Distribution, Sorption and Desorption of Tylosin, Chlortetracycline and their Metabolites in Pig Manure

Abstract

Effects of pH on sorption, desorption and hysteresis of chlortetracycline (CTCs), tylosin (TYL) and their metabolites have been studied in pig manure samples collected from different pig farms. Approximately 36% of the samples analyzed tested positive (concentration > quantitative detection limit) for the antibiotics and metabolite residues. The degree of contamination depended upon the manure’s pH. The acidic TYL-positive manure samples contained TYL-A and TYL-B, while the basic TYL-positive samples contained TYL-A, TYL-ALD and TYL-D.  The CTC-positive manure samples contained mostly CTC, ECTC and ACTC at acidic pH, but mostly CTC, ICTC, EICTC and EACTC at basic pH. For acidic and neutral manure samples, the logK_D^des values were greater than the K_D^s values for TYL-B, TYL-A, TYL-ALD, CTC, ACTC, ECTC and EACTC, indicating sorption-desorption hysteresis. TYL-D, ICTC and EICTC did not exhibit sorption-desorption hysteresis. At acidic and neutral pH, the residues remained solid-bound, but an increase in pH decreased hysteresis, resulting in greater leaching and contamination of the environment. Thus, environmental pH may determine the antibiotics and metabolite leaching in freshwater at or away from the site of production. In addition, analysis of the parent antibiotic residues may not provide an accurate assessment of the environmental health.