Parts of Lake Victoria filled with toxins from overgrown bacteria
In 2020, Kenyan researchers showed that Nyanza Gulf in Lake Victoria, as well as nearby household water sources may contain harmful chemicals called microcystins. Microcystins are toxins that may cause liver damage in people who use the water for cooking and drinking.
Microcystins are produced by cyanobacteria. A large group of cyanobacteria may appear as a green-blue layer floating on dams or lakes, because these organisms photosynthesise (produce energy using sunlight) in the same way that green plants do.
Parts of Kenya’s Lake Victoria are overgrown with cyanobacteria because of eutrophication, which is when the water becomes too rich in the nutrients that these bacteria thrive on. Cyanobacteria produce harmful chemicals called microcystins that damage the liver if ingested.
Because of this potential danger to communities who rely on the lake, researchers wanted to find out how much microcystins are in the Nyanza Gulf beach of Lake Victoria, as well as nearby household water. They also wanted to see which type of microcystin was most common in these water sources.
The researchers took samples of water from 6 beaches along the Nyanza Gulf of Lake Victoria, and 127 samples from households along those beaches, between May and October, 2015. They checked if microcystins were present, and which types.
They said 80% of all the water samples, both beach and households, contained microcystins, and that the amount of toxins were higher than what is normally deemed safe.
They also found different strains of microcystins. A strain called MC-RR was the most common, followed by MC-YR and MC-LR.
Interestingly, the researchers noticed that there were more microcystins in May and October, and said this was because of the high rainfall during those months.
The results from their study agrees with previous studies that also found MC-RR is the most common, and that toxins found in these beaches are above the limit that is considered safe. But, they added more detail about exactly how much and what type of microcystins are found.
The researchers advised that current water treatments are not adequate to remove the toxins, and they suggested that the government must keep the communities who rely on this water aware about the potential danger to their health.
The authors of this paper are from Kenya and their study was done at Lake Victoria, Kenya.
Cyanobacteria are single-celled algae that thrive in warm and nutrient rich water bodies. They can produce different kinds of toxins called cyanotoxins that can affect the liver. Cyanobacteria have been reported in Lake Victoria, which is an important source of drinking water for the riparian communities. This is as a result of eutrophication in Lake Victoria increasing the levels of cyanobacteria in the Nyanza Gulf. The purpose of this study was to identify and quantify microcystins in household and Lake Victoria water in Nyanza Gulf. In a longitudinal study adopting experimental design, six beaches were studied and 127 samples collected monthly from both households and beaches over six months. Cyanobacterial levels were determined using an enzyme assay method (PP2A) and microcystin strains identified using High Performance Liquid Chromatography (HPLC). Two-way ANOVA was done to determine statistical significance of microcystins. The results showed that all beaches were eutrophic resulting in flourishing of cyanobacteria. 84% of water samples contained microcystins. Concentration of microcystins was 3.44µg/L. Microcystin RR (MC-RR) is the most abundant cyanotoxins followed by Microcystin YR (MC-YR) and Microcystin LR (MC-LR) is the least abundant in the Nyanza Gulf. There was significant variation between different beaches and different months (ANOVA: F=12.09, p<0.0005). This information provides an insight into the quality of Lake Victoria water for drinking based on quantities of microcystins in the sampled water. The study recommends regular monitoring of cyanobacterial cells in the lake water.
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