Toxin producing freshwater cyanobacteria of Sri Lanka

Abstract

Abstract:Cyanobacteria are photosynthetic, prokaryotic microorganisms commonly found among the phytoplankton of stagnant waters. Some of them produce toxins and these have been implicated to contribute to environmental health problems including kidney disease of uncertain etiology. This paper is a review of published literature on freshwater cyanobacteria of Sri Lanka with special emphasis on toxigenic genera. It is evident that the freshwater cyanobacterial populations of Sri Lanka have undergone significant changes from the beginning of the 20 th century until recent times. While toxigenic genera such as Microcystis and Cylindrospermopsis have been observed occasionally during the early 20 th century they have now become dominant in most of our waters except in those whose catchment areas are protected forests devoid of human habitation. Eutrophication through nutrient loading and other sources of pollution by anthropogenic activities triggers off cyanobacterial bloom formation which is an environmental health hazard. Minimizing pollution of lentic water bodies by the reduction of the use of chemical fertilizer and other agro-chemicals, restoration of riparian vegetation, biomanipulation to control cyanobacterial populations and breakdown of cyanotoxins through chemical, physical and microbiological methods have been proposed for the amelioration of this hazard. Extensive research studies on such aspects are warranted to develop solutions to overcome this environmental problem.

Glyphosate’s Synergistic Toxicity in Combination with Other Factors as a Cause of Chronic Kidney Disease of Unknown Origin

“…One ecosystem approach is to replace chemical-based nitrogen and phosphate fertilizers with organic fertilizers in crop production, while improving soil health. This would, for example, help reduce water pollution and prevent the overgrowth of toxin-producing cyanobacteria [156]. Switching from chemical-based phosphate fertilizers to organic fertilizers would also help reduce arsenic exposure [167].…”

“…Toxigenic cyanobacteria present a growing problem in Sri Lanka’s waterways, particularly in the North Central province where CKDu is endemic [156]. It is clear that their overgrowth is related to human activities, particularly in agricultural areas, where agricultural runoff of phosphate and nitrate fertilizers are supporting their growth.…”

The water chemistry and microbiome of household wells in Medawachchiya, Sri Lanka, an area with high prevalence of chronic kidney disease of unknown origin (CKDu)

“…In particular, the toxin-producing cyanobacteria genera, including Microcystis and Cylindrospermopsis , as well as Leptospira interrogans can lead to kidney disease 14 , 18 , 24 , 25 and have, therefore, been put forward as potential causes of CKDu 21 , 26 , 27 . Significant increases of cyanobacteria in freshwater resources in Sri Lanka have occurred over the past century as a result of eutrophication and rising temperatures 21 , 28 , demonstrating that altered water chemistry is likely to promote the presence of pathogenic bacteria in this region.…”

Quantitative observations of Cyanobacteria and Dinoflagellata in reservoirs of Sri Lanka

“…4 25 20 24 23 3 44 40 39 34 42 41 26 28 10 16 27 12 38 11 35 43 17 33 31 18 21 19 15 13 22 9 45 32 36 5 29 7 14 30 8 6 8 6 14 29 7 5 33 27 32 28 26 12 45 44 42 34 40 38 30 31 18 13 35 16 43 36 15 19 17 11 41 37 9 10 21 22 23 24 25 20 39 4 3 Perera et al, (2012b). Cyanobacterial species are known to occur under different limnological conditions as they can tolerate wider ranges of temperature, light and nutrient conditions which are important for their survival (Kulasooriya, 2017). These tolerance levels of different species determine the dominance and community structure of phytoplankton at different periods and seasons (Fogg, 1975).…”

“…Unfortunately, a quantitative assessment was not done to get a clear idea on the role of macrophytes in absorbing nutrients. When considering the presence of dominant toxic algae in macrophyte dominant reservoirs, it was interesting to see that species such as C. rasciborski and M. aeruginosa are not available showing importance of macrophytes in balancing an ecosystem (Kulasooriya 2017). Weerakoon et al (1998) also reported that high density and diversity of aquatic macrophytes in Basawakkulama reservoir compared to Tisawewa may provide a favourable ecological niche to zooplanktons which will regulate the Cylindrospermopsis abundance.…”