Cyanotoxins occurrence in drinking waters and risk of exposure to human in Ukerewe district Mwanza, Tanzania

Abstract

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.