Study on the occurrence forms of oxytetracycline and sulfamethoxazole in saline soil and their influencing factors

The contamination of soil with antibiotics has become a hot issue for the environment and global public health. However, there are scarcely any studies on the occurrence forms of antibiotics in saline soil. Occurrence forms of antibiotics are related to bioavailability. Therefore, this study facilitates the evaluation of the ecological risk of antibiotics in saline soil.

An experiment with artificial antibiotic contamination of soil and salinization simulations was conducted. The changes in the occurrence forms of oxytetracycline (OTC) and sulfamethoxazole (SMX) in saline soil were analyzed by continuous ultrasonic extraction. The factors for occurrence forms, including aging time and particle size fraction, were considered.

Soil salinization promoted the conversion of OTC and SMX from acid-soluble and bound states to water-soluble and locked states. Oxytetracycline in saline soil was predominantly in the water-soluble and acid-soluble states, accounting for 54.9–83.7% of the total. Sulfamethoxazole as well is accounting for 66.1–82.1%. In addition, the aging process from 7 to 63 days facilitated the conversion of OTC and SMX from the water-soluble, acid-soluble, and bound states to the non-extractable locked states, resulting in reduced bioavailability. Since the content of extractable forms of OTC and SMX in saline clay was high, it favors conversion to a locked state.

Oxytetracycline and sulfamethoxazole in saline soil were mainly in bioavailable states. The aging effect reduced the bioavailability of OTC and SMX in saline soil. Clay had the low proportion of OTC and SMX in the bioavailable state, reducing environmental risks.