ADSORPTION OF PESTICIDES ON SOIL COMPONENTS - A MICROCALORIMETRIC STUDY

The adsorption of two pesticides (2,4-phenoxy acetic acid (2,4D) and t hiabendazol) on silica, alumina, kaolin and montmorillonite is studied from adsorption isotherms and enthalpies. 2,4D is nor adsorbed by sil ica, kaolinite and montmorillonite even in the presence of 0.01 mol l( -1) divalent cations. On alumina, the energy of adsorption is comparab le with that of the formation of an acid-base complex. Thiabendazol ca n be adsorbed on silica and clays from an ethanol solution. Most adsor ption isotherms are of the Langmuir type and correspond to roughly con stant adsorption enthalpies as a function of coverage except for kaoli n where adsorption on both lateral and basal faces can be involved. Ad sorption after introducing humic acids to the system was also studied for kaolin.