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.