Sorption of Veterinary Pharmaceuticals in Soils:  A Review

Veterinary pharmaceuticals (VPs) are used in large amounts in modern husbandry. Due to their use pattern, they possess a potential for reaching the soil environment. To assess their mobility in soil, the literature on sorption of chemicals used as VPs is reviewed and put into perspective of their physicochemical properties. The compilation of sorption coefficients to soil solids (Kd,solid) demonstrates that these chemicals display a wide range of mobility (0.2 < Kd,solid < 6,000 L/kg). Partition coefficients for association of tetracycline and quinolone carboxylic acid VPs to dissolved organic matter (Kd,DOM) vary between 100 and 50,000 L/kg. The variation in Kd,solid for a given compound in different soils can be significant. For most of the compounds, the variation is not considerably lower for the organic carbon-normalized sorption coefficient Koc. In addition, prediction of log Koc by log Kow leads to significant underestimation of log Koc and log Kd,DOM values. This suggests that mechanisms other than hydrophobic partitioning play a significant role in sorption of VPs. A number of hydrophobicity-independent mechanisms such as cation exchange, cation bridging at clay surfaces, surface complexation, and hydrogen bonding appear to be involved. These processes are not accounted for by organic carbon normalization, suggesting that this data treatment is conceptually inappropriate and fails to describe the sorption behavior. Moreover, prediction of log Koc based on the hydrophobicity parameter log Kow is not successful.