Imidacloprid and pyrimethanil soil sorption

The sorption of imidacloprid and pyrimethanil was measured in different soils 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 carbon content and increased with time when the soil was incubated at 25 degreesC 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 values are used to predict pesticide fate in soil, particularly for regulatory purposes during pesticide registration.