Kinetics and degradation mechanism of Anatoxin-a during UV-C/H2O2 reaction

Abstract

Cyanobacteria can produce toxins which are responsible for the livestock and human poisoning. Anatoxin-a is one of the toxins mainly secreted by cyanobacteria Anabaena flos-aquae. In this study, the removals of anatoxin-a (0.3 µM) during UV-C photolysis and UV/H2O2 reactions were compared using a photo-reactor system consisting of a stirred 2-L glass bottle by applying the UV intensity of 3.5-4.0 mW/cm2 and H2O2 dose of 0.01 mM. All samples were measured after pre-treated by solid-phase extraction (SPE), followed by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The result showed that the removal of anatoxin-a was more effective during UV/H2O2 reaction than either UV-C photolysis or H2O2 alone. Anatoxin-a was completely degraded within 30 min during UV/H2O2 reaction, which might be due to the effective production of OH radicals. UV/H2O2 reaction of anatoxin-a resulted in an approximately 60% TOC decrease after 7 hr, and 30% acetate were produced as the organic short chain by-product. For nitrogen recovery, NH4+, NO2-, and NO3- ions were produced from UV/H2O2 reaction, and more than 50% of the total nitrogen was mineralized mainly to NO3- ion. Using LC-ESI-MS/MS, we newly identified 6 degradation by-products during UV/H2O2 reaction ([M+H]+ values of 142, 127, 113, 132, 117, and 124). Using the identified by-products, we proposed the degradation pathway of anatoxin-a during UV/H2O2 reaction based on the identified by-products. Our results imply that anatoxin-a can be effectively controlled by UV/H2O2 reaction during water treatment processes.