Effect Of Napropamide On Soil Environment And Study On Analysis Of Pesticide Multiresidues

Napropamide(N,N-diethyl-2-(1-naphthalenyloxy)propanamide) is a kind of highly effective broadspectmm amide herbicide,which has been used in agriculture to weed out most annual monocotyledon grasses and many broad leaf weeds such as lamb's-quarter,wide amaranth.With its broad spectrum of activities,napropamide is registered for use in many countries worldwide,including the United States,Europe and China,on a variety of fruits,vegetables and crops,either alone or with other pesticides such as monolinuron,nitralin,simazine,trifluralin,tefurthrin,and tebuta. Consequently,the environmental concerns about napropamide become increasing due to its relatively long persistence in soil.However,systemic reports about these are very few.A set of experiments were conducted to investigate effects of napropamide residues on soil enzymes,microbial biomass,soil respiration and microbial community structure(denaturing gradient gel electrophoresis(DGGE) analysis),degradation and adsorption of napropamide in soils also were studied.The major results were summarized as follows:The residue monitoring method for determination the napropamide in soil and water by HPLC and GC-MS was developmented,and different extraction methods for napropamide were compared.The result showed that the optimal methods for soil and water sample were ultrasonic extraction and liquid-liquid extraction,respectively. HPLC and GC-MS were characterized with simple operation,high sensitivation and recoveries.The accuracy and precision met the need of pesticide residues analysis.The degradation of napropamide in soils was studied.The results showed:(1) The decomposition of napropamide in Black Soil was fastest while slowest in Yellow-brown Soil in three kinds of different soils.(2) Soil temperature affected napropamide-degradation rate which increased with temperature rise from 15℃to 35℃,and difference of degradation rate between 25℃and 35℃was not significant. (3) Organic matter content in soil was the most important factor which influenced the degradation half-life of napropamide in soil,and their relative coefficient(r) arrived at 0.9794,but pH value,CEC and clay content correlated little.(4) The degradation half-life of napropamide in sterilized soil was far more than that in non-sterilized soil,maybe which contributed to microorganism in soil.(5) The probable degradation products were N-ethyl-2-(1-naphthoxy)-propionamide, naphthoxy acetyl and N-methyl-N-ethyl-2-(1-naphthoxy)-propionamide.The possible degradation pathways were dealkylation and dediethylamine.The adsorption and its mechanisms of herbicide napropamide on soils were studied in the laboratory.Results indicated:(1) Adsorption isoterms of napropamide on the soils such as Yellow-brown soil,Latersol and Black Soil can be described by Freundlich equation with the corresponding adsorption coefficient(K_f) of 1.29,3.43 and 13.36.The mean partial molar free energy(F) of napropamide on Yellow-brown Soil,Latersol and Black Soil was 1328.7,1964.5 and 3296.0 J mol^-1 respectively, and K_OM was 6686.15-9214.28,suggesting that napropamide had a very weak mobility in soils according to McCall's classification system.(2) Adsorption free energy(â–³G) of napropamide on Yellow-brown Soil,Latersol and Black Soil was 11.24,10.43 and 10.58 KJ mol^-1,showing that the adsorption largely resulted from the physical adsorption involving in hydrogen-bonding,hydrophobic bonding, coordination and van der waals force.(3) There had a good correlation between adsorption coefficient(K_f) of napropamide on the three different kinds of soils and the soil organic matter,indicating that organic matter was a predominant factor influencing adsorption of napropamide on soils.(4)Ultraviolet spectrum absorption of three different original DOM with same concentration in Black Soil was highest while lowest in Yellow-brown Soil,which was consistent with the adsorption capacity of the three soils.This result might due to the much more fuctional group in Black Soil which can bound with napropamide.(5) FT-IR spectra indicated that three soils had some same chemical structure,but intensity of absorption peak was different at same position.Comparison of the FT-IR spectra of the three soils certificated that the sorption capacity of three soils is Black Soil＞Latersol＞Yellow-brown Soil.The influence of napropamide on the soil microbial biomass,respiration and enzymes activities were investigated.The results showed that soil microbial biomass C and N content decreased apparently at the initial period of incubation,and the variation tendency of soil microbial biomass C and N were similar during the whole incubation time.The soil respiration was activated after napropamide application for 7 days,and at 2-20mg kg^-1 dry soil,the higher the applied concentration was,the stronger the activation was observed.Follow that,compared to the control,all napropamide treatments inhibited the soil respiration from 7 to 42 days.During the whole experiment phase,the total CO₂ was least at 80 mg kg^-1 dry soil,the total CO₂ of 2-20 mg kg^-1 dry soil treatments was near that of control and there were not significant differences(P＞0.05) between the treatments and control.Urease activities in three soils treated with all range of napropamide concentrations were suppressed as compared to the control,and there were significant differences(P＜0.05) in urease activities between the Black soil or Latersol and the control.The effect of napropamide on invertase was similar to that on urease.Generally,enzyme activities of napropamide treatments were lower than that of the control,significant differences(P＜0.05) were found in the enzyme activities between treated soil samples and the control during the whole the incubation period in three soils.However,dose-dependent change in invertase activity in napropamide-treated soils was found at the time point of day 7 in Yellow-brown Soil,when the invertase activity decreased with the increasing napropamide concentration applied,showing a clear negative correlation between the invertase activity and napropamide concentration of soils(r=-0.8480).Catalase and dehydrogenase activities irregularly fluctuated with incubation time in three soils. Although in the most cases,there were no dose-responses of catalase activities to napropamide exposure,at the time of day 7 the catalase activity in napropamide treated soils was gradually promoted with increasing concentrations of napropamide applied.Indeed,significant positive correlations were found between catalase activity and napropamide concentrations applied in Yellow-brown Soil(r=0.9796).According to the enzymatic activities in Yellow-brown soil,we chose the 7 days and 14 days as sample time.DGGE method was applied to determine the relative genetic complexity of microbial communities in soils treated with napropamide.The result showed that there were certain differences in bacterial communities diversity in soils treated with different concentrations of napropamide.Microbial diversity in soils treated with napropamide changed with time.At 7 days,the bands in napropamide treatments were much more than those of control and similarities over 95%,showing that there were some similar microorganism between soil samples treated with napropamide and control,and napropamide stimulated the growth of some specides of bacteria.These results were correlated to those conclusion based on the traditional techniques.On d 14,the predominant bands in all soil samples treated with all range of napropamide concentrations include the control were increased as compared to the 7 d,similarities between treated soil samples and control were less than 40%,these results suggested that application of napropamide affected the structure of microbial communities.The residue monitoring methods for determination the pesticides in Chinese herbs and cow's milk by GC were developmented.The Chinese herbs and milk sample were extracted with acetone-petroleum and acetone-acetonitrile,respectively. The extract was purified and collated by solid-phase extraction.The pesticide residues were separated by SPB-5 capillary gas chromatographic column under the condition of temperature-programmed and ECD.The result showed the accuracy and precision met the need of pesticide residues analysis.