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

Abstract EN

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 < sulfadimethoxine.

This was primarily attributed to the sulfonamides' H-bond donor/acceptor properties.

Sorption to the oligomer indicated that in addition to π-π interactions with aromatics phenolic, aldehyde and methoxyl moieties of the oligomer are specific binding sites.

Stronger sorption to humic acid than to the oligomer was related to the more complex structure and functional group diversity of humic acid.

At pH 7.5 sorption sequence was changed to sulfadimethoxine < 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.