Sample extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS) method development and validation for the quantitative detection of cyanobacterial hepatotoxins and neurotoxins in Singapore's reservoirs

Cyanobacterial blue-green algal toxins are produced by harmful algal blooms (HABs). Most species of phytoplankton are not harmful, but excessive amounts of certain HAB taxa can cause harm to human and animal health, aquatic ecosystems and local economies. To investigate the prevalence of cylindrospermopsin (CYN) and anatoxin-a (ANA) in Singapore's reservoirs, a hazard analysis was initiated to profile the CYN and ANA levels present. Water samples from 17 reservoirs were monitored monthly over a 12-month period (November 2012-October 2013). Analyses were conducted by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using a triple-stage quadrupole mass spectrometer with a turbo-assisted ion spray source. CYN was more prevalent than ANA. Intracellular CYN concentrations exceeded 0.4 mu g L-1 in 6 of 17 man-made reservoirs surveyed, and slightly exceeded the provisional CYN drinking water guidelines of 1 mu g L-1 (National Health and Medical Research Council and National Resource Management Ministerial Council 2011) on one occasion (1.1 mu g L-1, July 2013) in one reservoir. The dominant cyanobacteria genera during that period were Cylindrospermopsis, Planktolyngbya, Pseudanabaena and Microcystis. For ANA, all 17 reservoirs had concentrations below 0.1 mu g L-1. Based on random forest analysis, the most important environmental factors affecting CYN concentrations were total nitrogen (most important), nitrate, total phosphorus and Cylindrospermopsis counts (least important). The findings of this study indicate that reducing total nitrogen concentrations may be useful in minimising CYN concentrations in tropical reservoirs.