Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Abstract.

Antimicrobials are used therapeutically during production of food animals to maintain herd health. Much of the administered antimicrobials passes through the animal unchanged and enters the environment through manure management practices such as irrigation with feedlot runoff wastewater. The scientific community is concerned this antimicrobial loading will alter the natural biota resulting in increased resistance, thereby making antimicrobials that are critical for human and animal health ineffective. Therefore, effective methods are needed to mitigate this environmental risk. The objective of this study was to characterize the partitioning of selected antibiotic residues between the aqueous and sorbed phases on solids in beef lagoon runoff wastewater. Three radiolabeled antimicrobials, i.e., [¹⁴C]-erythromycin (ERY), [³H]-chlortetracycline (CTC), and [³H]-monensin (MON), were selected for a laboratory batch partitioning study utilizing beef lagoon runoff wastewater. Liquid scintillation counting and combustion were used to quantify the radioactivity in the aqueous and sorbed fractions over time. Slightly more ERY sorbed to the suspended solids fraction than the aqueous fraction, and equilibrium conditions were achieved quickly, i.e., 2 hours. CTC partitioning occurred in two phases: a rapid sorption to the solids fraction between 0.5 and 8 hours with desorption into the aqueous fraction at 24 hours, suggesting degradation to more polar compounds. The most lipophilic antibiotic tested, MON, quickly and significantly sorbed into the suspended solids layer and remained in equilibrium with the aqueous fraction from 4 to 168 hours. These identified differences underscore the utility of testing such large-use antimicrobials.