Effect of Colloids in Sediment and Soil on Their Sorption Behavior of Chloramphenicol

Abstract

Natural colloids (NCs) are ubiquitous in sediments and soils, which could affect the environmental fate of antibiotics. Focusing on chloramphenicol (CAP), different sources of the sediments and soil samples were selected to research the sorption capacity of NCs with different relative molecular weights towards CAP, as well as the impactors, combined with a multi-method approach including cross-flow ultrafiltration, dynamic light scattering, UV-visible absorption spectroscopy, and three-dimensional excitation-emission matrix fluorescence spectroscopy. The results revealed that the low molecular weight (LMW) of NCs was associated with a low autochthonous origin and a higher humification degree. The high molecular weight (HMW) of NCs were mainly terrestrial sources, and the aromatic rings contained more oxygen-containing functional groups such as carboxyl, hydroxyl, and carbonyl groups. Four fluorescence components were identified using the parallel factor analysis model, and the humic-like substances were the primary fluorescent components. Moreover, based on batch experiments, the study investigated the sorption behavior of CAP by the different fractions of the solid samples. The results showed that the sorption processes of CAP were well fitted by the linear model and Freundlich model. The average sorption rate of CAP by the original solid samples and the solid samples with removed organic and inorganic carbon were 4.46%, 3.93%, and 6.61%, respectively, indicating that organic carbon played an important role in the sorption behavior of CAP. The results of the sorption experiments indicated that CAP was more easily adsorbed on the LMW NCs that had a high degree of humification and a more aliphatic chain on the aromatic rings. In addition, tryptophan-like protein substances in NCs showed the inhibiting effect on the sorption progress of CAP. Redundancy analysis indicated that the sorption of CAP by NCs in sediment and soil was mainly related to the source, aromatics, oxygen functional groups on aromatic rings, humification degree, and humic-like substances of NCs.