Elucidating Bioreductive Transformations within Physically Complex Media: Impact on the Fate and Transport of Uranium and Chromium

The greatest challenge to elucidating geochemical and biological chromium reduction in natural sediments is to create a sterile environment without destroying the chemical and physical properties of the system. In this study we determined the potential for geochemical and biological chromium reduction in a naturally reducing soil using carbon amendments and sterilization. To minimize alterations to the sediment samples, soils were sterilized via exposure to ?-irradiation which causes fewer changes in the physical and chemical properties of the soil compared to other methods of sterilization. The objective of our research was to determine if the absence of viable microorganisms significantly affected the extent of chromium reduction in a reducing soil. Our hypothesis was that if geochemical reduction pathways dominated the system then soil sterilization should have little to no effect on the amount and rate of chromium that was reduced. However, if the reduction of chromium in these soils was a synergistic process then significantly different amounts of chromium should be reduced in the sterilized versus non-sterilized samples

XANES speciation of phosphorus in organically amended and fertilized vertisol and mollisol

Knowledge of the dominant P species present in the soil following the application of organic amendments and fertilizer is important in understanding the fate of P in the environment. This study was performed to identify P species in two calcareous soils, an Osborne series (Typic Humicryert) and a Lakeland series (Typic Calciudoll), treated with organic amendments (biosolids and hog and dairy cattle manure) and fertilizer (monoammonium phosphate, MAP). Phosphorus 1s x-ray absorption near-edge structure (XANES) spectroscopy was used to speciate P compounds in these amended soils. The result showed that "adsorbed P" was the dominant P species in both soils. For the Osborne soil, the unamended soil (control) and those amended with biosolids and MAP contained an appreciable amount of hydroxyapatite (HAP), the most thermodynamically favored Ca phosphate. In addition, soils amended with biosolids or hog or dairy manures contain β-tricalcium phosphate (TRICAL), a more soluble form of Ca phosphate than HAP. The amended Lakeland soils contained a variety of species in addition to the dominant "adsorbed P." While TRICAL was found in all the amended soils except in that amended with hog manure, HAP was present in appreciable amount only in the unamended soil. Overall, the adsorbed P, most likely through inner-sphere complexation, in these amended soils may not be readily available as a source of P into the environment. In addition, the HAP and TRICAL will have limited solubility, and thus, are probably only a very minor source of P in the environment.Babasola Ajiboye, Olalekan O. Akinremi, Yongfeng Hu and Astrid Jürgense