High Microcystin Concentrations Research Articles

Evaluating putative ecological drivers of microcystin spatiotemporal dynamics using metabarcoding and environmental data

Microcystin is a cyanobacterial hepatotoxin of global concern. Understanding the environmental factors that cause high concentrations of microcystin is crucial to the development of lake management strategies that minimize harmful exposures. While the literature is replete with studies linking cyanobacterial production of microcystin to changes in various nutrients, abiotic stressors, grazers, and competitors, no single biotic or abiotic factor has been shown to be reliably predictive of microcystin concentrations in complex ecosystems. We performed random forest regression analyses with 16S and 18S rRNA gene sequencing data and environmental data to determine which putative ecological drivers best explained spatiotemporal variation in total microcystin and several individual congeners in a eutrophic freshwater reservoir. Model performance was best for predicting concentrations of the congener MC-LR, with ca. 88% of spatiotemporal variance explained. Most of the variance was associated with changes in the relative abundance of the cyanobacterial genus Microcystis. Follow-up RF regression analyses revealed that factors that were the most important in predicting MC-LR were also the most important in predicting Microcystis population dynamics. We discuss how these results relate to prevailing ecological hypotheses regarding the function of microcystin.

An efficient and affordable laboratory method to produce and sustain high concentrations of microcystins by Microcystis aeruginosa

Microcystis aeruginosa is a cosmopolitan cyanobacteria that continues to jeopardize freshwater ecosystem services by releasing the hepatotoxin microcystin, which can, in some cases, cause death to aquatic fauna and even humans. Currently, our abilities to understand the mechanisms of microcystin toxicology are limited by the lack of a method for producing high concentrations, which are central to large-scale and long-term research in natural systems. Here we present an efficient and affordable laboratory method to produce high concentrations of microcystins by a toxigenic strain of M. aeruginosa. Through batch culture studies, we yielded microcystins at concentrations that are environmentally relevant to freshwaters around the world (1–300 μg L−1), maintained these concentrations without resupplying fresh medium (further reducing costs), and utilized rate equations to model the relationship between the environmental conditions in the cultures and changes occurring within the M. aeruginosa cells. Our assessment suggests that steady production of microcystins depends on the availability of carbon throughout the experiment. Hence, we recommend the use of tissue culture treated flasks with a vented cap to ensure the production of microcystins is uninterrupted. This method demonstrates that microcystins can be produced in the laboratory at concentrations relevant to freshwater ecosystems.•The method demonstrates M. aeruginosa CPCC 300 is a reliable strain of freshwater cyanobacteria that can yield microcystins at environmentally relevant concentrations.•Validation showed M. aeruginosa CPCC 300 is resilient in carbon-limited situations and may respond to stress by shifting the ratio of microcystin congeners.•Cell culture flasks with vented caps —filled no more than 50 % of the flask volume to allow for sufficient air exchange— are an excellent and cost-effective approach to maintaining cell growth and producing microcystins at a range between 300 to 1200 μg L−1.

Variation and diversity of genus microcystis in the water environment of the Nui Coc reservoir, Thai Nguyen province

The Nui Coc reservoir, Thai Nguyen province was built on the Cong River for multi-purposes of providing water for local people such as agricultural irrigation, aquaculture, tourism activities and especially the drinking water supply for the Thai Nguyen city and other surrounding areas. This paper presents the results of the monthly surveys which were conducted during the year 2011 for determination of diversity of Microcytis and the microcystin contents in the isolated Microcystis strains in the water environment of the Nui Coc reservoir. The present results showed that eight species of Microcytis genus of which Microcystis aeruginosa in the water environment of the Nui Coc reservoir was the most abudance. The Microcystis cell density of the Nui Coc reservoir varied seasonally and the highest values were observed in high temperature in the rainy season. The results from the High-Performance Liquid Chromatography (HPLC) analysis showed that the microcystin contents in the isolated Microcystis strains from the Nui Coc reservoir ranged from 0.116 to 0.40 µg MC/mg dried mass. The high cell density of Microcystis and high microcystin concentrations in the isolated Microcystis strains from the Nui Coc reservoir revealed the potential risk for human health. The results also highlighted that it is very necessary and urgent to carry out regular monitoring programs for detecting the occurrence of cyanobacteria and phytoplankton in the water environment of the Nui Coc reservoir in order to timely warn the potential risk of cyanobacteria boom and the adverse impacts on the aquatic ecosystem and especially on human health.

First observation of microcystin- and anatoxin-a-producing cyanobacteria in the easternmost part of the Gulf of Finland (the Baltic Sea)

The aim of this study was to obtain the first data on the occurrence and distribution of potentially toxic cyanobacteria and cyanotoxins in the Russian Easternmost part of the Gulf of Finland of the Baltic Sea. Studied samples were collected from 2012 to 2017 and three independent approaches – HPLC-HRMS, PCR and light microscopy were applied for cyanotoxins analysis and detection of toxigenic cyanobacteria. Aphanizomenon flos-aquae Ralfs ex Born. et Flah., Planktothrix agardhii (Gom.) Anag. et Kom., Microcystis aeruginosa (Kütz.) Kütz. and Dolichospermum spp. dominated among cyanobacteria in collected samples. In 2012–2013 during research cruises, microcystins concentrations varied from below detection levels to low (0.01–0.6 μg L−1) values. In the autumn of 2015 and 2017, during cyanobacterial bloom events very high concentrations of microcystins (dissolved up to 49 μg L−1, intracellular up to 466 μg g−1) and dissolved anatoxin-a (1.4 μg L−1) were detected. The evaluated toxin profile was represented by most common arginine-containing variants of microcystins (MC-LR, MC-RR, MC-YR) and their desmethylated forms. Leucine-containing congeners (MC-LF; MC-LY; MC-LW for the biomass sample from the coast of Komarovo, 2015) were found at low concentrations. In environmental DNA from bloom samples, we identified mcy genes regions responsible for MC biosynthesis that are specific for Dolichospermum, Microcystis, and Planktothrix. This study is the first molecular evidence the ability of Microcystis aeruginosa and Planktothrix agardhii from the Gulf of Finland to produce microcystins. On the basis of the obtained data of genus-specific PCR and microscopy, we suppose the presence of anatoxin-a-producing Apanizomenon flos-aquae population in the phytoplankton of Russian part of the Gulf of Finland.

Effects of Wind Mixing in a Stratified Water Column on Toxic Cyanobacteria and Microcystin-LR Distribution in a Subtropical Reservoir.

We analyzed the effects of stratification changes due to wind on the vertical cyanobacteria distribution and microcystin-LR concentrations in a reservoir and assessed the implications for water management. Under stratified conditions, the highest microcystin concentrations (up to 4.16µg/L) and toxic cyanobacteria biovolume occurred in the epilimnion (~ 1m). The lowest microcystin concentrations were between 0.02 and 1.28µg/L and occurred in the hypolimnion (~ 20m). A cold front passage associated with high wind velocities induced water column mixing, promoting the redistribution of microcystin-LR and cyanobacteria throughout the water column and increasing their concentrations in deeper zones. Microcystin-LR concentration was positively correlated with cyanobacteria biovolume (r = 0.747) and chlorophyll a concentration (r = 0.798). Changes in thermal profile due to wind would imply a greater challenge for drinking water treatment plants, since high cyanobacterial and microcystin concentrations could reach deep-water intakes.

Concentrations of microcystins in the muscle and liver tissues of fish species from Koka reservoir, Ethiopia: A potential threat to public health

Herein, we report the presence and concentrations of three most common variants of microcystin (MC–LR, –RR and –YR) in the liver and muscle tissues of wild Nile Tilapia (Oreochromis niloticus), Common Carp (Cyprinus carpio) and African Sharp Tooth Catfish (Clarias gariepinus), which were collected from two study sites of the present study on Koka reservoir, Ethiopia. A total of 36 fish liver and 36 fish muscle samples were collected for six months. Microcystins (MCs) were quantified using LC-ESI-HRMS. The results show that MCs were found in most of the fish liver samples, while they were below the detection limit of the method of analysis used in the muscle samples. In addition to the three most common congeners of MCs, eight other microcystin variants and cylindrospermopsin were detected in the fish liver samples although further detailed study is needed. Among the three most common MC congeners, MC-LR was more prevalent than MC-RR and MC-YR in the liver samples of the three fish species. The highest MC concentration was found in Nile Tilapia collected in April (591.60 μg/g DW of MC-LR), whereas the lowest detected concentration was in Catfish collected in March (2.23 μg/g DW of MC-RR). The results of this study suggest that further intensive assessment and monitoring of the reservoir from different perspectives should be conducted in order to reduce the concentrations of the MCs and seek solutions to the potential public health risk. Moreover, this is the first study ever to report detailed quantification of MCs in fish liver and muscle samples collected from Ethiopia.

Environmental factors influencing the quantitative distribution of microcystin and common potentially toxigenic cyanobacteria in U.S. lakes and reservoirs

Many species of cyanobacteria are capable of producing toxins and causing nuisance blooms, however response to environmental conditions is likely taxon-specific. Environmental factors influencing cyanobacterial composition and toxin production in lakes have been examined in many studies; yet are often confined to individual water bodies, or to a small number of systems within the same region. Here, data from the 2012 USEPA National Lakes Assessment are used to examine relationships between biovolume of common potentially-toxigenic cyanobacteria (Aphanizomenon spp., Cylindrospermopsis spp., Dolichospermum spp., Microcystis spp. and Planktothrix spp.) and environmental variables across the entire conterminous United States, and results are compared across nine distinct ecoregions. Total phosphorus and water clarity were identified as the most influential environmental factors correlated with phytoplankton community composition. The Northern, Southern and Temperate Plains ecoregions displayed the highest biovolumes of potentially toxigenic taxa on average, as well as highest mean concentrations of microcystin. In those three ecoregions, samples with microcystin concentrations greater than 1 ppb were primarily dominated by Planktothrix spp. while in all other ecoregions Dolichospermum spp. was the dominant genus. Canonical Correlation Analysis revealed a strong association between high microcystin concentrations and high nutrient concentrations (total nitrogen and total phosphorus), and between high microcystin concentrations and low percentage of watershed forest cover. Results from this study indicate that the likely occurrence of potentially toxigenic taxa in lakes and reservoirs is predictable on a biogeographical basis, depending on morphological and water quality characteristics. Data from this study may be useful to regional managers attempting to prevent or mitigate nuisance cyanobacterial blooms.

Evaluation of a Norwegian-developed ELISA to determine microcystin concentrations in fresh water

Abstract Cyanobacteria are known for their extensive and highly visible blooms in rivers or dams in Africa. One of the most important cyanobacteria is Microcystis aeruginosa which can synthesise various microcystins that may affect the health of humans and animals. Accurate and efficient detection of microcystins in water is thus important for public and veterinary health. Two enzyme-linked immunosorbent assays (ELISA), a commercially-available ELISA kit (Abraxis) and a newly-developed Norwegian ELISA (putatively cheaper and more robust) were used to detect microcystins in fresh water in South Africa. Water samples were collected monthly at two sites, the Hartbeespoort Dam and a crocodile breeding dam. Extremely high microcystin concentrations (exceeding 360 μg L−1) were detected in the Hartbeespoort Dam during January 2015, whereas the microcystin concentrations in the crocodile breeding dam peaked during March–April 2015. Both ELISAs were positively correlated when analysing water samples ‘as is’ and following resin adsorption and methanol extraction. However, following resin adsorption and methanol extraction of the water samples, the correlation between the two assays was much stronger. These results suggests that the two ELISAs provide comparable results. If the Norwegian-developed ELISA can be packaged and made available as a user-friendly kit, it could be used successfully in surveillance programmes to monitor microcystin concentrations in fresh water bodies in Africa.

Occurrence of the First Toxic Microcystis Bloom in a Recent Moroccan Reservoir

In order to understand initial conditions that promote the first occurrence of a Microcystis aeruginosa bloom and to evaluate its toxic potential, we studied spatio-temporal dynamics of phytoplankton, including Microcystis, microcystins concentrations, the relative proportion of potentially microcystin producing cells and physicochemical parameters in the recently setup Moroccan reservoir “Yaacoub Al Mansour.” High summer temperatures, thermal stability, hydrological stability of the water column and the decrease of nutrient contributions seem to be the major environmental factors responsible of this first bloom occurrence. Despite the low cellular abundance, high microcystins concentrations, associated with low percentage of toxic strains, were measured. Thus, microcystins analysis and associated management of the reservoir are necessary from the beginning of the setup and can help managers to find the better environmental strategy against early cyanobacteria proliferations.

Effects of microcystins contamination on soil enzyme activities and microbial community in two typical lakeside soils

A 30-day indoor incubation experiment was conducted to investigate the effects of different concentrations of microcystin (1, 10, 100 and 1000 μg eq. MC-LR L−1) on soil enzyme activity, soil respiration, physiological profiles, potential nitrification, and microbial abundance (total bacteria, total fungi, ammonia-oxidizing bacteria and archaea) in two lakeside soils in China (Soil A from the lakeside of Lake Poyanghu at Jiujiang; Soil B from the lakeside of Lake Taihu at Suzhou). Of the enzymes tested, only phenol oxidase activity was negatively affected by microcystin application. In contrast, dehydrogenase activity was stimulated in the 1000 μg treatment, and a stimulatory effect also occurred with soil respiration in contaminated soil. The metabolic profiles of the microbial communities indicated that overall carbon metabolic activity in the soils treated with high microcystin concentrations was inhibited, and high concentrations of microcystin also led to different patterns of potential carbon utilization. High microcystin concentrations (100, 1000 μg eq. MC-LR L−1 in Soil A; 10, 100 1000 μg eq. MC-LR L−1 in Soil B) significantly decreased soil potential nitrification rate. Furthermore, the decrease in soil potential nitrification rate was positively correlated with the decrease of the amoA gene abundance, which corresponds to the ammonia-oxidizing bacterial community. We conclude that application of microcystin-enriched irrigation water can significantly impact soil microbial community structure and function.

Influence of light and mixing regime on bloom‐forming phytoplankton in a subtropical reservoir

AbstractThe joint influence of local climatic and hydrological conditions on the vertical distribution of bloom‐forming phytoplankton was analysed for the Salto Grande Reservoir, a large and enriched subtropical system on the Uruguay River (South America). Threshold of physical factors hindering or impeding blooms was obtained and then contrasted with worldwide observations in reservoirs at similar latitudes. Inflowing discharge, water level, and wind velocity intensity interacted with temperature, producing mixing and light regimes with overriding influence on the vertical distribution of Microcystis spp., Dolichospermum spp., and Ceratium furcoides, hence affecting their maximum abundance and biomass. Cyanobacteria (Microcystis > Dolichospermum) showed the most heterogeneous distribution in the depth profile during strong thermal stratification, showing surface scums prone to horizontal displacements. C. furcoides was evenly distributed in the water column in correspondence to windy periods. Blooms of both Cyanobacteria and dinoflagellates did not occur when inflowing discharge exceeded 10,000 m3 s−1. Nutrient influence on phytoplankton vertical distribution appeared strongly subordinate to the effect of light. Highest microcystin concentrations (>WHO alert Level 2) occurred especially after blooms collapsed during highly turbulent situations.

Vertical transmission of microcystins to Nile crocodile (Crocodylus niloticus) eggs

Cyanobacteria or blue green algae are known for their extensive and highly visible blooms in eutrophic, stagnant freshwater bodies. Climate change and global warming have also contributed to a rise in toxic cyanobacterial blooms. One of the most important cyanobacteria is Microcystis aeruginosa, which can synthesize various microcystins that can affect the health of terrestrial and aquatic animals. Commercial Nile crocodile (Crocodylus niloticus) farming in South Africa is based on keeping breeders (adult males and females) in big dams on farms (captive-bred approach). Unfortunately, cyanobacterial blooms in the breeder dams are a concern to farm owners, managers and veterinarians. The main objectives of this research project were to determine if microcystins were present in the contents of crocodile eggs and the liver and yolk of dead hatchlings, and to determine if the reduced hatchability on commercial farms might be caused by these toxins. Furthermore, the concentration of microcystins in the breeder dam was monitored on a monthly basis spanning the ovulation and egg laying period. During the hatching season microcystin concentrations in unfertilised eggs, egg shell membranes and in the yolk and liver of dead hatchlings were determined using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Microcystins were detected in Nile crocodile egg and hatchling samples. Microcystin (MC-LR, MC-RR, MC-YR) concentrations in the crocodile egg and hatchling samples collected from clutches with a good hatching rate (≥90%) ranged between 0 and 1.76 ng g−1, with the highest concentration in the egg shell membranes. Microcystin concentrations in samples collected from clutches with a bad hatching rate (≤10%) ranged from 0 – 1.63 ng g−1 with the highest concentration detected in the hatchling yolk. However, the concentrations were probably underestimated as the percentage recovery from spiked samples was very low with the extraction method employed. Bayesian analysis suggests that the liver, yolk and unfertilised egg all have similar microcystin concentrations, while the membranes have (with moderate to high certainty) higher microcystin concentrations. There appears to be no difference in microcystin concentrations among good and bad clutches across all tissue types or within a specific tissue type, but due to the small sample size, it was not possible to determine whether microcystin affected the hatchability of Nile crocodile eggs. However, vertical transmission of microcystin variants to the Nile crocodile egg does occur and the possible implications for the survival of wild Nile crocodile populations should be ascertained.

Accumulation of microcystins in a dominant Chironomid Larvae (Tanypus chinensis) of a large, shallow and eutrophic Chinese lake, Lake Taihu.

Although there have been numerous studies on microcystin (MC) accumulation in aquatic organisms recently, the bioaccumulation of MCs in relatively small sized organisms, as well as potential influencing factors, has been rarely studied. Thus, in this study, we investigated the bioaccumulation of three MC congeners (-LR, -RR and -YR) in the chironomid larvae of Tanypus chinensis (an excellent food source for certain fishes), the potential sources of these MCs, and potentially relevant environmental parameters over the course of one year in Lake Taihu, China. MC concentrations in T. chinensis varied temporally with highest concentrations during the warmest months (except August 2013) and very low concentrations during the remaining months. Among the three potential MC sources, only intracellular MCs were significantly and positively correlated with MCs in T. chinensis. Although MC concentrations in T. chinensis significantly correlated with a series of physicochemical parameters of water column, cyanobacteria species explained the most variability of MC accumulation, with the rest primarily explained by extraMC-LR. These results indicated that ingestion of MC-producing algae of cyanobacteria accounted for most of the MC that accumulated in T. chinensis. The high MC concentrations in T. chinensis may pose a potential health threat to humans through trophic transfer.

Microcystins affect zooplankton biodiversity in oxbow lakes.

The authors tested the hypothesis that zooplankton diversity and density are affected by the presence of cyanotoxins in the water. The authors focused on 4 oxbow lakes of the Vistula River in southern Poland, which are subjected to mass cyanobacterial development. In 2 of the oxbows (Piekary and Tyniec), microcystins released into the water were found. The highest concentration of microcystins (0.246 μg/L) was observed for microcystins LR. Zooplankton diversity showed a weak response to the presence of microcystins released into the water. The Shannon index (H') of total zooplankton diversity decreased in the Piekary and Tyniec oxbows during periods when the microcystin concentrations were highest. The same trend was noted for diversity of rotifers in both oxbows and for diversity of copepods in Piekary, but not for copepods in Tyniec. No such trends were found for the diversity of cladocerans in any of the oxbows, nor was a relationship found between density of zooplankton and microcystins. Statistical analyses showed that the number of species in individual samples was negatively correlated with the levels of sulfates, phosphates, and ammonia, but the microcystin concentration was positively related to those levels. This points to the complexity of the interactions and synergies among toxins, abiotic factors, and zooplankton biodiversity. In focusing on the problem of cyanotoxins, conservation studies should pay attention to this complexity. Environ Toxicol Chem 2017;36:165-174. © 2016 SETAC.

Groundwater contamination by microcystin from toxic cyanobacteria blooms in Lake Chaohu, China.

Lake Chaohu is a eutrophic lake that experiences massive cyanobacterial blooms. The high concentrations of microcystin observed in this lake are the result of the bloom's high proportion of toxic cyanobacteria strains. Groundwater is the important source of water for drinking, washing, and irrigation in the watershed of Lake Chaohu. This study examines the space-time distribution of microcystins and related environmental factors in wells near Lake Chaohu. All collected groundwater samples from the Lake Chaohu region had detectable concentrations of microcystins. The highest concentration of microcystins, 1.07 μg L(-1), occurred in a well hundreds of meters from the western coast of the lake in September. The distance from the lake shore to the well was significantly and positively correlated with the microcystin concentration in the groundwater. Moreover, a correlation analysis shows that the microcystin concentration in the groundwater was positively correlated with the total dissolved phosphorus (TDP) and microcystin concentration of the nearby lake water. Therefore, the microcystin in the groundwater likely originates from penetration by nearby lake water. Our results suggest that the groundwater near Lake Chaohu poses a significant health risk for the local residents when used for drinking water.

Temporal dynamics of microcystins in Limnodrilus hoffmeisteri, a dominant oligochaete of hypereutrophic Lake Taihu, China

We examined the bioaccumulation of three microcystin (MC) congeners (MC-LR, MC-RR and MC-YR) in the oligochaete Limnodrilus hoffmeisteri from July 2013 through June 2014 in Lake Taihu, China. Environmental parameters and MCs in sediment, phytoplankton and water column also were examined. L. hoffmeisteri accumulated extremely high MC concentrations during the warmest months, with a maximum value of 11.99 μg/g (MC-LR: 1.76 μg/g, MC-RR: 2.51 μg/g, and MC-YR: 7.73 μg/g). Total MC concentrations in L. hoffmeisteri declined after October (2013) and began to increase in May (2014). Between July and October, MC-YR concentration was higher than MC-LR and MC-RR. MC concentrations in L. hoffmeisteri were positively correlated with pH, water temperature, conductivity, chlorophyll a, nitrite and the biomass of Microcystis, and negatively correlated with dissolved oxygen (DO), nitrate, total nitrogen (TN), dissolved total inorganic carbon and the biomass of Bacillariophyta. In addition, MCs in phytoplankton were more strongly correlated with MCs in L. hoffmeisteri than in the water column or sediment. Our results demonstrated that L. hoffmeisteri could accumulate high MC concentrations in the bloom season, which might transfer to the edible zoobenthos and fish through trophic transfer, thereby posing a significant health threat to humans.

Microcystin accumulation in bighead carp (Aristichthys nobilis) during a Microcystis-dominated bloom and risk assessment of the dietary intake in a fish pond in China.

Microcystins (MCs) produced by cyanobacteria can accumulate in freshwater fish tissues and pose potential risk to human health. In this study, variations in MC content were examined in water samples and fish tissues during a Microcystis aeruginosa-dominated bloom in a fish pond in China, from June 2009 to August 2009. A total of ten microcystin variants were detected in water samples in the fish pond, including MCLR, MCRR, MCYR, MCLF, MCLY, MCLA, and MCLW, and other three undefined MC variants. MCLR was the dominant variant in the water samples, followed by MCLF and MCLY. The highest MC concentration in the common carp (Aristichthys nobilis) was found in the order intestine > spleen > muscle; however, the order with the most MC variants detected was muscle > spleen = kidney = gallbladder > liver = intestine. The highest overall MC concentration detected in the water samples was 12.24μgL-1, and the estimated daily intake for humans from the consumption of fish was about 0.48μgMCLReqkg-1 body weight (BW), 12-fold the tolerable daily intake (TDI) proposed by the World Health Organization. Therefore, the combined risks from skin exposure and food intake in this fish pond should not be overlooked.

Dominant factors associated with microcystins in nine midlatitude, maritime lakes

The study objective was to identify factors most closely associated with the presence of cyanotoxins in 9 lakes in the Puget Sound lowlands region of western Washington, USA. Four cyanotoxins (microcystins, anatoxina, saxitoxin, and cylindrospermopsin), phytoplankton, and limnological parameters were monitored twice per month from June through October 2012. Microcystin (MC) was the most commonly detected cyanotoxin and was detected in every lake at least once. Nonparametric decision forests and classification trees were used to identify variables that best predicted MC categories for 2 models; (1) presence–absence of MC, and (2) MC concentrations. The best predictors of MC in concentration categories for both models were epilimnetic total nitrogen to total phosphorus (TN:TP) ratios and the abundance of potential MC-producing cyanobacteria. Model 1 showed that observations with TN:TP ratios ≤25.7 were associated with MC presence, while MC was generally absent when TN:TP ratios were >25.7 and MC-producing cyanobacteria were ≤330 cells mL−1. Model 2 showed that Microcystis abundance >1300 cells mL−1 captured moderate (>1 and ≤6 μg L−1) and high (>6 μg L−1) MC concentrations. Low MC concentrations (>0.05 and ≤1 μg L−1) were found when TN:TP was ≤28.8 or when Dolichospermum abundance was >110 cells mL−1. Because of their broad applicability, thresholds for these variables may be useful in evaluating public health risk in the absence of MC measurements from lakes in this and similar regions. Decision forest and classification tree models may be promising tools for lake mangers to identify dominant factors and threshold limnological values associated with cyanotoxins.

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.

Bioaccumulation of microcystins in invasive bivalves: A case study from the boreal lagoon ecosystem

Summary In the current study we present the first report on the bioaccumulation of microcystins (MC) in zebra mussel Dreissena polymorpha from the eutrophic brackish water Curonian Lagoon. The bioaccumulation capacity was related to age structure of mussels and ambient environmental conditions. We also discuss the relevant implications of these findings for biomonitoring of toxic cyanobacteria blooms in the Curonian Lagoon and potential consequences for D. polymorpha cultivation activities considered for the futures as remediation measure. Samples for the analysis were collected twice per year, in June and September, in 2006, 2007 and 2008, from two sites within the littoral zone of the lagoon. The highest microcystin concentrations were measured in mussels larger than 30 mm length and sampled in 2006 (when a severe toxic cyanobacteria bloom occurred). In the following years, a consistent reduction in bioaccumulated MC concentration was noticed. However, certain amount of microcystin was recorded in mussel tissues in 2007 and 2008, when no cyanotoxins were reported in the phytoplankton. Considering high depuration rates and presence of cyanotoxins in the bottom sediments well after the recorded toxic blooms, we assume mechanism of secondary contamination when microcystin residuals could be uptaken by mussels with resuspended sediment particles.