Characterization Of Dissolved Organic Matter In Sediments From The Urbanized Rivers And Its Interactions With Heavy Metals

Dissolved organic matter(DOM)is ubiquitous in the environment,which can affect the speciation,distribution,bioavailability,and transformation of pollutant mixtures.The variations of DOM and heavy metals are complicated in urbanized rivers due to effluents from industrial wastewater and domestic sewage.The heavy metal contamination has been a worldwide concern due to its toxicity,persistence,bioavailability,complexation with DOM in aquatic environment,which would cause deleterious effects on the health of ecological environment and human in urban.Therefore,a comprehensive understanding of DOM fractions and its binding mechanisms with heavy metals could provide a theoretical guide for the treatment and management of the compound pollution in urbanized rivers.Ultraviolet visible spectroscopy(UV-Vis)and three-dimensional excitationemission matrix fluorescence spectroscopy(3DEEMs)combined with parallel factors analysis(PARAFAC)were applied for investigating the DOM fractions in sediments.Two-dimensional correlation spectroscopy(2D-COS),hierarchical cluster analysis(HCA),structural equation modeling(SEM),and canonical correlation analysis(CCA)were used to analyze the spatial distribution of physic-chemical parameters and DOM fractions.Quenching titration experiments coupled with a modified Stern-Volmer model were carried out to evaluate the interaction between DOM and heavy metals from Xihe River,an urbanized river,in Shenyang City of China.The principal results are as follows:(1)The distribution of heavy metals and DOM fractions was inconsistency in sediments from Xihe River,both of them affected by anthropogenic activities.The concentrations of Cd,Cu,Hg and Zn were 15.18-51.69 times higher than its background values,indicating the Xihe River seriously polluted.As,Cr,Ni and Pb were closed to its background values in sediments of Xihe River.The values of fluorescence indexes were closed to 1.9,and the biological index values were larger than 1.0 in surface sediments.Both of them decreased with the increase of the sediment depth.Five fluorescent components were extracted from the DOM in Xihe River,i.e.,tyrosine-like,tryptohan-like,microbial humic-like,fulvic-like,and humic-like,among which tryptohan-like and fulvic-like were dominated.The fluorescence intensity of tryptohanlike in the upstream were highest,and fulvic-like showed the opposite trend to tryptohan-like.This indicated that the composition of DOM was affected by anthropogenic activities.(2)Nutrients,protein-like,and humic could impact the distribution of heavy metals,and the weights of them were inconsistency.Nutrients(44.72%)had higher effect on heavy metals than humic(29.59%)and protein-like(25.69%).Nutrients mainly affected heavy metal pollution through total carbon(12.28%),total organic carbon(11.37%),and total nitrogen(11.37%).Protein-like mainly affected heavy metal pollution through the relative molecular mass(10.99%),and humic mainly affected heavy metal pollution through microbial humic-like(7.62%),fulvic-like(8.10%),and humic-like(7.62%).(3)The binding mechanisms of DOM with heavy metals can be determined by binding parameters of DOM with heavy metals.The binding ratio of fluorescent components with copper ions showed a trend of first increasing and then decreasing with the increase of sediment depth.In the upstream and downstream,the binding parameters of fulvic-like(0.06-1.00)with copper were largest,and the microbial humic-like(0.11-0.78)was lowest.The tryptohan-like(0.03-1.00)was stronger than other substances in the midstream,which might attributed to the point sources.Additionally,the binding parameters of DOM fractions with copper from farmland recession were higher than that from industrial wastewater and domestic sewage.