Degradation of RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine) in contrasting coastal marine habitats: Subtidal non-vegetated (sand), subtidal vegetated (silt/eel grass), and intertidal marsh.

Hundreds of explosive-contaminated marine sites exist globally, many of which contain the common munitions constituent hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Quantitative information about RDX transformation in coastal ecosystems is essential for management of many of these sites. Isotopically labelled RDX containing N in all 3 nitro groups was used to track the fate of RDX in three coastal ecosystem types.

Constraining the Oxygen Isotopic Composition of Nitrate Produced by Nitrification.

Measurements of the stable isotope ratios of nitrogen (N/N) and oxygen (O/O) in nitrate (NO) enable identification of sources, dispersal, and fate of natural and contaminant NO in aquatic environments. The O/O of NO produced by nitrification is often assumed to reflect the proportional contribution of oxygen atom sources, water, and molecular oxygen, in a 2:1 ratio. Culture and seawater incubations, however, indicate oxygen isotopic equilibration between nitrite (NO) and water, and kinetic isotope effects for oxygen atom incorporation, which modulate the NO O/O produced during nitrification.

Tracing the cycling and fate of the munition, Hexahydro-1,3,5-trinitro-1,3,5-triazine in a simulated sandy coastal marine habitat with a stable isotopic tracer, N-[RDX].

Coastal marine habitats become contaminated with the munitions constituent, Hexahydro-1,3,5-trinitro-1,3,5-trazine (RDX), via military training, weapon testing and leakage of unexploded ordnance. This study used N labeled RDX in simulated aquarium-scale coastal marine habitat containing seawater, sediment, and biota to track removal pathways from surface water including sorption onto particulates, degradation to nitroso-triazines and mineralization to dissolved inorganic nitrogen (DIN). The two aquaria received continuous RDX inputs to maintain a steady state concentration (0.

Preliminary assessment of stable nitrogen and oxygen isotopic composition of USGS51 and USGS52 nitrous oxide reference gases and perspectives on calibration needs.

Rationale: Despite a long history and growing interest in isotopic analyses of N O, there is a lack of isotopically characterized N O isotopic reference materials (standards) to enable normalization and reporting of isotope-delta values. Here we report the isotopic characterization of two pure N O gas reference materials, USGS51 and USGS52, which are now available for laboratory calibration (https://isotopes.usgs.

Seeking excellence: An evaluation of 235 international laboratories conducting water isotope analyses by isotope-ratio and laser-absorption spectrometry.

Rationale: Water stable isotope ratios (δ H and δ O values) are widely used tracers in environmental studies; hence, accurate and precise assays are required for providing sound scientific information. We tested the analytical performance of 235 international laboratories conducting water isotope analyses using dual-inlet and continuous-flow isotope ratio mass spectrometers and laser spectrometers through a water isotope inter-comparison test.

Methods: Eight test water samples were distributed by the IAEA to international stable isotope laboratories.

Optimization of on-line hydrogen stable isotope ratio measurements of halogen- and sulfur-bearing organic compounds using elemental analyzer-chromium/high-temperature conversion isotope ratio mass spectrometry (EA-Cr/HTC-IRMS).

Rationale: Accurate hydrogen isotopic analysis of halogen- and sulfur-bearing organics has not been possible with traditional high-temperature conversion (HTC) because the formation of hydrogen-bearing reaction products other than molecular hydrogen (H ) is responsible for non-quantitative H yields and possible hydrogen isotopic fractionation. Our previously introduced, new chromium-based EA-Cr/HTC-IRMS (Elemental Analyzer-Chromium/High-Temperature Conversion Isotope Ratio Mass Spectrometry) technique focused primarily on nitrogen-bearing compounds. Several technical and analytical issues concerning halogen- and sulfur-bearing samples, however, remained unresolved and required further refinement of the reactor systems.

Density-Driven Free-Convection Model for Isotopically Fractionated Geogenic Nitrate in Sabkha Brine.

Subsurface brines with high nitrate (NO ) concentration are common in desert environments as atmospheric nitrogen is concentrated by the evaporation of precipitation and little nitrogen uptake. However, in addition to having an elevated mean concentration of ∼525 mg/L (as N), NO in the coastal sabkhas of Abu Dhabi is enriched in N (mean δ N ∼17‰), which is an enigma. A NO solute mass balance analysis of the sabkha aquifer system suggests that more than 90% of the nitrogen is from local atmospheric deposition and the remainder from ascending brine.

Comment on "Reconciliation of the Devils Hole climate record with orbital forcing".

Moseley et al's (Reports, 8 January 2016, p. 165) preferred-Termination-II age is subjective, as evidenced by variation in their Termination-II ages of 2500 years per meter. Termination-II-age bias decreases to zero at ~1.

Stable isotope analyses of oxygen ( O: O: O) and chlorine ( Cl: Cl) in perchlorate: reference materials, calibrations, methods, and interferences.

Rationale: Perchlorate (ClO ) is a common trace constituent of water, soils, and plants; it has both natural and synthetic sources and is subject to biodegradation. The stable isotope ratios of Cl and O provide three independent quantities for ClO source attribution and natural attenuation studies: δ Cl, δ O, and δ O (or Δ O or Δ) values. Documented reference materials, calibration schemes, methods, and interferences will improve the reliability of such studies.

A revision in hydrogen isotopic composition of USGS42 and USGS43 human-hair stable isotopic reference materials for forensic science.

The hydrogen isotopic composition (δ(2)HVSMOW-SLAP) of USGS42 and USGS43 human hair stable isotopic reference materials, normalized to the VSMOW (Vienna-Standard Mean Ocean Water)-SLAP (Standard Light Antarctic Precipitation) scale, was originally determined with a high temperature conversion technique using an elemental analyzer (TC/EA) with a glassy carbon tube and glassy carbon filling and analysis by isotope-ratio mass spectrometer (IRMS). However, the TC/EA IRMS method can produce inaccurate δ(2)HVSMOW-SLAP results when analyzing nitrogen-bearing organic substances owing to the formation of hydrogen cyanide (HCN), leading to non-quantitative conversion of a sample into molecular hydrogen (H2) for IRMS analysis. A single-oven, chromium-filled, elemental analyzer (Cr-EA) coupled to an IRMS substantially improves the measurement quality and reliability of hydrogen isotopic analysis of hydrogen- and nitrogen-bearing organic material because hot chromium scavenges all reactive elements except hydrogen.

Organic Reference Materials for Hydrogen, Carbon, and Nitrogen Stable Isotope-Ratio Measurements: Caffeines, n-Alkanes, Fatty Acid Methyl Esters, Glycines, L-Valines, Polyethylenes, and Oils.

An international project developed, quality-tested, and determined isotope-δ values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope-δ scales. The RMs span a range of δ(2)H(VSMOW-SLAP) values from -210.

A new organic reference material, l-glutamic acid, USGS41a, for δ(13) C and δ(15) N measurements - a replacement for USGS41.

Rationale: The widely used l-glutamic acid isotopic reference material USGS41, enriched in both (13) C and (15) N, is nearly exhausted. A new material, USGS41a, has been prepared as a replacement for USGS41.

Methods: USGS41a was prepared by dissolving analytical grade l-glutamic acid enriched in (13) C and (15) N together with l-glutamic acid of normal isotopic composition.

Identification of Groundwater Nitrate Contamination from Explosives Used in Road Construction: Isotopic, Chemical, and Hydrologic Evidence.

Explosives used in construction have been implicated as sources of NO3(-) contamination in groundwater, but direct forensic evidence is limited. Identification of blasting-related NO3(-) can be complicated by other NO3(-) sources, including agriculture and wastewater disposal, and by hydrogeologic factors affecting NO3(-) transport and stability. Here we describe a study that used hydrogeology, chemistry, stable isotopes, and mass balance calculations to evaluate groundwater NO3(-) sources and transport in areas surrounding a highway construction site with documented blasting in New Hampshire.

LIMS for Lasers 2015 for achieving long-term accuracy and precision of δ(2)H, δ(17)O, and δ(18)O of waters using laser absorption spectrometry.

Rationale: Although laser absorption spectrometry (LAS) instrumentation is easy to use, its incorporation into laboratory operations is not easy, owing to extensive offline manipulation of comma-separated-values files for outlier detection, between-sample memory correction, nonlinearity (δ-variation with water amount) correction, drift correction, normalization to VSMOW-SLAP scales, and difficulty in performing long-term QA/QC audits.

Methods: A Microsoft Access relational-database application, LIMS (Laboratory Information Management System) for Lasers 2015, was developed. It automates LAS data corrections and manages clients, projects, samples, instrument-sample lists, and triple-isotope (δ(17)O, δ(18)O, and δ(2)H values) instrumental data for liquid-water samples.

A new isotopic reference material for stable hydrogen and oxygen isotope-ratio measurements of water - USGS50 Lake Kyoga Water.

Rationale: As a result of the need for isotopic reference waters having high δ(2) HVSMOW-SLAP and δ(18) OVSMOW-SLAP values for daily use, especially for tropical and equatorial-zone freshwaters, a new secondary isotopic reference material for international distribution was prepared from water collected from Lake Kyoga, Uganda.

Methods: This isotopic reference lakewater was filtered through a membrane with 0.2-µm pore size, homogenized, loaded into glass ampoules that were sealed with a torch and autoclaved to eliminate biological activity, and measured by dual-inlet isotope-ratio mass spectrometry.

Role of Anaerobic Ammonium Oxidation (Anammox) in Nitrogen Removal from a Freshwater Aquifer.

Anaerobic ammonium oxidation (anammox) couples the oxidation of ammonium with the reduction of nitrite, producing N2. The presence and activity of anammox bacteria in groundwater were investigated at multiple locations in an aquifer variably affected by a large, wastewater-derived contaminant plume. Anammox bacteria were detected at all locations tested using 16S rRNA gene sequencing and quantification of hydrazine oxidoreductase (hzo) gene transcripts.

Tracing the Cycling and Fate of the Explosive 2,4,6-Trinitrotoluene in Coastal Marine Systems with a Stable Isotopic Tracer, (15)N-[TNT].

2,4,6-Trinitrotoluene (TNT) has been used as a military explosive for over a hundred years. Contamination concerns have arisen as a result of manufacturing and use on a large scale; however, despite decades of work addressing TNT contamination in the environment, its fate in marine ecosystems is not fully resolved. Here we examine the cycling and fate of TNT in the coastal marine systems by spiking a marine mesocosm containing seawater, sediments, and macrobiota with isotopically labeled TNT ((15)N-[TNT]), simultaneously monitoring removal, transformation, mineralization, sorption, and biological uptake over a period of 16 days.

Chemical Considerations for an Updated National Assessment of Brackish Groundwater Resources.

Brackish groundwater (BGW) is increasingly used for water supplies where fresh water is scarce, but the distribution and availability of such resources have not been characterized at the national scale in the United States since the 1960s. Apart from its distribution and accessibility, BGW usability is a function of the chemical requirements of the intended use, chemical characteristics of the resource, and treatment options to make the resource compatible with the use. Here, we discuss relations between these three chemical factors using national-scale examples and local case studies.

On-line hydrogen-isotope measurements of organic samples using elemental chromium: an extension for high temperature elemental-analyzer techniques.

The high temperature conversion (HTC) technique using an elemental analyzer with a glassy carbon tube and filling (temperature conversion/elemental analysis, TC/EA) is a widely used method for hydrogen isotopic analysis of water and many solid and liquid organic samples with analysis by isotope-ratio mass spectrometry (IRMS). However, the TC/EA IRMS method may produce inaccurate δ(2)H results, with values deviating by more than 20 mUr (milliurey = 0.001 = 1‰) from the true value for some materials.

Long-term groundwater depletion in the United States.

The volume of groundwater stored in the subsurface in the United States decreased by almost 1000 km3 during 1900-2008. The aquifer systems with the three largest volumes of storage depletion include the High Plains aquifer, the Mississippi Embayment section of the Gulf Coastal Plain aquifer system, and the Central Valley of California. Depletion rates accelerated during 1945-1960, averaging 13.

Biscayne aquifer drinking water (USGS45): a new isotopic reference material for δ2H and δ18O measurements of water.

Rationale: As a result of the scarcity of isotopic reference waters for daily use, a new secondary isotopic reference material for international distribution has been prepared from drinking water collected from the Biscayne aquifer in Ft. Lauderdale, Florida.

Methods: This isotopic reference water was filtered, homogenized, loaded into glass ampoules, sealed with a torch, autoclaved to eliminate biological activity, and measured by dual-inlet isotope-ratio mass spectrometry.

Caution on the use of NBS 30 biotite for hydrogen-isotope measurements with on-line high-temperature conversion systems.

Rationale: The supply of NBS 30 biotite is nearly exhausted. During measurements of NBS 30 and potential replacements, reproducible δ(2)HVSMOW-SLAP values could not be obtained by three laboratories using high-temperature conversion (HTC) systems. The cause of this issue has been investigated using the silver-tube technique for hydrogen-isotope measurements of water.

Lake Louise water (USGS47): a new isotopic reference water for stable hydrogen and oxygen isotope measurements.

Rationale: Because of the paucity of isotopic reference waters for daily use, a new secondary isotopic reference material has been prepared from Lake Louise water from Alberta, Canada, for international distribution.

Methods: This water was filtered, homogenized, loaded into glass ampoules, sealed with a torch, autoclaved to eliminate biological activity, and measured by dual-inlet isotope-ratio mass spectrometry. This isotopic reference water is available by the case of 144 glass ampoules containing 5 mL of water in each ampoule.

Guidelines and recommended terms for expression of stable-isotope-ratio and gas-ratio measurement results.

To minimize confusion in the expression of measurement results of stable isotope and gas-ratio measurements, recommendations based on publications of the Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry (IUPAC) are presented. Whenever feasible, entries are consistent with the Système International d'Unités, the SI (known in English as the International System of Units), and the third edition of the International Vocabulary of Basic and General Terms in Metrology (VIM, 3rd edition). The recommendations presented herein are approved by the Commission on Isotopic Abundances and Atomic Weights and are designed to clarify expression of quantities related to measurement of isotope and gas ratios to ensure that quantity equations instead of numerical value equations are used for quantity definitions.

USGS42 and USGS43: human-hair stable hydrogen and oxygen isotopic reference materials and analytical methods for forensic science and implications for published measurement results.

Because there are no internationally distributed stable hydrogen and oxygen isotopic reference materials of human hair, the U.S. Geological Survey (USGS) has prepared two such materials, USGS42 and USGS43.