Following the route of veterinary antibiotics tiamulin and tilmicosin from livestock farms to agricultural soils.

Veterinary antibiotics (VAs) are not completely metabolized in the animal body. Hence, when animal excretes are used as soil manures, VA residues are dispersed with potential implications for environmental quality and human health. We studied the persistence of tiamulin (TIA) and tilmicosin (TLM) along their route from pig administration to fecal excretion and to agricultural soils. TLM was detected in feces at levels folds higher (4.27-749.6 μg g) than TIA (0.55-5.99 μg g). Different administration regimes (feed or water) showed different excretion patterns and residual levels for TIA and TLM, respectively. TIA and TLM (0.5, 5 and 50 μg g) dissipated gradually from feces when stored at ambient conditions (DT 5.85-35.9 and 23.5-49.8 days respectively), while they persisted longer during anaerobic digestion (DT >365 days) with biomethanation being adversely affected at VA levels > 5 μg g. When applied directly in soils, TLM was more persistent than TIA with soil fumigation extending their persistence suggesting microbial degradation, while soil application through feces increased their persistence, probably due to increased sorption to the fecal organic matter. The use of TIA- and TLM-contaminated feces as manures is expected to lead to VAs dispersal with unexplored consequences for the environment and human health.