WATER-BLOOMING AND TOXIN-PRODUCING CYANOBACTERIA IN SWEDISH FRESH ANDBRACKISH WATERS, 1981-1995

During the period 1981-1995 331 phytoplankton samples from 153 station s in different parts of Sweden were analysed regarding species composi tion and possible toxicity. Toxins were indicated in 156 samples which gives a percentage of 47. The toxicity was confirmed by mouse bioassa y. All samples were collected from water-blooming lakes, mainly contai ning taxa belonging to the cyanobacterial genera Anabaena, Aphanizomen on, Microcystis and Planktothrix. In addition to information about occ urrence of neuro- or hepatotoxins, knowledge about the distribution of water-blooming lakes in the country was obtained as well as about the ir predominating taxa. Microcystis aeruginosa, Anabaena flos-aquae and Aphanizomenon flos-aquae were the most frequently occurring taxa in t he lakes. Among the taxa observed, nine different cyanobacterial speci es with certainty produce toxins. Microcystis spp. most frequently pro duced toxic blooms (only hepatotoxins). Anabaena spp., however, caused the majority of waterblooms. The Anabaena flos-aquae-group produced n eurotoxins [incl. anatoxin-a(s)], neurotoxins + hepatotoxins or only h epatotoxins. Aphanizomenon flos-aquae was only recorded as toxin-produ cing in three Swedish lakes, which may be compared with the conditions in Finland, where it was toxic in 36 bloom samples. Aspects are given on toxicity versus lake acidification and trophic conditions, as well as on health effects on animals and human beings.