The occurrence and spatial distribution of typical antibiotics in soils along the Fenhe River in Shanxi Province

Purpose

Antibiotics are emerging contaminants of increasing concern in recent years. A total of 71 representative farmland soils along the Fenhe River in Shanxi Province were collected to investigate the occurrence of tetracyclines (TCs), sulfonamides (SAs), and quinolones (QLs). Additionally, the effects of population, livestock and poultry density, and soil properties on antibiotic distribution were also evaluated.

Materials and methods

Farmland topsoil samples along the Fenhe River were collected and freeze-dried at ??20 °C. The antibiotics in soils were extracted with a mixture of acetonitrile, EDTA-SPB, and Mg(NO₃)₂-NH₃·H₂O at the ratio of 2:1:1 (v/v/v). The extracted antibiotics were analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS).

Results and discussion

The antibiotics were universally detected. The detection frequencies of sulfaclozine, enrofloxacin, norfloxacin, and ciprofloxacin reached 100%. Norfloxacin was the most abundant antibiotic in soils (27.21 μg kg^?1). The distribution of antibiotics in soils along Fenhe River varied as midstream (8.62 μg kg^?1) > downstream (4.58 μg kg^?1) > upstream (3.49 μg kg^?1). Oxytetracycline along the upstream and midstream was mainly caused by the emission of livestock and poultry and the overuse of human. The main sources of antibiotics along the downstream were livestock and poultry farms. Antibiotics were generally negatively correlated with sand content, pH, and organic matter, while cation exchange capacity had positive correlation with most of antibiotics such as tetracycline, sulfamonomethoxine, enrofloxacin, sulfameter, and sulfachinoxalin. SAs and TCs had little ecological risk, while QLs posed low or medium ecological risks.

Conclusions

This study provided a scientific basis for antibiotic pollution control and agricultural safety supervision along the Fenhe River. Although no high risk of antibiotics was observed in soil samples based on the calculation, the widespread distribution of antibiotics in farmland soil along Fenhe River should be addressed.