Kỵ nước hóa chất hữu cơ, chẳng hạn như PCBs và PAHs, thường có hệ số phân vùng lớn, thứ tự 103 đến 106 L / kg hoặc thậm chí cao hơn. Trong trường hợp này, nhiều hóa chất là sorbed hạt vật chất và được vận chuyển với nó. Hạt vật chất này, cùng với HOC sorbed, thường được giải quyết vào dưới cùng của một hệ thống thuỷ sản và các hình thức tiền gửi của các trầm tích bị ô nhiễm có thể được nhiều mét dày. Tại hầu hết các trang web với các lớp trầm. | 8 Modeling the Transport and Fate of Hydrophobic Chemicals Hydrophobic organic chemicals such as PCBs and PAHs often have large partition coefficients on the order of 103 to 106 L kg or even higher. In this case much of the chemical is sorbed to particulate matter and is transported with it. This particulate matter along with the sorbed HOC usually settles onto the bottom of an aquatic system and forms deposits of contaminated sediments there that can be many meters thick. At most sites with contaminated sediments approximate calculations of the amounts of contaminants in these bottom sediments and also in the overlying water lead to the conclusion that there are orders of magnitude more contaminant in the bottom sediments than in the overlying water. As a result even after the cleanup of point sources of contamination these bottom sediments can serve as a major and long-lasting source of contaminants to the overlying water. To predict sediment and water quality over long periods of time the flux of these contaminants between the bottom sediments and the overlying water needs to be quantitatively understood and modeled. The sediment-water flux of contaminants is primarily due to sediment ero-sion deposition molecular diffusion bioturbation and groundwater flow. Each of these processes acts in a different way and hence each must be described and modeled in a different way. In general they occur more or less simultaneously and there are interactions among them. All these processes are continuously and often significantly modified by the finite rates of adsorption and desorption of the HOC between the solid sedimentary particles and the surrounding waters. These rates of sorption and the resulting partitioning depend on the hydrophobicity of the chemical that is on Kp. Because of this the transport of an HOC also strongly depends on Kp. This is especially true for HOCs with large partition coefficients and is a major emphasis in this chapter. As bottom sediments erode
