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Comparisons in molecular weight distributions and size-dependent optical properties among model and reference natural dissolved organic matter. | LitMetric

Comparisons in molecular weight distributions and size-dependent optical properties among model and reference natural dissolved organic matter.

Environ Sci Pollut Res Int

School of Freshwater Sciences, University of Wisconsin-Milwaukee, 600 E Greenfield Ave., Milwaukee, WI, 53204, USA.

Published: April 2023

AI Article Synopsis

  • This study compares humic acid (HA) and natural organic matter (NOM) from different sources (Suwannee and Mississippi Rivers, and freshly collected NOM) to understand their characteristics and chemical properties.
  • Researchers found that the size, molecular weight distributions, and other chemical properties of NOM vary significantly with their source and pH levels, leading to differences in how they behave in the environment.
  • The findings suggest that commonly used model NOMs like HA and Suwannee NOM may not accurately represent the bulk organic matter found in natural settings, indicating a need for better evaluation of NOM’s roles in contaminant toxicity and bioavailability in aquatic ecosystems.

Article Abstract

Humic acid (HA) and reference natural organic matter (NOM) have been widely used in environmental assessment, biogeochemistry, and ecotoxicity studies. Nevertheless, similarities and differences among the commonly used model/reference NOMs and bulk dissolved organic matter (DOM) have rarely been systematically evaluated. In this study, HA, SNOM (Suwannee River NOM) and MNOM (Mississippi River NOM), both from International Humic Substances Society, and freshly collected unfractionated NOM (FNOM) were concurrently characterized to evaluate their heterogeneous nature and size-dependent chemical properties. We found that molecular weight distributions, PARAFAC-derived fluorescent components, and size-dependent optical properties are NOM-specific and highly variable with pH. The < 1 kDa DOM abundance followed the order of HA < SNOM < MNOM < FNOM. In addition, FNOM was more hydrophilic and contained more protein-like and autochthonous components with a higher UV-absorbance ratio index (URI) and biological fluorescence index, whereas HA and SNOM contained more allochthonous, humic-like components with a higher aromaticity and lower URI. Significant differences in molecular composition and size spectra between FNOM and model/reference NOMs suggest that environmental role of NOMs should be evaluated at the levels of molecular weight and functionalities under the same experimental conditions and that HA and SNOM may not represent bulk NOM in the environment. This study provides new information about similarities and differences in DOM size-spectra and chemical properties between reference NOMs and in-situ NOM and highlights the need to better understand the heterogenous roles of NOMs in regulating the toxicity/bioavailability and environmental fate of pollutants in aquatic environments.

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Source
http://dx.doi.org/10.1007/s11356-023-26398-3DOI Listing

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