First report of cyanotoxins in benthic mats from Lake Garda

Cyanobacteria represent a health hazard in aquatic environments due to their ability to produce a range of toxic metabolites, which can cause either immediate illness or long-term effects in both humans and animals. In the large subalpine lakes planktonic species Planktothrix rubescens and Tychonema bourrellyi are the main responsible of toxin production (microcystins and anatoxins, respectively) in pelagic environments. Considering Lake Garda, the largest Italian water basin, toxin measurements conducted in the last decade with a monthly frequency indicate a constant presence of both microcystins and anatoxins, yet at concentrations well below the safety thresholds indicated by the World Health Organization. Moreover, in this time span, anatoxin-a has become dominant, reaching annual maximum concentrations even two orders of magnitude higher than microcystins. However, a recent investigation, conducted in the frame of the Eco-AlpsWater project (financed by the Interreg Alpine Space programme), has revealed the presence of cyanotoxins also in benthic samples; in particular, remarkable quantities of anatoxins have been found in biofilms collected from rocks in different sites of Lake Garda shores. Considering that benthic cyanobacteria can grow in high abundance in mats, anatoxins can reach dangerous concentrations in this material and constitute a potential threat for people and animals nearby