title: Sorption of sulfonamide pharmaceutical antibiotics on whole soils and particle-size fractions.
abstract: Residues of pharmaceutical antibiotics are found in the environment, whose fate and effects are governed by sorption. Thus, the extent and mechanisms of the soil sorption of p-aminobenzoic acid and five sulfonamide antibiotics (sulfanilamide, sulfadimidine, sulfadiazine, sulfadimethoxine, and sulfapyridine) were investigated using topsoils of fertilized and unfertilized Chernozem and their organic-mineral particle-size fractions. Freundlich adsorption coefficients (K(f)) ranged from 0.5 to 6.5. Adsorption increased with aromaticity and electronegativity of functional groups attached to the sulfonyl-phenylamine core. Adsorption to soil and particle-size fractions increased in the sequence: coarse silt < whole soil < medium silt < sand < clay < fine silt and was influenced by pH. Sorption nonlinearity (1/n </= 0.76) indicated specific interactions with functional groups of soil organic matter (SOM). Phenolic and carboxylic groups, N-heterocyclic compounds, and lignin decomposition products were tentatively assigned as preferred binding sites using statistical analysis of pyrolysis-mass spectra and adsorption coefficients. Adsorption of sulfonamides to mineral soil colloids was weaker and resulted in a stronger desorption from clay-size fractions. Moreover, steric accessibility of organic-mineral complexes in clay-size fractions was significantly reduced. With a quantitative structure-property relationship (QSPR) model, combining the organic carbon concentration, the sulfonamides' chromatographic capacity factor (k'), and nondissociated species concentration (CF(a)), distribution coefficients (K(d)) were estimated with a cross-validated regression coefficient Q(2) = 0.71. Modeling and molecular mechanics calculations of antibiotic-SOM complexes showed preferred site-specific sorption via hydrogen bonds and van der Waals interactions. Distinct chemical structural properties, such as aromaticity and van der Waals volumes, correlated with the sorption data.
authors.affiliation: Institute of Soil Science and Plant Nutrition, University of Rostock, Justus-von-Liebig-Weg 6, 18051 Rostock, Germany. soeren.thiele@auf.uni-rostock.de
authors.forename: S
authors.initials: S
authors.lastname: Thiele-Bruhn
authors.forename: T
authors.initials: T
authors.lastname: Seibicke
authors.forename: H-R
authors.initials: HR
authors.lastname: Schulten
authors.forename: P
authors.initials: P
authors.lastname: Leinweber
mesh_terms: D000327:Adsorption; D000890:Anti-Infective Agents / Q000032:analysis / Q000737:chemistry*; D004784:Environmental Monitoring; D008962:Models, Theoretical; D010316:Particle Size; D012989:Soil Pollutants / Q000032:analysis*; D013449:Sulfonamides / Q000032:analysis / Q000737:chemistry*
chemical_list: D000890:Anti-Infective Agents; D012989:Soil Pollutants; D013449:Sulfonamides