Cyanobacteria and their toxins severely contaminate water sources and pose a danger to the health of humans and animals. A way to disinfect water is needed to create safe drinking water without creating additional hazards. The use of disinfectants was hypothesised to create cellular stress. Cellular stress was hypothesized to trigger increased production of cyanotoxins.Here, chlorine dioxide (ClO2) was tested to inhibit a toxin-producing strain of Microcystis aeruginosa. Through a series of experiments, ClO2 was exposed to M. aeruginosa, and the production of microcystin was monitored. The first experiment, batches of M. aeruginosa were exposed to ClO2 (0-10 mg/L) for 30 minites. Chlorophyll a and microcystin concentrations were lowered at higher levels of disinfection, suggesting that ClO2 can treat both M. aeruginosa and its toxins.The second investigation focused on the effective treatment of ClO2 to viability of cells, stress and microcystin production. M. aeruginosa, during four stages of population growth, were exposed to 0-5 mg/L ClO2 for various contact times (3 hours to 3 days) Population growth was measured by chlorophyll a and optical density. Viability was assayed by MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) and electrolyte leakage (conductivity). Cellular stress was measured by malondialdehyde (MDA) lipid peroxidation, catalase (CAT), superoxide dismutase (SOD), and carotenoids (CARs) levels.Microcystin was quantified by enzyme-linked immunosorbent assay (ELISA). ClO2 affected the viability of cells. In addition, increased electrolyte leakage illustrated the membrane damage that directly related to the deterioration of cells in every growth phase. Early populations (or early blooms) were more responsive to ClO2 inhibition than late-growth populations. In term of stress, ClO2 treatments at 1.5 mg/L induced oxidative stress. SOD activity increased in all three quartiles of population growth. Carotenoids and chlorophyll a became oxidized. The residual carotenoids may react to quench stress induced by ClO2. However, catalase activity increased to scavenge reactive oxygen species.The experiment suggests that crucial parameters for evaluation should include the viability of cells and metabolic activity. The study suggests relationships between ClO2 treatment and stress as well as microcystins production exist. However, no relationship was observed between stress and microcystins production. Further, low population densities exhibited a greater response to the disinfection, and had the greatest ClO2 related cyanotoxin release. These findings have implications that the timing and dosage of disinfection are very important in treating water with cyanobacteria to avoid the additional release of cyanotoxins and additional risk to human and animal health.
|Date of Award||30 Jul 2020|
- University Of Strathclyde
|Supervisor||Charles Knapp (Supervisor) & Christine Switzer (Supervisor)|