Toxin Release from Microcystis Aeruginosa after Chemical Treatment

Abstract

Cyanobacterial (blue-green algal) blooms in agricultural dugouts and eutrophic lakes or reservoirs are common across the Canadian prairies. These blooms have caused livestock and wildlife poisonings that have been attributed to neurotoxins and/or hepatotoxins produced by various species of cyanobacteria. The hepatotoxins are extremely potent acute poisons. For example, microcystin LR has an LD50 of 50 µg/kg, by intraperitoneal injection, in mice. Hepatotoxins may also pose chronic health risks. Consequently, their presence in drinking water sources is attracting increasing attention. Chemical treatment with copper sulfate is the most common technique used to control algal blooms in drinking water reservoirs. Application of lime (calcium hydroxide) is an alternative treatment for the control of blooms. The effects of copper sulfate versus lime treatment on the release of microcystin LR from a naturally occurring bloom, involving three species of cyanobacteria including toxin-producing Microcystis aeruginosa, were studied. Water samples collected after chemical treatment of algal bloom material were monitored for microcystin LR at specific time intervals. In three replicate trials, the cells treated with coppa- sulfate released the majority of the toxin present within cellular biomass during the first three days after treatment. Substantial toxin release was not observed when cells were untreated (control) or treated with lime. After release, the persistence of microcystin LR was monitored. The aqueous toxin concentrations declined according to first order kinetics with a decay constant of 0.25 d−1. The experimental conditions, involving high biomass content, may have favoured toxin degradation. The microcystin LR half life, under laboratory conditions, was 3 d from the time of maximum toxin release (2 to 4 d after chemical treatment), meaning that a 99% reduction would take approximately 3 weeks. These findings indicate that copper sulfate should not be used to treat potentially toxic cyanobacterial blooms in waters to be consumed by humans or animals within several weeks following treatment.

Toxin release in response to oxidative stress and programmed cell death in the cyanobacterium Microcystis aeruginosa

“…Post lysis, free toxin was detected at concentrations reaching 1.8 g l −1 in mesocosm studies. This release can be quite rapid and occurs within 3-24 h of algicide application depending on the administered dose (Jones and Orr, 1994;Kenefick et al, 1993). Paraquat (methyl viologen) is a well known herbicide/algicide that elicits toxicity in a catalytic manner requiring the presence of molecular oxygen and chloroplast photo-activation.…”

Cyanobacterial population and harmful metabolites dynamics during a bloom in Yanghe Reservoir, North China

“…7 and 8. All of the four cyanotoxins were detected, and most of cyanotoxins were located within the cells, indicating that appropriate treatment was required to prevent cells from being disrupted (Watanabe et al, 1992;Kenefick et al, 1993;Daly et al, 2007;Sakai et al, 2007) . These values occurred on 2 July, the day which coincided with the maximum total cyanobacterial density (81,000 cells mL À1 ), whereas the maximum Microcystis spp.…”

Cyanobacterial and microcystins dynamics following the application of hydrogen peroxide to waste stabilisation ponds

“…Although it is common practice to remove cyanobacteria using copper sulfate, chlorine, or coagulants and flocculants (Hrudey et al, 1999), the dynamics of the removal of cyanobacteria and cyanotoxins from wastewater have not been thoroughly investigated. Additionally, the cyanobacterial removal methods currently practiced may negatively impact the environment, and may not be effective at removing cyanotoxins (Hrudey et al, 1999;Kenefick et al, 1993).…”