Investigation Of Dissipation Of Trifloxystrobin In Rice Paddy Field And The Related Factors

Trifloxystrobin, a strobilurin fungicide, has been widely applied to control fungal diseases in various crops such as tomato, grape and apple trees. Recently, it has been introduced to rice cultivation against sheath blight, false smut, rice blast and other rice diseases to ensure yields. However, profiles of residual pattern of trifloxystrobin in environment, particularly in the rice paddy ecosystem, are poorly understood. Therefore, trifloxystrobin has been selected as the research object to study its dissipation dynamics in rice paddy ecosystem and the factors contributed to its degradation. The whole investigation included four sections:(1) The analytical method for determination of trifloxystrobin residues in paddy water, paddy soil and rice straw;(2) The dissipation dynamics of trifloxystrobin in rice paddy ecosystem;(3) The environmental behavior of trifloxystrobin;(4) Rice epiphyte-mediated biodegradation of trifloxystrobin and the related characteristics. Major results are shown as follows:Firstly, an analytical method for residual determination of trifloxystrobin and its hydrolysis metabolite trifloxystrobin acid in rice paddy ecosystem has been developed with favorable accuracy and precision, which is applicable for detection of trace amounts of residual trifloxystrobin in the rice paddy-associated samples. The trial of dissipation of trifloxystrobin in the rice paddy ecosystem indicated that decline dynamics of trifloxystrobin in paddy water, paddy soil and rice straw were in accordance with the first-order kinetics equation, illustrating that trifloxystrobin generally degraded in a rapid rate in the rice paddy with the half-life between0.5-7.5days. Additionally, trifloxystrobin acid was identified as the primary metabolite of trifloxystrobin in the rice paddy, which was found to be accumulated in the paddy water, suggesting that long-term and frequent application of this fungicide may pose a high risk towards aquatic organisms in surrounding aqueous ecosystems.Besides, the trial of environmental behavior indicated trifloxystrobin can be easily hydrolyzed in alkaline conditions. Trifloxystrobin can be photolyzed rapidly and its photolysis products were exclusive of trifloxystrobin acid. The dissipation of trifloxystrobin in soil can be influenced by its absorption on earth, while the degradation of trifloxystrobin in soil was dominantly attributed to the decomposition by soil microbes. In consideration of the results of hydrolysis trial and field trial, the further hydrolysis product of trifloxystrobin was speculated as C10H10NO3.Eventually, the trial of degradation of trifloxystrobin by epiphytes on rice straw showed that strain M and N isolated from rice straw samples had resistance towards trifloxystrobin, and the strain N has been identified as Pantoea ananatis. The test of degradation indicated that trifloxystrobin could be degraded by strain M and its metabolite trifloxystrobin could be degraded by both strains M and N. Moreover, it was found that biofilm formation of P. ananatis was positively correlated with the degradation of trifloxystrobin acid. As mentioned above, the further biofilm development of strain N promoted the biodegradation of trifloxystrobin and trifloxystrobin acid.