Use of cholinesterase activity as an ecotoxicological marker to assess anatoxin-a(s) exposure: Responses of two cladoceran species belonging to contrasting geographical regions.

The specificity of cholinesterase (ChE) activity to detect the presence of anatoxin-a(s) and sublethal effects of a 7-day exposure to Anabaena spiroides extract containing anatoxin-a(s) were assessed in two freshwater cladoceran species. Activities of ChE of both Pseudosida ramosa and Daphnia magna can be used to indicate the presence of the neurotoxin anatoxin-a(s), but not for the hepatotoxic microcystin. Activity of ChE of P. ramosa, however, performed better as a biomarker of exposure to A. spiroides than that of D. magna. Furthermore, sublethal exposure to A. spiroides extract significantly inhibited the ChE activity in P. ramosa and negatively affected both individual and population endpoints. For D. magna, the inhibition of ChE activity was not related to effects at higher levels of biological organization, since no direct effect was recorded on the individual and population endpoints. The activity of ChE in P. ramosa also proved to be a good predictor of chronic effects of the A. spiroides extract at higher levels of biological organization, since 48-h ChE inhibition was linked to the sublethal effects on the individual and population. These relationships could not be established for D. magna. Since relationships between the effects of A. spiroides extract at different levels of biological organization were species-specific, it can be concluded that the choice of test organism interferes with the accuracy of the environment risk assessment of this neurotoxin and, hence, the use of native species is recommended for its assessment.