Degradation And Residue Of Niclosamide Ethanolamine In The Paddy Field And Its Environment Behavior

Niclosamide ethanolamine which is used in most areas planted rice is recommended as an agent of killing molluscs in China. The study on niclosamide ethanolamine almost focus on its toxicology and its control effectiveness. But little information was available about its final residue, hydrolysis, adsorption in rice ecosystem. In order to assess the safety of niclosamide ethanolamine in paddy field, this paper had studied its degradation and residue in paddy soil, paddy water and paddy straw, its hydrolysis in water, adsorption in different paddy soils. The results could provide some basic datas for scientific application of niclosamide ethanolamine or its relative dose. The main contents were as follows:(1) A high performance liquid chromatographic method was developed for the detemination of niclosamide ethanolamine residue in rice ecosystem. Its residue in paddy water and in rice plant were extracted with alkaline ethylacetate, while those in paddy soil, rice shell and unpolished rice were extracted with alkaline ethanol and ethylacetate. All the obtained extracts were then purified by a florisil column and analyzed quantitatively by high performance liquid chromatography with ultraviolet detector on a welchrom C18column. The calibration curve for niclosamide ethanolamine had a good linearity in the range of0.01-5mg/L. The average recoveries of the method ranged from93.47%to100.9%with the relative standard deviations of1.46%-5.82%at spiked level of0.01-5.00mg/kg. This proposed method is simple, fast, sensitive, reproducible and practical for the determination of niclosamide ethanolamine residue in environmental systems.(2) A field experiment was conducted to reveal residual dynamics and final residue of niclosamide ethanolamine in rice and paddy system in Changsha, Hangzhou and Guiyang of China. Its degradation dynamics and the final residue results in rice and paddy system showed that the degradation half-lives in rice plant, paddy water and soil were1.69～3.01d,8.66～13.86d and5.33～7.70d respectively in three places. Its final residue in unpolished rice was lower than1.00mg.kg-1at an interval of62d. However, Its final residue in rice plant were higher than those in rice husk, unpolished rice and paddy soil. According to this results, when70%wettable powder of niclosamide ethanolamine were sprayed in paddy field for twice according to the recommended dose of900g.hm-2(630g. a.i.ha-1), its safe period in rice could be set as62d.(3) The hydrolysis of niclosamide ethanolamine were different at different pH values. Its hydrolysis rate in alkaline solution was lower than in acid solution or neuter solution. Its hydrolysis rate accelerated with the rise of temperature. Bacause NaCl, KCl, CaCl2, NaNO3belong to strong acid and strong base salts which have salting-out effect, and restrained hydrolysis of niclosamide ethanolamine, when it were added into niclosamide ethanolamine solution. NaHCO3belong to strong base and weak acid salt, Due to dissociation of this salt making water alkaline, it also restrained the niclosamide ethanolamine when it was added into niclosamide ethanolamine solution.(4) The adsorption equilibrium times of niclosamide ethanolamine were24hours. Its adsorption in five kinds of tested soil could be described with the Freundlich isotherm equation, and adsorption was physical adsorption. Its adsorption was strongest in the black soil from Heilongjiang, and it was weakest in the brown soil from Henan; The pH played an important role in this adsorption. The impact factor which affect the adsorption of niclosamide ethanolamine was the organic matter of soil, then cation exchange capacity.