Evaluation of the Interactions between Water Extractable Soil Organic Matter and Metal Cations (Cu(II), Eu(III)) Using Excitation-Emission Matrix Combined with Parallel Factor Analysis.

Jing Wei,Jing Song,Lu Han,Mengfang Chen

doi:10.3390/ijms160714464

Abstract

The objectives of this study were to evaluate the binding behavior of Cu(II) and Eu(III) with water extractable organic matter (WEOM) in soil, and assess the competitive effect of the cations. Excitation-emission matrix (EEM) fluorescence spectrometry was used in combination with parallel factor analysis (PARAFAC) to obtain four WEOM components: fulvic-like, humic-like, microbial degraded humic-like, and protein-like substances. Fluorescence titration experiments were performed to obtain the binding parameters of PARAFAC-derived components with Cu(II) and Eu(III). The conditional complexation stability constants (logKM) of Cu(II) with the four components ranged from 5.49 to 5.94, and the Eu(III) logKM values were between 5.26 to 5.81. The component-specific binding parameters obtained from competitive binding experiments revealed that Cu(II) and Eu(III) competed for the same binding sites on the WEOM components. These results would help understand the molecular binding mechanisms of Cu(II) and Eu(III) with WEOM in soil environment.

Highlights

Dissolved organic matter (DOM) is ubiquitous in soil system
Trace metals complexation with DOM remains poorly defined at the molecular scale under relevant environmental conditions, such as low concentrations of metals relative to DOM [5]
Visual inspection of the water extractable organic matter (WEOM) spectrum suggests the presence of three fluorophores at Excitation/Emission (Ex/Em) wavelength pairs of 230/440, 330/400, and 350/450 nm

Summary

Introduction

Dissolved organic matter (DOM) is ubiquitous in soil system. Being small in weight percentages, DOM is the most labile and reactive fraction of the multicomponent soil organic matter pool. As DOM plays a significant role in the biogeochemical cycling of trace metals, remarkable efforts have been made to classify the processes involved in trace metal interacting with DOM, through both experimental and modeling approaches [1,2,3]. Determination of metal binding constants with DOM is still hampered, due to the intrinsic complexity of DOM, the lack of stoichiometric information, and analytical limitations [4]. Trace metals complexation with DOM remains poorly defined at the molecular scale under relevant environmental conditions, such as low concentrations of metals relative to DOM [5]

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Conclusion