Sorption of tetracycline and chlortetracycline on K- and Ca-saturated soil clays, humic substances, and clay-humic complexes |
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Authors: | Pils Jutta R V Laird David A |
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Affiliation: | Agronomy Department, Iowa State University, 100 Osborne Drive, Ames, Iowa 50011, USA. jutta.pils@usa.dupont.com |
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Abstract: | Tetracycline (TC) and chlortetracycline (CTC) are used extensively for growth promotion and therapeutic purposes in livestock production. The sorption of TC and CTC on clays, humic substances (HS), and clay-humic complexes (clay-HC) derived from two agricultural soils was quantified using dilute CaCl2 (Ca) and KCI (K) as background solutions. In all systems, the soil components sorbed > 96% of added tetracyclines. Strongest sorption was observed for clays, followed by HS, and then clay-HC. Greater sorption by the Ca systems than the K systems and decreased sorption with increasing pH suggests that cation bridging and cation exchange contribute to sorption. X-ray diffraction analysis showed that TC and CTC were sorbed in the interlayers of smectites and that the presence of HS reduced interlayer sorption of tetracyclines by smectites in clay-HC. The results indicate that tetracyclines are dominantly sorbed on soil clays and that HS in clay-HC either mask sorption sites on clay surfaces or inhibit interlayer diffusion of tetracyclines. |
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