Cyanobacteria species identified in the Weija and Kpong reservoirs, Ghana, and their implications for drinking water quality with respect to microcystin

Abstract

The Kpong and Weija reservoirs supply drinking water to Accra, Ghana. This study was conducted to identify the cyanobacteria present in these reservoirs and to ascertain whether current treatment processes remove whole cyanobacteria cells from the drinking water produced. Cyanotoxins are mostly cell bound and could easily be removed during water treatment. However, certain water treatment practices, such as pre-chlorination and the use of algicides, lead to lyses of cyanobacteria cells and the release of toxins into the water. The study shows that the water treatment process in the two reservoirs is not effective in the removal of all cyanobacterial cells. Out of the six cyanobacteria species identified in the reservoirs, four produce toxins: Anabaena flos-aquae, Cylindrospermopsis raciborskii, Microcystis aeruginosa and Planktothrix agardhii. These four species constituted about 70–90% of the total algal biomass at all the water treatment stages, including the final product supplied to consumers. Preliminary toxicological analysis of intracellular toxin of samples from the raw water intakes of the two reservoirs indicated the presence of microcystin, with the highest concentration (3.21μg l⁻¹) found in the Weija Reservoir. This study provides the first report of microcystins in drinking water supplies in Ghana.