Molecular Weight-Dependent Binding Heterogeneity of Heavy Metals with Dissolved Organic Matter in Plateau Waters: Insights from EEM-PARAFAC and moving-window

This study investigated the binding interactions between heavy metals (Cu2+, Pb2+ and Cd2+) and size-fractionated dissolved organic matter (DOM) derived from plateau lake and river waters, combining fluorescence excitation-emission matrix (EEM) spectroscopy, parallel factor analysis (PARAFAC), and two-dimensional correlation spectroscopy (2D-COS). The results reveal significant heterogeneity in DOM-metal binding behaviors, driven by DOM source (autochthonous vs. allochthonous), molecular weight (high vs. low), and metal type. Cu2+ exhibited the strongest binding affinity, particularly with humic-like components in high-MW DOM, while Cd2+ showed minimal interaction. Protein-like materials in low-MW DOM facilitated metal mobility, whereas aromatic-rich high-MW DOM promoted metal sequestration. Moving-window 2D-COS (MW2D-COS) further identified critical concentration thresholds for metal-induced DOM structural changes. These findings highlight the dual role of DOM in mitigating or exacerbating heavy metal pollution, with implications for water quality management, ecological risk assessment, and remediation strategies in aquatic systems. Advanced spectral techniques proved effective in deciphering DOM-metal dynamics, offering a framework for predictive modeling and targeted pollution control.