Microcystin-LR equivalents and their correlation with Anabaena spp. in the main reservoir of a hydraulic system of Central Mexico

The occurrence of cyanobacterial blooms is a characteristic of eutrophic inland water bodies. Valle de Bravo reservoir (Mexico State, Mexico) is the main source of water for the Cutzamala Hydraulic System, which supplies drinking water to the west of Mexico City (~6 million consumers) and suburban areas of Mexico State. The goal of this study was to determine the presence of microcystins (MC-LR equivalents) and their relationship with toxic populations of cyanobacteria recorded some years ago in this important reservoir. We measured the concentration of MC-LR equivalents using a commercial kit (EnviroLogix) based on the ELISA test. The calculation of abundance and biovolume was carried out monthly from February to November 2010. The presence of MC-LR equivalents was related to the biovolume of Anabaena planctonica. The values of this toxin from February to June exceeded the World Health Organization (WHO) provisional guideline (1 µg L-1) for finished drinking water sources, particularly in April when the highest value was recorded (5.56 μg L-1). In addition, in April, May, June, and August, the abundance of cyanobacteria exceeded the WHO moderate risk level (10 × 104 cells mL-1) for recreational activities. This study furthers investigations ranging from the characteristics of the water column to benthic cyanobacteria and molecular biology tests to establish which species are toxic in the reservoir