First evidence of MC-HtyR associated to a Plankthothrix rubescens blooming in an Italian lake based on a LC-MS method for routinely analysis of twelve microcystins in freshwaters

Abstract

A recent Italian regulatory level for microcystins (MCs) in drinking water was set at 1.0μg/L, intended as the sum of all variants that can be determined using commercially available standards. A selective multi-residue method for analyzing twelve variants of MCs (MC-RR, MC-YR, MC-LR, MC-LA, MC-LW, MC-LF, MC-LY, [D-Asp3]-MC-RR, [D-Asp3]-MC-LR, MC-WR, MC-HilR, MC-HtyR) in surface and drinking waters was optimized and validated in accordance with the Italian implementation of the Drinking Water Directive 98/83/EC. The proposed method was robust as proved by using nodularin as quality control, with inter-matrices reproducibility better than 17% and matrix effects not significantly dependent among different water samples. LODs were in the range of 0.003–0.030μg/L for all the analytes, allowing the quantitative analysis of selected MCs at levels lower than 1/10 of the proposed new Italian parametric values. The method was tailored for the routine analysis of MCs in the frame of risk management related to MCs production during toxic algal blooms.The optimized analytical protocol was then applied to the analysis of water samples collected in Occhito Lake (Apulia, Italy), used as a source of drinking water, after an extraordinary bloom of Planktothrix rubescens. In October 2010, the presence of MC-HtyR was detected here with maximum concentration level of 0.025μg/L. To our knowledge, this is the first report on MC-HtyR presence, obtained with a confirmatory method, associated to a P. rubescens bloom in surface waters.