Cyanobacteria and their toxins in Guanting Reservoir of Beijing, China

Improving on mapping long-term surface water with a novel framework based on the Landsat imagery series

Surface water plays a crucial role in the ecological environment and societal development. Remote sensing detection serves as a significant approach to understand the temporal and spatial change in surface water series (SWS) and to directly construct long-term SWS. Limited by various factors such as cloud, cloud shadow, and problematic satellite sensor monitoring, the existent surface water mapping datasets might be short and incomplete due to losing raw information on certain dates. Improved algorithms are desired to increase the completeness and quality of SWS datasets. The present study proposes an automated framework to detect SWS, based on the Google Earth Engine and Landsat satellite imagery. This framework incorporates implementing a raw image filtering algorithm to increase available images, thereby expanding the completeness. It improves OTSU thresholding by replacing anomaly thresholds with the median value, thus enhancing the accuracy of SWS datasets. Gaps caused by Landsat7 ETM + SLC-off are respired with the random forest algorithm and morphological operations. The results show that this novel framework effectively expands the long-term series of SWS for three surface water bodies with distinct geomorphological patterns. The evaluation of confusion matrices suggests the good performance of extracting surface water, with the overall accuracy ranging from 0.96 to 0.97, and user's accuracy between 0.96 and 0.98, producer's accuracy ranging from 0.83 to 0.89, and Matthews correlation coefficient ranging from 0.87 to 0.9 for several spectral water indices (NDWI, MNDWI, ANNDWI, and AWEI). Compared with the Global Reservoirs Surface Area Dynamics (GRSAD) dataset, our constructed datasets promote greater completeness of SWS datasets by 27.01%-91.89% for the selected water bodies. The proposed framework for detecting SWS shows good potential in enlarging and completing long-term global-scale SWS datasets, capable of supporting assessments of surface-water-related environmental management and disaster prevention.

Internal reference self-powered aptasensor for on-site detection of MC-RR used sunlight as light source and CoMoS4 hollow nanospheres as photocathode

As a liver toxin, long-term exposure of microcystin-arginine-arginine (MC-RR) is harmful to the ecological environment and human health, so it is necessary to realize on-site detection of MC-RR. The self-powered sensor has enormous potential for on-site detection in battery-free devices. However, due to the low photoelectric conversion efficiency and poor anti-interference ability to environmental fluctuation, the field detection of self-powered sensor is limited. Herein, we tackled above problems according to the following two aspects. For one hand, CoMoS₄ hollow nanospheres modified internal reference electrode was arranged in the self-powered sensor, which effectively avoided the influence of unstable sunlight caused by different space, time, weather and other factors. For the other hand, dual-photoelectrode could absorb and convert sunlight, so as to improve the solar capture and energy utilization, and realized the sunlight instead of traditional external light source (Xenon lamp or LED, etc.). This method effectively simplified the sensing device and solved the interference of environment in on-site detection. In addition, multimeter was used to measure the output voltage instead of electrochemical workstation, achieving the purpose of portability. This work established a sunlight-driven internal reference self-powered sensor with miniaturization, portability and anti-interference to realize MC-RR on-site monitoring in lake water.

Improvement in water pollution control alters nutrient stoichiometry of Guanting Reservoir near Beijing, North China

Significant improvement in wastewater treatment is the most effective way for eutrophication control, especially in semiarid regions. However, its effect on the nutrient status and stoichiometry of the receiving water body has remained poorly considered and understood at broad temporal scales. Taking Guanting Reservoir (GR) in Hebei-Beijing (P. R. China) as an example, we present a study that links a continuous monitoring dataset for GR with corresponding estimates of human-induced nutrient discharges in its watershed from the year 2006 to 2019. We find that current GR belongs to strict P limitation and the faster decrease of TP than TN concentrations and continuous increase of TN/TP mass ratios in GR are attributed to the water restoration investment-induced declining of nutrient loadings. The improved municipal wastewater treatment capacity is mainly responsible for these significant changes, due to the higher removal efficiency of TP than TN in municipal wastewater. Given the potential ecological impact on aquatic biodiversity as well as ecosystem function of changes in TN/TP ratios and higher retention rate of TP (97.4%) compared with TN (93.1%) in GR, our findings highlight that future strategy for water pollution control should not only concentrate on more nutrient reduction efficiencies but attach importance to their stoichiometric balance to reduce the potential risk of phytoplankton blooms and toxin production during the water quality recovery of lakes or reservoirs.

Pre-oxidation enhanced cyanobacteria removal in drinking water treatment: A review

Cyanobacterial bloom has many adverse effects on source water quality and drinking water production. The traditional water treatment process can hardly achieve satisfactory removal of algae cells. This review examines the impact of pre-oxidation on the removal of cyanobacteria by solid-liquid separation processes. It was reported that the introduction of chemical oxidants such as chlorine, potassium permanganate, and ozone in algae-laden water pretreatment could improve algae removal by the subsequent solid-liquid separation processes. However, over dosed oxidants can result in more serious water quality risks due to significant algae cell lysis and undesirable intracellular organic matter release. It was suggested that moderate pre-oxidation may enhance the removal of cyanobacteria without damaging algae cells. In this article, effects of moderate pretreatment on the solid-liquid separation processes (sedimentation, dissolved air flotation, and membrane filtration) are reviewed.

Environmental controls of harmful cyanobacterial blooms in Chinese inland waters

Harmful cyanobacterial blooms (CyanoHABs) are expanding world-wide, adversely affecting aquatic food production, recreational and tourism activities and safe drinking water supplies. China's inland waters have been increasingly threatened by CyanoHABs during the past several decades. The environmental factors controlling CyanoHABs are highly variable in space and time in China due to significant variations in climate, geography, geological and geochemical conditions among its many regions. Here, we synthesize diverse examples among Chinese water bodies regarding interactive effects of anthropogenic, climatic and geographic drivers influencing CyanoHAB potentials and dynamics in lakes and reservoirs; in order to provide a perspective and integrative approach to mitigating CyanoHABs. In China's many shallow water bodies, water quality is highly susceptible to human activity and to changing climatic and hydrological conditions, when compared to deeper lakes. Rapid increases in population, economic activity, and wastewater have accelerated CyanoHABs in China since 1980s, especially in the heavily urbanized, agricultural and industrial regions in the middle and lower Yangtze River basins. Climatic changes have provided an additional catalyst for expansion of CyanoHABs. In particular, rising spring temperatures have accelerated the onset and proliferation of Microcystis spp, blooms in the middle and lower reaches of Yangtze River basin. Large hydroelectric and water supply projects, like the Three Gorges Reservoir (TGR), have altered hydrological regimes, and have led to an increase of CyanoHABs in reservoirs and tributaries due to increases in water residence times. Manipulating water level fluctuations in the TGR may prove useful for controlling CyanoHAB in its tributary bays. Overall,CyanoHAB mitigation strategies will have to incorporate both N and P input reductions in these shallow systems. Furthermore, nutrient reduction strategies must consider climate change-induced increases in extreme weather events, including more intense rainfall and protracted heat waves and droughts, which can extend the magnitudes and duration of CyanoHABs. Ensuring the maintenance of natural hydrologic connectivity between lakes and rivers is of utmost importance in mitigating CyanoHABs throughout China.

Cyanobacterial blooms in China: diversity, distribution, and cyanotoxins

Cyanobacterial blooms, which refer to the massive growth of harmful cyanobacteria, have altered the global freshwater ecosystems during the past decades. China has the largest population in the world, and it is suffering from the harmful effect of water eutrophication and cyanobacterial blooms along with rapid development of the economy and society. Research on cyanobacterial blooms and cyanotoxins in China have been overwhelmingly enhanced and emphasized during the past decades. In the present review, the research on cyanobacterial blooms in China is generally introduced, including the history of cyanobacterial bloom studies, the diversity of the bloom-forming cyanobacteria species (BFCS), and cyanotoxin studies in China. Most studies have focused on Microcystis, its blooms, and microcystins. Newly emerging blooms with the dominance of non-Microcystis BFCS have been gradually expanding to wide regions in China. Understanding the basic features of these non-Microcystis BFCS and their blooms, including their diversity, occurrence, physio-ecology, and harmful metabolites, will provide direction on future studies of cyanobacterial blooms in China.

Cyanotoxins in drinking water supply reservoir (Legedadi, Central Ethiopia): implications for public health safety

Cyanobacterial blooms in drinking water supply affect its quality, which ultimately impacts ecosystem and public health. Thus, this cross-sectional study was conducted to perform a preliminary study on cyanotoxins via analysis of samples collected only once from two sites during the month of peak algal bloom and to subsequently prompt a comprehensive risk assessment in a major drinking water source, Legedadi Reservoir, of Addis Ababa, the capital city of Ethiopia. Samples were collected during peak algal bloom month (January 2018) from two sampling sites, near the dam (S1) and at the center of the reservoir (S2). Identification and enumeration of phytoplankton taxa were done and the measurement of common hepatotoxin (MCs and NOD) concentrations was conducted using liquid chromatography-tandem mass spectrometry. In the reservoir, cyanobacteria made up to 98% of total phytoplankton abundance, with Dolichospermum and Microcystis spp, dominating the phytoplankton community. In these first cyanotoxin analyses conducted for a drinking water supply source in Ethiopia, six major MC variants, namely MC-dmRR, MC-RR, MC-YR, MC-dmLR, MC-LR, and MC-LA, were detected in both algal seston and water samples. MC-LR was the most dominant MCs variant, while nodularin was not detected for both sampling sites. Extracellular total MC concentrations (μg L−1) of 453.89 and 61.63 and intracellular total MC concentrations (μg L−1) of 189.29 and 112.34 were recorded for samples from S1 and S2, respectively. The high concentrations of extracellular MCs, with MC-LR constituting the greatest proportion, indicate the extremely high potential public health risk for end-users.

Bacterial eutrophic index for potential water quality evaluation of a freshwater ecosystem

Water quality evaluation of freshwater ecosystems has been widely reported based on the physical and chemical parameters of water (e.g., Carlson's trophic state index (TSI)), while the aquatic microorganisms are actually a more intuitive way to reflect the eutrophic levels. This article was based on 27 global freshwater ecosystems including freshwater rivers, lakes, and reservoirs. Bacterial eutrophic index (BEI) was determined as the function of temperature and abundances of Cyanobacteria and Actinobacteria. BEI and TSI values of the freshwater ecosystems were determined and the correlation analysis of TSI and BEI indicated their positive correlation (ρ = 0.452, p < 0.01). Furthermore, an eutrophication classification based on BEI was proposed. It turned out that BEI was a possible feasible method for water quality evaluation. The aquatic microorganism-based method such as BEI should be considered for water quality evaluation of a freshwater ecosystem. Complicated models combined with physicochemical (e.g., TSI) and microbial (e.g., BEI) method are recommended for water quality evaluation of a freshwater ecosystem in future.

Role of pre-coagulation in ultralow pressure membrane system for Microcystis aeruginosa-laden water treatment: Membrane fouling potential and mechanism

This work systematically studied the role of pre-coagulation in the performance of ultralow pressure membrane system for algae-laden water treatment. The membrane performance with/without pre-coagulation was compared in terms of membrane permeate flux, water quality and membrane fouling. Ultralow pressure membrane system can effectively reduce TOC of Microcystis aeruginosa-laden water from 5.8 to 2.1 mg/L, and pre-coagulation removed most large inorganic particles but few small organic particles. Interestingly, pre-coagulation aggravated the fouling of ultralow membrane system which is generally acknowledged method to alleviate the ultrafiltration membrane fouling. According to Extended Derjaguin-Landau-Verwey-Overbeek theory (XDLVO), the interaction energy of membrane-foulants (ΔG_fm^TOT = - 41.95mJ/m²), and foulant-foulant (ΔG_ff^TOT = - 30.15mJ/m²) with coagulation were higher than those without coagulation (ΔG_fm^TOT = - 36.54mJ/m²) and (ΔG_ff^TOT = - 15.73mJ/m²) suggesting greater adherence between membrane and foulants & foulant and foulant after coagulation, which well agreed with SEM results. Membrane fouling models were also applied to analyze the fouling mechanism of ultralow-pressure membrane filtration. Based on above analysis, the possible fouling mechanisms for membrane filtration with/without precoagulation were proposed and then confirmed by pre-filtration experiment, where large inorganic particles played important roles. Our study could be indicative for membrane fouling control of ultralow-pressure membrane filtration for the treatment of algae-laden water.

Increasing perfluoroalkyl substances and ecological process from the Yongding Watershed to the Guanting Reservoir in the Olympic host cities, China

Perfluoroalkyl substances (PFASs) have raised great attention, particularly in regions of rapid urbanization. Zhangjiakou and Beijing will jointly host the Winter Olympic Games in 2022, which will likely increase local PFASs pollution and their associated risks over the coming period. In this study, we identified ecological process of PFASs, including sources, environmental fate, and risks, from the Yongding Watershed to the Guanting Reservoir. The concentrations of total 12 PFASs in water of the Guanting Reservoir were higher than that from the Yongding Watershed, with mean of 48.9 and 33.7 ng/L, respectively. The concentrations of PFASs in sediment of the Yongding Watershed and the Guanting Reservoir were similar, with mean of 1.01 and 0.827 ng/g dry weight, respectively. Detected levels of PFASs in the Guanting Reservoir significantly increased during the past eight years, possibly due to an improving economy and a rapidly developed service industry. Moderate PFASs levels in fish of the Guanting Reservoir were detected relative to other lakes and reservoirs. The daily intake of PFASs via fish and water ranged from 4.96 to 15.0 ng/kg bw/day, with higher levels found in children relative to adults. In total, approximately 9.06 kg of PFASs from riverine flow and atmospheric deposition annually entered the Guanting Reservoir. PFASs from the Yongding River significantly contributed to the pollution of Guanting Reservoir, with predominance of perfluorobutanoic acid (PFBA) in water, and long-chain perfluorinated carboxylic acids (PFCAs) and perfluorooctane sulfonate (PFOS) in sediment in both the Yongding Watershed and the Guanting Reservoir. Most of the PFASs (23.5 kg) were stored in water of the Guanting Reservoir, while the annual storage of PFASs in sediment and fish was only 4.68 × 10^-2 kg and 4.36 × 10^-2 kg via deposition and accumulation, respectively. The results suggest that water quality management of the Yongding Watershed is necessary for effective control on PFASs pollution in the Guanting Reservoir.

Effects of nutrient temporal variations on toxic genotype and microcystin concentration in two eutrophic lakes

Harmful cyanobacterial blooms are a growing threat to freshwater ecosystems worldwide due to the production of microcystin (MC), which can have detrimental effects on water quality and human health. The relations between MC-producing Microcystis, MC production, and environmental variables especially nutrient conditions in eutrophic lakes, Lake Taihu and Lake Yanghe, were investigated during the bloom season of 2015. Results showed that toxigenic cells contributed to 8.94-75.68% and 7.87-58.69% of the total Microcystis in Lake Taihu and Lake Yanghe, respectively. The dynamics of toxigenic cells and MC production were positively associated with NH₃-N concentration in Lake Taihu, while positively associated with the concentrations of TP, TDP and PO₄-P in Lake Yanghe, indicating that the dominant nutrient factor affecting the toxic blooms was nitrogen in Lake Taihu, whereas it was phosphorus in Lake Yanghe. The significant relationship between TLR eq (total MC after transformation of MC-RR and MC-YR into MC-LR) and Chlorophyll-a (Chl-a) concentration implied that Chl-a could be an alternative measure to predict MC risk in the two lakes, and the safe threshold value of Chl-a was proposed as 25.38 and 31.06 μg/L in Lake Taihu and Lake Yanghe, respectively.

The production and release of microcystin related to phytoplankton biodiversity and water salinity in two cyanobacteria blooming lakes

To find the connections between microcystins and the phytoplankton community, coupled with environmental factors, we investigated 2 cyanobacteria blooming lakes, Lake Taihu (at the center of the Yangtze River Delta, eastern China) and Lake Yanghe (near Qinhuangdao City, northern China). Two years of data, including water quality and the amounts of phytoplankton, microcystins, and the congeners in both algal cells and water, were collected from the 2 lakes during 2013 and 2014. The results showed that both the microcystin quota and release percentage were positively correlated with biodiversity of phytoplankton and the Chlorophyta to phytoplankton ratio, but were negatively correlated with cyanobacteria abundance and the cyanobacteria to phytoplankton ratio; both the microcystin quota and release percentage were closely related to the intensity of competition between cyanobacteria and other phytoplankton; meanwhile, microcystins played a role in the competition between cyanobacteria and other phytoplankton. Salinity had a significantly negative relationship with both cellular and total microcystins, but a significantly positive relationship with the microcystin releasing percentage, indicating that an increase in salinity inhibited the production of microcystins but promoted their release into the aquatic environment. In addition, the average number of microcystins in Lake Yanghe was several times higher than the provisional guideline value adopted by the World Health Organization, indicating a possible health risk to local people. Environ Toxicol Chem 2018;37:2312-2322. © 2018 SETAC.

TiO2 nanoparticles for the remediation of eutrophic shallow freshwater systems: Efficiency and impacts on aquatic biota under a microcosm experiment

The application of nanomaterials (NMs) in the remediation of eutrophic waters, particularly in the control of internal loading of nutrients, has been started, but limited investigations evaluated the effectiveness of these new treatment approaches and of their potential impacts on species from shallow freshwater lakes. The present work investigated, under a microcosm experiment, the application of a TiO2 nanomaterial both for reducing nutrient (mainly phosphorus and nitrogen forms) desorption and release from sediments (preventive treatment-PT) and for eliminating algal blooms (remediation treatment-RT). Furthermore, we also intended to assess the potential impacts of nano-TiO2 application on key freshwater species. The results showed the effectiveness of nano-TiO2 in controlling the release of phosphates from surface sediment and the subsequent reduction of total phosphorus in the water column. A reduction in total nitrogen was also observed. Such changes in nutrient dynamics contributed to a progressive inhibition of development of algae after the application of the NM in PT microcosms. Concerning the ability of nano-TiO2 to interact with algal cells, this interaction has likely occurred, mainly in RT, enhancing the formation of aggregates and their rapid settlement, thus reducing the algal bloom. Both treatments caused deleterious effects on freshwater species. In PT, Daphnia magna and Lemna minor showed a significant inhibition of several endpoints. Conversely, no inhibitory effect on the growth of Chironomus riparius was recorded. In opposite, C. riparius was the most affected species in RT microcosms. Such difference was probably caused by the formation of larger TiO2-algae aggregates in RT, under a high algal density, that rapidly settled in the sediment, becoming less available for pelagic species. In summary, despite the effectiveness of both treatments in controlling internal nutrient loading and in the mitigating algal bloom episodes, their negative effects on biota have to be seriously taken into account.

Bioaccumulation and Quantitative Variations of Microcystins in the Swartspruit River, South Africa

The bioaccumulation and quantitative variations of cyanobacterial peptide hepatotoxin intracellular microcystin in floating scums of cyanobacterium microcystis flos aquae collected from predetermined sampling sites in the Swartspruit River was investigated. Three distinct MCs variants (MC-YR, MC-LR, and MC-RR) were isolated, identified, and quantified. Additionally, two minor microcystin congeners (MC-(H4) YR), (D-Asp(3), Dha(7))MC-RR) also were identified but were not quantified. Quantitative analysis was achieved using peak areas substituted on linear regression equations: Y = 10085x - 19698 (R (2) = 0.9998), Y = 201387x + 20328 (R (2) = 0.9929), Y = 2506x + 15659 (R (2) = 0.9999), and 9859x + 208694 (R (2) = 0.9929) of standard curves for 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 μg/mL MC-LR, MC-RR, MC-YR respectively. Variant dominance followed the order MC-LR > MC-RR > MC-YR across the sampling sites. Analysis of maximum and minimum concentrations of quantified MCs variants showed 270.7, 14.10 (µg/g), 141.5, 1.43 (µg/g), and 72.28, 0.15 (µg/g) for MC-LR, MC-RR, and MC-YR, respectively. This implies there was quantitative variations of microcystin congeners across the sampled sites. Significant differences between means were assessed by an analysis of variance with P < 0.05 being considered significant. Results showed that there were no significant difference between mean MCs concentrations across the sampling periods (P > 0.05) and significant difference between mean MCs concentrations across sampling sites (P < 0.05).

A Systematic Investigation into the Environmental Fate of Microcystins and The Potential Risk: Study in Lake Taihu

A systematic investigation was conducted in Lake Taihu in autumn of 2013 and 2014, in order to understand the environmental fate of microcystins (MCs) and evaluate the health risk from MCs. Samples of water, algal cells, macrophytes, shrimps and fish were taken to detect MCs by HPLC-MS/MS after solid phase extraction. Widespread MC contamination in water, algal cells, macrophytes, shrimps and fish was found in Lake Taihu. The ubiquitous presence of MCs in water, algal cells and biota was found in 100% of samples. MC accumulation was in the order of primary producer > tertiary consumer > secondary consumer > primary consumer. The highest levels of MCs in macrophytes, shrimps and fish tissue were found in Potamogeton maackianus, Exopalaemon modestus, and Hyporhamphus intermedius, respectively. The MCs level in shrimps and the tissues of three fish species, Neosalanx tangkahkeii taihuensis, Coilia ectenes and silver carp, was closely linked to their dietary exposure. Ceratophyllum demersum L. was an ideal plant for introduction into lakes to protect against Microcystis blooms and MCs, due to its ability to absorb nutrients, accumulate large amounts of MCs and tolerate these toxins compared to other macrophytes. The average daily intakes (ADIs) of MCs for Exopalaemon modestus and three fish species, Coilia ectenes, Hyporhamphus intermedius and Carassius carassius, were all above the tolerable daily intakes (TDI) set by the World Health Organization (WHO), implying there existed potential threats to human health.

Spatiotemporal Dynamics of Microcystin Variants and Relationships with Environmental Parameters in Lake Taihu, China

Excessive anthropogenically-caused nutrient loading from both external and internal sources has promoted the growth of cyanobacteria in Lake Taihu from 2005 to 2014, suggesting increased production and release of cyanotoxins. In order to explain the spatial distribution and temporal variation of microcystins (MCs), the intracellular concentrations of MCs (MC-LR, -RR and -YR, L, R and Y are abbreviations of leucine, arginine and tyrosine) were monitored monthly from July 2013 to June 2014. Three MC variants are present simultaneously in Lake Taihu; the MC-LR and -RR variants were dominant (accounting for 40% and 39% of the total), followed by MC-YR (21%). However, MC-YR accounted for a higher proportion in colder months, especially in March. The highest concentrations of intracellular MCs were found in July and October when cyanobacteria cell density also reached the maximum. The average concentrations of MC-LR, -RR and -YR in July were 4.69, 4.23 and 2.01 μg/L, respectively. In terms of the entire lake, toxin concentrations in northern parts were significantly higher than the eastern part in summer, when MC concentrations were several times higher than the guideline value by WHO throughout much of Lake Taihu. Results from correlation and redundancy analysis (RDA) showed that total MCs, including all variants, were strongly and positively correlated with cyanobacteria cell density, water temperature, total phosphorus (TP) and pH, whereas each variant had different correlation coefficients with each of the considered environmental variables. MC-RR showed a stronger relationship with temperature, in contrast to MC-YR and -LR. Dissolved inorganic carbon (DIC) showed a negative relationship with each variant, suggesting that rising DIC concentrations may inhibit cyanobacterial growth and thereby reduce MC production in the future.

Phytoplankton succession in a tropical freshwater lake, Bhoj Wetland (Bhopal, India): spatial and temporal perspective

Bhoj Wetland is tropical freshwater system in central India "Bhopal" serving the citizens as one of the major source of water since its inception. Understanding the process of phytoplankton variation can be particularly useful in water quality improvement and management decision. In this study, phytoplankton taxonomic composition, temporal and spatial distribution, and diversity along with limnological abiotic characteristics were studied based on monthly sampling from four sampling stations (between May 2005 and April 2006). A total of 4 classes, 68 genera, and 98 species which belong to Chlorophyceae (52 species), Cyanobacteria (24 species), Bacillariophyceae (19 species), and Euglenophyceae (3 species), respectively, were identified. Phytoplankton assemblages were dominated by Cyanobacteria during summer months and were the most abundant. On an annual average scale, the phytoplankton density varied between 0.24×10(4) units/l at station 4 to 0.46×10(4) units/l at station 2, and station 2 represented highest population density. The predominant indices of the most predominant species varied between 0.03 and 0.26. Among physicochemical variables, temperature and total dissolved solids played a key role in phytoplankton growth as represented by statistical linear regression drawn between temperature, total dissolved solids, nitrate, and phytoplankton with R2 values of 0.6, 0.46, and 0.5, respectively.

Temporal variations in microcystin-producing cells and microcystin concentrations in two fresh water ponds

The relationship between microcystin production, microcystin-producing cyanobacteria, including Microcystis spp., and various biological and physicochemical parameters in Sankuldhara and Lakshmikund, situated in the same geographical area was studied over a period of 1.5 years. Seasonal variation in cyanobacterial 16S rRNA, Microcystis spp. 16S rRNA, mcyA and mcyB genes were quantitatively determined by real-time PCR. Microcystis was the dominant microcystin producer in both study sites constituting 67% and 97% of the total microcystin-producing cyanobacteria at Sankuldhara and Lakshmikund, respectively. Microcystin concentrations were 2.19-39.60 μg/L and 15.22-128.14 μg/L at Sankuldhara and Lakshmikund, respectively, as determined by LC-MS. Principal component analysis revealed a strong positive correlation between microcystin concentration and the copy number of mcyA and mcyB, chlorophyll a and cyanobacterial biomass at both sites. The higher microcystin concentrations in Lakshmikund pond were attributed to the high copy number of mcy genes present coupled with the pond's eutrophication status, as indicated by high total algal biomass, high chlorophyll a content, high nutrient load and low DO. Therefore, a significant difference in microcystin concentrations, correlating with these various biological and physicochemical parameters, confirms the importance of local environmental variables in the overall regulation of microcystins production.

The role of silver nanoparticles functionalized on TiO2for photocatalytic disinfection of harmful algae

Silver loaded TiO₂samples were prepared by photodeposition of different amounts of Ag⁺ions over commercial titanium dioxide (Evonik TiO₂P25) in aqueous media without the presence of sacrificial agents.

Occurrence and spatial distributions of microcystins in Poyang Lake, the largest freshwater lake in China

Occurrence and spatial distributions of microcystins (MCs; MC-RR, -YR, -LR, -LA, -LF, -LW) in Poyang Lake were studied during the period from July 6 to July 18, 2012, by using ultra-high-performance liquid chromatography-electrospray ionization tandem triple quadrupole/mass spectrometry (UPLC-MS/MS). MC-RR was the most dominant variant (94.70 and 84.73 % for intracellular (cellular MCs) and extracellular (dissolved MCs) MCs, respectively) in Poyang Lake, followed by MC-LR (4.65 and 13.17 %, respectively), MC-YR (0.8 and 2.63 %, respectively), and MC-LA (0.02 and 0.00 %), while MC-LW and MC-LF were not detected. Total MCs concentrations (intracellular +extracellular MCs) ranged between 0.0036 and 7.97 μg/L, with an average of 0.79 μg/L, and only two sampling stations with the total MCs concentrations exceeded the drinking water guideline level of 1 μg/L for MC-LR proposed by World Health Organization. The overall spatial pattern of intracellular and extracellular MCs in Poyang Lake demonstrates decreasing trends from east to west, and the south part higher than the north part. Intracellular MCs content was negatively correlated with total nitrogen (r = -0.34, p < 0.01) and NO3 (r = -0.35, p < 0.01), while no significant correlation was found between intracellular MCs concentration and total phosphorus, NH4, and NO2 (p > 0.05), suggesting that NO3 might be a regulating factor for MCs production in Poyang Lake. In addition, intracellular MCs concentrations were positively correlated with wind speed, Microcystis and Cyanobacteria biomass (r = 0.34-0.51, p < 0.05), indicating that wind speed plays an important role in the spatial distributions of MCs, and NO3, toxic cyanobacteria (mainly Microcystis), and wind speed seem to be the important forcing factors driving MCs spatial distributions in Poyang Lake.

Mn(VII)-Fe(II) pre-treatment for Microcystis aeruginosa removal by Al coagulation: simultaneous enhanced cyanobacterium removal and residual coagulant control

A novel Mn(VII)-Fe(II) pre-treatment was proposed to simultaneously enhance the removal of Microcystis aeruginosa by aluminum chloride (AlCl3) coagulation and enabled lowering the dose of Al as effective coagulation can be achieved only by Al, however, at higher doses. In this process, permanganate [Mn(VII)] and ferrous sulfate [Fe(II)] were dosed sequentially prior to Al. The application of Fe(II) not only avoids the extensive oxidation of M. aeruginosa by Mn(VII) but also introduces Fe(III) formed in situ into the system. Results show that, at Al doses of 83.3-108.3 μM, Mn(VII)-Fe(II) pretreatment (Mn(VII) dose: 8.3-16.7 μM; Fe(II) dose: 39.5 μM) is capable of enhancing M. aeruginosa removal by 73.4-81.4%. In contrast, only 0-65.4% and 2.7-8.2% increase in M. aeruginosa removal is achieved by Mn(VII) and Fe(II) pre-treatment, respectively. The ESI-MS spectrum shows that the freshly formed Fe(III) hydrolyzes much more slowly than pre-formed Fe(III) does, and this effect results in its higher efficiency towards the removal of M. aeruginosa. Moreover, in the co-existing system, Fe tends to hydrolyze preferentially and the presence of Fe salts improves the precipitation of Al and vice versa. Thus, the use of Fe and Al as dual-coagulants is practically valuable to control the residual level of coagulant(s) besides its improvement on the removal of M. aeruginosa.

Identification of thyroid-receptor antagonists in water from the Guanting Reservoir, Beijing, China

Thyroid hormone (TH) has long been known to be essential for normal brain development in both humans and animals, and increasing evidence suggests that environmental components may disrupt TH signaling. In the present study, two-hybrid yeast bioassay and chemical analysis were used to evaluate and identify thyroid-receptor (TR) disruptors in water from the Guanting Reservoir, Beijing, China. Modified yeast bioassay showed that the water samples could affect TH signaling. The bioassay-derived amiodarone hydrochloride equivalents ranged from 33.8 ± 3.3 to 308.5 ± 31.8 µg/L. Solid-phase extraction was used to separate the organic extracts, which were subjected to bioassay and chemical analysis. The organic extracts significantly antagonized the TR, which accounted for >86.0 % of the total effects. Thus, organic extracts may play a major role in the TR-disruption activity of the water. Phenols, organochlorine pesticides, and phthalate esters were detected in the organic extracts. Chemical analysis and toxic-equivalent calculation showed that a major cause of the TR antagonism of the water was dibutyl phthalate (80.1 to 122.7 %).

Thyroid hormone disrupting activities of sediment from the Guanting Reservoir, Beijing, China

In the present study, yeast bioassays were used to evaluate and characterize the thyroid receptor (TR) disrupting activities of the organic extracts and elutriates of the sediments from the Guanting Reservoir, Beijing, China. An accelerated solvent extraction was used to separate the organic extracts, which were subjected to a yeast bioassay. The organic extracts could affect thyroid hormone signaling by decreasing the binding of the thyroid hormone. The TR antagonistic activity equivalents (TEQbio) referring to amiodarone hydrochloride were calculated and the observed TEQbio-organic extracts ranged from 25.4 ± 3.7 to 176.9 ± 18.0 μg/g. Elutriate toxicity tests using the modified yeast bioassay revealed that the elutriates also significantly antagonized the TR, with the TEQbio-elutriates ranging from N.D. to 7.8 ± 0.8 μg/L. To characterize the toxic compounds, elutriates were extracted by using a C18 cartridge or treated with ethylenediaminetetraacetic acid (EDTA, 30 mg/L). The results suggested that the addition of EDTA eliminated over 74.3% of the total effects, and the chemical analysis revealed that heavy metals, some of which exhibited TR disrupting potency, for example Zn and Cd, were detectable with higher concentrations in the elutriates. Thus, the cause(s) of toxicity in the elutriate appear to be partly related to the heavy metals.

Occurrence and dominance of Cylindrospermopsis raciborskii and dissolved cylindrospermopsin in urban reservoirs used for drinking water supply, South China

The tropical cyanobacterium Cylindrospermopsis raciborskii is of particular concern for its invasive characteristics and production of the toxin cylindrospermopsin (CYN). The present study represents the first attempt to determine the distribution of C. raciborskii and CYN in tropical China. The presence of C. raciborskii and CYN, as well as the composition of phytoplankton, was determined from a total of 86 samples from 25 urban reservoirs for drinking water supply in Dongguan City of South China. The presence of C. raciborskii was observed in 21 of the 25 reservoirs and confirmed that this species has been widely distributed in the investigated reservoirs. C. raciborskii accounted for between 0.1 and 90.3 % of the total phytoplankton biomass and contributed to the majority of the phytoplankton in some reservoirs such as Tangkengbian and Xiagongyan. Its biomass was negatively correlated with NO3 (-)-N concentration and Secchi depth. Dissolved CYN was detected in more than one-half of the reservoirs with concentrations up to 8.25 μg L(-1), and it positively correlated with C. raciborskii biomass. Dissolved microcystins (MCs) were detected in 12 of the 25 reservoirs with a maximum concentration 1.99 μg L(-1). Our data strongly suggest that C. raciborskii and CYN could be important health hazards in urban reservoirs of South China and that more data are needed for further assessment.

A yeast bioassay for direct measurement of thyroid hormone disrupting effects in water without sample extraction, concentration, or sterilization

The present study introduces an improved yeast bioassay for rapid yet sensitive evaluation of thyroid hormone disruption at the level of thyroid receptor (TR) in environmental water samples. This assay does not require water sample preparation and thus requires very little hands-on time. Based on different β-galactosidase substrates, two modified bioassays, a colorimetric bioassay and a chemiluminescent bioassay, were developed. The compounds tested included the known thyroid hormone 3,3',5-triiodo-l-thyronine (T3), the specific TR antagonist amiodarone hydrochloride (AH) and phthalate esters (PAEs), which potentially disrupt thyroid hormone signaling. The EC50 values for T3 were similar to those previously obtained using a 96-well plate bioassay. TR antagonism by AH was studied in the presence of 2.5 × 10(-7)M T3, and the concentration producing 20% of the maximum effect (RIC20) for AH was 3.1 × 10(-7)M and 7.8 × 10(-9)M for the colorimetric bioassay and chemiluminescent bioassay, respectively. None of the tested PAEs induced β-galactosidase expression, but diethylhexyl phthalate, benzyl butyl phthalate and dibutyl phthalate demonstrated TR antagonism. Furthermore, water samples collected from Guanting reservoir in Beijing were evaluated. Although TR agonism was not observed, antagonism was detected in all water samples and is expressed as AH equivalents. The toxicology equivalent quantity values obtained by the chemiluminescent bioassay ranged from 21.2 ± 1.6 to 313.9 ± 28.8 μg L(-1) AH, and similar values were obtained for the colorimetric bioassay. The present study shows that the modified yeast bioassay can be used as a valuable tool for quantification of thyroid hormone disrupting effects in environmental water samples.

Dissolved microcystins in surface and ground waters in regions with high cancer incidence in the Huai River Basin of China

Microcystins (MCs) are potent hepatotoxins and have also implicated in liver tumor promotion. The present study investigates the temporal and spatial variations of MCs in different water bodies in the Huai River Basin in China. Water samples including rivers, ponds and wells were collected every quarter during December 2008 and December 2009. MCs were determined by high pressure liquid chromatography after solid phase extraction. MCs concentrations in river samples were 0.741±0.623μgL(-1) with maximum of 1.846μgL(-1). MCs in pond were 0.597±0.960μgL(-1) with maximum of 2.298μgL(-1). MCs were also detected in 51.7% of the groundwater samples, MCs in groundwater were 0.060±0.085μgL(-1) with maximum of 0.446μgL(-1). MCs concentrations in groundwater did not differ significantly among different depths or towns (Wilcoxon test, p>0.05). The average MCs in groundwater in each sampling period were 0.068μgL(-1), 0.118μgL(-1), 0.052μgL(-1), 0.059μgL(-1) and 0.020μgL(-1). Through multi linear regression, the best fit model was built on MCs in groundwater with River B (R(2)=0.13, p<0.05), rather than with pond water. The results suggested that MCs contamination in groundwater originated from rivers, causing potential health risk on population who drink groundwater directly.

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).

Fast removal of cyanobacterial toxin microcystin-LR by a low-cytotoxic microgel-Fe(Ⅲ) complex

Eutrophication has become a serious environmental threat throughout the world. In particular, the presence of cyanobacteria toxins, especially microcystins (MCs), has become a severe problem. Inhibition of Microcystis growth in water resources is the most effective way to reduce MCs, but it is a long-term investment. In the present study, a microgel-Fe(Ⅲ) complex was developed for the fast removal of MC-LR. The microgel-Fe(Ⅲ) characteristics and the MC-LR removal dynamics in Milli-Q water and natural water were evaluated. The removal efficiency negatively correlated to the initial MC-LR concentration and pH value (2.0-11.5), but the kinetics was not significantly influenced. The presence of natural organic matter (NOM) in water slightly reduced MC-LR removal using microgel-Fe(Ⅲ). In addition, microgel-Fe(Ⅲ) removed 98.99% of MC-LR in 12 min, while for activated carbon, it took 15-24 h to reach equilibrium. Furthermore, methanol was found to regenerate the microgel-Fe(Ⅲ) after MC-LR removal for at least five regeneration cycles. Finally, the microgel-Fe(Ⅲ) material was made into a membrane so that MCs could be removed by filtration. Therefore, microgel-Fe(Ⅲ) is an effective technology and has a great potential in removing MC-LR from drinking water resources.

Temporal variation in density and diversity of cyanobacteria and cyanotoxins in lakes at Nagpur (Maharashtra State), India

Toxic cyanobacteria (TCB) are known worldwide for the adverse impacts on humans and animals. Species composition and the seasonal variation of TCB in water bodies depend on interactions between physical and chemical factors. The present investigation delineates temporal variations in physico-chemical water quality parameters, viz. nutrients and density, diversity, and distribution of toxic cyanobacteria and cyanotoxins in Lake Ambazari (21 degrees 7'52''N, 79 degrees 2'22''E) and Lake Phutala (21 degrees 9'18''N, 79 degrees 2'37''E) at Nagpur (Maharashtra State), India. These lakes are important sources of recreational activities and fisheries. Toxic cyanobacterial diversity comprised Anabaena, Oscillatoria, Lyngbya, Phormidium, and Microcystis, a well-known toxic cyanobacterial genus, as dominant. Chlorophyll-a concentrations in the lakes ranged from 1.44 to 71.74 mg/m(3). A positive correlation of Microcystis biomass existed with orthophosphate-P (p < 0.05) and nitrate-N (p > 0.05). Identification and quantification of microcystin variants were carried out by high performance liquid chromatography equipped with photodiode array detector. Among all the tested toxin variants, microcystin-RR (arginine-arginine) was consistently recorded and exhibited a positive correlation (p < 0.05) with Microcystis in both the water bodies. Microcystis bloom formation was remarkable between post-monsoon and summer. Besides nutrient concentrations governing bloom formation, the allelopathic role of microcystins needs to be established.

Model AVSWAT apropos of simulating non-point source pollution in Taihu lake basin

Accelerated eutrophication and nutrient loads in the lakes are of major concern for human health and environment. This study was undertaken for modeling the non-point source pollution of Taihu lake basin in eastern China. The SWAT model having an interface in ArcView GIS was employed. Model sensitive parameters related to hydrology and water quality were obtained by sensitivity analysis, and then calibrated and validated by comparing model predictions with field data. The GIS showed good potential for parameterization of hill-slopes, channels, and representative slope profiles for SWAT model simulations. In a monthly and daily time step, the model's Nash-Sutcliffe coefficient (E) and the coefficient of determination (R(2)) indicated that values of simulated runoff, NH(4)(+)-N and total phosphorus were acceptably closer to the measured data. Surface water parameters especially CN, Soil-AWC and ESCO were the most sensitive and had more recognition in the model. It is concluded that runoff carrying N and P nutrients from chemical fertilizer inputs in agricultural areas is the major contributor to NPSP in the lake basin. So, decrease in excessive use of N and P fertilizers and their synergism with organic manures is recommended that would significantly reduce nutrient pollution in the lake ecosystem.

Analysis of dissolved microcystins in surface water samples from Kovada Lake, Turkey

Dissolved (extracellular) microcystin (MC) concentrations were determined at 3 sampling stations on Lake Kovada, Turkey. The dominant species of cyanobacteria found in August and September of 2006 were Microcystis aeruginosa, Synechococcus sp., Phormidium limosum, Phormidium formosa and Planktothrix limnetica. MC concentrations in water were measured by ELISA and MC variants were examined by HPLC-PDA. Quantitative analysis by HPLC indicated that five MC variants (MC-LR, -RR, -LA, -LW, -LF) were identified in water samples from Kovada Lake. The maximum concentration of dissolved MC-LW was 98.9 microg l(-1) in October. MC-LR was only detected in May at a concentration of 0.5 microg l(-1). The cross reactivity of the antibody (MC10E7) to variants such as MC-LA MC-LW & MC-LF was low. Hence the results determined by ELISA were lower than those determined by HPLC in September and October samples due to differences in the specificity of the antibody to MC variants. Total extracellular MCs was quantified by ELISA and ranged from 0.73 to 48.5 microg MC-LR equivalents l(-1), which in some cases exceeded the WHO provisional Guideline Value for MC-LR in drinking water. This study confirms that the lakes of Turkey should be monitored for toxic cyanobacteria and for MCs to avoid or reduce the potential exposure of people to these health hazards.