Physicochemical Properties Of Dissolved Organic Matter In Sediments And Its Effect On Adsorption Of Antibiotics

There has been serious soil pollution,water pollution,etc.,caused by antibiotic abuse,as well as a huge health risk.The adsorption of antibiotics in various environmental media,such as rivers,lakes,and soils,plays an important role in their migration and transformation.Dissolved organic matter(DOM)is an organic mixture that can pass through a 0.45μm filter membrane,which has high activity and migration ability to pollutants.The high activity and migration ability of these organisms can affect the distribution,migration transformation,and bioavailability of pollutants.As the largest freshwater lake in China,antibiotic pollution in the basin of Poyang Lake has attracted increasing attention.Thus,this paper investigated sediment DOM in Poyang Lake area,and studied the fluorescence characteristics and spatial distribution characteristics of DOM in Poyang Lake sediment by three-dimensional excitation-emission matrix spectroscopy,ultraviolet-visible spectroscopy and parallel factor analysis model(PARAFAC).At the same time,four typical antibiotics were selected and the effects of DOM in sediment samples(Poyang Lake in December(PYH 12),Poyang Lake in April(PYH 4),Dexing in December(DX 12))with different molecular weight sizes and concentration levels on the adsorption behavior of antibiotics were studied by tangential ultrafiltration and balanced dialysis experiments.This study can provide a theoretical basis for identifying and evaluating the sources of water pollution in Poyang Lake,and also provide data support for understanding the tendency and risk of typical antibiotics under different DOM.The main conclusions are as follows:(1)The DOM in sediments from Poyang Lake originated from both terrestrial and autochthonous sources with a high humification.Compared with the sub-lakes,the DOM from the main lake was characterized with a higher concentration of colored dissolved organic matter,larger particle size,and higher aromaticity and humification degree.In addition,four fluorescence components of DOM in sediments were identified by the PARAFAC model,including three humic-like components(C1,C2 and C4)and one protein-like component(C3).The fluorescence intensity of the humic substances in the sub-lakes was higher than those in the main lake.Furthermore,the percentage of fluorescence abundance of C1 was the highest both in the sub-lakes(42%)and main lake(46%).The spatial distribution of the fluorescence intensity of four components gradually increased from west to east,and the peak values were observed in the Duchang and Nanji Wetland.It may be related to the death of a large number of plants due to the rise of the water level during the wet season and human activities.Principal component analysis showed that although there are no significant differences of the four fluorescent components between the sub-lakes and the main lake,the humification degree of DOM in the sub-lakes was slightly higher than that in the main lake.(2)Five humic-like components(C1,C2,C3,C5 and C7)and two protein-like components(C4 and C6)were resolved by PARAFAC,and humic-like components were mainly present in DOM with relatively small molecular weights,while protein-like substances mainly existed in DOM with relatively large molecular weights.The autogenous characteristics of small molecular weight DOM were relatively strong,and it also has terrestrial sources.The average particle size of soil samples was PYH 12>PYH 4>DX 12,while the sediment fluorescence intensity was PYH 4>DX 12>PYH12.In the three sediments,mean antibiotic concentration in DOM reached a maximum value at the molecular weight range of 1～10 KDa,that is,DOM with small molecular weights were better at adsorbing the selected antibiotic.The partition coefficient K_dvalue of DOM of different molecular weights was generally greater than 1,indicating that DOM had stronger adsorption capacity for these four antibiotics.Equilibrium dialysis experiments showed that DOC concentration had less promoting effect on the adsorption of antibiotics in DOM.In different environmental media,increased DOM concentrations may also inhibit antibiotic adsorption.The results of redundancy analysis showed that DOM and tyrosine-like substances mainly from autogenic sources had inhibitory effects on the adsorption of antibiotics,while CDOM concentration,DOM humification degree and aromatization had a promoting effect on the adsorption of these four antibiotics.