Basic Research For Environmental Behavior And Relative Thermodynamics Of Sulfonamides

With the booming of intensive stockbreeding, poultry diseases have became complex and difficult, and more and more species and quantities of veterinary drugs are used for solving the problem. Subsequently, the impact of contaminated ecological environmental on human being's health has been aggrandized dramatically. Some measures revealed that most of the veterinary drugs used in China are of the category of drugs for food animals in which antimicrobial drugs, especially sulfonamides, macrolides and quinolones, are predominant and their market share over 60%. Nowadays, systematic studies on the accumulation, transportation, and transformation of veterinary drugs in aquatic and terrestrial environment, as well their effects on various organisms are still scarce, especially compared to that of developed countries. Consequently, it is critically to conduct researches to investigate the environmental behavior of veterinary drugs, which would be helpful for accessing the security of veterinary drugs utilization in aquatic and terrestrial environment and modifying the contaminated soil. This research was financed by the Natural Science Fund (No.0611033400) of Henan Provincial Department of Science and Technology in 2006, and by the Natural Science Fund (No.2006610002) of Henan Provincial Education Department in 2006 for basic research.A method of UV spectrophotometry was established to determine the concentration of sulfadiazine in soil by using sodium hydroxide solution as extractant. It was shown in the tests that the linear range of standard carve was 2-10mg·L^-1 and the correlation coefficient was 0.9999 (RSD=1.74%); the average recovery was 98.9%. Compared with method of titration dead-stop, results for two methods were identical approximately. This method had many advantages, such as convenience, speed, and accurate.A shake-flask method was used to determine the 1-octanol/water partition coefficients of sulfamethazine, sulfadimethoxine, sulfamethoxydiazine, sulfamonomethoxine, sulfamethoxazole, sulfaquinoxaline and sulfachloropyrazine from (298.15 to 333.15) K. The results showed that the 1-octanol/water partition coefficient of each sulfonamide decreased with the increase of temperature. Based on the fluid phase equilibrium theory, the thermodynamic relationship of 1-octanol/water partition coefficient depending on the temperature is proposed, and the changes of enthalpy, entropy, and the Gibbs free energy function for sulfonamides partitioning in 1-octanol/water are determined, respectively. Sulfonamides molecules partitioning in 1-octanol/water is mainly an enthalpy driving process, during which the order degrees of system increased. The temperature effect coefficient of 1-octanol/water partition coefficient is discussed. The results show that its magnitude is the same as that of values in the literature. However, from the viewpoint of the fluid phase equilibrium theory, the effect on 1-octanol/water partition coefficient cannot be ignored when temperature varies drastically. It is necessary that the temperature should be controlled exactly on determining the 1-octanol/water partition coefficient.Using a static equilibrium method, the solubilities of sulfadiazine, sulfamethazine, sulfadimethoxine, sulfamethoxydiazine, sulfamonomethoxine and sulfamethoxazole in water have been determined experimentally from (298.15 to 333.15) K. The melting points and heats of fusion for 4 sulfonamides have been determined experimentally through DSC. According to Scatchard-Hildebrand theory and solubility parameters, the solubility change law for sulfonamides in water and its probable causes were discussed. The experimental data were correlated withλh equation and modified Apelblat equation; the constants of equations were obtained. Based on relationship between the parameter h inλh equation and excess enthalpies H^E, the excess enthalpies for six systems, the solution enthalpiesâ–³H_s and solution entropiesâ–³S_s for seven sulfonamides in water, were calculated using experimental data. Their variation law for sulfonamides aqueous solution and probable causes were discussed in terms of molecular interaction. Mathematical models for the molecular valance connectivity indexes and aqueous solubilities of sulfonamides were established; the constants of equations were obtained; the aqueous solubilities for 12 sulfonamides were predicted successfully. A study of 12 sulfonamides showed high correlations (r=0.9103) between their aqueous solubilities and molecular connectivity indexes, making possible the prediction of the partition behaviors of sulfonamides on the basis of their connectivity.Static experiments for sorption behavior of sulfadiazine in soils were carried out to investigate the influence of temperature, and pH on adsorption. The results indicated that the adsorption isotherms of sulfadiazine in three kinds of soils were well described by the Freundlich type, adsorption constant of organic mater of sulfadiazine averaged 0.103, and the Gibbs free energy function variations for sulfadiazine adsorption were 4.771-6.440kJ·mol^-1 at 298.15K. Adsorption of sulfadiazine decreases with increasing temperature and its maximum adsorption is noticed at pH=8.Leaching experiments of dynamic soil column were conducted to study the transport of sulfadiazine in soils. Sulfadiazine showed different ability to be transported downward with moving water in three kinds of soil column. The transportation sequence of sulfadiazine in the tested soils was sand＞clay＞loam. Soil texture and soil organic matter content are two important influencing factors. Through indoor simulation degradation experiments, microbial degradation for sulfadiazine in lake water and piggery wastewater were carried out to investigate the influence of oxygen supply mode and organic matter content in water on microbial degradation for sulfadiazine. The results indicated that the anaerobic degradation rate of sulfadiazine in piggery wastewater was more rapid than that for aerobic degradation; the anaerobic degradation rate of sulfadiazine in lake water was slower than that for aerobic degradation. Moreover, the study also showed that the number of bacteria except fungi and actinomycete grew significantly.Through indoor simulation degradation experiments, microbial degradations for six sulfonamides in sandy soil were carried out to investigate the influence of soil types, concentrations and temperatures on degradation for sulfadiazine. The results indicated that the microbial degradations of six sulfonamides in sandy soil were slow, which their rate constants order was SMD=SMX＞SDM＞SMM＞SD＞SM₂. Their degradations were mainly caused by non-biological degradations, rather than by microbial degradation, which was mostly related to their strong antibacterial activities.