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Focused clinical question: What factors identify the optimal bone augmentation techniques for managing slight, moderate, and severe horizontal alveolar ridge deficiency (ARD) at dental implant sites? Summary: Horizontal ARD is a concern at a high proportion of sites receiving dental implants, and clinicians have developed a variety of surgical procedures to address such defects. In a particular case, selection of the optimal treatment may depend predominantly on defect severity, location (anterior versus posterior), and configuration (contained versus noncontained). This report provides a framework for selecting an augmentation method when presented with a slight, moderate, or severe horizontal ARD at a site requiring dental implant placement. Conclusion: Multiple treatment options are available for planned implant sites exhibiting horizontal ARD; severe posterior and slight anterior defects intuitively call for different approaches. Although rigid guidelines for selecting the optimal augmentation method do not exist, some techniques are poorly suited for esthetically demanding sites. A framework considering defect severity, location, and configuration may help guide clinical decisions on this topic. [ABSTRACT FROM AUTHOR]

Focused Clinical Question: Under what circumstances may a clinician consider dental implant placement at a site exhibiting a focal high or mixed density (HMD) osseous lesion radiologically? Summary: Some conditions and pathologic entities exhibiting high and mixed density radiological appearance pose low risk for dental implant failure or complications following implant surgery. However, other lesions represent contraindications to implant placement, and implant surgery at such sites can result in severe morbidity. Conclusion: Potential implant sites exhibiting focal HMD osseous lesions/conditions present varying levels of risk. In most cases, optimal management will include advanced imaging of the site, multidisciplinary consultations, and detailed informed consent to assure full understanding of procedural risks, benefits, and complications. Currently, clinical recommendations rely on case reports, opinion, and usual practice (level 3 evidence). The strength of each recommendation provided in this report is categorized as level C. [ABSTRACT FROM AUTHOR]

Introduction: Existing evidence supports superior treatment outcomes in guided bone regeneration (GBR) procedures employing membrane fixation. The purpose of this report is to present a specific flap design and suturing method for stabilizing GBR barrier membranes. Case Presentation: Two generally healthy patients received GBR using native collagen membranes stabilized with absorbable sutures. In both cases, we fixed barrier membranes apically using "triangle" sutures. Sling sutures (Case 1) or triangle sutures (Case 2) secured the crestal and palatal aspects of the membranes. No postoperative complications occurred, and both sites exhibited favorable alveolar ridge volume for implant placement. Conclusions: The described triangle suture technique reliably stabilized GBR barrier membranes without the need for fixation hardware. Compared with suturing methods that limit graft volume and apply pressure over the grafted area, the triangle suture may offer clinical advantages. [ABSTRACT FROM AUTHOR]

Focused Clinical Question: In generally healthy patients receiving third molar, periodontal, or dental implant surgery, do postoperative oral corticosteroids effectively limit pain and swelling compared with placebo or alternative medications? [ABSTRACT FROM AUTHOR]

Introduction: Guided bone regeneration (GBR) is the most commonly utilized procedure for augmenting deficient alveolar ridges in support of dental implant placement. In a GBR procedure, barrier membrane dimensions, bone graft volume, and surgical complexity may influence the risk of postsurgical morbidity. Case presentation: A 25-year-old female in good general health received GBR at two mandibular first molar sites exhibiting horizontal ridge deficiency. High-density polytetrafluoroethylene membranes were intentionally limited in size, and small-volume freeze-dried bone allografts were applied only where clinically beneficial for implant site development. Treatment resulted in clinically favorable ridge augmentation with no appreciable swelling and minimal postoperative discomfort. Conclusion: At dental implant sites exhibiting modest alveolar ridge deficiency, limiting GBR barrier membrane dimensions and bone graft volumes may enhance patient-centered outcomes while accomplishing clinical goals. [ABSTRACT FROM AUTHOR]

Objective: To assess stability of laser periodontal therapy (LPT) results after orthodontic tooth movement. Background: Periodontitis and malocclusion each exhibit high global prevalence. Thus, dentists inevitably face increasing demand for orthodontic treatment in patients with reduced periodontal support. Many of these patients benefit from orthodontic treatment, provided that periodontal inflammation is controlled. Materials and methods: We present a case demonstrating successful orthodontic treatment of periodontally compromised teeth after LPT. A patient with severe attachment and alveolar bone loss received orthodontic treatment 13 months after neodymium-doped: yttrium aluminum garnet LPT (1064 nm). We utilized three laser parameter sets for various purposes during the procedure--ablation of the periodontal pocket epithelium (2.8 W, 20 Hz, 100 ls), clot stabilization (2.8 W, 20 Hz, 550 ls), and photobiomodulation (2.8 W, 20 Hz, 100 ls, noncontact). Results: Treatment resulted in improved radiographic bone levels, clinical parameters consistent with periodontal health, and favorable occlusal relationships. Conclusions: In the presented case, we successfully treated a patient presenting with malocclusion and reduced periodontal support while avoiding the risk and morbidity of conventional periodontal surgery. Controlled clinical research to establish the predictability of the described approach appears warranted. [ABSTRACT FROM AUTHOR]

Introduction: Schneiderian membrane perforation (SMP), which is usually readily manageable, is the most common intraoperative complication of sinus elevation surgery. Some evidence suggests that SMP is associated with increased risk for postoperative complications, including maxillary sinusitis. Antral wall discontinuity (AWD) is an acquired condition that may increase SMP likelihood and lead to larger, less‐manageable perforations. Case Presentation: A generally healthy patient receiving sinus elevation surgery exhibited an AWD in the palatine process of the maxilla. The osseous defect was isolated intraoperatively, and the Schneiderian membrane was sharply dissected from the palatal connective tissue. Favorable augmentation of the maxillary sinus was noted on cone‐beam computed tomography (CBCT) assessment at postoperative month 34. Conclusions: AWD (fusion of the Schneiderian membrane with the periosteum of the maxilla) is a condition identifiable on preoperative CBCT images, which may increase the incidence and severity of SMP during sinus elevation procedures. Careful assessment for integrity of antral osseous walls before surgery is essential. Presence of AWD may obligate modifications to the surgical plan, or in some cases, contraindicate sinus elevation surgery. [ABSTRACT FROM AUTHOR]

Introduction: Continuous and interrupted sling sutures (ISSs) are used around teeth in contemporary periodontics. However, conventional ISSs depend upon favorable tooth morphology for stability through the early healing period. The purpose of this report is to present a variation of the classic ISS that does not rely on favorable tooth morphology. Case Series: Tissue‐supported sling sutures (TSSs) were used for six patients undergoing root coverage, gingival augmentation, or pontic site development (guided bone regeneration) procedures. Conclusions: Although techniques such as vertical mattress suturing may support greater coronal flap advancement, the TSS technique does maintain coronal flap position while minimizing trauma to papillae. TSS stability is independent of tooth morphology and may offer clinicians flexibility in achieving reliable closure over hard and soft tissue implants. Like mattress sutures, TSSs reduce tension at the crestal incision line in tissue grafting procedures. [ABSTRACT FROM AUTHOR]

Focused Clinical Question: What factors identify the optimal surgical technique when a distal wedge procedure is indicated at a terminal maxillary or mandibular molar site? Summary: Incision design for the distal wedge procedure is based primarily on the dental arch (maxilla or mandible), the distance from the terminal molar to the hamular notch or ascending ramus, and the dimensions of the attached gingiva. Conclusions: In most situations, favorable clinical results are achievable irrespective of the chosen distal wedge method, and technique selection is based more on operator preference than evidence. However, anatomic limitations can render distal wedge procedures challenging in some cases, and procedural advantages of specific techniques can simplify treatment. One systematic approach to distal wedge technique selection is presented in this report. Additionally, a laser‐assisted distal wedge protocol is presented for cases in which unfavorable tooth‐to‐ramus distance or presence of a prominent external oblique ridge contraindicates conventional distal wedge techniques. [ABSTRACT FROM AUTHOR]

Focused Clinical Question: For a generally healthy patient with no risk indicators for postoperative infection, what is the most appropriate perioperative antibiotic regimen for sinus elevation surgery in terms of reducing postoperative infection risk and minimizing untoward effects? Clinical Scenario: A 38‐year‐old female patient in good general and periodontal health presents missing tooth #14 (Fig.). She reports no systemic conditions, no history of sinusitis, and no allergies. Medications include acetaminophen and ibuprofen as needed for pain. The patient's dentition is minimally restored, with no active caries. Cone‐beam computed tomography reveals a clear, pneumatized left maxillary sinus and inadequate bone volume to support dental implant placement (Fig.). No septa or pathologic lesions are present, the ostium appears patent, and no thickening of the Schneiderian membrane is appreciable. The patient states that she wants to replace her missing molar without restoring adjacent teeth (Figs. and). Baseline clinical appearance (example sinus elevation case). The patient is a healthy 38‐year‐old female missing tooth #14. Inadequate bone volume is present for dental implant placement due to pneumatization of the left maxillary sinus. Preoperative cone‐beam computed tomography images. 2a Sagittal view. 2b Coronal view. Cone‐beam computed tomography images at postoperative month 6. 3a Sagittal view. 3b Coronal view. Definitive implant‐supported restoration, tooth #14. [ABSTRACT FROM AUTHOR]

Introduction: Postoperative discomfort is a documented complication of the epithelialized palatal graft (EPG) procedure, and the expectation of an unpleasant patient experience may cause some practitioners to avoid EPG altogether. However, EPG affords distinct advantages in a variety of clinical situations, and the postoperative discomfort associated with the procedure can be minimized. Case Series: Three generally and periodontally healthy patients with gingival recession defects and minimal zones of attached gingiva received mandibular anterior EPG procedures. In all cases, collagen membranes were trimmed to fit the palatal donor sites and sutured in place. Two patients reported minimal donor site discomfort at any time point. One patient with large bilateral donor sites reported moderate palatal discomfort limited to the first postoperative week. All patients reported overall positive treatment experiences. Conclusions: Placement of a resorbable collagen membrane at large EPG harvest sites appears to limit topical irritation of the wound and may substantially improve patient comfort postoperatively. Combining local and systemic measures to minimize patient discomfort may render EPG procedures very tolerable for patients. Controlled clinical trials comparing patient‐centered outcomes following EPG harvest with and without collagen membrane placement appear warranted. [ABSTRACT FROM AUTHOR]

Prior studies have defined minimum mesiodistal space (MS) and faciolingual alveolar width (FAW) requirements for dental implant sites, and failure to observe these constraints may adversely impact peri-implant health and esthetics. However, to the authors' knowledge, no previous reports have established frequencies at which anterior tooth positions present favorable MS and FAW for implant accommodation. A single examiner analyzed 205 cone-beam computed tomographic images, recording MS and FAW available for implant placement at anterior tooth positions. The examiner compared measurements with standardized implant diameters to assess anticipated implant-to-tooth distances and peri-implant bone thicknesses. In the esthetic zone, lateral incisor sites most frequently failed to present favorable MS. At maxillary lateral incisor positions, 22% (left) and 27% (right) of sites offered less than 2 millimeters between the proposed implant platform and the adjacent teeth. In mandibular incisor positions, implant-to-tooth distance was less than 2 mm at 79% through 97% of sites and less than 1.5 mm at 35% through 76% of sites. Over one-half of maxillary incisor sites and 78% through 95% of mandibular incisor sites exhibited FAW of less than 4 mm beyond implant diameter. In the population evaluated, mandibular incisor positions frequently presented unfavorable MS to accommodate conventional narrow-diameter implants. In addition, considerable proportions of mandibular incisor and maxillary lateral incisor sites may be at risk of developing unfavorable peri-implant bone thickness when conventional narrow-diameter implants are used. Practitioners should consider small-diameter implants and nonimplant tooth replacement methods for many patients missing single mandibular incisors or maxillary lateral incisors. [ABSTRACT FROM AUTHOR]

Introduction: The epithelialized palatal graft (EPG), introduced in 1963, has persisted as the gold standard for gingival augmentation, and in the present era, mucosal augmentation around dental implants has become an important concern. A limited body of evidence suggests peri‐implant mucosal augmentation may favorably impact bone and mucosal stability and peri‐implant health under some circumstances. Although more contemporary procedures for peri‐implant mucosal augmentation are often preferred based on convenience and esthetic considerations, EPG augmentation at dental implant sites is distinguishable from methods which do not deepen the vestibule and eliminate unfavorable superficial soft tissue. Implant sites augmented with EPG are qualitatively distinct from sites augmented using other methods. Case Series: Seven generally healthy patients received EPG augmentation before dental implant placement, at implant placement, before implant uncovering, or after implant uncovering. In each case, the patient exhibited a favorable zone of attached peri‐implant mucosa following treatment. Conclusions: Reliable mucosal augmentation with EPG is achievable at multiple phases in the course of dental implant therapy. EPG augmentation offers distinct clinical advantages and may be preferable to other mucosal augmentation strategies at some dental implant sites. [ABSTRACT FROM AUTHOR]

Introduction: The mandibular anterior can be a challenging anatomic location for achieving root coverage irrespective of the selected graft and surgical technique. The epithelialized palatal graft (EPG), often dismissed in deference to esthetic and patient‐centered considerations, is well‐suited for treating gingival recession in this region. Although a considerable volume of data exists assessing root coverage procedure outcomes, little evidence supports superiority of any one technique specifically applied to the mandibular anterior. Case Presentation: Two periodontally and systemically healthy patients with multiple adjacent Class I and III recession defects in the mandibular anterior were treated with EPG. Recipient site dimensions in one case obligated bilateral palatal donor sites. In this case, the two autogenous grafts were carefully sutured extraorally before placement. Favorable increases in attached gingival dimensions and partial or complete root coverage were noted after 12‐ or 18‐month follow‐up periods. In the case requiring bilateral donor sites, no transition between the two grafts could be appreciated after healing. Conclusions: Overall, subepithelial connective tissue graft (SCTG)‐based techniques reportedly produce higher mean root coverage percentages and more frequent complete root coverage compared with EPG. However, when observations are limited to the mandibular anterior, there are insufficient data to conclude SCTG is superior to EPG. In the presented cases, EPG at multiple adjacent mandibular anterior recession defects produced favorable clinical outcomes. Extraoral suturing of bilaterally harvested grafts facilitated graft stabilization and minimized irregularities in gingival architecture after healing. [ABSTRACT FROM AUTHOR]

Background: Delivery of a high‐quality provisional restoration at a maxillary anterior immediate implant site enhances patient‐centered outcomes and promotes development of favorable hard and soft tissue architecture. The purpose of this report is to present a protocol relying upon compatible guided surgery and laboratory systems for fabrication of a custom provisional crown prior to immediate implant surgery in the esthetic zone. Methods and Results: A female patient, aged 33 years, presented to the Army Postgraduate Dental School, Fort Gordon, Georgia, with an unfavorable prognosis for tooth #9. The patient elected extraction with immediate implant placement. Prior to the surgery, we utilized a cone‐beam computed tomography volume, stone models, implant planning software, and an implant indexing system to fabricate a custom provisional crown. Following extraction of tooth #9 and immediate implant placement, the provisional crown exhibited excellent fit and finish, requiring virtually no chairside adjustment. We noted minimal change in baseline mucosal contours throughout the healing phase. Conclusion: The clinical/restorative protocol described in this report assured accurate three‐dimensional implant positioning and permitted indirect fabrication of a high‐quality custom provisional crown in advance of surgery. The laboratory workflow—which dental technicians/auxiliaries can master—has the potential to shorten surgery, enhance treatment outcomes, and increase patient satisfaction. Key points: Why is this case new information? This report provides a stepwise workflow guiding indirect fabrication of a custom provisional crown prior to immediate implant placement. What are the keys to successful management of this case? The described technique requires compatible laboratory and guided surgery systems to assure that the restoration accounts for the three‐dimensional position and timing of the implant. What are the primary limitations to success in this case? Dental technicians/auxiliaries can master this protocol and independently produce high‐quality provisional implant restorations under supervision, potentially enhancing practice efficiency. However, practitioners should provide adequate staff training to optimize reliability and quality. [ABSTRACT FROM AUTHOR]

Introduction: Sinus graft infection with consequent acute bacterial rhinosinusitis (ABRS) is a complication that can occur during the postoperative period following sinus augmentation surgery. A small group of bacteria appear to predominate in ABRS, and these bacteria are empirically susceptible to tetracycline antibiotics, barring the presence of resistant strains. Historically, clinicians have mixed tetracycline with various biomaterials or hydrated biomaterials in a dilute tetracycline solution in the treatment of periodontal disease and for ridge preservation/augmentation indications. Case Presentation: In the present case, a 39‐year‐old African‐American male with sinus graft infection and signs and symptoms consistent with ABRS was successfully treated by removing the initial graft material, thoroughly debriding and irrigating the antrum, and placing a freeze‐dried bone allograft hydrated in an aqueous tetracycline solution. Conclusion: Given the typical bacteria present in ABRS, locally applied tetracycline may be useful prophylactically in sinus elevation surgery or as an adjunct in managing postoperative sinus graft infection. [ABSTRACT FROM AUTHOR]

Traumatic Brain Injury (TBI) has been described as the “signature injury” of the Global War on Terror. Explosive blast TBI has become a leading cause of injury as a result of the widespread use of improvised explosive devices in Iraq and Afghanistan. We present a retrospective cross-sectional study of patients with blast-related mild TBI (mTBI, N = 303) seen at the Intrepid Spirit Concussion Recovery Center at Naval Medical Center Camp Lejeune. The objective was to predict outcomes of return to duty (RTD) vs. medical retirement via medical evaluation board (MEB), based on brain imaging, neuropsychological data, and history of mTBI. The motivation is to inform prognosis and target resources to improve outcomes for service members who are less likely to RTD through the standard treatment program. The RTD was defined operationally as individuals who completed treatment and were not recommended for medical retirement or separation for TBI or related sequelae. Higher scores on the Repeatable Battery for Neuropsychological Status (RBANS) test were associated positively with RTD (p = 0.001). A history of three or more lifetime concussions was associated negatively with RTD, when compared with one concussion (p = 0.04). Elevated apparent diffusion coefficient (ADC) in the anterior corona radiata was associated negatively with RTD (p = 0.04). A logistic regression model was used to classify individuals with RBANS and imaging data (n = 81) as RTD or MEB according to RBANS, ADC, and a history of multiple (≥3) concussions. The RBANS (p = 0.003) and multiple concussions (p = 0.03) were significant terms in the logistic model, but ADC was not (p = 0.27). The area under the receiver operating characteristic curve was 0.77 (95% confidence interval 0.66–0.86). These results suggest cognitive testing and TBI history might be used to identify service members who are more likely to be retired medically from active duty. [ABSTRACT FROM AUTHOR]

Introduction: Minimally invasive surgical techniques in periodontics, including methods for ridge augmentation, have been shown to achieve surgical goals while minimizing swelling, decreasing postoperative discomfort, and enhancing soft tissue architecture. The present case illustrates a minimally invasive guided bone regeneration technique for augmentation of a deficient alveolar ridge in the esthetic zone. Case Presentation: A 30‐year‐old patient received localized ridge augmentation utilizing tunnel access for guided bone regeneration with a dense polytetrafluoroethylene membrane and a freeze‐dried bone allograft. The patient experienced minimal postoperative swelling and discomfort, and the procedure resulted in favorable ridge dimensions for implant placement. Conclusions: The tunnel access for guided bone regeneration presented in this case may offer advantages similar to other minimally invasive ridge augmentation techniques. Further controlled clinical study is warranted. [ABSTRACT FROM AUTHOR]

Introduction: Numerous biomaterials are available for augmenting bone around dental implants. In contained extraction sockets, a demineralized freeze‐dried bone allograft (DFDBA) appears capable of maintaining dimensional stability of the alveolar ridge as well as mineralized alternatives but may yield a higher percentage of new vital bone. When DFDBA is used in large horizontal gap defects at molar immediate implant sites, graft containment and protection must occur through provisional restoration, an anatomic custom healing abutment, or by other means. Case Series: Two mandibular molar immediate implant sites received DFDBA covered by dense polytetrafluoroethylene membranes. Conclusion: The present report suggests a protocol for maintaining favorable dimensional stability of the alveolar ridge at molar immediate implant sites, while possibly minimizing residual peri‐implant biomaterial. [ABSTRACT FROM AUTHOR]

Introduction: A contemporary protocol for managing horizontal alveolar defects adjacent to immediate implants includes placement of a well‐designed provisional restoration to contain graft material and seal the socket. However, immediate provisionalization is not always possible or practical. Case Presentation: A 39‐year‐old male presented with a non‐restorable tooth #29, which was extracted. An immediate implant was placed in the tooth #29 position, and a freeze‐dried bone allograft was placed in the horizontal defect between the implant platform and osseous walls. A neodymium:yttrium‐aluminum‐garnet (Nd:YAG) laser was used to create a stable fibrin clot over the graft material. After 31 months, favorable radiographic bone levels and complete papilla fill were noted. Conclusion: The present case illustrates use of an Nd:YAG laser in the management of an immediate implant horizontal defect in lieu of an immediate provisional restoration. [ABSTRACT FROM AUTHOR]

The article looks at a study regarding the risk of cigarette smoking for periodontitis as bacteria appear necessary for initiation of inflammatory periodontal tissue destruction. Topics discussed include possible effect of smoking on the attendant pathogenic ecosystem, neutrophils exhibit reduced chemotaxis and various other functional abnormalities and surgical treatment of periodontitis tends to cluster within patients who smoke.

Objectives: Emerging therapies designed to improve soft tissue flap survival include the use of angiogenic factors. However, endogenous expression patterns for these factors have not been characterized. The purpose of this study was to identify spatial and temporal variations in expression patterns of angiogenesis-associated genes in ischemic rat skin flaps. Study Design: This is an observational animal study characterizing spatial and temporal angiogenesis associated gene expression patterns in rat ischemic skin flaps. Methods: Dorsal skin flaps were created on 15 male Sprague-Dawley rats. The flap tissue was harvested and sectioned at 1, 3, or 7 days postsurgery. Total RNA was isolated, amplified, labeled with biotin, and hybridized to microarrays containing probes for 113 angiogenesis-associated genes. Microarray analysis revealed unique spatial and temporal patterns with statistically significant gene modulation over the length of the flap (P<.05). Results: The molecular analysis performed in this study correlates with the hemodynamic profile previously published. Expression patterns associated with blood flow were markedly different from patterns associated with stasis and avascularity. Conclusions: To our knowledge, this study is the first to characterize endogenous spatial and temporal angiogenesisassociated gene expression in rat ischemic skin flaps. Further characterization of expression patterns may allow clinicians to differentiate ischemic tissue that may be rescued via pharmacological or surgical intervention from tissue destined to succumb. Additionally, comparison of the expression profiles observed in this study with profiles generated from pharmacologically treated rats may suggest mechanisms for enhanced healing. [ABSTRACT FROM AUTHOR]

Selenium poisoning is a significant health problem in parts of Punjab, India, which is an area of intense agricultural productivity. To determine the complex soil dynamics that control distribution of Se in this area, we measured concentrations and δ82/76Se of bulk Se and individual Se pools in four soil profiles. This was compared against δ82/76Se of crops and groundwater used for irrigation. The isotopic composition of bulk Se and component Se pools reveal spatial heterogeneity. The bulk δ82/76Se show progressively lower values with increasing soil depth indicating the preferential migration of isotopically lighter Se downward through the soil profile. The δ82/76Se of water-soluble Se is isotopically heavier than δ82/76Se of adsorbed Se, suggesting Se isotope fractionation by reduction prior to scavenging by reactive minerals in the soil. The organically bound Se is isotopically lighter than water-soluble Se and correlates with the C/N ratio at different soil depths. Thus, Se immobilization by redox cycling controls the biogeochemical Se cycle in the soil. Se isotope ratios help to trace biochemical processes of Se in agricultural seleniferous soils and provide an important assessment for better soil management mitigating Se concentrations of ecotoxicological levels. [ABSTRACT FROM AUTHOR]

Measurements of the uranium (U) isotope ratio 238 U/ 235 U provide an emerging redox proxy in environmental and paleoredox studies, but many key parameters concerning U isotope fractionation are still poorly constrained. Here we report the equilibrium isotopic fractionation between dissolved U(IV) and dissolved U(VI), and rates of isotope exchange between solid-phase U(IV) and dissolved U(VI). We conducted one experiment at high concentration [35 mM U(IV) and 32 mM U(VI)] and low pH (0.2) in hydrochloric acid media at room temperature to determine the equilibrium isotopic fractionation between dissolved U(IV) and dissolved U(VI). Isotopic equilibrium was reached in about 19 days under such experimental conditions. The equilibrium isotope fractionation was determined to be 1.64 ± 0.16‰, with U(IV) being enriched in 238 U relative to U(VI). Applicability of the determined equilibrium fractionation is discussed. We also conducted a set of experiments to determine isotopic exchange rates between dissolved U(VI) and nanouraninite U(IV) under conditions closer to those in natural system, with lower concentrations and neutral pH. The exchange rate was found to conform to the rate law R = k [U(VI)] adsorbed , in which R is the isotopic exchange rate (μM day −1 ); k is the rate constant determined to be 0.21 day −1 ; and [U(VI)] adsorbed is the concentration of U(VI) adsorbed to nanouraninite (μM). Our results, combined with consideration of the variables controlling U(VI)–U(IV) contact in natural settings, indicate that the timescale for significant isotope equilibration varies depending on environmental conditions, mostly uranium concentrations. In natural uncontaminated sediments with low uranium concentrations, equilibration is expected to occur on a timescale of hundreds to thousands of years. In contrast, in U-contaminated aquifers with high U concentrations, significant equilibration could occur on timescales of weeks to years. [ABSTRACT FROM AUTHOR]

We determined the equilibrium isotope fractionation between Cr(III) and Cr(VI), defined as Δ 53 Cr VI-III = δ 53 Cr(VI) − δ 53 Cr(III), and the rates of isotopic exchange between the two redox species under different conditions. In high Cr concentration, low-pH experiments we determined the Δ 53 Cr V-III between CrO 4 2− and Cr(H 2 O) 6 3+ to be 5.2 ± 0.3‰ and 5.5 ± 0.3‰ at 60 °C and 40 °C, respectively. At 25 °C, the system only progressed 25% toward isotopic equilibrium after 684 days. By extrapolating from the 60 °C and 40 °C experiments we estimated the Δ 53 Cr VI-III between CrO 4 2− and Cr(H 2 O) 6 3+ to be 5.8 ± 0.5‰ at 25 °C. Isotope exchange rates between dissolved Cr(III) and dissolved Cr(VI) at 25 °C, 40 °C, and 60 °C were determined to be 3.13 × 10 −5 M day −1 , 6.83 × 10 −4 M day −1 , and 8.37 × 10 −3 M day −1 , respectively. In low concentration, neutral-pH experiments we determined the isotopic exchange rates between dissolved Cr(VI) and solid Cr(III) oxyhydroxide at 25 °C. In these experiments, significant isotopic exchange was found on time scales of months, though the magnitude of isotopic shifts was limited by the small mass of Cr(III) available for exchange on the surfaces of Cr(III) oxyhydroxide particles. Exchange rates were relatively fast, compared to rates obtained from high concentration, low-pH experiments. This faster isotopic exchange is attributed to adsorption of Cr(VI) to Cr(III) particle surfaces, which keeps Cr(III) and Cr(VI), and potentially intermediate species Cr(V), in close proximity long enough to allow multiple electron transfers. The isotopic exchange rate at neutral-pH was found to conform to the rate law R = k ·[Cr(VI)] adsorbed , in which R is the isotopic exchange rate (M day −1 ); k is the rate constant, determined to be 0.00047 day −1 ; [CrO 4 2− ] adsorbed is the concentration of Cr(VI) adsorbed to Cr(III) oxyhydroxide (M). The impact of isotopic exchange on the 53 Cr/ 52 Cr ratio of the dissolved Cr(VI) depends on the relative masses and 53 Cr/ 52 Cr ratios of the starting Cr(III) and Cr(VI), as well as the fraction of Cr(III) atoms exposed to solution. In many natural settings, isotopic exchange will have little impact, because only very small amounts of Cr(VI) are adsorbed onto Cr(III) oxyhydroxide surfaces. However in certain settings with low Cr(VI) concentrations and abundant, exposed Cr(III)-bearing solids, significant isotopic exchange could happen within about 20 years. [ABSTRACT FROM AUTHOR]

We conducted laboratory experiments to investigate isotopic fractionations during oxidation of tetravalent uranium, U(IV), by dissolved oxygen. In hydrochloric acid media with the U(IV) dissolved, the δ 238 U value of the remaining U(IV) increased as the extent of oxidation increased. The δ 238 U value of the product U(VI) paralleled, but was offset to 1.1 ± 0.2‰ lower than the remaining U(IV). In contrast, oxidation of solid U(IV) by dissolved oxygen in 20 mM NaHCO 3 solution at pH = 9.4 caused only a weak fractionation (∼0.1‰ to 0.3‰), with δ 238 U being higher in the dissolved U(VI) relative to the solid U(IV). We suggest that isotope fractionation during oxidation of solid U(IV) is inhibited by a “rind effect”, where the surface layer of the solid U(IV) must be completely oxidized before the next layer is exposed to oxidant. The necessity of complete conversion of each layer results in minimal isotopic effect. The weak shift in δ 238 U of U(VI) is attributed to adsorption of part of the product U(VI) to the solid U(IV) surfaces. [ABSTRACT FROM AUTHOR]

Reduction of Cr(VI) is an important process that determines the geochemical behavior, mobility and bioavailability of Cr in both terrestrial and marine environments. Many metabolically diverse microorganisms possess Cr(VI) reduction capacity. Cr(VI) reduction fractionates Cr isotopes and thus 53 Cr/ 52 Cr ratios can be used to monitor Cr(VI) reduction and redox conditions. The magnitude of isotopic fractionation ( ε ) for a variety of microbial reduction mechanisms must be known for accurate interpretation of observed shifts in 53 Cr/ 52 Cr ratios. We determined isotopic fractionation factors for Cr(VI) reduction by metal reducers Geobacter sulfurreducens and Shewanella sp. strain NR, a denitrifying soil bacterium Pseudomonas stutzeri DCP-Ps1, and a sulfate reducer Desulfovibrio vulgaris . All bacteria investigated in this study produced significant Cr isotope fractionation. The fractionation ( ε ) for G. sulfurreducens , Shewanella sp. (NR), P. stutzeri DCP-Ps1, and D. vulgaris were −3.03‰ ± 0.12‰, −2.17‰ ± 0.22‰, −3.14‰ ± 0.13‰, and −3.01‰ ± 0.11‰, respectively. Despite differences in microbial strains in this study, the ε did not vary significantly except for Shewanella sp. (NR). Our results suggest that strong isotopic fractionation is induced during Cr(VI) reduction under electron donor poor (∼300 μM) conditions. [ABSTRACT FROM AUTHOR]

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]

Selenium isotopes are becoming an important paleoenvironmental proxy. However, few studies have focused on the behavior of Se isotopes during oxidative weathering. In this paper, a comprehensive set of Se isotopic composition and concentration data were collected from the weathering profiles of Se-rich shales of the Permian Maokou Formation in Yutangba and Shadi, China to investigate Se isotopic fractionation and Se enrichment during weathering processes. The δ82/76Se in fresh shales (148±118mg/kg Se, 1SD, n =40) from Shadi and Yutangba drill cores varies from −1.69‰ to 1.74‰ with an average of 0.40±0.71‰ (1SD, n =40), consistent with the range in other Phanerozoic shales, suggesting that Se isotopes are not strongly fractionated during Se sequestration in the primary sedimentary environment. However, the strongly weathered Se-rich shales from Shadi and Yutangba profiles are isotopically lighter with average δ82/76Se values of −1.96±1.08‰ (1SD, n =5) and −1.08±1.83‰ (1SD, n =23), respectively. These data suggest that Se isotopes can be fractionated during oxidation and reduction processes associated with weathering, with heavier isotopes removed preferentially during oxidative weathering of shales. Such a shift, if found to be a global phenomenon, would have implications for models of the global Se cycle and interpretation of Se isotope data from past biogeochemical regimes. Locally altered shales exposed in a quarry at Yutangba are extremely enriched in Se with 1642±1505mg/kg (1SD, n =45), approximately 10 times greater than that in unaltered drill core samples. These rocks display very strong variation in δ82/76Se over short distances, with a single 60cm transect showing the most strongly negative and positive δ82/76Se values (−14.20‰ to +11.37‰) observed to date in natural samples. This suggests that Se has undergone multiple cycles of oxidation, mobilization, and re-reduction, resulting in a Se-rich redox front that has migrated downward through the organic-rich shales over time. δ82/76Se values vary sharply over distances as small as 10cm, indicating that Se redox conditions change strongly with position and are controlled by fractures and rock layering. Our data and a simple conceptual model suggest that zones of increased permeability that are accessed first by infiltrating waters are isotopically light, whereas less accessible zones are heavy. Repeated redox cycling accentuates this pattern. Furthermore, the average δ82/76Se in Se-rich shales at the Yutangba weathering system is 0.45±5.77‰ (1SD, n =39), identical with that (0.40±0.71‰) in fresh shales from same locality, implying that Se released by weathering accumulates in the redox front with little loss. The strong Se isotopic fractionation occurring in the redox front implies that Se isotopes can be extensively used in tracing geochemical processes of Se in groundwater system, especially related to fractures. [ABSTRACT FROM AUTHOR]

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: Iron isotope compositions of various Fe pools in aquifer sediments were measured at a known As-contaminated site in the Datong Basin, China. The δ 56Fe values of HCl-extracted poor-crystalline Fe(III) range widely from −0.41‰ to 0.36‰. We interpret the low Fe(II)/FeExtractable ratios (<50%) and the negative correlation between Fe(II)/FeExtractable and δ 56Fe values in HCl-extracted poor-crystalline Fe to be best explained by redox cycling of Fe induced by microbial Fe(III) reduction. However, the high Fe(II)/FeExtractable ratios (≳70%) and positive correlation between Fe(II)/FeExtractable and δ 56Fe values for HCl-extracted poor-crystalline Fe indicates production of sulfides (FeSs). The δ 56Fe values of crystalline Fe(III) extracted by reductant appears to be comparatively small varying from −0.01‰ to 0.24‰, which is consistent with the δ 56Fe values for ferric oxides/hydroxides having undergone microbial Fe(III) reduction. The Fe isotope composition of various Fe pools shows the transformation between crystalline Fe(III) and poor-crystalline crystalline Fe(III) and the secondary Fe(II) phases has already occurred or is occurring in aquifer sediments. More importantly, there is a significant difference in the As concentrations in crystalline Fe(III) oxides/hydroxides and HCl-extracted Fe phases. The concentrations of As range from 1.6 to 29.9mgkg−1 and from 0.6 to 3.0mgkg−1, for crystalline Fe(III) and HCl-extracted Fe phases respectively. Accordingly, the transformation of Fe minerals induced by microbial Fe(III) reduction can contribute to the mobilization of As. This study is the first to examine the Fe isotope compositions in high As aquifer sediments; the results show that the Fe isotope would be an important tool in demonstrating the enrichment of As in groundwater. [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]

Abstract: Chromium stable isotope ratios are useful as indicators of Cr redox reactions and Cr sources in both modern and ancient geochemical systems. Correct interpretation of Cr isotope data requires a quantitative understanding of isotopic fractionation by various processes, the most important of which is reduction of Cr(VI) to Cr(III). We determined the magnitude of isotopic fractionation, for the 53Cr/52Cr ratio, induced by abiotic, dark reduction of Cr(VI) by aqueous Fe(II) and a few organic substances. The isotopic fractionation for reduction by dissolved Fe(II), expressed as ε (≈δ 53Crproduct flux − δ 53Crreactant) is −4.20±0.11‰ from pH=4.0 to 5.3. Lesser fractionation was observed in preliminary experiments with very rapid reaction; we attribute this to transient heterogeneity and diffusive limitation of the reaction as reactants were mixed. This phenomenon is a general problem with batch isotopic fractionation experiments, if significant reaction occurs before mixing of reactants is complete. ε =−3.11±0.11‰ for reduction by three organic reductants (a humic acid at pH=4.5 and 5.0, a fulvic acid at pH=5.0, and mandelic acid catalyzed by goethite or γ-Al2O3 at pH=4.0). [Copyright &y& Elsevier]

Cr stable isotope measurements can provide improved estimates of the extent of Cr(VI) reduction to less toxic Cr(III). The relationship between observed 53Cr/52Cr ratio shifts and the extent of reduction can be calibrated by determining the isotopic fractionation factor for relevant reactions. Permeable reactive barriers (PRB) made of Fe0 and in situ redox manipulation (ISRM) zones effectively remediate Cr-contaminated aquifers. Here, we determine the isotopic fractionations for dominant reductants in reactive barriers and reduced sediments obtained from an ISRM zone at the US DOE's Hanford site. In all cases, significant isotopic fractionation was observed; fractionation (expressed as e) was -3.91‰ for Fe(II)-doped goethite, -2.11‰ for FeS, -2.65‰ for green rust, -2.67‰ for FeCO3, and -3.18‰ for ISRM zone sediments. These results provide a better calibration of the relationship between Cr isotope ratios and the extent of Cr(VI) reduction and aid in interpretation of Cr isotope data from systems with reactive barriers. [ABSTRACT FROM AUTHOR]

A combination of sequential extraction with stable isotope ratio measurements of Se might offer new insights into biogeochemical processes governing Se turnover in soils. Therefore, we determined the Se partitioning among three operationally defined sequential extracts (0.1 mol L-1 K2HPO4-KH2PO4 at pH 7,0.05 mol L-1 NaOH, cone. HNO3) and the stable isotope ratios of total Se (δ82/76Se values) in 10 topsoils under 5 different land uses (alluvial grasslands, forests, house gardens, parks, and roadside grassland) from the city of Bayreuth (ca. 73,000 inhabitants) in Germany. Furthermore, we determined S and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. concentrations and stable isotope ratios of total S (δ34S values) to support our interpretation of the Se concentrations and isotope ratios because of the chemical similarity of Se and S. All topsoils had low total Se concentrations (0.09-0.52 mgkg-1). The largest contribution to total Se was extracted with NaOH comprising up to 42%,which is thought to be associated with organic matter and metal oxides. The (δ82/76Se values)Se values of total Se in the topsoils were dose to the bulk Earth composition with an average S Se value of-0.03 ± SD 0.38‰ suggesting that there was no or little Se isotope fractionation in soil. We attribute the small isotope fractionation to the low bioavailability of Se as a consequence of the presence of Fe oxides (adsorbing the dominating Se(IV) forms strongly), organic matter, and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (prevents biouptake of the Se(IV) forms) in the study soils. Small Se isotope fractionations of -0.59 to -0.35‰ in mainly forest soils and of 0.26 to 0.45‰ in mainly alluvial soils were presumably caused by soil/plant-recycling and Se contamination by river water, respectively. In spite of the similarities in the assimilation of S and Se by organisms, the total S and Se isotope ratios in soil were not correlated. Our results demonstrate that Se in urban soils developed from Se-poor substrates is minimally cycled through the biosphere likely because of low bioavailability and competition with Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. [ABSTRACT FROM AUTHOR]

The natural abundance of stable Se isotopes may reflect sources and formation conditions of methylated Se. We aimed at (l) quantifying the degree of methylation of selenate [Se(VI)] and (hydro)selenite [Se(IV)] by the fungus Alternaria alternata at pH 4 and 7 and (2) determining the effects of these different Se sources and pH values on 82Se/76 Se ratios (δ82/76 Se) in methylselenides. Alterenaria alternata was incubated with Se(VI) and Se(IV) in closed microcosms for 11-15 days and additionally with Se(IV) for 3-5 days at 30 °C. We determined Se concentrations and δ82/76Se values in source Se(VI) and Se(IV), media, fungi, and trapped methylselenides. In Se(VI) incubations, methylselenide volatilization ended before the 11th day, and the amounts of trapped methylselenide were not significantly different among the 11 - 15 day incubations. In 11 - 15 days, 2.9-11% of Se(VI) and 21-29% of Se(IV) were methylated, and in 3-5 days, 3-5% of Se(IV) was methylated. The initial δ82/76 Se values of Se(VI) and Se(IV) were -0.69 ± SD 0.07%o, and -0.20 ± 0.05%o, respectively. The δ82/76Se values of methylselenides differed significantly between Se(VI) (-3.97%o to -3.25%o) and Se(IV) (- 1.44%o to -0.l6%o) as sources after 11-15 days of incubation; pH had little influence on δ82/76 Se values. Thus, the δ82/76 Se values of methylselenide indicate the source species of methylselenides used in this study. The strong isotope fractionation of Se(VI) is probably attributable to the different reduction steps of Se(VI) to Se(-II) which were rate-limiting explaining the low methylation yields, but not to the methylation itself. The shorter incubation of Se(IV) for 3-5 days showed a large Se isotope fractionation of at least -6%o before the biomethylation reaction reached its end. This initial Se isotope fractionation during methylation of Se(IV) is much larger than previously published. [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]

In the past several years, various ontologies and terminologies such as the Gene Ontology have been developed to enable interoperability across multiple diverse medical information systems. They provide a standard way of representing terms and concepts thereby supporting easy transmission and interpretation of data for various applications. However, with their growing utilization, not only has the number of available ontologies increased considerably, but they are also becoming larger and more complex to manage. Toward this end, a growing body of work is emerging in the area of modular ontologies where the emphasis is on either extracting and managing "modules" of an ontology relevant to a particular application scenario (ontology decomposition) or developing them independently and integrating into a larger ontology (ontology composition). In this paper, we investigate state-of-the-art approaches in modular ontologies focusing on techniques that are based on rigorous logical formalisms as well as well-studied graph theories. We analyze and compare how such approaches can be leveraged in developing tools and applications in the biomedical domain. We conclude by highlighting some of the limitations of the modular ontology formalisms and put forward additional requirements to steer their future development. [ABSTRACT FROM AUTHOR]

Wetlands remove many dissolved pollutants from surface waters by various mechanisms. Stable isotope ratio measurements may provide a means of detecting and possibly quantifying certain removal processes, such as reduction of SeO42-, Cr(Vl), NO3-, and HCIO4-, that fractionate isotopes. However, the magnitude of the isotopic fractionation for a given reaction depends on the setting in which it occurs. We explore the case where isotope ratio shifts in surface waters are used to detect or quantify reactions occurring in pore waters of underlying sediments. A series of SeO42- reduction experiments reveals that the effective isotopic fractionation, observed in the water column as a result of SeO42- diffusion into underlying, Se-reducing sediments, is weaker than the intrinsic fractionation induced by the same reduction reactions in well-mixed systems in which reaction sites are not separated from measured SeO42-. An intact sediment core yielded an effective ϵ (≈ δreact — δinstantaneous prod) of 0.20‰, whereas the intrinsic ϵ was 0.61‰. These results are consistent with previously published reactive transport models. Isotopic studies of sediment-hosted reactions in wetlands and other surface water systems should use the smaller effective fractionation values, which can be estimated using the models. [ABSTRACT FROM AUTHOR]

Abstract: Mass-dependent fractionation of Cr isotopes occurs during dissimilatory Cr(VI) reduction by Shewanella oneidensis strain MR-1. Cells suspended in a simple buffer solution, with various concentrations of lactate or formate added as electron donor, reduced 5 or 10μM Cr(VI) to Cr(III) over days to weeks. In all nine batch experiments, 53Cr/52Cr ratios of the unreacted Cr(VI) increased as reduction proceeded. In eight experiments covering a range of added donor concentrations up to 100μM, isotopic fractionation factors were nearly invariant, ranging from 1.0040 to 1.0045, with a mean value somewhat larger than that previously reported for abiotic Cr(VI) reduction (1.0034). One experiment containing much greater donor concentration (10mM lactate) reduced Cr(VI) much faster and exhibited a lesser fractionation factor (1.0018). These results indicate that 53Cr/52Cr measurements should be effective as indicators of Cr(VI) reduction, either bacterial or abiotic. However, variability in the fractionation factor is poorly constrained and should be studied for a variety of microbial and abiotic reduction pathways. [Copyright &y& Elsevier]

A new way of thinking about groundwater age is changing the field of groundwater age dating. Following a rigorous definition of age, a groundwater sample is seen not as water that recharged the flow regime at a point in the past, but as a mixture of waters that have resided in the subsurface for varying lengths of time. This recognition resolves longstanding inconsistencies encountered in age dating and suggests new ways to carry out age dating studies. Tomorrow's studies will likely employ sets of marker isotopes and molecules spanning a broad spectrum of age and incorporate a wide range of chemical and physical data collected from differing stratigraphic levels. The observations will be inverted using reactive transport modeling, allowing flow to be characterized not in one direction along a single aquifer, but in two or three dimensions over an entire flow regime. [ABSTRACT FROM AUTHOR]

The contribution of transcriptional activation to the p53 effector functions critical for tumor suppression, apoptosis and cellular senescence, remains unclear because of p53's ability to regulate diverse cellular processes in a transactivation-independent manner. Dissociating the importance of transactivation from other p53 functions, including regulating transcriptional repression, DNA replication, homologous recombination, centrosome duplication, and mitochondrial function, has been difficult because of overlapping motifs for these functions in the amino terminus. To determine the relative contribution of these activities and transactivation to p53 function, we generated knockin mice expressing a p53 mutant lacking domains involved in these transactivation-independent functions, while remaining competent for transactivation through fusion to the Herpes Simplex Virus VP16 transactivation domain. This chimeric mutant, termed p53VP16, robustly activates the transcription of a range of p53 targets involved in both apoptosis and senescence. Intriguingly, despite being transactivation-competent, this chimeric protein shows selectivity in p53 effector function in mouse fibroblasts, with a capacity to trigger senescence but not apoptosis under a variety of conditions. Our study highlights the central role of p53 transactivation for senescence while suggesting that transactivation is insufficient for apoptosis, and provides insight into the mechanisms by which pS3 serves as a tumor suppressor. [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]

Chromium stable isotope values can be effectively used to monitor reduction of Cr(Vl) in natural waters. We investigate effects of sorption during transport of Cr(Vl) which may also shift Cr isotopes values, complicating efforts to quantify reduction. This study shows that Cr stable isotope fractionation caused by sorption is negligible. Equilibrium fractionation of Cr stable isotopes between dissolved Cr- (VI) and Cr(Vl) adsorbed onto γ-Al2O3 and goethite is less than 0.04%o (53Cr/52Cr) under environmentally relevant pH conditions. Batch experiments at pH 4.0 and pH 6.0 were conducted in series to sequentially magnify small isotope fractionations. A simple transport model suggests that adsorption may cause amplification of a small isotope fractionation along extreme fringes of a plume, leading to shifts in 53Cr/52Cr values. We therefore suggest that isotope values at extreme fringes of Cr plumes be critically evaluated for sorption effects. A kinetic effect was observed in experiments with goethite at pH 4 where apparently lighter isotopes diffuse into goethite clumps at a faster rate before eventually reaching equilibrium. This observed kinetic effect may be important in a natural system that has not attained equilibrium and is in need of further study. Cr isotope fractionation caused by speciation of Cr(Vl) between HCro4 and CrO4² was also examined, and we conclude that it is not measurable. In the absence of isotope fractionation caused by equilibrium speciation and sorption, most of the variation in δ53Cr values may be attributed to reduction, and reliable estimates of Cr reduction can be made. [ABSTRACT FROM AUTHOR]