Seasonal occurrence of Microcystin-LR with respect to physico-chemical aspects of Beira lake water
Cyanobacteria are well known for their ability to produce a group of cyanotoxins referred as microcystins(MCs). MCs show both acute and chronic hepatotoxic effects on animals and humans. Microcystin-LR(MCLR) is the dominant type of MCs prevailing in Sri Lankan water bodies. The present study records theseasonal variation of MCLR, in the Beira lake waters from January 2013 to January 2014 with respect tosome physico-chemical parameters of the lake. Quantification of MCLR was done using photodiode array -High Pressure Liquid Chromatography method (PDA-HPLC). The physico-chemical parameters of the waterbody were measured using standard methods. Microcystis aeruginosa, Microcystis wesenbergii andMicrocystis incerta, were the toxic cyanobacterial species present in the Beiralake while Microcystisaeruginosa (49.63%) was the dominant species. MCLR concentration of the lake varied between 11.45±0.73to 17.57±0.13 μg/ml throughout the dry season of the sampling period while varied between 13.21 ±0.73 to25.23±0.42 μg/ml during the rainy season. The Pearsons correlation coefficient analysis done for total toxinconcentration and the water quality parameters suggested that the water temperature (r=0.914, pvalue=0.000), and the total phosphate concentration (r=0.988, p-value=0.000) have a strong positivecorrelation with the total MCLR concentration, while pH (r=0.766, p-value=0.002) has a moderatecorrelation for the production of total MCLR.
KYWORDS: Cyanobacteria, Microcystin-LR (MCLR), Microcystis aeruginosa, Physico-chemicalparameters, High Pressure Liquid Chromatography method (PDA-HPLC).