Li Dan, Lin Hui, Guo Laodong
School of Freshwater Sciences, University of Wisconsin-Milwaukee, 600 E Greenfield Ave., Milwaukee, WI, 53204, USA.
Ecology School, Shanghai Institute of Technology, Shanghai, 201418, China.
Environ Sci Pollut Res Int. 2023 Apr;30(20):57638-57652. doi: 10.1007/s11356-023-26398-3. Epub 2023 Mar 27.
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.
腐殖酸（HA）和参考天然有机物（NOM）已广泛应用于环境评估、生物地球化学和生态毒性研究。然而，常用的模型/参考NOM与大量溶解有机物（DOM）之间的异同很少得到系统评估。在本研究中，同时对来自国际腐殖质协会的HA、SNOM（苏万尼河NOM）和MNOM（密西西比河NOM）以及新鲜采集的未分级NOM（FNOM）进行了表征，以评估它们的异质性和尺寸依赖性化学性质。我们发现，分子量分布、PARAFAC衍生的荧光成分以及尺寸依赖性光学性质具有NOM特异性，并且随pH值变化很大。<1 kDa的DOM丰度顺序为HA < SNOM < MNOM < FNOM。此外，FNOM更亲水，含有更多类似蛋白质和自源的成分，具有更高的紫外吸光度比指数（URI）和生物荧光指数，而HA和SNOM含有更多的外源、类似腐殖质的成分，具有更高的芳香性和更低的URI。FNOM与模型/参考NOM之间在分子组成和尺寸光谱上的显著差异表明，应在相同实验条件下，在分子量和官能团水平上评估NOM的环境作用，并且HA和SNOM可能无法代表环境中的大量NOM。本研究提供了关于参考NOM与原位NOM在DOM尺寸光谱和化学性质方面异同的新信息，并强调需要更好地理解NOM在调节水生环境中污染物的毒性/生物有效性和环境归宿方面的异质作用。
