Sorption of Sulfonamide Antibiotics to Soil Organic Sorbents: Batch Experiments with Model Compounds and Computational Chemistry

Abstract

Sorption of the sulfonamide antibiotics sulfanilamide, sulfadimethoxine, and sulfapyridine to model soil organic matter was investigated. Therefore, Fluka humic acid and an enzymatically reacted vanillin oligomer were used in batch experiments at pH 4.5, 6.0, and 7.5. Sorption of the amphoteric sulfonamides was nonlinear and pH dependent. At pH 4.5 and 6.0 sorption to both humic acid and oligomer increased in the order sulfanilamide < sulfapyridine < sulfanilamide < sulfapyridine, indicating a changed sorption behavior due to different sulfonamide speciation. In part sorption non-reversibility was strong. This was attributed to surface complexation, rate-limiting intra-particle diffusion processes and entrapment of sulfonamides in voids of organic matter. Molecular mechanics (MM+) computational modeling using a DOM-trimer model confirmed that H-bonding and dipole-dipole interactions are crucial for entrapment of sulfonamides in voids of organic matter.