Abstract:
Microcystins are a class of cyanobacterial toxins largely found in water and are often responsible
for poisoning animals as well as humans. A more recent scenario is the poisoning of domestic
water supply system in Toledo (Ohio), USA. Consequently, water supply to the city had to be
suspended for weeks in order for authorities to ascertain the commodity's safety before restoring
supply. In Kenya, there have been very few studies on cyanotoxins and their adverse health
effects in spite of the fact that cyanobacteria have been implicated in several poisoning episodes
of humans and animals worldwide, occasioned by drinking microcystin contaminated water. This
paper therefore, reports data on the first identification and characterization of hepatotoxic
microcystins in water samples of Lake Naivasha. Samples from the lake were investigated over a
modest period of three months. The phytoplankton community was mainly dominated by the
cyanobacterium Microcystis aeruginosa. The colour of the water samples was found to be 520 ±
91 ptco, while the conductivity was 234 ± 0.8 us/ern and the total dissolved solids was 1035 ± 12
mg/L. Due to the high turbidity (59.0 ± 24 ntu), phytoplankton biomass was low, ranging between
1.5 and 8.2 mg L-1• Using UV-Vis and HPLC techniques, the microcystin-LR, -RR and -YR were
detected in all the water samples collected from the lake. HyperChem computational package was
used to estimate the toxicity index of microcystin-RR based on the octanol-water partition
coefficient and found to be 230 times more soluble in water than in octanol. Thus, microcyctin
RR is highly soluble in polar biological tissues which may result in cell injury, oxidative stress,
and ultimately cancer. To the best of our knowledge, this is the first evidence of microcystins in
Lake Naivasha.