Search

The sequential extraction (SEP) of selenium to determine the isotopic composition of different Se pools in soils is an important tool for tracking biogeochemical cycling of Se in soils. An appropriate Se extraction method for the stable Se isotope analysis was established and tested for different Se pools in soils in terms of reproducibility and recovery. Soil samples (n = 4) from a seleniferous field site in Punjab, India and two standard reference materials were chosen because of their relatively high total Se concentration of 2 to 4.5 mg kg-1. Additionally, a soil sample with low Se content was utilized to verify the procedure and reproducibility. The isotopic mass-balance calculation gives consistent δ82Se values for the sum of the extracted pools, relative to δ82Se of the bulk soils. For instance, in one studied soil (soil-1), the sum of δ82Se of all individual Se-pools (δ82Semass-balance = 3.35‰) is in good agreement with the analysis of δ82Se of the bulk soil (δ82Sebulk of 3.56‰). We observed up to a 2‰ range in δ82Se among the different Se soil-pools (soil-3). Our Se isotopic results of Se soil pools provide more detailed observations of the Se linked processes in soils compared to bulk δ82Se. Thus, quantitative Se isotopic analysis of different Se pools can be an important tool for predicting the environmental cycling of selenium in soils or sediments. [ABSTRACT FROM AUTHOR]

Abstract: Reduction of toxic Cr(VI) to less toxic Cr(III) is an important process for attenuating Cr(VI) transport in groundwater. This process results in immobilization of chromium as Cr(III) and effectively decreases the overall mobility of the chromium inventory. During both abiotic and biotic reduction of Cr(VI) to Cr(III), a kinetic isotope effect occurs in which the lighter isotope, 52Cr, reacts preferentially, leaving the remaining dissolved Cr(VI) enriched in the heavier isotope, 53Cr. Cr isotopes have proven to be a useful tool for estimating the magnitude of Cr(VI) reduction and for determining where in a hydrologic system reduction is occurring. In this paper, we discuss patterns of reduction in perched-intermediate and regional aquifer systems contaminated with Cr(VI) related to historical use of potassium dichromate as an anticorrosion agent in cooling towers at a power plant at the Los Alamos National Laboratory in northern New Mexico. We utilize Cr isotopes to assess the relative effects of mixing and reduction on measured δ53Cr in groundwater, with an emphasis on where in the system reduction occurs. Chromium isotope measurements provide strong evidence for reduction of Cr(VI) in vadose zone basalts. [Copyright &y& Elsevier]

Highlights: [•] We present an iron isotope explication on the arsenic mobilization in the hyporheic zone. [•] The variation of δ56Fe values and the As concentration water are similar at each depth. [•] Microbial reduction of Fe(III) oxides/hydroxides is the dominant process that promotes As mobility in the hyporheic zones. [Copyright &y& Elsevier]

Abstract: The natural abundance of stable Se isotopes in methylselenides reflects sources and formation conditions of methylselenides. We tested the effects of (i) different inorganic Se species spiked to soils and (ii) different soil samples on the extent of fungal biomethylation of Se and the Se isotope ratios (δ82/76Se) in methylselenides. Furthermore, we assessed the decrease of dissolved, bioavailable Se during three days of equilibration of the soils with Se-enriched solutions. We conducted closed microcosm experiments containing soil spiked with Se(IV) or Se(VI), a growth medium, and the fungus species Alternaria alternata for 11d. The concentrations and isotope ratios of Se were determined in all components of the microcosm with multicollector ICP-MS. The equilibration of the spiked Se(IV) and Se(VI) for 3d resulted in a decrease of dissolved, bioavailable Se concentrations by 32 to 44% and 8 to 14%, respectively. Very little isotope fractionation occurred during this phase, and it can be attributed to mixing of the added Se with the pre-existing Se in the soils and minor Se(IV) reduction in one experiment. In two of the incubated soils – moderately acidic roadside and garden soils – between 9.1 and 30% of the supplied Se(IV) and 1.7% of the supplied Se(VI) were methylated while in a strongly acidic forest soil no Se methylation occurred. The methylselenides derived from Se(IV) were strongly depleted in 82Se (δ82/76Se=−3.3 to −4.5‰) compared with the soil (0.16–0.45‰) and the added Se(IV) (0.20‰). The methylselenide yield of the incubations with Se(VI) was too small for isotope measurements. Our results demonstrate that Se source species and soil properties influence the extent of Se biomethylation and that the produced methylselenides contain isotopically light Se. [Copyright &y& Elsevier]

Abstract: Several Se-bearing minerals have been identified in Se-rich stone coal, spoils, and their adjacent organic-rich soils in Yutangba of Enshi, China, where human Se toxicity occurred in the 1960s. These minerals mainly include native Se (Se0), krutaite (CuSe2), klockmannite (CuSe), mandarinoite (Fe2(SeO3)3·6H2O), Se-bearing chalcopyrite (CuFe(Se, S)2), and pyrite (Fe(Se,S)2). The assemblage of native Se, krutaite, klockmannite, and Se-bearing pyrite and chalcopyrite is primarily present in the stone coal near a fault plane, while the assemblage of native Se and krutaite is found in the Se-rich carbonaceous mudstone and organic-rich soils which are 60m away from the stone coal exposure. The assemblage of mandarinoite and native Se is present in abandoned stone coal spoils, where natural combustion occurred. Native Se is quite extensive in the stone coal spoils and nearby soils derived from them. The co-occurrence of Cu–Se minerals and native Se indicates that these minerals could have formed under a relatively acidic and reducing environment below 220°C, and suggests that Cu could play a significant role in fixing reduced Se ions in the acidic, organic-rich surface environment. Furthermore, the occurrence of mandarinoite suggests that iron-oxides constrain the geochemical behavior of Se in oxidizing environments. Our observations provide new insights into the mechanisms of Se fixation and accumulation during weathering of Se-rich rocks. [Copyright &y& Elsevier]

Over half of all human cancers, of a wide variety of types, sustain mutations in the p53 tumor suppressor gene. Although p53 limits tumorigenesis through the induction of apoptosis or cell cycle arrest, its molecular mechanism of action in tumor suppression has been elusive. The best-characterized p53 activity in vitro is as a transcriptional activator, but the identification of numerous additional p53 biochemical activities in vitro has made it unclear which mechanism accounts for tumor suppression. Here, we assess the importance of transcriptional activation for p53 tumor suppression function in vivo in several tissues, using a knock-in mouse strain expressing a p53 mutant compromised for transcriptional activation, p5325,26. p5325,26 is severely impaired for the transactivation of numerous classical p53 target genes, including p21, Noxa, and Puma, but it retains the ability to activate a small subset of p53 target genes, including Bax. Surprisingly, p5325,26 can nonetheless suppress tumor growth in cancers derived from the epithelial, mesenchymal, central nervous system, and lymphoid lineages. Therefore, full transactivation of most p53 target genes is dispensable for p53 tumor suppressor function in a range of tissue types. In contrast, a transcriptional activation mutant that is completely defective for transactivation, p5325,26,53,54, fails to suppress tumor development. These findings demonstrate that transcriptional activation is indeed broadly critical for p53 tumor suppressor function, although this requirement reflects the limited transcriptional activity observed with p5325,26 rather than robust transactivation of a full complement of p53 target genes. [ABSTRACT FROM AUTHOR]

At Idaho National Laboratory, Cr(VI) concentrations in a groundwater plume once exceeded regulatory limits in some monitoring wells but have generally decreased over time. This study used Cr stable isotope measurements to determine if part of this decrease resulted from removal of Cr(VI) via reduction to insoluble Cr(III). Although waters in the study area contain dissolved oxygen, the basalt host rock contains abundant Fe(II) and may contain reducing microenvironments or aerobic microbes that reduce Cr(VI). In some contaminated locations, 53Cr/52Cr ratios are close to that of the contaminant source, indicating a lack of Cr(VI) reduction. In other locations, ratios are elevated. Part of this shift may be caused by mixing with natural background Cr(VI), which is present at low concentrations but in some locations has elevated 53Cr/53Cr. Some contaminated wells have 53Cr/53Cr ratios greater than the maximum attainable by mixing between the inferred contaminant and the range of natural background observed in several uncontaminated wells, suggesting that Cr(VI) reduction has occurred. Definitive proof of reduction would require additional evidence. Depth profiles of 53Cr/53Cr suggest that reduction occurs immediately below the water table, where basalts are likely least weathered and most reactive, and is weak or nonexistent at greater depth. [ABSTRACT FROM AUTHOR]

elevated sex hormones such as puberty and pregnancy. Possible molecular mechanisms responsible for the appearance of pyogenic granuloma in this demographic have been suggested. Increased incidence of pyogenic granuloma in post menopausal women on hormone replacement therapy has not been reported. A 49-year-old woman with preexisting titanium implant placement in the left posterior mandible presented with complaint of food impaction and slight discomfort associated with the implant. Clinical examination revealed slight soft tissue erythema and edema, but no foreign body could be identified. Subsequently, a nodular gingival lesion associated with the implant developed and was treated by conservative surgical excision. Histologic characteristics of the lesion were consistent with pyogenic granuloma. The patient was informed of the diagnosis. No evidence of recurrence could be identified after 6 months. Like peripubertal and pregnant women, postmenopausal women treated with hormone replacement therapy may be at increased risk for pyogenic granuloma. Observational studies designed to establish an association between hormone replacement therapy and pyogenic granuloma have not been conducted. Dentists should be aware of putative pathophysiologic mechanisms for pyogenic granuloma formation and the possibility that hormone replacement may trigger these mechanisms. [ABSTRACT FROM AUTHOR]

Recent publications suggest great potential for analysis of Hg stable isotope abundances to elucidate sources and/or chemical processes that control the environmental impact of mercury. We have developed a new MC-ICP-MS method for analysis of mercury isotope ratios using the double-spike approach, in which a solution containing enriched 196Hg and 204Hg is mixed with samples and provides a means to correct for instrumental mass bias and most isotopic fractionation that may occur during sample preparation and introduction into the instrument. Large amounts of isotopic fractionation induced by sample preparation and introduction into the instrument (e.g., by batch reactors) are corrected for. This may greatly enhance various Hg pre-concentration methods by correcting for minor fractionation that may occur during preparation and removing the need to demonstrate 100% recovery. Current precision, when ratios are normalized to the daily average, is 0.06‰, 0.06‰, 0.05‰, and 0.05‰ (2 σ) for 202Hg/198Hg, 201Hg/198Hg, 200Hg/198Hg, and 199Hg/198Hg, respectively. This is slightly better than previously published methods. Additionally, this precision was attained despite the presence of large amounts of other Hg isotopes (e.g., 5.0% atom percent 198Hg) in the spike solution; substantially better precision could be achieved if purer 196Hg were used. [ABSTRACT FROM AUTHOR]

Chromium stable isotope ratios show promise at indicators of Cr(VI) reduction in groundwater, but no published study has yet demonstrated that expected relationships between 53Cr/52Cr and Cr(VI) concentration, position, and time occur in an actual groundwater plume. We present an extensive data set from a point-source plume in Berkeley, CA; data extend over 5 years and 14 locations covering the entire plume. We interpret the data using a Rayleigh distillation model with an effective fractionation factor that incorporates an intrinsic fractionation factor determined from incubations of site sediments and accounts for reservoir effects in the restricted subsurface zones where Cr(VI) reduction is thought to occur. The groundwater 53Cr/52Cr and Cr(VI) concentration data are consistent with a scenario where the system has reached a steady state: Cr(VI) reduction continues, the extent of reduction at any point is constant over time, reduction proceeds to completion at the downgradient edge of the plume, and the plume is no longer advancing. The overall consistency of the results with a reasonable model for the site supports the use of Cr isotope-based estimates of reduction, hut we discuss current uncertainties and limitations of the approach as well. [ABSTRACT FROM AUTHOR]

Many biomedical terminologies, classifications, and ontological resources such as the NCI Thesaurus (NCIT), International Classification of Diseases (ICD), Systematized Nomenclature of Medicine (SNOMED), Current Procedural Terminology (CPT), and Gene Ontology (GO) have been developed and used to build a variety of IT applications in biology, biomedicine, and health care settings. However, virtually all these resources involve incompatible formats, are based on different modeling languages, and lack appropriate tooling and programming interfaces (APIs) that hinder their wide-scale adoption and usage in a variety of application contexts. The Lexical Grid (LexGrid) project introduced in this paper is an ongoing community-driven initiative, coordinated by the Mayo Clinic Division of Biomedical Statistics and Informatics, designed to bridge this gap using a common terminology model called the LexGrid model. The key aspect of the model is to accommodate multiple vocabulary and ontology distribution formats and support of multiple data stores for federated vocabulary distribution. The model provides a foundation for building consistent and standardized APIs to access multiple vocabularies that support lexical search queries, hierarchy navigation, and a rich set of features such as recursive subsumption (e.g., get all the children of the concept penicillin). Existing LexGrid implementations include the LexBIG API as well as a reference implementation of the HL7 Common Terminology Services (CTS) specification providing programmatic access via Java, Web, and Grid services. [ABSTRACT FROM AUTHOR]

The role of transcriptional activation in p53 function is highly controversial. To define this role in vivo, we generated a Trp53 knock-in construct encoding a protein carrying mutations of two residues that are crucial for transactivation (L25Q,W26S). Here we show that these mutations have selective effects on the biological functions of p53. Although its ability to activate various p53 target genes is largely compromised, the p53QS protein retains the ability to transactivate the gene Bax. The ability of the p53QS mutant protein to elicit a DNA damage-induced G1 cell cycle-arrest response is also partially impaired. p53QS has selective defects in its ability to induce apoptosis: it is completely unable to activate apoptosis in response to DNA damage, is partially unable to do so when subjected to serum deprivation and retains substantial apoptotic activity upon exposure to hypoxia. These findings suggest that p53 acts through distinct, stimulus-specific pathways to induce apoptosis. The importance of the biological activity of p53QS in vivo is underscored by our finding that expression of p53QS, which cannot bind mdm2, induces embryonic lethality. Taken together, these results suggest that p53 has different mechanisms of action depending on specific contextual cues, which may help to clarify the function of p53 in preventing cancer. [ABSTRACT FROM AUTHOR]

We use reactive transport modeling to consider how diffusion and hydrodynamic dispersion, cross-formational flow, and subsurface production affect the steady state distribution in flow regimes of the radioactive isotope 36Cl, and the relationship of the isotope distribution to groundwater residence time, or 'age.' The isotope forms naturally in the atmosphere, dissolves in rainwater, and then decays in the subsurface with a half-life of ∼301,000 years; hence it is important for age dating very old groundwater. In a simple flow regime composed of an aquifer confined above and below by aquitards, isotopic age may correspond rather well with a groundwater's 'piston flow' age. This correspondence is favored where the aquifer is thick, cross-formational flow is insignificant, salinity is low, and the diffusion coefficient within the aquitards is small. The maximum dateable age, however, is somewhat smaller than expected from the isotope's half-life. Owing to the effect of 'dead' chloride, dating based on isotope abundance (the 36Cl/Cl ratio) may be less accurate than that based on 36Cl concentration. Cross-formational flow can strongly affect the 36Cl distribution and abundance, preventing the rates and even direction of flow within an aquifer from being interpreted using the piston flow model. Where salinity is moderate or high, the isotope distribution is controlled by subsurface production, and dating on the basis of the decay of atmospheric 36Cl is not possible. In models of simple flow regimes the 36Cl method fails to predict groundwater age accurately where groundwater chlorinity exceeds ∼75-150 mg kg−1. Reactive transport models hold considerable promise for improving interpretation of the rates and patterns of groundwater flow from radioisotope distributions. [ABSTRACT FROM AUTHOR]

Examines apoptosis mediated solely by p53 to resolve the role of reactive oxygen species (ROS) in different apoptotic pathways. Use of a recombinant adenoviral construct containing the human p53 cDNA under the control of the cytomegalovirus immediate early promoter Adp53; Adenoviral infections and detection of protein expression; Assays for cell death; Detection of ROS.

Through a case study of a facility for the medical care of indigent patients, the interpenetration of politics, personality, and medicine is revealed. The nature of community health problems is examined from both medical and political perspectives. [ABSTRACT FROM AUTHOR]