Survey of microcystins in Singapore's reservoirs using liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Microcystins (MCs) are a group of toxins produced by certain cyanobacteria that occur naturally in fresh waters and can cause acute poisoning in humans and animals. Because cyanobacteria have been found in the freshwater reservoirs of Singapore, a comprehensive survey for cyanotoxins was undertaken over a 12-month period in 17 reservoirs from November 2012 to October 2013. For the quantitative analysis of the reservoir samples, an liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed that targeted the following hepatotoxins: MC-LR, MC-RR, MC-LW, MC-LF, MC-WR and MC-LY. The most prevalent MC variants identified were MC-LR and MC-RR. Results showed that the level of intracellular MC-LR in the raw or untreated water was close to the World Health Organisation (WHO) provisional MC-LR drinking water guideline of 1 mu g L-1 for 1 of 200 samples tested (0.8 mu g L-1), and that intracellular MC concentrations were above 0.3 mu g L-1 in samples collected from four reservoirs. Based on random forest analysis, total monthly rainfall and total nitrogen concentrations were found to be the most important factors affecting intracellular MC concentrations for these four reservoirs. The toxin levels for the other reservoirs were relatively low compared with the WHO provisional MC-LR guideline limit of 1.0 mu g L-1.