Fluorescence of Size-Fractioned Humic Substance Extracted from Sediment and Its Effect on the Sorption of Phenanthrene

Insight into the hetero-interactions of 4-nonylphenol with dissolved organic matter: multiple spectroscopic methods, 1H NMR study and principal component analysis

Understanding the interactions between heterogeneous dissolved organic matter (DOM) and nonylphenols (NPs) is essential for predicting their behavior and fate in the environment. Herein, we firstly obtained different MW-fractionated humic acids (HAs) using the ultrafiltration method. Afterward, the molecular weight (MW)-dependent interactions of HAs with 4-nonylphenol (4-NP) were analysed by excitation emission matrix (EEM) fluorescence spectroscopy, fluorescence quenching, UV-vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and principal component analysis (PCA). EEM spectra indicated that the quenching mechanism was static. In the binding process, the higher MW fractions showed stronger interaction with 4-NP than the lower MW counterparts, exhibiting a clear MW-dependent interaction heterogeneity. The interaction constants for the 4-NP–HAs system were suppressed as the ionic strength decreased and pH increased, which was especially obvious in the binding of 4-NP to the lower MW-fractionated HAs. The FTIR spectra revealed that hydroxyl and aromatics were involved in the interaction process of HA fractions with 4-NP. It was also found from ¹H NMR that π–π interactions between aromatic rings of 4-NP and MW-fractionated HAs were responsible for the complexation. The correlation analysis and PCA results indicated that aromaticity and MW play important roles in the interaction process and confirmed an obvious interaction heterogeneity among MW-fractionated HAs samples. This work highlighted MW-dependent interaction heterogeneities of HA, which suggested that heterogeneity in MW distribution should be taken into consideration when exploring the fate and biogeochemistry cycling of 4-NP from contaminated environments.

Multiple spectroscopic methods, ¹H NMR study and PCA were used to investigate the heterointeractions of 4-nonylphenol with humic acids.

Differences in quinone redox system of humic substances between endemic and disease-free areas in Kashin-Beck disease-affected Changdu Region, Tibet, China

Kashin-Beck disease (KBD) is an endemic disease in China with the highest incidence rate in Tibet region. Promoted generation of oxygen free radicals by semiquinone structure of humic substance (HS) in drinking water was considered to be one of its pathogeneses. Therefore, detailed analysis of HS was performed in water and sediment samples collected from three endemic and three disease-free areas in Changdu Region, Tibet, China. After purification of the HS in the samples, the fractions of HS were characterized using electron paramagnetic resonance, ¹³C nuclear magnetic resonance, fluorescence spectroscopy with parallel factor analysis and Fourier transform infrared spectroscopy (FTIR). The organic carbon content of HS did not show a significant difference between endemic and disease-free areas or correlation with KBD-associated morbidity. Except FTIR, all techniques succeeded in characterization of the quinone redox system, indicating their validity and consistency. The quinone redox system in aquatic HS exhibited significantly higher level of the following indexes in endemic areas than disease-free areas: semiquinone radical content of fulvic acid (FA) (p < 0.05), aromaticity of FA (p < 0.05), fluorescence intensity (per gram carbon) of reduced quinone-like component of FA (p < 0.05) and humic acid (HA) (p < 0.1). Semiquinone radical content (r = 0.781, p < 0.1), aromaticity of FA (r = 0.891, p < 0.05), intensity of oxidized quinone-like component (r = 0.875, p < 0.05) and reduced quinone-like component of FA (r = 0.793 p < 0.1) showed medium to strong correlation with KBD-associated morbidity. Generally, the content of reduced quinone and aquatic FA showed stronger differences between endemic and disease-free areas than oxidized quinone and aquatic HA, respectively. The quinone redox system in sediment HS did not show any significant relationship with KBD. The present study is a successful attempt to combine the three indexes, semiquinone radical content, aromaticity and fluorescence intensity, in characterizing quinone redox system in HS, facilitating more comprehensive understanding of the characteristics of HS in KBD-affected regions.