Residual Status of 25 Veterinary Drugs and Dietary Exposure Assessment of Commercially Available Pork in Guiyang

Intensive farming practices have necessitated the extensive use of veterinary drugs, raising significant concerns regarding residue contamination. Consequently, long-term monitoring of residues and the evaluation of dietary exposure risks are essential. In this study, 326 pork samples were collected from local supermarkets between October 2024 and April 2025. Methods were developed for the analysis of 25 veterinary drugs (including sulfonamides, tetracyclines, fluoroquinolones, β-agonists, amphenicols, macrolides, and roxarsone) using high-performance liquid chromatography-tandem mass spectrometry. Roxarsone was extracted using a methanol/water solution (6:4, v/v), and amphenicols were extracted with a 2% ammonia in ethyl acetate solution. Other analytes were extracted with acetonitrile containing 2% acetic acid, followed by cleanup via dispersive solid-phase extraction. Chromatographic separation and detection were performed under multiple reaction monitoring conditions in both positive and negative ionization modes. The method exhibited good linearity (r² > 0.99) for all target analytes. Recoveries ranged from 70% to 110% with relative standard deviations below 13%, and limits of quantitation ranged from 0.02 to 5.0 µg/kg. Tetracyclines were the most frequently detected class (detection rate of 63.6%), whereas prohibited substances (β-agonists and roxarsone) were not detected. Residue levels exhibited seasonal fluctuations, with tetracyclines peaking in October and fluoroquinolones and amphenicols in November. Hazard quotient values for dietary intake were consistently below 1, indicating a low health risk to consumers. The dynamic monitoring of drug residue levels offers a more comprehensive approach compared to static methods, which provides valuable insights to guide the rational use of veterinary drugs.