Investigating binding characteristics of cadmium and copper to DOM derived from compost and rice straw using EEM-PARAFAC combined with two-dimensional FTIR correlation analyses.

The binding of Cd and Cu to dissolved organic matter (DOM) derived from compost (CP) and rice straw (ST) was studied through an approach combining parallel factor (PARAFAC) analysis and two-dimensional correlation spectroscopy (2DCOS). Both humic-like and protein-like substances have been observed in CP and ST. Comparing with the Cu, Cd exhibited a lower affinity to DOM, and the quenching curve of Cd failed to be fitted by the Ryan and Weber Model, indicating that the environmental risk caused by applying CP or ST to Cd-polluted soil should be considered. The stability constants (log K) of Cu ranged from 3.87 to 5.03, and a larger value was found in CP than those in ST. Protein-like component also showed obvious fluorescence quenching with heavy metals addition. Besides, in CP, phenol-OH and carboxyl showed the fastest response to Cd and Cu, respectively; however, in ST, amide group and phenol-OH displayed the fastest response to Cd and Cu, respectively. These results provide a more detailed knowledge of the interaction mechanism of heavy metals with DOM at the molecular level, which is of great significance for reasonable application of compost and rice straw and efficient control of heavy metal in farmland soil.