Immobility of emamectin benzoate in soils

The soil mobility of 4 ''-deoxy-4 ''-(epi-methylamino)avermectin B-1a (MAB(1a)) benzoate, the major (>90%) component of emamectin benzoate (MK-0244), was determined by a batch equilibrium technique and also by thin layer chromatography (TLC). Four concentrations of [H-3]MAB(1a) benzoate (10-650 ng/5 mL) in calcium chloride solution were equilibrated with 1 g of sandy loam, sand, clay loam, and silt loam soil types. The test compound was very tightly bound (greater than or equal to 99%) to each of the four soils and did not significantly desorb (<1.3%). The values of the Freundlich distribution constant extrapolated to 100% carbon content (sorption K-oc) were 2.5 x 10(4) to 7.3 x 10(5). The high K-oc values indicate that MAB(1a) benzoate is immobile in soils. The mobility of [C-14]MAB(1a) benzoate was also assessed in six different soils by using the soils as adsorbent phases in TLC. Mobile and immobile pesticide controls were also assayed in these systems for comparison. [C-14]MAB(1a) benzoate was classified as immobile in all soils. The results of batch equilibrium and of soil TLC experiments demonstrate that MAB(1a) benzoate will bind tightly to soil and not move readily in the environment.