Stability of solid-phase selenium species in fly ash after prolonged submersion in a natural river system.

Selenium (Se) chemistry can be very complex in the natural environment, exhibiting different valence states (-2, 0, +4, +6) representing multiple inorganic, methylated, or complexed forms. Since redox associated shifts among most of known Se species can occur at environmentally relevant conditions, it is important to identify these species in order to assess their potential toxicity to organisms. In June of 2009, researchers from the US Army Engineer Research & Development Center (ERDC) conducted investigations of the fly ash spilled 6 months previously into the Emory River at the TVA Kingston Fossil Plant, TN. Ash samples were collected on site from both the original ash pile (that did not move during the levee failure), from the spill zone (including the Emory River), and from the ash recovery ditch (ARD) containing ash removed during dredging cleanup operations. The purpose of this work was to determine the state of Se in the spilled fly ash and to assess its potential for transformation and resultant chemical stability from its prolonged submersion in the river and subsequent dredging. Sequential chemical extractions suggested that the river environment shifted Se distribution toward organic/sulfide species. Speciation studies by bulk XANES analysis on fly ash samples showed that a substantial portion of the Se in the original ash pile had transformed from inorganic selenite to a mixture of Se sulfide and reduced (organo)selenium (Se(-II)) species over the 6-month period. µ-XRF mapping data showed that significant trends in the co-location of Se domains with sulfur and ash heavy metals. Ten-d extended elutriate tests (EETs) that were bubbled continuously with atmospheric air to simulate worst-case oxidizing conditions during dredging showed no discernible change in the speciation of fly ash selenium. The enhanced stability of the organo- and sulfide-selenium species coincided with the mixture of the ash material with humic materials in the river, corresponding with notable shifts in the ash carbon- and nitrogen-functionality.

Local Structure of ZnO micro flowers and nanoparticles obtained by micro-segmented flow synthesis.

The micro-segmented flow technique was applied for continuous synthesis of ZnO micro- and nanoparticles with short residence times of 9.4 s and 21.4 s, respectively. The obtained particles were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Small angle X-ray scattering (SAXS) and photoluminescence spectroscopy were used to determine the size and optical properties of ZnO nanoparticles. In addition, extended X-ray absorption fine structure (EXAFS) spectroscopy was employed to investigate local structural properties. The EXAFS measurements reveal a larger degree of structural disorder in the nanoparticles than the microparticles. These structural changes should be taken into consideration while evaluating the size-dependent visible emission of ZnO nanoparticles.

The potential of Thelypteris palustris and Asparagus sprengeri in phytoremediation of arsenic contamination.

The potential of two plants, Thelypteris palustris (marsh fern) and Asparagus sprengeri (asparagus fern), for phytoremediation of arsenic contamination was evaluated. The plants were chosen for this study because of the discovery of the arsenic hyperaccumulating fern, Pteris vittata (Ma et al., 2001) and previous research indicating asparagus fern's ability to tolerate > 1200 ppm soil arsenic. Objectives were (1) to assess if selected plants are arsenic hyperaccumulators; and (2) to assess changes in the species of arsenic upon accumulation in selected plants. Greenhouse hydroponic experiments arsenic treatment levels were established by adding potassium arsenate to solution. All plants were placed into the hydroponic experiments while still potted in their growth media. Marsh fern and Asparagus fern can both accumulate arsenic. Marsh fern bioaccumulation factors (> 10) are in the range of known hyperaccumulator, Pteris vittata Therefore, Thelypteris palustris is may be a good candidate for remediation of arsenic soil contamination levels of < or = 500 microg/L arsenic. Total oxidation of As (III) to As (V) does not occur in asparagus fern. The asparagus fern is arsenic tolerant (bioaccumulation factors < 10), but is not considered a good potential phytoremediation candidate.