Abstract
Cyanobacterial blooms are a global concern. Chemical coagulants are used in water treatment to remove contaminants from the water column and could potentially be used in lakes and reservoirs. The aims of this study was to: 1) assess the efficiency of ferric sulfate (Fe2(SO4)3) coagulant in removing harmful cyanobacterial cells from lake water with cyanobacterial blooms on a short time scale, 2) determine whether some species of cyanobacteria can be selectively removed, and 3) determine the differential impact of coagulants on intra- and extra-cellular toxins. Our main results are: (i) more than 96% and 51% of total cyanobacterial cells were removed in mesocosms with applied doses of 35 mgFe/L and 20 mgFe/L, respectively. Significant differences in removing total cyanobacterial cells and several dominant cyanobacteria species were observed between the two applied doses; (ii) twelve microcystins, anatotoxin-a (ANA-a), cylindrospermopsin (CYN), anabaenopeptin A (APA) and anabaenopeptin B (APB) were identified. Ferric sulfate effectively removed the total intracellular microcystins (greater than 97% for both applied doses). Significant removal of extracellular toxins was not observed after coagulation with both doses. Indeed, the occasional increase in extracellular toxin concentration may be related to cells lysis during the coagulation process. No significant differential impact of dosages on intra- and extra-cellular toxin removal was observed which could be relevant to source water applications where optimal dosing is difficult to achieve.
Highlights
Cyanobacteria are well adapted to survive and proliferate in water bodies worldwide.Eutrophication and climate change are the main drivers of cyanobacterial blooms [1]
Cyanotoxins can be classified into several main groups: hepatotoxins, cytotoxins, neurotoxins, dermatotoxins, endotoxins and other toxins [3,4]
The genera Dolichospermum, Microcystis, Aphanizomenon were found in both control and coagulated mesocosms at both studied sites and they accounted for more than 70% of total taxonomic cell counts (Figure S1)
Summary
Cyanobacteria are well adapted to survive and proliferate in water bodies worldwide.Eutrophication and climate change are the main drivers of cyanobacterial blooms [1]. Cyanotoxins are the byproducts of metabolite formation processes. They may appear within the cell (intracellular) or released into in the water column (extracellular). Cyanotoxins can be classified into several main groups: hepatotoxins (microcystins and nodularins), cytotoxins (cylindrospermopsins), neurotoxins (e.g., anatoxin-a), dermatotoxins (e.g., lyngbyatoxin), endotoxins (lipopolysaccharides) and other toxins [3,4]. Microcystins are the most commonly detected hepatotoxins associated with cyanobacterial blooms worldwide [5,6]. Several health impacts, such as gastroenteritis and cutaneous reactions, have been identified [7]. They are one of the many potential causes of water quality degradation in aquatic systems, having potential consequences for biological communities [8]
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