Effect of acid mine drainage on colloidal organic matter in the river: Changes in composition and copper binding behavior

Abstract

Acid mine drainage (AMD) releases heavy metals, deteriorating the regional environment. Copper (Cu) is often found in AMD, and the migration and transformation are controlled by colloidal organic matter (COM). In this study, COM in the AMD-affected river was extracted by ultrafiltration, compositions of COM were detected by ultraviolet–visible and fluorescence spectra, and the binding behavior of COM with Cu was revealed by two-dimensional correlation spectroscopy analysis of synchronous fluorescence. The results found that COM in the AMD-affected river mainly originated from autochthonous sources, including microbial-derived humic-like, fulvic-like, and tryptophan-like fluorescence components. The fluorescence proportion of the first two was relatively higher, accounting for 78.71–83.90% in river and 78.65–91.03% in sediment. AMD decreased riverine COC by 0.24 mg·L⁻¹ and a(350) by 13.83%, but increased the aromaticity and molecular weight of riverine COM downstream, while AMD increased COM contents in river sediment. The redundancy analysis found the explanatory power of Cu was 44.4%, and thus Cu was the primary environmental driving factor in the AMD-affected river. Fluorescence quenching titration found that microbial-derived humic-like substances were the most sensitive to Cu(II) titration. Cu(II) was preferentially bound to fulvic-like substances of riverine COM and with tryptophan-like substances of sediment COM. AMD delayed the binding sequences of tryptophan-like substances in riverine COM at the inlet and fulvic-like substances in downstream sediment COM with Cu(II), and weakened the binding affinity of COM with Cu(Ⅱ) at 2.03%–6.61% in downstream sediment to increase the risks of heavy metal pollution.