| Thifluzamide is a bactericide of the thiazole amide class developed by Monsanto Company.It can be used to control a variety of diseases in field crops,lawns,and meadows.In order to provide scientific basis for reasonable using and evaluating environmental safety of thifluzamide,the residual dynamics in paddy field and behavior(hydrolysis,photolysis,soil degradaton,absorption and mobility)in environment for thifluzamide were studied systematically in this paper.The main results were as follows:1.An analytical method for thifluzamide residues in water,soil,paddy straw,brown rice and rice husk samples was developed by GC-ECD.The results showed the recoveries of thifluzamide in different paddy samples ranged from 89.3%to 109.4%at the spiked concentration of 0.05?2 mg/kg,the relative standard deviations(RSD)ranged from 0.9%to 10.0%.The limit of detection(LOD)was 0.05 mg/L in different rice field samples.The stability,sensitivity,accuracy and precision of the analysis meet the requirements of detection.2.The results of residues degradation dynamics of thifluzamide at three paddy fields of Jiangsu,Guangdong and Shandong in two years showed that the degradation dynamics accord with the kinetic equation.The half-lives of thifluzamide were 1.3?4.6 d,3.1?7.9 d and 7.7?13.9 d in paddy water,soil and straw,respectively.The results of the final residue experiments showed that the residues of thifluzamide in plants,soil,rice and rice husk after 14 days on the last use were 0.16-3.01 mg/kg?<0.05?0.39 mg/kg,0.06-0.81 mg/kg and 0.53?5.46 mg/kg,respectively.The residues of thifluzamide in plants,soil,rice and rice husk after 21 days on the last use were 0.12?1.25 mg/kg,0.05?0.19 mg/kg,0.05?0.52 mg/kg and 0.21?4.13 mg/kg,respectively.According to the maximum residue limit standard of thifluzamide in our country,the maximum dosage of 78 g a.i/ha,the most times of 2 and the safty interval of 21d are recommended,when 50%thifluzamide water dispersible granules is used to control rice sheath blight.3.The photodegradation rate of thifluzamide was decreased with increasing the initial concentration,under ultraviolet irradiation.Thifluzamide was easy photodegradation in alkaline and neutral conditions,and medium photodegradation inacidic condition.The photodegradation rate of thifluzamide in alkaline condition was improved 24 times compared to this in acidic condition.The photodegradation rate of thifluzamide in different solvents followed the sequence:n-hexane>acetonitrile>methanol>ethyl acetate>ultrapure water.In addition,environmental matters of the ferric ions,ferrous ions and humic acid could inhibit the degradation of thifluzamide.4.Temperature is one of the important factors to affect the hydrolysis of thifluzamide.The hydrolysis rate of thifluzamide could be accelerated with increasing the temperature.The hydrolysis of thifluzamide was promoted by acid condition.The surface active agent CTAB and SDS could inhibit the hydrolysis of thifluzamide.The inhibitions were enhanced with increasing the concentrations of CTAB and SDS,and CTAB showed greater inhibition for the hydrolysis of thifluzamide.5.The degradation half-lives of thifluzamide in yellow-brown soil of Nanjing,black soil of Northeast China and red soil of Jiangxi were 9.34,17.76 and 20.08 days,respectively,suggesting that this chemical was degraded rapidly in soils.The degradation rate of thifluzamide was accelerated with increasing the soil moisture,but it was decreased in 80%moisture treatments because microbial growth was inhibited.When the microbial and organic matters are present in soils,the degradations of thifluzamide were accelerated 2.7 and 17.2 times,respectively.6.The adsorptions of thifluzamide accorded with Freundich equation in yellow-brown soil of Nanjing,black soil of Northeast China and red soil of Jiangxi,the adsorption coefficients were in the range of 7.09?12.28,suggesting thifluzamide belong to difficult adsorption pesticides.The adsorption free energies(AG)in three soils were in the range of-22.70 to-21.30 kJ·mol-1,suggesting the adsorptions of thifluzamide belong to physical absorption.The desorption coefficients and(H)of thifluzamide in three soils were in the range of 15.08?28.22 and 0.69?1.20,respectively.The hysteresis coefficient of thifluzamide in black soil of Northeast China was 1.02,the desorption rate was greater than the adsorption rate,meant negative hysteresis.The hysteresis coefficient was 0.74 in yellow-brown soil of Nanjing,desorption rate was similar to adsorption rate,meant without hysteresis.The hysteresis coefficient was 0.69 in red soil of Jiangxi,desorption rate was lower than that of the adsorption,meant positive hysteresis.7.The results of soil thin-layer chromatography(TLC)showed that the Rf of thifluzamide were 0.234,0.233 and 0.224 in Jiangxi red soil,Nanjing yellow-brown soil and Northeast China black soil,respectively.These results indicated that thifluzamide was not easy to move in three kinds of soils.The results of soil column leaching showed that thifluzamide with poor mobility in three kinds of soils is a hard leaching pesticide,indicated that it is not easy to pollution ground water by leaching. |
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