| Pesticides used in agriculture have greatly improved food production. However, extensive use of pesticides in conventional agricultural practices has resulted in continuous and serious environmental pollution. Soil is an important habitat of pesticide residues. The sorption-desorption, mobility and biological toxicity of pesticides residues in soil influenced the safety of environment and agricultural product quality. So now preventing and remedying the pestiside pollution of soil, protecting the safety of soil environment and achieving the persistent using of soil resource are the focuses worldwidely. Dissolved organic matter (DOM), one of the most active chemical components in terrestrial and water ecosystem, is ubiquitous in soil and aqueous environment. It has a great effect on the solubility, adsorption-desorption equilibrium, biodegradation and translocation of organic pollutants in soil and water. DOM is a sort of mixture which has complex structure. It can be divided into different fractions of polarity and molecular weight size. In this paper, we studied the effects of different polarities and molecular weight fractions of DOMs from straw and sludge on the mobility of prometryne in soil, and measured the characteristics and component of different fractions by spectroscopy.According to the difference of polarity, we divided DOMs from straw and sludge into hydrophilic matter (HiM) fraction and hydrophobic acid (HoA) fraction using XAD-8 sorption resin. The results showed that the polar distributions of two DOMs were similar. The total DOC contents of HiM fractions of two DOMs were higher than HoA fractions, and the content of HiM-SL fraction (67.77%) were higher than the content of HiM-ST fraction (56.03%). At the same time, we also divided the two DOMs into three fractions using dialysis bag (MWCO 3500Da and 14000Da):low molecular weight fraction (MW< 3500Da), moderate molecular weight fraction (3500Da< MW<14000Da) and high molecular weight fraction (MW>14000Da).The molecular weight distributions of DOM-SL were similar with DOM-ST, in the following content order:low molecular weight fraction> high molecular weight fraction> moderate molecular weight fraction, and the low molecular weight fraction content of DOM-SL were higher than DOM-ST. These results indicated that the putridness of straw was greater than sludge.Batch experiments, soil columns and soil plate were conducted the effect of different polarities fractions and different molecular weight fractions of DOMs on herbicide prometryne sorption onto soil, desorption from soils and mobility. The results indicated that all fractions of DOM could markedly constrain sorption of prometryne onto soil, enhance greatly desorption of prometryne from soil, quickened the leaching down of the prometryne and significantly facilitate the mobility of prometryne in soil. Compare to hydrophobic acid, the hydrophilic matter reduced the sorption and enhanced the mobility of prometryne. The macromolecule fraction had the greatest effect on the mobility of prometryne in soil among three different molecular weight fractions of DOMs, the explanation might be that the macromolecule fraction competed with prometryne for adsorption sites of soil. Moreover, DOM-ST had a stronger effect on prometryne behavior in soil than DOM-SL.At last, we studied the component and structural character of all fractions of DOMs. We found that:hydrophilic matter contained more N content and lower H/C ratio than hydrophobic acid, and all fractions contained components such as carbohydrate, aromatic matter, protein-like, humic-like and fulvic-like. But hydrophilic matter had more protein-likes and amino acids than hydrophobic acid and macromolecule fraction contained more contents of components. |
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