SREL Reprint #2827

Characterization of Colloidal and Humic-Bound Ni and U In the "Dissolved" Fraction of Contaminated Sediment Extracts

Brian P. Jackson1, James F. Ranville2, Paul M. Bertsch1, and Andrew G. Sowder1

1Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina 29802
2Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401

Abstract: The dissolved phase of environmental aqueous samples is generall defined by filtration at 0.2 µm or even 0.45 µm. However, it is also acknowledged that colloids <0.2 µm suspended in the aqueous phase can be important for determining contaminant availability and mobility. We have used flow field-flow fractionation (FI FFF) and size exclusion chromatography (SEC) coupled to UV-absorbance (UVA) and inductively coupled plasma mass spectrometry (ICP-MS) to study the dissolved organic matter (DOM) and colloidal binding of U and Ni water extracts of sediments collected from a contaminated area of the Savannah River River Site, a U.S. Department of Energy former nuclear materials production and processing facility, near Aiken, SC. High-performance SEC-UVA-ICP-MS was well-suited to the separation of DOM over the molecular weight (MW) range of ~200-7000 Da. The ICP-MS element specific data indicated that a significant fraction of U was associated with DOM. Uranium exhibited a bimodal distribution and the other fraction was greater than the exclusion limit for the column and coeluted with Al. Flow FFF was used to size this fraction as colloidal with an approximate effective sperical diameter of 0.09-0.12 µm. Element specific ICP-MS data confirmed that U and Al were associated with the colloidal phase. High-field FI FFF was also applicable to sizing DOM but resolutiuon was pooer than SEC. The results of this study suggest that "dissolved" U at this site is predominantly either complexed by DOM or bound to a colloidal fraction while Ni is predominately present as labile complexes or the free cation and, therefore, potentailly bioavailable.

SREL Reprint #2827

Jackson, B. P., J. F. Ranville, P. M. Bertsch, and A. G. Sowder. 2005. Characterization of colloidal and humic-bound Ni and U in the "dissolved" fraction of contaminated sediment extracts. Environmental Science & Technology 39:2478-2485.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).