Using Three-Dimensional Fluorescence Spectrum Technology to Analyze the Effects of Natural Dissolved Organic Matter on the Pesticide Residues in the Soil

The behavior of pesticide in soil is influenced by dissolved organic matter (DOM) through competition adsorption, adsorption, solubilization, accelerated degradation, and so on. Thus DOM and its components play an important role in the environmental risk in the soil ecosystem and groundwater environment. Currently, most studies focused on the short-term effect of high concentration of DOM on the pesticide residues. However, soil DOM is mainly at low level. Therefore, there is of some practical significance to probe into the environmental behavior of soil pesticides under natural level of DOM. Thus a site investigation was conducted in the farmland with long-term application history of pesticide. By using the three dimensional excitation-emission fluorescence matrix (3D-EEM) technology, together with the fluorescence regional integration (FRI) quantitative method, the long-term effects of pesticide residues under low concentration of natural DOM were analyzed. Results showed that: (1) The long-term effects of the natural DOM components on the environment behavior of most soil organo-chlorine pesticides were not significant except for a few pesticides such as gamma-HCH, p,p'-DDE, etc. (2) The influencing effects of DOM components on different type of pesticides were varied. Among which, the content of tyrosine component showed a significantly negative correlation (p<0. 05) with the concentration of gamma-HCH and p, p'-DDE. There were significant positive correlations (p<0. 05) between the by-products of microbial degradation in DOM components and the concentration of heptachlor. There were also a significant positive correlation (p<0. 05) between the content of active humus component of humic acid in the DOM and the concentration of heptachlor epoxide. These results suggested that the distribution of different types of pesticides residue in the soil was influenced by different components at different levels of significance. (3) The humification degree of soil organic matter showed minor effect of DOM on the pesticide residues in the soil. In this study, 3D-EEM and FRI technology were firstly coupled in use for studying the influence of different components of DOM in soil on the environmental behavior of pesticides, which provides a new idea for the research on the mechanism of pesticides transportation and transformation in soil and groundwater environment.