Abstract: Slow-Release agrochemical formulations for the prevention of leaching and contamination of soil and ground water, are described. The agrochemicals are organic compounds with non-ionic and non polar molecular structures, which are adsorbed to clays whose surface properties have been transformed from hydrophilic to hydrophobic by previous adsorption of an organic cation, usually of quaternary ammonium structure, having at least one aryl group attached to the ammonium nitrogen atom. The intermolecular interactions of the agrochemical with the organo-clay surface result in a reduction of its leaching in the field.