Colloid transport may facilitate off-site transport of radioactive wastes at the Hanford site, Washington State. In this study, column experiments were conducted to examine the effect of irrigation schedule on releases of in situ colloids from two Hanford sediments during saturated and unsaturated transientflow and its dependence on solution ionic strength, irrigation rate, and sediment texture. Results show that transient flow mobilized more colloids than steady-state flow. The number of short-term hydrological pulses was more important than total irrigation volume for increasing the amount of mobilized colloids. This effect increased with decreasing ionic strength. At an irrigation rate equal to 5% of the saturated hydraulic conductivity, a transient multipulse flow in 100 mM NaNO3 was equivalent to a 50-fold reduction of ionic strength (from 100 mM to 2 mM) with a single-pulse flow in terms of their positive effects on colloid mobilization. Irrigation rate was more important for the initial release of colloids. In addition to water velocity, mechanical straining of colloids was partly responsible for the smaller colloid mobilization in the fine than in the coarse sands, although the fine sand contained much larger concentrations of colloids than the coarse sand.

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We derived two new expressions for the intrinsic permeability (k) of fractal porous media. The first approach, the probabilistic capillary connectivity (PCC) model, is based on evaluating the expected value of the cross‐sectional area of pores connected along various flow paths in the direction in which the permeability is sought. The other model is a modified version of Marshall's probabilistic approach (MPA) applied to random cross matching of pores present on two parallel slices through a fractal porous medium. The Menger sponge is a three‐dimensional mass fractal that represents the complicated pore space geometry of soil and rock. Predictions based on the analytical models were compared with estimates of k derived from lattice Boltzmann method (LBM) simulations of saturated flow in virtual representations of Menger sponges. Overall, the analytically predicted k values matched the k values from the LBM simulations with <14% error for the deterministic sponges simulated. While the PCC model can represent variation in permeability due to the randomization process for each realization of the sponge, the MPA approach can capture only the average permeability resulting from all possible random realizations. Theoretical and empirical analyses of the surface fractal dimension (D2) for successive slices through a random Menger sponge show that the mean D2 value 〈D2〉 = D3 − 1, where D3 is the three‐dimensional mass fractal dimension. Incorporating 〈D2〉 into the MPA approach resulted in a k that compared favorably with the modal value of k from LBM simulations performed on 100 random realizations of a random Menger sponge.

Ultrastructural localization of a P29 protein of Toxoplasma gondii was examined on thin sections by an immunogold technique using a P29 antigen-specific monoclonal antibody (5-241-178). Immunolocalization of the P29 protein in extracellular tachyzoites demonstrated that this antigen was present in the dense granules. Thus, we have identified this P29 antigen as the seventh protein (GRA7) to be localized to the dense granules of T. gondii. P29 immunolocalization in intracellular tachyzoites demonstrated association of this antigen with the parasite membrane complex, tubular elements of the intravacuolar network, and with the parasitophorous vacuolar membrane. Our immunolabeling data suggest trafficking of the P29 (GRA7) antigen from the dense granule via the intravacuolar network to the parasitophorous vacuolar membrane on invasion of the tachyzoite into the host cell. (J Histochem Cytochem 46:1411-1421, 1998)