title: Can mixtures of cyanotoxins represent a risk to the zooplankton? The case study of Daphnia magna Straus exposed to hepatotoxic and neurotoxic cyanobacterial extracts.
abstract: Worldwide, cyanobacterial blooms have been increasing in intensity and frequency, with toxic cyanobacteria sometimes dominant throughout the year in many freshwater bodies. Since the coexistence of more than one type of cyanotoxins in freshwater environments is a common phenomenon, studies on the joint effects of these toxins would be very useful. In this study, the single and combined effects of two cyanotoxins with different modes of action (hepatotoxic and neurotoxic) on the survival (lethal exposure) and feeding (sublethal exposure) of the cladoceran Daphnia magna were investigated. With the single exposures, it was observed that both the survival and feeding activity of the daphnids were impaired by the hepatotoxic and neurotoxic extracts at environmentally relevant concentrations. In the combined exposures, both survival and feeding rate endpoints showed a good fit to the independent action model. For the acute assay and 24h exposure period in the feeding inhibition test, there was no interaction between components of the hepatotoxic and neurotoxic extracts, although a slight tendency to a synergistic deviation could be seen in the feeding rates. On the other hand, for the 4h post-exposure period, a synergistic deviation was found in feeding rates at all mixture concentrations tested. Hence, the combined exposure of hepatotoxins and neurotoxins should also be taken into account in risk assessments of freshwater bodies, since the mixture of these toxins can result in more severe post-exposure effects on the feeding of daphnids than the sum of those expected for single exposures.
authors.affiliation: Department of Ecology and Evolutionary Biology, Federal University of São Carlos, Rodovia Washington Luis, km 235, CEP 13565-905 São Carlos, SP, Brazil. Electronic address: emanuelacfreitas@gmail.com.
authors.forename: Emanuela Cristina
authors.initials: EC
authors.lastname: Freitas
authors.affiliation: Department of Biology and Centre for Environmental and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: carlos.pinheiro@ua.pt.
authors.forename: Carlos
authors.initials: C
authors.lastname: Pinheiro
authors.affiliation: Department of Ecology and Evolutionary Biology, Federal University of São Carlos, Rodovia Washington Luis, km 235, CEP 13565-905 São Carlos, SP, Brazil. Electronic address: doro@ufscar.br.
authors.forename: Odete
authors.initials: O
authors.lastname: Rocha
authors.affiliation: Department of Biology and Centre for Environmental and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: sloureiro@ua.pt.
authors.forename: Susana
authors.initials: S
authors.lastname: Loureiro
keywords: Anatoxin-a(s); Binary mixtures; Cyanobacterial extracts; Daphnia magna; Microcystin-LR; Synergism