Characteristics Of Dissolved Organic Matter And Complexation With Typical Heavy Metal Ions In The Waters Near The Yangtze River Estuary

Dissolved organic matter（DOM）is a mixture of different functional groups and complex molecular structures,including humic acid,protein and carbohydrate.As an important carrier of carbon cycle,dissolved organic matter widely exists in water and sediment environment,which has an important impact on the migration and transformation process of heavy metals and organic pollutants.Dissolved organic carbon（DOC）refers to the dissolved organic carbon contents in DOM,and the dissolved organic carbon（DOC）is abundant in the Marine system,and it is one of the largest circulating reservoirs of organic matter on Earth.In this paper,DOM in the water bodies and sediments near the Yangtze River Estuary is taken as the research object.Based on the distribution characteristics and composition structure of DOM,the composition and structure characteristics of DOM are explored by parallel factor method combined with characteristic parameters of fluorescence spectrum.The complexation characteristics between DOM and heavy metal ions were explored by fluorescence quenching titration experiment combined with Stern-Volmer model,which provided a basis for environmental protection and pollution prevention in the waters near the Yangtze River Estuary.The main research conclusions are summarized as follows:（1）The concentration of DOC in autumn（2.76mg/L）was the highest,followed by summer（2.56mg/L）,spring（1.96mg/L）and winter（2.11mg/L）,and the difference was not significant.The regional distribution of DOC concentration was characterized as3.20mg/L in the South Branch and Beigang（2.21mg/L）in the North branch and1.82mg/L in the North branch.DOM in water can be divided into four components,namely,aromatic amino acid component C1,terrestrial and Marine source humus component C2,tryptophan-like component C3,and Marine source humus component C4.There is homology among components C1,C2 and C3,in which C1 and C2 occupy the dominant position,followed by C3,and C4 occupies the smallest proportion.The proportion of components C1 and C4 increased with the increase of offshore distance,while the proportion of components C3 decreased.The proportion of component C1was the largest in winter and the smallest in summer,while the proportion of component C3 and C1 was opposite.The analysis results of fluorescence characteristic parameters showed that most of the DOM in the water body was the interaction between terrigenous input and the endogenous activities of aquatic organisms,and the autogenic characteristics were significant,while the humification characteristics were weak.（2）The average contents of Cr,Cu,Hg,Pb and Zn in sediments near the Yangtze River Estuary were 9.08μg/g,5.98μg/g,2.78μg/g,2.91μg/g and 75.15μg/g,respectively.Except Hg,the high values of heavy metal content were found in the northern port of the South Branch and the coast of the North Branch.The concentration of DOC in sediments ranged from 4.29 to 13.63mg/L,with an average value of 8.65mg/L.The concentration of DOC in sediments in summer was higher than that in autumn,which was somewhat different from that in water,and the regional distribution was consistent with that in water.DOM in sediments can be divided into three components,namely,Marine humus component C1,terrestrial humus component C2 and tryptophan-like component C3.Marine humus component C1 occupies the dominant position,while terrestrial humus component C2 occupies the smallest proportion,and there is no significant difference in the distribution characteristics of each component.The characteristic parameters of UV-visible absorption spectra showed that the relative molecular weight of DOM in sediments from the northern port of the southern branch was larger,while that of DOM in the northern branch was smaller.The humus components of DOM in sediments are mainly humic acid,and the humification degree is strong.The humification characteristics of DOM in sediments in the North port of the southern branch are strong,and the humification characteristics of DOM in summer are significantly stronger than that in autumn.DOM hydrophobicity in sediments showed that DOM hydrophobicity in sediments of Beisha in Beigang was stronger,while DOM hydrophobicity in the northern branch was weaker.In terms of seasonal distribution,DOM hydrophobicity in summer was stronger than that in autumn.The distribution characteristics of aromatic and hydrophobicity were consistent,mainly because the aromatic structure of DOM mainly existed in hydrophobic components.（3）The synchronous fluorescence spectra of DOM and heavy metal ions in sediments near the Yangtze River Estuary showed that DOM and heavy metal ions had different degrees of complexation,and the complexation between protein-like components and heavy metal ions was significantly stronger than that between humus-like components.The reduction of fluorescence intensity of DOM components after complexation with heavy metal ions indicated that the complexation of DOM with Hg²⁺and Pb²⁺was stronger than that of other heavy metal ions,while the complexation of DOM with Cr³⁺was relatively weak.The complex stability constant indicated that the complexes between protein-like components C3 and heavy metal ions were more stable and had stronger complexation.Because protein-like components contained strong complexation sites such as nitrogen-containing groups,they showed stronger complexation ability.Two-dimensional correlation spectra showed that there were some differences in the complexation sites and complexation ability between DOM components and different heavy metal ions.The complexation sites at the positive peak of 285nm were preferentially compared with other sites,while the complexation sites at the negative peak were significantly different.The complexation sites of protein-like components were stronger than those of humus-like components.The complexation site strength of different heavy metal ions is DOM-Pb>DOM-Hg>DOM-Cu>DOM-Zn>DOM-Cr.