| Chloramphenicol（CAP）has been widely used as a veterinary drug,but its toxic and side effects and the emergence of drug resistance genes pose a serious threat to human health.Colloids are heterogeneous mixtures with particle sizes ranging from 1nm to 1μm,which are ubiquitous in the environment.Compared with large particles,colloids showed stronger adsorption behavior towards the pollutants.In this study,different sources of the soils（sediment-A1 and A2,natural soil-B1 and B2,and commercial nutrient soil-B3）were selected to analyze the physicochemical properties of the soil,colloids and their effects on the adsorption behavior of CAP using cross-flow ultrafiltration combined with a variety of multi-method analytical approach.The aims of this study were to understand the structure and composition of natural colloids from the sediment and soil and to provide an important scientific basis for understanding the fate of CAP.Results of the fluorescence regional integration method showed that the fluorescence components of soil colloids were mainly tryptophan-like,fulvic-like and humic-like,while there were few tyrosine-like and dissolved microbial metabolites.In addition,five fluorescent components were identified by PARAFAC,including aquatic humic-like（C1）,terrestrial humic-like（C2-C4）and tryptophan-like（C5）.Humic-like components were mainly in the 1-10 k Da fractions,and the tryptophan-like were relatively abundant in the 1-10 k Da and the 100 k Da-0.45μm fractions in soil and sediments,respectively.Results from the spectral characteristics suggested that a higher degree of humification was found for the colloids of nutrient soil.Additionally,the colloids of sediments and flower garden soil were mainly autochthonous.Besides,it revealed that the relatively large colloids were terrestrial sources,while the relatively small colloids were significantly autochthonous.The colloids in nutrient soil had the highest molecular weight,high concentration of the colored dissolved organic matter（CDOM）and the dissolved organic carbon（DOC）,aromaticity and proportion of oxygen-containing functional groups on aromatic rings,followed by sediments,and the counterparts for the colloids in natural soil were lowest.The degree of humification,aromaticity and abundance of CDOM of 1-10 k Da fractions were slightly higher,followed by 100 k Da-0.45μm fractions.The aromatic rings of 10-100 k Da fractions were rich in carbonyl,hydroxyl and other functional groups.The results of adsorption experiments showed that nutrient soil colloids within the size range from 1 k Da to 0.45μm had the highest adsorption rate（36.25%）and partition coefficient（1.91）,and the lowest normalized organic carbon binding coefficient（3.93）.Compared with natural soil colloids,the adsorption rate of sediment colloids was higher,with the lower binding capacity with CAP.The CAP concentration and adsorption rate in fractionated colloids were 0.43-1.33 mg·L-1and 8.32-27.20%,respectively.The higher CAP concentration and adsorption rate of sediment colloids were in 1-10 k Da fractions,and the counterparts of soil colloids were in 10-100 k Da fractions.In addition,the distribution coefficient of CAP between colloids and the truly dissolved phases was relatively high in 10-100 k Da fractions,followed by 1-10 k Da fractions.The results of redundancy analysis showed that the adsorption capacity of CAP was mainly related to the aromaticity,concentration of CDOM and DOC,and molecular weight.Hereinto,molecular weight was the most important influence factor.The humification degree of colloids and the specific gravity of carboxyl and carbonyl groups on aromatic rings also had a great influence on the adsorption behavior of CAP.The soluble microbial metabolites and humic-like fluorescent components promoted the adsorption of CAP on colloids,while colloidal photoproducts and tryptophan-like fluorescent components inhibited the process. |
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