Study On The Systemic Conduction Characteristics And Degradation Dynamics Of Agricultural Organosilicon Spray Adjuvants On Ric

Pesticide spray additives are used in the process of pesticide spraying.They are considered to be relatively safe and can improve the efficacy of pesticides,but their impact on the environment is often ignored.In recent years,the toxicity and harm of pesticide additives have attracted wide attention.As a polyoxyethylene ether surfactant,agricultural organosilicone spray agent is a kind of polymer itself,and the structure has a variety of types.So far,there are few reports on the residual level and degradation metabolism of agricultural organosilicone spray agent in the environment.After determining the structure type of agricultural organosilicon spray agent commonly used in our country,a sensitive and accurate quantitative analysis method of organosilicon spray agent in various substrates of rice(rice roots,stems and leaves)is established.The residual quantity of agricultural organosilicon spray agent in rice plants is detected and the absorption,conduction,distribution and degradation characteristics of the agent in crops are explored.The main results are as follows:(1)Using high performance liquid chromatography,high resolution mass spectrometry and evaporative light scattering double detector to identify the common agricultural silicone spray auxiliaries in the Chinese market,the results show that the structure of the common silicone spray auxiliaries is mostly polyether modified trisiloxane(SS-H)polymer,the number of repeating unit--ethoxy group(EO)is from3 to 15.(2)Degradation analysis of TSS-H in 9 different aqueous solutions at 25℃showed that the degradation of TSS-H was faster in the buffer solution with a pH of 4,and the half-life of TSS-H was only 1.19 h,while that of the buffer solution with a pH of 5 was 10.66 h,about 0.44 d.The half-life of TSS-H in the buffer solution at pH 9 is0.93 d.The half-life of TSS-H in pH 6,8,tap water,pure water,tap water + nutrient solution was 3.73 d,4.81 d,4.08 d,5.92 d,3.41 d,and the half-life of TSS-H in pH 7solution was 12.38 d.TSS-H was easily degraded in aqueous solution(t1/2 < 30 d).(3)The transmission and distribution of TSS-H in rice plants were studied by leaf application and root application.The results showed that the original deposition amount of each compound with different EO number(a= 4～12)in TSS-H ranged from 3.96 to11.85 mg/kg after application on the middle and lower leaves of rice.The contents of nine EO compounds ranged from 0.0022 to 0.0063 mg/kg in roots and from 0.0013 to0.0026 mg/kg in stems.The residues in roots and stems were significantly lower than those in leaves,indicating that the conductivity of TSS-H from leaves to roots was weak.The content of TSS-H in the unapplied upper leaves ranged from 0.0011 to 1.5313mg/kg,indicating that TSS-H could be absorbed from the applied leaves,transported and accumulated to the top leaves of the plant after application.After root application,TSS-H of each a value reached the maximum value in all parts at 48 h,with the content range of 0.29～1.50 mg/kg on leaves,0.51～1.34 mg/kg on stems and 3.10～4.09 mg/kg on roots.The root concentration factor(RCF),bioenrichment factor(BCF),transpiration factor(TSCF),and stem and leaf transport factor(TF)in TSS-H ranged from 0.20 to 0.56,0.36 to 0.68,0.073 to 0.086,0.08 to 0.43,respectively.RCF,BCF,TSCF and TF were all less than 1,which indicated that TSS-H could be absorbed by rice and conducted to the above-ground part of rice plants.However,the absorption degree of TSS-H in rice roots was small,the enrichment degree of TSS-H in rice plants was also small,and the transfer ability of TSS-H in rice xylate was not strong.The conduction ability from the root to the upper part of the plant(stem,leaf)is also not strong.The results of leaf application and root application showed that TSS-H had no bidirectional conduction ability between leaf and root of rice.(4)The residue test of additives on rice was carried out under field conditions.After spraying rice with 2000 times dilution solution,the total residue range of 9compounds in TSS-H was 0.14～3.12 mg/kg at 0～14 days.The reduction of each compound with different EO number in TSS-H could be fitted by the first-order kinetic equation.By calculating the half-lives of 9 compounds(a= 4～12)on rice,the digestion half-lives were 2.62,2.65,2.48,2.62,3.27,3.59,2.94,2.75,2.69 d,respectively.The degradation rates of the nine compounds(a=4～12)in TSS-H were all faster,and the difference of the value of the ethoxy base a in TSS-H would lead to the difference of the degradation rates and half-lives.When a=4,5,6,7,10,11,12,the half-lives were all less than 3d and relatively similar,and when a=8,9,the half-lives were more than3 d.