Studies On The Sorption Characteristics Of Organochlorine Pesticides On Solid Materials In Natural Water

Natural water is a complicated biological system. Besides aqueous phase, various solid materials including sediments, suspended particles, biofilms adhering to the surface of other solid materials are also the necessary parts of natural water. These solid materials play a decisive role to a large extent in the migration, transformation and fate of many contaminants in the whole natural aquatic environment. Currently, many studies on interactions between solid materials and various pollutants have been carried out home and abroad, but these studies mainly focused on interactions between specific pollutants and single solid materials. Simultaneous studies on interactions between multiple solid materials and multiple pollutants were rare. The components and structures of these solid materials have their respective features, but due to their coexistence in the same water environment, they can interact with each other during their development and formation. For example, suspended particles and biofilms have many similar features. The formation of biofilms is effected by suspended particles to a certain extent, while the deposition of suspended particles and the suspension of sediments are the sources of their formation. Consequentially, the transformation of various substances can be involved in the process of interactions among solid materials. Therefore, the effects of multiple solid materials and pollutants are inevitably affected by the interactions among solid materials.Nowadays, the research on the environmental rules, eco-toxicology, health hazards, environmental risk theories, and advanced control technologies of persistent toxic substances has been one of the important parts in the field of environmental science. The key object of relevant researches is the compounds which can lead to great destruction to biological system, have relatively strong carcinogenicity, mutagenicity and even environmental hormone effects and are hard to be degraded and eliminated while has persistence and take part in earth cycle. As the research objects of this dissertation, hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs), two categories of organochlorine pesticides, were once the widest used chemicals in the world. Most of them have high octanol-water partition coefficients and low water solubility, so they are easy to distribute to environmental organic matters and can accumulate in organisms. Although their usage has been prohibited and limited, they are hard to be degraded, leaving constant residues and potential risk in environment. They are typical representatives of hydrophobic organic contaminants, persistent organic pollutants and persistent toxic substances. Besides, many researches on migration and transformation, toxicity and environmental fate of single pollutant were carried out in the field of environmental science in the past. But with the rapid development of industry and agriculture in China and the mushrooming species and amout of pollutants into the environment, the environmental effects of multiple pollutants may be different from those of single pollutant. Thus, research on the combined pollution caused by multiple pollutants has also become a hot spot in the field of environmental science.Sorption is supposed to be the critical step in the further migration and transformation processes of pollutants in the environment. In this dissertation, sorption characteristics of two typical organochlorine pesticides, HCHs and DDTs on the biofilms, suspended particles and surface sediments and their major components gathered from the same natural water were studied simultaneously; the differences of kinetics and thermodynamics of the organochlorine pesticides sorption on these solid materials were comparatively analyzed; the effects of main environmental factors on sorption were investigated; the relations between components and structures of these solid materials and the sorption characteristics were discussed; and the possible sorption mechanisms were analyzed. Meanwhile, the effects of typical heavy metals, Pb, Cd and Cu on the organochlorine pesticides sorption on these solid materials were examined; combined pollution generated from heavy metals-organic pollutants were studied. Furthermore, the sorption characteristics of the organochlorine pesticides on these solid materials in multiphase coexisting system were studied in this dissertation. Using the simulation system designed according to real natural waters to study the environmental behaviors of pollutants in it, not only the results of the experiment were more close to the fate in real natural waters, but also the real environmental behaviors of pollutants were deeply understood. Therefore, it has theoretical and practical significances to deal with the problem of pollution. The results of kinetics and thermodynamics of HCHs and DDTs sorption on these solid materials indicated that: pseudo second-order model can fit the data of sorption kinetics. The HCHs and DDTs sorption on these solid materials reached observed equilibrium after 48 hours. The order of initial sorption rate of these solid materials from big to small was as follow: surface sediments > suspended particles > biofilms. Dual mode model (DMM) can fit the sorption isotherms of HCHs and DDTs on biofilms, suspended particles and surface sediments. The sorption isotherm of surface sediments obviously represented a linear characteristic, and those of biofilms and suspended particles obviously represented nonlinear characteristics. The sorption abilities of the biofilms and suspended particles to HCHs and DDTs were far greater than those of the surface sediments, because the biofilms and suspended particles have higher TOC contents than the surface sediments. Sorption rates and amounts of DDTs were higher and larger than HCHs on the same solid materials.The effects of environmental factors temperature and pH on the organochlorine pesticides sorption on these solid materials were investigated. Within the range of temperature and pH selected in the study,low temperature and pH increased the sorption, while high temperature and pH decreased the sorption.The effects of heavy metals, Pb, Cd and Cu, which typically exist in polluted natural waters, on the organochlorine pesticides sorption on these solid materials were investigated. The results indicated that it had greater effects of Pb, Cd and Cu on the organochlorine pesticides sorption on the surface sediments contained less TOC contents and simpler organic components, and Pb, Cd and Cu obviously enhanced the surface sediments'sorption ability and the nonlinearity of the isotherms; The organochlorine pesticides sorption on the biofilms was generally inhibited by the effects of Pb, Cd and Cu. But the inhibition was significant only in the case of low organochlorine pesticides concentration. The inhibition became weakened as the organochlorine pesticides concentration became higher; there was seemingly little effect of coexisting heavy metals on the organochlorine pesticides sorption on the suspended particles. Among these solid materials, the sorption to organochlorine pesticides of the biofilms and suspended particles with higher TOC contents and more complicated organic components was affected by heavy metals less obviously than that of surface sediments. The phenomenon was related to that complicated components and structures have buffer action to the changes of outer environmental factors.The effects of the coexistence of multiple heavy metals on the organochlorine pesticides sorption onto these solid materials were investigated and the differences among the effects by single and multiple heavy metals were compared using calculating the contributed values of joint effects. It indicated that the differences of the effects of single and multiple heavy metals on the sorption were tiny. But the promotions of single heavy metals on the organochlorine pesticides sorption on the sediments were weaker than those of binary and ternary heavy metals.The components of the solid materials exerted different effects on the organochlorine pesticides sorption were separated and the sorption characteristics of the organochlorine pesticides onto these components were investigated using a batch-equilibration method. Sorption abilities and contributions of these components were compared, and the sorption mechanisms of organochlorine pesticides onto these solid materials were primarily analyzed. The results indicated that heterogeneities of these solid materials made the apparent sorption behaviors be the results of the interaction of linear partition and nonlinear pore-filling mechanism. As for the biofilms and suspended particles with greater heterogeneities and more complicated structures, the sorption of organochlorine pesticides on them showed nonlinearity because linear partition and nonlinear pore-filling mechanism taken place simultaneously. The main sorption mechanism of the surface sediments was linear partition because the surface sediments composed mainly by minerals and amorphous organic matters.The sorption characteristics of the organochlorine pesticides onto these solid materials in designed single-phase and multi-phase coexisting sorption systems were investigated and comparatively analyzed. The results indicated that there were certain differences of sorption abilities of these solid materials between in the single-phase sorption system and in the multi-phase coexisting sorption system. The sorption abilities of the biofilms and suspended particles in the multi-phase coexisting sorption system were weaker than those in the single-phase sorption system, while the sorption ability of the surface sediments in the multi-phase coexisting sorption system were slightly stronger than that in the single-phase sorption system. Compared with the biofilms and suspended particles, the surface sediments had a greater competitive ability.