Toxin Producing Cyanobacteria in Labugama, Kalatuwawa Drinking Water Reservoirs

Abstract

Cyanobacteria are photosynthetic bacteria found naturally in lakes, streams, ponds, and
reservoirs. Microcystis aeruginosa, Anabaena sp., Nostoc sp., Oscillatoria sp. are some
harmful cyanobacteria that produce cyanotoxins. Microcystin-LR (MC-LR) is the dominant
type of cyanotoxin produced by these cyanobacteria. MC-LR causes hepatotoxic effect on
human beings and are harmful to animals as well. Therefore, World Health Organisation
(WHO) has recommended a guideline value of less than 1 μg/l of MC-LR should be present
in drinking water. The present study assesed the presence of toxin producing cyanobacteria
and quantifies MC-LR in Labugama and Kalatuwawa drinking water reservoirs, from June to
December 2014. Water samples were collected from five sampling locations of both water
bodies and plankton samples were collected using 55 μm plankton net. Filtered water
samples were fixed in acidified lugols‟ solution at a final concentration of 1%. Following
natural sedimentation, identification of cyanobacteria was carried out. Quantification of MCLR
was done using photodiode array-high pressure liquid chromatography method (PDAHPLC).
M. aeruginosa (54.6±0.17%) was the dominant cyanobacteria whereas Pediastrum
duplex (30.4±1.89%), Coelastrum sp. (12±0.19%) and Ankistrodesmus sp. (3±0.02%) were
the non-toxic algae strains present in Labugama reservoir. M. aeruginosa (68.2±0.09%) and
Anabaena sp. (16.2±0.12%) were the toxic cyanobacteria present in Kalatuwawa reservoir
whereas P. duplex (7.3±0.08%), Coelastrum sp. (5.6±0.24%), Staurastrum sp. (1.2±0.05%)
and Scenedesmus sp. (1.5±0.004%) were found as non-toxic algae species. MC-LR
concentration of Labugama and Kalatuwawa reservoirs ranged between 0-1.27±0.04 μg/ml
and 0.76±0.001-1.45±0.02 μg/ml respectively. Based on the results of the present study, both
reservoirs were contaminated with MC-LR and responsible cyanobacteria strains would be
M. aeruginosa and Anabaena sp. Thus, continuous monitoring is essential in order to assess
the suitability of these two water bodies for human drinking purpose.
Keywords: Cyanobacteria, Microcystis. aeruginosa, MC-LR, Drinking water, PDA-HPLC