Dynamic Distribution Of HCHs And DDTs In Simulated Aquatic System

Persistent Organic Pollutants have been one of the most important research areas in Environmental Science. 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. They were prohibited from use all over the world. However, due to the high octanol-water partition coefficients and low water solubility, they are easy to distribute into environmental organic matters and accumulate in organism. Thus, HCHs and DDTs are hard to be degraded, leaving constant residues and potential risk in environment.Natural water is a complicated multi-phases system. Beside water phase, suspended particles, sediments and biofilms are included. Solid phases in natural water system have their own characters, and they can interact with each other while they exist in same water system. Sediments and biofilms exist in water system largely; they play important roles in the fate and distribution of all kind of pollutants in environment. Heavy metals and organic pollutants enter environment through different ways, so studies on the combined pollution caused by multiple pollutants is also one important research area.In this dissertation, simulated aquatic systems were built. Sorption kinetics of HCHs and DDTs on biofilms and sediment were studies, distribution of HCHs and DDTs in multi-phases system were studied. The effect of typical heavy metals Cu on the sorption of organochlorine pesticides on biofilms and sediments were studies, and the effect of Cu on distribution of organochlorine pesticides in simulated aquatic systems were discussed. The result of the experiment could reflect the fate of organochlorine pesticides in natural water system, so it has theoretical and practical meanings.The results of kinetics of HCHs and DDTs sorption on sediment and biofilms indicated that, pseudo second-order model can fit the data of sorption kinetics of HCHs and DDTs. The order of initial sorption rate was:sediments>biofilms, and the order of equilibrium sorption quantity was:biofilms>sediments. Sorption ability of biofilms with a higher TOC content is greater than sediments with a lower TOC contents. Sorption rates and quantity of DDTs on sediments and biofilms were greater than HCHs in same solid phases.Dynamic distribution of HCHs and DDTs in simulated aquatic system was studies. In the beginning of experiment, the concentration of HCHs and DDTs decreased quickly, they were transferred into sediments and biofilms. The concentration of HCHs and DDTs in biofilms grew quickly, and reached the summit in about 30 hours, and then the concentration dropped a little, and reached equilibrium in 50 hours. The concentration of HCHs and DDTs in sediment increased continually, and reached equilibrium in 50 hours. Due to the physical and chemical properties of biofilms, it can react to the change of pollution concentration in water phase quickly. The sorption rate pollution on sediment is slow.The effect of coexist heavy metal on HCHs and DDTs sorption on biofilms and sediment were studied. The results indicated that, Cu can enhance the sorption of HCHs and DDTs on sediment and prohibited the sorption of HCHs and DDTs on biofilms in system with low HCHs and DDTs concentration.