Tetracycline and fluoroquinolone antibiotics contamination in agricultural soils fertilized long-term with chicken litter: Trends and ravages.

We investigated the potential accumulation of tetracyclines (TCs) such as chlortetracycline (CTC), oxytetracycline (OTC) and doxycycline (DC), and fluoroquinolones (FQs) like enrofloxacin (ENR) and ciprofloxacin (CIP) in chicken litter and agricultural soils fertilized over short-term to long-term (<1-30 yrs) with chicken litter in a poultry hub for the first time from Tamil Nadu, India. CTC, OTC, DC, CIP, and ENR were detected in 46-92 % of the selected chicken litter samples, with mean levels ranging from 2.90 to 23.30 μg kg-1. Higher concentrations of TCs and FQs were observed in freshly collected chicken litter from poultry sheds than in those stockpiled in cultivated lands. CTC was the prevalent antibiotic in chicken litter. The overall occurrence, as well as the ecological risks of TCs and FQs, changed over a 30-yr period. The accumulation of veterinary antibiotics (VAs) (in μg kg-1) in short-term (>1 yr) to medium-term (1-3 yrs) chicken litter-fertilized soils reached a maximum of 11.60 for CTC, 6.50 for OTC, 0.80 for DC, 3.70 for CIP, and 3.60 for ENR, but decreased in long-term (10-30 yrs) fertilized soils. Ecological risk assessment revealed a Risk Quotient (RQ) of ≤0.10 for CTC, OTC, and DC in all soils, while an average risk (RQ >0.10-<1.0) was evident with CIP and ENR in short-term and medium-term fertilized soils. Antibiotic resistance genes (ARGs), including tetA, tetB, qnrA, qnrB and qnrS were detected in most of the chicken litter samples and litter-fertilized soils. Thus, it is critical to develop and adopt effective mitigation strategies before applying chicken litter in farmlands to decrease VAs and ARGs, reducing their associated risks to public health and ecosystems in India considering 'One Health' approach. Future investigations on the occurrence of other VAs and ARGs in soils fertilized with poultry litter at regional scale are required for effective risk mitigation of the widely used VAs.