Molecular insights into the bonding mechanisms between selenium and dissolved organic matter

Zhe Zhang; Lance M Miller; Huan He; Mallikarjuna N Nadagouda; Thomas Borch; Kevin E O'Shea; Dionysios D Dionysiou

doi:10.1016/j.scitotenv.2023.169429

Molecular insights into the bonding mechanisms between selenium and dissolved organic matter

Sci Total Environ. 2024 Mar 10:915:169429. doi: 10.1016/j.scitotenv.2023.169429. Epub 2023 Dec 19.

Authors

Zhe Zhang¹, Lance M Miller², Huan He³, Mallikarjuna N Nadagouda⁴, Thomas Borch⁵, Kevin E O'Shea⁶, Dionysios D Dionysiou⁷

Affiliations

¹ Environmental Engineering and Science Program, Department of Chemical and Environmental Engineering (DCEE), University of Cincinnati, OH 45221, USA.
² Department of Chemical Engineering, Purdue University, IN 47907, USA.
³ Environmental Science and Engineering, Kunming University of Science and Technology, Kunming 650500, China.
⁴ The U.S. Environmental Protection Agency, ORD, CESER, WID, CMTB, 26 W. Martin Luther King Jr. Drive, Cincinnati, OH 45268, USA.
⁵ Department of Soil and Crop Sciences and Department of Chemistry, Colorado State University, 1170 Campus Delivery, Fort Collins, CO 80523, USA.
⁶ Department of Chemistry and Biochemistry, Florida International University, University Park, Miami, FL 33199, USA. Electronic address: osheak@fiu.edu.
⁷ Environmental Engineering and Science Program, Department of Chemical and Environmental Engineering (DCEE), University of Cincinnati, OH 45221, USA. Electronic address: dionysdd@ucmail.uc.edu.

PMID: 38123086
DOI: 10.1016/j.scitotenv.2023.169429

Abstract

Natural organic matter (NOM) plays a critical role in the mobilization and bioavailability of metals and metalloids in the aquatic environment. Selenium (Se), an environmental contaminant of aquatic systems, has drawn increasing attention over the years. While Se is a vital micronutrient to human beings, animals and plants, excess Se intake may pose serious long-term risks. However, the interaction between Se and dissolved organic matter (DOM) remains relatively unexplored, especially the reaction mechanisms and interactions of specific NOM components of certain molecular weight and the corresponding functional group change. Herein, we report an investigation on the interactions between Se and DOM by focusing on the mass distribution profile change of operationally defined molecular weight fractions of humic acid (HA) and fulvic acid (FA). The results showed that across all molecular weights studied, HA fractions were more prone to enhanced aggregation upon introduction of Se into the system. For FA, the presence of Se species results in aggregation, dissociation, and redox reactions with the first two being the major mechanisms. Total organic carbon analysis (TOC), UV-vis spectroscopy (UV-vis), and Orbitrap MS data showed that [10, 30] kDa MW fraction had the largest aromatic decrease (CRAM-like, lignin-like and tannin-like) upon addition of SeO₂ via dissociation as the dominant mechanism. Fourier transform infrared spectroscopy (FT-IR) revealed that Se based bridging or chelation of functional groups from individual DOM components through hydrogen bonding in the form of SeO⋯H and possibly Se⋯H and/or attractive electrostatic interactions lead to aggregated DOM₁⋯Se⋯DOM₂. It was concluded from two-dimensional correlation analyses of excitation emission matrix (EEM) and FT-IR that the preferred Se-binding follows lipid ➔ peptide ➔ tannin ➔ aromatic functionalities. These results provide new understanding of Se interactions with various NOM components in aquatic environments and provide insight for Se assessing health risk and/or treatment of Se contaminated water.

Keywords: 2-D COS; Aggregation; Characterization; NOM; Natural organic matter; Selenium species.