Microcystis aeruginosa: behaviour and toxic features in San Roque Dam (Argentina)

M. aeruginosa is a cyanophyte frequently found in the water at the San Roque Dam (raw water supply conditioned for human use in Córdoba city) that causes a bad smell and taste, as well as potential toxic hazards of a still unknown extent. A heavy bloom tested by mouse bioassay (i.p.) for the first time on January 27, 1989, revealed toxicity. The dominant cyanobacterial species in the water sample was M. aeruginosa. The lyophilized bloom material (LD50: 14.5 mg/kg body weight) and the toxin isolated (LD50 estimated: 500 micrograms/kg), when administered to mice i.p., induced clinical signs similar to those induced by peptide toxins produced by M. aeruginosa. HPLC detected toxin traces from a sample of drinking water collected on the same day as the bloom. A seasonal follow-up was carried out for the next 4 years in order to compare bloom toxicity values during the most significant water blooms; these never yielded LD50 values lower than 200 mg liophilized bloom material/kg mice.