Diversity and distribution of cyanobacterial toxins in the Italian subalpine lacustrine district

Nine lakes (Garda, Maggiore, Como, Iseo, Lugano, Idro, Pusiano, Ledro and Levico) located in the Italian subalpine lacustrine district have been chosen for a comparative study about the diversity and the distribution of cyanobacterial toxins. All lakes are known to host different toxic cyanobacteria, mainly Planktothrix rubescens. An analytical protocol has been used, based on LC-MS technique, for determining 20 different toxins (14 microcystins, 2 nodularins, anatoxin-a and 3 cylindrospermopsins). In the investigation microcystins were constantly found in all lakes, anatoxin-a could be detected in 6 lakes, but only in 4 it was present in all sampling dates (lakes Garda, Iseo, Como and Maggiore), and finally nodularins and cylindrospermopsins were not detected at all. The number of microcystins detected in the survey was 9, but 4 were the most abundant (dmRR, YR, dmLR, and LR); they were differently distributed among the lakes, thus providing each lake a typical toxic potential. Statistical analysis has shown the presence of positive correlations between total microcystin concentrations and eutrophication indicators and also between anatoxin-a concentrations and water temperature, suggesting that anthropic and climate-related stressors can have different impacts on the selection of different cyanotoxins.