Dissolved organic matter (DOM) molecular models are controversial because they portray complex mixtures as discrete molecular structures. These models have progressed from representing organic solute macromolecules (ORSMAC) from a cartoon caterpillar structure in 1976 to a three-dimensional nucleophilic clamshell charge-transfer complex structure in 2016. Advances in DOM isolation and fractionation methods have reduced mixture complexity to where estimates of compound class precursors and metabolites are represented by the models. Molecular models are constructed by combining elemental analyses, infrared spectrometry, mass spectrometry, nuclear magnetic resonance spectrometry, and titrimetric data.  Ultrahigh resolution mass spectrometry is currently providing elemental analyses of discrete DOM compounds. The molecular model approach has shown that Suwannee River DOM is derived from carbohydrate, lignin, tannin, and terpenoid precursors; the Santa Ana River in Orange County, CA sampled before and after storm flow contained DOM derived from N-acetyl amino sugars, proteins, terpenoids plus cyanuric acid and black carbon during storm flow; DOM isolated from the Great Salt Lake contained N-acetyl aldaric acids, N-acetyl amino sugars, and carboxyl-rich alicyclic molecules (CRAM); and DOM isolated from deep-ocean seawater contained N-acetyl amino sugars, CRAM, and lactam carboxylic acids likely derived from oxidation of porphyrins in algae.   With regard to DOM composition in wastewaters, various reclaimed waters contained benzene sulfonic acids, polyethylene and polypropylene glycol carboxylic acids, and alkylphenol carboxylic acids as major components. Chlorinated benzene sulfonic acids derived from DDT synthesis were found in large concentrations in wastewater from the Stringfellow Superfund Site near Riverside, California.  DOM composition in a nutrient-rich, highly-reducing swine wastewater lagoon was largely composed of fatty acids and hydrocinnamic  plus phenyl acetic acids derived from the reductive degradation of lignin.  These above examples of various compound classes estimated by molecular modeling provide comprehensive assessments of DOM in various waters.<br/>

In defense of DOM molecular models

253rd National Meeting (2017)

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