Decision support tool

Background information

Occurrence of cyanotoxins

Within populations of potentially toxic cyanobacteria different genotypes usually coexist: these can be morphologically identical and some produce toxins while others do not. Furthermore, genotypes may well differ in the type and amount of toxin(s) produced. Often only one or a few genotypes are dominant within populations, although the abundance of a certain genotype may vary both within and between years. If, for example, a genotype producing a high amount of toxin gains dominance, this can lead to an increase in the overall toxin concentration in the water body, whilst the overall biomass of cyanobacteria may be unchanged. This variability makes it impossible to predict toxin concentrations in a water body – despite certain trends (see occurrence of specific toxins below) observed under natural conditions.

For all cyanotoxins the concentration within a water body depends upon

  • the biomass of the toxin-producing cyanobacteria
  • the share of the toxin-producing genotypes in the whole population and
  • the toxin content of the toxin-producing genotypes

Environmental factors modulate the toxin concentration at all levels, whereas the influence (especially by phosphorus) on cyanobacterial biomass seems to be the most important: the higher the phosphorus concentration, the more cyanobacteria and therefore higher toxin concentrations are to be expected.




Neurotoxins (ATX-a, ATX-a(s), PSPs)

[1] Genotyp

The genetic constitution (genome) of a cell, an individual, or an organism.