Cyanotoxin production in seven Ethiopian Rift Valley Lakes

Abstract

We hypothesized that unusual deaths and illnesses in wild and domestic animals in lake areas of the Rift Valley south of Addis Ababa were caused by toxic cyanobacteria. In the first cyanotoxic analyses conducted in samples from Ethiopia, we found lakes Chamo, Abaya, Awassa, Chitu, Langano, Ziway, and Koka all had concentrations of microcystins (MC) ranging from trace to hazardous, whereas only traces less than limits of detection (LOD) of cylindrospermopsin (CYN) were found. In the December 2006 dry season we sampled the lakes for analyses of MC, CYN, species structures, and calculations of cyanobacteria biomass. We used the Utermöhl technique to analyse cyanobacterial biomass and monitored MC toxins using HPLC-DAD, LC-ESI-MS-MRM, and ELISA-test and CYN with HPLC-DAD and ELISA. The various toxicity tests coincided well. In 4 of the lakes (Chamo, Langano, Ziway, and Koka), the inter-lake range of total MC concentration was 1.3-48 µg L −1 ; in 3 (Abaya, Awassa, and Chitu), we found only traces of MC. Microcystis aeruginosa was the dominant species, with Microcystis panniformis, Anabaena spiroides, and Cylindrospermopsis spp. as subdominants. The MC concentration, especially in Lake Koka, exceeded levels for serious health hazards for humans, cattle, and wildlife.

Dietary map of Nile tilapia using stable isotopes in three tropical lakes, Ethiopia

“…Lakes Hawassa, Ziway and Koka are situated in the Ethiopian rift valley ( Figure 1) and are nearby to each other with similar landscape setting, land use and altitude (Willén et al, 2011). Lake Hawassa is relatively small and deep, lakes Ziway and Koka are large and shallow ( Figure 1).…”

Characterization of phytoplankton by pigment analysis and the detection of toxic cyanobacteria in reservoirs with aquaculture production

“…Cyanobacteria are widely distributed and can form dense blooms in lakes and reservoirs in both temperate, subtropical, and tropical regions (Willén et al 2011). Many species of cyanobacteria produce toxic compounds, which have been shown to cause serious blooms of cyanobacteria may be the consequence of aquaculture production, since fish excreta and unassimilated feed can introduce eutrophic or hypereutrophic conditions into intensively operated fish farms (Smith et al 2008).…”

“…However, microcystins appear to contribute to more than 90% of the cyanotoxins detected in northern and middle European waters (Spoof et al 2010), and microcystins also appear to be dominant toxins in many other parts of the world (Willén et al 2011, Sant'Anna et al 2008. Microcystins consist of 3 dominant toxin variants: the arginine-containing microcystins (MC)-RR, MC-YR, and MC-LR, with different degrees of methylation (Spoof et al 2010).…”

Hazard Assessment of Microcystins From the Household’s Drinking Water

“…It was shown that the death of wildlife, in the study area, was due to toxic Microcystis. Willen et al (2011) studied the deaths of wild and domestic animals around the Rift Valley in Kenya and reported traces of microcystins produced by Microcystis aeruginosa as the dominant species. The toxins were found to exceed 1 µg L -1 levels.…”