Nonionic Organic Pollutants' Sorption Behavior In Loess Soil

Petrochemical pollution is one of the critical environmental issues in the Northwest China where vast and thick loess soils are expended i aphy. In the last two decades, Exploration of oil fields and leakage of oil pipes has been resulted in the contamination of large area of agricultural land and ground water. Organic pollutants in soil may influence the normal function of the soil, contaminate ground water, air and food chain, and therefore impact human health and environmental quality. It is necessary to look into the fate and mobility of organic pollutants in soil in order to assess the soil environmental quality and to control the soil pollution. In this work, we selected benzene homologous compounds, as representative substances of nonionic organic pollutants, to study the sorption behavior of organics in loess soil.On the basis of above facts and ideas, a series of experiments were carried out in the research and the relevant results are reported in the following four parts.Chapter 1. Literature reviewSection ABackground and problem statementIn this part, we reviewed the status quo and hazards of petrochemical pollutants in Northwest District of China, and set forth the thoughts of the experiment and the significance of the study on the sorption of organic pollutants in loess soils in brief. Section BReview on the perspective of sorption / desorption of organic pollutants in soil ( sediments ) system A review is reported herein with 62 references about the basic principals, methodology, and situation of the sorption/desorption mechanism of organics in soil/sediments system.Chapter 2. Determination of the properties of organic pollutants and loess soilsSection A Measurement and estimation of water solubility and octanol-water partition coefficient for benzene homologous compounds Water solubility (Sw) and octanol water partition coefficient (Kow) of organic pollutants have been widely used to correlate environmental partitioning phenomena such as sorption and bioconcentration. In this section, shake-flask gas-chromatography (GC) method was utilized to measure water solubility (Sw) and n-octanol-water partition coefficient (Kow) for benzene, toluene and ethyl benzene, respectively. The results showed that Sw and Kow followed a linear relationship as InKow= 0.4558-0.9176InSw. Additionally, the experimental values well agreed to that calculated by structure information estimation method ( Irmann method ) and molar volume method ( Mv method ).Section B Measurement of the physical and chemical properties of loess soilsThe characteristics of the soil may play an important role in the sorption process. In this section, a series of selected physical and chemical properties of loess soils such as soil moisture, batch density, soil texture, pH, cationic exchange capacity (CEC), organic matter (OC), were determined in detail. The results indicated that the loess soils were low CEC and low OC, which have a great potential threaten for the contamination of the ground water when organic pollutants leaching with water in soil matrix.Chapter 3. Sorption characteristics of toluene in loess soilIn this work, toluene as a priority pollutant is taken to be the indicator of hydrophobic organic chemicals. The sorption-desorption equilibrium of toluene was studied on three loess soils of various physical and chemical properties by using the batch equilibration method. Sorption isotherms could be appropriately described by the Freundlich equation (Cs=KpCen). The desorption process, however, exhibited pronounced "hysteresis" in the soil at every level of initially adsorbed toluene which was subjected to desorption. Some quantitative factors for sorption were studied as well. pH values and ionic strength of the soils had little effect on the sorption of nonionic organic compounds (NOCs). In contrast, the soil organic matter content could make a great difference on the sorption.Natural loess soils with a low organic matter had a limited sorptiv...