HR: 10:50h
AN: B11E-03    [PDF]
TI: Effects of Fe on Physicochemical Characteristics of Natural Organic Matter
AU: * Maurice, P A
EM: pmaurice@nd.edu
AF: University of Notre Dame, Dept. of Civil Engineering & Geological Sciences, Notre Dame, IN 46556 United States
AU: Pullin, M J
EM: mpullin@nd.edu
AF: University of Notre Dame, Dept. of Civil Engineering & Geological Sciences, Notre Dame, IN 46556 United States
AU: Anthony, C
EM: canthony@nd.edu
AF: University of Notre Dame, Dept. of Civil Engineering & Geological Sciences, Notre Dame, IN 46556 United States
AB: Natural organic matter (NOM) is ubiquitous in aquatic and terrestrial environments, and it plays an important role in controlling many biogeochemical processes. NOM molecular weight (MW) is a key property that affects NOM reactivity. Polyvalent metals such as Fe and Al bind strongly to NOM and also can cause its coagulation. Thus, we hypothesized that the presence of Fe would affect NOM MW determinations, even at relatively low Fe and NOM concentrations. This hypothesis was tested by adding increasing amounts of Fe(III) to aqueous solutions of NOM isolate (XAD-8) at pH 5.5, in the dark, and following changes in the NOM MW (measured by size exclusion chromatography), absorbance, and fluorescence. No change in MW was observed to 3 uM total Fe concentration, but at 10 uM total Fe concentration, there was a loss of low MW components and an increase in higher MW components. The weight average MW increased from 3661 Da to 3975 Da. Absorbance at 254 nm (typically monitored in water treatment processes) was unchanged by added Fe, but absorbance increase over parts of the visible spectrum (350-600 nm), and decreased in the far UV (200-225 nm), thus altering spectral slope. The two fluorescence maxima observed for this sample (Ex 325, Em 450; Ex 230, Em 435) decreased in intensity with increasing Fe concentration, with no shift in peak location. These results have important implications for our understanding of the concept of 'molecular weight' as applied to NOM, and for NOM reactivity including bioavailability, adsorption, and other processes.
DE: 0317 Chemical kinetic and photochemical properties
DE: 0330 Geochemical cycles
SC: Biogeosciences [B]
MN: 2003 Fall Meeting