Showing papers by "Ingrid Chorus published in 2001"

Introduction: Cyanotoxins — Research for Environmental Safety and Human Health

Abstract: How dangerous are toxic cyanobacteria? Numerous lethal animal poisonings worldwide and a number of cases of human illness have drawn the attention of the World Health Organization, the public and an increasing scientific community to cyanobacteria and their toxins. Gradually, a clearer picture is emerging on the occurrence, causes and consequences of the proliferation of toxic cyanobacteria in surface waters.

Cyanotoxin Occurrence in Freshwaters

Abstract: How likely is a given cyanobacterial bloom to be toxic? This question was addressed in a number of countries already in the 1980s, even before the structures of many cyanotoxins were known. Thus, early surveys were conducted using the mouse bioassay, and results generally showed toxicity in more than half of the cyanobacterial samples tested (e.g. Leeuwangh et al. (1983) in The Netherlands, Torokne-Kozma and Gabor (1988) in Hungary, and the NRA Report (1990) in England). In the wake of the development of chemical methods of cyanotoxin identification and quantification, these have been employed in a number of countries for more extensive surveys of cyanotoxin occurrence in relation to dominant cyanobacterial taxa. In some cases they were combined with bioassays for toxicity. Further, limnological aspects are increasingly being included in study designs and data interpretation.

Cyanobacterial Toxicity and Human Exposure

Abstract: In spite of numerous documented cases of animal deaths after drinking water with cyanobacteria, data on exposure of humans to cyanotoxins are scarce worldwide, usually because incidents of illness are not related to cyanotoxins as potential cause quickly enough in order to investigate whether they occur, and at which concentrations. Toxicological knowledge of the effects of cyanobacterial toxins on mammals is, however, sufficiently developed to indicate diverse health hazards qualitatively, and for some cyanotoxins, quantitative assessments are also possible. Chapter 5.1 provides an overview of the information currently available for hazard assessment. Chapter 5.2 assesses ambient microcystin concentrations found in recreational waters in Germany and relates them to concentrations likely to have a health impact.

“Toxic cyanobacteria—towards a global perspective,” fifth international conference on toxic cyanobacteria, Noosa, Queensland, Australia, July 15–20, 2001

Abstract: ICTC-V was a highly successful conference, from both a scientific and a cultural perspective. Much robust debate was generated in an environment of good will and shared experience. The expansion of scientific and government interest throughout many emerging countries is heartening and significant. The new cyanobacterial species and, in some cases, new cyanotoxins, being reported in these countries, many of which are in the tropics and arid zones of the world, are enhancing the richness and quality of the global research effort on toxic cyanobacteria. The selected articles on toxic cyanobacteria published in this special edition of Environmental Toxicology provide just a few examples of the quality and breadth of work that is currently being undertaken throughout the world.

Effects of Microcystis spp. and Selected Cyanotoxins on Freshwater Organisms

Abstract: Cyanobacterial toxins have adverse effects on mammals, birds and fish and are being increasingly recognized as a potent stress and health hazard factor in the aquatic ecosystem. Microcystins, one main group of the cyanotoxins, are mainly retained within the producer cells during cyanobacterial population growth (see Chapter 2.1.2 and 2.3). However, these toxins are released into the surrounding medium by senescence and lysis of blooms. A wide range of aquatic organisms — phytoplankton, submerged aquatic plants (macrophytes), invertebrates, fish and amphibians — are then directly exposed to dissolved toxin, which may cause diverse effects. Exposure of aquatic organisms may occur both orally by uptake of toxin-containing cells as food, or through the surface tissues of organisms submersed in water containing dissolved toxin.

Toxic Effects and Substances in Cyanobacteria other than Microcystins, Anatoxin-a and Saxitoxins

Abstract: Cyanobacteria produce a number of biologically active substances. In addition to their well-known alkaloid toxins (see Sivonen and Jones 1999 for an overview), these encompass peptides and depsipeptides. While approximately 60 structural variants of the hepatotoxic microcystins are already known (Sivonen and Jones 1999), the non-hepatotoxic peptides and depsipeptides have been studied to a far lesser extent. These substances have been detected irrespective of whether the object was the study of toxic or of non-toxic strains (Namikoshi and Rinehart 1996). On the other hand, evidence is increasing for biological effects of cyanobacteria which cannot be accounted for by those cyanobacterial metabolites currently understood to encompass “the cyanotoxins”. This suggests that cyanobacteria contain not only numerous metabolites whose bioactivity is poorly understood, but also further currently unknown toxins. Chapter 7.1 presents a review of peptides and depsipeptides potentially relevant as bioactive substances.

Contributions to Toxicity Testing and Toxin Analysis

Abstract: Toxicity testing is of key importance both for cyanotoxin research as well as for monitoring and can only partially be replaced by chemical analysis of cyanotoxins. Analytical methods were developed to detect selected known substances, whereas toxicological assays aim at determining the effects of all substances, known or unknown, in a sample. Extracts of cyanobacteria may contain a variety of chemical substances, numerous of which may be unknown, and their potential effect can only be detected by toxicological testing complementary to chemical toxin analysis. The mouse bioassay has been the most widely used toxicity test in cyanotoxin research and in the screening programmes published from several countries in the 1980s and early 1990s (Sivonen and Jones 1999). It involves intraperitoneal injection of cyanobacterial material or extracts into mice and determination of the dose that kills 50% of the mice, the classical LD50 (Berg and Soli 1985; Falconer 1993). Skulberg et al. (1994) classified cyanobacterial toxins (cyanotoxins) by the response to them as observed in the mouse bioassay as hepatotoxins, neurotoxins and toxins with protracted effects. The time of survival and pathologically observable damage to organs were used as parameters for this classification. For ethical reasons (especially pertaining to LD50 tests), because of stringent animal wefare regulations in many countries, and because of time and costs involved, mouse test are unsuitable for large-scale testing of field samples, and the need to replace the mouse bioassay with alternative methods at the suborganismic level is urgent (another reason being a lack of adequeate diagnostic/mechanistic end points). Chapter 8.1 shows that cellular assays are a promising tool for monitoring cyanobacterial toxicity, and Chapter 8.2 provides verification for a cellular microcystin aasay comparing the results to those of the mouse bioassay.

Routine Analytical Methods Applied in the German Cyanotox Project

Abstract: The following chapter describes the methods used by several partners in the German cyanotoxin survey; reference to these is made in other chapters of the book.

Factors Affecting Cyanotoxin Concentrations in Natural Populations

Abstract: As discussed in the introduction to Chapter 3, understanding how environmental factors influence cyanotoxin concentrations in waterbodies requires differentiation between two potential mechanisms: a direct impact on cellular toxin content, and/or an impact on competition between genotypes which would lead to dominance of strains or species with or without microcystin. The field results reported in Chapter 2 reinforce published observations that some taxa produce microcystins, others contain certain neurotoxins, and some may contain both or neither. However, further differentiation is possible: Chapter 4.1 shows that Microcystis spp., Planktothrix agardhii and Planktothrix rubescens each typically contain specific microcystin variants, though relative shares of variants as well as total microcystin content of the field populations may vary. Section 4.2 also addresses the level below that of species — i.e. the level of strains or genotypes — by investigating microcystin content in different strains of Microcystis aeruginosa isolated from two lakes. This results demonstrate a substantial variability of of microcystin content between different strains of M. aeruginosa. In conjunction with culture study results reoported in Chapter 3 (which showed little impact of environmental factors on cellular toxin content), this result suggests competition between strain of a species to be a decisive determinant of microcystin concentration in natural populations.

Factors Controlling Cellular Microcystin Content

Abstract: It is still unclear why cells contain cyaontoxins ie what the benefit is of producing cyanotoxins in competition against cells without them? One approach to addressing this question is the study of their toxin content (or their toxicity) in relation to environmental factors If toxin content or toxicity increased substantially under certain growth conditions, this would indicate a benefit for toxin production under those conditions From such results the biochemical function of these substances in the cells could perhaps be inferred Earlier laboratory experiments and field studies, chiefly addressing microcystin concentrations or heptatotoxicity, indicated some gradients in relation to environmental factors relevant for growth, such as temperature, light, nutrient concentrations, salinity and pH A comprehensive overview of experiments published up to 1998 is provided by Sivonen and Jones (1999)