Evaluation of environmental residues of ivermectin produced by swine farms

In recent years, interest in ecotoxicology has increased, especially regarding pharmaceutical residues. The toxic effect of environmental residues of ivermectin is proven in several species. Those residues may represent a possible threat to non-target organisms, among which fish and some arthropods, who suffer serious effects when in contact with the lowest doses of the drug (33.3 PPB in dung beetle 1). In this study, our aim was to follow the route of ivermectin from the animal (feces) to the sewage, ending in the soil, and to understand if the concentrations reached in the soil were capable of causing the toxic effects reported in the literature. The same number of samples were collected from two swine farms in Emilia Romagna, Italy: an intensive and an extensive organic farm, which served as the negative control. We analyzed fecal samples from the rectal ampoule of sows one day after subcutaneous treatment (300 μg per kilogram of body weight), and samples of sewage from collection tanks and soil at the time of fertilization. An analytical method recently published was used for the extraction and purification of samples 2. The method was then adapted and validated for LC/MS/MS analysis to reach PPT concentrations. The limit of detection (LOD) was 150 PPT and the limit of quantification (LOQ) was 300 PPT in the extract. Doramectin, a macrocyclic lactone like ivermectin, was used as the process standard. The samples were concentrated to the fourth or eighth power to measure the analyte in feces, sewage, and soil. The results were interpreted using a calibration curve, with intercept values, indicating excellent linearity (R2>0.999). The measured levels in the intensive farm samples were 156-589 PPB in feces, 327-674 PPT in sewage, and 150-500 PPT in soil. Even if ivermectin in feces reaches concentrations measurable in PPB, the dilution provoked by sewage stocking and distribution on the fields for fertilization may considerably reduce the environmental risk. Ivermectin was not detected in samples from the organic farm, confirming that the antiparasitic drug was not in use at the farm. These preliminary results suggest that ivermectin residues could be irrelevant to cause toxic effects on non-target species. Moreover, further studies and analysis will be necessary to deepen the knowledge of the impact of ivermectin on the swine farm.