Mojtaba Mahmoudi
Mohammad Jafar Malakouti

Adsorption and degradation of pesticides are the key processes affecting their fate in the environment. A thorough understanding of these processes is important for prediction of pesticides mobility in soils and movement to surface and ground waters. The soil sorption coefficient Kd and the soil organic carbon sorption coefficient KOC of pesticides are basic parameters used by environmental scientists and regulatory agencies worldwide in describing the environmental fate and behavior of pesticides. They are a measure of the strength of sorption of pesticides to soils and other geosorbent surfaces at the water/solid interface, and are thus directly related to both environmental mobility and persistence. KOC is regarded as a "universal" parameter related to the hydrophobicity of the pesticide molecule, which applies to a given pesticide in all soils. This assumption is known to be inexact, but it is used in this way in modeling and estimating risk for pesticide leaching and runoff. This paper attempts to explain theory, uses, and measurement or estimation of these parameters.

Soil sorption; Soil organic matter; Adsorption isotherms; Spatial variability; Pesticide mobility; Risk assessment