Characterizing Molecular Weight Distribution and Optical Properties of Dissolved Organic Matter and Unraveling the Origins of Anthropogenic Fluorophores in Yangtze River and Its Tributaries

In this study, size exclusion chromatography (SEC) coupled with multiple detectors was used to characterize the composition, molecular weight (MW), and optical properties of dissolved organic matter (DOM) in the Yangtze River main stream and its 88 tributaries. The SEC chromatograms revealed that DOM in the investigated water samples mainly comprised nonhumic proteinaceous biopolymers with apparent MW > 20 kDa and humic substances with apparent MW ranging from similar to 0.5 to similar to 7 kDa. The SEC fluorescence chromatograms further unraveled that there was a kind of characteristic fulvic-acid-like fluorophore in downstream tributaries, which showed triple-excitation peaks at similar to 250, 310, and 365 nm with an emission peak at similar to 460 nm (designated as HS-Em460-Ex3 hereinafter). Via field investigation and parallel factor analysis, this characteristic HS-Em460-Ex3 fluorophore was identified to originate from the discharge of residual naphthol and naphthylamine moieties in biologically treated textile wastewater. The SEC fluorescence fingerprints also demonstrated the occurrence of the characteristic HS-Em460-Ex3 fluorophore in the Yangtze River main stream from Changzhou to Nantong, suggesting that the discharge of textile wastewater might have altered the optical properties of riverine DOM and advanced treatment processes should be applied to eliminate residual aromatic fluorophores in textile wastewater.

Automated summary

This study used size exclusion chromatography (SEC) coupled with multiple detectors to analyze the dissolved organic matter (DOM) in the Yangtze River and its tributaries. The results showed that the DOM mainly consisted of proteinaceous biopolymers and humic substances. A characteristic fulvic-acid-like fluorophore was found in downstream tributaries, which originated from the discharge of residual naphthol and naphthylamine moieties in biologically treated textile wastewater. The occurrence of this fluorophore in the Yangtze River main stream suggested that the discharge of textile wastewater had altered the optical properties of riverine DOM, emphasizing the importance of advanced treatment processes.