ABSTRACT
The basic chemical turnover processes treated in the previous chapter play a key role in the ultimate fate of pollutants in the environment. Since the nature and intensity of these processes are very variable in space, pollution studies are traditionally performed in units or environmental compartments that are more or less homogenous with respect to the prevailing physico-chemical conditions. A common subdivision into environmental compartments is based on the major phase present (gas, liquid, or solid phase) and distinguishes between soil, water, and air. Water is usually further classified in surface waters that are in contact with the free atmosphere and subsurface waters (groundwater). It is, however, important to realise that the gas, liquid, and solid phases are often all present in these environmental compartments. Although in principle the same wide range of chemical processes brings about the variation in the overall composition of soil and water, their direction and equilibrium state are different in the different compartments. The governing chemical processes include silicate weathering , carbonate dissolution and precipitation, redox processes , and sorption to solid surfaces. The redox processes in particular are often biologically mediated. These processes control amongst others the genesis of soil profile s, the total concentrations of substances in water, the decomposition of organic substances, and the retention of chemicals in sediment .
