Sorption and photolysis studies in soil and sediment of the herbicide napropamide

The influence of soil and sediment composition on sorption and photodegrada tion of the herbicide napropamide [N,N-diethyl-2-(1-naphthyloxy)propionamid e] was investigated. Five soils and one sediment were selected for this stu dy and the clay fractions were obtained by sedimentation. Sorption-desorpti on was studied by batch equilibration technique and photolysis in a photore actor emitting within 300-450 nm wavelenght with a maximum at 365 nm. Sorpt ion increased with clay content and was not related to organic matter *cont ent. High irreversibility of sorption was related to the greater montmorill onite content. The presence of soil or sediment reduced photolysis rate due to screen effect and this process did not depend on solid composition but an particle size distribution.