Abstract
Microcystins (MCs) are toxins profusely synthesized by cyanobacteria, causing livestock poisonings and endangering human health. We design and execute an experiment to investigate the attenuation (degradation) of microcystins by exposing them to gamma radiation and electron beams at doses of 0 (control), 3, 5, 10 and 15 kGy. The experimental conditions simulate microcystin contamination of aquatic environments; we thus consider (1) microcystins inside whole cells and extracellular dissolved in water, simulated by non-sonicated and sonicated cells, respectively, and (2) two acute microcystin concentrations within water. Toxicity tests of Microcystis aeruginosa detected immobilization (i.e., paralysis) of Ceriodaphniasilvestrii exposed to aqueous crude extracts of irradiated and non-irradiated M. aeruginosa (NPLJ-4 strain) at concentrations of 45 and 90 mg.L-1 (mg dry weight of freeze-dried material), and the results were analyzed using the Trimmed Spearman-Karber statistical program to obtain 48-h EC50, the average effective concentration causing immobility in 50% of organisms after 48 hours. We conclude that electron beams are effective physical agents for toxin attenuation (degradation) and reach 100% effectiveness at 5 kGy and above; their efficiency is two orders of magnitude greater than that of gamma radiation. This new body of information contributes to (1) remediating environmental water sources; (2) designing water/wastewater treatment facilities; (3) combatting chronic microcystin environmental contamination; and (4) inspiring further studies to promote the use of biomonitors (e.g., Cladocerans) to detect and evaluate microalgae contamination.
Highlights
Toxic cyanobacteria blooms in surface waters are a major worldwide environmental concern
Toxicity tests of Microcystis aeruginosa detected immobilization of Ceriodaphnia silvestrii exposed to aqueous crude extracts of irradiated and non-irradiated M. aeruginosa (NPLJ-4 strain) at concentrations of 45 and 90 mg.L-1, and the results were analyzed using the Trimmed Spearman-Karber statistical program to obtain 48-h EC50, the average effective concentration causing immobility in 50% of organisms after 48 hours
Toxicity Test with Toxic Strain of Microcystis Aeruginosa (NPLJ-4), and Exposure to Ionizing Radiation: All tests performed with the control dose 0 kGy of the toxic culture represented by strain NPLJ-4 showed toxic effects on C. silvestrii, with a mean value of 48-h EC50 equal to 31.4 mg.L-1 dry weight of freeze-dried material and a 95% confidence interval of 26.0–38.0 mg.L-1 dry weight of freeze-dried material (Table-1)
Summary
Toxic cyanobacteria blooms in surface waters are a major worldwide environmental concern. They produce bioactive molecules such as microcystins (MC), some of which produce cyanotoxins [1,2]. Microcystins cause poisonings in livestock and wildlife worldwide and threaten human health by contaminating drinking water and recreational waters [3,4]. C. Bittencourt-Oliveira has researched micro cystin-related food poisoning by studying the photosynthetic effects and bioaccumulation of microcystin congeners in lettuce irrigated with contaminated water [5]
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