Stability of microcystins from cyanobacteria--IV. Effect of chlorination on decomposition

Unlocking the potential of bacterioplankton-mediated microcystin degradation and removal: A bibliometric analysis of sustainable water treatment strategies

Microcystins (MCs) constitute a significant threat to human and environmental health, urging the development of effective removal methods for these toxins. In this review, we explore the potential of MC-degrading bacteria as a solution for the removal of MCs from water. The review insights into the mechanisms of action employed by these bacteria, elucidating their ability to degrade and thus remove MCs. After, the review points out the influence of the structural conformation of MCs on their removal, particularly their stability at different water depths within different water bodies. Then, we review the crucial role played by the production of MCs in ensuring the survival and safeguarding of the enzymatic activities of Microcystis cells. This justifies the need for developing effective and sustainable methods for removing MCs from aquatic ecosystems, given their critical ecological function and potential toxicity to humans and animals. Thereafter, challenges and limitations associated with using MC-degrading bacteria in water treatment are discussed, emphasizing the need for further research to optimize the selection of bacterial strains used for MCs biodegradation. The interaction of MCs-degrading bacteria with sediment particles is also crucial for their toxin removal potential and its efficiency. By presenting critical information, this review is a valuable resource for researchers, policymakers, and stakeholders involved in developing sustainable and practical approaches to remove MCs. Our review highlights the potential of various applications of MC-degrading bacteria, including multi-soil-layering (MSL) technologies. It emphasizes the need for ongoing research to optimize the utilization of MC-degrading bacteria in water treatment, ultimately ensuring the safety and quality of water sources. Moreover, this review highlights the value of bibliometric analyses in revealing research gaps and trends, providing detailed insights for further investigations. Specifically, we discuss the importance of employing advanced genomics, especially combining various OMICS approaches to identify and optimize the potential of MCs-degrading bacteria.

Microcystins in water containers used in the home: A review of their potential health effects

Cyanobacteria produce toxins that are harmful to humans. They are found mostly in surface water, which is the main water source for drinking water before treatment. However, most of the water treatment plants are inadequate to treat toxins such as microcystins in raw water sources from contaminated surface water that has blooming and/or decaying cyanobacteria. Microcystins are harmful toxins produced by cyanobacteria that cause both acute and chronic health problems in humans. However, little is known about microcystins in water containers at the household level. This article therefore focuses on a review of the effects of microcystins in drinking water containers at the household level, including types of microcystins, their health effects, and cases reported in both animals and humans. Therefore, there is a need to develop the water quality management for cyanobacteria toxins, particularly microcystins in household containers.

Chlorination of microcystin-LR in natural water: Kinetics, transformation products, and genotoxicity

Microcystin-LR (MC-LR), a type of cyanotoxin commonly found in natural water bodies (sources of drinking water), poses a threat to human health due to its high toxicity. It is essential to successfully remove this cyanotoxin from drinking water sources. In this study, chlorine was used to oxidize MC-LR in Milli-Q water (MQ) (control test) and natural water collected from Lake Longhu (LLW) as a drinking water source. The removal efficiency, proposed transformation pathways, and genotoxicity were investigated. In the chlorine dose range investigated (4.0 mg L^-1 - 8.0 mg L^-1), the apparent second-order rate constants for MC-LR chlorination varied from 21.3 M^-1s^-1 to 31.9 M^-1s^-1 in MQ, higher than that in LLW (9.06 M^-1s^-1 to 17.7 M^-1s^-1) due to a faster chlorine decay attributed to the water matrix (e.g., natural organic matter) of LLW. Eleven transformation products (TPs) of MC-LR were identified in the two waters. The conjugated diene moieties and benzene ring of Adda moiety (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid), and the double bond of Mdha moiety (N-methyldehydroalanine) were the major susceptible reaction sites. Attacking unsaturated bonds by hydroxyl and chlorine radicals to generate monochloro-hydroxy-MC-LR was the primary initial transformation pathway, followed by nucleophilic substitution, dehydration, and cleavage in MC-LR. Chlorine substitution on the benzene ring was also observed. Based on the bacterial reverse-mutation assay (Ames assay), TPs in treated natural water did not induce genotoxicity/mutagenicity. These findings shed light on the role of chlorination in controlling the risk of cyanotoxins in drinking water treatment plants.

Mechanism for the Potential Inhibition Effect of Microcystin-LR Disinfectant By-Products on Protein Phosphatase 2A

The secondary contamination of microcystin disinfection by-products (MC-DBPs) is of concern due to the residual structure similar to their original toxin. Based on identification and preparation, the potential inhibition effect of typical MCLR-DBPs (associated with the oxidation of Adda⁵) on PP2A was confirmed in the sequence of MCLR > P1 > P4 > P3 ≈ P2 > P7 ≈ P6 ≈ P5 > P8. To elucidate the molecular mechanism underlying the inhibition effect, the interaction models for typical MCLR-DBPs and PP2A were constructed using a modeling-based-on-ligand-similarity approach, and the candidate interaction parameters between typical MCLR-DBPs and PP2A were obtained by molecular docking. By analyzing the correlation between inhibition data and candidate interaction parameters, the key interaction parameters were filtered as hydrogen bonds "Adda⁵"←Asn₁₁₇, "Adda⁵"←His₁₁₈, MeAsp³←Arg₈₉, Arg⁴←Arg₂₁₄, Arg⁴→Pro₂₁₃; ionic bonds Glu⁶-Arg₈₉, Asp₈₅-Mn₁²⁺, Asp₅₇-Mn₂²⁺; and metal bonds Glu⁶-Mn₁²⁺, Glu⁶-Mn₂²⁺. With the gradual intensification of chlorination, Adda⁵ was destroyed to varying degrees. The key interactions changed correspondingly, resulting in the discrepant inhibition effects of typical MCLR-DBPs on PP2A.

The Use of Sodium Hypochlorite at Point-of-Use to Remove Microcystins from Water Containers

Most conventional water treatment plants are not sufficiently equipped to treat both intracellular and extracellular Microcystins in drinking water. However, the effectiveness of sodium hypochlorite in removing Microcystin in containers at the point-of-use is not yet known. This study aimed to assess point-of-use water container treatment using bleach or sodium hypochlorite (NaOCl) and to assess the health problems associated with microcystins. Thirty-nine percent (29 of 74) of the total selected households were randomly selected to receive and treat their stored container water with sodium hypochlorite. The level of microcystin in the container water was measured after 30 min of contact with sodium hypochlorite. Microcystin concentrations in both the blooming and decaying seasons were higher (mean 1.10, 95% CI 0.46–1.67 µg/L and mean 1.14, 95% CI 0.65–1.63 µg/L, respectively) than the acceptable limit of 1 µg/L in households that did not treat their water with NaOCl, whilst in those that did, there was a significant reduction in the microcystin concentration (mean 0.07, 95% CI 0.00–0.16 µg/L and mean 0.18, 95% CI 0.00–0.45 µg/L). In conclusion, sodium hypochlorite treatment decreased microcystin s to an acceptable level and reduced the related health problems.

Fenton-based technologies as efficient advanced oxidation processes for microcystin-LR degradation

In recent years, the safety and ecology threat of cyanobacterial burst has drawn wide concern, especially the release of toxic microcystin-LR (MC-LR). To break through the bottleneck of uncomplete MC-LR degradation by conventional physical-chemistry methods, Fenton-based advanced oxidation processes (AOPs) developed rapidly due to striking degradation efficiency through the potent hydroxyl radicals (HO·) oxidation. Herein, a comprehensive overview is presented on the recent achievements of the various Fenton-based technologies (including conventional Fenton, photo-Fenton, electro-Fenton, ozone-Fenton and sono-Fenton) for MC-LR degradation. In particular, the comparisons between various Fenton-based technologies about advantages and drawbacks are discussed. Based on analyzing the degradation intermediates and pathways, the destruction of Adda chain via hydroxylation was confirmed to be essential for detoxification of MC-LR. Roles of influencing factors such as MC-LR initial concentration, dosages of the catalyst and oxidant, environment alkalinity, natural organic matters (NOMs) as well as other inorganic ions are specifically summarized. This Review also gave special emphasis on technique optimization trends for Fenton application of MC-LR degradation, as well as key challenges and future opportunities in this fast developing field.

Microcystin-LR degradation kinetics during chlorination: Role of water quality conditions

Microcystin-LR (MCLR) produced during certain cyanobacteria blooms can contaminate drinking water sources and pose a threat to public health. Previous studies of MCLR degradation by free chlorine may have artifacts from using strong reducing agents to quench chlorination reactions, and they also have not explored the influence of water quality characteristics such as pH, alkalinity, temperature and dissolved organic matter (DOM). Using a novel quencher, 1,3,5-trimethoxybenzene (TMB), the apparent MCLR degradation rate constants were found to be higher than those obtained with thiosulfate (S₂O₃^2-), a traditionally used strong reducing quencher. Thiosulfate converted N-chlorinated MCLR degradation products back to the parent MCLR, thereby underestimating MCLR loss over time. The second-order rate constants for HOCl (k_HOCl) and OCl^- (k_OCl-) during chlorination of MCLR were determined to be 72 ± 13 and 28 ± 1.8 M^-1s^-1, respectively, allowing for determination of the apparent MCLR rate constants (k_app,MCLR) for any known pH condition. The MCLR reaction with free chlorine was strongly affected by temperature and the presence of DOM, while changes in ionic strength and alkalinity had little effect. Free chlorine in the presence of DOM, originating from both terrestrial and microbial sources, exhibited two-stage decay. The initial chlorine demand in the first 15 s of reaction can be determined by the dissolved organic carbon (DOC) concentration (initial chlorine demand = 1.8 × DOC), and the second-order rate constants for the later slower decay correlated well with SUVA₂₅₄ (k_app,DOM = 0.73 × SUVA₂₅₄ - 0.41). The results yielded a practical model to predict the decay of MCLR during chlorination of waters with varied water quality characteristics.

The chemodiversity of algal dissolved organic matter from lysed Microcystis aeruginosa cells and its ability to form disinfection by-products during chlorination

Algal-derived dissolved organic matter (ADOM) originating from lysed Microcystis aeruginosa cells was investigated as precursor material to form disinfection by-products upon disinfection with free chlorine. Non-targeted ultrahigh resolution 12 T negative mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed high molecular diversity in solid-phase extracted and ionizable components of Microcystis aeruginosa ADOM. The toxin microcystin LR was effectively degraded by free chlorine, which was expected. However, we found a high diversity of disinfection by-products associated with the addition of free chlorine to the water-soluble and solid-phase extractable fraction of ADOM and of double-bond moieties in abundant and known unsaturated fatty acids. Aromatic DOM precursors were absent from known metabolites of Microcystis aeruginosa and no evidence for aromatic disinfection by-products (DBPs) was found, despite N-containing compounds. A large diversification of N-containing molecular formulas was observed after chlorination, which seems indicative for the breakdown and oxidation of larger peptides. Additionally, a diverse group of N-compounds with presumed chloramine functional groups was observed. This study highlights the importance to evaluate ADOM and its ability to form different DBPs when compared to allochthonous or terrestrially-derived DOM.

Elimination kinetics and detoxification mechanisms of microcystin-LR during UV/Chlorine process

Microcystin-LR (MC-LR), a toxin produced by cyanobacteria, is very toxic and poses a threat to public health when entering water treatment works. In this study, UV/chlorine process, as an advanced oxidation process (AOP), has been demonstrated for effective elimination of MC-LR levels and associated toxicity. At a chlorine dose of 3.0 mg L^-1 and UV fluence of 125 mJ cm^-2, MC-LR (initial concentration 1.0 μM) was reduced by 92.5%, which was much higher than 20.3% removal under UV irradiation alone and 65.1% removal during dark chlorination. Enhanced degradation was attributed by hydroxyl radicals (HO) and reactive chlorine species (RCS), mainly Cl₂^- and ClO. Increasing chlorine doses or lowering pH favored MC-LR removal. Increased bicarbonate and natural organic matter concentrations inhibited MC-LR removal, but bromide ions enhanced MC-LR removal instead. MC-LR elimination rates in natural waters were roughly two times smaller than those in ultrapure water. The reactive radicals promoted hydroxylation of both diene of Adda moiety and double bond of Mdha moiety in MC-LR. UV exposure enhanced the dechlorination of chloro-MC-LR via the cleavage of CCl bond. The toxicity was evaluated by a protein phosphatase (PP2A) inhibition assay. At a chlorine dose of 3.0 mg L^-1 and UV fluence of 125 mJ cm^-2, the toxicity of the treated water was reduced by 75.0%, which was also higher than 25.7% and 46.7% removal under UV irradiation alone and during dark chlorination, respectively. These results highlight UV/chlorine is an efficient AOP for MC-LR degradation and detoxification.

Susceptibility of the Algal Toxin Microcystin-LR to UV/Chlorine Process: Comparison with Chlorination

Microcystin-LR (MC-LR), an algal toxin (cyanotoxin) common in sources of drinking water, poses a major human health hazard due to its high toxicity. In this study, UV/chlorine was evaluated as a potentially practical and effective process for the degradation of MC-LR. Via mass spectrometry analysis, fewer chlorinated-MC-LR products were detected with UV/chlorine treatment than with chlorination, and a transformation pathway for MC-LR by UV/chlorine was proposed. Different degrees of rapid degradation of MC-LR were observed with varying pH (6-10.4), oxidant dosage (0.5-3 mg L^-1), natural organic matter (0-7 mg L^-1), and natural water sources. In contrast to the formation of primarily chloroform and dichloroacetic acid in deionized water where MC-LR serves as the only carbon source, additional chlorinated disinfection byproducts were produced when sand filtered natural water was used as a background matrix. The UV/chlorine treated samples also showed quantitatively less cytotoxicity in vitro in HepaRG human liver cell line tests than chlorination treated samples. Following 16 min (96 mJ cm^-2) of UV irradiation combined with 1.5 mg L^-1 chlorine treatment, the cell viability of the samples increased from 80% after exposure to 1 mg L^-1 MC-LR to 90%, while chlorination treatment evidenced no reduction in cytotoxicity with the same reaction time.

Adsorptive removal of microcystin-LR from surface and wastewater using tyre-based powdered activated carbon: Kinetics and isotherms

Microcystin LR (MC-LR) is a highly toxic compound and it is known for its adverse health effect on both humans and animals. Due to the ineffectiveness of conventional water treatments methods, for the past decades, researchers have been developing cost-effective ways of removing MC-LR from water bodies. This study reports the application of powdered activated carbon (PAC) obtained from the waste tyre for the removal of MC-LR. The choice of the adsorbent was chosen due to its attractive properties. The prepared tyre-based PAC was found to have the large surface area (1111 m² g^-1). The detection of MC-LR was achieved using high performance liquid chromatography (HPLC) coupled with a PDA detector. The experimental parameters (such as optimum pH, dosage and contact time) affecting the removal of MC-LR using tyre based-powdered activated carbon were optimized using response surface methodology (RSM). Maximum removal of MC-LR was achieved under the following optimum conditions; sample pH 4, carbon dosage concentration 10,000 mg L^-1 and contact time of 34 min. Under optimum conditions, kinetic studies and adsorption isotherms reflected better fit for pseudo-second-order rate and Langmuir isotherm model, respectively. The optimized method was applied for the removal of MC-LR in wastewater sample. The effluent and influent sample contained initial concentrations ranging from 0.52 to 8.54 μg L^-1 and the removal efficiency was 100%.

Effect of chlorination by-products on the quantitation of microcystins in finished drinking water

Microcystins are toxic peptides that can be produced by cyanobacteria in harmful algal blooms (HABs). Various analytical techniques have been developed to quantify microcystins in drinking water, including liquid chromatography tandem mass spectrometry (LC/MS/MS), enzyme linked immunosorbent assay (ELISA), and oxidative cleavage to produce 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) with detection by LC/MS/MS, the "MMPB method". Both the ELISA and MMPB methods quantify microcystins by detecting a portion of the molecule common to most microcystins. However, there is little research evaluating the effect of microcystin chlorination by-products potentially produced during drinking water treatment on analytical results. To evaluate this potential, chlorinated drinking water samples were fortified with various microcystin congeners in bench-scale studies. The samples were allowed to react, followed by a comparison of microcystin concentrations measured using the three methods. The congener-specific LC/MS/MS method selectively quantified microcystins and was not affected by the presence of chlorination by-products. The ELISA results were similar to those obtained by LC/MS/MS for most microcystin congeners, but results deviated for a particular microcystin containing a variable amino acid susceptible to oxidation. The concentrations measured by the MMPB method were at least five-fold higher than the concentrations of microcystin measured by the other methods and demonstrate that detection of MMPB does not necessarily correlate to intact microcystin toxins in finished drinking water.

Analysis of individual and total microcystins in surface water by on-line preconcentration and desalting coupled to liquid chromatography tandem mass spectrometry

A fast and high-throughput method is proposed for the determination of total microcystins (ΣMC) in environmental surface waters. After a 1-h Lemieux-von Rudloff oxidation step to yield the 2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) moiety, samples were quenched, filtered, and directly analyzed. This was achieved via solid phase extraction (SPE) coupled on-line to ultra-high performance liquid chromatography electrospray ionization triple stage quadrupole mass spectrometry. The choice of on-line SPE settings was conducted using experimental designs. Given the matrix complexity of oxidation extracts, the on-line desalting step was found to be a critical parameter to ensure suitable method robustness. The on-line sample loading volume was 5mL, and the wash volume applied for on-line desalting was 3mL. Instrumental analysis was performed in just 8min. The method limit of quantification was 0.5ngL^-1 ΣMC (i.e. 2000 times lower than the current World Health Organization - WHO drinking water guideline). Excellent determination coefficients were observed for matrix-free and matrix-based calibration curves alike, and the linearity range tested spanned∼4 orders of magnitude. Accuracy and intermediate precision did not depend on the spike level and proved satisfactory (in the range of 93-110% and 3-6%, respectively). A thorough assessment of instrumental matrix effects was conducted by comparing standard additions curves in several lake and river oxidation extracts with the matrix-free reference. Regardless of the internal standard used (4-PB or D3-MMPB), instrumental matrix effects were efficiently compensated. The matrix effect that may occur at the earlier sample preparation stage was evaluated separately. While the oxidation step was generally not complete (yield ∼65%), the conversion rates of MCs into MMPB remained within a consistent range of values regardless of matrix type. No significant back-pressure was observed upon consecutive injections of oxidation-based samples, while the instrumental sensitivity remained unaffected. The herein described method could therefore be eligible for future large-scale monitoring surveys. The method was applied to a selection of surface water samples (n=30) collected across the province of Québec, Canada, and the results were compared to those achieved by an individual variant analysis of 8 MC congeners and a commercial ELISA kit.

Cyanobacterial Toxins in Freshwater and Food: Important Sources of Exposure to Humans

A recent ecological study demonstrated a significant association between an increased risk of nonalcoholic liver disease mortality and freshwater cyanobacterial blooms. Moreover, previous epidemiology studies highlighted a relationship between cyanotoxins in drinking water with liver cancer and damage and colorectal cancer. These associations identified cyanobacterial blooms as a global public health and environmental problem, affecting freshwater bodies that are important sources for drinking water, agriculture, and aquafarms. Furthermore, as a result of climate change, it is expected that our freshwater environments will become more favorable for producing harmful blooms that produce various cyanotoxins. Food is an important source of cyanotoxin exposure to humans, but it has been less addressed. This paper synthesizes information from the studies that have investigated cyanotoxins in freshwater and food on a global scale. We also review and summarize the health effects and exposure routes of cyanotoxins and candidates for cyanotoxin treatment methods that can be applied to food.

Chlorine/UV Process for Decomposition and Detoxification of Microcystin-LR

Microcystin-LR (MC-LR) is a potent hepatotoxin that is often associated with blooms of cyanobacteria. Experiments were conducted to evaluate the efficiency of the chlorine/UV process for MC-LR decomposition and detoxification. Chlorinated MC-LR was observed to be more photoactive than MC-LR. LC/MS analyses confirmed that the arginine moiety represented an important reaction site within the MC-LR molecule for conditions of chlorination below the chlorine demand of the molecule. Prechlorination activated MC-LR toward UV254 exposure by increasing the product of the molar absorption coefficient and the quantum yield of chloro-MC-LR, relative to the unchlorinated molecule. This mechanism of decay is fundamentally different than the conventional view of chlorine/UV as an advanced oxidation process. A toxicity assay based on human liver cells indicated MC-LR degradation byproducts in the chlorine/UV process possessed less cytotoxicity than those that resulted from chlorination or UV254 irradiation applied separately. MC-LR decomposition and detoxification in this combined process were more effective at pH 8.5 than at pH 7.5 or 6.5. These results suggest that the chlorine/UV process could represent an effective strategy for control of microcystins and their associated toxicity in drinking water supplies.

Effect of chlorination on the protein phosphatase inhibition activity for several microcystins

Microcystins are of particular concern due to their toxicity to both humans and animals and may be the most prominent cyanotoxin observed in freshwater. Although a number of studies have investigated the fate of microcystins and other algal toxins through drinking water treatment facilities, measurement of their potential for toxic activity after chlorination, a popular form of treatment in the United States, has not been investigated. In this study, six microcystin variants are subjected to chlorine oxidation. The degradation of each microcystin variant is measured by liquid chromatography/mass spectrometry simultaneously with protein phosphatase inhibition (PPI) response over reaction time with chlorine. Results show that inhibition is dependent on the incorporated amino acid residues, their placement within the microcystin structure, as well as pH. This pH dependence may have practical implications to such activities such as drinking water treatment when the pH is usually adjusted to around 8. Namely, at this pH, even with chlorine addition for disinfection, PPI activity may not be totally eliminated even when the initial MYCs are eliminated.

Ozonation degradation of microcystin-LR in aqueous solution: intermediates, byproducts and pathways

The intermediates and byproducts formed during the ozonation of microcystin-LR (MC-LR, m/z = 995.5) and the probable degradation pathway were investigated at different initial molar ratios of ozone to MC-LR ([O3]0/[MC-LR]0). Seven reaction intermediates with m/z ≥ 795.4 were observed by LC/MS, and four of them (m/z = 815.4, 827.3, 853.3 and 855.3) have not been previously reported. Meanwhile, six aldehyde-based byproducts with molecular weights of 30-160 were detected for the first time. Intermediates structures demonstrated that ozone reacted with two sites of MC-LR: the diene bonds in the Adda side chain and the Mdha amino acid in the cyclic structure. The fragment from the Adda side chain oxidative cleavage could be further oxidized to an aldehyde with a molecular weight of 160 at low [O3]0/[MC-LR]0. Meanwhile, the polypeptide structure of MC-LR was difficult to be further oxidized, unless [O3]0/[MC-LR]0 > 10. After further oxidation of the intermediates, five other aldehyde-based byproducts were detected by GC/MS: formaldehyde, acetaldehyde, isovaleraldehyde, glyoxal and methylglyoxal. Formaldehyde, isovaleraldehyde and methylglyoxal were the dominant species. The yields of the aldehydes varied greatly, depending on the value of [O3]0/[MC-LR]0.

Cyanotoxin management and human health risk mitigation in recreational waters

The occurrence and severity of harmful cyanobacterial or blue-green algal blooms (HABs) have increased in recent decades, posing a serious threat of illness to humans. In some countries, water contaminated with cyanotoxins that is used for drinking or haemodialysis has posed a particularly serious risk. However, it is now recognized that recreational exposure to natural toxins by skin contact, accidental swallowing of water or inhalation can also cause a wide range of acute or chronic illnesses. In this review, we focus on the importance of cyanotoxin management in recreational waters. The symptoms related with HAB poisonings, the recommended safety concentrations limit for cyanobacteria and cyanotoxins in such waters, as well as early health hazard indicators of their presence and their monitoring are all discussed. We also present in this review an overview of the methods developed in recent decades for eliminating cyanobacteria and the toxic compounds that they produce.

State of knowledge and concerns on cyanobacterial blooms and cyanotoxins

Cyanobacteria are ubiquitous microorganisms considered as important contributors to the formation of Earth's atmosphere and nitrogen fixation. However, they are also frequently associated with toxic blooms. Indeed, the wide range of hepatotoxins, neurotoxins and dermatotoxins synthesized by these bacteria is a growing environmental and public health concern. This paper provides a state of the art on the occurrence and management of harmful cyanobacterial blooms in surface and drinking water, including economic impacts and research needs. Cyanobacterial blooms usually occur according to a combination of environmental factors e.g., nutrient concentration, water temperature, light intensity, salinity, water movement, stagnation and residence time, as well as several other variables. These environmental variables, in turn, have promoted the evolution and biosynthesis of strain-specific, gene-controlled metabolites (cyanotoxins) that are often harmful to aquatic and terrestrial life, including humans. Cyanotoxins are primarily produced intracellularly during the exponential growth phase. Release of toxins into water can occur during cell death or senescence but can also be due to evolutionary-derived or environmentally-mediated circumstances such as allelopathy or relatively sudden nutrient limitation. Consequently, when cyanobacterial blooms occur in drinking water resources, treatment has to remove both cyanobacteria (avoiding cell lysis and subsequent toxin release) and aqueous cyanotoxins previously released. Cells are usually removed with limited lysis by physical processes such as clarification or membrane filtration. However, aqueous toxins are usually removed by both physical retention, through adsorption on activated carbon or reverse osmosis, and chemical oxidation, through ozonation or chlorination. While the efficient oxidation of the more common cyanotoxins (microcystin, cylindrospermopsin, anatoxin and saxitoxin) has been extensively reported, the chemical and toxicological characterization of their by-products requires further investigation. In addition, future research should also investigate the removal of poorly considered cyanotoxins (β-methylamino-alanine, lyngbyatoxin or aplysiatoxin) as well as the economic impact of blooms.

Cyanotoxins: characteristics, production and degradation routes in drinking water treatment with reference to the situation in Serbia

Cyanobacteria are members of phytoplankton of the surface freshwaters. The accelerated eutrophication of freshwaters, especially reservoirs for drinking water, by human activity has increased the occurrence and intensity of cyanobacterial blooms. They are of concern due to their ability to produce taste and odors compounds, a wide range of toxins, which have a hepatotoxic, neurotoxic, cytotoxic and dermatotoxic behavior, being dangerous to animal and human health. Therefore, the removal of cyanobacteria, without cell lysis, and releasing of intracellular metabolites, would significantly reduce the concentration of these metabolites in the finished drinking water, as a specific aim of the water treatment processes. This review summarizes the existing data on characteristics of the cyanotoxins, their productions in environment and effective treatment processes to remove these toxins from drinking water.

Next generation planar waveguide detection of microcystins in freshwater and cyanobacterial extracts, utilising a novel lysis method for portable sample preparation and analysis

The study details the development of a fully validated, rapid and portable sensor based method for the on-site analysis of microcystins in freshwater samples. The process employs a novel lysis method for the mechanical lysis of cyanobacterial cells, with glass beads and a handheld frother in only 10 min. The assay utilises an innovative planar waveguide device that, via an evanescent wave excites fluorescent probes, for amplification of signal in a competitive immunoassay, using an anti-microcystin monoclonal with cross-reactivity against the most common, and toxic variants. Validation of the assay showed the limit of detection (LOD) to be 0.78 ng mL(-1) and the CCβ to be 1 ng mL(-1). Robustness of the assay was demonstrated by intra- and inter-assay testing. Intra-assay analysis had % C.V.s between 8 and 26% and recoveries between 73 and 101%, with inter-assay analysis demonstrating % C.V.s between 5 and 14% and recoveries between 78 and 91%. Comparison with LC-MS/MS showed a high correlation (R(2)=0.9954) between the calculated concentrations of 5 different Microcystis aeruginosa cultures for total microcystin content. Total microcystin content was ascertained by the individual measurement of free and cell-bound microcystins. Free microcystins can be measured to 1 ng mL(-1), and with a 10-fold concentration step in the intracellular microcystin protocol (which brings the sample within the range of the calibration curve), intracellular pools may be determined to 0.1 ng mL(-1). This allows the determination of microcystins at and below the World Health Organisation (WHO) guideline value of 1 μg L(-1). This sensor represents a major advancement in portable analysis capabilities and has the potential for numerous other applications.

Quantitative variations of intracellular microcystin-LR, -RR and -YR in samples collected from four locations in Hartbeespoort Dam in North West Province (South Africa) during the 2010/2011 summer season

The Hartbeespoort (HBP) Dam is a reservoir used for agricultural, domestic supply of raw potable water and recreational activities in South Africa’s North-West Province. Eutrophication and cyanobacterial blooms have long been a cause of water-quality problems in this reservoir. The most prevalent bloom-forming species is Microcystis aeruginosa, often producing the toxin microcystin, a hepatotoxin which can negatively impact aquatic animal and human health, and poses a problem for potable water supply. Algal samples were collected monthly from four pre-determined sites in the dam during the summer months (December 2010–March 2011). Intracellular microcystins (MCs) were extracted using SPE C₁₈ cartridges, followed by separation, identification and quantification using LC-ESI-MS techniques. Quantitative variation studies of MCs were conducted with respect to MC congener isolated, sampling site and month. Three main MC congeners (MC-RR, -LR and-YR) were isolated, identified and quantified. In addition, three minor MCs (MC-WR, MC-(H₄)YR and (D-Asp³, Dha⁷)MC-RR were also identified, but were not quantified. The MC dominance followed the order MC-RR>MC-LR>MC-YR across all sites and time. The maximum and minimum concentrations were 268 µg/g and 0.14 µg/g DW for MC-RR and MC-YR, respectively, of the total MCs quantified from this study. One-way ANOVA showed that there were no significant differences between average MC concentrations recorded across months (P = 0.62), there was, however, a marginally-significant difference in concentrations among MC congeners (P = 0.06). ANCOVA revealed a highly significant interaction between sites and MC congeners on MC concentration (P < 0.001).

Characterization of the first step involved in enzymatic pathway for microcystin-RR biodegraded by Sphingopyxis sp. USTB-05

Enzymes encoded by genes biodegrading microcystins (MCs) can help reveal the function of genes and biodegradation pathway of MCs. Here the first and important gene (USTB-05-A, 1,008 bp) involved in biodegradation of microcystin-RR (MC-RR) was cloned from Sphingopyxis sp. USTB-05 and firstly expressed in Escherichia coli BL21 (DE3) with an expression vector of pGEX4T-1 successfully. The nucleotide sequences of cloned USTB-05-A possessed 92.5% homology to that of mlA reported in Sphingomonas sp. strain ACM-3962. The deduced amino acid sequences containing the cleavage sites of 26th (alanine) and 27th (leucine) showed 83% identical to that of MlrA. The cell-free extract (CE) of recombinant E. coli BL21 (DE3) containing USTB-05-A had high activity for biodegrading MC-RR. Initial MC-RR of 40 mg L(-1) was completely biodegraded under total protein of 350 mg L(-1) within 0.25 h. A product derived from MC-RR appeared distinctly with the decrease of MC-RR peak on the profile of HPLC. The product (m/z 1056.5) had molecular weight of 18 higher than that of MC-RR (m/z 1038.7). The findings provided the positive evidences that biodegradation of MC-RR began with the breakage of cyclic MC-RR and then it was converted to linear MC-RR as the first product catalyzed by first enzyme of Sphingopyxis sp. USTB-05.

Removal of microcystin-LR from drinking water using a bamboo-based charcoal adsorbent modified with chitosan

A new kind of low-cost syntactic adsorbent from bamboo charcoal and chitosan was developed for the removal of microcystin-LR from drinking water. Removal efficiency was higher for the syntactic adsorbent when the amount of bamboo charcoal was increased. The optimum dose ratio of bamboo charcoal to chitosan was 6:4, and the optimum amount was 15 mg/L; equilibrium time was 6 hr. The adsorption isotherm was non-linear and could be simulated by the Freundlich model (R2 = 0.9337). Adsorption efficiency was strongly affected by pH and natural organic matter (NOM). Removal efficiency was 16% higher at pH 3 than at pH 9. Efficiency rate was reduced by 15% with 25 mg/L NOM (UV254 = 0.089 cm(-1)) in drinking water. This study demonstrated that the bamboo charcoal modified with chitosan can effectively remove microcystin-LR from drinking water.

Assessment of detoxification of microcystin extracts using electrochemical oxidation

Microcystins, cyclic heptapeptide toxins produced by cyanobacteria, possess tumor-promoting activity, which act through inhibition of protein phosphatases 1 and 2A. In this study, the variation in toxicity of microcystins from Microcystis aeruginosa during electrooxidation was assessed using bioassays. The microcystin-LR samples (MCLR) were prepared by crude extracts dissolved in electrolytes, e.g., 0.02 mol L(-1) Na(2)SO(4), 0.02 mol L(-1) Na(2)SO(4) containing 0.5 mmol L(-1) NaCl, and tap water. Electrooxidation was conducted at a current density of 4 mA cm(-2) at room temperature (20-26°C), using Ti/RuO(2) anodes. Toxicological profiles for acute toxic effects (Vibrio fischeri) and genotoxic effects (Vicia faba micronucleus assay and single cell gel electrophoresis assay of mice lymphocytes) were determined for both untreated and treated MCLR samples. Results showed that acute toxicity during treatment was caused mainly by residual oxidants from electrooxidation. The by-products from the degradation of MCLR samples showed very weak acute toxicity to V. fischeri. Before electrooxidation, MCLR samples could induce obvious cell damage to V. faba root tips and mice lymphocytes. Electrooxidation degradation significantly decreased the genotoxicity of MCLR samples until the final by-products showed no toxicity. Thus, electrooxidation can detoxify MCLR samples via degradation processes.

Degradation of microcystin-RR using boron-doped diamond electrode

Microcystins (MCs), produced by blue-green algae, are one of the most common naturally occurring toxins found in natural environment. The presence of MCs in drinking water sources poses a great threat to people's health. In this study, the degradation behavior of microcystin-RR on boron-doped diamond (BDD) electrode was investigated under galvanostatic conditions. Such parameters as reaction time, supporting electrolyte and applied current density were varied in order to determine their effects on this oxidation process. The experimental results revealed the suitability of electrochemical processes employing BDD electrode for removing MC-RR from the solution. However, the efficient removal of MC-RR only occurred in the presence of sodium chloride that acted as redox mediators and the reaction was mainly affected by the chloride concentration (c(NaCl)) and applied current density (I(appl)). Full and quick removal of 0.50 microg/ml MC-RR in solution was achieved when the operating conditions of c(NaCl) and I(appl) were 20mM and 46.3 mA/cm(2), or 35 mM and 18.2 mA/cm(2) respectively. The kinetics for MC-RR degradation followed a pesudo-first order reaction in most cases, indicating the process was under mass transfer control. As a result of its excellent performance, the BDD technology could be considered as a promising alternative to promote the degradation of MC-RR than chlorination in drinking water supplies.

Ms identification of microcystin-LR chlorination by-products

Drinking water disinfection by chlorine is known to reduce concentration of microcystin, but compounds formed are rarely considered. In this work the chlorination of microcystin-LR has been studied by monitoring reactants consumption and reaction products using the linear trap quad-Orbitrap (LTQ-Orbitrap) technology. Microcystin-LR was totally transformed within 2 min, meanwhile chlorine was consumed until 30 min with a rate of 12 mol per mol of toxin. Four new by-products of microcystin-LR were identified as well as their isomers: monochloro-microcystin, monochloro-dihydroxy-microcystin, dichloro-dihydroxy-microcystin and trichloro-hydroxy-microcystin. In addition, four new isomers were also observed, corresponding to the dihydroxy-microcystin already known. Besides, another compound previously observed was identified as monochloro-hydroxy-microcystin.

Oxidation of MC-LR and -RR with chlorine and potassium permanganate: toxicity of the reaction products

Toxin-producing cyanobacteria are abundant in surface waters used as drinking water resources. Microcystins (MC) produced by certain cyanobacteria present acute and chronic toxicity, and their removal in drinking water treatment processes is of increasing concern. Previous studies have demonstrated that chlorine and potassium permanganate are feasible oxidants for the removal of MCs present in drinking water resources, although the oxidation might lead to toxic oxidation products. In this paper, the toxicity of the oxidation products of MC-LR and -RR has been studied using protein phosphatase 1 inhibition assay (PPIA). The HPLC and ELISA analyses correlated with the PPIA results for both toxins. The samples containing the oxidation products were fractionated by HPLC and the toxicity of the fractions was tested with PPIA. The results revealed that protein phosphatase 1 inhibition emerged only from intact MC, while the oxidation products were non-toxic. Similar results were obtained in experiments performed in natural waters: no reaction products or interactions exhibiting protein phosphatase 1 inhibition were detected.

In vivo DNA damage induced by the cyanotoxin microcystin-LR: comparison of intra-peritoneal and oral administrations by use of the comet assay

Microcystin-LR (MC-LR), involved in human and animal poisonings by cyanobacteria, has been shown to be both a potent tumour promoter in rat liver and an inhibitor of serine/threonine protein phosphatases, specifically PP1 and PP2A. The research on the genotoxic potential of MC-LR counts only few in vivo studies. In order to determine the target organs for DNA-damage induction by MC-LR, the single-cell gel electrophoresis (SCGE) or comet assay was performed in mice. Following a single oral administration of 2 and 4mg/kg bw of MC-LR, a statistically significant induction of DNA damage in blood cells was obtained after 3h. However, after an intra-peritoneal injection (ip), DNA lesions were mainly induced in the liver, but were also reported in the kidney, the intestine and the colon. The sensitivity of the ip route compared to the oral route suggested a difference in the bio-disponibility of the toxin. In any case, DNA damage was induced by MC-LR irrespective of the administration route. Among the target organs, the DNA damage induced in the intestinal tissues (ileum and colon) may contribute to an increased cancer risk.

Oxidative elimination of cyanotoxins: comparison of ozone, chlorine, chlorine dioxide and permanganate

As the World Health Organization (WHO) progresses with provisional Drinking Water Guidelines of 1 microg/L for microcystin-LR and a proposed Guideline of 1 microg/L for cylindrospermopsin, efficient treatment strategies are needed to prevent cyanotoxins such as these from reaching consumers. A kinetic database has been compiled for the oxidative treatment of three cyanotoxins: microcystin-LR (MC-LR), cylindrospermopsin (CYN), and anatoxin-a (ANTX) with ozone, chlorine, chlorine dioxide and permanganate. This kinetic database contains rate constants not previously reported and determined in the present work (e.g. for permanganate oxidation of ANTX and chlorine dioxide oxidation of CYN and ANTX), together with previously published rate constants for the remaining oxidation processes. Second-order rate constants measured in pure aqueous solutions of these toxins could be used in a kinetic model to predict the toxin oxidation efficiency of ozone, chlorine, chlorine dioxide and permanganate when applied to natural waters. Oxidants were applied to water from a eutrophic Swiss lake (Lake Greifensee) in static-dose testing and dynamic time-resolved experiments to confirm predictions from the kinetic database, and to investigate the effects of a natural matrix on toxin oxidation and by-product formation. Overall, permanganate can effectively oxidize ANTX and MC-LR, while chlorine will oxidize CYN and MC-LR and ozone is capable of oxidizing all three toxins with the highest rate. The formation of trihalomethanes (THMs) in the treated water may be a restriction to the application of sufficiently high-chlorine doses.

Effect of chlorination on Microcystis aeruginosa cell integrity and subsequent microcystin release and degradation

The proliferation of cyanobacteria in drinking water sources is problematic for water authorities as they can interfere with water treatment processes. Studies have shown that oxidants such as chlorine can enhance the coagulation of cyanobacteria; however, chlorine can potentially lyse cyanobacterial cells, releasing toxic metabolites. Chlorine also has the potential to effectively degrade these toxins. This study evaluated the effect of chlorine on the cell integrity of toxic Microcystis aeruginosa in reservoir water using flow cytometry. In addition, the effect of chlorine on the subsequent release and degradation of microcystin toxins was systematically assessed. Cell lysis occurred at chlorine exposure values between 7 and 29 mg min/L, which is within the range of normal disinfection practices. Intracellular toxin was shown to be released from damaged cells at a rate three times faster than it was degraded by chlorine. The degradation of extracellular microcystin by chlorine was found to be dependent upon the pH, chlorine exposure, and the presence of cyanobacterial cells.

Liquid Chromatography−Tandem Mass Spectrometry Application, for the Determination of Extracellular Hepatotoxins in Irish Lake and Drinking Waters

A novel method for the determination of hepatotoxins; microcystins (MCs), and nodularin (Nod) in lake water and domestic chlorinated tap water has been developed using liquid chromatography hyphenated with electrospray ionization triple quadrupole mass spectrometry (LC-ESI-MS/MS). Optimization of the mass spectrometer parameters and mobile-phase composition was performed to maximize the sensitivity and reproducibility of the method. Detection of the hepatotoxins was carried out using multiple reaction monitoring experiments, thus improving the selectivity of the method. A total ion chromatogram and a precursor ion scan on ion m/z 135 was also applied to all samples to detect unknown microcystins or microcystins for which there are no standards available. A comprehensive validation of the LC-ESI-MS/MS method was completed that took into account matrix effects, specificity, linearity, accuracy, and precision. Good linear calibrations were obtained for MC-LR (1-200 microg/L; R2=0.9994) in spiked lake and tap water samples (1-50 microg/L; R2=0.9974). Acceptable interday repeatability was achieved for MC-LR in lake water with RSD values (n=9) ranging from 9.9 (10 microg/L) to 5.1% (100 microg/L). Excellent limits of detection (LOD) and limits of quantitation (LOQ) were achieved with spiked MCs and Nod samples; LOD=0.27 microg/L and LOQ=0.90 microg/L for MC-LR in the "normal linear range" and LOD=0.08 microg/L and LOQ=0.25 microg/L in the "low linear range" in both lake and chlorinated tap water. Similar results were obtained for a suite of microcystins and nodularin. This sensitive and rapid method does not require any sample preconcentration, including the elimination of solid-phase extraction (SPE) for the effective screening of hepatotoxins in water below the 1 microg/L WHO provisional guideline limit for MC-LR. Furthermore, SPE techniques are time-consuming, nonreproducible at trace levels, and offer poor recoveries with chlorinated water. The application of this LC-ESI-MS/MS method for routine screening of hepatotoxins in lake and chlorinated tap water (average Cl2=0.23 mg/L) is achieved and this study represents the first direct method for the screening of hepatotoxins in chlorinated tap water.

Inhibition of nucleotide excision repair (NER) by microcystin-LR in CHO-K1 cells

Microcystin-LR (MC-LR), a potent inhibitor of PP1 and PP2A protein phosphatases, is related to tumor promotion and initiation. Although the genotoxic properties of this toxin have been extensively investigated with a variety of non-mammalian and mammalian test systems, the existing results are contradictory. Based on our previous results regarding the impact of MC-LR on the processes of DNA repair we decided to examine in greater detail its effect on the capacity of nucleotide excision repair (NER). CHO-K1 cells were pre-treated with increasing doses of MC-LR (1, 10 and 20 microg/ml) and then exposed to UV radiation (25 J/m(2)). Apoptosis was analyzed to exclude the possibility of false positive results in the comet assay. The results suggest that MC-LR targets the nucleotide excision repair mechanisms by interference with the incision/excision phase as well as the rejoining phase of NER and leads to an increased level of UV-induced cytogenetic DNA damage in CHO-K1 cells.

Degradation of microcystins using immobilized microorganism isolated in an eutrophic lake

The final purpose of our series of studies is to establish a biological removal method of cyanobacteria and their toxic products using immobilized microorganisms that can lyse cyanobacteria and decompose microcystins. To establish the biological removal method in non-point areas and water purification plants, as the first step, we explored bacteria active against the cyanobacterial hepatotoxin microcystin in the present study. Eleven active bacteria were isolated from samples taken from Lakes Tsukui and Sagami, Japan. Among 3 strains (B-9 to B-11) with degradative activity, strain B-9 exhibited the strongest activity. The 16S rDNA sequence of the strain B-9 showed the highest similarity to that of Sphingomonas sp. Y2 (AB084247, 99% similarity). Microcystins-RR and -LR were completely degraded by strain B-9 (SC16) within 1d, which led to an immobilized microorganism with a polyester resin. The degradation of microcystin-RR in a bioreactor using the immobilized strain B-9 was observed and microcystin-RR (> 90%) was completely degraded after 24 h. Microcystin-RR was added to the lake water at regular intervals and the degradation after 24 h was observed in the bioreactor over a 72-d period. An over 80% removal efficiency continued for 2 months, showing that the life of the immobilized B-9 in terms of activity was at least 2 months under the optimized conditions. From these results, this immobilized B-9 is feasible for the practical treatment of microcystins in non-point areas and water purification plants.

Evaluating genotoxicity associated with microcystin-LR and its risk to source water safety in Meiliang Bay, Taihu Lake

In recent years cyanobacteria blooms have become a severe problem in Taihu Lake, a large shallow eutrophic lake in China. Microcystins produced by certain genera of cyanobacteria can affect public health in this area because of their acute and chronic toxic effects. In this study, samples of cyanobacteria were collected and extracted by two solvent systems. The extracts were tested with three short-term genotoxicity assays, the ara test, the Ames test, and the SOS/umu test. In addition, temporal variation in the concentrations of microcystin-LR in the water samples was determined and monitored by an ELISA assay. Then the concentration of microcystin-LR in the drinking water was estimated. The risk of microcystin-LR exposure by drinking water was assessed according to tolerable daily intake (TDI). The three genotoxicity assays showed negative results regardless of the solvent system used, and there were clear inconsistencies in the spatiotemporal profiles of genotoxic potential and microcystin concentrations in Taihu Lake. Risk assessment showed that the drinking water from Taihu Lake was not safe from the end of July to the beginning of November because of a high concentration of microcystin-LR. Our study indicated the drinking water from Taihu Lake posed a risk because of the microcystin-LR, although it was neither genotoxic nor associated with genotoxicity of the lake water.

Differences in the chlorine reactivity of four microcystin analogues

The presence of microcystin toxins in drinking water is highly undesirable as they have the potential to adversely affect human health. Consequently, effective removal of these toxins from water is a major goal for water authorities. In this study, four microcystin analogues were chlorinated in two treated waters, and two of the analogues were chlorinated in deionised water. The oxidation of the microcystins was related to the chlorine exposure (CT) of the sample waters with the ease of oxidation following the trend: microcystin-YR > microcystin-RR > microcystin-LR > or = microcystin-LA. This trend was in agreement with published data on model compounds and free amino acids. Values of CT of up to 25 mg min L(-1) were required for oxidation of all microcystin analogues to below the World Health Organization guideline value of 1.0 microg L(-1). Results from this study indicate that for some water resources it is important to determine the speciation of the microcystin analogues to optimise chlorination practices.

Ultrasonically induced degradation and detoxification of microcystin-LR (cyanobacterial toxin)

Cyanobacterial toxins (CBTs), produced by glue-green algae, are one of the most common naturally occurring toxins found in potable waters. The microcystin family of CBTs present in drinking water sources poses a considerable threat to human health. In this study, we have demonstrated that ultrasonic irradiation at 640 kHz leads to rapid degradation of microcystin-LR (MC-LR). Degradation of MC-LR present in the crude cyanobacterial extracts containing cell constituents has been studied with ultrasound under a variety of conditions. The degradation of MC-LR was demonstrated over a concentration range from 0.03 to 3.0 microM. Hydroxyl radical scavenger experiments indicate that hydroxyl radical is responsible for a significant fraction of the observed degradation, but other processes (hydrolysis/ pyrolysis) are also important. Analysis of the protein phosphatase inhibition activity of the reaction products indicates that the products from ultrasonic degradation of MC-LR do not exhibit any measurable biological activity. The results demonstrate that ultrasonic irradiation maybe an effective and practical method for the detoxification of microcystins from drinking water.

Degradation of microcystins in aqueous solution with in situ electrogenerated active chlorine

A new and efficient method for the degradation of microcystins (one family of blue algal toxins) was developed and studied. Microcystins (MCs) in water were directly and effectively removed by active chlorine transformed in situ from the naturally existing Cl- in water resource using electrochemical method. Titanium coated with RuO2 and TiO2 was used as the anode. Microcystin-RR (MCRR) and Microcystin-LR (MCLR) were chosen as the model compounds of MCs. The results suggested that 20.87 mgl(-1) MCs (12.58 mgl(-1) MCRR and 8.29 mgl(-1) MCLR) in aqueous solution with 1.85 mM Cl- could be synchronously decomposed within 15 min electrolysis under the condition of the current density 8.89 mAcm(-2), 20 degrees C and pH 7.00. The qualitative analysis showed that the heptapetide ring and the Adda group of both treated MCs were changed. The results also indicated that the removal rates of both MCs increased with the increasing of chloride concentration and applied current density, but decreased with the increasing of initial concentration of MCs and initial pH of electrolyte. In the absence of Cl-, only a small fraction of both MCs were decomposed by direct anodic oxidation, while their almost complete removals could be obtained in the case of indirect electrooxidation with in situ electrogenerated active chlorine from Cl- in water.

Elimination of microcystins by water treatment processes-examples from Sulejow Reservoir, Poland

Eutrophication is a serious problem in Polish freshwaters. Mass occurrences of toxic cyanobacteria in reservoirs cause problems in the production of safe drinking water and the diversity of produced toxins complicates monitoring of freshwaters. The aim of this study was to estimate the efficiency of water treatment processes in the removal of microcystins (MCs), cyanobacterial hepatotoxins. Elimination of microcystins was studied at two waterworks, which supply drinking water to the city of Lodz from Sulejow Reservoir. The consecutive steps of pre-oxidation, coagulation, sand filtration, ozonation and chlorination used in the water treatment showed effective elimination of microcystins in water from Sulejow Reservoir in 2002 and 2003. The highest total concentration of microcystin (variants MC-RR, MC-YR, MC-LR) amounted to 6.7 microgl(-1) in raw water and was detected on the 13th of August 2002. In 2003 the water utility decided to increase the contribution of ground water in the production of drinking water. This resulted in a decrease of microcystin in water during and after the treatment process. The current management strategy of the waterworks company includes mixing of surface water and ground water, which reduces the hazards caused by toxic cyanobacterial blooms in the reservoir.