Occurrence and distribution of veterinary antibiotics and tetracycline resistance genes in farmland soils around swine feedlots in Fujian Province, China.

Six antibiotics, tetracyclines (TCs), and quinolones (QNs) in farmland soils from four coastal cities in Fujian Province of China were investigated. Oxytetracycline was most frequently detected, followed by enrofloxacin, ciprofloxacin, chlorotetracycline, ofloxacin, and tetracycline, with maximum concentrations of 613.2, 637.3, 237.3, 2668.9, 205.7, and 189.8 μg kg(-1), respectively. Samples from Putian City contained the highest maximum concentration of ∑TCs (3,064.2 μg kg(-1)), whereas those from Fuzhou City contained the highest maximum concentration of ∑QNs (897.8 μg kg(-1)). It is noteworthy that the ∑TCs and ∑QNs in 46.4 and 28.6 % of samples exceeded the ecotoxic effect trigger value (100 μg kg(-1)), respectively. The concentrations of these antibiotics and five tetracycline resistance genes in four soil plots at depth profiles were quantified thereafter. In most cases, both antibiotics and resistance genes decreased with the increase of depth. Some antibiotics can be detected at a depth of 60-80 cm where the abundance of tetO, tetM, and tetX reached up to 10(7) copies g(-1). Additionally, the sum of all tet genes (normalized to 16S rRNA genes) correlated with ∑TCs significantly (r=0.676). Our results suggest that resistance determinants can migrate to deeper soil layers and would probably contaminate groundwater by vertical transport.