The Environmental Behaviors Of Two Bensulfuron-methyl Mixed-herbicides In Soils

With the sore increasing of pesticide varieties and usage, more and more residuals are accumulated and co-existed in the environment, thus caused combined pollution. In the past, the studies mainly focused on the environmental behaviors of pesticides when used alone or in combination with other heavy metals, little information is available for describing the fate of multiple pesticides which are co-existed in the environment.In this study, two Bensulfuron-methyl herbicides (Bensulfuron-methyl+Quinclorac, Bensulfuron-methyl+Butachlor) were chosen as models to examine. Through comparing their environmental behaviors when used alone and in combination, we can understand the interaction between these co-existed components. Moreover, in order to provide available information on the innovation of pesticides, safety usage of pesticides and eastablishment of environmental standards, the effects of surfactants on the environmental behaviors of these two Bensulfuron-mixed herbicides were also evaluated, and the main conclusions were listed as follows:1Samples pre-treatment and HPLC analysis methodsThe HPLC methods of multiple-residuals analysis were developed for determination of two Bensulfuron mixed-herbicides systems. As to Bensulfuron-methyl and Quinclorac, a reverse phase C18column (4.6×250nm) was chosen to analysis, and the flow rate was10.mL/min. The mobile phase was composed by water (contain0.1mL phosphoric acid per600mL water) and acetonitrile(V:V=60:40). The determination wavelength was240nm. Chromatography was performed at30℃, and the injection volumn was lOuL. The retention time of Bensulfuron-methyl and Quinclorac was15.91min and8.21min, respectively.As to Bensulfuron-methyl and Butachlor, a reverse phase C18column (4.6X250nm) was used to analysis, and the flow rate was0.8mL/min. The mobile phase was composed by water and aceonitrile(V:V=28:72). The determination wavelength was 230nm. Chromatography was performed at40℃, and the injection volumn was lOuL, The retention time of Bensulfuron-methyl and Butachlor was14.479min and4.134min, respectively.In the adsorption experiments, the DLLME technique was used to extract Bensulfuron-methyl and Butachlor in water samples. Under the optimize condition of HPLC analysis, the fortified recoveries of Bensulfuron-methyl were101.28%-105.14%, and the coefficient of variation were3.39%-4.55%. The fortified recoveries of Butachlor were90.66%-97.44%, and the coefficient of variation were0.84%-5.96%. All these data were in accordance with the qualification of CIPAC.In the degradation experiments, the fortified recoveries of Bensulfuron-methyl were90.58%-95.81%, and the coefficient of variation were1.00%-4.13%.The fortified recoveries of Quinclorac were89.93%-92.60%, and the coefficient of variation were0.80%-3.35%. The fortified recoveries of Butachlor were89.67%-96.12%, and the coefficient of variation were0.93%-3.18%.2Adsorption of two Besulfuron-methyl mixed-herbicides in soilsThe adsorption behaviors of tested chemicals in three different soils were evaluated by the batch equilibrium experiments. In the solo-component adsorption experiments, all of the adsorption isotherms of Bensulfuron-methyl, Quinclorac and Butachlorwere could be well fitted with the Freundlich Equation(R2≥0.94), and the sequence of Kd was listed as:Butachlor> Bensulfuron-methyl> Quinclorac. Moreover, different soils also led to different Kd, and the sequence was as follows:Beibei soil>Pengshui soil> Zhengzhou soil. In the multiple-components competitive adsorption experiments, Bensulfuron-methyl inhibited the adsorption of Quinclorac in different soils, and enhanced the adsorption of Butachlor in soils, and both of Butachlor and Quinclorac had little impacts on the adsorption of Bensulfuron-methyl in soils.3Degradation of two Besulfuron-methyl mixed-herbicides in soilsAs to the Bensulfuron-methy+Quinclorac mixed-herbicides, the degradation of Quinclorac was not affected by Bensulfuron-methyl at different levels(10mg/kg,20mg/kg and40mg/kg), while the degradation of Bensulfuron-methyl would be inhibited by Quinclorac at the concentration of20mg/kg, and compared with that of control groups, the degradation half-lives of Bensulfuron-methyl woule be extended by1.17d. As to Bensulfuron-methyl+Butachlor mixed-herbicides, the degradation of Butachlor was inhibited by the co-existed of Bensulfuron-methyl at levels of10mg/kg and20mg/kg, especially at10mg/kg, the half-lives of Butachlor would be extended by1.49d, arriving at the maximum. While the degradation would be enhanced by Bensulfuron-methyl at40mg/kg. Meanwhile, the degradation of Bensulfuron-methyl would be also inhibited by Butachlor of different levels, especially at40mg/kg, the degradation half-lives of Butachlor could be extended by1.93d.4The effects of surfactants on the adsorption of two Bensulfuron-methyl-mixed herbicides in soilsIn this study, the adsorption behaviors of two Bensulfuron-methyl mixed herbicides were evaluated at the different concentrations (50%cmc,100%cmc and200%cmc) of surfactants.(CTAB or SDBS), and the results were as follows:(1) In the solo-component adsorption experiments, all levels of CTAB could significantly enhance the adsorption of three tested herbicides in soils, and the Kd value would gradually increase as the addition of CTAB. As to Bensulfuron-methyl, SDBS increased its adsorption in Beibei soil, decreased its adsorption in Zhengzhou soil, and had little impacts on its adsorption in Pengshui soil. As to Quinclorac and Butachlor, both of their adsorption behaviors would be enhanced with the addition of SDBS, and the increment is much smaller than that of CTAB.(2) In the multiple-components competitive adsorption experiments, all levels of CTAB would inhabit the competitive adsorption of Bensulfuron-methyl and Quinclorac, especially at100%cmc of CTAB, the inhibition reached maximum. SDBS had little impacts on the competitive adsorption of Bensulfuron-methyl and Quinclorac. As to Bensulfuron-methyl-Butachlor-mixed herbicides, the simultaneous existence of CTAB (50%cmc) and Bensulfuron-methyl (5mg/kg) could lead to the maximum adsorption increments of Butachlor, and co-existence of SDBS (50%cmc) and Bnesulfuron-methyl (lmg/kg) could also cause the maximum adsorption increments of Quinclorac.5The effects of surfactants on the degradation of Bensulfuron-methyl, Quinclorac and Butachlor.In this study, the degradation of three tested herbicides were estimated under the existence of surfactants at different levels, and the main conclusions were as follows:(1) As to Bensufuron-methyl, either of SDBS and CTAB would inhibit its degradation in soils, and in the existence of50%cmc,100%cmc and200%cmc of CTAB(or SDBS), the degradation half-lives of Bensulfuron-methyl would be extended by1.17d(0.94d),0.39d(0.91d) and1.05d(1.60d), respectively. (2) As to Butachlor, the half-lives could be extend by0.92d at50%cmc of CTAB, and0.73d at200%cmc of SDBS. CTAB at100%cmc and200%cmc, and SDBS at50%cmc and100%cmc had little impacts on its degradation behaviors.(3) As to Quinclorac, both CTAB and SDBS had little impacts on its degradation behaviors.