Use of sulfadimethoxine in intensive calf farming: evaluation of transfer to stable manure and soil

After prophylactic treatment of 50 calves with 62 mg kg−1 day−1 of sulfadimethoxine (SDM) for five days, the levels of the drug over time were followed in feces, bedding and stable manure, and then in the soil of a manured field and surrounding drainage courses. Analysis were done by HPLC after applying to the different matrices a quick and simple extraction procedure. The half-life of the drug in bedding was very short (24 h). In stable manure the degradation rate of the drug slowed down and the calculated half-life was 64 days, with 390 μg kg−1 of SDM still detectable after three months maturation. However, in a five months matured stable manure obtained from other groups of calves subjected to the same prophylactic treatment, levels of SDM were <50 μg kg−1 (LOD of the analytical method). After field fertilization with this manure, no traces of SDM were found in soil (LOD 10 μg kg−1) or in the water (LOD 2 μg l−1) from the surrounding drainage courses. Using the internationally recognised DAPHTOXKIT-F™, a SDM toxicity test toward Daphnia magna was performed in the range 10–100 mg l−1. The test gave negative results both after 24 and 48 h, confirming that microcrustaceans are less sensitive than other models to the toxicity of antibacterials. However, based on data from other authors, concerning algal toxicity and microbial inhibition, and on the analytical results from the current field study, the calculated worst-case EC50/PEC ratio for SDM both in freshwater and in soil was still >1000.