scholarly journals In Situ Quantification of Degradation Is Needed for Reliable Risk Assessments and Site-Specific Monitored Natural Attenuation

2018 ◽  
Vol 53 (1) ◽  
pp. 1-3 ◽  
Author(s):  
Cecilie B. Ottosen ◽  
Alexandra M. Murray ◽  
Mette M. Broholm ◽  
Poul L. Bjerg
Keyword(s):  
Natural Attenuation ◽  
Risk Assessments ◽  
Site Specific ◽  
Monitored Natural Attenuation

Application of monitored natural attenuation to remediate a petroleum-hydrocarbon spill site

2006 ◽  
Vol 53 (2) ◽  
pp. 321-328 ◽  
Author(s):  
C.M. Kao ◽  
W.Y. Huang ◽  
L.J. Chang ◽  
T.Y. Chen ◽  
H.Y. Chien ◽  
...  
Keyword(s):  
Natural Attenuation ◽  
Petroleum Hydrocarbons ◽  
Iron Sulfide ◽  
Contaminant Removal ◽  
Passive Remediation ◽  
Monitored Natural Attenuation ◽  
Transport Path ◽  
Spill Site ◽  
Benzene Toluene

Contamination of groundwater by petroleum-hydrocarbons is a serious environmental problem. The Monitored Natural Attenuation (MNA) approach is a passive remediation to degrade and dissipate groundwater contaminants in situ. In this study, a full-scale natural bioremediation investigation was conducted at a gasoline spill site. Results show that concentrations of major contaminants (benzene, toluene, ethylbenzene, and xylenes) dropped to below detection limit before they reached the downgradient monitor well located 280 m from the spill location. The results also reveal that natural biodegradation was the major cause of the observed contaminant reduction. The calculated natural first-order attenuation rates for BTEX and 1,2,4-trimethylbenzene (1,2,4-TMB) ranged from 0.051 (benzene) to 0.189 1/day (1,2,4-TMB). Evidence for the occurrence of natural attenuation includes the following: (1) depletion of dissolved oxygen, nitrate, and sulfate; (2) production of dissolved ferrous iron, sulfide, and CO2; (3) decreased BTEX concentrations and BTEX as carbon to TOC ratio along the transport path; (4) increased alkalinity and microbial populations; (5) limited spreading of the BTEX plume; and (6) preferential removal of certain BTEX components along the transport path. Additionally, the biodegradation capacity (44.73 mg/L) for BTEX and 1,2,4-TMB was much higher than other detected contaminants within the plume. Hence, natural attenuation can effectively contain the plume, and biodegradation processes played an important role in contaminant removal.

Natural attenuation of naphthalene and benzene at a former gasworks site

2007 ◽  
Vol 7 (3) ◽  
pp. 145-153
Author(s):  
V. Micic ◽  
K. Straub ◽  
P. Blum ◽  
A. Kappler
Keyword(s):  
Natural Attenuation ◽  
Sole Carbon Source ◽  
Geochemical Data ◽  
Carbon Stable Isotope ◽  
Site Specific ◽  
Anaerobic Microorganisms ◽  
Geochemical Parameters ◽  
Monitored Natural Attenuation ◽  
High Sorption ◽  
Concentration Changes

Naphthalene and benzene are ubiquitously found at former gasworks sites. In order to demonstrate that monitored natural attenuation (MNA) is an alternative strategy for remediation of groundwater at the investigated site, biodegradation was characterized by: (1) reduction of contaminants; (2) correlation of contaminants concentration changes with geochemical parameters; (3) enumeration of anaerobic microorganisms and correlation with geochemical data; (4) laboratory assays with site-specific enrichment cultures and naphthalene as the sole carbon source and electron donor; (5) modeling plume extension of naphthalene along the centerline and (6) carbon stable isotope (CSIA) analysis. The study demonstrated that naphthalene attenuation mainly depends on high sorption on aquifer material. In contrast, benzene is predominantly attenuated by biodegradation.

To Eliminate Curtain Effect of FIB TEM Samples by a Combination of Sample Dicing and Backside Milling

2014 ◽  
Author(s):  
Jian-Shing Luo ◽  
Hsiu Ting Lee
Keyword(s):  
Sample Preparation ◽  
Focused Ion Beam ◽  
Preparation Method ◽  
Low Cost ◽  
Ion Beam ◽  
Sample Preparation Method ◽  
Site Specific ◽  
Dual Beam ◽  
Transmission Electron

Abstract Several methods are used to invert samples 180 deg in a dual beam focused ion beam (FIB) system for backside milling by a specific in-situ lift out system or stages. However, most of those methods occupied too much time on FIB systems or requires a specific in-situ lift out system. This paper provides a novel transmission electron microscopy (TEM) sample preparation method to eliminate the curtain effect completely by a combination of backside milling and sample dicing with low cost and less FIB time. The procedures of the TEM pre-thinned sample preparation method using a combination of sample dicing and backside milling are described step by step. From the analysis results, the method has applied successfully to eliminate the curtain effect of dual beam FIB TEM samples for both random and site specific addresses.

scholarly journals Monitored natural attenuation to manage PFAS impacts to groundwater: Potential guidelines

2021 ◽  
Author(s):  
Charles J. Newell ◽  
David T. Adamson ◽  
Poonam R. Kulkarni ◽  
Blossom N. Nzeribe ◽  
John A. Connor ◽  
...  
Keyword(s):  
Natural Attenuation ◽  
Groundwater Potential ◽  
Monitored Natural Attenuation

Molecular modulation of calcium oxalate crystallization

2006 ◽  
Vol 291 (6) ◽  
pp. F1123-F1132 ◽  
Author(s):  
James J. De Yoreo ◽  
S. Roger Qiu ◽  
John R. Hoyer
Keyword(s):  
Molecular Modeling ◽  
Calcium Oxalate ◽  
Stone Formation ◽  
Energy Levels ◽  
Critical Role ◽  
Specific Interactions ◽  
Crystal Surfaces ◽  
Site Specific

Calcium oxalate monohydrate (COM) is the primary constituent of the majority of renal stones. Osteopontin (OPN), an aspartic acid-rich urinary protein, and citrate, a much smaller molecule, are potent inhibitors of COM crystallization at levels present in normal urine. Current concepts of the role of site-specific interactions in crystallization derived from studies of biomineralization are reviewed to provide a context for understanding modulation of COM growth at a molecular level. Results from in situ atomic force microscopy (AFM) analyses of the effects of citrate and OPN on growth verified the critical role of site-specific interactions between these growth modulators and individual steps on COM crystal surfaces. Molecular modeling investigations of interactions of citrate with steps and faces on COM crystal surfaces provided links between the stereochemistry of interaction and the binding energy levels that underlie mechanisms of growth modification and changes in overall crystal morphology. The combination of in situ AFM and molecular modeling provides new knowledge that will aid rationale design of therapeutic agents for inhibition of stone formation.

scholarly journals Prohormone convertases 1/3 and 2 together orchestrate the site-specific cleavages of progastrin to release gastrin-34 and gastrin-17

2008 ◽  
Vol 415 (1) ◽  
pp. 35-43 ◽  
Author(s):  
Jens F. Rehfeld ◽  
Xiaorong Zhu ◽  
Christina Norrbom ◽  
Jens R. Bundgaard ◽  
Anders H. Johnsen ◽  
...  
Keyword(s):  
Structural Factors ◽  
Cleavage Sites ◽  
Wild Type ◽  
Prohormone Convertases ◽  
Site Specific ◽  
G Cells ◽  
Processing Site ◽  
Vitro Effect

Cellular synthesis of peptide hormones requires PCs (prohormone convertases) for the endoproteolysis of prohormones. Antral G-cells synthesize the most gastrin and express PC1/3, 2 and 5/6 in the rat and human. But the cleavage sites in progastrin for each PC have not been determined. Therefore, in the present study, we measured the concentrations of progastrin, processing intermediates and α-amidated gastrins in antral extracts from PC1/3-null mice and compared the results with those in mice lacking PC2 and wild-type controls. The expression of PCs was examined by immunocytochemistry and in situ hybridization of mouse G-cells. Finally, the in vitro effect of recombinant PC5/6 on progastrin and progastrin fragments containing the relevant dibasic cleavage sites was also examined. The results showed that mouse G-cells express PC1/3, 2 and 5/6. The concentration of progastrin in PC1/3-null mice was elevated 3-fold. Chromatography showed that cleavage of the Arg36Arg37 and Arg73Arg74 sites were grossly decreased. Accordingly, the concentrations of progastrin products were markedly reduced, α-amidated gastrins (-34 and -17) being 25% of normal. Lack of PC1/3 was without effect on the third dibasic site (Lys53Lys54), which is the only processing site for PC2. Recombinant PC5/6 did not cleave any of the dibasic processing sites in progastrin and fragments containing the relevant dibasic processing sites. The complementary cleavages of PC1/3 and 2, however, suffice to explain most of the normal endoproteolysis of progastrin. Moreover, the results show that PCs react differently to the same dibasic sequences, suggesting that additional structural factors modulate the substrate specificity.

Evaluation of monitored natural attenuation of explosives at selected Department of Defense sites

2020 ◽  
pp. 349-350
Author(s):  
M. Zakikhani ◽  
J.C. Pennington ◽  
D.W. Harrelson ◽  
D. Gunnison ◽  
J.M. Brannon ◽  
...  
Keyword(s):  
Natural Attenuation ◽  
Department Of Defense ◽  
Monitored Natural Attenuation
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