Toxicity and microcystin content of extracts from a Planktothrix bloom and two laboratory strains.

Toxic effects and microcystin content from various extracts of a Planktothrix agardhii bloom and two different strains of Planktothrix agardhii, HUB 076, and NIVA 34 were investigated. Extracts were obtained with solvents of different polarity such as hexane, dichloromethane, methanol, and water. Additionally, different pre-treatments were used to break the cells before extraction. Acute toxicity was determined with the fairy shrimp Thamnocephalus platyurus, subchronic effects were detected in embryos and larvae of the zebrafish Danio rerio. The extracts affected the test species to a different extent. Effects were severe in polar extracts (water and methanol) of all strains tested. Although the strain NIVA 34 did not contain any microcystins, aqueous extracts of this strain showed the highest acute toxicity to the crustacean species tested (LC50= 0.08 mg ml(-1)). In contrast aqueous extracts of the Planktothrix bloom containing high amounts of microcystins were less acutely toxic (LC50 = 0.46 mg ml(-1)). Our results indicate the existence of further toxic metabolites in different Plankorothrix agardhii strains.