Microcystin accumulation in cladocerans: First evidence of MC uptake from aqueous extracts of a natural bloom sample

• This study reports the accumulation of microcystins (MC) from aqueous extracts of natural bloom samples in cladoceran species.
• Results showed that the animals uptake of MC increased with increasing exposure concentrations of aqueous extracts.
• Moina micrura and Daphnia laevis presented MC concentrations as high as 1170–1260 μg g−1 in their tissues.
• This study shows for the first time that dissolved MC uptake by zooplankton is possible.

Bioaccumulation of microcystins (MC) in zooplankton has been shown in several studies, mainly in field samples. A few studies, however, have demonstrated MC bioaccumulation in laboratory experiments. Although ingestion of cell-bound MC is considered the main route of MC accumulation, another important source is the MC from the dissolved fraction (DMC). This study reports the accumulation of DMC from aqueous extracts of natural bloom samples in three cladoceran species: Moina micrura, Daphnia laevis and Daphnia similis. Animals were exposed for 96 h to aqueous extracts of lyophilized matter from two bloom samples from Colombian reservoirs in different concentrations (25–1000 mg DW L−1). Analysis by HPLC-MS detected MC-LR in these samples at concentrations of 434–538 μg g−1. For the analysis of MC in animal tissues the samples were homogenized and sonicated in methanol:water (75%) and analyzed by ELISA. Results showed that the animals uptake of MC increased with increasing exposure concentrations of aqueous extracts, with M. micrura and D. laevis clones presenting the highest MC concentrations in their tissues (up to 1170–1260 μg g−1) while D. similis the lowest (184 μg g−1). This study shows, for the first time, that MC uptake from dissolved fraction by zooplankton is possible, not only from the ingestion of seston or cell-bound MC as previously demonstrated.

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