Jackson W.A.,Texas Tech University |
Bohlke J.K.,U.S. Geological Survey |
Andraski B.J.,U.S. Geological Survey |
Fahlquist L.,U.S. Geological Survey |
And 19 more authors.
Geochimica et Cosmochimica Acta | Year: 2015
Natural perchlorate (ClO4 -) is of increasing interest due to its wide-spread occurrence on Earth and Mars, yet little information exists on the relative abundance of ClO4 - 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 ClO4 - 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 ClO4 - to the more well-studied atmospherically deposited anions NO3 - and Cl- as a means to understand the prevalent processes that affect the accumulation of these species over various time scales. ClO4 - is globally distributed in soil and groundwater in arid and semi-arid regions on Earth at concentrations ranging from 10-1 to 106 μg/kg. Generally, the ClO4 - concentration in these regions increases with aridity index, but also depends on the duration of arid conditions. In many arid and semi-arid areas, NO3 - and ClO4 - co-occur at molar ratios (NO3 -/ClO4 -) that vary between ~104 and 105. 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 N2 fixation, N mineralization, nitrification, denitrification, and microbial ClO4 - reduction, as indicated in part by NO3 - isotope data. In contrast, much larger ranges of Cl-/ClO4 - and Cl-/NO3 - ratios indicate Cl- varies independently from both ClO4 - and NO3 -. The general lack of correlation between Cl- and ClO4 - or NO3 - 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 NO3 -/ClO4 - molar ratio ~103. The relative enrichment in ClO4 - compared to Cl- or NO3 - and unique isotopic composition of Atacama ClO4 - 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 ClO4 - reported on the surface of Mars, and its enrichment with respect to Cl- and NO3 -, could reveal important clues regarding the climatic, hydrologic, and potentially biologic evolution of that planet. Given the highly conserved ratio of NO3 -/ClO4 - 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 NO3 - pool terrestrially. © 2015 Elsevier Ltd.
Fuller M.E.,CB and I Federal Services |
Heraty L.,University of Delaware |
Condee C.W.,CB and I Federal Services |
Vainberg S.,CB and I Federal Services |
And 3 more authors.
Applied and Environmental Microbiology | Year: 2016
Kinetic isotopic fractionation of carbon and nitrogen during RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) biodegradation was investigated with pure bacterial cultures under aerobic and anaerobic conditions. Relatively large bulk enrichments in 15N were observed during biodegradation of RDX via anaerobic ring cleavage (ε15N=-12.7‰±0.8‰) and anaerobic nitro reduction (ε15N=-9.9‰±0.7‰), in comparison to smaller effects during biodegradation via aerobic denitration (ε15N=-2.4‰± 0.2‰). 13C enrichment was negligible during aerobic RDX biodegradation (ε13C=-0.8‰±0.5‰) but larger during anaerobic degradation (ε13C=-4.0‰±0.8‰), with modest variability among genera. Dual-isotope ε13C/ε15N analyses indicated that the three biodegradation pathways could be distinguished isotopically from each other and from abiotic degradation mechanisms. Compared to the initial RDX bulk δ15N value of+9‰, δ15N values of the NO2 - released from RDX ranged from-7‰ to+2‰during aerobic biodegradation and from-42‰ to-24‰ during anaerobic biodegradation. Numerical reaction models indicated that N isotope effects of NO2 - production were much larger than, but systematically related to, the bulk RDX N isotope effects with different bacteria. Apparent intrinsic ε15N-NO2 - values were consistent with an initial denitration pathway in the aerobic experiments and more complex processes of NO2 - formation associated with anaerobic ring cleavage. These results indicate the potential for isotopic analysis of residual RDX for the differentiation of degradation pathways and indicate that further efforts to examine the isotopic composition of potential RDX degradation products (e.g., NOx) in the environment are warranted. © 2016, American Society for Microbiology. All Rights Reserved.
Cho K.-C.,Texas A&M University |
Lee D.G.,Texas A&M University |
Fuller M.E.,CB and I Federal Services |
Hatzinger P.B.,CB and I Federal Services |
And 2 more authors.
Journal of Hazardous Materials | Year: 2015
This study identified microorganisms capable of using the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) or its metabolites as carbon and/or nitrogen sources under different electron-accepting conditions using 13C and 15N stable isotope probing (SIP). Mesocosms were constructed using groundwater and aquifer solids from an RDX-contaminated aquifer. The mesocosms received succinate as a carbon source and one of four electron acceptors (nitrate, manganese(IV), iron(III), or sulfate) or no additional electron acceptor (to stimulate methanogenesis). When RDX degradation was observed, subsamples from each mesocosm were removed and amended with 13C3- or ring-15N3-, nitro-15N3-, or fully-labeled 15N6-RDX, followed by additional incubation and isolation of labeled nucleic acids. A total of fifteen 16S rRNA sequences, clustering in α- and γ-Proteobacteria, Clostridia, and Actinobacteria, were detected in the 13C-DNA fractions. A total of twenty seven sequences were derived from different 15N-DNA fractions, with the sequences clustered in α- and γ-Proteobacteria, and Clostridia. Interestingly, sequences identified as Desulfosporosinus sp. (in the Clostridia) were not only observed to incorporate the labeled 13C or 15N from labeled RDX, but also were detected under each of the different electron-accepting conditions. The data suggest that 13C- and 15N-SIP can be used to characterize microbial communities involved in RDX biodegradation, and that the dominant pathway of RDX biodegradation may differ under different electron-accepting conditions. © 2015 Elsevier B.V.
Conley J.M.,U.S. Environmental Protection Agency |
Conley J.M.,Oak Ridge Institute for Science and Education |
Evans N.,U.S. Environmental Protection Agency |
Mash H.,U.S. Environmental Protection Agency |
And 6 more authors.
Science of the Total Environment | Year: 2016
In vitro bioassays have been successfully used to screen for estrogenic activity in wastewater and surface water, however, few have been applied to treated drinking water. Here, extracts of source and treated water samples were assayed for estrogenic activity using T47D-KBluc cells and analyzed by liquid chromatography-Fourier transform mass spectrometry (LC-FTMS) for natural and synthetic estrogens (including estrone, 17β-estradiol, estriol, and ethinyl estradiol). None of the estrogens were detected above the LC-FTMS quantification limits in treated samples and only 5 source waters had quantifiable concentrations of estrone, whereas 3 treated samples and 16 source samples displayed in vitro estrogenicity. Estrone accounted for the majority of estrogenic activity in respective samples, however the remaining samples that displayed estrogenic activity had no quantitative detections of known estrogenic compounds by chemical analyses. Source water estrogenicity (max, 0.47ng 17β-estradiol equivalents (E2Eq) L-1) was below levels that have been linked to adverse effects in fish and other aquatic organisms. Treated water estrogenicity (max, 0.078ngE2EqL-1) was considerably below levels that are expected to be biologically relevant to human consumers. Overall, the advantage of using in vitro techniques in addition to analytical chemical determinations was displayed by the sensitivity of the T47D-KBluc bioassay, coupled with the ability to measure cumulative effects of mixtures, specifically when unknown chemicals may be present. © 2016.