[DFT study on the relationship between the structure and water solubility of dioxin compounds].

With DFT method of quantum chemistry, the electronic structures of all polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were fully optimized at the level of B3LYP/6-311G**, and the corresponding quantum parameters, viz. the mean polarizability(alpha), entropy(S) as well as the tensor components of polarizability and quadrupole moment (alpha(xx), alpha(yy), alpha(zz) and Q(xx), Q(yy), Q(zz)) and so on were used to the study on quantitative structure-property relationship (QSPR) of water solubility. And three QSPRs were successfully proposed on the basis of the internally consistent experimental values. The determination coefficients are 0.977, 0.968 and 0.961 respectively and the cross-validated correlation coefficients are 0.968, 0.959 and 0.946 respectively. It is indicated that water solubility of PCDD/Fs should mainly be related to the molecular volume, but much less influenced by the molecular interactions. And the differences of predicted values of QSPRs for the whole dioxins are probably related to the limited available experimental values and the characteristics of introduced variables. In comparison with the newly developed QSPR, the performance of QSPRs in this study is improved, which may attribute to both the precise calculations of electronic properties of PCDD/Fs by B3LYP/6-311G** and the introduction of tensor components of quadrupole moment into models.

[Effects of several low-molecular-weight organic acids on the release kinetic of DDTs from red soil].

The kinetic release behavior of DDTs from red soil with three kinds of low-molecular-weight (LMW) organic acids solution and water leaching was investigated by kinetic device designed. The results show that the release percentage of DDTs from red soil by LMW organic acid can increase by 15% - 18% more than that by water, especially for the initial 250 mL leaching solution. When using water as leaching solution, the data of release kinetics of DDTs from red soil conformed to the apparently first dynamics equation (R2 > 0.99, p < 0.000 1), it implied that the surface diffuse of soil mineral is primary release mechanism of DDTs from red soil in water leaching system. The kinetic release behavior of DDTs in LMW organic acid leaching system can be described by parabola diffuse equation, double constant equation or Elovich equation. It implied that the LMW organic acids induced the complication of the release mechanisms of DDTs from red soil, this maybe related to the dissolution of soil mineral surface and structure change of inherent organic material that coating onto the soil mineral surface induced by LMW organic acid.

[Effect of chlorpyrifos residue in red soil on crops].

The pot cultivation experiment method, integrating with laboratory analysis, was employed for exploring the influence of chlorpyrifos residue in red soil on growth of wheat and oil-seed rape seedlings, and the uptake of crops to chlorpyrifos residue. The results show that, wheat seedlings and oil-seed rape seedlings can absorb chlorpyrifos residue from soil to reach the concentration of 0.257 to approximately 4.50 microg/g and 0.249 to approximately 2.021 microg/g, respectively, 20 days later since chlorpyrifos was introduced into the pots, on condition that the initial concentration of chlorpyrifos residue in red soil was 1 to approximately 10 microg/g. The initial concentration of chlorpyrifos residue in red soil equivalent to or below 10 micro/g has not significant influence on growth of wheat seedlings. Similarly, the concentration equivalent to or below 5 microg/g has not significant influence on growth of oil-seed rape seedlings. The degradation rate in oil-seed rape rhizosphere soil is 1.4 to approximately 4.2 times more than in that in unvegetated soil. The amount of bacterium and fungus in oil-seed rape rhizosphere is 3.18 times and 1.84 times as much as these in unvegetated soil, respectively. However, there is no substantial difference of actinomyces between in rhizosphere soil and in unvegetated soil. Compared with unvegetated soil, pH in rhizosphere soil is lowered by 0. 19 to approximately 0.23.

[Hysteretic characteristics of atrazine desorption from fluvo-aquic soil].

Kinetic batch experiments are carried out in order to investigate the effects of a wide range of atrazine initial concentrations and consecutive desorption time on the desorption characteristics of atrazine from fluvo-aquic soil. The results reveal that, atrazine concentrations in soil solution gradually decreased with desorption time increasing, whose relationship can be expressed with empirically exponential functions. After consecutive five steps (or 5 days), when atrazine initial concentrations increased from 50 microg x L(-1) to 2000 microg x L(-1), the average desorption percentages were 23.1%, 30.4%, 33.0%, 36.4% and 38.5%, respectively. The relationships between the amount of atrazine adsorbed by soil colloids and corresponding atrazine concentrations in soil solutions may be described through the traditional and time-dependent desorption isotherms. The obvious discrepancies in two families of both traditional and time-dependent desorption isotherms from adsorption isotherm, which retention time last for 168 hours before commencement of desorption, were indicative of hysteresis. Two sets of Freundlich parameters derived from both desorption isotherms can quantify the hysteresis between desorption and adsorption isotherms. However, hysteresis coefficient, omega, was applicable only for the traditional desorption isotherms, H and lamda applicable for both.