Transport and mobilization of pathogenic microbes and microspheres in unsaturated fractured media: Effect of microbe size, soil physical heterogeneity, and intermittent flow and effect of redox conditions on the release of trace elements from submerged co

The potential of intermittent rainfall to mobilize microbes of diverse size, shape, and taxa in heterogeneous soil systems is important in assessing groundwater contamination risks. We investigated the transport, retention, and mobilization of microbes through an intact soil core. Microbes (MS-2 bacteriophage, Pseudomonas stutzeri bacteria, and Cryptosporidium parvum oocysts), microspheres, and a bromide tracer were applied to the core and breakthrough was measured to resolve the effect of soil physical heterogeneity. After breakthrough, the core was subjected to intermittent rainfalls to mobilize the attached microbes and microspheres. This study demonstrated that intermittent flows mobilize attached microbes and microspheres in a physically heterogeneous soil regardless of size or taxa; however, the degree of mobilization was dependent on microbe size and shape. Mobilization of larger, spherical C. parvum oocysts was greater than that of smaller, spherical MS-2 bacteriophage and rod-shaped P. stutzeri bacteria. Cumulatively, the order of recovery was C. parvum oocysts > microspheres > MS-2 bacteriophage > P. stutzeri cells.;The release of coal ash because of a storage pond dike failure at the Tennessee Valley Authority's Kingston Fossil Plant in December 2008 is a concern because of the potential ecological and human health risks posed by the release of toxic elements from the coal ash into surrounding waters. The effects of redox conditions were examined in this study, which focused on how the differences between elements affect their release as a function of varied redox conditions. Using Emory River sediments and water, and Kingston coal ash, a batch reactor system was created. This experiment was conducted in three stages -- oxidizing, transition, and reducing -- in order to simulate redox changes that might occur during weathering of the released coal ash on riverbed sediments. The results suggest that the release of several trace elements, from the coal ash may present water quality issues based on their increasing concentrations during the reducing stage. The differences in release can be attributed to changes in chemical properties (e.g., pH, redox potential), presence and aromaticity of DOC, dissolution of mineral phases, competition or interaction with other species, precipitation of immobile phases, or release of mobile phases.