Photodegradation of imazapyr in the presence of humic substances

The photodegradation of imazapyr ( 30 mg/l) was investigated under simulate d sunlight experiments. This photodegradation was evaluated at pH = 7 in th e presence of humic acids (HA) isolated from oxidized coal (Eniricerche, Sp A), known for their interaction with pesticides. The study was realized at different imazapyr/HA ratios ( 1/0.1; 1/0.5; 1/1). Irradiation was carried out with polychromatic light using Heraeus apparatus equipped with Xenon la mp. The concentration of remaining herbicide was followed using an high pre ssure liquid chromatograph ( HPLC) equipped with UV detecor at 230 nm. The role of HA on the photodegradation of imazapyr was evaluated by the quantum yield determination. Kinetic parameters of photoreaction show a first order dependence of concen tration of imazapyr versus time. The presence of HA induced a decrease of t he photodegradation of the pesticide with respect to pure water solution. A short of protection and screen effect of humic substances on the pesticide molecule was observed.