Degradation of ortho-phenylphenol in soil starts with rapid binding to the soil matrix within hours, with no pronounced formation of soluble intermediates. Humic substances fractionation indicated the non- extractable residues to be predominantly associated with the soil humin and humic acid fractions. Although not extractable, the immobilized residues are moderately mineralized, indicating their participation in breakdown of the radiolabel-containing phenylphenol core structure. The observed behaviour is in-line with literature information on rapid and irreversible soil binding of similar phenolic type compounds. Such effect has been attributed to oxidative coupling reactions, which may be both biologically mediated, or abiotic surface-catalyzed processes.