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

Abstract

Phenanthrene (Phe) is a toxin and is ubiquitous in the environment. The sediment humic substances (HS) that bind Phe affect the fate, transport, degradation, and ecotoxicology of Phe. This study investigated Phe sorption constants on size-fractioned HS extracted from river sediment. Fractions were identified as HHS (10 kDa to 0.45 µm), MHS (1-10 kDa), and LHS (<1 kDa). A fluorescence quenching (FQ) method was used to determine the Phe log K HS on size-fractioned HS; the values ranged from 3.97 to 4.68 L/kg-C. The sorption constant (log K HS ) is a surrogate of the binding capacity between HS and Phe, where a high log K HS reduces the toxicity and degradation of Phe. The log K HS values on HHS and MHS were significantly higher than the values on LHS (p = 0.015). The SUVA 254 values of HHS and MHS were also significantly higher than the LHS value (p = 0.047), while fluorescence index (FI) and S 275-295 values were significantly lower than the LHS values (p < 0.005). The HHS and MHS had a higher aromaticity and more terrestrial sources than LHS. The log K HS had a significant correlation with the selected optical indicators (p < 0.002), which suggested that the HS-bound Phe was positively affected by high aromaticity, terrestrial sources, and HS molecular weight. The results demonstrated that optical methods successfully obtained log K HS and the chemical properties of fractioned HS as well as the influenced factors of log K HS . Moreover, even the LHS had a capacity to bind with Phe.

Fluorescence Properties of the Air- and Freeze-Drying Treatment on Size-Fractioned Sediment Organic Matter

“…Moreover, SHS is a highly heterogeneous and complex organic mixture with a broad molecular weight range [5]. The chemical structure and composition of SHS and the molecular weight are significant properties that associate pollutants distribution, transport, and biotoxicity in an aquatic environment [6][7][8][9][10]. High molecular weight DOM and SHS have high specific surface areas and form aggregated structures by inter-or intra-molecular interactions within the DOM and SHS.…”

“…Fluorescence and ultraviolet spectroscopy are sensitive and fast techniques that are widely used to investigate the composition and structure of SHS [11,[22][23][24][25]. The aromaticity index (SUVA 254 ) and the humification index (HIX) have been widely employed to investigate the chemical properties of DOM and SHS [2,5,9,10,18,19]. Moreover, the fluorescence regional integration (FRI) method divides the excitation and emission matrix (EEM) into five regions and utilizes the fluorescence intensity at all EEM wavelength pairs for sample characterization [22,[26][27][28].…”

“…Additionally, collected sediment generally has been pre-treated with air-drying (AD) or freeze-drying (FD). These two pre-treatment methods have resulted in different SHS quantities and qualities [10,[32][33][34], due to biological activity. Shi et al [10] reported that AD pre-treated sediment had slightly lower pH, organic matter, and total organic carbon compared to the FD pre-treated sediment.…”

“…These two pre-treatment methods have resulted in different SHS quantities and qualities [10,[32][33][34], due to biological activity. Shi et al [10] reported that AD pre-treated sediment had slightly lower pH, organic matter, and total organic carbon compared to the FD pre-treated sediment. Since the SHS is a complex organic mixture with a wide-range molecular weight, size-fractioned SHS can be used as an effective method to investigate the differences between the chemical properties of SHS pre-treated by AD and FD [10].…”

“…Shi et al [10] reported that AD pre-treated sediment had slightly lower pH, organic matter, and total organic carbon compared to the FD pre-treated sediment. Since the SHS is a complex organic mixture with a wide-range molecular weight, size-fractioned SHS can be used as an effective method to investigate the differences between the chemical properties of SHS pre-treated by AD and FD [10]. This study investigated the SHS extracted from river sediment; it was pre-treated with both AD and FD methods.…”