The kinetics of oxytetracycline degradation in deionized water under varying temperature, pH, light, substrate, and organic matter

The kinetics of oxytetracycline (OTC) degradation in deionized water was st udied under the influence of various environmental factors. The experiment was conducted with a solution of 10 pg aqueous OTC/mL in 600-mL glass beake rs under controlled laboratory conditions. The aqueous concentration of OTC was determined by high-performance liquid chromatography. Low temperatures (4 degreesC) favored high drug stability, and high temperatures (43 degree sC) 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 alkalin e 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 appro ximate 17% decrease in OTC concentration within 5 min of contact. Addition of organic matter (fish feed) along with the substrate resulted in a 41% de crease in OTC concentrations within 5 min of contact.