Dissipation kinetics and mobility of chlortetracycline, tylosin, and monensin in an agricultural soil in Northumberland County, Ontario, Canada.

A robust high-throughput method was refined to extract three growth-promoting antibiotics, tylosin (TYL), chlortetracycline (CTC), and monensin (MON), from soil. Analysis was performed by electrospray liquid chromatography tandem mass spectrometry. Soil dissipation rate studies were performed in a farm field soil for antibiotics applied with and without manure. Tylosin, CTC, and MON followed first-order dissipation kinetics with half-lives of 4.5, 24, and 3.3 d, respectively, with the addition of manure and 6.1, 21, and 3.8 d, respectively, without manure. Manure application significantly increased TYL dissipation rate, perhaps because of the introduced microbial flora, but had no significant effect on CTC or MON. Monensin dissipation half-life was found to be much shorter in the field study than in a controlled laboratory study, perhaps because of differences in microbial communities. The antimicrobials were not highly mobile. Chlortetracycline was the only antibiotic detected at 25 to 35 cm depth and only up to 2% of the initial concentration in a sandy loam soil. These antibiotics are therefore expected to degrade primarily in agricultural soils before moving to greater depths or to groundwater in significant concentrations in most agricultural systems.