The Kinetics of Oxytetracycline Degradation in Deionized Water under Varying Temperature, pH, Light, Substrate, and Organic Matter

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Abstract
The kinetics of oxytetracycline (OTC) degradation in deionized water was studied under the influence of various environmental factors. The experiment was conducted with a solution of 10 μg aqueous OTC /mL in 600-mL glass beakers under controlled laboratory conditions. The aqueous concentration of OTC was determined by high-performance liquid chromatography. Low temperatures (4°C) favored high drug stability, and high temperatures (43°C) speeded OTC degradation, resulting in a very short half-life of 0.26 ± 0.11 d. Light exposure caused photodecomposition, reflecting degradation rates threefold higher than those under dark conditions. Acidic conditions (pH 3.0) favored drug stability (half-life = 46.36 ± 4.92 d), and alkaline conditions (pH 10.0) increased the degradation rate (half-life = 9.08 ± 4.22 d). The presence of a substrate (bentonite clay) resulted in an approximate 17% decrease in OTC concentration within 5 min of contact. Addition of organic matter (fish feed) along with the substrate ...