Chapter 58 – Hydrophobicity as a Key Physicochemical Parameter of Environmental Toxicology of Pesticides

Publisher Summary The aquatic toxicity of “simple” organic compounds has been recognized as being closely related to their lipophilicity (hydrophobicity). The environmental behaviors of pesticides, such as accumulation in soil, contamination of aquasphere, residue levels in crops, and bioaccumulation through food chains as well as nondietary routes, are dependent on their distribution properties among various environmental phases. These distribution features are modeled by phase-distribution equilibrium constants such as soil absorption coefficient, water solubility, and bio-concentration factors in biota, including crops. This chapter reviews the measurement and estimation procedures of the log P for a wide range of organic compounds and the significance of the log P value in elucidating and predicting the environmental behavior of pesticides in terms of the quantitative structure–activity relationship (QSAR). The most frequently used hydrophobicity parameter is the log P [or log k(o/w)], where P [or k(o/w)] is the 1-octanol/water partition coefficient. Thus, the environmental toxicology of pesticides covering distribution patterns, persistence, and toxicity could be quantitatively analyzable in terms of physicochemical molecular descriptors including hydrophobic, electronic, steric, and others with the use of regression analyses, in which the log P value is regarded as playing a central role.