Differential absorbance spectroscopy of mercury-induced changes in dissolved organic matter: Influence of DOM aromaticity.

Mercury addition to dissolved organic matter (DOM) can induce changes in its optical properties that may be detected using differential absorbance spectra (DAS). This study evaluated the influence of DOM aromaticity on mercury-induced DAS responses using acetic acid, l-tyrosine, and tannic acid as model compounds representing different molecular and chromophoric characteristics, together with peat water and upland river water as contrasting natural-water matrices. Ultraviolet-visible (UV-Vis) spectra were recorded from 200 to 800 nm, with characteristic DAS responses observed at Δ229, Δ222, and Δ216 for acetic acid, tyrosine, and tannic acid, respectively. The three model compounds showed strong concentration-dependent relationships with mercury concentration, with coefficients of determination (R2) of 0.8905, 0.9026, and 0.9094, respectively. Natural-water samples also exhibited concentration-dependent DAS responses, with logarithmic relationships over 0.01-10 mg/L. Independent blind-spike recovery experiments using peat water and upland river water yielded recoveries of 88-101%. The results demonstrate measurable changes in DOM optical properties following mercury addition, with response magnitude varying among DOM matrices. DAS therefore shows potential as a rapid, non-destructive screening approach under the investigated conditions, while further validation using independent environmental samples and environmentally relevant mercury concentrations is required.