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The occurrence and removal of cyanobacterial metabolites microcystin-LR and geosmin from source waters with powdered activated carbon




Sam, Victor, author
Ömur-Özbek, Pinar, advisor
Legare, Marie, committee member
Carlson, Ken, committee member

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Cyanobacteria blooms may result in the release of problematic algal metabolites, such as geosmin and microcystin-LR in source waters. The World Health Organization has set a guideline limit of 1 μg/L for the Microcystin-LR in drinking water to prevent adverse health effects. Microcystin-LR is the most common and potent cyanotoxin which can cause severe gastro-enteritis and hepatoritis. Unlike microcystin-LR, geosmin is not known to be harmful however, it imparts an unpleasant earthy off-flavor to drinking water detectable to humans at 2-10 ng/L. Understanding the occurrence of these metabolites is the first step in mitigating waters contaminated with these algal metabolites. To understand their occurrence in Northern Colorado, environmental sampling was performed in local rivers, lakes and municipal waters. Results of environmental sampling in the Northern Colorado area revealed that microcystins frequently was detected with geosmin however; geosmin alone, without microcystin-LR, was more frequently detected. This common co-occurrence of both compounds may be helpful in the surveillance, prevention and elimination of geosmin and microcystin-LR from drinking water sources. Since neither of the metabolites can be sufficiently removed by most conventional water treatment processes. This study also investigated the concurrent removal of microcystin-LR and geosmin from spiked raw Horsetooth Reservoir water, in Fort Collins CO, by powdered activated carbon (PAC). Water samples were spiked with microcystin-LR and geosmin to achieve various concentrations from 2 to 10 μg/L and 10 to 50 ng/L respectively, with PAC concentrations ranging from 10 to 30 mg/L. Jar testing was employed for the experiments with 30 min mixing and 30 min settling. Geosmin was quantified by solid phase micro-extraction and gas chromatography/mass spectrometry. Microcystin-LR was quantified by liquid chromatography/mass spectrometry coupled with electrospray ionization. A PAC dose of 30 mg/L removed microcystin-LR concentrations up to 6 μg/L below WHO guidelines of 1 μg/L. Geosmin concentrations up to 50 ng/L were removed below human detection threshold (5 ng/L) with 20 mg/L of PAC. Competitive absorption by PAC was observed between microcystin-LR and geosmin where the removal efficiency of both metabolites; because of its smaller size geosmin was slightly better absorbed by PAC than microcystin-LR. PAC is a viable method to remove both metabolites. To evaluate the toxicity of microcystin-LR, H4IIE, rat liver cells were cultured and exposed to microcystin-LR in-vitro. Cell viability and histological observations concluded that the toxin induced cellular apoptosis and cell viability is cyanotoxin concentration dependent.


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powdered activated carbon
northern Colorado


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