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The toxicology of microcystins in freshwater organisms of the Great Lakes

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Title: The toxicology of microcystins in freshwater organisms of the Great Lakes
Author: Shahmohamadloo, René Sahba
Department: School of Environmental Sciences
Program: Toxicology
Advisor: Sibley, Paul
Abstract: Harmful algal blooms dominated by Microcystis aeruginosa are causing ecological and socio-economic disturbances to freshwater ecosystems, in particular the Great Lakes, through the production of microcystin toxins, which can cause disease-related effects in freshwater organisms. This thesis investigated the mechanisms of microcystin toxicity to freshwater organisms of the Great Lakes and assessed the human health risks from consuming fish exposed to cyanobacterial blooms. I began by developing a method for producing high concentrations of microcystins by a toxigenic strain of M. aeruginosa in the laboratory—a method that was yet to be developed and could assist in understanding the mechanisms of microcystin toxicology. Once the method was established, I then ran a series of experiments on pelagic and benthic invertebrates by chronically exposing them to microcystin concentrations typically found in the Great Lakes. Pelagic invertebrates experienced lethality and reproductive impairment at low doses of microcystins, while no effects were observed in benthic invertebrates. I next ran a series of microcystin kinetics experiments on fish by, again, exposing them to microcystin concentrations typically found in the Great Lakes. In these series of experiments, I first sought to distinguish the accumulation potential of microcystins in their intracellular and extracellular states (i.e., within and outside M. aeruginosa cells), and then measured the uptake and depuration potential of microcystins in organs and tissues. Fish accumulated microcystins at significantly higher levels in extracellular than intracellular, and biomarkers related to oxidative stress and carcinogenesis were significantly abundant in all tissues exposed to both microcystin states. Additionally, in the uptake and depuration studies, microcystins carried into the depuration phase and dysregulated proteins that are necessary to fend off oxidative stress, disease, and cancer in fish. Finally, I assessed the risks to human health from consuming fish that were exposed to a cyanobacterial bloom in the field (Lake St. Clair) by collecting organs and tissues from several species that are typically sold and consumed in the market. Microcystins were below fish consumption advisory guidelines, which suggests edible muscle tissues from Lake St. Clair can be safely consumed by humans.
Date: 2021-02-12
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Related Publications: Shahmohamadloo, R. S., Almirall, X. O., Holeton, C., Chong-Kit, R., Poirier, D. G., Bhavsar, S. P., & Sibley, P. K. (2019). An efficient and affordable laboratory method to produce and sustain high concentrations of microcystins by Microcystis aeruginosa. MethodsX, 6, 2521-2535.

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