Concentrations of particulate and dissolved cylindrospermopsin in 21 Aphanizomenon-dominated temperate lakes.

The cyanobacterial toxin cylindrospermopsin (CYN) is widely distributed in German lakes, but volumetric data for risk assessment are lacking and it is unclear which cyanobacterial species produce CYN in Europe. We therefore analyzed CYN concentration and cyanobacterial composition of 21 German lakes in 2005. CYN was detected in 19 lakes (102 of 115 samples). In total, 45 samples contained particulate CYN only, and 57 contained both dissolved and particulate CYN. The concentrations were 0.002-0.484 microg L(-1) for particulate CYN and 0.08-11.75 microg L(-1) for dissolved CYN with a maximum of 12.1 microg L(-1) total CYN. A drinking water guideline value of 1 microg L(-1) proposed by Humpage and Falconer [2003. Oral toxicity of the cyanobacterial toxin CYN in male Swiss albino mice: determination of no observed adverse effect level for deriving a drinking water guideline value. Environ. Toxicol. 18, 94-103] was exceeded in 18 samples from eight lakes due to high concentrations of dissolved CYN. CYN occurrence in the German lakes could not be ascribed to the three known CYN-producing species Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon flos-aquae, which were detected in some lakes in low abundances. The highest correlation coefficients were observed between particulate CYN and the native Aphanizomenon gracile. It occurred in 98 CYN-positive samples, was the most abundant Nostocales and was the only Nostocales in five samples. This indicates that A. gracile is a potential CYN producer in German lakes.     

First evidence of “paralytic shellfish toxins” and cylindrospermopsin in a Mexican freshwater system, Lago Catemaco, and apparent bioaccumulation of the toxins in “tegogolo” snails (Pomacea patula catemacensis)

Exposure to cyanobacterial toxins in freshwater systems, including both direct (e.g., drinking water) and indirect (e.g., bioaccumulation in food webs) routes, is emerging as a potentially significant threat to human health. We investigated cyanobacterial toxins, specifically cylindrospermopsin (CYN), the microcystins (MCYST) and the “paralytic shellfish toxins” (PST), in Lago Catemaco (Veracruz, Mexico). Lago Catemaco is a tropical lake dominated by Cylindrospermopsis, specifically identified as Cylindrospermopsis catemaco and Cylindrospermopsis philippinensis, and characterized by an abundant, endemic species of snail (Pomacea patula catemacensis), known as “tegogolos,” that is both consumed locally and commercially important. Samples of water, including dissolved and particulate fractions, as well as extracts of tegogolos, were screened using highly specific and sensitive ELISA. ELISA identified CYN and PST at low concentrations in only one sample of seston; however, both toxins were detected at appreciable quantities in tegogolos. Calculated bioaccumulation factors (BAF) support bioaccumulation of both toxins in tegogolos. The presence of CYN in the phytoplankton was further confirmed by HPLC-UV and LC-MS, following concentration and extraction of algal cells, but the toxin could not be confirmed by these methods in tegogolos. These data represent the first published evidence for CYN and the PST in Lago Catemaco and, indeed, for any freshwater system in Mexico. Identification of the apparent bioaccumulation of these toxins in tegogolos may suggest the need to further our understanding of the transfer of cyanobacterial toxins in freshwater food webs as it relates to human health.     

Toxicity of cylindrospermopsin, and other apparent metabolites from Cylindrospermopsis raciborskii and Aphanizomenon ovalisporum, to the zebrafish (Danio rerio) embryo

Cyanobacteria produce a diverse array of toxic or otherwise bioactive compounds that pose growing threats to human and environmental health. We utilized the zebrafish (Danio rerio) embryo, as a model of vertebrate development, to investigate the inhibition of development pathways (i.e. developmental toxicity) by the cyanobacterial toxin, cylindrospermopsin (CYN), as well as extracts from various isolates of Cylindrospermopsis raciborskii and Aphanizomenon ovalisporum. CYN was toxic only when injected directly into embryos, but not by direct immersion at doses up to 50 μg/ml. Despite the dose dependency of toxicity observed following injection of CYN, no consistent patterns of developmental defects were observed, suggesting that toxic effects of CYN may not target specific developmental pathways. In contrast, direct immersion of embryos in all of the extracts resulted in both increased mortality and reproducible, consistent, developmental dysfunctions. Interestingly, there was no correlation of developmental toxicity observed for these extracts with the presence of CYN or with previously reported toxicity for these strains. These results suggest that CYN is lethal to zebrafish embryos, but apparently inhibits no specific developmental pathways, whereas other apparent metabolites from C. raciborskii and A. ovalisporum seem to reproducibly inhibit development in the zebrafish model. Continued investigation of these apparent, unknown metabolites is needed.     

Cylindrospermopsin induces alterations of root histology and microtubule organization in common reed (Phragmites australis) plantlets cultured in vitro

We aimed to study the histological and cytological alterations induced by cylindrospermopsin (CYN), a protein synthesis inhibitory cyanotoxin in roots of common reed (Phragmites australis). Reed is an ecologically important emergent aquatic macrophyte, a model for studying cyanotoxin effects. We analyzed the histology and cytology of reed roots originated from tissue cultures and treated with 0.5-40 μg ml⁻¹ (1.2-96.4 μM) CYN. The cyanotoxin decreased root elongation at significantly lower concentrations than the elongation of shoots. As general stress responses of plants to phytotoxins, CYN increased root number and induced the formation of a callus-like tissue and necrosis in root cortex. Callus-like root cortex consisted of radially swollen cells that correlated with the reorientation of microtubules (MTs) and the decrease of MT density in the elongation zone. Concomitantly, the cyanotoxin did not decrease, rather it increased the amount of β-tubulin in reed plantlets. CYN caused the formation of double preprophase bands; the disruption of mitotic spindles led to incomplete sister chromatid separation and disrupted phragmoplasts in root tip meristems. This work shows that CYN alters reed growth and anatomy through the alteration of MT organization.     

Cylindrospermopsin Biodegradation Abilities of Aeromonas sp. Isolated from Rusa?ka Lake

The occurrence of the cyanobacterial toxin cylindrospermopsin (CYN) in freshwater reservoirs is a common phenomenon. However, the biodegradation of this toxin in environmental samples has been observed only occasionally. In this work the biodegradation ability of cylindrospermopsin was investigated based on isolates from lakes with previous cyanotoxin history. Bacterial strains were identified based on the 16S rDNA and rpoD gene comparison. CYN biodegradation was monitored using the HPLC method. The R6 strain identified as Aeromonas sp. was documented as being capable of CYN removal. This biodegradation was dependent on the pH and temperature. Additionally, the stimulation of the growth of the R6 strain in the presence of CYN was indicated. Our discovery supports the hypothesis that (in analogy to the well-known phenomenon of microcystin biodegradation) in lakes dominated by potential CYN-producing cyanobacteria, the processes of microbial utilization of this toxin may occur.     

First report of (homo)anatoxin-a and dog neurotoxicosis after ingestion of benthic cyanobacteria in The Netherlands

In April and May 2011, three dogs died and one dog became ill after swimming in Lake IJmeer (The Netherlands). At the time, the lake was infested with the benthic cyanobacterial species Phormidium. A Eurasian Coot (Fulica atra) and a Black-headed Gull (Chroicocephalus ridibundus) also died near Lake IJmeer in the same period. One of the dogs and both birds were subjected to a pathological investigation. Furthermore, the Phormidium mat; algal samples from the dikes; contents of the animals’ digestive systems and organ tissues were analysed for the following cyanobacterial toxins: (homo)anatoxin-a; (7-deoxy-)cylindrospermopsin; saxitoxins and gonyautoxins by LC-MS/MS. Samples were also analysed for the nontoxic (homo)anatoxin-a metabolites dihydro(homo)anatoxin-a and epoxy(homo)anatoxin-a. The dog necropsy results indicated neurotoxicosis and its stomach contained Phormidium filaments. Anatoxin-a was detected in the Phormidium mat (272 μg g⁻¹ dry weight, stdev 65, n = 3) and in the dog’s stomach contents (9.5 μg g⁻¹ dry weight, stdev 2.4, n = 3). Both samples also contained the anatoxin-a metabolite dihydroanatoxin-a, and a trace of homoanatoxin-a was detected in the Phormidium mat. The birds were in bad nutritive condition at the time of necropsy and their stomachs and intestines did not contain any cyanobacterial material. Furthermore, no cyanobacterial toxins were detected in their stomachs, intestines and organs and they both had lesions that are not associated with cyanobacterial intoxication. This is the first report of anatoxin-a and homoanatoxin-a occurrence in The Netherlands, these toxins have likely caused the deaths of three dogs. The birds probably died of other causes. Dutch recreational waters are at this moment only screened for pelagic cyanobacterial species, the current bathing water protocol therefore does not protect humans and animals from negative effects of blooms of benthic cyanobacteria.     

A comparative study of Florida strains of Cylindrospermopsis and Aphanizomenon for cylindrospermopsin production.

The toxin cylindrospermopsin (CYN) is produced by a variety of cyanobacterial genera. One of these, Cylindrospermopsis raciborskii, is generally assumed to be the source of CYN in lakes and rivers in Florida, USA. However, in this study, none of the eight Florida isolates of this species tested contained the genetic determinants involved in toxin production nor did they produce CYN. We show for the first time that Aphanizomenon ovalisporum isolated from a pond in this state has the genes putatively associated with CYN production. Analysis by liquid chromatography with mass spectrometric detection (LC/MS) revealed that it produced CYN in the range of 7.39-9.33 microg mg(-1) freeze-dried cells. 16S rDNA sequences of this strain showed 99.6% and 99.9% identity to published A. ovalisporum and Anabaena bergii 16S sequences, respectively. These results help to explain the general lack of a defined relationship between the abundance of C. raciborskii in freshwater ecosystems of Florida and observed concentrations of CYN. The latter observation raises the potential that previous reports of CYN may be coincidental with unrecorded presence of another CYN-producing species.     

Recreational exposure to microcystins during algal blooms in two California lakes

We conducted a study of recreational exposure to microcystins among 81 children and adults planning recreational activities on either of three California reservoirs, two with significant, ongoing blooms of toxin-producing cyanobacteria, including Microcystis aeruginosa (Bloom Lakes), and one without a toxin-producing algal bloom (Control Lake). We analyzed water samples for algal taxonomy, microcystin concentrations, and potential respiratory viruses (adenoviruses and enteroviruses). We measured microcystins in personal air samples, nasal swabs, and blood samples. We interviewed study participants for demographic and health symptoms information. We found highly variable microcystin concentrations in Bloom Lakes (<10 μg/L to >500 μg/L); microcystin was not detected in the Control Lake. We did not detect adenoviruses or enteroviruses in any of the lakes. Low microcystin concentrations were found in personal air samples (<0.1 ng/m³ [limit of detection]-2.89 ng/m³) and nasal swabs (<0.1 ng [limit of detection]-5 ng). Microcystin concentrations in the water-soluble fraction of all plasma samples were below the limit of detection (1.0 μg/L). Our findings indicate that recreational activities in water bodies that experience toxin-producing cyanobacterial blooms can generate aerosolized cyanotoxins, making inhalation a potential route of exposure. Future studies should include collecting nasal swabs to assess upper respiratory tract deposition of toxin-containing aerosols droplets.     

Nitrogen Limitation Promotes Accumulation and Suppresses Release of Cylindrospermopsins in Cells of Aphanizomenon Sp.

As the biosynthesis of cylindrospermopsin (CYN) is assumed to depend on nitrogen availability, this study investigated the impact of nitrogen availability on intra- and extracellular CYN and deoxy-CYN (D-CYN) contents in three Aphanizomenon strains from temperate waters. Nitrogen deficient (−N) cultures showed a prolonged growth phase and intracellular toxin accumulation by a factor of 2–6. In contrast, cultures with additional nitrate supply (+N) did not accumulate CYN within the cells. Instead, the maximum conceivable CYN release estimated for dead cells (identified by SYTOX^® Green staining) was much lower than the concentrations of dissolved CYN actually observed, suggesting these cultures actively release CYN from intact cells. Furthermore, we found remarkably altered proportions of CYN to D-CYN: as batch cultures grew, the proportion of D-CYN increased by up to 40% in +N medium, whereas D-CYN remained constant or decreased slightly in −N medium. Since +N cultures showed similar toxin patterns as −P cultures with increased extracellular CYNs and higher proportion of D-CYN we conclude that nitrogen limitation may affect the way the cells economize resources, especially the yield from phosphorus pools, and that this has an impact on CYN production and release. For water management, these result imply that nutrient availability not only determines the abundance of potentially CYN-producing cyanobacteria, but also the amount of extracellular CYNs (challenging drinking-water treatment) as well as the ratio of D-CYN to CYN (affecting toxicity).     

Occurrence of the cyanobacterial toxin cylindrospermopsin in northeast Germany

The frequent occurrence of the cyanobacterial toxin cylindrospermopsin (CYN) in the (sub)tropics has been largely associated with cyanobacteria of the order Nostocales of tropical origin, in particular Cylindrospermopsis raciborskii. C. raciborskii is currently observed to spread northwards into temperate climatic zones. In addition, further cyanobacteria of the order Nostocales typically inhabiting water bodies in temperate regions are being identified as CYN-producers. Therefore, data on the distribution of CYN in temperate regions are necessary for a first assessment of potential risks due to CYN in water used for drinking and recreation. A total of 127 lakes situated in the north-eastern part of Germany were investigated in 2004 for the presence of the toxin CYN and the phytoplankton composition. The toxin could be detected in half of the lakes (n = 63) and in half of 165 samples (n = 88). Concentrations reached up to 73.2 microg CYN/g DW. CYN thus proved more widely distributed than previously demonstrated. The analyses of phytoplankton data suggest Aphanizomenon sp. and Anabaena sp. as important CYN producers in Germany, and confirm recent findings of Aphanizomenon flos-aquae as CYN-producing species frequently inhabiting water bodies in temperate climatic regions. The data shown here suggest that CYN may be an important cyanobacterial toxin in German water bodies and that further data are needed to assess this.     

First report of anatoxin-a-producing cyanobacterium Aphanizomenon issatschenkoi in northeastern Germany

The neurotoxin anatoxin-a (ATX), has been detected in several northeast German lakes during the last two decades, but no ATX producers have been identified in German water bodies so far. In 2007 and 2008, we analyzed phytoplankton composition and ATX concentration in Lake Stolpsee (NE Germany) in order to identify ATX producers. Sixty-one Aphanizomenon spp. strains were isolated, morphologically and phylogenetically characterized, and tested for ATX production potential by liquid chromatography-tandem mass spectrometry (LC-MS/MS). New primers were specifically designed to identify a fragment of a polyketide synthase gene putatively involved in ATX synthesis and tested on all 61 Aphanizomenon spp. strains from L. Stolpsee and 92 non-ATX-producing Aphanizomenon spp., Anabaena spp. and Anabaenopsis spp. strains from German lakes Langersee, Melangsee and Scharmützelsee.As demonstrated by LC-MS/MS, ATX concentrations in L. Stolpsee were undetectable in 2007 and ranged from 0.01 to 0.12 μg l⁻¹ in 2008. Fifty-nine of the 61 strains isolated were classified as Aphanizomenon gracile and two as Aphanizomenon issatschenkoi. One A. issatschenkoi strain was found to produce ATX at concentrations of 2354 ± 273 μg g⁻¹ fresh weight, whereas the other A. issatschenkoi strain and A. gracile strains tested negative. The polyketide synthase gene putatively involved in ATX biosynthesis was found in the ATX-producing A. issatschenkoi strain from L. Stolpsee but not in the non-ATX-producing Aphanizomenon spp., Anabaena spp. and Anabaenopsis spp. strains from lakes Stolpsee, Langersee, Melangsee, and Scharmützelsee.This study is the first confirming A. issatschenkoi as an ATX producer in German water bodies.     

Detection of the neurotoxin BMAA within cyanobacteria isolated from freshwater in China

The cyanobacterial neurotoxin, β-N-methylamino-l-alanine (BMAA), has been suggested as an important environmental factor for neurodegenerative disease such as amyotrophic lateral sclerosis- Parkinsonism dementia complex (ALS/PDC) in Guam. BMAA was detected within the majority of cyanobacterial isolates surveyed in both free and symbiotic cyanobacteria, living in freshwater as well as marine environments. In this study, we report two methods using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS/MS) each coupled with a different type of hydrophilic interaction liquid chromatography (HILIC) column to detect BMAA. A third method using AQC-derivatized BMAA was also used for comparison. Axenic cultures of Microcystis aeruginosa and Nostoc sp. isolated from Chinese freshwater were analyzed for both free and protein-bound BMAA at the exponential growth stage. Cultures of two strains of M. aeruginosa collected at four growth stages were also analyzed for the presence of BMAA. BMAA was detected in the Nostoc sp. at very low concentrations (<0.07 pmoles on column) only when precolumn AQC derivatization was used. No BMAA was detected in the Chinese derived axenic cultures of Microcystis; detection limits for the LC-ESI-MS and LC-ESI-MS/MS without precolumn derivatization were 10 ng and 2 pg BMAA on column, respectively. We suggest that cyanobacteria grown under some culture conditions may be relatively free of BMAA.     

Detection of microcystin contamination by the measurement of the variability of the in vivo chlorophyll fluorescence in aquatic plant Lemna gibba

In recent years, chlorophyll fluorescence analysis has become one of the most powerful and widely used techniques available to plant ecophysiologists. In this work, the chlorophyll fluorescence is used in order to evaluate the biotic stress induced by exposure to cyanobacterial toxins (microcystins). Experiments were carried on the aquatic plant Lemna gibba exposed to various concentrations of a microcystins (0.01, 0.03, 0.05, 0.07, 0.15, 0.22 and 0.3 μg equivalent MC-LR.mL⁻¹) during 5 h. The reversibility of the stress changes was also studied following 24 h of treatment. The efficiency and the utility of this biophysical technique were compared to biochemical analysis priory used to evaluate the plant stress induced by such contamination. The results showed that there is a concentration-dependent effect on the measured in vivo chlorophyll fluorescence with significant differences between the control and all concentrations except for 0.01 μg equivalent MC-LR.mL⁻¹. The reversibility tested showed also that after avoiding the contact with the microcystins, the chlorophyll fluorescence measurements were not significantly different from the control. The results showed that if the contact with the microcystins is short and not repeated plants may not suffer from a significant stress. We concluded that this simple and rapid technique based on the variable fluorescence, could be recommended and applied to test the plant stress caused by cyanobacterial toxins.     

Pharmacokinetics of prenylflavonoids and correlations with the dynamics of estrogen action in sera following ingestion of a standardized Epimedium extract

To explore pharmacokinetic properties of prenylflavonoids from the Traditional Chinese Medicinal plant Epimedium, three doses of a standardized extract (100, 300 and 600 mg/kg body weight), were administered to ovariectomized rats and serial blood samples were obtained. Serum concentrations of the Epimedium prenylflavonoids icariin, icariside I, icariside II, icaritin and desmethylicaritin were determined by LC–MS/MS. Aliquots of sera were also applied to human cell lines that permanently express ERα and ERβ proteins for the ex vivo measurement of estrogenic activity. All five prenylflavonoids exhibit non-linear dose-dependent increases in the area under concentration versus time curves. Two distinct pharmacokinetic patterns were evident, an early phase wherein icariin and icariside II reached t_max 0.5–1 h, and a late phase wherein icariside I, icaritin and desmethylicaritin peaked at t_max 8 h. Total concentrations of icaritin and desmethylicaritin reached C_max ∼2 μM and ∼0.25 μM respectively. Estrogenic activity in Epimedium-treated rat sera lagged by several hours compared to animals treated with control drug estradiol benzoate, corresponding to the appearance of bioactive metabolites desmethylicaritin, icaritin and icariside I. Following glucuronidase/sulphatase treatment, prolonged estrogenic activity at higher Epimedium doses (300 and 600 mg/kg of body weight) was evident, and correlated with the persistence of micromolar levels of icaritin at the 48–72 h sampling period. The depot effect resulted in time–concentration bioactivity profiles at the three Epimedium doses (area under curve 374, 543, and 771 pM E2 h⁻¹) that exceeded that observed for estradiol benzoate (148 pM E2 h⁻¹). Our study correlated the pharmacokinetics of prenylflavonoids with the dynamics of their estrogenic effects and reveals the potential estrogenicity of this Epimedium extract. This study may aid the development of prenylflavonoids as drugs for menopause and other conditions requiring estrogenic action.     

17β-Oestradiol may prolong reproduction in seasonally breeding freshwater gastropod molluscs

Whilst the effects of oestrogenic contaminants in the aquatic environment are well documented in fish, effects in invertebrate species has been subject to debate, possibly due to differences in experimental conditions (temperature, timing and duration of exposure) between studies. It has been suggested that molluscs are only susceptible to oestrogens in periods either following the main spawning or leading up to the maturation of gametes. To investigate this possibility, two temperate, seasonally reproducing gastropods (Planorbarius corneus and Viviparus viviparus) were exposed to two concentrations of 17β-oestradiol (E2; 10 ng/l and 100 ng/l nominal) in an outdoor mesocosm (subject to natural seasons). In addition, P. corneus was also exposed to E2 (1, 10 and 100 ng/l) in the laboratory at temperatures and photoperiods to simulate summer and autumn.In the mesocosm, both snail species produced similar numbers of eggs/embryos as reference groups in the summer, but the groups exposed to 10 ng E2/l (nominal) had significantly higher productivities after the onset of autumn, when entering their quiescent phase, whilst the snails exposed to a higher concentration (100 ng/l, nominal) had an increased rate of mortality, and did not experience increased reproduction. In the laboratory, the rate of egg laying in P. corneus was unaffected in simulated summer (20 °C, 16 h photoperiod), but snails exposed to 10 and 100 ng/l (nominal) in simulated autumn (15 °C, 12 h photoperiod) showed a concentration-dependent inhibition of the natural decline in egg laying observed in the control snails. Overall, rather than an increase in reproductive rate, the response of this species was a perpetuation of summer reproductive rates into autumn. We conclude that exposure to E2 can affect reproduction in the freshwater gastropods studied, but in P. corneus at least, this is dependent on the seasonal conditions (temperature and photoperiod) at which exposures are made.     

First report on cylindrospermopsin producing Aphanizomenon flos-aquae (Cyanobacteria) isolated from two German lakes.

Three single-filament isolates of Aphanizomenon flos-aquae from two German lakes were found to produce remarkable amounts of the cyanobacterial hepatotoxin cylindrospermopsin (CYN). CYN-synthesis of the strains were evidenced both by LC-MS/MS analysis and detection of PCR products of gene fragments which are implicated in the biosynthesis of the toxin. The strains contain CYN in the range of 2.3-6.6 mg g(-1) of cellular dry weight. To our knowledge this is the first report of CYN in A. flos-aquae.     

The first occurrence of the cyanobacterial alkaloid toxin cylindrospermopsin in the Czech Republic as determined by immunochemical and LC/MS methods

Cylindrospermopsin (CYN) is a newly emerging carcinogenic alkaloid originally identified in tropical cyanobacteria Cylindrospermopsis raciborskii. Some recent studies reported production of this toxin also by other cyanobacteria in European countries. Here we report comparison of the immunochemical ELISA determination with the liquid chromatography/mass spectrometry (LC/MS) method for CYN analyses in the samples from the Czech Republic, Central Europe. We have analysed 56 samples of raw lake waters collected from 32 localities. CYN was found at 3 localities with Aphanizomenon sp. sub-dominated water blooms. Results of the ELISA and LC/MS showed good qualitative agreement. However, concentrations determined by ELISA (0.4-4 μg/L) were systematically higher than concentrations determined by LC/MS (0.01-0.3 μg/L). Differences between methods could be attributed to matrix effects (both in ELISA and LC/MS) or ELISA cross-reactivity with other unidentified derivatives of CYN. Our study demonstrates for the first time occurrence of CYN in the Central Europe. With respect to its suspected carcinogenicity, further research on distribution, concentrations and risks of this cyanobacterial toxin is needed.     

Oxidation of Cylindrospermopsin by Fenton Process: A Bench-Scale Study of the Effects of Dose and Ratio of H2O2 and Fe(II) and Kinetics

The cyanotoxin cylindrospermopsin (CYN) has become a significant environmental and human health concern due to its high toxicological potential and widespread distribution. High concentrations of cyanotoxins may be produced during cyanobacterial blooms. Special attention is required when these blooms occur in sources of water intended for human consumption since extracellular cyanotoxins are not effectively removed by conventional water treatments, leading to the need for advanced water treatment technologies such as the Fenton process to produce safe water. Thus, the present study aimed to investigate the application of the Fenton process for the degradation of CYN at bench-scale. The oxidation of CYN was evaluated by Fenton reaction at H₂O₂/Fe(II) molar ratio in a range of 0.4 to 4.0, with the highest degradation of about 81% at molar ratio of 0.4. Doubling the concentrations of reactants for the optimized H₂O₂/Fe(II) molar ratio, the CYN degradation efficiency reached 91%. Under the conditions studied, CYN degradation by the Fenton process followed a pseudo-first-order kinetic model with an apparent constant rate ranging from 0.813 × 10⁻³ to 1.879 × 10⁻³ s⁻¹.     

Retention and degradation of the cyanobacterial toxin cylindrospermopsin in sediments - The role of sediment preconditioning and DOM composition

Recent results show that cylindrospermopsin is more frequent and widespread in surface waters than previously assumed. Studies on the fate of CYN in sediments are lacking, but this is important if these resources are used for drinking-water production via sediment passage. Therefore, the aim of our study was to determine a) CYN retention in two sandy sediments as a function of flow rate, CYN concentration, the presence of DOM and the content of fines (1% and 4%, respectively) and b) the influence of sediment preconditioning and DOM composition of the water (aquatic DOM versus DOM released from lysed cells) on CYN degradation. Retention of CYN proved negligible under the investigated conditions. Degradation in virgin sediments showed the highest lag phases (20 days). Preconditioned sediments showed no lag phase. The presence of aquatic DOM yielded highest degradation rates (κ₁ = 0.46 and 0.49 day⁻¹) without a lag phase. Readily available organic carbon sources were preferentially metabolized and hence induced a lag phase. Thus, the presence and composition of DOM in the water proved important for both CYN degradation rates in preconditioned sediments and for the lag phase. Cylindrospermopsin degradation took place solely in the sediment and not in the water body.