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This study contrasts the use of high-resolution passive sampling and traditional groundwater monitoring wells (GWMW) to characterize a chlorinated solvent site and assess the effectiveness of a biowall (mulch, compost and sand) that was installed to remediate trichloroethene (TCE), the primary contaminant of concern. High-resolution passive profilers (HRPPs) were direct driven hydraulically upgradient, within, and hydraulically downgradient of the biowall and in close proximity to existing GWMWs. Compared with hydraulically upgradient locations, the biowall was highly reducing, there were higher densities of bacteria/genes capable of reductive dechlorination, and TCE was being reductively transformed, but not completely, as cis-1,2-dichloroethene (cis-DCE) was detected within and hydraulically downgradient of the biowall. However, based on the high-resolution data, there were a number of important findings which were not discoverable using data from GWMWs alone. Data from the HRPPs indicate that the biowall was completely transforming TCE to ethene (C

Microbes are widely assumed to be capable of colonizing even the most challenging terrestrial surface environments on Earth given enough time. We would not expect to find surface soils uninhabited by microbes as soils typically harbor diverse microbial communities and viable microbes have been detected in soils exposed to even the most inhospitable conditions. However, if uninhabited soils do exist, we might expect to find them in Antarctica. We analyzed 204 ice-free soils collected from across a remote valley in the Transantarctic Mountains (84 – 85°S, 174 – 177°W) and were able to identify a potential limit of microbial habitability. While most of the soils we tested contained diverse microbial communities, with fungi being particularly ubiquitous, microbes could not be detected in many of the driest, higher elevation soils - results that were confirmed using cultivation-dependent, cultivation-independent, and metabolic assays. While we cannot confirm that this subset of soils is completely sterile and devoid of microbial life, our results do show that microbial habitability and activity can be restricted by near-continuous exposure to cold, dry, and salty conditions, establishing the environmental conditions that constrain habitability in terrestrial surface environments. Constant exposure to these conditions for thousands of years has generated uninhabited surface soil environments, with either no detectable microbes or conditions which are not suitable to sustain microbial activity. Such uninhabited soils are unlikely to be unique to the studied region with this work challenging expectations about where microbes might, or might not, be able to thrive on Earth and other planets. Significance Statement Certain surface soils in Antarctica have remained effectively uninhabited due to a near-continuous exposure to cold-dry-salty conditions. This is an unexpected result because soils, even those in hyper-arid deserts, typically contain detectable microorganisms. Additionally, the prevalence of fungi at the colder, drier, higher elevation sites suggests that certain fungi may in fact be better adapted than bacteria or archaea to some of the most challenging soil environments on Earth.

This paper presents findings from a side-by-side operational comparison of granular road salt (RS) and MeltDown 20 (MD) deicing chemicals for snow and ice control from the perspective of “...

Natural chlorate (ClO

Microbes are widely assumed to be capable of colonizing even the most challenging terrestrial surface environments on Earth given enough time. We would not expect to find surface soils uninhabited by microbes as soils typically harbor diverse microbial communities and viable microbes have been detected in soils exposed to even the most inhospitable conditions. However, if uninhabited soils do exist, we might expect to find them in Antarctica. We analyzed 204 ice-free soils collected from across a remote valley in the Transantarctic Mountains (84 – 85°S, 174 – 177°W) and were able to identify a potential limit of microbial habitability. While most of the soils we tested contained diverse microbial communities, with fungi being particularly ubiquitous, microbes could not be detected in many of the driest, higher elevation soils - results that were confirmed using cultivation-dependent, cultivation-independent, and metabolic assays. While we cannot confirm that this subset of soils is completely sterile and devoid of microbial life, our results do show that microbial habitability and activity can be restricted by near-continuous exposure to cold, dry, and salty conditions, establishing the environmental conditions that constrain habitability in terrestrial surface environments. Constant exposure to these conditions for thousands of years has generated uninhabited surface soil environments, with either no detectable microbes or conditions which are not suitable to sustain microbial activity. Such uninhabited soils are unlikely to be unique to the studied region with this work challenging expectations about where microbes might, or might not, be able to thrive on Earth and other planets.Significance StatementCertain surface soils in Antarctica have remained effectively uninhabited due to a near-continuous exposure to cold-dry-salty conditions. This is an unexpected result because soils, even those in hyper-arid deserts, typically contain detectable microorganisms. Additionally, the prevalence of fungi at the colder, drier, higher elevation sites suggests that certain fungi may in fact be better adapted than bacteria or archaea to some of the most challenging soil environments on Earth.

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.

Natural chlorate (ClO3−) is widely distributed in terrestrial and extraterrestrial environments. To improve understanding of the origins and distribution of ClO3−, we developed and tested methods to determine the multi-dimensional isotopic compositions (δ18O, Δ17O, δ37Cl, 36Cl/Cl) of ClO3− 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 ClO3− indicate that its production involved reaction with O3, while its Cl isotopic composition is consistent with a tropospheric or near-surface source of Cl. The Δ17O and δ18O values of natural ClO3− are positively correlated, as are those of ClO4− and NO3− from the same localities, possibly indicating variation in the relative contributions of O3 as a source of O in the formation of the oxyanions. Additional isotopic analyses of ClO3− 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.

Nitrate was recently detected in Gale Crater sediments on Mars at abundances up to approximately 600 mg/kg, confirming predictions of its presence at abundances consistent with models based on impact-generated nitrate and other sources of fixed nitrogen. Terrestrial Mars analogs, Mars meteorites, and other solar system materials help establish a context for interpreting in situ nitrate measurements on Mars, particularly in relation to other cooccuring salts. We compare the relative abundance of nitrates to oxychlorine (chlorate and/or perchlorate, hereafter (per)chlorate) salts on Mars and Earth. The nitrate/(per)chlorate ratio on Mars is greater than 1, significantly lower than on Earth (nitrate/(per)chlorate greater than 10(exp.3)), suggesting not only the absence of biological activity but also different (per)chlorate formation mechanisms on Mars than on Earth.

This paper presents findings from a side-by-side field comparison of the effectiveness of sodium chloride-based road salt brine (RSB) and magnesium chloride-based Meltdown Apex™ liquid (MDA) as anti-icing chemicals for snow and ice control associated with winter roadway maintenance. The study was sponsored by the Texas Department of Transportation (TxDOT) to support operational decision-making for chemical treatment selections based on the perspective of pavement conditions observed by “the maintenance worker in the truck.” The field test site was a portion of rural service road near Canyon, Texas, located at latitude 35° N. The site was divided into eight 305 m sections that were treated with RSB at 141 l/lane km, MDA at 47 l/lane km, or left untreated for control. Two storm events at the test site during Winter 2014–2015 met pre-established research criteria for snow accumulation and other variables. Test sections were subjected to cycles of plowing, slushing, and additional anti-icing liquid treatment. Digital video data and still image (photo) data were collected throughout the storm events to allow estimation of visible pavement, and vehicle-based decelerometer tests were used to measure pavement friction. Overall results from multiple performance measures indicated comparable effectiveness of RSB and MDA at the applied rates. It was also noted that application of MDA on dry pavement prior to the storm events significantly reduced the pavement friction.

The cold (−13.4°C), cryoencapsulated, anoxic, interstitial brine of the >27 m thick ice of Lake Vida (Victoria Valley, Antarctica) contains 49 µg · L−1 of perchlorate and 11 µg · L−1 of chlorate. Lake Vida brine (LVBr) may provide an analog for potential oxychlorine-rich subsurface brine on Mars. LVBr volatiles were analyzed by solid-phase microextraction (SPME) gas chromatography–mass spectrometry (GC-MS) with two different SPME fibers. With the exception of volatile organic sulfur compounds, most other volatiles observed were artifacts produced in the GC injector when the thermal decomposition products of oxychlorines reacted with reduced carbon derived from LVBr and the SPME fiber phases. Analysis of MilliQ water with perchlorate (40 µg · L−1) showed low level of organic artifacts, reflecting carbon limitation. In order to observe sample-derived organic compounds, both in analog samples and on Mars, the molar abundance of reduced carbon in a sample must exceed those of O2 and Cl2 produced during decomposition of oxychlorines. This suggests that the abundance of compounds observed by the Sample Analysis at Mars (SAM) instruments in Sheepbed samples (CB-3, CB5, and CB6) may be controlled by an increase in the reduced-carbon/oxychlorine ratio of these samples. To increase chances of in situ detection of Martian organics during pyrolysis-GC-MS, we propose that the derivatization agents stored on SAM may be used as an external source of reduced carbon, increasing artificially the reduced-carbon to perchlorate ratio during pyrolysis, allowing the expression of more abundant and perhaps more diverse Martian organic matter.

The objective of this study was to investigate Joule heating/electric swing adsorption (ESA) as a mode of regeneration and to compare the carbon dioxide (CO2) adsorption capacity of pristine graphene films and reduced graphene oxide (rGO) aerogels. Joule heating/ESA has not been previously demonstrated in graphene based structures. Various forms of graphene have been previously evaluated for their use as a CO2 adsorbent, but most of these studies have focused on graphene oxide powders and films. We utilize both pristine graphene and rGO; we also highlight regeneration through Joule heating in contrast to heating under vacuum or by pressure swing. The amount of CO2 captured by graphene films and rGO aerogels was 0.52 ± 0.02 and 0.94 ± 0.02 g of CO2 per g of adsorbate, respectively. This adsorption capacity of pristine graphene films and rGO aerogels was found to be stable over multiple samples and multiple cycles of adsorption and electrical current stimulated desorption.

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.

The identification and characterization of aqueous minerals within ancient lacustrine environments on Mars are a high priority for determining the past habitability of the red planet. Terrestrial analog studies are useful both for understanding the mineralogy of lacustrine sediments, how the mineralogy varies with location in a lacustrine environment, and for validating the use of certain techniques such as visible–near-infrared (VNIR) spectroscopy. In this study, sediments from the Pilot Valley paleolake basin of the Great Salt Lake desert were characterized using VNIR as an analog for Martian paleolake basins. The spectra and subsequent interpretations were then compared to mineralogical characterization by ground truth methods, including X-ray diffraction, automated scanning electron microscopy, and several geochemical analysis techniques. In general, there is good agreement between VNIR and ground truth methods on the major classes of minerals present in the lake sediments and VNIR spectra can also easily discriminate between clay-dominated and salt-dominated lacustrine terrains within the paleolake basin. However, detection of more detailed mineralogy is difficult with VNIR spectra alone as some minerals can dominate the spectra even at very low abundances. At this site, the VNIR spectra are dominated by absorption bands that are most consistent with gypsum and smectites, though the ground truth methods reveal more diverse mineral assemblages that include a variety of sulfates, primary and secondary phyllosilicates, carbonates, and chlorides. This study provides insight into the limitations regarding the use of VNIR in characterizing complex mineral assemblages inherent in lacustrine settings.

Natural perchlorate (ClO4−) in soil and groundwater exhibits a wide range in stable isotopic compositions (δ37Cl, δ18O, and Δ17O), indicating that ClO4− may be formed through more than one pathway and/or undergoes post-depositional isotopic alteration. Plants are known to accumulate ClO4−, but little is known about their ability to alter its isotopic composition. We examined the potential for plants to alter the isotopic composition of ClO4− in hydroponic and field experiments conducted with snap beans (Phaseolus vulgaris L.). In hydroponic studies, anion ratios indicated that ClO4− was transported from solutions into plants similarly to NO3− but preferentially to Cl− (4-fold). The ClO4− isotopic compositions of initial ClO4− reagents, final growth solutions, and aqueous extracts from plant tissues were essentially indistinguishable, indicating no significant isotope effects during ClO4− uptake or accumulation. The ClO4− isotopic composition of field-grown snap beans was also consistent with that of ClO4− in varying proportions from irrigation water and precipitation. NO3− uptake had little or no effect on NO3− isotopic compositions in hydroponic solutions. However, a large fractionation effect with an apparent e (15N/18O) ratio of 1.05 was observed between NO3− in hydroponic solutions and leaf extracts, consistent with partial NO3− reduction during assimilation within plant tissue. We also explored the feasibility of evaluating sources of ClO4− in commercial produce, as illustrated by spinach, for which the ClO4− isotopic composition was similar to that of indigenous natural ClO4−. Our results indicate that some types of plants can accumulate and (presumably) release ClO4− to soil and groundwater without altering its isotopic characteristics. Concentrations and isotopic compositions of ClO4− and NO3− in plants may be useful for determining sources of fertilizers and sources of ClO4− in their growth environments and consequently in food supplies.

We report on 475 measurements of depth to ice-cemented ground in four high-elevation valleys of the Quartermain Mountains, McMurdo Dry Valleys, Antarctica. These valleys have pervasive ice-cemented ground, and the depth to ice-cemented ground and the ice composition may be indicators of climate change. In University Valley, the measured depth to ice-cemented ground ranges from 0–98 cm. There is an overall trend of increasing depth to ice-cemented ground with distance from a small glacier at the head of the valley, with a slope of 32 cm depth per kilometre along the valley floor. For Farnell Valley, the depth to ice-cemented ground is roughly constant (c. 30 cm) in the upper and central parts of the valley, but increases sharply as the valley descends into Beacon Valley. The two valleys north of University Valley also have extensive ice-cemented ground, with depths of 20–40 cm, but exhibit no clear patterns of ice depth with location. For all valleys there is a tendency for the variability in depth to ice-cemented ground at a site to increase with increasing depth to ice. Snow recurrence, solar insolation, and surface albedo may all be factors that cause site to site variations in these valleys.

Reverse osmosis (RO) is a treatment technology that may be used for the recovery of graywater terrestrially as well as the recovery of wastewater on board long duration, manned space flights. As with terrestrial RO applications, concentration polarization and membrane fouling lead to decreased productivity and increased energy demands with time. Physiochemical and biological pretreatment options can enhance the performance of the RO system; also, biological pretreatment has the advantages of low energy and consumable requirements as compared to other physiochemical pretreatment options. To determine the degree to which the incorporation of biological treatment enhances RO performance, a series of bench-scale experiments were performed. Observed resistances indicate that biological pretreatment alleviated the degree of non-reversible fouling while also improving the rate of permeate flux in a downstream RO process to further treat water. Results also indicated that enhanced urea hydrolysis, pH reduction, and carbon oxidation serve as the primary benefits of biological pretreatment of space-based graywater. The observations of this study may also benefit engineers considering the treatment of graywaters for terrestrial water-reuse applications.

GeneDB (http://www.genedb.org) is a genome database for prokaryotic and eukaryotic pathogens and closely related organisms. The resource provides a portal to genome sequence and annotation data, which is primarily generated by the Pathogen Genomics group at the Wellcome Trust Sanger Institute. It combines data from completed and ongoing genome projects with curated annotation, which is readily accessible from a web based resource. The development of the database in recent years has focused on providing database-driven annotation tools and pipelines, as well as catering for increasingly frequent assembly updates. The website has been significantly redesigned to take advantage of current web technologies, and improve usability. The current release stores 41 data sets, of which 17 are manually curated and maintained by biologists, who review and incorporate data from the scientific literature, as well as other sources. GeneDB is primarily a production and annotation database for the genomes of predominantly pathogenic organisms.

Natural perchlorate is believed to be of atmospheric origin, yet no systematic study has been conducted to evaluate perchlorate deposition rate and possible seasonal or spatial variations. This study evaluated perchlorate concentrations in weekly composite wet deposition samples acquired through the National Atmospheric Deposition Program from 26 sites across the continental United States, Alaska, and Puerto Rico for a 1-3 year period. Perchlorate concentrations varied from5 ng/L to a high of 102 ng/L with a mean of 14.1 +/- 13.5 ng/L for the 1578 total samples. The annual perchlorate flux by site ranged from a low of 12.5 (TX) to 157 mg/ha-year (NE) and averaged 65 +/- 30 mg/ha-year for all sites. Perchlorate concentrations and flux in wet deposition were generally highest in May-August declining to lows in December-February. Average annual perchlorate flux was correlated (r0.5; p0.001) with Ca2+, K+, NH4+, NO3(-), Cl(-), and SO4(-2). Wet deposition rate of ClO4(-) in the conterminous United States (excluding Alaska, Hawaii, and Puerto Rico) while diffuse, represents a potential annual net mass flux of 51,000 kg, a value comparable to the estimated annual environmental releases from other known ClO4(-) sources.

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 SO42−), 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 (160–1600 mg/(m2 day)) at a hydraulic retention time of approximately 2 days. RDX degradation occurred in both NO3− and SO42− dominated electron acceptor zones. RDX and NO3− degradation rate constants (kRDX and k N O 3 − ) were also determined using a 1D transport model with dispersion. KRDX declined with the increase of influent RDX (6.2 − 0.8 d−1 for planted mesocosms). Changes in degradation rates may be the result of changing bioavailability of carbon released by the peat moss. k N O 3 − followed similar trends but was relatively greater than kRDX. 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.

The transit mission wastewater may represent a future graywater, in which toilet waste is separated from other household waste streams, and dilution water is minimal. A loading rate study indicated that denitrification is stoichiometrically limited, and nitrification was kinetically limited. Denitrification stoichiometry was developed by deriving hypothetical molecular formulas of organic carbon inputs to be represented by the relative proportions of carbon, hydrogen, oxygen, and nitrogen. The derived stoichiometry was validated against experimental data by adjusting the values of f e and f s and multiplying the total dissolved organic carbon loss across the system by the overall R equation and then comparing the total nitrogen removed in the reaction to experimentally observed total nitrogen removal. The nitrification stoichiometry was similarly validated by multiplying the R equation by the ammonium-nitrogen removed and then comparing the NO x -N formed in the equation to actual NO x -N production values. The f s values for the denitrifying and nitrifying bacteria were 0.33 and 0.15, respectively.

Abiotic transport characteristics of a nitrifying membrane-aerated bioreactor were empirically analyzed and a model was developed. The orientation of the membranes in the bioprocessor is novel and the membrane/reactor length ratio is much larger than similar reactors for enhanced mass conversion. While mass conversion may be improved due to increases in total specific surface area, abiotic transport was characterized to ensure transport properties were similar to other membrane aeration bioprocessors. The developed model indicated that oxygen mass transfer and nutrient convection may limit bioreactor performance. Peclet numbers indicated that the bioreactor could be modeled as a complete-mix reactor for an initial approximation, but further research should be conducted to characterize non-ideal hydraulic behavior. The random “coiled” orientation of the membranes provided enhanced surface area for microbial attachment, but may have caused flow misdistribution issues. In contrast to abiotic modeling, experiments with nitrifying biofilm indicated sufficient electron acceptor and nutrient transport for the operational conditions tested. It was concluded that the complex nature of the silicon membrane geometry and assumption of parameter interdependency caused the under prediction of bioreactor transport. This model is intended to establish a platform for future models attempting to predict transport conditions in developing robust bioprocessors under stringent size, mass and energy restrictions. The random coiled geometry of the membranes is a viable option for long-lifetime bioprocessors requiring high specific surface area.

The major objectives of this work were to operate and construct an autohydrogenotrophic reactor and estimate perchlorate degradation kinetics. The results show that autohydrogenotrophic bacteria were cultured in the reactor and capable of removing 3.6 mg/d of perchlorate in the presence of excess hydrogen (99% removal). The reactor was successful in treating the average influent perchlorate concentration of 532 microg/L to the level of 3 microg/L. A first-order relationship was obtained between the concentration of active biomass in the reactor and the hydraulic retention time for the given amount of substrate. During the kinetic loading study, perchlorate removal ranged from 100 to 50%. The kinetic rate of perchlorate degradation observed in this study was 1.62 hr(-1). The significant degradation of perchlorate in these samples indicates the ubiquity of perchlorate-reducing organisms. Additionally, nitrate was simultaneously removed during water treatment (greater than 90% removal). Because of the excess levels of hydrogen, simultaneous removal of nitrate was not believed to significantly affect perchlorate removal. The area of concern was the lack of complete control over biological treatment. The growth of sulfate-reducing organisms in the reactor negatively affected perchlorate removal efficiency. There were no significant effects observed on the dissolved organic carbon and total suspended solids concentration of the effluent, suggesting that the treatment did not produce a large amount of biomass washout.

A cylindrical dialysis sampler (1.2 m in length; 5 cm in diameter) was designed and constructed to sample small-scale phytoremediation processes in the root zone of poplar trees. The study site was a 183-tree plantation of hybrid poplars located at Aberdeen Proving Ground, Maryland, at the J-Field Area of Concern. The grove was planted in 1996 to intercept a chlorinated solvent plume containing 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA, trichloroethene (TCE) and daughter products. Two dialysis samplers were installed: one directly in the poplar grove (approximately 0.3 m from the trunk of a mature tree) and the other outside of the grove but in the plume. Data collected included concentrations of chlorinated VOCs, organic acids, chloroacetic acids, Cl-, and dissolved gases (ethane, ethene, CH4, CO2). At the control location, the VOC profile was dominated by cis-1,2-dichloroethene (cis-1,2-DCE) and trans-1,2-dichloroethene (trans-1,2-DCE) with concentrations ranging from 0.88-4.5 to 4.4-17.6 mg/L, respectively. Concentrations of VOCs were similar across the vertical profile. At the tree location, 1,1,2,2-TeCA and TCE were the dominant VOCs detected but as opposed to the control location were highly variable within the root zone, with the greatest variability associated with locations in the sampler where roots were observed. This highly variable profile at the tree location is indicative of VOC rhizosphere biodegradation and uptake near the active roots. This variability appears to be on the centimeter scale, emphasizing the importance of these high-resolution samplers for the study of rhizosphere influences.

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.

Perchlorate is a persistent and mobile contaminant in the environment with both natural and anthropogenic sources. Stable isotope ratios of oxygen (δ^(18)O, Δ^(17)O) and chlorine (δ^(37)Cl) along with the abundance of the radioactive isotope ^(36)Cl were used to trace perchlorate sources and behavior in the Laurentian Great Lakes. These lakes were selected for study as a likely repository of recent atmospheric perchlorate deposition. Perchlorate concentrations in the Great Lakes range from 0.05 to 0.13 μg per liter. Δ^(37)Cl values of perchlorate from the Great Lakes range from +3.0‰ (Lake Ontario) to +4.0‰ (Lake Superior), whereas δ^(18)O values range from −4.1‰ (Lake Superior) to +4.0‰ (Lake Erie). Great Lakes perchlorate has mass-independent oxygen isotopic variations with positive Δ^(17)O values (+1.6‰ to +2.7‰) divided into two distinct groups: Lake Superior (+2.7‰) and the other four lakes (∼+1.7‰). The stable isotopic results indicate that perchlorate in the Great Lakes is dominantly of natural origin, having isotopic composition resembling that measured for indigenous perchlorate from preindustrial groundwaters of the western USA. The ^(36)Cl/Cl ratio of perchlorate varies widely from 7.4 × 10^(–12) (Lake Ontario) to 6.7 × 10^(–11) (Lake Superior). These ^(36)ClO_4– abundances are consistent with an atmospheric origin of perchlorate in the Great Lakes. The relatively high ^(36)ClO_4– abundances in the larger lakes (Lakes Superior and Michigan) could be explained by the presence of ^(36)Cl-enriched perchlorate deposited during the period of elevated atmospheric ^(36)Cl activity following thermonuclear bomb tests in the Pacific Ocean.

This research was conducted to evaluate the use of biological nitrification-denitrification systems as pre-processors for recycling wastewater to potable water in support of space exploration. A packed-bed bioreactor and membrane-aerated nitrification reactor were operated in series with a 10:1 recycle ratio over varying loading rates. The dissolved organic carbon (DOC) removal exceeded 80% for all loading rates (theta = 1 to 6.8 days), while total nitrogen removal generally increased with decreasing retention time, with a maximum removal of 55%. The degree of nitrification generally declined with decreasing retention time from a high of 80% to a low of 60%. Maximum DOC and total nitrogen volumetric removal rates exceeded 1000 and 800 g/m3 x d, respectively, and maximum nitrification volumetric conversion rates exceeded 300 g/m3 x d. At low hydraulic loading rates, the system was stoichiometrically limited, while kinetic limitations dominated at high hydraulic loading rates. Incomplete nitrification occurred at high loading rates, likely as a result of the high pH and large concentrations of ammonia.

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 (p0.001) 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.

Perchlorate (CLO4-) occurrence in groundwater has previously been linked to industrial releases and the historic use of Chilean nitrate fertilizers. However, recently a number of occurrences have been identified for which there is no obvious anthropogenic source. Groundwater from an area of 155,000 km2 in 56 counties in northwest Texas and eastern New Mexico is impacted bythe presence of ClO4-. Concentrations were generally low (4 ppb), although some areas are impacted by concentrations up to 200 ppb. ClO4- distribution is not related to well type (public water system, domestic, agricultural, or water-table monitoring) or aquifer (Ogallala, Edward Trinity High Plains, Edwards Trinity Plateau, Seymour, or Cenozoic). Results from vertically nested wells strongly indicate a surface source. The source of ClO4- appears to most likely be atmospheric deposition. Evidence supporting this hypothesis primarily relates to the presence of ClO4- in tritium-free older water, the lack of relation between land use and concentration distribution, the inability of potential anthropogenic sources to account for the estimated mass of ClO4-, and the positive relationship between conserved anions (e.g., IO3-, Cl-, SO4(-2)) and ClO4-. The ClO4- distribution appears to be mainly related to evaporative concentration and unsaturated transport. This process has led to higher ClO4- and other ion concentrations in groundwater where the water table is relatively shallow, and in areas with lower saturated thickness. Irrigation may have accelerated this process in some areas by increasing the transport of accumulated salts and by increasing the number of evaporative cycles. Results from this study highlight the potential for ClO4- to impact groundwater in arid and semi-arid areas through long-term atmospheric deposition.

Perchlorate (ClO(4)(-)) has been detected widely in groundwater and soils of the southwestern United States. Much of this ClO(4)(-) appears to be natural, and it may have accumulated largely through wet and dry atmospheric deposition. This study evaluates the isotopic composition of natural ClO(4)(-) indigenous to the southwestern U.S. Stable isotope ratios were measured in ClO(4)(-) (delta(18)O, Delta(17)O, delta(37)Cl) and associated NO(3)(-) (delta(18)O, Delta(17)O, delta(15)N) in groundwater from the southern High Plains (SHP) of Texas and New Mexico and the Middle Rio Grande Basin (MRGB) in New Mexico, from unsaturated subsoil in the SHP, and from NO(3)(-)-rich surface caliche deposits near Death Valley, California. The data indicate natural ClO(4)(-) in the southwestern U.S. has a wide range of isotopic compositions that are distinct from those reported previously for natural ClO(4)(-) from the Atacama Desert of Chile as well as all known synthetic ClO(4)(-). ClO(4)(-) in Death Valley caliche has a range of high Delta(17)O values (+8.6 to +18.4 per thousand), overlapping and extending the Atacama range, indicating at least partial atmospheric formation via reaction with ozone (O(3)). However, the Death Valley delta(37)Cl values (-3.1 to -0.8 per thousand) and delta(18)O values (+2.9 to +26.1 per thousand) are higher than those of Atacama ClO(4)(-). In contrast, ClO(4)(-) from western Texas and New Mexico has much lower Delta(17)O (+0.3 to +1.3 per thousand), with relatively high delta(37)Cl (+3.4 to +5.1 per thousand) and delta(18)O (+0.5 to +4.8 per thousand), indicating either that this material was not primarily generated with O(3) as a reactant or that the ClO(4)(-) was affected by postdepositional O isotope exchange. High Delta(17)O values in ClO(4)(-) (Atacama and Death Valley) are associated with high Delta(17)O values in NO(3)(-), indicating that both compounds preserve characteristics of O(3)-related atmospheric production in hyper-arid settings, whereas both compounds have low Delta(17)O values in less arid settings. Although Delta(17)O variations in terrestrial NO(3)(-) can be attributed to mixing of atmospheric (high Delta(17)O) and biogenic (low Delta(17)O) NO(3)(-), variations in Delta(17)O of terrestrial ClO(4)(-) are not readily explained in the same way. This study provides important new constraints for identifying natural sources of ClO(4)(-) in different environments by multicomponent isotopic characteristics, while presenting the possibilities of divergent ClO(4)(-) formation mechanisms and(or) ClO(4)(-) isotopic exchange in biologically active environments.