OCCURRENCE OF MICROCYSTIN-CONTAINING CYANOBACTERIAL BLOOMS IN FRESH-WATERS OF BRITTANY (FRANCE)

A survey of the occurrence of microcystin-containing cyanobacterial bl ooms in the freshwaters of Brittany was made in September 1994. Twenty -nine sites, including rivers, ponds and reservoirs were studied. Cyan obacteria were present in twenty-five sites. The microcystin content o f twenty-two natural samples and nineteen Microcystis aeruginosa strai ns isolated from six samples was investigated using HPLC analysis. Mos t of the bloom samples were dominated by M. aeruginosa spe cies. More than 70 % of the samples collected from the water bodies contained mic rocystins. microcystin-LR was the main microcystin found. The microcys tin content varied generally from undetectable to 0.73 mg g(-1) (freez e-dried cells). Only one sample contained a high concentration of micr ocystins, 4 mg g(-1). Both microcystin-containing and microcystin-non- containing strains were found in cyanobacteria cultures isolated from natural samples. Microcystin content in isolated strains ranged from u ndetectable to 0.81 mg g(-1). This study showed for the first time tha t microcystin-containing cyanobacteria are frequent in the freshwaters of Brittany. Hence, it is necessary to monitor the cyanobacterial dev elopments in this region to prevent human health hazards.