Cylindrospermopsin toxicity in mice following a 90-d oral exposure.

Cylindrospermopsin (CYN) is a toxin associated with numerous species of freshwater cyanobacteria throughout the world. It is postulated to have caused an episode of serious illnesses in Australia through treated drinking water, as well as lethal effects in livestock exposed to water from farm ponds. Toxicity included effects indicative of both hepatic and renal dysfunction. In humans, symptoms progressed from initial hepatomegaly, vomiting, and malaise to acidosis and hypokalemia, bloody diarrhea, and hyperemia in mucous membranes. Laboratory animal studies predominantly involved the intraperitoneal (i.p.) route of administration and confirmed this pattern of toxicity with changes in liver enzyme activities and histopathology consistent with hepatic injury and adverse renal effects. The aim of this study was designed to assess subchronic oral exposure (90 d) of purified CYN from 75 to 300 µg/kg/d in mouse. At the end of the dosing period, examinations of animals noted (1) elevated organ to body weight ratios of liver and kidney at all dose levels, (2) treatment-related increases in serum alanine aminotransferase (ALT) activity, (3) decreased blood urea nitrogen (BUN) and cholesterol concentrations in males, and (4) elevated monocyte counts in both genders. Histopathological alterations included hepatocellular hypertrophy and cord disruption in the liver, as well as renal cellular hypertrophy, tubule dilation, and cortical tubule lesions that were more prominent in males. A series of genes were differentially expressed including Bax (apoptosis), Rpl6 (tissue regeneration), Fabp4 (fatty acid metabolism), and Proc (blood coagulation). Males were more sensitive to many renal end points suggestive of toxicity. At the end of exposure, toxicity was noted at all dose levels, and the 75 µg/kg group exhibited significant effects in liver and kidney/body weight ratios, reduced BUN, increased serum monocytes, and multiple signs of histopathology indicating that a no-observed-adverse-effect level could not be determined for any dose level.

[Cyanobacterial toxins in bank filtrate. Under which conditions is their elimination reliable?]. / Cyanobakterientoxine bei der Uferfiltration : Unter welchen Umständen ist ihre Elimination sicher?

Cyanobacterial toxins are substances produced by cyanobacteria or blue-green algae. They can occur in surface waters worldwide and have to be reliably removed when using affected surface waters as a drinking water source. Bank filtration has been used for 150 years for drinking water (pre-)treatment. It utilizes natural elimination processes like sorption and degradation in the sub-surface. Retention of cells on the sediment surface is the most prominent process for eliminating these primarily cell-bound toxins. Middle to coarse grained sands eliminated more than 99.9 % of intracellular toxins within the first 10 cm of flow path. Elimination of extracellular microcystin during underground passage is mainly due to biodegradation. Reversible adsorption processes do not reduce the total load but lead to longer contact times for extended biodegradation. Laboratory experiments showed that the sediment structure, i.e. high clay/silt and organic content, is crucial for maximum adsorption. However, redox conditions play an important role for degradation rates: under aerobic conditions half-lives of less than one day occurred frequently, whereas anoxic conditions resulted in lag phases of one day and more, as well as in half lives of more than 25 days. Field experiments showed that temperature is crucial for degradation velocity under natural conditions. Under optimal conditions 10 d residence time are sufficient to reduce microcystin concentrations to values below the WHO guidelines value for drinking water (1 microg/L). Under sub-optimal conditions a residence time of up to 90 days may be necessary.

Strategy and current status of combating eutrophication in two Berlin lakes for safeguarding drinking water resources.

After reduction of the external phosphorus load by phosphorus elimination plants, Lake Tegel and Schlachtensee in Berlin underwent a significant trophic improvement. The phosphorus elimination plants work by precipitation/coagulation/flocculation--sedimentation--post precipitation--filtration. The external load was reduced by one to two orders of magnitude down to 10-20 mgg PL(-1). The inlake phosphorus concentration followed. The development of algae and cyanobacteria was reduced substantially below a threshold value of about 50 microg PL(-1) clearly due to phosphorus limitation. In Lake Tegel, the external load reduction of the main inflow was counteracted partially by the external load of the second main inflow by the River Havel and the internal load. This has to be managed further in future.

Cylindrospermopsin occurrence in two German lakes and preliminary assessment of toxicity and toxin production of Cylindrospermopsis raciborskii (Cyanobacteria) isolates.

Cylindrospermopsis raciborskii, a freshwater cyanobacterium of tropical origin, is not only increasingly found in (sub) tropical water bodies, but also in temperate regions. Since this species may produce potent toxins such as cylindrospermopsin (CYN) and paralytic shellfish poisons, its massive occurrence in water bodies used as drinking water sources or for recreation is of major concern. The proliferation of C. raciborskii in German water bodies has been documented for the past decade. We investigated the occurrence of CYN in field populations and isolates of C. raciborskii from two lakes, and assessed the toxicity of culture isolates using the mouse bioassay, primary rat hepatocytes and human derived cell lines. We show for the first time the occurrence of CYN in German water bodies. None of seven isolates of C. raciborskii contained CYN, however, all isolates were toxic to primary rat hepatocytes, human hepatoblastoma (HEP-G2) and human colon adenocarcinoma (CACO-2) cells. Methanolic extracts were more toxic than aqueous extracts. Three isolates tested in the mouse bioassay were toxic at a concentration of 800 mg kg(-1) showing liver and spleen damage and inflammation of the intestine. These results give strong evidence that the German isolates of C. raciborskii contain currently not identified or unknown toxins.

Toxicity and microcystin content of extracts from a Planktothrix bloom and two laboratory strains.

Toxic effects and microcystin content from various extracts of a Planktothrix agardhii bloom and two different strains of Planktothrix agardhii, HUB 076, and NIVA 34 were investigated. Extracts were obtained with solvents of different polarity such as hexane, dichloromethane, methanol, and water. Additionally, different pre-treatments were used to break the cells before extraction. Acute toxicity was determined with the fairy shrimp Thamnocephalus platyurus, subchronic effects were detected in embryos and larvae of the zebrafish Danio rerio. The extracts affected the test species to a different extent. Effects were severe in polar extracts (water and methanol) of all strains tested. Although the strain NIVA 34 did not contain any microcystins, aqueous extracts of this strain showed the highest acute toxicity to the crustacean species tested (LC50= 0.08 mg ml(-1)). In contrast aqueous extracts of the Planktothrix bloom containing high amounts of microcystins were less acutely toxic (LC50 = 0.46 mg ml(-1)). Our results indicate the existence of further toxic metabolites in different Plankorothrix agardhii strains.

Diversity of microcystin genes within a population of the toxic cyanobacterium Microcystis spp. in Lake Wannsee (Berlin, Germany).

In order to find out how many genotypes determine microcystin production of Microcystis spp. in field populations, single colonies (clones) were sampled from Lake Wannsee (Berlin, Germany), characterized morphologically, and subsequently analyzed by PCR for a region within the mcyB gene encoding the activation of one amino acid during microcystin biosynthesis. The different morphospecies varied considerably in the proportion of microcystin-producing genotypes. Most colonies (73%) of M. aeruginosa contained this gene whereas only 16% of the colonies assigned to M. ichthyoblabe and no colonies of M. wesenbergii gave a PCR product of the mcyB gene. Restriction fragment length polymorphism revealed seven restriction profiles showing low variability in nucleotide sequence within each restriction type (0.4-4%) and a low to high variability (1.6-38%) between restriction types. In addition, the sequences of amino acids within the mcyB gene were analyzed to compare the specificity of the amino acid activation during microcystin biosynthesis between restriction types and with the occurrence of amino acids in microcystin variants as detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Most of the microcystin-producing colonies showed high similarity in the sequence of amino acids and contained microcystin-LR (LR refers to leucine and arginine in the variable positions of the heptapeptide), microcystin-RR, and microcystin-YR, as well as other variants in minor concentrations. It is concluded that the gene product found for most of the microcystin-producing colonies in the lake is rather unspecific and the diversity of microcystin variants in the lake results from activation of various amino acids during microcystin biosynthesis in the same genotypes.

Health risks caused by freshwater cyanobacteria in recreational waters.

Toxic cyanobacteria are increasingly being perceived as a potential health hazard, particularly in waters used for recreation. A few countries are developing regulations to protect human health from these toxins, and the World Health Organization (WHO) has published both a guideline value for one cyanotoxin in drinking water and a procedural guideline for recreational waters. This article presents an overview of the currently known cyanotoxins and of documented cases of human illnesses attributed to them. It further discusses exposure pathways and approaches to risk management. In this context, the WHO guideline for recreational waters is presented, and monitoring approaches are outlined.

Mueggelone, a novel inhibitor of fish development from the fresh water cyanobacterium Aphanizomenon flos-aquae.

A novel C18 lipid, containing a 10-membered lactone, mueggelone (1), was isolated from a field-collected sample of Aphanizomenon flos-aquae, together with the known compound lupenyl acetate (3). Both structures were secured using extensive spectroscopic analysis (1D and 2D NMR, MS, IR). Biological activity assessment of both compounds indicated them to have significant inhibitory effects on fish embryo larval development.