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Centralized systems employ biological treatments to remove nutrients, whereas decentralized systems, especially in rural areas, face challenges in implementing them. These systems are low flow but high carbon and nitrogen concentrations, and low C/N ratios. Source-separated wastewater (urine + flush) is an extreme example, like confined animal-feeding wastewater. High nutrient concentrations necessitate innovative technologies typically not employed for decentralized systems. This research demonstrates a simple two-stage nitritation-anammox system to treat high N concentration wastewater (pure urine + flush water). The systems consisted of a Membrane Aerated Biological Reactor (MABR) which performed carbon oxidation and nitritation and novel anammox reactors, (Pancopia AnammoX (PAXs)). The MABRs achieved OC removal over 108–198 g-C/m3-day with ∼ 97% removal, TAN oxidation rates up to 156 g-N/m3-day and nitrite/AN ratios were near 1 with no external control (e.g. pH, DO, cell wasting) other than urine loading rate. The PAXs achieved maximum AN removal efficiencies of 85–97%. The main limitation to complete TN removal in the PAXs was insufficient NO 2 - in the influent (nonideal influent NO 2 -/AN ratio). This system was not optimized for energy efficiency and had low volumetric conversion rates compared with other systems. However, it demonstrates that source-separated wastewater can be effectively treated with near complete N removal using a system with minimal process control requirements, lack of solid production, and elimination of diffuse aeration preventing odor generation. These attributes are attractive for applications where conditions do not allow for more complex high-rate systems such as developing societies and rural areas. • A MABR performing nitritation coupled to a novel anammox reactor treating urine removed 85–97% of the nitrogen. • The system required no solids processing or diffuse aeration. • The system was controlled by varying loading rates and no active control was required. • The MABR-PAX represents a simple robust system for the treatment of N-rich wastewater. [ABSTRACT FROM AUTHOR]

The assessment of a cap for remediation of sediments requires long-term monitoring because of the slow migration of contaminants in porous media. In this study, coring and passive sampling tools were used to assess the transport and degradation of polycyclic aromatic hydrocarbons (PAHs) in an amended cap (sand + Organoclay® PM-199) in the Grand Calumet River (Indiana, USA) during four sampling events from 2012 to 2019. Measurements of three PAHs (phenanthrene (Phe), pyrene (Pyr) and benzo[a]pyrene (BaP), representing low, medium, and high molecular weight compounds, respectively) showed a difference of at least two orders of magnitude between bulk concentrations in the native sediments and the remediation cap. Averages of pore water measurements also showed lower levels in the cap respective to the native sediments by a factor of at least 7 for Phe and 3 for Pyr. In addition, between the baseline (BL), which corresponds to observations from 2012 to 2014, and the measurements in 2019, there was a decrease in depth-averaged pore water concentrations of Phe (C 2019 / C B L = 0.20 − 0.07 + 0.12 in sediments and 0.27 − 0.10 + 0.15 in cap) and Pyr (C 2019 / C B L = 0.47 − 0.12 + 0.16 in sediments and 0.71 − 0.20 + 0.28 in the cap). In the case of BaP in pore water, no change was observed in native sediments (C 2019 / C B L = 1.0 − 0.24 + 0.32) and there was an increase in the cap (C 2019 / C B L = 2.0 − 0.54 + 0.72). Inorganic anions and estimates of pore water velocity along with measurements of PAHs were used to model the fate and transport of contaminants. The modeling suggested that degradation of Phe (t 1 / 2 = 1.12 − 0.11 + 0.16 years) and Pyr (t 1 / 2 = 5.34 − 1.8 + 5.3 years) in the cap is faster than migration, thus the cap is expected to be protective of the sediment-water interface indefinitely for these constituents. No degradation was noted in BaP and the contaminant is expected to reach equilibrium in the capping layer over approximately 100 years if there exists sufficient mass of BaP in the sediments and there is no deposition of clean sediment at the surface. [Display omitted] • Remediation cap effectively isolates contaminated solids from surface water • Passive sampling measurements are statistically consistent over multiple years • Passive sampling of conservative tracers can aid in conceptual model development • Observations indicate larger attenuation rates for low molecular weight compounds [ABSTRACT FROM AUTHOR]

Natural perchlorate (ClO 4 − ) is of increasing interest due to its wide-spread occurrence on Earth and Mars, yet little information exists on the relative abundance of ClO 4 − compared to other major anions, its stability, or long-term variations in production that may impact the observed distributions. Our objectives were to evaluate the occurrence and fate of ClO 4 − in groundwater and soils/caliche in arid and semi-arid environments (southwestern United States, southern Africa, United Arab Emirates, China, Antarctica, and Chile) and the relationship of ClO 4 − to the more well-studied atmospherically deposited anions NO 3 − and Cl − as a means to understand the prevalent processes that affect the accumulation of these species over various time scales. ClO 4 − is globally distributed in soil and groundwater in arid and semi-arid regions on Earth at concentrations ranging from 10 −1 to 10 6 μg/kg. Generally, the ClO 4 − concentration in these regions increases with aridity index, but also depends on the duration of arid conditions. In many arid and semi-arid areas, NO 3 − and ClO 4 − co-occur at molar ratios (NO 3 − /ClO 4 − ) that vary between ∼10 4 and 10 5 . We hypothesize that atmospheric deposition ratios are largely preserved in hyper-arid areas that support little or no biological activity (e.g. plants or bacteria), but can be altered in areas with more active biological processes including N 2 fixation, N mineralization, nitrification, denitrification, and microbial ClO 4 − reduction, as indicated in part by NO 3 − isotope data. In contrast, much larger ranges of Cl − /ClO 4 − and Cl − /NO 3 − ratios indicate Cl − varies independently from both ClO 4 − and NO 3 − . The general lack of correlation between Cl − and ClO 4 − or NO 3 − implies that Cl − is not a good indicator of co-deposition and should be used with care when interpreting oxyanion cycling in arid systems. The Atacama Desert appears to be unique compared to all other terrestrial locations having a NO 3 − /ClO 4 − molar ratio ∼10 3 . The relative enrichment in ClO 4 − compared to Cl − or NO 3 − and unique isotopic composition of Atacama ClO 4 − may reflect either additional in-situ production mechanism(s) or higher relative atmospheric production rates in that specific region or in the geological past. Elevated concentrations of ClO 4 − reported on the surface of Mars, and its enrichment with respect to Cl − and NO 3 − , could reveal important clues regarding the climatic, hydrologic, and potentially biologic evolution of that planet. Given the highly conserved ratio of NO 3 − /ClO 4 − in non-biologically active areas on Earth, it may be possible to use alterations of this ratio as a biomarker on Mars and for interpreting major anion cycles and processes on both Mars and Earth, particularly with respect to the less-conserved NO 3 − pool terrestrially. [ABSTRACT FROM AUTHOR]

Abstract: We measured chlorate (ClO3 −) and perchlorate (ClO4 −) concentrations in ice covered lakes of the McMurdo Dry Valleys (MDVs) of Antarctica, to evaluate their role in the ecology and geochemical evolution of the lakes. ClO3 − and ClO4 − are present throughout the MDV Lakes, streams, and other surface water bodies. ClO3 − and ClO4 − originate in the atmosphere and are transported to the lakes by surface inflow of glacier melt that has been differentially impacted by interaction with soils and aeolian matter. Concentrations of ClO3 − and ClO4 − in the lakes and between lakes vary based on both total evaporative concentration, as well as biological activity within each lake. All of the lakes except the East lobe of Lake Bonney support biological reduction of ClO3 − and ClO4 − either in the anoxic bottom waters or sediment. The younger less saline lakes (Miers and Hoare), have surface ClO3 − and ClO4 − concentrations, and ratios of ClO3 −/Cl− and ClO4 −/Cl−, similar to source streams, while Lake Fryxell has concentrations similar to input streams but much lower ClO3 −/Cl− and ClO4 −/Cl− ratios, reflecting the influence of a large Cl− source in bottom sediments. ClO3 − and ClO4 − in Lake Bonney are the highest of all the lakes reflecting the lake’s greater age and higher concentration of Cl−. ClO4 − appears to be stable in the East Lobe and its concentration is highly correlated with Cl− concentration suggesting that some ClO4 − at depth is a remnant of the initial seawater that formed Lake Bonney. ClO3 − and ClO4 − concentrations provide a simple and sensitive means to evaluate microbial activity in these lakes due to their relatively low concentrations and lack of biological sources, unlike NO3 −, NO2 −, and SO4 −2. [Copyright &y& Elsevier]

Nitritation can help lower ammonia oxidation treatment costs through traditional nitrogen removal processes for wastewaters with high nitrogen (N) concentrations or low carbon to nitrogen ratios (C/N) and facilitate the anammox process. Free nitrous acid (FNA) or free ammonia (FA) can inhibit nitrite oxidizing bacteria (NOB). Only a few studies have evaluated control of nitritation at elevated TN concentrations and none for TN concentrations > 2000 mg/L, characteristic of confined animal feeding operation (CAFOs) or source separated wastewaters. This study evaluated the factors that promote nitritation in membrane aerated bioreactors (MABRs) treating urine dominated wastewaters (670–4900 mg-N/L) at DO > 3 mg/L and without solids wasting. FNA concentrations > 0.2 mg-N/L and/or FA concentrations > 3 mg-N/L partially inhibit NOB similar to inhibitory concentrations observed in studies for lower strength wastewaters. FNA > 1 mg-N/L completely inhibited NOB. Direct addition of nitrite (NO 2 -) or pH manipulation to increase either FNA or FA can inhibit even established NOB populations, leading to stable nitritation. For urine dominated wastewaters with TN concentrations > 1000 mg/L or reactors designed to produce an effluent with ~1:1 total ammonia nitrogen (TAN) to NO 2 - (pre-anammox), all operating regimes (loading or pH) inhibit NOB. These results extend the applications of MABRs to treat high TN concentration, urine dominated wastewaters. MABRs are ideal for remote locations or other applications (off grid communities, CAFOs, underdeveloped countries) that cannot support complex control systems for pH or DO control and eliminate the need for solids processing. [Display omitted] • MABRs were used to control nitritation for urine dominated high N concentration wastewaters. • This study eliminated the need for low DO or long SRT to control nitritation. • FNA concentrations > 1 mg-N/L and/or FA concentrations > 3 mg-N/L completely inhibit NOB activity. • Addition of NO 2 - to increase FNA or pH manipulation to increase either FNA or FA can lead to stable nitritation. • No pH exists that will not lead to inhibition of NOB, for urine dominated wastewaters with TN > 1000 mg/l. [ABSTRACT FROM AUTHOR]

Overwhelming evidence now exists that perchlorate is produced through natural processes and can be ubiquitously found at environmentally relevant concentrations in arid and semi-arid locations. A number of potential production mechanisms have been hypothesized and ClO4 − production by ozone oxidation of surface bound Cl− was demonstrated. However, no information concerning the impact of concentration, final reaction products distribution, impact of reaction phase, or oxidation of important oxychlorine intermediates has been reported. Using IC-MS–MS analysis and replicate oxidation experiments, we show that exposing aqueous solutions or Cl− coated sand or glass surfaces to O3 (0.96%) generated ClO4 − with molar yields of 0.007 and 0.01% for aqueous Cl− solutions and 0.025 and 0.42% for Cl− coated sand and glass, respectively. Aqueous solutions of Cl− produced less ClO4 − than Cl− coated sand or glass as well as a higher ratio of ClO3 − to ClO4 −. Reduction of the initial Cl− mass resulted in substantially higher molar yields of ClO4 − and ClO3 −. In addition, alkaline absorbers that captured gaseous products contained substantial quantities of Cl−, ClO3 −, and ClO4 −. Solutions of possible oxychlorine intermediates (OCl− and ClO3 −) exposed to O3 produced only scant amounts of ClO4 − while a ClO2 − solution exposed to O3 produced substantial molar yields of ClO4 − (4% molar yield). Scanning electron microscopy coupled with energy energy-dispersive X-ray analysis demonstrated a significant loss of Cl− and an increase in oxygen on the Cl− coated silica sand exposed to O3. While the experimental conditions are not reflective of natural conditions this work clearly demonstrates the relative potential of Cl− precursors in perchlorate production and the likely importance of dry aerosol oxidation over solution phase reactions. It also suggests that ClO2 − may be a key intermediate while ClO3 − and OCl− are unlikely to play a significant role. [Copyright &y& Elsevier]

Abstract: Soil and topical tests were employed to investigate the effect of two N-nitroso metabolites of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) on earthworm reproduction. The lowest observed effect concentration (LOEC) for cocoon production and hatching was 50mg/kg for both hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) in soil. MNX and TNX also significantly affected cocoon hatching in soil (p <0.001) and in topical tests (p =0.001). The LOECs for cocoon hatching were 1 and 10mg/kg for MNX and TNX in soil, respectively, and 10mg/L in the topical test. Greater than 100mg/kg MNX and TNX completely inhibited cocoon hatching. In soil, the EC20 values for MNX were 8.7 and 8.8mg/kg for cocoon and juvenile production, respectively, compared to 9.2 and 9.1mg/kg for TNX, respectively. The EC20 values for the total number of cocoon hatchlings were 3.1 and 4.7mg/kg for MNX and TNX, respectively, in soil and 4.5 and 3.1mg/L in the topical test. Both MNX and TNX inhibited cocoon production and hatching, suggesting that they may have a negative affect on soil ecosystems at contaminated sites. [Copyright &y& Elsevier]

Abstract: The fate of perchlorate (ClO4-) in streambed sediments is becoming a concern due to the increasing number of groundwater and surface water contamination sites in the United States. Dialysis samplers were deployed at three sites over a period of 1 year to determine the vertical distribution of ClO4- in sediment pore water. Results indicated that the spatial and temporal ClO4- penetration into sediments could be affected by numerous factors, such as temperature, microbial degradation, ClO4- surface water concentration, and sediment physico-geological properties. In general, maximum ClO4- penetration into sediments at the studied sites was 30 cm below the sediment-water surface. The vertical sequential depletion of electron acceptors in sediments suggested that microbial reduction was responsible for ClO4- depletion in stream sediments. Biodegradation of ClO4- occurred over a seasonally variable active depth zone of 1–10 cm. Results implied that there was a rapid natural attenuation potential of perchlorate in saturated near-surface sediments. [Copyright &y& Elsevier]

The potential of natural wetland systems to treat perchlorate-contaminated water was investigated in vertical upflow wetland columns planted with and without Bulrush (Scirpus sp.). In the absence of nitrate (NO3-–N <1mg/L), wetland columns were capable of removing ClO4- to levels below the detection limit (<4μg/L) for a series of influent ClO4- (4, 8, 16, and 32mg/L). At an influent ClO4- concentration of 32mg/L, ClO4- breakthrough was observed with the increase in nitrate concentration. ClO4- and NO3- degradation rate constants (Kpc and ) were also determined using a 1-D transport model with dispersion. Kpc declined with the increase of influent ClO4- and NO3- –N concentration (6.49–0.42 day-1 for unplanted columns, and 7.80–0.21 day-1 for planted columns, respectively). followed similar trends but was relatively higher than Kpc. Plant uptake was directly linked with ClO4- concentration in the rhizosphere, and the stem bio-concentration factor (BCF) was estimated to be 57. A mass balance indicated plant uptake accounted for 0–14.3% of initial ClO4- input. Microbial degradation played a more important role than plant uptake and transformation in ClO4- degradation in this wetland system. This study suggests that constructed wetlands may be a promising technology to treat perchlorate-contaminated waters. [Copyright &y& Elsevier]

Bioreactors for space habitation systems have unique constraints. One type of reactor that could meet these constraints are membrane aerated biological reactors (MABRs). The objective of this work was to establish the performance and optimal loading capacities of multiple MABRs with a variety of habitation waste streams. The MABRs operated over a large range of organic nitrogen (ON) and organic carbon (OC) loading rates (36–220 g/m3-d and 20–200 g/m3-d, respectively) across all wastewaters excluding humidity condensate (HC) where ON and OC loading rates ranged from 1.6 to 11 g/m3-d and 7–55 g/m3-d, respectively. OC and ON transformation rates (29–210 g/m3-d and 23–170 g/m3-d, respectively) were proportional to loading rates and similar to MABRs treating terrestrial high strength wastewaters at similar loadings. MABR maximum loading rates are limited by ON oxidation which controls pH. Above a pH of ~7.8 ON removal is inhibited by free ammonium due to the elevated concentrations of ON in all wastewaters excluding HC. While loading rates are lower than typical terrestrial systems, the MABRs stably operated for up to 5 years with limited maintenance and no solids processing. This work supports the use of MABRs to reliably stabilize habitation wastewaters with minimal consumables. These results also support the use of these MABRs for terrestrial high strength, low volume wastewaters where complex technology may be unsupportable, such as in rural or developing communities with no centralized treatment or for applications where typical two-phase aeration can lead to undesirable off gassing. [Display omitted] • MABRs were evaluated for long term operation to treat a variety of space habitation wastewaters. • Large range of organic nitrogen and organic carbon were tested. • Organic nitrogen and organic carbon transformation rates were proportional to loading rates. • MABRs were able to stabilize habitation wastewaters with minimal consumables and no solids processing. [ABSTRACT FROM AUTHOR]

Natural chlorate (ClO 3 −) is widely distributed in terrestrial and extraterrestrial environments. To improve understanding of the origins and distribution of ClO 3 −, we developed and tested methods to determine the multi-dimensional isotopic compositions (δ18O, Δ17O, δ37Cl, 36Cl/Cl) of ClO 3 − and then applied the methods to samples of natural nitrate-rich caliche-type salt deposits in the Atacama Desert, Chile, and Death Valley, USA. Tests with reagents and artificial mixed samples indicate stable-isotope ratios were minimally affected by the purification processes. Chlorate extracted from Atacama samples had δ18O = +7.0 to +11.1‰, Δ17O = +5.7 to +6.4‰, δ37Cl = −1.4 to +1.3‰, and 36Cl/Cl = 48 × 10−15 to 104 × 10−15. Chlorate from Death Valley samples had δ18O = −6.9 to +1.6‰, Δ17O = +0.4 to +2.6‰, δ37Cl = +0.8 to +1.0‰, and 36Cl/Cl = 14 × 10−15 to 44 × 10−15. Positive Δ17O values of natural ClO 3 − indicate that its production involved reaction with O 3 , while its Cl isotopic composition is consistent with a tropospheric or near-surface source of Cl. The Δ17O and δ18O values of natural ClO 3 − are positively correlated, as are those of ClO 4 − and NO 3 − from the same localities, possibly indicating variation in the relative contributions of O 3 as a source of O in the formation of the oxyanions. Additional isotopic analyses of ClO 3 − could provide stronger constraints on its production mechanisms and/or post-formational alterations, with applications for environmental forensics, global biogeochemical cycling of Cl, and the origins of oxyanions detected on Mars. • Developed and validated method for purification and isotopic analyses of chlorate. • Natural chlorate isotopic composition is distinct from anthropogenic chlorate. • Natural chlorate from the Atacama and Death Valley have distinct isotopic compositions. • Isotopic compositions of natural chlorate are different from those of coexisting perchlorate. • Natural chlorate is partially formed from reactions with ozone. [ABSTRACT FROM AUTHOR]

• MABR system was tested at low C:N ratio (< 1) for space-based wastewater. • HRT, Recycle Ratio & intramembrane partial pressure of O 2 influences N removal. • MABR achieved maximum TN removal efficiency of 36.5 %. • High liquid velocity increases the O 2 diffusion resulting in low denitrification. A membrane-aerated biofilm reactor (MABR) was designed for the treatment of a source-separated urine wastewater formulated to mimic conditions on an early planetary space habitation. Literature suggested that a MABR would not work effectively for nitrogen removal for this wastewater since it is nitrogen dominant (total organic carbon to nitrogen ratio < 1). The MABR studied in this study confirmed that hypothesis by recording average nitrification and denitrification efficiencies as high as ∼65 % and ∼35 %, respectively. Nonetheless, the simultaneous nitrification and denitrification performance was unexpectedly high when compared to the reactor's low liquid velocities (0.004 cm/s) and it's relatively high bulk dissolved oxygen (DO) levels (> 2 mg/L). Dissolved organic carbon (DOC) removal and nitrification rates were reported as high as 0.33 ± 0.12 g-C/m2-d and 0.32 ± 0.02 g-N/m2-d, respectively. Additionally, the MABR achieved total nitrogen (TN) removal efficiency of 36.5 %. Additionally, the operational parameters of hydraulic retention time, intramembrane partial oxygen pressure, recycle ratio and liquid velocity linked with bulk DO concentration were evaluated. It was observed that TN removal was significantly impacted by the variation of those parameters, but DOC removal efficiency and nitrification rate did not change significantly. This study helps to establish the efficacy of MABR systems for the treatment of nitrogen dominant, space-based wastewater. [ABSTRACT FROM AUTHOR]

Widely distributed perchlorate on the Martian surface and over three orders of magnitude variation in bromine abundances in surface samples are difficult to explain solely by chloride and bromide aqueous geochemistry. New experiments show that photochemical oxidation (ultraviolet wavelength 254 nm) of chloride- and bromide-bearing evaporative brines in the presence of silica beads produces substantial perchlorate (ClO − 4 ), chlorate (ClO − 3 ), and bromate (BrO − 3 ) under conditions relevant to Mars. Neutral to alkaline aqueous environments result in the dominance of chlorate over perchlorate. Preferential atmospheric recycling of Br over Cl causes variable Br/Cl ratios, consistent with numerous in-situ measurements of Cl and Br abundances on Mars. Bromate reacts with organics more readily than chlorate or perchlorate, and its presence in subsurface brines could challenge habitability in the Martian subsurface. [ABSTRACT FROM AUTHOR]

Perchlorate (ClO 4 −) has synthetic and natural sources. Synthetic ClO 4 − is released to the environment from its use as an oxidant in military and aerospace applications, and from its presence in a variety of common commercial products, such as safety flares, chlorate herbicides, and fireworks. Natural sources of ClO 4 − in the environment include imported nitrate fertilizers derived from salt deposits in the Atacama Desert of Chile and indigenous natural ClO 4 − that accumulates in unsaturated soils and groundwaters in other arid and semi-arid environments, largely from atmospheric deposition. The stable isotope ratios of chlorine (37Cl/35Cl) and oxygen (18O/16O, 17O/16O) and the isotopic abundance of radioactive 36Cl in ClO 4 − can be used to discriminate these different sources. Perchlorate was previously detected at relatively high concentrations (3.8–34.7 μg/L) in groundwater from many wells in the Boardman-Umatilla area near the Columbia River in northeastern Oregon, which is a semi-arid, highly agricultural, heavily irrigated area that includes several past and current military installations. Eight representative groundwater wells were sampled throughout this region and isotopic characteristics of ClO 4 − collected from each well were measured along with other chemical and isotopic parameters including tritium and other groundwater age indicators. Isotopic data indicate that indigenous natural ClO 4 − was present in groundwater from all sampled wells and was the predominant source in five of the wells. Synthetic ClO 4 − was present in the three remaining wells with natural ClO 4 −, and a minor fraction of Atacama-fertilizer-derived ClO 4 − was indicated in one of the wells. Data from this study expand the geographic area of the USA in which indigenous natural ClO 4 − has been detected to include the semi-arid northwest. This study also illustrates the role of irrigation recharge as a mechanism for producing relatively high concentrations of indigenous natural ClO 4 − in groundwater by flushing accumulated salts from the unsaturated zone. • ClO 4 − from three different sources was identified isotopically in groundwater. • Indigenous natural ClO 4 − appears to be the predominant source in groundwater. • ClO 4 − was flushed from unsaturated zone salt accumulations into groundwater by irrigation recharge. [ABSTRACT FROM AUTHOR]

Natural perchlorate (ClO 4 − ) in soil and groundwater exhibits a wide range in stable isotopic compositions (δ 37 Cl, δ 18 O, and Δ 17 O), indicating that ClO 4 − may be formed through more than one pathway and/or undergoes post-depositional isotopic alteration. Plants are known to accumulate ClO 4 − , but little is known about their ability to alter its isotopic composition. We examined the potential for plants to alter the isotopic composition of ClO 4 − in hydroponic and field experiments conducted with snap beans ( Phaseolus vulgaris L.). In hydroponic studies, anion ratios indicated that ClO 4 − was transported from solutions into plants similarly to NO 3 − but preferentially to Cl − (4-fold). The ClO 4 − isotopic compositions of initial ClO 4 − reagents, final growth solutions, and aqueous extracts from plant tissues were essentially indistinguishable, indicating no significant isotope effects during ClO 4 − uptake or accumulation. The ClO 4 − isotopic composition of field-grown snap beans was also consistent with that of ClO 4 − in varying proportions from irrigation water and precipitation. NO 3 − uptake had little or no effect on NO 3 − isotopic compositions in hydroponic solutions. However, a large fractionation effect with an apparent ε ( 15 N/ 18 O) ratio of 1.05 was observed between NO 3 − in hydroponic solutions and leaf extracts, consistent with partial NO 3 − reduction during assimilation within plant tissue. We also explored the feasibility of evaluating sources of ClO 4 − in commercial produce, as illustrated by spinach, for which the ClO 4 − isotopic composition was similar to that of indigenous natural ClO 4 − . Our results indicate that some types of plants can accumulate and (presumably) release ClO 4 − to soil and groundwater without altering its isotopic characteristics. Concentrations and isotopic compositions of ClO 4 − and NO 3 − in plants may be useful for determining sources of fertilizers and sources of ClO 4 − in their growth environments and consequently in food supplies. [ABSTRACT FROM AUTHOR]

Abstract: Runoff of organic and inorganic contaminants from live firing ranges is a challenging issue because of the extensive size, the variable nature of runoff, the random occurrence of surface contamination, and general inaccessibility. This is particularly true with energetic compounds such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). One potentially promising technology for addressing runoff in a passive, sustainable, and low-cost manner is the use of constructed wetlands to intercept flow. This research effort investigated the ability of down-flow constructed wetlands to remediate RDX-contaminated water at varying loading rates over a period of 2 years. The impact of competing electron acceptors (NO3 − and SO4 2−), the role of plants in the remediation process, and the production of initial daughter products were determined. Significant RDX removal occurred (89–96%) for all loading rates (160–1600mg/(m2 day)) at a hydraulic retention time of approximately 2 days. RDX degradation occurred in both NO3 − and SO4 2− dominated electron acceptor zones. RDX and NO3 − degradation rate constants (k RDX and ) were also determined using a 1D transport model with dispersion. K RDX declined with the increase of influent RDX (6.2−0.8d−1 for planted mesocosms). Changes in degradation rates may be the result of changing bioavailability of carbon released by the peat moss. followed similar trends but was relatively greater than k RDX. Removal of plants is believed to have a small impact on overall RDX removal. RDX concentration in plant tissue was found to be semi-logarithmically related to RDX concentration in the rhizosphere. MNX, DNX, and TNX were observed as transient products generally proportional to RDX loading and low concentrations of MNX and DNX were detected in plant tissue at high RDX loading rates. Cessation of RDX exposure substantially reduced RDX concentrations plants over 6 weeks. These results support the use of constructed wetlands for the remediation of low-level RDX-contaminated water. [Copyright &y& Elsevier]