Assessment of Veterinary Antimicrobial Residues in Feedlot Soils in Argentina

Abstract

Background/Objectives: This prospective cross-sectional study quantified veterinary antimicrobial residues in soils from 27 commercial beef feedlots across multiple regions of Argentina and production scales. Methods: Using a validated Ultra-Fast Liquid Chromatography–tandem mass spectrometry (UFLC-MS/MS) method, we measured 15 target antimicrobials in pooled corral soil samples. Results: Monensin was detected in all feedlots and showed the highest detection frequency and widest concentration range; peak concentrations exceeded 15,000 ppb in some sites. Oxytetracycline presented pronounced, site-specific peaks (approaching 14,000 ppb), consistent with its strong adsorption to soil organic matter and limited biodegradation. These results indicate localised hotspots of antimicrobial loading in feedlot environments. These elevated concentrations signify substantial antimicrobial loading in confined animal environments and potential hotspots for environmental selection pressure. Compounds absent from farm treatment records were detected in 40.7% of feedlots, correlating with antimicrobial residues not matching available AMU records, including oxytetracycline, tulathromycin, cefquinome, enrofloxacin, and ciprofloxacin among others. Multiple non-exclusive explanations are plausible (historical persistence, manure redistribution, incomplete records, off-label use, or cross-contamination). The detection of critically important antimicrobials (e.g., fluoroquinolones and advanced cephalosporins) in soils raises One Health concerns about environmental selection pressure and the potential dissemination of resistance determinants. Conclusions: These findings underscore gaps in stewardship and the need for integrated environmental monitoring and improved antimicrobial usage traceability. These data provide a baseline for ecological risk assessment and resistome studies and can inform evidence-based policy and stewardship interventions in Argentine feedlot systems.