Characterization
of Colloidal and Humic-Bound Ni and U In the "Dissolved" Fraction
of Contaminated Sediment Extracts
BRIAN P. JACKSON, JAMES F. RANVILLE, PAUL M. BERTSCH AND ANDREW G. SOWDER
Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina 29802 and Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401
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 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 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 whiel 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.
