Mechanism of binding between dissolved organic matter and cadmium in constructed wetland sediments:taking a constructed wetland in Zhuzhou City as an example
In this study,the changes of differences between the components of sedimentary dissolved organic matter(DOM)in different seasons and stages of a constructed wetland,as well as their binding interactions with cadmium(Cd),were investigated.Various spectral characterization techniques,such as ultraviolet spectroscopy,fluorescence spectroscopy,Fourier-transform infrared spectroscopy(FTIR),and X-ray photoelectron spectroscopy(XPS),as well as parallel factor analysis(PARAFAC)and two-dimensional correlation spectroscopy(2D-COS),were used to analyze the DOM in the wetland sediments in spring and autumn.The results revealed that the DOM components in the wetland sediments were mainly derived from microbial activities,plant litter,and root exudates and were strongly hydrophilic and low in aromatics.The DOM contents in spring and autumn were 434 mg·kg-1 and 700 mg·kg-1,respectively,with those in spring being mainly composed of two kinds of proteins and two kinds of humus,while those in autumn comprised one kind of protein and three kinds of humus.Static quenching was the main Cd-quenching process of each DOM component,among which the protein residues in spring showed the most obvious effect with more than two types of binding sites.By contrast,the protein-and fulvic acid-like compounds in autumn formed monodentate complexes.Compared with the other components,the proteinoids and fulvic acid bound more strongly and stably to Cd,with binding between the proteinoids and Cd being preferred.In the binding process,Cd mainly interacted with the amide,phenolic hydroxyl,and carboxyl functional groups of DOM,with the amide group showing the fastest binding rate,followed by the phenolic hydroxyl and carboxyl groups.
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