Effect of temperature, pH, and soil texture on pirlimycin fate in dairy manure-amended soils

Antibiotics applied to soil through application of manure are of increasing concern due to their adverse environmental impacts, including their potential contribution to the development of antibiotic resistance in the environment. Two 90-d laboratory incubation studies were conducted to determine the effects of temperature (10 or 21 °C), pH (5, 7, 9), and soil texture (sandy loam, loam) on the persistence of two antibiotics (pirlimycin and cephapirin) applied to soils with dairy manure amendment. Dairy manure from treated and untreated cows was used as the source for this study. However, cephapirin was not detected in manure used for the study. Initial manure pH affected pirlimycin concentration of the manure, and there were differences in initial soil concentration between soil types. In the temperature experiment, pirlimycin concentration was significantly affected by temperature and soil type. In the 10 °C treatments, pirlimycin concentration initially decreased at 7 d but increased to levels similar to 0 d concentrations at 14 d, indicating possible deconjugation of pirlimycin ribonucleotide adducts in the manure applied. Although the loam soil type had a higher pirlimycin concentration in the temperature experiment at 0 d and 14 d, concentrations decreased below the sandy loam soil at 56 d and continued in the 90-d sampling period. Pirlimycin dissipation from dairy manure-amended soils was enhanced by higher temperature and finer soil texture, both of which could affect development of resistance genes if soil microbes are exposed to pirlimycin for longer periods of time.