Abstract:
Microcystins (MCs) are emerging contaminants produced by toxigenic cyanobacteria
and are reported to be hepatotoxic. The Kelani River is a drinking water repository in
the Gampaha District; which is the most polluted river in Sri Lanka. A water treatment
plant facility (WTPF) with two water treatment plants (WTP I and WTP II) belonging
to the NationalWater Supply and Drainage Board (NWSDB) was selected for this study
as it purifies the water of the Kelani River to provide drinking water for most of the areas
of the Gampaha District. This study investigated the presence of cyanobacteria and
MC variants in both the river and WTPF. Water samples were collected in November
2021 from the Kelani River just before the intake, after band screening, flocculation
stage, after settling, clear-water reservoir, and a distribution point for each WTP in
triplicates. Physicochemical parameters including temperature, pH, dissolved oxygen,
conductivity, total dissolved solids, and salinity were recorded in situ using a multiparameter
and they met the Sri Lanka Standards (SLS) for drinking water. Water samples
were cultured in cyano-specific media, and eight cyanobacterial genera were tentatively
identified as Phormidium, Planktothrix, Lyngbya, Anabaena, Pseudanabaena, Oscillatoria,
Anabaenopsis, and Nostoc. Intracellular and extracellular MCs were extracted from
collected water samples using 70% methanol and subjected to High-Performance Liquid
Chromatography (HPLC). MC-RR-YR-LR standard (SIGMA-ALDRICH 33578) was
used to detect MC variants and their concentrations by comparing the peak retention
times and area of the peaks. It revealed the presence of MC-YR in the water samples
collected from Kelani River at a concentration of 281.18 µg/L. The distribution point
of WTP I had MC-RR (3.41 µg/L) while both MC-RR and MC-YR were detected
in the distribution point of WTP II at concentrations of 2.07 µg/L and 250.21 µg/L
respectively. Hence this study emphasizes the necessity of routine detection of MCs in
this WTPF. Although the results indicate the absence of the most toxic MC variant
(MC-LR) at the distribution points, research is needed to understand the MC variants
and their temporal variation to minimize the health risk of people who rely on this
WTPF for drinking water.
