Ofloxacin sorption in soils after long-term tillage: The contribution of organic and mineral compositions

Intensive human activities in agricultural areas resulted in significant alteration of soil properties, which consequently change their interactions with various contaminants. This process needs to be incorporated in contaminant behavior prediction and their risk assessment. However, the relevant study is missing. This work was designed to examine the change of soil properties and ofloxacin (OFL) sorption after tillage. Soil samples were collected in Yuanyang, Mengzi, and Dianchi areas with different agricultural activities. Although the mineral compositions of soils from Yuanyang and Dianchi differed greatly, these compositions are similar after tillage, especially for paddy soils. Soil pH decreased generally after OFL sorption, suggesting that ion exchange of OFL with protons in soil organic matter (SOM) was important for OFL sorption. However, a positive relationship between SOM and OFL sorption was not observed. On the contrary, increased SOM decreased OFL sorption when soils from the same geological location were compared. Generally speaking, tillage activities or dense vegetations greatly decreased OFL sorption. The higher OFL sorption in B horizon than A horizon suggested limited leaching of OFL through soil columns. The summed sorption calculated based on the sorption of individual soil components and their percentages in soils was higher than the intact soil. This phenomenon may be understood from the interactions between soil components, such as the coating of SOM on mineral particles. This study emphasizes that soil should be treat as a dynamic environmental matrix when assessing antibiotic behaviors and risks, especially in the area with intense human activities.