Adsorption of Tetracycline Antibiotic Onto Iron Oxide Mineral in Soil.

Tetracyclines(TCs) is one of the most widely-used antibiotics in the world, which are commonly used as human infection medicines, veterinary medicines, and animal growth promoters. Because only small amount of TCs are absorbed during metabolism, the majority of TC are excreted via feces and urine as unchanged form. Upon TC release, iron oxide-hydroxides (IOH), common minerals in soils, may play an important role in controlling the behavior and bioavailability of TC in the environment. However, the interactions of TC with IOH may be subject to change while TC forming a strong complex with divalent or trivalent cations. In this report, TC adsorptions on iron oxide-hydroxides, such as goethite and ferrihydride, as influenced by pH and metal cations with various molar ratios, were examined. Results indicated that TC adsorption on ferrihydrite and goethite exhibited relatively fast, and it reached the maximum at pH 6. The presence of metals (Zn²⁺°BCu²⁺ and Al³⁺) would increase TC adsorption on the minerals, attributing probably to the formations of metal bridge and ternary complexes. TC and metal ratios influenced strongly the interactions of TC with the iron minerals. A maximum adsorption of TC was observed for TC-Zn/TC-Al and TC-Cu with a TC-metal ratio of 1:1 and 1:3, respectively. However, an increase of metal concentrations behind the specific ratio would lead to a decrease of TC adsorption Modifications of mineral surfaces by extra metal ions may create an unfavorable local environment for TC or TC-metal complexes adsorptions.