Fate of microbial pollutants and evolution of antibiotic resistance in three types of soil amended with swine slurry.

Swine waste is a reservoir of microbial pollutants, including pathogens, antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB); therefore, soil fertilized with swine waste is an essential pathway for the dissemination of microbial pollutants from concentrated swine farms to the public. To rationalize the intervals of swine wastes application and investigate the effects of soil type on the occurrences of microbial pollutants and antibiotic resistance, pot experiments were conducted with three typical soils, humic acrisol, calcaric cambisols and histosols, being collected from south, northwest and northeast China (soil-R, soil-Y and soil-B, respectively). The soils were amended with swine slurry, digestate and chemical fertilizers and then conducted for 172 days. The influence of microbial pollutants and antibiotic resistance in soil posed by digestate application was similar to that of the chemical fertilizers, while swine slurry posed high risks to the soil. Soil-B which had the highest organic matter and neutral pH was least influenced by the swine slurry amendment. tetG, tetM and ermF were persistent ARGs in the slurry treated soil, and their decay rates fitted to first-order kinetics in the order soil-B> soil-Y > soil-R. Putative pathogens showed strong correlations with ARGs, suggesting a risk of dissemination. The initial 43-82 days was the active phase of microbial pollution in slurry treated soil, during which time heavy metals, moisture content, total organic carbon and the microbial community were key factors contributing to changes in antibiotic resistance. Fertilization intervals of livestock wastes should be lengthened over the ARG active phase.