The Occurrence of Microcystin-LR Photoisomerization Products in a New York State Local Lake

The hepatotoxin, Microcystin-LR (MC-LR) is common in New York State lakes. Microcystins undergoes a photochemical isomerization to form several photoisomerization products. These photoisomerization products were generated in the laboratory, characterized by high-field NMR spectroscopy, and an in-house LC-MS microcystin method modified to allow for their detection in natural waters. Lake Neatahwanta (Fulton County, NY) experiences persistent cyanobacteria blooms. Samples were taken weekly from the Lake Neatahwanta during the 2016 and 2017 bloom season to measure the occurrence and concentration of these photoisomerization products in the lake. The products were detected in ~95% of samples and had a strong positive correlation with the in-situ concentration of MC-LR. The proportion of photoisomerization products were higher in dissolved phase than in the particulate phase. There was no significant daily variation observed in a diurnal experiment conducted in both 2016 and 2017. Different analytical method (LC-MS, LC-MSMS and ELISA) were evaluated for their ability to detect these photoisomerization products. This study provides important information on the fate of microcystins in natural waters and the impact of these products on different microcystin detection methods.