Sonochemical degradation of PFAS in ion exchange regeneration wastes.

One of the primary technologies currently being deployed for the removal of per- and polyfluoroalkyl substances (PFAS) from water is ion exchange (IX). For regenerable IX resins, concentrated PFAS in the resulting spent brine and/or still bottoms requires further treatment. This research demonstrated that PFAS in spent brine and still bottoms can be effectively degraded sonochemically at 1000 kHz. Overall, PFAS degradation was negatively impacted by high total organic carbon (TOC) and residual methanol (MeOH) solvent (up to 50 g/kg; 5% w:w), but was enhanced by the high chloride. The addition of caustic (up to 1 N NaOH) partially mitigated the inhibition by TOC and MeOH. Sonochemical degradation of individual PFAS compounds resulted in significant mineralization to form inorganic fluoride, but small quantities of volatile organic fluorine species (VOF) were noted. This is believed to be the first report of sonochemical degradation of PFAS in ion exchange regeneration wastes, and indicates the possibility for the application of this technology as part of a complete PFAS capture and destruction treatment train.

Carbon and Nitrogen Isotope Fractionations During Biotic and Abiotic Transformations of 2,4-Dinitroanisole (DNAN).

2,4-Dinitroanisole (DNAN) is a main constituent in various new insensitive munition formulations. Although DNAN is susceptible to biotic and abiotic transformations, in many environmental instances, transformation mechanisms are difficult to resolve, distinguish, or apportion on the basis solely of analysis of concentrations. We used compound-specific isotope analysis (CSIA) to investigate the characteristic isotope fractionations of the biotic (by three microbial consortia and three pure cultures) and abiotic (by 9,10-anthrahydroquinone-2-sulfonic acid [AHQS]) transformations of DNAN. The correlations of isotope enrichment factors (ΛN/C) for biotic transformations had a range of values from 4.93 ± 0.53 to 12.19 ± 1.23, which is entirely distinct from ΛN/C values reported previously for alkaline hydrolysis, enzymatic hydrolysis, reduction by Fe2+-bearing minerals and iron-oxide-bound Fe2+, and UV-driven phototransformations. The ΛN/C value associated with the abiotic reduction by AHQS was 38.76 ± 2.23, within the range of previously reported values for DNAN reduction by Fe2+-bearing minerals and iron-oxide-bound Fe2+, albeit the mean ΛN/C was lower. These results enhance the database of isotope effects accompanying DNAN transformations under environmentally relevant conditions, allowing better evaluation of the extents of biotic and abiotic transformations of DNAN that occur in soils, groundwaters, surface waters, and the marine environment.

Formation of volatile chlorinated and brominated products during low temperature thermal decomposition of the representative PFAS perfluorohexane sulfonate (PFHxS) in the presence of NaCl and NaBr.

Per- and polyfluoroalkyl substances (PFAS) are synthetic organofluorine compounds known for their chemical and physical stability as well as their wide range of uses. Some PFAS are widely distributed in the environment, leading to concerns related to both environmental and human health. High temperature thermal treatment (i.e., incineration) has been utilized for PFAS treatment, but this requires significant infrastructure and energy, prompting interest in lower temperature approaches that may still lead to efficient destruction. Lower treatment temperatures, however, increase the potential for incomplete PFAS mineralization and formation of volatile organofluorine (VOF) products. Herein, we report the formation of novel VOF products that include chlorinated and brominated compounds during the thermal treatment of potassium perfluorohexane sulfonate (PFHxS), a representative perfluoroalkyl acid (PFAA). By comparing the gas chromatography-mass spectrometry (GC-MS) results of known VOF stocks to evolved VOF during thermal treatment of PFAS, the formation of perfluorohexyl chloride and perfluorohexyl bromide was observed when PFHxS was heated at temperatures between 275 and 475 °C in the presence of NaCl and NaBr, respectively. To our knowledge, this is the first report of chlorinated or brominated VOF products during thermal treatment of a PFAA. These findings suggest that a range of mixed halogenated VOF may form during thermal treatment of PFAS at relatively low temperature (e.g., 500 °C) and that these can be a function of salts present in the matrix.

Isolation and characterization of nitroguanidine-degrading microorganisms.

Nitroguanidine (NQ) is a component of newly developed insensitive munition (IM) formulations which are more resistant to impact, friction, heat, or sparks than conventional explosives. NQ is also used to synthesize various organic compounds and herbicides, and has both human and environmental health impacts. Despite the wide application and associated health concerns, limited information is known regarding NQ biodegradation, and only one NQ-degrading pure culture identified as Variovorax strain VC1 has been characterized. Here, we present results for three new NQ-degrading bacterial strains isolated from soil, sediment, and a lab-scale aerobic membrane bioreactor (MBR), respectively. Each of these strains -utilizes NQ as a nitrogen (N) source rather than as a source of carbon or energy. The MBR strain, identified as Pseudomonas extremaustralis strain NQ5, is capable of degrading NQ at a rate of approximately 150 µmole L-1 h-1 under aerobic conditions with glucose as a sole carbon source - and NQ as a sole N source. The addition of NH4+ to strain NQ5 during active growth with NQ as a sole N source slowed the growth rate for several hours, and the strain released NH4+, presumably from NQ. When NO3- was added as an alternate N source under similar conditions, the NO3- was not consumed, but NH4+ release into the culture medium was again observed. Strain NQ5 was also able to utilize guanylurea, guanidine, and ethyl allophanate as N sources, and - tolerate salt concentrations as high as 4 % (as NaCl). The other two stains, NQ4 and NQ7, both identified as Arthrobacter spp., grew significantly slower than strain NQ5 under similar culture conditions and tolerated only ∼1 % NaCl. In addition, neither strain NQ4 nor strain NQ7 was able to degrade guanlyurea or ethyl allophanate, but each degraded guanidine. These strains, particularly strain NQ5, may have practical applications for in-situ and ex-situ NQ bioremediation.

Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents.

New energetic formulations containing insensitive high explosives (IHE), such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazole-5-one (NTO), and nitroguanidine (NQ) are being developed to provide safer munitions. The addition of IHE to munitions formulations results in complex wastewaters from explosives manufacturing, load and pour operations and demilitarization activities. New technologies are required to treat those wastewaters. The core objective of this research effort was to develop and optimize a dual anaerobic-aerobic membrane bioreactor (MBR) system for treatment of wastewater containing variable mixtures of traditional energetics, IHE, and anions. The combined system proved highly effective for treatment of traditional explosives (TNT, RDX, HMX), IHE (DNAN, NTO, NQ) and anions commonly used as military oxidants (ClO4-, NO3-). The anaerobic MBR, which was operated for more than 500 d, was observed to completely degrade mg L-1 concentrations of TNT, DNAN, ClO4- and NO3- under all operational conditions, including at the lowest hydraulic residence time (HRT) tested (2.2 d). The combined system generally resulted in complete treatment of mg L-1 concentrations of RDX and HMX to <20 µg L-1, with most of the degradation occurring in the anaerobic MBR and polishing in the aerobic system. No common daughter products of DNAN, TNT, RDX, or HMX were detected in the effluent. NTO was completely transformed in the anaerobic MBR, but residual 3-amino-1,2,4-triazole-5-one (ATO) was detected in system effluent. The ATO rapidly decomposed when bleach solution was added to the final effluent. NQ was initially recalcitrant in the system, but microbial populations eventually developed that could degrade >90% of the ∼10 mg L-1 NQ entering the anaerobic MBR, with the remainder degraded to <50 µg L-1 in the aerobic system. The dual MBR system proved to be capable of complete degradation of a wide mixture of munitions constituents and was resilient to changing influent composition.

Draft genomes of three nitroguanidine-degrading bacteria: Pseudomonas extremaustralis NQ5, Arthrobacter strain NQ4, and Arthrobacter strain NQ7.

We report the draft genome sequences of Pseudomonas extremaustralis NQ5, Arthrobacter strain NQ4, and Arthrobacter strain NQ7 isolated from a laboratory-scale membrane bioreactor, soils from San Antonio, TX, USA and sediments from Galveston Bay, TX, USA, respectively. These bacteria degrade the explosive compound nitroguanidine, which is present in some insensitive munitions.

AWAREness of Diagnosis and Treatment of Chronic Kidney Disease in Adults With Type 2 Diabetes (AWARE-CKD in T2D).

OBJECTIVES: Diabetes remains the leading contributor to the development of chronic kidney disease (CKD) and end-stage kidney disease, emphasizing the urgency of identifying barriers to early diagnosis and intervention. The primary objective of this study was to describe the awareness, values and preferences of physicians and patients with respect to managing CKD among patients with type 2 diabetes (T2D). METHODS: A cross-sectional survey was conducted among physicians and adult patients with T2D and CKD based on estimated glomerular filtration rate and urine albumin-to-creatinine ratio (uACR) measured within 1 year. Physicians were recruited from email networks across Canada, excluding Alberta, and patients were recruited from LMC Diabetes and Endocrinology clinics in Ontario and Quebec. Two separate surveys were developed by a steering committee. Survey responses from 160 physicians (60 general practitioners, 50 endocrinologists and 50 nephrologists) and 169 patients were analyzed descriptively. RESULTS: Gaps in physician care included insufficient use of uACR screening, limited knowledge or use of Kidney Disease Improving Global Outcomes (KDIGO) and KidneyWise resources and lower than expected prescription of recommended therapies. The patient data showed 51.5% of patients were unaware of a CKD diagnosis, and 75.6% of patients who received a prior CKD diagnosis would have preferred an earlier diagnosis. CONCLUSIONS: The results highlight several opportunities for improving CKD in T2D management. More education and clarity are needed for physicians interpreting uACR levels that should prompt a referral to a nephrologist, and additional understanding of kidney risk progression is vital for patients.

Abiotic reduction of 3-nitro-1,2,4-triazol-5-one (NTO) and other munitions constituents by wood-derived biochar through its rechargeable electron storage capacity.

The environmental fate of 3-nitro-1,2,4-triazol-5-one (NTO) and other insensitive munitions constituents (MCs) is of significant concern due to their high water solubility and mobility relative to legacy MCs. Plant-based biochars have been shown to possess a considerable electron storage capacity (ESC), which enables them to undergo reversible electron transfer reactions. We hypothesized biochar can act as a rechargeable electron donor to effect abiotic reduction of MCs repeatedly through its ESC. To test this hypothesis, MC reduction experiments were performed using wood-derived biochars that were oxidized with dissolved oxygen or reduced with dithionite. Removal of aqueous NTO, an anion at circumneutral pH, by oxidized biochar was minimal and occurred through reversible adsorption. In contrast, NTO removal by reduced biochar was much more pronounced and occurred predominantly through reduction, with concomitant formation of 3-amino-1,2,4-triazol-5-one (ATO). Mass balance and electron recovery with ferricyanide further showed that (1) the amount of NTO reduced to ATO was relatively constant (85-100 µmol per gram of biochar) at pH 6-10; (2) the fraction of biochar ESC reactive toward NTO was ca. 30% of that toward ferricyanide; (3) the NTO-reactive fraction of the ESC was regenerable over multiple redox cycles. We also evaluated biochar transformation of other MCs, including nitroguanidine (NQ), 2,4-dinitroanisole (DNAN), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). While mass and electron balances could not be established due to sorption, DNAN and RDX reduction by reduced biochar was confirmed via detection of multiple reduction products. In contrast, NQ was not reduced under any of the conditions tested. This study is the first demonstration of organic contaminant degradation through biochar's rechargeable ESC. Our results indicate biochar is a regenerable electron storage medium and sorbent that can remove MCs from water through concurrent reduction and sorption, and is thus potentially useful for pollution control and remediation at military facilities.

Density-dependent winter survival of immatures in an irruptive raptor with pulsed breeding.

Highly mobile predators can show strong numerical responses to pulsed resources, sometimes resulting in irruptions where large numbers of young invade landscapes at a continental scale. High production of young in irruption years may have a strong influence on the population dynamics unless immature survival is reduced compared to non-irruption years. This could occur if subordinate individuals (mainly immatures) are forced into suboptimal habitats due to density-dependent effects in irruption years. To test whether irruptive individuals had lower survival than non-irruptive ones, we combined necropsy results (N = 365) with telemetry (N = 185) from more than 20 years to record timing and causes of mortality in snowy owls (Bubo scandiacus), which irrupt into eastern North America during winter following high breeding output caused by lemming peaks in the Arctic. Mortality was more than four times higher in irruption years than non-irruption years, but only for immatures, and occurred disproportionately in early winter for immatures, but not adults. Mortality was also higher in eastern North America, where owl abundance fluctuates considerably between years, compared to core winter regions of the Arctic and Prairies where populations are more stable. Most mortality was not due to starvation, but rather associated with human activity, especially vehicle collisions. We conclude that immature snowy owls that irrupt into eastern North America are limited by density-dependent factors, such as increased competition forcing individuals to occupy risky human-altered habitats. For highly mobile, irruptive animals, resource pulses may have a limited impact on population dynamics due to low subsequent survival of breeding output during the nonbreeding season.

Removal of munition constituents in stormwater runoff: Screening of native and cationized cellulosic sorbents for removal of insensitive munition constituents NTO, DNAN, and NQ, and legacy munition constituents HMX, RDX, TNT, and perchlorate.

Technologies are needed to address contamination with energetic compounds at military installations. This research developed and evaluated novel and sustainable materials that can be used to remove munition constituents (MC) from stormwater runoff. Initial work focused on 3-nitro-1,2,4-triazol-5-one (NTO), as it is both highly soluble and ionized at environmentally relevant pH values. Screening cellulosic materials indicated that cationized (CAT) versions of pine shavings (pine, henceforth) and burlap (jute) demonstrated >70% removal of NTO from artificial surface runoff. CAT materials also demonstrated >90% removal of the anionic propellant perchlorate. NTO removal (~80%) by CAT pine was similar across initial pH values from 4 to 8.5 S.U. An inverse relationship was observed between NTO removal and the concentration of the major anions chloride, nitrate, and sulfate due to competition for anion binding sites. Sorption isotherms were performed using a mixture of the three primary legacy explosives (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5-trinitro-s-triazine (RDX), 2,4,6-trinitrotoluene (TNT)), the three insensitive MC (nitroguanidine (NQ), NTO, 2,4-dinitroanisole (DNAN)), and perchlorate. Isotherm results indicated that effective removal of both legacy and insensitive MC would best be achieved using a mixture of peat moss plus one or more of the cationized cellulosic materials.

Extensive diet-induced atherosclerosis in scavenger receptor class B type 1-deficient mice is associated with substantial leukocytosis and elevated vascular cell adhesion molecule-1 expression in coronary artery endothelium.

High levels of low density lipoprotein (LDL) cholesterol and low levels of high density lipoprotein (HDL) cholesterol are risk factors for cardiovascular disease. Mice that lack genes involved in the clearance of LDL from the bloodstream, such as the LDL receptor and apolipoprotein E, are widely used models of experimental atherosclerosis. Conversely, mice that lack the HDL receptor, scavenger receptor class B type I, and therefore have disrupted HDL functionality, also develop diet-inducible atherosclerosis but are a seldom-used disease model. In this study, we compared atherosclerosis and associated phenotypes in scavenger receptor class B type I knockout mice with those of wild type, LDL receptor knockout, and apolipoprotein E knockout mice after 20 weeks of being fed an atherogenic diet containing sodium cholate. We found that while scavenger receptor class B type I knockout mice had substantially lower plasma cholesterol than LDL receptor and apolipoprotein E knockout mice, they developed atherosclerotic plaques with similar sizes and compositions in their aortic sinuses, and more extensive atherosclerosis in their descending aortas and coronary arteries. This was associated with elevated tumor necrosis factor alpha levels in scavenger receptor class B type I knockout mice compared to wild type and LDL receptor knockout mice, and lymphocytosis, monocytosis, and elevated vascular cell adhesion molecule expression in coronary artery endothelial cells compared to the other mice examined. We conclude that extensive atherosclerosis in arteries that are not generally susceptible to atherosclerosis in scavenger receptor class B type I knockout mice is driven by factors in addition to hypercholesterolemia, including inflammation, dysregulation of the immune system and increased sensitivity of endothelial cells in arteries that are normally resistant to atherosclerosis. Scavenger receptor class B type I knockout mice fed a cholate containing atherogenic diet may prove to be a useful model to study mechanisms of atherosclerosis and evaluate treatments that rely on intact LDL clearance pathways.

Prevalence of Chronic Kidney Disease in Type 2 Diabetes: The Canadian REgistry of Chronic Kidney Disease in Diabetes Outcomes (CREDO) Study.

PURPOSE: Chronic kidney disease (CKD) in patients with type 2 diabetes (T2D) is associated with an elevated risk of end-stage kidney disease, cardiovascular disease (CVD), and death. As the breadth of treatment options for CKD in patients with T2D (CKD in T2D) continues to expand, an analysis of the current use of therapies and cardiovascular and kidney outcomes is necessary. The objectives of the study were to assess the prevalence of CKD in T2D among a contemporary cohort of patients, to describe patient characteristics and treatment patterns, and to examine health care practitioner rationale for initiating therapies. METHODS: The study was a retrospective, observational study (module A) with a prospective component (module B). For module A, sociodemographic data, medical history, prescription information, and laboratory investigations for patients seen by an endocrinologist in 2019 were retrieved from the LMC Diabetes Registry. Module B included a subset of patients for health care practitioner surveys to understand rationale for administering angiotensin-converting enzyme inhibitors (ACEis) or angiotensin receptor blockers (ARBs), steroidal mineralocorticoid receptor antagonists (MRAs), sodium-glucose cotransporter 2 inhibitors (SGLT2is), and glucagon-like peptide 1 receptor agonists (GLP-1RAs). Descriptive analyses were conducted. FINDINGS: The study included 14,873 patients (59% male). Mean patient age was 67 years, mean body mass index was 31 kg/m2, and mean glycosylated hemoglobin was 7.6%. Mean diabetes duration was 16 years. The prevalence of CKD in patients with T2D was 47.9%. Common comorbidities were hypertension (76%), dyslipidemia (71%), and obesity (51%). CVD was reported in 22%. The proportion of kidney medications and emerging therapies varied, with 76% of patients using an ACEi or ARB, 48% using an SGLT2i, 30% using a GLP-1RA, and 3% using a steroidal MRA. In module B, physicians identified that ACEis/ARBs, SGLT2is, GLP-1RAs, or steroidal MRAs were administered to primarily treat CKD in 33%, 12%, 0%, and 4% of the patients (n = 500), respectively. IMPLICATIONS: These findings improved our understanding of the current landscape and treatment patterns of CKD inT2D and highlighted the importance of considering treatments that will provide a comprehensive strategy for cardiovascular and kidney risk protection. Despite the high prevalence of CKD and comorbidities reported in a large, Canadian T2D specialist population, ACEis/ARBs, SGLT2is, and GLP-1RAs were underused, especially considering recent clinical trial reports. The relative use of steroidal MRAs was expectedly low. With an immense burden of CKD progression and among patients with T2D, the use of treatments that provide a comprehensive strategy for kidney protection will transform the landscape of CKD in T2D. ClinicalTrials.gov identifier: NCT04445181.

Position-specific isotope effects during alkaline hydrolysis of 2,4-dinitroanisole resolved by compound-specific isotope analysis, 13C NMR, and density-functional theory.

Compound-specific isotope analysis (CSIA), position-specific isotope analysis (PSIA), and computational modeling (e.g., quantum mechanical models; reactive-transport models) are increasingly being used to monitor and predict biotic and abiotic transformations of organic contaminants in the field. However, identifying the isotope effect(s) associated with a specific transformation remains challenging in many cases. Here, we describe and interpret the position-specific isotope effects of C and N associated with a SN2Ar reaction mechanism by a combination of CSIA and PSIA using quantitative 13C nuclear magnetic resonance spectrometry, and density-functional theory, using 2,4-dinitroanisole (DNAN) as a model compound. The position-specific 13C enrichment factor of O-C1 bond at the methoxy group attachment site (εC1) was found to be approximately -41‰, a diagnostic value for transformation of DNAN to its reaction products 2,4-dinitrophenol and methanol. Theoretical kinetic isotope effects calculated for DNAN isotopologues agreed well with the position-specific isotope effects measured by CSIA and PSIA. This combination of measurements and theoretical predictions demonstrates a useful tool for evaluating degradation efficiencies and/or mechanisms of organic contaminants and may promote new and improved applications of isotope analysis in laboratory and field investigations.

Photocatalytic mechanisms of 2,4-dinitroanisole degradation in water deciphered by C and N dual-element isotope fractionation.

In surface water environments, photodegradation may be an important process for the natural attenuation of 2,4-dinitroanisole (DNAN). Understanding the photolysis and photocatalysis mechanisms of DNAN is difficult because the photosensitivity of nitro groups and the behavior of DNAN as a potential photosensitizer are unclear in aqueous solutions. Here, we investigate the degradation mechanisms of DNAN under UV-A (λ ~ 350 nm) and UV-C (λ ~ 254 nm) irradiation in a photolysis reactor where aqueous solution was continuously recycled through a UV-irradiated volume from a non-irradiated external reservoir. By tracking C and N isotopic fractionation in DNAN and its reaction products, we observed normal 13C fractionation (εC = -3.34‰) and inverse 15N fractionation (εN = +12.30‰) under UV-A (λ ~ 350 nm) irradiation, in contrast to inverse 13C fractionation (εC = +1.45‰) and normal 15N fractionation (εN = -3.79‰) under UV-C (λ ~ 254 nm) irradiation. These results indicate that DNAN can act as a photosensitizer and may follow a product-to-parent reversion mechanism in surface water environments. The data also indicate that photocatalytic degradation of DNAN in aqueous systems can be monitored via C and N stable isotope analysis.

Biotransformation of the insensitive munition constituents 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN) by aerobic methane-oxidizing consortia and pure cultures.

We present the first report of biotransformation of 3-nitro-1,2,4-triazol-5-one (NTO) and 2,4-dinitroanisole (DNAN), replacements for the explosives 1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT), respectively, by methane-oxidizing cultures under aerobic conditions. Two consortia, dominated by Methylosinus spp., degraded both compounds with transient production of reduced NTO products, and non-stoichiometric production of reduced DNAN products. No release of inorganic nitrogen was observed with either compound, indicating that NTO and DNAN may be utilized as nitrogen sources by these consortia. The pure culture Methylosinus trichosporium OB3b also degraded both compounds. Degradation was observed in the presence of acetylene (a known inhibitor of methane monooxygenase; MMO) when methanol was supplied, indicating that MMO was not involved. Furthermore, studies with purified soluble MMO (sMMO) from OB3b indicated that neither compound was a substrate for sMMO. Degradation was inhibited by 2-iodosobenzoic acid, but not by dicoumarol, suggesting involvement of an oxygen- and dicoumarol-insensitive (nitro)reductase. These results indicate methanotrophs can aerobically degrade NTO and DNAN via one or more (nitro)reductases, with sMMO serving a supporting role deriving reducing equivalents from methane. This finding is important because methanotrophic bacteria are widely dispersed, and may represent a previously unrecognized route of NTO and DNAN biotransformation in aerobic environments.

The Use of Music by Adolescents and Young Adults With Sickle Cell Disease.

Pain is common and often severe in people with sickle cell disease (SCD), occurring as acute intermittent pain episodes called vaso-occlusive episodes (VOEs), as well as chronic pain conditions including bone infarctions, avascular necrosis of joints, and neuropathic pain. Analgesics such as opioids, nonsteroidal anti-inflammatory medications (NSAIDS), and anticonvulsants for neuropathic pain, although often necessary to manage these types of pain, are associated with side effects. Nonpharmacologic interventions such as to listening to music and music therapy may reduce pain. The objectives of this study were to determine whether the use of music by adolescents and young adults with SCD was helpful, and if so, the types of music that helped, and how music helped them. A convenience sample of nine English-speaking inpatients ages 13 to 21 years, with SCD and at least two prior hospitalizations for VOE, took part in interviews with music therapists. Participants were asked open-ended questions about both pain and music. Participants identified that music was helpful for pain relief as well as for mood regulation, focusing attention during cognitive tasks such as homework, distraction, relaxation, and feeling understood or connected with others. Despite this, while hospitalized, participants reported that they did not tend to use music to help with pain. These findings support the use of both music medicine and music therapy as interventions for pain and distress in adolescents and young adults with SCD.

Application of a multiple lines of evidence approach to document natural attenuation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in groundwater.

This study utilized innovative analyses to develop multiple lines of evidence for natural attenuation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in groundwater at the U.S. Department of Energy's Pantex Plant. RDX, as well as the degradation product 4-nitro-2,4-diazabutanal (NDAB; produced by aerobic biodegradation or alkaline hydrolysis) were detected in a large portion of the plume, with lower concentrations of the nitroso-containing metabolites produced during anaerobic biodegradation. 16S metagenomic sequencing detected the presence of bacteria known to aerobically degrade RDX (e.g., Gordonia, Rhodococcus) and NDAB (Methylobacterium), as well as the known anoxic RDX degrader Pseudomonas fluorescens I-C. Proteomic analysis detected both the aerobic RDX degradative enzyme XplA, and the anoxic RDX degradative enzyme XenB. Groundwater enrichment cultures supplied with low concentrations of labile carbon confirmed the potential of the extant groundwater community to aerobically degrade RDX and produce NDAB. Compound-specific isotope analysis (CSIA) of RDX collected at the site showed fractionation of nitrogen isotopes with δ15N values ranging from approximately -5‰ to +9‰, providing additional evidence of RDX degradation. Taken together, these results provide evidence of in situ RDX degradation in the Pantex Plant groundwater. Furthermore, they demonstrate the benefit of multiple lines of evidence in supporting natural attenuation assessments, especially with the application of innovative isotopic and -omic technologies.

A modular, multi-diagnostic, automated shock tube for gas-phase chemistry.

A new shock tube has been constructed for investigations of high-temperature chemical kinetics with an emphasis on combustion chemistry. This instrument includes a diaphragmless driver and electrical control of valving. A diaphragmless design significantly improves repeatability of experimental conditions vs the use of diaphragms and leads to an approximate order of magnitude reduction in turnaround time between experiments. Electrical control of valves, combined with diaphragmless operation, also enables remote and automated operation of the shock tube. The design allows for both incident and reflected shock experiments with multiple diagnostics. The performance of the shock tube is demonstrated by reproducing previous literature measurements on the unimolecular decomposition of isobutyl nitrite and cyclohexene.

Shock Tube Laser Schlieren Study of the Pyrolysis of Isopropyl Nitrate.

The decomposition of isopropyl nitrate was measured behind incident shock waves using laser schlieren densitometry in a diaphragmless shock tube. Experiments were conducted over the temperature range of 700-1000 K and at pressures of 71, 126, and 240 Torr. Electronic structure theory and RRKM Master Equation methods were used to predict the decomposition kinetics. RRKM/ME parameters were optimized against the experimental data to provide an accurate prediction over a broader range of conditions. The initial decomposition i-C3H7ONO2 ⇌ i-C3H7O + NO2 has a high-pressure limit rate coefficient of 5.70 × 1022T-1.80 exp[-21287.5/T] s-1. A new chemical kinetic mechanism was developed to model the chemistry after the initial dissociation. A new shock tube module was developed for Cantera, which allows for arbitrarily large mechanisms in the simulation of laser schlieren experiments. The present work is in good agreement with previous experimental studies.

Passive in situ biobarrier for treatment of comingled nitramine explosives and perchlorate in groundwater on an active range.

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and perchlorate (ClO4-) are common, and often co-mingled, contaminants at military ranges worldwide. This project investigated the feasibility of using a passive emulsified oil biobarrier plus a slow release pH buffering reagent to remediate RDX, HMX, and ClO4- in a low pH aquifer at an active range. A 33 m biobarrier was emplaced perpendicular to the contaminant plumes, and dissolved explosives, perchlorate, and other relevant parameters were monitored. The pH increased and the DO and ORP decreased after emulsified oil injection, leading to >90% reductions in perchlorate, RDX, and HMX compared to upgradient groundwater. Some nitroso breakdown products were observed immediately downstream of the barrier, but generally decreased to below detection limits farther downgradient. First-order rate constants of approximately 0.1/d were obtained for all three contaminants. Dissolved metals (including As) also increased in the wells immediately adjacent to the barrier, but attenuated as the plume re-aerated in downgradient areas. Biobarrier installation and sampling were performed during scheduled range downtime and had no impacts to ongoing range activities. The field trial suggests that an emulsified oil biobarrier with pH buffering can be a viable alternative to remove explosives and perchlorate from shallow groundwater on active ranges.