxide application based on water quality characteristics. Our findings can provide knowledge for the water industry to produce a suitable model which can be used to optimise the application of hydrogen peroxide for the control of cyanobacteria.

Field evaluation of seven products to control cyanobacterial blooms in aquaculture

Harmful algal blooms negatively impact water quality in hypereutrophic systems that are common in aquaculture. However, few algaecides are approved for use in food-fish aquaculture. This study assessed the effectiveness of seven products, including hydrogen peroxide (as a concentrated liquid or in granular form (PAK-27)), peracetic acid (as VigorOx SP-15 and Peraclean), copper (as copper sulfate in unchelated (powder) or chelated (Captain) forms), and a clay-based product (as Phoslock) on phytoplankton (including cyanobacteria) and zooplankton biomass. Each product was tested in a 14-day laboratory and 35-day field experiment to assess their short- and long-term performance. Although some products (i.e., copper-based and liquid hydrogen peroxide) quickly reduced phytoplankton, effects were short-lived given that chlorophyll concentrations returned to starting concentrations within 21 days. In contrast, all but one product (i.e., concentrated liquid hydrogen peroxide) maintained low phycocyanin concentrations for 35 days. Zooplankton biomass trends showed large, negative effects for most algaecides; however, zooplankton rebounded for most treatments except for copper-based products. In general, copper-based products remain the most efficient and cheapest choice to reduce total phytoplankton biomass in aquaculture systems. However, peracetic acid-based products effectively and quickly reduced cyanobacteria while having marginal effects on beneficial algae and zooplankton. Such algaecides could be effective alternatives to copper-based products for aquaculture farmers.

Combined impact of silver nanoparticles and chlorine on the cell integrity and toxin release of Microcystis aeruginosa

Silver nanoparticles (AgNPs) have shown to be toxic to freshwater cyanobacterial species, and sodium hypochlorite (NaOCl) is a common oxidant for the treatment of cyanobacterial cells. AgNPs have a high possibility of co-existing with the cyanobacterial cells in the aqueous environments leading to its exposure to NaOCl during water treatment; however, their combined effects on the cyanobacterial cells are largely undocumented. This work compares the individual and combined effect of AgNP and NaOCl on the integrity and toxin (microcystins) release of Microcystis aeruginosa at varying levels. The results show that the AgNP (0.2-0.6 mg/L) alone has negligible effects on the cell lysis, while NaOCl alone shows concentration-dependent (0.2 < 0.4 < 0.6 mg/L) rupturing of cells. In contrast, the AgNP + NaOCl (0.2-0.6 mg/L) samples show increasing loss in cell integrity at higher AgNP (0.4 and 0.6 mg/L) levels than the NaOCl only samples. NaOCl exposure results in increasing dissolution of AgNPs with time, releasing silver ions (Ag⁺), affecting its size and morphology. The cell-associated total Ag declines over time with an increase in NaOCl levels, maybe due to increasing cell-lysis or NaOCl induced oxidative dissolution of AgNPs. The cell-associated total Ag and released Ag⁺ possibly weaken the cellular membrane, thus assisting NaOCl in faster cell-lysis. The combined exposure of AgNP and NaOCl also results in a higher release of toxin from the cells. This work collectively reveals that the AgNPs combined with NaOCl can enhance the cell lysis and release of toxins.

Growth inhibition of harmful algae using TiO2-embedded expanded polystyrene balls in the hypereutrophic stream

TiO₂-embedded expanded polystyrene (TiO₂EPS) balls were produced in large quantities using continuous manufacturing plants and four processes (i.e., fixing-coating-freeze drying-air drying). Two mesocosms [i.e., a photocatalytic zone (PZ) vs. a control zone (CZ)] and in-situ real-time monitoring device were installed to monitor the water quality within the hypereutrophic stream and to elucidate the long-term effect of TiO₂EPS balls on the growth inhibition of harmful algae for two years (i.e., 2016-2017). The difference in the concentrations of both Chl-a and phycocyanin between CZ and PZ was temporally variable and was significant from August to October with higher solar irradiation levels. Although the effective depth of TiO₂EPS balls varied as a complex function of the photocatalytic reactions of TiO₂EPS balls and various environmental factors, the photooxidation effect of TiO₂EPS balls decreased with the increase in water depth and the effective water depth for growth inhibition was less than 0.5 m. Compare to bimodal distributions in concentrations of both Chl-a and phycocyanin in CZ, both shifted and lowered peaks were mainly due to the photocatalytic degradation and irradiation shading under natural solar irradiation by applying TiO₂EPS balls in hypereutrophic water body. Consequently, the TiO₂EPS balls developed in this study can prevent both growth and reproduction of harmful algae in hypereutrophic water body, regardless of the environmental factors.

Evaluating the harvesting efficiency of inorganic coagulants on native microalgal consortium enriched with human urine

Flocculation is a common technique to harvest microalgae, where the negatively charged algal cells coalesce together to form larger flocs that settle under gravity. Although several inorganic flocculants have been applied for algal biomass recovery, the dosage varies depending on the algal strain-specific features. Thus, the selection of inorganic coagulant that can be applied at a low dosage for achieving the maximal biomass recovery under normal physiological conditions is necessary. The present study analyses the influence of different inorganic flocculants like ferric chloride (FeCl₃), alum, calcium hydroxide, ferrous sulphate and copper sulphate on the biomass removal efficiency of a mixed microalgal consortium isolated from the open ponds of the National Institute of Technology Rourkela and further enriched with diluted human urine. Flocculation experiments were carried out with varying coagulant dosages, pH between 7.5 and 7.8, and 0.5 g L^-1 algal concentration. The results revealed that FeCl₃ at the dosage of 0.05 g L^-1 and KAl(SO₄)₂ with the dosage of 0.04 g L^-1 could be utilized to achieve the biomass recovery efficiency of 99.5% and 97.9%, respectively, within a duration of 5 min. An economic evaluation of the harvesting process showed KAl(SO₄)₂ to be the cheapest coagulant that could be feasibly used to recover algae at a large scale.

Effect of hydrogen peroxide on Microcystic aeruginosa: Role of cytochromes P450

Cyanobacterial bloom has been rising as a worldwide issue owing to its adverse effects to water quality and ecological health. To solve this problem, hydrogen peroxide (H₂O₂) has been considered as a potential algaecide because no by-products are generated after treatment and because it kills cyanobacteria selectively. In addition, cytochromes P450 (CYPs) was reported to be related with H₂O₂, but the roles of CYPs in the regulation of H₂O₂ in cyanobacteria have yet to be investigated. In this study, the CYPs suicide inhibitor 1-aminobenzotriazole (ABT) was added to the representative cyanobacteria Microcystis aeruginosa (M. aeruginosa) exposed to H₂O₂. The results showed that CYPs mediates the effects of H₂O₂ on M. aeruginosa. To be exact, the addition of ABT induced greater inhibitory effects on the growth and higher reactive oxygen species levels in M. aeruginosa comparing to those treated with H₂O₂ alone. At the same time, photosynthetic parameters significantly decreased, and the content of extracellular microcystins (MCs) increased but the total MCs decreased due to the combined effect of H₂O₂ and ABT. ABT also intensified the aggregation of Fe, which might explain the effects on photosynthesis and synthesis of MCs. Furthermore, the transcriptional levels of MCs-synthesis genes (mcyA and mcyD) decreased but MCs-release gene (mcyH) increased, and photosynthetic genes (psaB, psbD1 and rbcL) decreased, which confirmed the effects on the MC production/release and electron transport of photosynthesis, respectively. In summary, this study illuminated the mediation role of CYPs in the adverse effects on M. aeruginosa induced by H₂O₂, thus providing new theoretical basis for the explanation of H₂O₂ as potential algaecide.

Impact of copper sulfate application at an urban Brazilian reservoir: A geostatistical and ecotoxicological approach

A landscape ecotoxicology approach was used to assess the spatial distribution of copper in the recent bottom sediment (surficial sediment) of a Brazilian subtropical reservoir (the Guarapiranga reservoir) and its potential ecotoxicological impacts on the reservoir ecosystem and the local society. We discuss the policies and procedures that have been employed for the management of this reservoir over the past four decades. Spatial heterogeneity in the reservoir was evaluated by means of sampling design and statistical analysis based on kriging spatial interpolation. The sediment copper concentrations have been converted into qualitative categories in order to interpret the reservoir quality and the impacts of management policies. This conversion followed the Canadian Water Framework Directive (WFD) ecotoxicological concentration levels approach, employing sediment quality guidelines (SQGs). The SQG values were applied as the copper concentration thresholds for quantitative-qualitative conversion of data for the surficial sediment of the Guarapiranga. The SQGs used were as follows: a) interim sediment quality guideline (ISQG), b) probable effect level (PEL), and c) regional reference value (RRV). The quantitative results showed that the spatial distribution of copper in the recent bottom sediment reflected the reservoir's management policy and the copper application protocol, and that the copper concentrations varied considerably, ranging from virtually-zero to in excess of 3g_copper/kg_ds. The qualitative results demonstrated that the recent bottom sediment was predominantly in a bad or very bad condition, and could therefore have impacts on the local society and the ecosystem. It could be concluded that the management policy for this reservoir was mainly determined by the desire to minimize short-term costs, disregarding long-term socioeconomic and environmental consequences.