Impact of Alteration Phase Formation and Microbial Activity on the Fate and Transport of the Actinides and Fission Products: Alteration Phase Analysis

The study of the behavior and movement of radionuclides in the environment is significant to many projects of interest to Southern Nevada, especially for the proposed Yucca Mountain Repository, as well as to the nation-wide issues of radiological releases from a variety of scenarios. Understanding and predicting the release, transport, and fate of radionuclides, particularly the actinide elements, in the Mojave/Great Basin geology is an extremely challenging, multi-faceted problem. In support of the national program to deepen our understanding of the behavior of radionuclides in the environment and to better predict the performance of a geological repository at Yucca Mountain, researchers at UNLV, under a cooperative agreement between and UNLV Research Foundation and the U.S. Department of Energy (#DE-FC28-04RW12237), will examine two key fate and transport issues: the potential impact of microorganisms and the impact of the formation of alteration phases due to the corrosion of the waste package and waste forms on the chemistry, fate, and transport of radionuclides released from the site. Task ORD-RF-01 (SIP-UNLV-046) is focused on the influence of microorganisms. Task ORD-RF-02 (SIP-UNLV-045) involves surface complexation and solid dissolution studies. This task, titled Impact of Alteration Phase Formation and Microbial Activity on the Fate and Transport of the Actinides and Fission Products: Alteration Phase Analysis, entails method development and elemental characterization of select alteration phases generated in Task ORD-RF-02. All of this work is subject to QARD and University and Community College System of Nevada (UCCSN) Quality Assurance (QA) Program requirement

Determination of metals in tree rings by ICP-MS using ash from a direct mercury analyzer

© 2020 by the authors. Elemental profiles in cores of tree trunks (bole wood) have been used for environmental monitoring and reconstruction of metal pollution history. Mercury (Hg) is a global pollutant that can be accurately measured in tree rings in a simple and pragmatic fashion using a direct mercury analyzer (DMA) that is based on thermal decomposition, amalgamation, and atomic absorption spectrophotometry. In this feasibility study, we demonstrate that the ash remaining after the DMA analyses can be used to quantify a wide range of other non-volatile elements (Ba, Be, Co, Cr, Cu, Fe, Ga, Mg, Mn, Ni, Pb, Sr, Th, and U) in that same sample of wood by inductively coupled plasma mass spectrometry (ICP-MS) after microwave-assisted acid digestion. Other elements (Ag, Cd, Cs, Rb, Tl, and V) exhibited poor recoveries, possibly due to losses during sample preparation. We assessed the accuracy with reference materials, spikes, and by comparison with EPA Method 3052 (Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices). For the first group of elements (deemed suitable for the method), recoveries ranged between 80% and 120% and the relative standard deviation was generally \u3c 15%, indicating acceptable precision. We applied the method to five species of trees: Eastern red cedar (Juniperus virginiana), loblolly pine (Pinus taeda), shortleaf pine (Pinus echinata), white oak (Quercus alba), and tulip poplar (Liriodendron tulipifera) from Holly Springs National Forest in north Mississippi, USA. Mercury concentrations (ng/g ± SE) were highest in the cedar (1.8 ± 0.3; n = 5), followed by loblolly pine (1.6 ± 0.3, n = 3), shortleaf pine (1.2 ± 0.2; n = 3), oak (1.1 ± 0.2; n = 5), and poplar (0.5 ± 0.1; n = 5). Concentrations of other elements were generally Fe \u3e Mg \u3e Ba ≈ Sr ≈ Mn \u3e Cr ≈ Cu \u3e Ni ≈ Rb \u3e Co \u3e Ga ≈ Ag, with the other elements generally below the method detection limit (MDL). Overall, we showed that the DMA can be used to not only determine total Hg in segments of tree core, but can serve as the ashing step in the preparation of wood for ICP-MS analysis, thus allowing the determination of non-volatile elements along with Hg in the very same sample

Determining the Redox Properties of Yucca Mountain-Related Groundwater Using Trace Element Speciation for Predicting the Mobility of Nuclear Waste

The objective of this task is to determine the principal oxidation state (redox) species of select elements in samples of groundwater in the vicinity of Yucca Mountain (YM), which is being evaluated as a site for geologic storage of the nation’s spent nuclear fuel and high-level nuclear waste. Samples to be analyzed include, but are not limited to, groundwater from wells of the Nye County Early Warning Drilling Program. Elements to be studied include arsenic (As), antimony (Sb), selenium (Se), chromium (Cr), manganese (Mn), iron (Fe), copper (Cu), molybdenum (Mo), vanadium (V), tungsten (W), rhenium (Re), and uranium (U). The purpose is to develop a more accurate and complete description of the redox properties of YM-related groundwater, which influences the solubility and consequently the transport of radionuclides. Indeed, a possible natural barrier to radionuclide migration in the saturated zone (SZ) is the presence of non-oxidizing or reducing environments. For example, the mobility of Tc-99 in oxic groundwater, ascribed to the pertechnetate ion, is greatly diminished in reducing groundwater. The containment of radionuclides away from the accessible environment is a key feature in the Yucca Mountain performance assessment

Can the MerPAS Passive air sampler discriminate landscape, seasonal, and elevation effects on atmospheric mercury? A feasibility study in Mississippi, USA

© 2019 by the authors. Accurately measuring gaseous elemental mercury (GEM) concentrations in the atmosphere is important to understand its sources, cycling, distribution, and temporal trends. The MerPAS passive air sampler from Tekran Inc. (Toronto, ON, Canada) captures GEM on sulfur-impregnated activated carbon after it passes through a Radeillo diffusive barrier. Because they are small, relatively low in cost, and require no power, they can be deployed at multiple locations, yielding a much greater spatial resolution, albeit at coarser temporal resolution, compared to active sampling. In this study, we used the MerPAS to measure GEM concentration gradients at a mixed hardwood forest, wetland, pond, and a mowed (grass) field, all within close proximity ( \u3c 500 m) to each other. Vertical profiles (0.5, 3.0, 5.5 m) were assessed during summer and winter. The sorbent was analyzed using a direct mercury analyzer. The samplers were captured between 0.90 to 2.2 ng over 2 weeks, well above the mean blank of 0.14 ng. We observed differences between the landscapes, elevation, and seasons. Nearest to the surface, GEM concentrations were lowest in the wetland (both seasons), where there was dense vegetation, and highest in the mowed field (both seasons). Generally, GEM levels increased with the elevation above the ground, except for the forest where the trend was slightly reversed. This suggests a possible net GEM deposition from the atmosphere to surfaces for three of the four landscapes. GEM concentrations were slightly higher in the winter than the summer at 5.5 m height where air masses were unimpeded by vegetation. Overall, we conclude that the MerPAS is indeed capable of measuring GEM gradients between landscapes, elevations, and seasons, if given sufficient collection time, good analytical precision, and low blank levels

Mercury Methylation Potentials in Sediments of an Ancient Cypress Wetland Using Species-Specific Isotope Dilution GC-ICP-MS

Wetlands are of a considerable environmental value as they provide food and habitat for plants and animals. Several important chemical transformations take place in wetland media, including the conversion of inorganic mercury (Hg) to monomethylmercury (MeHg), a toxic compound with a strong tendency for bioconcentration. Considering the fact that wetlands are hotspots for Hg methylation, we investigated, for the first time, Hg methylation and demethylation rates in an old growth cypress wetland at Sky Lake in the Mississippi Delta. The Sky Lake ecosystem undergoes large-scale water level fluctuations causing alternating periods of oxic and anoxic conditions in the sediment. These oscillating redox conditions, in turn, can influence the transformation, speciation, and bioavailability of Hg. In the present study, sediment cores from the wetland and Sky Lake itself were spiked with enriched stable isotope tracers of inorganic Hg and MeHg and allowed to incubate (in-situ) before freezing, sectioning, and analysis. Methylation rates (day−1) ranged from 0.012 ± 0.003 to 0.054 ± 0.019, with the lowest rate in the winter and the highest in the summer. Demethylation rates were about two orders of magnitude higher, and also greater in the warmer seasons (e.g., 1.84 ± 0.78 and 4.63 ± 0.51 for wetland sediment in the winter and summer, respectively). Methylation rates were generally higher in the open water sediment compared to wetland sediment, with the latter shaded and cooler. Both methylation (r = 0.76, p = 0.034) and demethylation (0.97, p = 0.016) rates (day−1) were positively correlated with temperature, but not with most other water quality parameters. MeHg concentration in the water was correlated with pH (r = 0.80, p \u3c 0.05), but methylation rates were only marginally correlated (r = 0.71). Environmental factors driving microbial production of MeHg in the system include warm temperatures, high levels of labile natural organic matter, and to a lesser extent the relatively low pH and the residence time of the water. This study also provides baseline data that can be used to quantify the impacts of modifying the natural flow of water to the system on Hg methylation and demethylation rates

Direct analysis of solid corrosion products by laser ablation ICP-MS: Method development and the interaction of aqueous uranium, gadolinium and neodymium with Iron Shot and Iron (III) Oxide

The purpose of this report is to summarize the work and present conclusions of Project Activity Task ORD-RF-03 conducted under cooperative agreement number DE-FC28-04RW12237 between the U.S. Department of Energy and the Nevada System of Higher Education (NSHE). The work was conducted in the Harry Reid Center for Environmental Studies of the University of Nevada Las Vegas from October 1, 2004 to September 30, 2006. The purpose of the study was to develop a method using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for the direct analysis of iron corrosion products, to evaluate its capabilities, advantages, and limitations, and to apply the method to examine the interaction of actinides, and other elements relevant to the long-term geologic storage of nuclear waste, with iron corrosion products. The desired quantification is for specific (targeted) sections of the surface; elemental ratios can be determined from the data if of interest

Bomb-Pulse Chlorine-36 At The Proposed Yucca Mountain Repository Horizon: An Investigation Of Previous Conflicting Results And Collection Of New Data

Previous studies by scientists at Los Alamos National Laboratory (LANL) found elevated ratios of chlorine-36 to total chloride ({sup 36}Cl/Cl) in samples of rock collected from the Exploratory Studies Facility (ESF) and the Enhanced Characterization of the Repository Block (ECRB) at Yucca Mountain as the tunnels were excavated. The data were interpreted as an indication that fluids containing 'bomb-pulse' {sup 36}Cl reached the repository horizon in the {approx}50 years since the peak period of above-ground nuclear testing. Moreover, the data support the concept that so-called fast pathways for infiltration not only exist but are active, possibly through a combination of porous media, faults and/or other geologic features. Due to the significance of {sup 36}Cl data to conceptual models of unsaturated zone flow and transport, the United States Geological Survey (USGS) was requested by the Department of Energy (DOE) to design and implement a study to validate the LANL findings. The USGS chose to drill new boreholes at select locations across zones where bomb-pulse ratios had previously been identified. The drill cores were analyzed at Lawrence Livermore National Laboratory (LLNL) for {sup 36}Cl/Cl using both active and passive leaches, with the USGS/LLNL concluding that the active leach extracted too much rock-Cl and the passive leach did not show bomb-pulse ratios. Because consensus was not reached between the USGS/LLNL and LANL on several fundamental points, including the conceptual strategy for sampling, interpretation and use of tritium ({sup 3}H) data, and the importance and interpretation of blanks, in addition to the presence or absence of bomb-pulse {sup 36}Cl, an evaluation by an independent entity, the University of Nevada, Las Vegas (UNLV), using new samples was initiated. This report is the result of that study. The overall objectives of the UNLV study were to investigate the source or sources of the conflicting results from the previous validation study, and to obtain additional data to determine whether or not there are bomb-pulse isotopes at the repository horizon. To that en4 we have engaged in discussions with previous investigators, reviewed reports, and analyzed archived samples. We have also collected new samples of rock from the ESF, soil profiles from the surface of Yucca Mountain, and opportunistic samples of seep water from inside the south ramp of the ESF

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Analysis of Lower Pecos Rock Paints and Possible Pigment Sources

Chemical analyses of prehistoric rock paints from the Lower Pecos Region of southwestern Texas were undertaken using laser ablation-inductively coupled plasma-mass spectrometry. This technique allowed us to measure the chemical composition of the paint pigments with minimal interference from a natural rock coating that completely covers the ancient paints. We also analyzed samples representing potential sources of paint pigments, including iron-rich sandstones and quartzite from the study area and ten ochre samples from Arizona. Cluster analysis, principle component analysis and bivariate plots were used to compare the chemical compositions of the paint and pigment sources. The results indicate that limonite extracted from the sandstone was the most likely source for some of the pigments, while ochre was probably used as well

Are rural and small community aerated wastewater stabilization ponds a neglected source of microplastic pollution?

Wastewater treatment systems collect and treat sewage that includes microplastics (MPs). However, we are not aware of any studies on the occurrence and distribution of MPs in wastewater stabilization ponds (WSPs), which serve small communities worldwide. Here, we characterized MPs (~45 µm–5 mm) in an aerated WSP serving ~500 houses and an adjacent lake. Putative MPs were most abundant in duckweed (Lemna minor) and sludge (75 ± 22 and 12.8 ± 3.1 particles/g, respectively: ±1 standard deviation (SD), n = 6, dry weight). In the water, average concentrations (particles/L ± 1 SD, n = 6) were highest in the pond (4.1 ± 0.6), followed by effluent (3.9 ± 0.5) and the lake (2.6 ± 0.6). Over 20 types of MPs were identified in each different compartment, with the distribution varying somewhat between the water, sludge, and duckweed. Polyester and polyethylene were the predominant types, followed by polyethylene terephthalate, polyacrylate, polyvinyl chloride, polystyrene, and others. Morphologies consisted of fibers (62–71%), fragments (28–37%), and beads (1–6%). High-density polymers were more frequently found in sludge. Potential sources of the MPs include synthetic textiles from laundry and other plastics washed down household drains. Overall, with ~786,000 MPs/day released in the pond effluent and with duckweed a source of food for waterfowl, we demonstrate that WSPs can be point sources of MPs to both aquatic and terrestrial ecosystems and thus deserve further scrutiny