Imidacloprid and pyrimethanil soil sorption

The sorption of imidacloprid and pyrimethanil was measured in different soi ls of southern Europe. Pyrimethanil sorption (Kf=1.2-4.60) was higher than that of imidacloprid (Kf=0.31-1.99). Sorption was influenced by organic car bon content and increased with time when the soil was incubated at 25 degre esC and 35% soil water content. Over a period of 14 days, the distribution coefficient between solid (soil) and solution phases increased by orders of magnitude of 2 and 4 respectively, for imidacloprid and pyrimethanil. The increment is consistent with the degradation rate measured, supporting the hypothesis of the two sites of sorption. Care should be taken when such val ues are used to predict pesticide fate in soil, particularly for regulatory purposes during pesticide registration.