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Microplastics are ubiquitous in the freshwater environment, while its abundance in the sediment profiles has received little attention. The vertical microplastic distribution in the sediment of the North (NTH) and Southwest (SWTH) of Lake Taihu was identified and characterized in this study. Microplastics could be detected at all depths (0–50 cm) at the two sites, with the total abundance of 8100 and 5300 particles kg−1 dry weight sediment at NTH and SWTH, respectively. This indicates that the microplastic storage in the sediment of the Lake Taihu may be underestimated, if only the surface sediment is considered. Microplastics composed of various polymer types were identified in the sediment of the two sites, including polyamide (PA), acrylic acid, polyethylene terephthalate and cellulose acetate, while high density polyethylene and polypropylene were only detected at NTH. The main type of polymers detected at NTH (42%) and SWTH (43%) were PA. The major shape of microplastics was fibers, with a ratio of 76% and 78%, respectively at the site NTH and SWTH. The colors of microplastics were mainly white (accounted for 42 and 43% at NTH and SWTH, respectively), which may be caused by the long-term decomposition of dyestuff in the syngenesis of sediment and/or probably the degradation during sample treatments. The textile industry and fishery activities may provide the source. In summary, our findings in the Lake Taihu provide better understanding of the microplastic pollution and tackle microplastics challenges.

The frequent occurrence of antibiotics in source waters may affect the formation of harmful algal blooms (HABs) dominated by the cyanobacterium Microcystis aeruginosa. However, it remains poorly understood whether dissolved algal organic matters (AOM) can be altered by the introduction of antibiotics in source waters. To resolve these discrepancies, this study investigated the physiological, biochemical, and transcriptional responses of a toxigenic strain of M. aeruginosa to the commonly-detected antibiotic roxithromycin (ROX) at environmentally relevant concentrations ranging from 30 to 8000 ng L

Potassium ferrate (K2FeO4) is an effective oxidant that may be used as a pre- or post-oxidant in the purification of source water with cyanobacterial issues. To provide a better basis for the application of this oxidant during water treatment processes, the impacts of K2FeO4 on the cell viability of Microcystis aeruginosa and the fate of associated microcystins (MCs) were investigated in various water matrices. The results showed that a water matrix can significantly affect the effectiveness of K2FeO4 on cyanobacteria inactivation. 10 mg L−1 K2FeO4 induced significant cell lysis of M. aeruginosa in Ran Yi Tan Reservoir (RYTR) water while the membrane integrity was relatively unaffected in ASM-1 media and Cheng Kung Lake (CKL) water. The reduced efficiency of K2FeO4 oxidation may be attributed to the manganese (Mn2+) and organic matter (Ethylenediaminetetraacetic acid, EDTA) in the ASM-1 media and high concentrations of natural organic matters (NOMs) in the CKL water. A delayed Chick-Watson model was applied to simulate the experimental data for cyanobacterial cell rupture, and the cell lysis rates of the M. aeruginosa samples were determined to be 128-242 M−1 s−1 (mol L−1 s−1). Generally, no significant increases in extracellular MCs were observed in the three different waters, even in the RYTR water where the membrane integrity of the cyanobacterial cells was severely disrupted. Therefore, K2FeO4 could be a potential pre-oxidant to enhance subsequent treatments for cyanobacteria removal without affecting the cell integrity, or could serve as a post-oxidant to inactivate cyanobacterial cells and degrade MCs effectively, depending on the specific water matrix.

Microcystis aeruginosa and Pseudanabaena are two common cyanobacterial species/genus and they can occur coincidently in many eutrophic lakes globally. These two cyanobacteria could produce Taste & Odor (T&O) compounds, and their production of T&O compounds might be changed when they are present coincidently. The amounts of T&O compounds and their producers may influence the effectiveness of water treatment processes. Therefore, the mutual interactions between Microcystis aeruginosa (FACHB-905, M) and Pseudanabaena sp. (FACHB-1277, P) on T&O compounds in co-cultures were evaluated in this study. Different initial cell concentrations of M and P, with ratios of M:P = 1:1, M:P = 1:2 and M:P = 2:1 were applied in the co-cultures. The growth of M was enhanced under all of the cyanobacterial cell ratios. The growth of P was enhanced under the ratio of M:P = 1:1, while it was inhibited under the ratios of M:P = 1:2 and M: P = 2:1. In addition, the growth of the two cyanobacteria and their production of β-cyclocitral and 2-methylisoborneol (2-MIB) in the filtrate of P were higher than those in the filtrate of M, which may be attributed to their associated secondary metabolites. The cell integrity and photosynthetic capacity of the two studied cyanobacteria are greatly affected by exposure to β-cyclocitral and 2-MIB. The results showed that β-cyclocitral and 2-MIB had the allelopathic effects on the two cyanobacteria species which might influence the composition of co-existing cyanobacteria and their production of T&O compounds.

Cyanobacteria blooms and micropollutants (e.g., antibiotics) in source waters are two increasing environmental issues worldwide. This study hypothesized that the coexisting antibiotics may possibly alter the efficiency of water treatment processes through affecting the physiological and biochemical characteristics of cyanobacterial cells. A toxic strain of Microcystis aeruginosa was exposed to the common antibiotic erythromycin (ERY) at environmentally relevant concentrations; then, samples were collected on days 1, 4 and 6 to assess the efficiency of potassium permanganate (KMnO4) in cyanobacteria oxidation. The percentage of intact cells remained constant after treatment with 2 mg L−1 KMnO4 in M. aeruginosa samples dosed with 0–5.0 μg L−1 ERY. Although 6 mg L−1 KMnO4 could damage cyanobacterial cells, its ability was considerably reduced as the concentrations of ERY increased. KMnO4 oxidation degraded the intracellular microcystins (MCs) in all of the cyanobacterial samples, even the samples with intact cells, possibly resulting from the stimulation of intracellular reactive oxygen species (ROS). The highest amounts of total MCs remained after oxidation with 2 and 6 mg L−1 KMnO4 in 0.2 μg L−1 ERY-treated cyanobacterial samples, which may be due to large amounts of MC production. The 5.0 μg L−1 ERY inhibited the growth of cyanobacterial cells and downregulated the expression of the MC synthesis gene (mcyB), which resulted in the lowest amounts of total MCs. However, it led to the highest concentration (4.6 μg L−1) of extracellular MCs after treatment with 2 mg L−1 KMnO4 for 300 min. Generally, this study indicates that the effectiveness of KMnO4 oxidation in cyanobacteria treatment decreased when the concentration of ERY increased. Hence, the possible risks caused by the coexistence of cyanobacteria and antibiotics, such as reduced efficiency of water treatment processes in cyanobacteria inactivation and degradation of the dissolved MCs, need to be taken into account.

Cyanobacterial blooms are one of the main contaminants that can degrade drinking water quality with the associated taste, odour and toxic compounds. Although a wide range of techniques have shown promise for cyanobacterial bloom control and cyanobacterial cell/metabolite removal in reservoirs and water treatment plants (WTPs), these treatments may have negative consequences through release of intracellular metabolites into the surrounding water. This study assessed the impact of copper sulphate (CuSO 4 ), chlorine, potassium permanganate (KMnO 4 ), hydrogen peroxide (H 2 O 2 ) and ozone on Microcystis aeruginosa culture and the toxins it produced . All of these agents induced the loss of cyanobacterial membrane integrity. However, no associated increase in dissolved toxins was detected during chlorine and H 2 O 2 treatments which may be due to faster toxin oxidation rates than release rates. KMnO 4 doses of 1 and 3 mg L −1 degraded dissolved toxins while having no impact on cyanobacterial membrane integrity. In contrast, ozone induced a significant increase in extracellular toxins but it was unable to degrade these toxins to the same degree as the other oxidants which may due to the lack of residual. All chemicals, except CuSO 4 , were able to reduce cyanotoxins and chlorine was the most effective with a rate up to 2161 M −1 s −1 .

Pesticide residues and nitrogen overload (which caused cyanobacteria blooms) have been two serious environmental concerns. In particular, chiral pesticides with different structures may have various impacts on cyanobacteria. Nitrogen may affect the behavior between pesticides and cyanobacteria (e.g., increase the adverse effects of pesticides on cyanobacteria). This study evaluated the impacts of Rac- and S-metolachlor on the cell integrity and toxin release of Microcystis aeruginosa cells at different nitrogen levels. The results showed that (both of the configurations: Rac-, S-) metolachlor could inhibit M. aeruginosa cell growth under most conditions, and the inhibition rates were increased with the growing concentrations of nitrogen and metolachlor. However, cyanobacterial growth was promoted in 48 h under environmental relevant condition (1 mg/L metolachlor and 0.15 mg/L nitrogen). Therefore, the water authorities should adjust the treatment parameters to remove possible larger numbers of cyaonbacteria under that condition. On the other hand, the inhibition degree of M. aeruginosa cell growth by S-metolachlor treatments was obviously larger than Rac-metolachlor treatments. S-metolachlor also had a stronger ability in compromising M. aeruginosa cells than Rac-metolachlor treatments. Compared to control samples, more extracellular toxins (12%–86% increases) were detected after 5 mg/L S-metolachlor treatment for 72 h at different nitrogen levels, but the variations of extracellular toxins caused by 5 mg/L Rac-metolachlor addition could be neglected. Consequently, higher concentrations of metolachlor in source waters are harmful to humans, but it may prevent cyanobacterial blooms. However, the potential risks (e.g. build-up of extracellular toxins) should be considered.

The occurrence of toxic cyanobacteria in drinking water sources is problematic for water authorities as they can impair drinking water quality. Chlorine as a commonly used oxidant in water treatment plants has shown the potential to lyse cyanobacterial cells, resulting in the release of secondary metabolites which are hard to be removed during conventional water treatment processes. The majority of cyanobacterial species such as Microcystis, often occur in colonial forms under natural conditions. However, previous studies have mainly focused on the influence of chlorination on individual cyanobacterial cells due to technique limitations. A syringe dispersion method combined with a fluorescence technique (SYTOX Green stain with flow cytometry), was successfully developed for the evaluation of cell integrity of colonial Microcystis. Chlorination of Microcystis-laden water was conducted at different chlorine dosages for different colonial sizes (

Cyanobacteria blooms are an increasing issue in wastewater-treatment systems as the associated toxins could induce health risks due to potential passage through irrigation practices using recycled water. The impacts of hydrogen peroxide (H2O2), chlorine, potassium permanganate (KMnO4), and ozone on Microcystis aeruginosa cell viability, and the concomitant toxin release and degradation in wastewater, were investigated. All of these treatments could inactivate M. aeruginosa cells to varying degrees in wastewater due to its chemically challenging matrix. In this paper chlorine was shown to be a feasible option to be used as the last barrier in wastewater-treatment plants due to its strong oxidizing potential resulting incomplete cell inactivation and subsequent degradation of the majority of cyanotoxins in 30 min. However, this was dose dependent as although the release of extracellular toxins was oxidized using 5 mg L−1 chlorine, lower doses of 3 and 4 mg L−1 chlorine were unable to effectively d...

Cyanobacterial blooms are continuously critical challenges in drinking water systems which can have various negative impacts such as production of taste, odour and toxic compounds. Furthermore, the intracellular metabolites could be released into surrounding waters when the cyanobacterial membranes are destroyed. Although a variety of techniques have been developed to control cyanobacterial blooms and remove cyanobacterial cells or metabolites in water treatment processes, the effect of these treatments on the membrane integrity of cyanobacterial cells have not been systematically studied and compared. This study evaluated the effectiveness of copper sulphate (CuSO4), chlorine, potassium permanganate (KMnO4), hydrogen peroxide (H2O2) and ozone on the cell integrity and densities of Microcystis aeruginosa. All of these technologies can compromise the cell membrane of cyanobacteria to varying degrees. Chlorine showed the strongest ability to impair the cell integrity with a majority (≥ 88%) of the cells compromised within the first minute and with the cell lysis rates ranging of 0.640-3.82 h(-1) during 1-60 min. Ozone dose of 6 mg L(-1) also could induce 90% lysis of the cyanobacterial cells in 5 min and the cell lysis rate of KMnO4 (10 mg L(-1)) was 0.829 h(-1). CuSO4 and H2O2 could not only destroy the viability of cyanobacterial cells but also showed algistatic potential over the 7 day treatment. The potential of all the oxidants (chlorine, KMnO4, H2O2 and ozone) considered as algicides were discussed in this study. The benefits and drawbacks of these control and water treatment options were assessed as well.

Potassium permanganate (KMnO4) is commonly used as a pre-treatment oxidant to remove soluble manganese (Mn) and iron (Fe) which can contribute to dirty water in drinking water supplies. Because Mn and Fe problems are commonly associated with thermal stratification in summer and autumn, they frequently coincide with the presence of cyanobacteria. The use of KMnO4 as an oxidant for Mn and Fe control therefore needs to consider the potential impacts on cyanobacterial cell integrity and toxin release. This study aims to assess the effect of KMnO4 on cyanobacteria cell integrity, toxin release and toxin oxidation. A toxic strain of Microcystis aeruginosa was exposed to various concentrations of KMnO4 and the cell integrity of cyanobacteria was measured with flow cytometry. Further the intra- and extra-cellular toxin concentrations were quantified and it was apparent that KMnO4 reduced both the intra- and extra-cellular toxins at low initial concentrations of 1 and 3 mg L(-1) without complete cell lysis. However, the cell integrity of cyanobacteria was compromised at KMnO4 concentrations of 5 mg L(-1) and 10 mg L(-1) and led to intracellular toxin release. In the 10 mg L(-1) KMnO4 treatment, the total toxin was oxidised after 7h contact time. A model describing the two step process of release and degradation was developed and may provide a tool to assess the risk water quality posed by toxin release. Consequently, it may be possible to use KMnO4 as a pre-treatment for Mn and Fe at concentrations3 mg L(-1) and short contact time when cyanobacteria are also present.