A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of
Doctor of Philosophy in Life Sciences of the Nelson Mandela African Institution of
Science and Technology
There is global concern regarding the increase of cyanobacteria and cyanotoxins in
freshwater and their potential effects on human health. This study was conducted to
determine the occurrence of cyanotoxins and assessed their risk of exposure to human. A
cross sectional study of 432 subjects was conducted to assess related health risk due to
cyanobacteria and cyanotoxins exposure in selected villages of the Ukerewe District in
Mwanza, Tanzania. A total of 138 water samples and 432 serum samples were collected in
two phases (February and December). Thirteen cyanotoxins namely; Microcystins (-LA, -LF,
-LR, -LY, -LW, -RR, -YR, -WR, dm MC-RR and dm MC-LR), anatoxin-a (AT-A), nodularin
(NOD) and cylindrospermopsin (CYN) were assessed in water and in human serum by
UPLC-MS/MS. Cylindrospermopsin was the most abundant cyanotoxin detected in the lake
water samples in both phases. Microcystin (MC) congeners; -RR, -LR and –YR were
detected in phase I while MC-RR and MC-LR were detected in phase II. No cyanotoxins
were detected in wells and treated pipe water samples. Furthermore, phycocyanin
concentration detected in Lake Victoria ranged from 5 to 58.4 μg/L which is above the WHO
limit. The concentrations of cyanobacteria cells were beyond WHO acceptable limits. Species
of Microcystis aeruginosa and Anabaena spp were identified as the most abundant
cyanobacteria. Acute illnesses such as throat, eye, skin irritation and gastrointestinal illnesses
were highly reported by lake water users as compared to wells and pipe water (P<0.001).
Cyanotoxins of CYN, NOD and MCs congener (-LR, -RR and dmMC-LR) were detected in
human serum. The concentration of CYN detected in humans ranged from 0.02 to 0.15
ng/mL and MCs ranged from 0.2 to 0.11 ng/mL. Concentration of cyanotoxin detected in
human serum and liver biochemistry indices elevation, shows an association between the two
with correlation coefficient of 0.33 for MC-LR while for combined cyanotixins of MC-LR,
CYN and NOD is 0.78. This is the first study to report CYN, dm MC-LR and NOD in human
serum, and CYN and NOD in freshwater of Lake Victoria. This study indicates the potential
health risk of using lake water without any treatment for human consumption.