Physical processes of soil/pollutant interactions include transport and retention. They depend mainly upon the physical parameters of the medium (temperature, grain size, electric charges, etc.). Chemical processes depend largely on the type of pollutants and their chemical nature. As for biological, or biologically controlled, soil pollution processes, we may include all processes of biotransformation and biodegradation, each depending on the microbial ecology, the depth, and the oxygen availability at the site of pollution.