Abstract: Antibiotics used in livestock and poultry production may be present in manure and slurry as the parent compound and/or metabolites. The environments may therefore be exposed to these antibiotics due to the application of animal manure to agricultural land. In order to understand the residue levels of antibiotics in livestock and poultry manures,and in agricultural soils after a long-term application of antibiotics-contained animal manure,both livestock and poultry manure samples as well as soil samples were collected from north Zhejiang Province. Concentrations of three selected tetracyclines,including chlorteracycline (CTC),tetracycline (TC),and oxytetracyline (OTC),in the samples were characterized. Residual levels of the TC,OTC,and CTC in manures varied from below determination limit to 16.75,29.60,and 11.63 mg·kg^-1,with their mean values at 1.57,3.10 and 1.80 mg·kg^-1,respectively. The residue level of selected antibiotics ranked from high to low as pig manure>chicken manure>cow manure,and the antibiotics residues were generally higher in animal manures from industrial scale farms than in those from farmer′s households. About 93%,88% and 93% of surface soils taken from the agricultural fields after application of manure contained OTC,TC,and CTC,respectively. The concentrations of the OTC,TC,and CTC in these soils ranged from below determination limit to 5.172,0.553,and 0.588 mg·kg^-1,respectively. The mean residues of the CTC,TC and OTC in the surface soils from agricultural fields treated with animal manures were 38,13,and 12 times as high as those from agricultural fields without manure application,suggesting that manure is an important source of antibiotics in the agricultural soils. The ratios of the OTC,TC,and CTC concentrations in the subsurface soils (20-40 cm) to those in the surface soils (0-20 cm) varied from to 2.13,0.02 to 1.91,and 0.02 to 1.36,with their mean values at 0.64,0.65,and 0.56,respectively. The residues of the CTC,TC,and OTC in the surface soils were positively correlated with clay content of the soils. The downward movement of antibiotics in sandy soils was more significant than in clayey soils,indicating that antibiotics is not stable but mobile in sandy soils.

Key words: antibiotics, residue, livestock and poultry manure, soil