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

The currency ratio in Tanzania: an econometric analysis

This study tested some key hypotheses on the determinants of the currency ratio in Tanzania. The econometric results suggest that real income is, as theorized, negatively related to and a significant determinant of the currency ratio in Tanzania. The estimated income elasticity coefficient, found to be far less than unity, suggests there is poor substitution between currency and demand deposits in Tanzania. The results also showed that expected inflation was negatively related to the currency ratio in Tanzania. While the structural adjustment programme was found to increase and shift upward the currency ratio function in Tanzania, the liberalization of the financial sector was found to shift decrease and shift downward the currency ratio function. Most institutional variables were found to lack the expected sign and significance in explaining the currency ratio in Tanzania, probably because of inadequacy of the proxies used

Effects of gamma-sterilization on the physico-chemical properties of natural sediments

Batch U(VI) sorption/reduction experiments were completed on sterilized and non-sterilized sediment samples to elucidate biological and geochemical reduction mechanisms. Results from X-ray absorption nearedge structure (XANES) spectroscopy revealed that γ-sterilized sediments were actually better sorbents of U(VI), despite the absence of any measurable biological activity. These results indicate that γ-irradiation induced significant physico-chemical changes in the sediment which is contrary to numerous other studies identifying γ-sterilization as an effective and minimally invasive technique. To identify the extent and method of alteration of the soil as a result of γ-sterilization, untreated soil samples, physically separated size fractions, and chemically extracted fractions of the soil were analyzed pre- and post-sterilization. The effects of sterilization on mineralogy, pH, natural organic matter (NOM), cation exchange capacity (CEC), and iron oxidation state were determined. Results indicated that major mineralogy of the clay and whole sediment samples was unchanged. Sediment pH decreased only slightly with γ-irradiation; however, irradiation produced a significant decrease in CEC of the untreated sediments and affected both the organic and inorganic fractions. Mössbauer spectra of non-sterile and γ-sterilized sedimentsmeasuredmore reduced iron present in γ-sterilized sediments compared to non-sterile samples. Our results suggest that sterilization by γ-irradiation induced iron reduction that may have increased the sorption and/or reduction of U(VI) onto these sediments. However, Mössbauer and batch sorption data are somewhat contradictory, the former indicates that the iron oxide or iron hydroxide minerals are more significantly reduced while the later indicates that reduced clay minerals account for greater sorption of U(VI)

Pentosidine accumulates in the aging vitreous body: A gender effect

The human vitreous body undergoes structural changes with aging. This can be followed by a posterior vitreous detachment, which can result in ocular pathology. As in many collagenous tissues, age-related changes in the vitreous could be caused by the formation of advanced glycation end products (AGEs). The goal of this study was to find out whether the AGE pentosidine accumulates in the human vitreous with aging. With this data we were able to estimate the half-life of vitreous collagen. Furthermore, we analyzed whether there was a gender difference in pentosidine accumulation, as this was seen in other tissues as well. Using high performance liquid chromatography, pentosidine contents were determined in whole vitreous bodies and in separate parts of vitreous bodies, which were all obtained from human donor eyes. Our results show that pentosidine accumulates in the human vitreous. From the rate of accumulation we could roughly estimate that vitreous collagen has as a similar or shorter half-life compared to skin collagen. This supports the concept of collagen turnover in the vitreous. In general, the female vitreous experiences a faster pentosidine accumulation than the male vitreous, and most of the pentosidine accumulation in the former occurs after 50 years of age. © 2009 Elsevier Ltd. All rights reserved