Saxitoxins (PSP toxins) in Danish lakes

The occurrence of neurotoxic cyanobacteria and saxitoxins in Danish lakes was investigated from 104 phytoplankton samples representing 96 localities. Mouse bioassays demonstrated neurotoxicity in 11 localities (13 samples) of which eight (10 samples) contained saxitoxins and the remaining three anatoxin-a(s). The common cyanobacterial neurotoxin anatoxin-a was not detected. The toxin profiles of the samples containing saxitoxins were characterised using standards of saxitoxin (STX), decarbamoyl STX (dcSTX), neoSTX and gonyautoxins 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 content varied between 5.9 and 224.1 μg STX equivalents g DW−1 with median at 34.1 μg STX equivalents g DW−1. Two lakes contained more than 100 μg STX equivalents g DW−1 (182.5 and 224.1 μg, respectively) with STX constituting more than 95% of the total toxin content. Nine of the neurotoxic samples also contained microcystins. Most of the samples were totally dominated by cyanobacteria but unambiguous identification of toxin-producing species was not possible. Anabaena lemmermannii P. Richter was very common in the neurotoxic lakes, and it was distinctly dominant in the two lakes with the highest total contents of saxitoxins. The high frequency of neurotoxic lakes with saxitoxins suggests that these toxins are more common in fresh waters than previously assumed.