Diffusion of Non-Electrolytes

Chemicals are characterised by their physicochemical properties such as molecular weight, volatility, ionisation constants, water solubility and solubility in lipids. Agrochemicals and environmental xenobiotics are often lipophilic, and these compounds are sorbed and accumulate in lipophilic compartments of the environment, such as the organic fraction in soil, the storage lipids of man, animals or plants. Rates of diffusion across cuticles and other membranes are proportional to the partition coefficient (2.17) of the compound, which is a measure for differential solubility in lipids and water (2.12). Thus, when analysing sorption in and penetration through cuticles, partition coefficients for the substances must be known or measured.