Applying synchronous fluorescence spectroscopy combined with Gaussian band fitting and two-dimensional correlation to characterize interactions of copper (II) with dissolved organic matter from urban river sediments

Abstract

Dissolved organic matter (DOM) and heavy metals can form strong complexes, which might determine distribution, toxicity, bioavailability, and environmental trend of heavy metals in aquatic environment. Synchronous fluorescence spectroscopy combined with Gaussian band fitting and two-dimensional correlation (2DCOS) was applied to characterize Cu2+ interactions with DOM fractions from sediments in Xihe River. DOM from four layers was mainly associated with tyrosine-like (TYLF), tryptophan-like (TRLF), microbial humic-like (MHLF), fulvic-like (FLF), and humic-like fluorescence (HLF) substances based on Gaussian band fitting. At the first layer, the f value of FLF was the highest among five components, while TRLF at the second and third layers represented the highest f values. Besides, at the fourth layer, the f value of TYLF was the highest. According to 2DCOS and moving window 2DCOS, the decreasing binding sensitivities were HLF→MHLF→TYLF→TRLF→FLF in the first layer, which almost represented high efficiencies at 40 μM Cu2+. The binding order was MHLF→HLF→FLF→TRLF→TYLF in the second layer, where TYLF and TRLF shared the identical efficiencies at 120 μM Cu2+. For the third layer, the varying order was TYLF→FLF→TRLF→MHLF→HLF, whose high efficiencies occurred at 10 μM Cu2+. In the fourth layer, the order was TYLF→FLF→MHLF→TRLF→HLF, whose efficiencies almost covered whole titrate concentrations. At a given layer, structural equation model showed Cu2+ concentration negatively affected the fluorescence intensity of DOM components except FLF at the substrate layer. This study might provide an effective method to illustrate the interaction mechanism of the heavy metals and DOM fractions.