Optical characteristic of humic acids from lake sediments by excitation-emission matrix fluorescence with PARAFAC model

Lilla Mielnik,Piotr Kowalczuk

doi:10.1007/s11368-018-1947-x

Abstract

PurposeThe study aimed to find out whether fluorescence parameters of humic acids (HA), obtained from excitation-emission matrix (EEM) fluorescence spectra, could be used to explain the origin and properties of lake sediments organic matter.Materials and methodsThe research material was HA extracted from lake sediments. Sediment samples were collected in the summer stagnation, from maximum depth of each lake. Humic acids extraction was performed using the method proposed by the International Humic Substances Society. In extracted HA, the elemental composition, free radical content, UV-Vis, and EEM fluorescence spectra were determined. EEM spectral modeling was performed using a multidirectional statistical method—parallel factor analysis PARAFAC.Results and discussionFour specific, two protein-like (C2 and C4) and humic- and fulvic-like (C1 and C3) components, components responsible for emission of fluorescence were identified in HA extracted from lake sediments. In the obtained EEM spectra, the dominant component was C2, while the smallest participation have C4 component. The mean contribution of C3 and C1 components to the total intensity of fluorescence was almost the same and was about 25%. Significant correlations were obtained between the concentration of EEM components and parameters characterizing the chemical properties of sediments and humic acids.ConclusionsThe study showed that the EEM fluorescence spectroscopy can be successfully used to characterize natural organic matter in aquatic environments. This method may provide supplementary information on the origin and transformation of organic matter in the water environments. By applying the parameters obtained from PARAFAC modeling, the relative degree of organic matter transformation (component C1) and autotrophic productivity (component C3) may be assessed. The analysis of the component C1 and C4 complete the information about the organic matter origin.

Highlights

Photoluminescent methods are significant tools to study natural organic matter (NOM) of various origins
There are available some results of studies in which excitation-emission matrix (EEM) fluorescence spectroscopy was used for characteristics of humic substances (HS) extracted from soil and lake sediments (Mobed et al 1996; Alberts and Takács 2004; Sierra et al 2005; Tang et al 2011; Derrien et al 2017) and their interactions with trace metals and organic contaminants, as pesticides, endocrine disruptors, PAHs, etc
Optical properties of humic acids (HA) extracted from bottom sediments of selected lobelia lakes were compared to the parameters describing structural and chemical properties of them in order to identify characteristic features which enable evaluation of various environmental changes

Summary

Introduction

Photoluminescent methods are significant tools to study natural organic matter (NOM) of various origins. Excitation-emission matrix (EEM) fluorescence spectroscopy, which records matrix excitation and emission spectra, has become a prevalent method to characterize OM originated from different environments. There are available some results of studies in which EEM fluorescence spectroscopy was used for characteristics of HS extracted from soil and lake sediments (Mobed et al 1996; Alberts and Takács 2004; Sierra et al 2005; Tang et al 2011; Derrien et al 2017) and their interactions with trace metals and organic contaminants, as pesticides, endocrine disruptors, PAHs, etc. The EEM fluorescence spectroscopy is often used in studies on interactions of humic substances with organic pollutants (Fukushima et al 1997; Provenzano et al 2004; Plaza et al 2006; Sun et al 2007)

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