Sorption of imidacloprid and its metabolites on tropical soils

The sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-i midazolid-inimine) (IMI) and its metabolites imidacloprid-urea (1-[(6-chlor o-3-pyridinyl)-methyl]-2- imidazol-idinone) (IU), imidacloprid-guanidine (1 -[(6-chloro-3-pyridinyl)-methyl]-4,5-dihydro-1H-imidazol-2-amine) (IG), and imidacloprid-guanidine-olefin (1-[(6-chloro-3-pyridinyl)methyl]-1H-imidazo l-2-amine) (IGO) was determined on six typical Brazilian soils. Sorption of the chemicals on the soil was characterized using the batch equilibration method. The range and order of sorption (Kd) on the six soils was IG (4.75- 134) greater than or equal to IGO (2.87-72.3) > IMI (0.55 - 16.9) > TU (0.3 1-9.50). For IMI and IU, Kd was correlated with soil organic carbon (OC) co ntent and CEC, the latter due to the high correlation between OC and cation exchange capacity (CEC) (R-2=0.98). For IG and IGO, there was no correlati on of sorption to clay, pH, OC or CEC due to the high sorption on all soils . Average Koc values were IU = 170, IMI = 362, IGO = 2433, and IG = 3500. A lthough Kd and Koc values found were consistently lower than those found in soils developed in non-tropical climates, imidacloprid and its metabolites were still considered to be slightly mobile to immobile in Brazilian soils .