The Binding Properties of Cu²⁺ onto Dissolved Organic Matter from Mushroom Residue and Rice Straw Compost

Dissolved organic matter (DOM) within compost readily complexes with heavy metals, influencing their migration and transformation in the natural environment. In this study, three-dimensional fluorescence-parallel factor (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2DCOS) protocol were used to comprehensively analyze the binding properties of Cu²⁺ onto DOM derived from mushroom residue compost (MRC) and rice straw compost (RSC). The EEM-PARAFAC results show that the two compost-derived DOM primarily comprised humic-like acid (C1), fulvic-like acid (C2) and protein-like substances (C3). These components accounted for 43%, 32% and 25% of the total fluorescence for MRC-DOM, and 39%, 29% and 32% for RSC-DOM, respectively. During the interaction between the compost-derived DOM and Cu²⁺, the fluorescence intensity of the three PARAFAC-derived components consistently decreased. The result indicate that both the MRC-DOM and RSC-DOM had significant complexing affinities with Cu²⁺. Moreover, the lg K of fluorescent components in MRC- and RSC-DOM was between 4.54 to 4.76, and followed the order of C3> C1> C2. The results suggest that the protein-like components exhibited a stronger binding ability to Cu²⁺ than humic-like acid and fulvic-like acid substances in both types of compost DOM. 2DCOS further confirm that protein-like fluorescent components had the highest binding affinity to Cu²⁺, while fulvic-like components exhibited a preferential reaction with Cu²⁺. In total, protein-like and humic-like substances within MRC- and RSC-DOM emerged as pivotal components for complexing with Cu²⁺. Furthermore, both types of compost-derived DOM exhibited similar binding behaviors, including the active binding sites, capacity and preferential sequence. These findings provide an important theoretical basis for comprehending the impact of compost application on the migration and transformation behavior of soil-bound Cu²⁺.