Residue And Degradation Of MCPA In Paddy Field And Its Behavior On Soil Effected By Biochar

In order to provide scientific reference basis for the reasonable usage of MCPA on rice and remediation and prevention of pesticide contaminated soil, this paper studied the detection methods of MCPA on paddy water, paddy soil, rice and other paddy field samples, the degradation dynamics and residual regularity of MCPA in compounded preparation on paddy fields in three provinces in two years. And the effects of adsorption and desorption behavior, natural degradation and biological toxicity of MCPA in soils were also studied. The conclusions are as follows:(1) A HPLC analysis detection method has been established for determination of MCPA in paddy water, soil, rice plant, rice straw, chaff and rice. The limits of quantification(LOQ) of MCPA in paddy water was 0.02 mg/L, and in paddy soil, rice plant, rice straw, chaff and rice was 0.05 mg/kg. The average recovery of MCPA in different samples ranged from 79.4% to 98.8%, the relative standard deviation(RSD) ranged from 1.9% to 6.5%. This method meet the requirements of pesticide residue analysis, and can be appied for the agricultural product quality monitoring department and the environmental monitoring department detectiong the residue of MCPA in paddy field samples.(2) The degradation of MCPA in paddy field accord with first-order kinetic equation Ct=Coe-kt. The half-lives of MCPA in paddy water, paddy soil and rice plant was 2.10d-3.65d,6.30 d?6.93 d,3.85 d?6.93 d respectively. The experiment show that MCPA can be easily degradated in paddy field.(3) 48% MCPA-bentazone AS* directly apply to paddy field to control annual broadleaf weeds and sedge weeds. In terms of its active ingredient MCPA, the highest recommendation dose of 48% MCPA-bentazone AS* is 160.0 grams per mu (active ingredient for 1152.0 g a.i./ha) and spray no more than one times.(4) The adsorption of MCPA on tested soils could be well described by the pseudo-second-order model and fitted well with the Freundlich isotherm adsorption model in the presence/absence of biochar, and the correlation coefficient had also reached significant level(p<0.01) and the adsorption process is mainly physical adsorption. Biochar can improve the adsorption of MCPA on tested soils, the Kf value of soil increased 5 times at least and 34 times at most and the maximum adsorption capacity of MCPA was 83.33 ?g/g after biochar added to soils. The adsorption capacity of MCPA decreased with the increase of pH and increased with the increase of temperature in tested soils, but this trend was affected to a certain extend when biochar added to soils.(5) The desorption of MCPA on tested soils could be fitted well with the Freundlich isotherm desorption model in the presence/absence of biochar, the correlation coefficient had reached significant level(p<0.01). The desorption process of MCPA on tested soils in the presence/absence of biochar is not reversible, the adsorption-desorption process exist obvious hysteresis and the hysteresis behavior was more obvious in the presence of biochar.(6) The degradation of MCPA in tested soils followed the first order kinetics equation in the presence/absence of biochar. Biochar can delay the degradation of MCPA in soils and the ability to delay related to the adsorption ability of MCPA.(7) MCPA had a great influence on the growth of pakchoi seedlings, When the concentration of MCPA in tested soils reached 0.18 mg/kg, the inhibition rate of root length and biomass of pakchoi seedlings was 100%. The resistence of pakchoi seedlings to MCPA was significantly improved after the addition of biochar in soils, the significant inhibitory concentration of root length and biomass was above 1.8 mg/kg, it was more than 10 times of significant inhibitory concentration in blank soils.