Biotransformation of PFAA Precursors by Oxygenase-Expressing Bacteria in AFFF-Impacted Groundwater and in Pure-Compound Studies with 6:2 FTS and EtFOSE.

Numerous US drinking water aquifers have been contaminated with per- and polyfluoroalkyl substances (PFAS) from fire-fighting and fire-training activities using aqueous film-forming foam (AFFF). These sites often contain other organic compounds, such as fuel hydrocarbons and methane, which may serve as primary substrates for cometabolic (i.e., nongrowth-linked) biotransformation reactions. This work investigates the abilities of AFFF site relevant bacteria (methanotrophs, propanotrophs, octane, pentane, isobutane, toluene, and ammonia oxidizers), known to express oxygenase enzymes when degrading their primary substrates, to biotransform perfluoroalkyl acid (PFAA) precursors to terminal PFAAs. Microcosms containing AFFF-impacted groundwater, 6:2 fluorotelomer sulfonate (6:2 FTS), or N-ethylperfluorooctane sulfonamidoethanol (EtFOSE) were inoculated with the aerobic cultures above and incubated for 4 and 8 weeks at 22 °C. Bottles were sacrificed, extracted, and subjected to target, nontarget, and suspect screening for PFAS. The PFAA precursors 6:2 FTS, N-sulfopropyldimethyl ammoniopropyl perfluorohexane sulfonamide (SPrAmPr-FHxSA), and EtFOSE transformed up to 99, 71, and 93%, respectively, and relevant daughter products, such as the 6:1 fluorotelomer ketone sulfonate (6:1 FTKS), were identified in quantities previously not observed, implicating oxygenase enzymes. This is the first report of a suite of site relevant PFAA precursors being transformed in AFFF-impacted groundwater by bacteria grown on substrates known to induce specific oxygenase enzymes. The data provide crucial insights into the microbial transformation of these compounds in the subsurface.

Perchlorate in the Great Lakes: isotopic composition and origin.

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)ClO4(-) abundances are consistent with an atmospheric origin of perchlorate in the Great Lakes. The relatively high (36)ClO4(-) 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.

Integration of Full-Size Graywater Membrane-Aerated Biological Reactor with Reverse Osmosis System for Space-Based Wastewater Treatment.

To date, life support systems on the International Space Center (ISS) or those planned for upcoming moon/Mars missions have not included biological reactors for wastewater treatment, despite their ubiquitous use for the treatment of terrestrial wastewaters. However, the new focus on partial gravity habitats reduces the required complexity of treatment systems compared with those operating in micro-gravity, and the likely addition of large-volume wastewaters with surfactant loads (e.g., laundry and shower) makes the current ISS wastewater treatment system inappropriate due to the foaming potential from surfactants, increased consumable requirements due to the use of non-regenerative systems (e.g., mixed adsorbent beds), the complexity of the system, and sensitivity to failures from precipitation and/or biological fouling. Hybrid systems that combine simple biological reactors with desalination (e.g., Reverse Osmosis (RO)) could reduce system and consumable mass and complexity. Our objective was to evaluate a system composed of a membrane-aerated bioreactor (MABR) coupled to a low-pressure commercial RO system to process partial gravity habitat wastewater. The MABR was able to serve as the only wastewater collection tank (variable volume), receiving all wastewaters as they were produced. The MABR treated more than 20,750 L of graywater and was able to remove more than 90% of dissolved organic carbon (DOC), producing an effluent with DOC < 14 mg/L and BOD < 12 mg/L and oxidizing >90% of the ammoniacal nitrogen into NOx-. A single RO membrane (260 g) was able to process >3000 L of MABR effluent and produced a RO permeate with DOC < 5 mg/L, TN < 2 mg/L, and TDS < 10 mg/L, which would essentially meet ISS potable water standards after disinfection. The system has an un-optimized mass and volume of 128.5 kg. Consumables include oxygen (~4 g/crew-day), RO membranes, and a prefilter (1.7 g/crew-day). For a one-year mission with four crew, the total system + consumable mass are ~141 kg, which would produce ~15,150 kg of treated water, resulting in a pay-back period of 13.4 days (3.35 days for a crew of four). Given that the MABR in this study operated for 500 days, while in previous studies, similar systems operated for more than 3 years, the total system costs would be exceedingly low. These results highlight the potential application of hybrid treatment systems for space habitats, which may also have a direct application to terrestrial applications where source-separated systems are employed.

Long-term monitoring and modeling of PAHs in capped sediments at the Grand Calumet River.

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 (C2019/CBL=0.20-0.07+0.12 in sediments and 0.27-0.10+0.15 in cap) and Pyr (C2019/CBL=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 (C2019/CBL=1.0-0.24+0.32) and there was an increase in the cap (C2019/CBL=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 (t1/2=1.12-0.11+0.16 years) and Pyr (t1/2=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.

Perchlorate production by photodecomposition of aqueous chlorine solutions.

Aqueous chlorine solutions (defined as chlorine solutions (Cl(2,T)) containing solely or a combination of molecular chlorine (Cl(2)), hypochlorous acid (HOCl), and hypochlorite (OCl(-))) are known to produce toxic inorganic disinfection byproduct (e.g., chlorate and chlorite) through photoactivated transformations. Recent reports of perchlorate (ClO(4)(-)) production-a well-known thyroid hormone disruptor- from stored bleach solutions indicates the presence of unexplored transformation pathway(s). The evaluation of this potential ClO(4)(-) source is important given the widespread use of aqueous chlorine as a disinfectant. In this study, we perform detailed rate analysis of ClO(4)(-) generation from aqueous chlorine under varying environmental conditions including ultraviolet (UV) light sources, intensity, solution pH, and Cl(2,T) concentrations. Our results show that ClO(4)(-) is produced upon UV exposure of aqueous chlorine solutions with yields ranging from 0.09 × 10(-3) to 9.2 × 10(-3)% for all experimental conditions. The amount of ClO(4)(-) produced depends on the starting concentrations of Cl(2,T) and ClO(3)(-), UV source wavelength, and solution pH, but it is independent of light intensity. We hypothesize a mechanistic pathway derived from known reactions of Cl(2,T) photodecomposition that involves the reaction of Cl radicals with ClO(3)(-) to produce ClO(4)(-) with calculated rate coefficient (k(ClO4-)) of (4-40) × 10(5) M(-1) s(-1) and (3-250) × 10(5) M(-1) s(-1) for UV-B/C and UV-A, respectively. The measured ClO(4)(-) concentrations for both UV-B and UV-C experiments agreed well with our model (R(2) = 0.88-0.99), except under UV-A light exposure (R(2) = 0.52-0.93), suggesting the possible involvement of additional pathways at higher wavelengths. Based on our results, phototransformation of aqueous chlorine solutions at concentrations relevant to drinking water treatment would result in ClO(4)(-) concentrations (~0.1 µg L(-1)) much below the proposed drinking water limits. The importance of the hypothesized mechanism is discussed in relation to natural ClO(4)(-) formation by atmospheric transformations.

Assessing Potential Perfluoroalkyl Substances Trophic Transfer to Crickets (Acheta domesticus).

Although many studies have assessed the bioaccumulation of perfluoroalkyl substances (PFAS) in plant tissues, to date there has been minimal research on the bioaccumulation of PFAS in soil invertebrates that results from consuming PFAS-contaminated media. The present study focused on two different consumption pathways in a population of crickets: individuals consuming PFAS-contaminated alfalfa and individuals consuming PFAS-spiked drinking water. Alfalfa was grown in a greenhouse and irrigated with PFAS-spiked water (∼1 ppm) containing seven unique PFAS. The alfalfa was then harvested and fed to crickets. Another population of crickets was supplied with PFAS-spiked drinking water at similar concentrations to irrigation water for direct consumption. Alfalfa accumulation of PFAS and subsequent consumption by the crickets resulted in overall similar tissue concentrations in the crickets who consumed PFAS-spiked water directly. This indicates that source concentration (water) may be an important factor in assessing the bioaccumulation of PFAS in organisms. To our knowledge, ours is the first study not only to assess the direct trophic transfer of PFAS from contaminated vegetation to invertebrates, but also to highlight the similarities in bioaccumulation regardless of ingestion pathway. Environ Toxicol Chem 2022;41:2981-2992. © 2022 SETAC.

Improved assessment and performance monitoring of a biowall at a chlorinated solvent site using high-resolution passive sampling.

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 (C2H4) except within a high velocity interval, where the concentrations were reduced, but breakthrough of cis-DCE was apparent. Hydraulically upgradient of the biowall, concentrations of TCE increased with depth where a very low permeability zone exists that will likely remain as a long-term source. In addition, although low concentrations of cis-DCE were present downgradient of the biowall, surfacing into a downgradient stream was not detected. This study demonstrates the advantages of high-resolution passive sampling of aquifers to assess the performance of remediation techniques compared to traditional methods such as GWMWs.

Species- and Tissue-Specific Chronic Toxicity Values for Northern Bobwhite Quail (Colinus virginianus) Exposed to Perfluorohexane Sulfonic Acid and a Binary Mixture of Perfluorooctane Sulfonic Acid and Perfluorohexane Sulfonic Acid.

Per- and polyfluoroalkyl substances (PFAS) are globally distributed and present in nearly every environmental compartment. Characterizing the chronic toxicity of individual PFAS compounds and mixtures is necessary because many have been reported to cause adverse health effects. To derive toxicity reference values (TRVs) and conduct ecotoxicological risk assessments (ERAs) of PFAS-contaminated ecosystems for wildlife, species-specific PFAS chronic toxicity values (CTVs) are needed. The present study quantified PFAS residues from liver and eggs of birds chronically exposed to perfluorohexanoic acid (PFHxA) or a mixture of perfluorooctane sulfonate (PFOS) and PFHxA that produced a no-observable-adverse-effect level (NOAEL) and/or a lowest-observable-adverse-effectlevel (LOAEL). The CTVs we present are lower than those previously reported for birds and should be considered in future regulatory evaluations. From the estimated species- and tissue-specific PFAS CTVs, we found that PFOS and perfluorohexane sulfonate (PFHxS) were more bioaccumulative than PFHxA in avian tissues, but PFHxA was more toxic to reproducing birds than either PFOS or a PFOS:PFHxS mixture. We further determined that avian toxicity was not necessarily additive with respect to PFAS mixtures, which could have implications for PFAS ERAs. The PFAS LOAEL CTVs can be used to predict reproductive and possible population-level adverse health effects in wild avian receptors. Environ Toxicol Chem 2022;41:219-229. © 2021 SETAC.

Limitations encountered for the treatment of a low C:N waste using a modified membrane-aerated biofilm reactor.

A modified membrane-aerated biofilm reactor (mMABR) that combined oxygen permeable membranes and inert attachment media to support both nitrification and denitrification was used to treat a carbon-limited (COD:N = 1.8) and ammonium-rich (NH4+ = 650 g-N/m3) space habitation waste stream. An eight-fold increase in intramembrane air pressure did not affect process performance; however, for an air pressure of 11 kPa (gauge), lower and upper hydraulic loading limits for the mMABR were identified at 30 g-N/m3 x d and 123 g-N/m3 x d, respectively. Oxygen limitation occurred at the highest loading rate and alkalinity limitation occurred at the lowest loading rate. Partial nitrification was noted at both limitations. Additionally, increased recirculation ratios were shown to decrease denitrification efficiency. Mean carbon and nitrogen removal rates were as high as 75.3 g-C/m3 x d (0.26 g-C/m2d) and 63.8 g-N/m3 x d (0.22 g-N/m2 x d), respectively. The mMABR achieved maximal nitrification and denitrification performance given the stoichiometric nature of the waste.

Determination of phosphite (HPO3-2) by a new IC/MS/MS method using an 18O-labeled HPO3-2 internal standard.

A new method has been developed to determine trace amounts of phosphite (HPO3-2) in environmental samples using ion chromatography with electrospray tandem mass spectrometry (IC-ESI/MS/MS). The method includes the production and use of an 18O-labeled HPO3-2 internal standard (IS). This isotopically labeled IS significantly improved sensitivity and could account for matrix suppression. The method detection limit (MDL) was determined as 0.017 and 0.034 µg L-1 of HPO3-2 (6.5 and 13 ng P L-1) using a 500 and 25 µL injection loop, respectively. Precision (1-10%) and accuracy (recoveries = 96-106%) were established for a range of environmental samples using known (spiked) addition. The impact of ionic interferences was investigated by evaluating the response of the internal standard in the presence of common anions with respect to distilled deionized water. The most significant interference was due to nitrate (100 mg-NO3- L-1) with a 99.99% reduction in IS intensity. The method was successfully applied to wastewater effluent, surface water, tap water, and soil samples. Relatively low concentrations <0.25 µg HPO3-2 L-1 were measured in tap water, surface water and wastewater effluent, and ~1.6 µg kg-1 HPO3-2 in soil samples, using both injection loops. Limited suppression was observed for all matrices. The largest IS peak area suppression (~98%) was observed in WW effluent with 500 µL injection loop; however, this method was able to quantify HPO3-2 with good recoveries and precision despite the mentioned suppression, supporting the ability of the proposed method to quantify HPO3-2 in different environmental matrices.

Isotopic composition of natural and synthetic chlorate (δ18O, Δ17O, δ37Cl, 36Cl/Cl): Methods and initial results.

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.

Chronic Reproductive Toxicity Thresholds for Northern Bobwhite Quail (Colinus virginianus) Exposed to Perfluorohexanoic Acid (PFHxA) and a Mixture of Perfluorooctane Sulfonic Acid (PFOS) and PFHxA.

Terrestrial toxicology data are limited for comprehensive ecotoxicological risk assessment of ecosystems contaminated by per- and polyfluoroalkyl substances (PFAS) partly because of their existence as mixtures in the environment. This complicates logistical dose-response modeling and establishment of a threshold value characterizing the chronic toxicity of PFAS to ecological receptors. We examined reproduction, growth, and survival endpoints using a combination of hypothesis testing and logistical dose-response modeling of northern bobwhite quail (Colinus virginianus) exposed to perfluorohexanoic acid (PFHxA) alone and to PFHxA in a binary mixture with perfluorooctane sulfonic acid (PFOS) via the drinking water. The exposure concentration chronic toxicity value (CTV) representative of the lowest-observable-adverse effect level (LOAEL) threshold for chronic oral PFAS toxicity (based on reduced offspring weight and growth rate) was 0.10 ng/mL for PFHxA and 0.06 ng/mL for a PFOS:PFHxA (2.7:1) mixture. These estimates corresponded to an adult LOAEL average daily intake CTV of 0.0149 and 0.0082 µg × kg body weight-1 × d-1 , respectively. Neither no-observable-adverse effect level threshold and representative CTVs nor dose-response and predicted effective concentration values could be established for these 2 response variables. The findings indicate that a reaction(s) occurs among the individual PFAS components present in the mixture to alter the potential toxicity, demonstrating that mixture affects avian PFAS toxicity. Thus, chronic oral PFAS toxicity to avian receptors represented as the sum of the individual compound toxicities may not necessarily be the best method for assessing chronic mixture exposure risk at PFAS-contaminated sites. Environ Toxicol Chem 2021;40:2601-2614. © 2021 SETAC.

Perchlorate, nitrate, and iodide intake through tap water.

Perchlorate is ubiquitous in the environment, leading to human exposure and potential impact on thyroid function. Nitrate can also competitively inhibit iodide uptake at the sodium-iodide symporter and thus reduce thyroid hormone production. This study investigates the intake of perchlorate, nitrate, and iodide attributable to direct and indirect tap water consumption. The National Health and Nutrition Examination Survey collected tap water samples and consumption data from 3262 U.S. residents during the years 2005-2006. The median perchlorate, nitrate, and iodide levels measured in tap water were 1.16, 758, and 4.55 µg/L, respectively. Measured perchlorate levels were below the United States Environmental Protection Agency (U.S. EPA) drinking water equivalent level for perchlorate (24.5 µg/L). Significant correlations were found between iodide and nitrate levels (r = 0.17, p < 0.0001) and perchlorate and nitrate levels (r = 0.25, p < 0.0001). On the basis of 24 h recall, 47% of the study participants reported drinking tap water; 89% reported either direct or indirect consumption of tap water. For the adult population (age ≥ 20 yrs) the median tap water consumption rate was 11.6 mL/kg-day. Using individual tap water consumption data and body weight, we estimated the median perchlorate, nitrate, and iodide dose attributable to tap water as 9.11, 11300, and 43.3 ng/kg-day, respectively, for U.S. adults. This perchlorate exposure dose from tap water is relatively small compared to the total perchlorate exposure dose previously characterized for the U.S. adults (median 64 ng/kg-day) and the U.S. EPA reference dose (700 ng/kg-day).

Natural chlorate in the environment: application of a new IC-ESI/MS/MS method with a Cl¹8O3-internal standard.

A new ion chromatography electrospray tandem mass spectrometry (IC-ESI/MS/MS) method has been developed for quantification and confirmation of chlorate (ClO3⁻) in environmental samples. The method involves the electrochemical generation of isotopically labeled chlorate internal standard (Cl¹8O3⁻) using ¹8O water (H2¹8O) he standard was added to all samples prior to analysis thereby minimizing the matrix effects that are associated with common ions without the need for expensive sample pretreatments. The method detection limit (MDL) for ClO3⁻ was 2 ng L⁻¹ for a 1 mL volume sample injection. The proposed method was successfully applied to analyze ClO3⁻ in difficult environmental samples including soil and plant leachates. The IC-ESI/MS/MS method described here was also compared to established EPA method 317.0 for ClO3⁻ analysis. Samples collected from a variety of environments previously shown to contain natural perchlorate (ClO4⁻) occurrence were analyzed using the proposed method and ClO3⁻ was found to co-occur with ClO4⁻ at concentrations ranging from < 2 ng L⁻¹ in precipitation from Texas and Puerto Rico to >500 mg kg⁻¹ in caliche salt deposits from the Atacama Desert in Chile. Relatively low concentrations of ClO3⁻ in some natural groundwater samples (0.1 µg L⁻¹) analyzed in this work may indicate lower stability when compared to ClO4⁻ in the subsurface. The high concentrations ClO3⁻ in caliches and soils (3-6 orders of magnitude greater) as compared to precipitation samples indicate that ClO3⁻, like ClO4⁻, may be atmospherically produced and deposited, then concentrated in dry soils, and is possibly a minor component in the biogeochemical cycle of chlorine.

Nitrification-denitrification biological treatment of a high-nitrogen waste stream for water-reuse applications.

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.

Evidence for Biotic Perchlorate Reduction in Naturally Perchlorate-Rich Sediments of Pilot Valley Basin, Utah.

The presence of perchlorate on Mars suggests a possible energy source for sustaining microbial life. Perchlorate-reducing microbes have been isolated from perchlorate-contaminated soils and sediments on the Earth, but to date, never from an environment that is naturally enriched in perchlorate. The arid Pilot Valley paleolake basin in Utah is a Mars analog environment whose sediments are naturally enriched with up to ∼6.5 µg kg-1 perchlorate oxyanions. Here, we present results of field and laboratory studies indicating that perchlorate-reducing microorganisms co-occur with this potential electron acceptor. Biogeochemical data suggest ongoing perchlorate reduction; phylogenetic data indicate the presence of diverse microbial communities; and laboratory enrichments using Pilot Valley sediments show that resident microbes can reduce perchlorate. This is the first article of the co-existence of perchlorate-reducing microbes in an environment where perchlorate occurs naturally, arguing for Pilot Valley's utility as an analog for studying biogeochemical processes that may have occurred, and may yet still be occurring, in ancient martian lacustrine sediments.

Estimation of Interstitial Velocity Using a Direct Drive High-Resolution Passive Profiler.

The fate and transport of groundwater contaminants depends partially on groundwater velocity, which can vary appreciably in highly stratified aquifers. A high-resolution passive profiler (HRPP) was developed to evaluate groundwater velocity, contaminant concentrations, and microbial community structure at ∼20 cm vertical depth resolution in shallow heterogeneous aquifers. The objective of this study was to use mass transfer of bromide (Br- ), a conservative tracer released from cells in the HRPP, to estimate interstitial velocity. Laboratory experiments were conducted to empirically relate velocity and the mass transfer coefficient of Br- based on the relative loss of Br- from HRPP cells. Laboratory-scale HRPPs were deployed in flow boxes containing saturated soils with differing porosities, and the mass transfer coefficient of Br- was measured at multiple interstitial velocities (0 to 100 cm/day). A two-dimensional (2D) quasi-steady-state model was used to relate velocity to mass transfer of Br- for a range of soil porosities (0.2-0.5). The laboratory data indicate that the mass transfer coefficient of Br- , which was directly-but non-linearly-related to velocity, can be determined with a single 3-week deployment of the HRPP. The mass transfer coefficient was relatively unaffected by sampler orientation, length of deployment time, or porosity. The model closely simulated the experimental results. The data suggest that the HRPP will be applicable for estimating groundwater velocity ranging from 1 to 100 cm/day in the field at a minimum depth resolution of 10 cm, depending on sampler design.

Perchlorate production by ozone oxidation of chloride in aqueous and dry systems.

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 ClO(4)(-) 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 O(3) (0.96%) generated ClO(4)(-) 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 ClO(4)(-) than Cl(-) coated sand or glass as well as a higher ratio of ClO(3)(-) to ClO(4)(-). Reduction of the initial Cl(-) mass resulted in substantially higher molar yields of ClO(4)(-) and ClO(3)(-). In addition, alkaline absorbers that captured gaseous products contained substantial quantities of Cl(-), ClO(3)(-), and ClO(4)(-). Solutions of possible oxychlorine intermediates (OCl(-) and ClO(3)(-)) exposed to O(3) produced only scant amounts of ClO(4)(-) while a ClO(2)(-) solution exposed to O(3) produced substantial molar yields of ClO(4)(-) (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 O(3). 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 ClO(2)(-) may be a key intermediate while ClO(3)(-) and OCl(-) are unlikely to play a significant role.

Effect of two major N-nitroso hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) metabolites on earthworm reproductive success.

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.

Treatment efficiency and stoichiometry of a high-strength graywater.

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 fe and fs 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 fs values for the denitrifying and nitrifying bacteria were 0.33 and 0.15, respectively.