Microcystin Content in Phytoplankton and in Small Fish from Eutrophic Nyanza Gulf, Lake Victoria, Kenya.

Benard Simiyu,Steve Oduor,Thomas Rohrlack,Rainer Kurmayer,Lewis Sitoki

doi:10.3390/toxins10070275

Abstract

The human health risks posed by exposure to cyanobacterial toxins such as microcystin (MC) through water and fish consumption remain poorly described. During the last two decades, coastal regions of Lake Victoria such as Nyanza Gulf (Kisumu Bay) have shown severe signs of eutrophication with blooms formed by Microcystis producing MC. In this study, the spatial variability in MC concentration in Kisumu Bay was investigated which was mostly caused by Microcystis buoyancy and wind drifting. Small fish (<6 cm) mainly composed of Rastrineobola argentea were examined for MC content by means of biological methods such as ELISA and protein phosphatase inhibition assay (PPIA) and partly by chemical-analytical methods such as LC-MS/MS. Overall, the MC content in small fish was related to the MC content observed in the seston. When comparing the MC content in the seston in relation to dry weight with the MC content in small fish the latter was found three orders of magnitude decreased. On average, the ELISA-determined MC contents exceeded the PPIA-determined MC contents by a factor of 8.2 ± 0.5 (SE) while the MC contents as determined by LC-MS/MS were close to the detection limit. Using PPIA, the MC content varied from 25–109 (mean 62 ± 7) ng/g fish dry weight in Kisumu Bay vs. 14 ± 0.8 ng MC/g in the more open water of L. Victoria at Rusinga channel. Drying the fish under the sun showed little effect on MC content, although increased humidity might indirectly favor photocatalyzed MC degradation.

Highlights

Lake Victoria has experienced major deterioration in its water quality mainly due to pollution and the introduction of exotic species [1]
Nyanza Gulf is one of the bays of Lake Victoria that is most affected by nutrient enrichment [5]
MCs, which is mainly caused by the dominance of the bloom-forming cyanobacterium of the genus Microcystis

Summary

Introduction

Lake Victoria has experienced major deterioration in its water quality mainly due to pollution and the introduction of exotic species [1]. Nyanza Gulf is one of the bays of Lake Victoria that is most affected by nutrient enrichment [5]. Which is coming from the highly populated catchment with mostly subsistence agriculture [2,6]. This has led to regular occurrence of bloom-forming cyanobacteria [7]. Some cyanobacterial species have the potential to produce cyanotoxins that pose a health risk to livestock and humans who rely on such water for drinking, sanitation, or as a food source [8]. The regular occurrence of cyanobacterial blooms in the Nyanza Gulf has been associated with fish kills and temporary shutdown of drinking water supply, i.e., from January to March 2004 [9]

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Conclusion