State of knowledge and concerns on cyanobacterial blooms and cyanotoxins

Abstract

Cyanobacteria are ubiquitous microorganisms considered as important contributors to the formation of Earth's atmosphere and nitrogen fixation. However, they are also frequently associated with toxic blooms. Indeed, the wide range of hepatotoxins, neurotoxins and dermatotoxins synthesized by these bacteria is a growing environmental and public health concern. This paper provides a state of the art on the occurrence and management of harmful cyanobacterial blooms in surface and drinking water, including economic impacts and research needs. Cyanobacterial blooms usually occur according to a combination of environmental factors e.g., nutrient concentration, water temperature, light intensity, salinity, water movement, stagnation and residence time, as well as several other variables. These environmental variables, in turn, have promoted the evolution and biosynthesis of strain-specific, gene-controlled metabolites (cyanotoxins) that are often harmful to aquatic and terrestrial life, including humans. Cyanotoxins are primarily produced intracellularly during the exponential growth phase. Release of toxins into water can occur during cell death or senescence but can also be due to evolutionary-derived or environmentally-mediated circumstances such as allelopathy or relatively sudden nutrient limitation. Consequently, when cyanobacterial blooms occur in drinking water resources, treatment has to remove both cyanobacteria (avoiding cell lysis and subsequent toxin release) and aqueous cyanotoxins previously released. Cells are usually removed with limited lysis by physical processes such as clarification or membrane filtration. However, aqueous toxins are usually removed by both physical retention, through adsorption on activated carbon or reverse osmosis, and chemical oxidation, through ozonation or chlorination. While the efficient oxidation of the more common cyanotoxins (microcystin, cylindrospermopsin, anatoxin and saxitoxin) has been extensively reported, the chemical and toxicological characterization of their by-products requires further investigation. In addition, future research should also investigate the removal of poorly considered cyanotoxins (β-methylamino-alanine, lyngbyatoxin or aplysiatoxin) as well as the economic impact of blooms.

Cyanobacteria and microcystin contamination in untreated and treated drinking water in Ghana

“…Interestingly, the overall frequency of samples containing dissolved MCs also increased after the flocculation step (Barekese, Owabi, Weija) or pre-chlorination (Kpong). This is in agreement with previous observations that these treatment steps can lead to the damage of cyanobacterial cells due to sheer stress or chemical oxidation, resulting in the release of cyanotoxins into the surrounding water (Hoeger et al, 2005;Hrudey et al, 1999;Merel et al, 2013;Pietsch et al, 2002;Westrick et al, 2010).…”

“…Correspondingly, intracellular or particle-associated MCs were found in the treated water, which indicates that the treatment process should be further optimized to remove cyanobacterial cells more effectively. This could include adjustments of the flocculant amount or application of a flocculant aid in response to changes in the raw water quality affecting coagulationflocculation-sedimentation process, such as turbidity, concentration of suspended solids and natural organic matter, phytoplankton abundance and composition (Hoeger et al, 2005;Merel et al, 2013;Westrick et al, 2010).…”

Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

“…They are detrimental to water quality and negatively affect the development of nautical sports and other recreational activities (Turner et al, 1990;Giannuzzi et al, 2011). Many Microcystis strains can produce the potent hepatotoxin microcystin (MC), of which there are more than 100 variants, causing liver damage as well as nephrotoxicity (Milutinovic et al, 2003;Merel et al, 2013;Niedermeyer, 2013). Harke et al (2016) conclude that the occurrence of Microcystis toxic blooms appears to be expanding, since 108 countries or territories around the world have documented their presence in recent years compared with fewer than 30 countries in earlier years (Zurawell et al, 2005).…”

Artificial mixing to control cyanobacterial blooms: a review

“…Cyanobacteria also can negatively affect domestic and wild animals as well as human health since they have the potential to produce toxins (see overview Merel et al 2013), and numerous animal and human intoxications by cyanobacterial toxins have been reported (e.g. Kuiper-Goodman et al 1999;Cox et al 2003;Griffiths and Saker 2003;Hilborn et al 2007).…”