Horizontal and Vertical Transport of Uranium in an Arid Weapon-Tested Ecosystem.

Armor-penetrating projectiles and fragments of depleted uranium (DU) have been deposited in soils at weapon-tested sites. Soil samples from these military facilities were analyzed by inductively coupled plasma-optical emission spectroscopy and X-ray diffraction to determine U concentrations and transport across an arid ecosystem. Under arid conditions, both vertical transport driven by evaporation (upward) and leaching (downward) and horizontal transport of U driven by surface runoff in the summer were observed. Upward vertical transport was simulated and confirmed under laboratory-controlled conditions, to be leading to the surface due to capillary action via evaporation during alternating wetting and drying conditions. In the field, the 92.8% of U from DU penetrators and fragments remained in the top 5 cm of soil and decreased to background concentrations in less than 20 cm. In locations prone to high amounts of water runoff, U concentrations were reduced significantly after 20 m from the source due to high surface runoff. Uranium was also transported throughout the ecosystem via plant uptake and wild animal consumption between trophic levels, but with limited accumulation in edible portions in plants and animals.

Distribution and Fractionation of Uranium in Weapon Tested Range Soils.

Uranium is a chemically toxic and radioactive heavy metal. Depleted uranium (DU) is the byproduct of the uranium enrichment process, with a majority of U as uranium-238, and a lower content of the fissile isotope uranium-235 than natural uranium. Uranium-235 is mainly used in nuclear reactors and in the manufacture of nuclear weapons. Exposure is likely to have an impact on humans or the ecosystem where military operations have used DU. Yuma Proving Ground in Arizona, USA has been using depleted uranium ballistics for 36 years. At a contaminated site in the Proving Grounds, soil samples were collected from the flat, open field and lower elevated trenches that typically collect summer runoff. Spatial distribution and fractionation of uranium in the fields were analyzed with total acid digestion and selective sequential dissolution with eight operationally defined solid-phase fractions. In addition to uranium, other trace elements (As, Ba, Co, Cr, Cu, Hg, Mo, Nb, Pd, Pb, V, Zn, Zr) were also assessed. Results show that the trench area in the testing site had a higher accumulation of total U (12.4%) compared to the open-field soil with 279 mg/kg U. Among the eight solid-phase components in the open-field samples, U demonstrated stronger affinities for the amorphous iron-oxide bound, followed by the carbonate bound, and the residual fractions. However, U in the trench area had a stronger binding to the easily reducible oxide bound fraction, followed by the carbonate-bound and amorphous iron-oxide-bound fractions. Among other trace elements, Nb, As, and Zr exhibited the strongest correlations with U distribution among solid-phase components. This study indicates a significant spatial variation of U distribution in the shooting range site. Fe/Mn oxides and carbonate were the major solid-phase components for binding U in the weapon test site.

Effects of primary sludge particulate (PSP) entrapment on ultrasonic (20 kHz) disinfection of Escherichia coli.

The role of primary sludge particulates (PSPs) in ultrasonic disinfection of Escherichia coli (E. coli) was investigated. Entrapment of E. coli by PSP was directly observed through scanning electron microscope (SEM) after E. coli and PSP were incubated together in water for 24 h at 35 °C. Entrapment coefficient was proposed for the first time to reflect the ability of PSP to entrap E. coli and was estimated as 1.4 × 10(3) CFU/mg PSP under our experimental conditions. Ultrasonication (20 kHz) of different E. coli-PSPs solutions showed that the entrapped E. coli cells were protected by PSP from ultrasonication and the unentrapped cells were not. However, the protection of entrapped E. coli cells gradually decreased as ultrasonication proceeded, suggesting the ability of power ultrasonication to deprotect the entrapped E. coli cells. SEM studies suggested a two-step mechanism for ultrasonic (20 kHz) disinfection of entrapped E. coli: breakdown of the protective PSP refugia and disinfection of the exposed E. coli cells. This research will enable more informed decisions about disinfection of aqueous samples where porous PSP are present.

Copper doping improves hydroxyapatite sorption for arsenate in simulated groundwaters.

Hydroxyapatite (HAP) has been widely used to immobilize many cationic heavy metals in water and soils. Compared with its strong sorption for metal cations, the abilities of HAP to sorb metal anions, such as arsenic, are less significant. Improving HAP sorption for anionic arsenic species is important for expanding its application potential because the presence of arsenic in the environment has raised serious health concerns and there is need for cost-effective remediation methods. In this work, we report an innovative method of copper doping to improve a synthetic HAP sorption for arsenate, which is a primary aqueous arsenic species, in simulated groundwaters. The undoped HAP and copper doped HAP (CuHAP) were characterized with XRD, FTIR, N(2) adsorption, and SEM, and then evaluated as sorbents for arsenate removal tests. The experimental results suggest that copper doping changed the morphology and increased the surface area of HAP. The CuHAP sorbed 1.6-9.1x more arsenate than the undoped HAP did in a simulated groundwater at pH of 7.7-8.0. The improved arsenate sorption is presumably due to the increase in surface area of HAP as a result of copper doping. In addition to the copper doping level, the arsenate sorption to HAP and CuHAP can also be increased with increasing water pH and calcium concentration. The experimental data indicate that sorbent dissolution is an important factor governing arsenate sorption to HAP and CuHAP.