Sorption of the Antibiotic Tetracycline to Humic-Mineral Complexes

Humic substances, by altering the surface properties and/or competing for available reaction sites, can either suppress or promote sorption of organic compounds to mineral surfaces. Limited literature evidence points to the reduction in sorption of the antibiotic tetracycline to clay minerals in the...

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Bibliographic Details
Published in:Journal of environmental quality 2008-03, Vol.37 (2), p.704-711
Main Authors: Gu, C, Karthikeyan, K.G
Format: Article
Language:English
Subjects:
Adsorption
Aluminum Oxide - chemistry
Anti-Bacterial Agents - chemistry
Antibiotics
Clay minerals
desorption
Heterogeneity
Humic acids
Humic Substances
Hydrogen-Ion Concentration
NMR
Nuclear magnetic resonance
Organic compounds
Soil Pollutants - chemistry
soil pollution
Soils
Solution chemistry
Sorption
sorption isotherms
Studies
tetracycline
Tetracycline - chemistry
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Summary:Humic substances, by altering the surface properties and/or competing for available reaction sites, can either suppress or promote sorption of organic compounds to mineral surfaces. Limited literature evidence points to the reduction in sorption of the antibiotic tetracycline to clay minerals in the presence of humic substances. We investigated the surface interaction of Elliott soil humic acid (ESHA) with hydrous Al oxide (HAO) and the effect of this association on tetracycline sorption. Strong interaction between ESHA and HAO led to ESHA-promoted dissolution of HAO and surface charge reversal. The ESHA-HAO sorption-desorption isotherms were successfully described using a modified Langmuir model that accounted for the heterogeneity of HAO surface and ESHA. Ligand exchange was proposed as the major interaction mechanism, and the edge Al atoms on HAO surface were considered as the sorption sites for ESHA macromolecules. ESHA was coated onto HAO to achieve two different organic content (foc) levels of 0.81 and 1.52%. Sorption results were compared for the binary ESHA-tetracycline and HAO-tetracycline systems, and the ternary ESHA-HAO-tetracycline system. The coating of ESHA on HAO significantly suppressed tetracycline sorption levels, attributable to altered HAO surface charge characteristics and/or direct competition between ESHA and tetracycline for potential sorption sites. Higher foc level, besides increasing the extent of sorption suppression, also resulted in greater ionic strength dependence and increased nonlinearity of sorption behavior. It, therefore, appears that the presence of humic substances, in both dissolved and mineral-bound forms, is likely to increase the environmental mobility of tetracycline compounds.
ISSN:0047-2425
1537-2537
1537-2537
DOI:10.2134/jeq2007.0030