4:15 PM - 4:30 PM
[MAG39-10] Classification and ion complexation properties of natural organic matters in deep groundwater using fluorescence spectroscopy and multivariate analysis
Keywords:Natural organic matters, Complexation, Emission excitation matrix, Multivariate analysis
Natural organic matters (NOMs) in groundwater play an important role for migration of radionuclides in subsurface environments, binding them to their active functional groups. NOMs are collectively defined as a group of various organic matters such as humic substances, biomolecules, and small organic molecules; they are poorly defined organic matters with various properties as polyfunctional polyelectrolytes. For NOMs in surface environments binding properties with a wide range of metal ions have been studied, and mechanistic models which can describe ion binding to NOMs over ranges of various environmental conditions are proposed. Nevertheless, the applicability of such models to deep groundwater NOMs remain unclear due to the considerable differences between deep groundwater NOMSs and their counterparts in surface environments.
This study aims to investigate the relationship of different NOM components in deep underground environments and their binding properties for metal ions with geochemical parameters of groundwater by combining emission-excitation-matrix (EEM) measurements and multivariate analyses. EEM is a type of fluorescence spectroscopy method which measures emission spectra by scanning excitation wavelength. EEM becomes a very powerful tool to study complex samples with multiple fluorescence components by combining PARAFAC (parallel factor analysis), which can reveal the number, concentration and EEM of fluorescent components in the entire dataset. We applied this EEM-PARAFAC to sedimentary groundwater samples collected from boring holes of various depths and locations in the Horonobe underground research laboratory operated by Japan Atomic Energy Agency (JAEA). The samples were amended with Eu3+, a known chemical homologue of trivalent actinide ions such as Am3+ and Cm3+. The binding of metals ions to NOM leads to a decrease of its fluorescence (quenching), which can be used to quantify the binding ability of NOM for the metal ion. The obtained EEM components and their Eu3+ binding properties from a set of groundwater samples were further correlated to groundwater geochemical parameters, using PLS (Partial Least Squares) to reveal the origins of the different components and reasons of their different Eu3+ binding properties.
This study aims to investigate the relationship of different NOM components in deep underground environments and their binding properties for metal ions with geochemical parameters of groundwater by combining emission-excitation-matrix (EEM) measurements and multivariate analyses. EEM is a type of fluorescence spectroscopy method which measures emission spectra by scanning excitation wavelength. EEM becomes a very powerful tool to study complex samples with multiple fluorescence components by combining PARAFAC (parallel factor analysis), which can reveal the number, concentration and EEM of fluorescent components in the entire dataset. We applied this EEM-PARAFAC to sedimentary groundwater samples collected from boring holes of various depths and locations in the Horonobe underground research laboratory operated by Japan Atomic Energy Agency (JAEA). The samples were amended with Eu3+, a known chemical homologue of trivalent actinide ions such as Am3+ and Cm3+. The binding of metals ions to NOM leads to a decrease of its fluorescence (quenching), which can be used to quantify the binding ability of NOM for the metal ion. The obtained EEM components and their Eu3+ binding properties from a set of groundwater samples were further correlated to groundwater geochemical parameters, using PLS (Partial Least Squares) to reveal the origins of the different components and reasons of their different Eu3+ binding properties.