Fluorescent EEM-PARAFAC considerations of Aldrich humic acid salt as an aquatic or terrestrial organic matter surrogate

The fluorescence of “long dead” terrestrially sourced organic carbon (Aldrich humic acid salt) was compared to “recently dead or excreted” aquatically sourced organic carbon (ornamental pond). This research eliminated the “living” (biologically active) category of organic carbon (by azide treatment and filtration) which prevented organic matter continuing to metabolize due to microbial activity during storage and analysis. The focus in this context is on the diagenetic (fulvic and humic) substances, which are considered the most recalcitrant organic carbon forms in water treatment. The purposes of this research were to investigate (a) what excitation-emission matrix (EEM) spectroscopy and PARAllel FACtor (PARAFAC) analysis (EEM-PARAFAC) modeling reveals about the limitations to the use of terrestrially derived Aldrich Humic Acid as an aquatic organic matter surrogate, (b) potential flaws observed in EEM spectra and incorrect PARAFAC component assignments gathered in contemporaneous studies, and (c) how EEM-PARAFAC modeling can be used to illustrate the continuum in organic matter aging or maturity. Additionally, to expand the analysis, data were compared to previously published PARAFAC models derived from other freshwater sources. An important result of this research was discovery of a PARAFAC component peak observed at the emission (EM) wavelength at 540 nm in Aldrich Humic Acid which has been rarely noted in the literature, and not previously recognized for its potential importance. This research implies that Aldrich humic acid should only be used as an aquatic surrogate with caution, and that it can be a surrogate for terrestrial soil or ore samples. • Longer fluorescence emission ranges up to 800 nm are recommended when scanning EEMs. • Aldrich humic acid PARAFAC component at EM 540 nm not observed in aquatic samples. • 20 % percent variance captured by Aldrich only PARAFAC model for EM 540 nm component. • Aldrich humic acid ore can be a surrogate for terrestrial soil or ore samples. • Aldrich humic acid should only be used as an aquatic surrogate with caution.