Delayed Release of Intracellular Microcystin Following Partial Oxidation of Cultured and Naturally Occurring Cyanobacteria

Abstract

Oxidation processes can provide an effective barrier to eliminate cyanotoxins by damaging cyanobacteria cell membranes, releasing intracellular cyanotoxins, and subsequently oxidizing these toxins (now in extracellular form) based on published reaction kinetics. In this work, cyanobacteria cells from two natural blooms (from the United States and Canada) and a laboratory-cultured Microcystis aeruginosa strain were treated with chlorine, monochloramine, chlorine dioxide, ozone, and potassium permanganate. The release of microcystin was measured immediately after oxidation (t ≤ 20 min), and following oxidant residual quenching (stagnation times = 96 or 168 h). Oxidant exposures (CT) were determined resulting in complete release of intracellular microcystin following chlorine (21 mg-min/L), chloramine (72 mg-min/L), chlorine dioxide (58 mg-min/L), ozone (4.1 mg-min/L), and permanganate (391 mg-min/L). Required oxidant exposures using indigenous cells were greater than lab-cultured Microcystis. Following partial oxidation of cells (oxidant exposures ≤ CT values cited above), additional intracellular microcystin and dissolved organic carbon (DOC) were released while the samples remained stagnant in the absence of an oxidant (>96 h after quenching). The delayed release of microcystin from partially oxidized cells has implications for drinking water treatment as these cells may be retained on a filter surface or in solids and continue to slowly release cyanotoxins and other metabolites into the finished water.

Assessing cyanobacterial frequency and abundance at surface waters near drinking water intakes across the United States

“…Moreover, satellite imagery can only detect cyanobacteria, not the presence of cyanotoxins ( Stumpf et al, 2016a ), and it is possible for both a visible bloom to be present without cyanotoxins and cyanotoxins to be present without a visible bloom. This issue is further complicated by the presence and the possibility of the growth and regrowth of cyanobacteria within the treatment utility, potentially leading to toxin or taste and odor production even in the absence of a bloom in the source water ( Almuhtaram et al, 2018 ; Greenstein et al, 2020 ).…”

Water Analysis: Emerging Contaminants and Current Issues

“…Release of microcystins in simulated drinking water treatment following chlorination, chloramination, ozonation, and treatment with chlorine dioxide and potassium permanganate was the focus of another study by Greenstein et al Substantial differences between lab-cultured and natural HAB cell lysis rates were observed, with lab-cultured algae more susceptible to chemical oxidation than natural HABs. Higher doses of 0.15 Cl 2 :DOC, 0.15 ClO 2 :DOC, 0.5/0.8 O 3 :DOC, and 2/2.7 KMnO 4 :DOC were required for the complete release of intracellular microcystins.…”

Comparative Assessment of Physical and Chemical Cyanobacteria Cell Lysis Methods for Total Microcystin-LR Analysis

“…During the water-treatment process, cells and corresponding intracellular cyanotoxins are often removed through sedimentation and filtration [ 7 , 8 ]. However, oxidation processes may result in either complete or partial cell lysis [ 9 , 10 ]. Adsorption processes have also been shown to cause shearing of cells, potentially resulting in the release of intracellular cyanotoxins [ 11 ].…”