Sorption/desorption of [14C]efrotomycin with soils

The sorption and subsequent desorption of efrotomycin, which is being developed as a growth promoter in swine, was investigated in five soils of various physical and chemical properties. Sorption equilibration occurred within 7 h. Sorption distribution coefficients ranged from 8 to 290. The Freundlich constant, K, spanned a similar range as n values were near 1. The sorption distribution coefficients, Kd, were not correlated with organic matter content; cation-exchange capacity; sand, silt, or clay content; or soil pH. Hysteresis was observed between the sorption and desorption isotherms for one of the soils. For four soils, only about 50% of the sorbed efrotomycin could be desorbed, even with organic solvents. Efrotomycin is classified as immobile in most soils by comparison of its Koc values (580-11,000) with those of other chemicals