Identification of Dissolved Organic Matter Origin Using Molecular Level Analysis Methods

Natural organic matter (NOM) is ubiquitous; however, its characteristics are not fully understood because NOM is a complex organic mixture that reflects the surrounding ecosystem. Identification of its molecular structure provides information for evaluating its environmental reactivity and behavior. This study characterized NOM regarding its molecular structure. The characteristics of different types of NOM, depending on their origin, were investigated using various analytical methods such as pyrolysis-gas chromatography-mass spectrometry, size exclusion chromatography, and fluorescence spectrometry. NOM was collected from three different sites: river water, wetland, and wastewater treatment plant effluent. The molecular size of NOM followed the order wetland > river water > wastewater treatment plant effluent. The fluorescence spectra distinguished the differences among the samples. The effluent contained the highest proportion of protein-like peaks, and the wetland sample showed the highest humic-like substance peak. The origin of NOM was investigated by classifying the pyrolyzed fragments from each sample. NOM from wetlands contains a large amount of lignin, which originates from terrestrial substances. Proteins were the major biocomponents of the effluent sample. The NOM in the river water contained proteins and lignin-derived compounds. The results show that NOM can be clearly identified through molecular-level analysis methods.