Particulate organic matter (POM) is a major antibiotic sorbent of the active soil organic carbon pool. Until now, the spatial heterogeneity of POM for ciprofloxacin (CFC) sorption at the microstructure scale has not been quantified. To our knowledge, this is the first study that combines a batch sorption experiment, NanoSIMS, and a 13C isotopic tracer to expound the distribution characteristics of CFC and the dominant sorption components of POM. Four POMs separated from soils (wetland, oil waste field, and farmlands) were utilized to study the sorption mechanisms using batch experiments. POM separated from the wetland was utilized for further study at the microstructure scale. The results revealed that the POM had a great CFC sorption capacity ranging from 65.20 mg g-1 to 77.51 mg g-1. Both the kinetics and NanoSIMS results showed that the sorption mechanisms included surface distribution and intra-particle diffusion. The microstructural distribution characteristics exhibited a marginal accumulation tendency and a surface accumulation effect. A combination of the NanoSIMS with the pH and salinity results explained that CFC adsorption was dominated by the organic components of POM. Overall, the present study demonstrates that the characteristics and organic components of the POM played a decisive role in the CFC-POM interactions. This study provides the first evidence of the vector potential of CFC rereleased into the environment during the POM turnover process.
Keywords: (13)C isotopic tracer; CFC; Marginal accumulation tendency; POM; Spatial heterogeneity; Surface accumulation effect.
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