| Modern agriculture requires substantial input of pesticides to soils to control weeds and insects. While the pesticide usage in farmland has brought great benefits to crop production, it simultaneously generates great concerns linked to the contamination to ecosystem and food safety. Isoproturon, a selective herbicide of the phenylurea chemical family, has been widely used for pre-and post-emergence control of annual grasses and broad-leaved weeds for wheat, barley, and rye. In spite of its effectiveness, the massive use of isoproturon in plant fields resulted in serious environmental problems. Because isoproturon is water soluble, moderately hydrophobic and weakly sorbed by soils, it has been detected with increasing frequency in ground and surface waters in concentrations exceeding the limit level. Thus, concern about the environment impact of isoproturon most frequently arises from its ability to leach from soil and contaminate water resources.Low-molecular-weight organic acids (LMWOA) occur widely in soils and mainly originate from root exudates, dead plant material and microbial decomposition products. Depending on the dissociation properties and numbers of these carboxylic groups, organic acids have been implicated in many soil processes. Dissolved organic matter (DOM) is another matter contained extensively in soil solution which primarily produces from litter and humus, and it is now recognized that DOM is a major controlling factor in soil formation, mineral weathering, and pollutant transport. Although abundant of research were focused on pesticide behavior, very limited information is available on the influences of LMWOA and DOM on the mobility of isoproturon in variable-and permanent-charge soils. The overall aim of this study was to evaluate the effect of LMWOA and DOM on sorption behavior of isoproturon in variable-and permanent-charge soils and to determine the potential movement of isoproturon to groundwater in order to test current risk assumptions. Batch experiments, soil columns and soil plate were conducted the effect of LMWOA on herbicide isoproturon sorption onto soil, desorption from soils and mobility. The results indicated that in permanent-charge soil, LMWOA could markedly constrain sorption of chlorotoluron onto soil, enhance greatly desorption of isoproturon from soil and significantly increased the mobility in soil. As compared in variable-charge soil, the behavior of isoproturon showed a completely converse tendency. That indicated the behavior of isoproturon appeared to be dependent upon soil types.The same above methods were introduced to study the impacts of DOM on herbicide isoproturon sorption-desorption and mobility in variable-and permanent-charge soils. Results showed that in permanent-charge soil adsorption of isoproturon was inhibited, while desorption was promoted which indicated that mobility of isoproturon was enhanced. However, consequences in variable-charge soil showed a completely converse trend. In conclusion, according to the present study, impacts of DOM on the sorption and mobility of isoproturon depend heavily on soil types.FT-IR,3D-EEM and UV-Vis spectra were used to comfirm the structure of two soils. The results showed that both of two typical soils contain carbohydrates, organic acids, phenols and peptides and other substances in spite of contents of organic components. In addition, the yellow brown soil contain fulvic and humic acid substances, adsorption of isoproturon on humic acid involves hydrogen bonding of the CO and NH groups of isoproturon with the COOH, C=O, OH and NH groups of humic acid. The results provide a theoretical support for the earlier studies of isoproturon environmental behaviors in two typical soils. |
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