Sorption and transformation of sulfonamide antimicrobial agents.

摘要

Sulfonamide antimicrobial agents are a group of synthetic sulfanilamide derivatives which are widely applied in human therapy, veterinary medicine and agriculture husbandry. Understanding sulfonamide antimicrobials sorption, desorption and transformation in soil and sediments is essential for assessing their potential to leach into groundwater and to be transported in aquifers and surface waters. Adsorption of sulfonamide antimicrobial to clay minerals exhibited pronounced pH dependence and influenced by clay charge density. Cation exchange appeared to contribute to adsorption of the cationic sulfonamide species to smectite surfaces. Sulfonamide antimicrobials do not intercalate into the interlamellar spaces of montmorillonite clays. The nature of the sulfonamide R group influenced the degree of adsorption of the cationic and neutral species. Humic acid coating changed clay particle surface properties and enhance sulfonamide sorption, especially at the higher humic acid-to-clay ratio. Substantial sorption-desorption hysteresis was observed as indicated by large values for the Thermodynamic Irreversibility Index (0.79-0.88). Apparent competitive sorption of two sulfonamides (sulfamethazine and sulfapyridine) was observed for humic-clay complexes at the higher humic acid loading. The transformation of sulfonamide antimicrobial was conducted in presence of manganese dioxide which indicated that molecular oxygen was an important reagent in sulfamethazine reaction at pH 5.0. The reaction order with respect to proton and sulfamethazine was 0.47 and 0.76. Structures of three major products from sulfonamide transformation were proposed. The results from this research suggested that sulfonamide antimicrobial agents are relatively mobile in soil but hard to desorb, and abiotic transformation by mineral is a possible pathway in nature.