Expedited artificial aging is described and demonstrated using a novel syst
em that circulates a solution of supercritical carbon dioxide and a hydroph
obic organic sorbate (phenanthrene) through a closed loop containing a poro
us substrate. Unlike traditional methods used to simulate the natural aging
process, our approach allows for realtime monitoring of sorption equilibri
a, and the process is highly accelerated due to the unique physical propert
ies of supercritcal carbon dioxide. The effectiveness of the system to simu
late aging was demonstrated with a series of experiments in which three sil
icas with varying particle and pore sizes were loaded with phenanthrene. Ba
tch aqueous desorption experiments were used to evaluate the extent of the
aging process. For the two types of particles containing the largest pores
(i.e., mean diameters of 202 and 66 Angstrom), 95% and 86%, respectively, o
f the phenanthrene was released to the aqueous fraction within 3 h. In cont
rast, only 16% of the phenanthrene was released from particles having a mea
n pore diameter of 21 Angstrom after 24 h. These results were confirmed by
the results from an aqueous column desorption experiment. Confounding facto
rs that might contribute to slow aqueous desorption such as the hydration s
tate of the particles' surfaces, the chemical form of the loaded phenanthre
ne, and the organic carbon content were investigated and/or normalized for
all three particle types. Consequently, we were able to attribute the slow
desorption behavior and the presence of the resistant fraction in the 21 A
silica to pore effects. With properly designed experiments, the results of
this study suggest that the supercritical fluid system could be extended to
the study of contaminant aging and bioavailability in natural soils and se
diments.