Transfer Mechanisms Of DDTs On Solid-gas Inerface And Cyromazine On Solid-liquid Inerface

The release of pesticides to environment is causing serious problems. Pesticidesin soil environment could not only harm the local environment, but also contribute tothe global environment contamination by long transport through atmosphere andwater flow. The hydrophobicity affects the distribution of pesticides, transportion andenvironmental fate. In view of the damage caused by pesticides in environmentsystem, it is very important to understand transportion and phase diffusion mechanismof different hydrophobic pesticides in the environment. Thus, the partition of DDTsbetween solid and gas phase under the conditions of different environmentaltemperatures and soil organic carbon contents (foc) was studied by solid fugacitymeter. The sorption mechanisms of cyromazine in solid-liquid systems under theconditions of different pH and coexisting cations were investigated by batchexperiments. The results of this study can provide a basis for the control andprevention of pesticide pollution. The main conclusions are as follows:(1) The increasing of foc(from0.62%to4.73%) results in an increase of soil-airpartition coefficients (KSA). However, the increasing trend is not in direct proportionto KSAdue to the decrease of the bulk density of the solids (from1.53g cm-3to1.39gcm-3).(2) With increasing temperature (T: above0oC), the slop between log KSAandlog KOA(octanol-air partition coefficients) is close to1. The enthalpy change of thesoil-air partition (ΔHSA) increases with the increasing hydrophobicity of pesticides.ΔHSAvalues of o,p’-isomers (DDT, DDE, DDD) are larger than those of p,p’-isomers, which means that more energy is required to remove o,p’-isomers from soilto air.(3) Based on the effects of different factors on KSA, a multi-parameter regressionequation including fOC, KOA, and T of dichloro-diphenyl-trichloroethanes and itsmetabolites (DDTs) was regressed (n=96, r2=0.909, RSSR=0.266), which can be usedto predict KSA. (4) In order to know the effects of property of organic matter on sorption, part ofthe humic acid was oxidized to fulvic acid by H2O2oxidation treatment. Because thequantity of sorption sites on fulvic acid is less than that of humic acid, the decreasingsorption sites led to negative influence on sorption. At an equilibrium aqueousconcentration of4mg L-1, sorption of cyromazine to solids decreased by13.37%afterH2O2oxidation.(5) Sorption mechanisms of cyromazine on artificial solid particle includeadsorption and partition. The sorption process of cyromazine on modified artificialsolid particle media is mainly partition. The increase of solution pH from4.0to7.2resulted in a decrease of kdfrom43.88L kg-1to30.55L kg-1. Coexisting cations (Na+and Ca2+) would compete with protonated cyromazine for sorption sites whichbrought negative effect on sorption.