However, the phototransformation of pesticide adsorbed by the soil components especially clays in absence of water is an important question. The aim of the present work was to study the kinetics of photodegradation of two model organic
compounds adsorbed on three types of clay; K-montmorillonite, Fe(III) exchanged montmorillonite (Fe(III)-montmorillonite) and montmorillonite complexed with humic acid (HA-montmorillonite) complexes. The two pesticides chosen; OPP and monuron are different in important aspects, namely in their adsorption properties by clays and their physico-chemical proprieties. OPP is commonly used as a fungi-static wax for coating vegetables, and as a disinfectant of storage materials (Appel, 2000), and monuron is an herbicide from the group of phenylurea derivatives (Zhou et al., 2001). Photodegradation experiments were performed in a Suntest photoreactor, in order to simulate the emission spectrum of sunlight.