Effect of temperature, pH and illumination on abiotic degradation of oxytetracycline in sterilized swine manure.

Tetracyclines such as oxytetracycline (OTC) are widely used veterinary chemicals. They are often poorly absorbed with a significant fraction being excreted in manure that can subsequently result in environmental contamination. In many countries throughout South East Asia swine manure is not composted, but sun-dried. Using sunlight to heat manure has been suggested as an effective and low-cost strategy to reduce OTC contamination, but this has previously been unexplored. Such conditions have also been shown to reduce bacterial numbers in manure meaning abiotic OTC degradation processes may become more significant. This work investigated for the first time, the role of temperature, illumination and pH in the abiotic degradation of OTC in sterilized swine manure. OTC loss from laboratory-based experiments simulating conditions likely to be experienced in sun-drying were assessed using simple first order and availability-adjusted loss models. ANOVA results suggested that neither model was superior to the other. In addition, pH and light had little influence. Temperature was shown to be the main factor influencing OTC loss. Kinetic results showed reductions in OTC concentrations of 65 % after 100 h at 40°C based on the availability-adjusted loss model, regardless of pH and illumination. Such temperatures are likely to be attained during the process of sun-drying. Therefore this may be a useful and practical means of reducing OTC contamination in manure.