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The Influence Of Dissolved Organic Matter On Atrazine Sorption And Desorption By Soils And Minerals

Posted on:2006-09-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:W T LingFull Text:PDF
GTID:1101360152471955Subject:Soil science
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With wide application of organic chemicals in soil, the coming problems of ecological risks and environmental pollution were increasingly serious. Various physico-chemical processes affect the fate of pesticides in soils. The sorption and desorption are the most important processes, which control other processes such as movement, persistence, and degradation. Soil organic matter (SOM) is regarded as the key factor affecting the behavior and fate of organic pollutants in soils. The addition of organic amendments to soils could change the SOM content and thus may greatly affect nonionic pesticide sorption/desorption processes. Dissolved organic matter (DOM) has been the subject of considerable interest in soil and environmental sciences in recent years because it has been reported to interact with organic pollutants and thus affect the fate of these pollutants in the soil environment.In this dissertation, the sorption behaviors of DOM from different sources on soils and minerals and the interaction of atrazine with DOM in aqueous solution was investigated. Furthermore, the influence and its mechanisms of DOM on atrazine sorption/desorption by soils and minerals were evaluated. Information provided in this work may contribute to a better understanding of DOM sorption and its impacts on the distribution of organic contaminants in soil-water system. Main original conclusions are shown as follows.(1) The desorption of atrazine in soils in the presence of DOM and the effects of ageing time of atrazine in soils on desorption was firstly reported. Results show that the deosrption of atrazine in the presence of SSI was related to the soil characteristics, the SSI concentrations, ionic strength, and pH values in desorption solution. The effects of SSI with low concentrations in solution showed no correlation with the SOM or clay contents. However, SSI with higher concentrations in desorption solution displayed a more significant influence on desorption of atrazine for soils with higher SOM or clay contents. With the increasing of ageing time of atrazine in soils from 0 to 200 days, the desorption of atrazine decreased in the presence of 0~60 mgDOC/L.(2) It was firstly proved that the combination coefficient (Aat/soc) of atrazine with the DOM (A2) sorbed on the soil and clay mineral surface was much higher than the combination constant {Kat/doc) of atrazine with A2 in aqueous solution. Thus it could be conclude that the dominant mechanism of the enhancement of atrazine sorption onsoil/mineral by the addition of A2 was not the increase of SOM content as a result of DOM sorption, but the change of the soil/mineral surface character and the enhanced sorption ability of these surfaces due to the DOM sorption. It was found that the addition of A2 significantly promoted the sorption of atrazine on soil/mineral. In addition, more significant promotion was observed in the presence of higher A2 concentrations. The enhancement of the atrazine sorption in the presence of A2 was positively correlated to the soil clay content and negatively to the SOM content.(3) It was found that the addition of DOM (Al) with less hydrophobic and high-weight-molecular DOM fractions evidently inhibited the atrazine sorption on soil and mineral. Moreover, the inhibition enhanced with the increasing of A2 concentrations. The decrease of atrazine adsorption on soil or mineral surfaces in the presence of Al could be due to (i) the changed mineral surfaces from hydrophobic to hydrophilic character which led to the preferential sorption of water molecules instead of atrazine molecules in solution, (ii) the competitive sorption between DOM and atrazine on soil/mineral surfaces, (iii) the release of hydrophobic DOM from indigenous SOM which led to the release of atrazine into solution.(4) There existed a critical concentration (DOMnp) for the atrazine sorption by soils in the presence of DOM (SSI). The sorption coefficient Kd* of atrazine on six tested soils initially increased and decreased thereafter with the increasing of SSI concentratio...
Keywords/Search Tags:Dissolved organic matter (DOM), atrazine, soil, mineral, interface-action, sorption/desorption
PDF Full Text Request
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