Binding characteristics of cadmium and zinc onto soil organic matter in different water managements and rhizosphere environments.

Soil organic matter (SOM) could immobilize most of metals, but it could promote the migration of a small part of metals in special environments. Heavy rainfall and drought makes wetlands affected by the alternation of drought and flood, altering the mobility of metals. Few studies have been conducted on the changes of binding characteristics of metals onto SOM which derived from different water conditions and rhizospheric environments. The objective of this paper was to explore the sequential differences of spectral variations of fluorescent groups and UV-Vis groups of metals onto SOM which derived from different water managements and rhizospheric environments. The method adopted was mainly two-dimensional correlation analysis (2DCOS). The results showed that flooding samples contained more aromatic substances compared to draining samples, which could promote metal binding. The binding characteristics were shown in the following: (1) Cd2+ and Zn2+ could react with aromatic substances, react with functional groups in SOM, and promote the formation of new groups such as carboxyl; (2) both Zn2+ and Cd2+ could bind with functional groups on proteins but relatively reductive environment can weaken the binding ability of Cd2+; (3) the protein-like or fulvic-like groups gave the fastest responses and then came the amide and carboxyl groups in nearly all flooding samples; (4) in flooding samples, Cd2+ was most easily to bind with fulvic-like groups, while Zn2+ was most easily to bind with protein-like groups. This work is conducive to the long-term management of heavy metal pollutants in wetlands.