Degradation of Oxolinic Acid in Soil Under Simulated Natural Degradation Processes

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Oxolinic acid (OA), a quinolone-class antibiotic commonly used in domestic agriculture, exhibits low bioavailability, raising concerns about its potential environmental persistence. Residual OA in the environment can undergo partial degradation through natural processes, which are influenced by various factors. This study aimed to investigate the photodegradation and biodegradation patterns of OA under various environmental factors, including temperature, light intensity, soil usage, soil organic matter content (OM). Additionally, adsorption and desorption experiments were conducted to elucidate the relationship between OA degradation and its adsorption-desorption behavior in soil. In this study, two UV-A intensities (2.3 and 1.5 mW cm<sup>-2</sup>) and two temperatures (21.8 and 35.0<sup>o</sup>C) were applied to examine the OA degradation behavior. Biodegradation tests were conducted using soil samples with varying land uses (rice paddy, field) and OM (6.4% and 2.3%). Additionally, sorption tests were performed using the soil samples and OA solutions, followed by desorption tests on the OA-sorbed soil samples. In the photodegradation experiment, the OA degradation rate ranged from 16.6% to 51% across all conditions after 20 d. Compared to other antibiotics reported in previous studies, OA exhibited relatively slow photodegradation, and the variations in degradation rates under the tested experimental conditions were not statistically significant. In the case of biodegradation, similar degradation rates were observed in the field and rice paddy soils, with faster degradation occurring in soils with lower OM. The differing biodegradation patterns observed across soil samples could be partially explained by the adsorption-desorption characteristics of OA in soils. The degradation of antibiotics through simulated natural processes such as photodegradation and biodegradation did not exhibit consistent trends depending on the environmental factors or soil properties. This suggests that the degradation of antibiotics is a complex process influenced by various factors, including, but not limited to, environmental factors and soil properties. This study highlights the need for further research to better understand the behavior of residual antibiotics in soil environments.