Saxitoxins (PSP toxins) in Danish lakes

occurrence of neurotoxic cyanobacteria and saxitoxins in Danish lakes was i nvestigated from 104 phytoplankton samples representing 96 localities. Mous e bioassays demonstrated neurotoxicity in 11 localities (13 samples) of whi ch eight (10 samples) contained saxitoxins and the remaining three anatoxin -a(s). The common cyanobacterial neurotoxin anatoxin-a was not detected. Th e toxin profiles of the samples containing saxitoxins were characterised us ing standards of saxitoxin (STX), decarbamoyl STX (dcSTX): neoSTX and gonya utoxins 1-5 (GTX1-5). Presence of C-toxins was not investigated. The lakes fell into two groups, in seven lakes STX was the dominant toxin and in four lakes GTX4 was dominant. In the first group, STX comprised 46-100% of the total toxin content; in the latter, GTX4 made up 40-75%. The total toxin co ntent varied between 5.9 and 224.1 mu g STX equivalents g DW-1 with median at 34.1 mu g STX equivalents g DW-1. Two lakes contained more than 100 mu g STX equivalents g DW-1 (182.5 and 224.1 mu g, respectively) with STX const ituting more than 95% of the total toxin content. Nine of the neurotoxic sa mples also contained microcystins. Most of the samples were totally dominat ed by cyanobacteria but unambiguous identification of toxin-producing speci es was not possible. Anabaena lemmermannii P. Richter was very common in th e neurotoxic lakes, and it was distinctly dominant in the two lakes with th e highest total contents of saxitoxins. The high frequency of neurotoxic la kes with saxitoxins suggests that these toxins are more common in fresh wat ers than previously assumed. (C) 2000 Elsevier Science Ltd. All rights rese rved.