Degradation Of Atrazine By Photoreaction And Sugarcane Endophytes

Atrazine is a widely used herbicide in farmland. It is difficult to degrade and easy to remain in the environment because of its stable molecular structure. It has caused serious pollution in soil and water system due to its long-term usage. Therefore, it is particularly important to remove the residual atrazine of environment by an efficient way. There are some methods to remove the residual atrazine including physical, chemical and biological techniques. Photodegradation as a chemical method has the ability to remove the atrazine of environment. Compared with other chemical methods, it won’t cause secondary pollution problem. As to biological aspect, most related researches still focused on the atrazine degrading bacteria or fungi separated from soil or activated sludge. The isolation of endophyte which can degrade atrazine under oligotrophic conditions was rarely reported. Based on the above, this study has been done:(1) To explore the effects of different light irradiation on the degradation of atrazine and its photodegradation kinetics, the photochemical degradation of atrazine in aqueous solution was investigated with HPLC. The products of degradation were identified by UPLC-MS and the pathway of degradation was also speculated. The results showed that the degradation rate under ultraviolet light was faster than under simulated sunlight. It could be enhanced by increasing the power of light irradiation. The process of photodegradation in aqueous solution followed first-order kinetics. The identification result by UPLC-MS showed that the products of photodegradation were hydroxy atrazine and cyanurodiamide.(2) The roots of sugarcane were collected from the sugarcane planting area in Guangxi Zhuang Autonomous Region which has been sprayed by atrazine for a long time. A strain of endophytic fungus N2 was successfully isolated by using basic inorganic salt medium for separation and enrichment. Based on its morphological characteristics in the medium and observation of its hypha and spore through the optical microscope, combined with the results of 18S rRNA and internal transcribed spacer (ITS) gene sequence determination, the fungus was initially identified as Fusarium fujikuroi. This strain of degrading atrazine is first reported in this paper.(3) The atrazine degrading ability of this fungus was determined by high performance liquid chromatography (HPLC). The result showed that the strain could use atrazine as its only nitrogen source to grow and was capable of degrading atrazine. The influence of degradation time, pH, temperature, primary concentration of atrazine and carbon source on atrazine degradation was investigated. It showed that, after 10 days incubation, the degrading fungus had the best degradation property under those conditions:pH 7-8, temperature 28℃, atrazine primary concentration 25 mg/L, glucose as carbon source. The degradation rate could reach 49.6% after 10 days. The result of adding metal ions showed that Cu2+ and Fe2+ could observably restrain the degradation property of the degrading fungus while the fungi had good tolerance with Zn2+, Mn2+, Ba2+.(4) The degradation products were determined by ultra performance liquid chromatography-mass spectrometry (UPLC-MS). The pathway of degradation was also speculated. The results showed that the degradation product after 10 days degradation was cyanuric acid. There was no new product after increasing the time of degradation. It illustrated that this degrading fungus couldn’t cause the ring-opening reaction of atrazine.