The effect of composting on the degradation of a veterinary pharmaceutical

Composting has been identified as a viable means of reducing the environmental impact of antibiotics in manure. The focus of the present study is the potential use of composting on the degradation of salinomycin in manure prior to its field application. Manure contaminated with salinomycin was collected from a poultry farm and adjusted to a C:N ratio of 25:1 with hay material. The manure was composted in three identical 120 L plastic containers, 0.95 m height × 0.40 m in diameter. The degradation potential for salinomycin was also ascertained under open heap conditions for comparison (control). Salinomycin was quantified on HPLC with a Charged Aerosol Detector, at an interval of every 3 days. The salinomycin level in the compost treatment decreased from 22 mg kg−1 to 2 × 10−5 μg kg−1 over 38 days. The corresponding decrease in the control was from 27.5 mg kg−1 to 24 μg kg−1. The changes in pH, EC (dS m−1), temperature, total kjeldahl nitrogen (TKN), total potassium (TK), total phosphorus (TP) and carbon content in both the composting and the control samples were monitored and found to be different in compost as compared to the control. During the composting process, the loss of TKN was 36%, which was substantially lower than corresponding loss of 60% in the control. The loss of carbon was 10% during composting, whereas the loss in the control was 2%. In composting, the temperature modulated from 27 °C (initially) to a high of 62.8 °C (after 4 days), and then declined to 27.8 °C at the end of 38 days. On the basis of the results obtained in this study, it appears that the composting technique is effective in reducing salinomycin in manure.