Do sulfate reducing bacteria help during the formation of the mineral dolomite in low temperature environments?

Do sulfate reducing bacteria help during the formation of the mineral dolomite in low temperature environments?

Wikipedia says

The actual role of bacteria in the low-temperature formation of dolomite remains to be demonstrated. The specific mechanism of dolomitization, involving sulfate-reducing bacteria, has not yet been demonstrated.

I wonder if someone has any updates on this. The reference given in the Wikipedia article is from 2000, from a source titled suspiciously "Journal of Conference Abstracts". Now it's 2013 and maybe someone else has found out something new.

The appropriate answer seems to be that bacteria help somewhat sometimes, maybe.

The evidence for this appears to be mixed, and appears to have been historically controversial.

One old-ish paper claims that bacteria (and more importantly, Archaea) are necessary at least under some conditions. Another somewhat later paper including some of the same authors claims to have found conditions for abiotic dolomite synthesis in the laboratory.

It appears that in terms of mechanisms, the relevant process may involve the proper state of magnesium ions, to which apparently microbes contribute via extracellular polysaccharides:

Literature values for carboxyl group density are not available for all bacteria involved in dolomite formation, however Braissant et al. (2007) demonstrated disordered dolomite phases forming in the presence of the EPS of sulfate reducing bacteria with a carboxyl group density of ~10-3 moles g-1, similar to our values. We suggest that these carboxyl groups promote desolvation of the Mg ion, known to be a kinetic inhibitor in dolomite precipitation (Wright and Wacey, 2004), but are needed in a high density for nucleation to commence.

However, what process exactly is generating geological dolomites appears to be still a matter of debate, and also here, with some suggestive evidence in favor of microbes affecting that process.

Frontiers in Earth Science

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Do sulfate reducing bacteria help during the formation of the mineral dolomite in low temperature environments? - Biology

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About the Cover:
In this issue:
Environmental health writ large
"Grassroots" global warming study | Congress weakens environmental laws with loopholes in hurricane-recovery legislation | Carbon storage for greenhouse gases | PBDEs overtaking PCBs | Natural resources can improve villagers' lives | India under threat from climate change | Sunita Narain | Distinguishing between sources of sewage contamination | Nanoparticle agglomeration restricts uptake into living cells
  • Paul D. Thacker ,
  • Janet Pelley ,
  • Catherine M. Cooney ,
  • Anke Schaefer , and
  • Ori Schipper
Cold-water laundry detergent is a hot idea
EPA proposes to relax TRI reporting rules
Chemical Reactivity as a Tool for Estimating Persistence
Molecular Structure in Soil Humic Substances: The New View

A critical examination of published data obtained primarily from recent nuclear magnetic resonance spectroscopy, X-ray absorption near-edge structure spectroscopy, electrospray ionization−mass spectrometry, and pyrolysis studies reveals an evolving new view of the molecular structure of soil humic substances. According to the new view, humic substances are collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and hydrogen bonds. These associations are capable of organizing into micellar structures in suitable aqueous environments. Humic components display contrasting molecular motional behavior and may be spatially segregated on a scale of nanometers. Within this new structural context, these components comprise any molecules intimately associated with a humic substance, such that they cannot be separated effectively by chemical or physical methods. Thus biomolecules strongly bound within humic fractions are by definition humic components, a conclusion that necessarily calls into question key biogeochemical pathways traditionally thought to be required for the formation of humic substances. Further research is needed to elucidate the intermolecular interactions that link humic components into supramolecular associations and to establish the pathways by which these associations emerge from the degradation of organic litter.

Improved Accounting of Emissions from Utility Energy Storage System Operation

Several proposed utility-scale energy storage systems in the U.S. will use the spare output capacity of existing electric power systems to create the equivalent of new load-following plants that can rapidly respond to fluctuations in electricity demand and increase the flexibility of baseload generators. New energy storage systems using additional generation from existing plants can directly compete with new traditional sources of load-following and peaking electricity, yet this application of energy storage is not required to meet many of the Clean Air Act standards required of new electricity generators (e.g., coal- or gas-fired power plants). This study evaluates the total emissions that will likely result from the operation of a new energy storage facility when coupled with an average existing U.S. coal-fired power plant and estimates that the emission rates of SO2 and NOx will be considerably higher than the rate of a new plant meeting Clean Air Act standards, even accounting for the efficiency benefits of energy storage. This study suggests that improved emissions “accounting” might be necessary to provide accurate environmental comparisons between energy storage and more traditional sources of electricity generation.

Learning from the U.S. National Assessment of Climate Change Impacts
  • M. Granger Morgan ,
  • Robin Cantor ,
  • William C. Clark ,
  • Ann Fisher ,
  • Henry D. Jacoby ,
  • Anthony C. Janetos ,
  • Ann P. Kinzig ,
  • Jerry Melillo ,
  • Roger B. Street , and
  • Thomas J. Wilbanks

The U.S. National Assessment of the Potential Consequences of Climate Variability and Change was a federally coordinated nationwide effort that involved thousands of experts and stakeholders. To draw lessons from this effort, the 10 authors of this paper, half of whom were not involved in the Assessment, developed and administered an extensive survey, prepared a series of working papers, and conducted an invitational workshop in Washington, DC, on April 29, 2004. Considering all these sources, the authors conclude that the Assessment was largely successful in implementing its basic design of distributed stakeholder involvement and in achieving its basic objectives. Future assessments could be significantly improved if greater attention were devoted to developing a collective understanding of objectives, preparing guidance materials and providing training for assessment participants, developing a budgeting mechanism which would allow greater freedom in allocating resources across various assessment activities, and creating an environment in which assessments were part of an ongoing process.

Effects of River Flooding on PCDD/F and PCB Levels in Cows' Milk, Soil, and Grass
  • Iain R. Lake ,
  • Christopher D. Foxall ,
  • Andrew A. Lovett ,
  • Alwyn Fernandes ,
  • Alan Dowding ,
  • Shaun White , and
  • Martin Rose

This paper presents the results of a study examining whether the flooding of pasture by rivers gives rise to higher PCDD/F and PCB concentrations in cows' milk. Over 180 milk, soil, and grass samples, taken from 38 farms across 3 different river systems (River Dee, Trent, and Doe Lea/Rother/Don) in the United Kingdom, were analyzed for PCDD/Fs and PCBs. The concentrations were compared between flood-prone farms, where the animals had access to pasture that is often flooded, and control farms where the land does not flood. The results indicated that concentrations of PCDD/Fs and PCBs in cows' milk were higher in samples taken from farms prone to flooding, but only from the river systems flowing through industrial and urban areas. Raised levels of PCDD/F and PCBs were also found in soil and grass from farms prone to flooding providing strong corroborative evidence that the higher concentrations in cows' milk from such areas is likely to be due to the ingestion of contaminated grass and soil. Overall, the results provide strong evidence that flooding of pastureland can indeed result in elevated concentrations of PCDD/Fs and PCBs in milk from the farms so affected.

Microbial Incorporation of 13 C-Labeled Acetate at the Field Scale: Detection of Microbes Responsible for Reduction of U(VI)
  • Yun-Juan Chang ,
  • Philip E. Long ,
  • Roland Geyer ,
  • Aaron D. Peacock ,
  • Charles T. Resch ,
  • Kerry Sublette ,
  • Susan Pfiffner ,
  • Amanda Smithgall ,
  • Robert T. Anderson ,
  • Helen A. Vrionis ,
  • John R. Stephen ,
  • Richard Dayvault ,
  • Irene Ortiz-Bernad ,
  • Derek R. Lovley , and
  • David C. White

A field-scale acetate amendment experiment was performed in a contaminated aquifer at Old Rifle, CO to stimulate in situ microbial reduction of U(VI) in groundwater. To evaluate the microorganisms responsible for microbial uranium reduction during the experiment, 13C-labeled acetate was introduced into well bores via bio-traps containing porous activated carbon beads (Bio-Sep). Incorporation of the 13C from labeled acetate into cellular DNA and phospholipid fatty acid (PLFA) biomarkers was analyzed in parallel with geochemical parameters. An enrichment of active δ-proteobacteria was demonstrated in downgradient monitoring wells: Geobacter dominated in wells closer to the acetate injection gallery, while various sulfate reducers were prominent in different downgradient wells. These results were consistent with the geochemical evidence of Fe(III), U(VI), and SO42- reduction. PLFA profiling of bio-traps suspended in the monitoring wells also showed the incorporation of 13C into bacterial cellular lipids. Community composition of downgradient monitoring wells based on quinone and PLFA profiling was in general agreement with the 13C-DNA result. The direct application of 13C label to biosystems, coupled with DNA and PLFA analysis, which combined detailed taxonomic description with a quantitative measure of metabolic diversity, allowed identification of the metabolically active portion of the microbial community during reduction of U(VI).

Gaseous and Particulate Emissions from Prescribed Burning in Georgia
  • Sangil Lee ,
  • Karsten Baumann ,
  • James J. Schauer ,
  • Rebecca J. Sheesley ,
  • Luke P. Naeher ,
  • Simone Meinardi ,
  • Donald R. Blake ,
  • Eric S. Edgerton ,
  • Armistead G. Russell , and
  • Mark Clements

Prescribed burning is a significant source of fine particulate matter (PM2.5) in the southeastern United States. However, limited data exist on the emission characteristics from this source. Various organic and inorganic compounds both in the gas and particle phase were measured in the emissions of prescribed burnings conducted at two pine-dominated forest areas in Georgia. The measurements of volatile organic compounds (VOCs) and PM2.5 allowed the determination of emission factors for the flaming and smoldering stages of prescribed burnings. The VOC emission factors from smoldering were distinctly higher than those from flaming except for ethene, ethyne, and organic nitrate compounds. VOC emission factors show that emissions of certain aromatic compounds and terpenes such as α and β-pinenes, which are important precursors for secondary organic aerosol (SOA), are much higher from active prescribed burnings than from fireplace wood and laboratory open burning studies. Levoglucosan is the major particulate organic compound (POC) emitted for all these studies, though its emission relative to total organic carbon (mg/g OC) differs significantly. Furthermore, cholesterol, an important fingerprint for meat cooking, was observed only in our in situ study indicating a significant release from the soil and soil organisms during open burning. Source apportionment of ambient primary fine particulate OC measured at two urban receptor locations 20−25 km downwind yields 74 ±11% during and immediately after the burns using our new in situ profile. In comparison with the previous source profile from laboratory simulations, however, this OC contribution is on average 27 ±5% lower.

Chlorinated, Brominated, and Perfluorinated Contaminants in Livers of Polar Bears from Alaska

The existence of two subpopulations of polar bears in Alaska, the Beaufort Sea and the Chukchi Sea populations, has been documented. In this study, differences in concentrations and profiles of organochlorine pesticides, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and perfluorinated acids were examined in livers of polar bears from the two subpopulations in Alaska. Concentrations of most of the organohalogens analyzed were greater in the Beaufort Sea subpopulation than in the Chukchi Sea subpopulation, except for HCHs and perfluorononanoic acid (PFNA), which were high in samples from the Chukchi Sea subpopulation. Concentrations of chlordanes, PCBs, and perfluorooctanesulfonate (PFOS) were significantly different between the two subpopulations. Chlordane was the predominant contaminant in the Beaufort Sea population, and PFOS was the major contaminant in the Chukchi Sea population. Polar bears from the Beaufort Sea showed significantly higher proportions of more highly chlorinated PCBs than those from the Chukchi Sea. Concentrations of several perfluorinated acids were significantly correlated. Overall, the concentrations and profiles of organohalogens analyzed in the two subpopulations of polar bears suggest differences in the sources of exposures between the two regions of Alaska.

Effect of Sewage-Sludge Application on Concentrations of Higher-Brominated Diphenyl Ethers in Soils and Earthworms
  • Ulla Sellström ,
  • Cynthia A. de Wit ,
  • Nadja Lundgren , and
  • Mats Tysklind

Polybrominated diphenyl ethers (PBDEs), including octa-decaBDEs, were found in soil and earthworm samples collected in 2000 from three research stations (reference plots and sewage-sludge-amended plots) and two farms (reference and amended/flooded soils) in Sweden. Sewage-sludge amendment at the research stations increased concentrations of all BDE congeners 2- to 13-fold, with the highest increases for BDE-209. Concentrations 100- to 1000-fold higher were seen in contaminated soils at both farms. BDE-209 was the predominant congener in all soils. ∑PBDE concentrations in worms ranged from 3.1 to 38 000 ng/g lipid weight and were correlated to soil concentrations, including the octa-decaBDEs. Biota−soil accumulation factors declined in the following order: TeBDE > PeBDE > HxBDE > OcBDE > NoBDE > DeBDE, and ranged from 0.3 to 2 for the octa-decaBDEs. Thus, higher-brominated PBDEs, including BDE-209, are bioavailable from soils and accumulate in earthworms, presenting an exposure pathway into the terrestrial food web. High levels found at one farm 20 years after the last use of PBDEs indicate high persistence of PBDEs in soils, including BDE-209. No evidence of photolytic debromination of BDE-209 in soils was seen.

Influence of Climate Change, Tidal Mixing, and Watershed Urbanization on Historical Water Quality in Newport Bay, a Saltwater Wetland and Tidal Embayment in Southern California
  • Abhishek M. Pednekar ,
  • Stanley B. Grant ,
  • Youngsul Jeong ,
  • Ying Poon , and
  • Carmen Oancea

Historical coliform measurements (n = 67 269 32 years) in Newport Bay, a regionally important saltwater wetland and tidal embayment in southern California, have been compiled and analyzed. Coliform concentrations in Newport Bay decrease along an inland-to-ocean gradient, consistent with the hypothesis that this tidal embayment attenuates fecal pollution from inland sources. Nearly 70% of the variability in the coliform record can be attributed to seasonal and interannual variability in local rainfall, implying that stormwater runoff from the surrounding watershed is a primary source of coliform in Newport Bay. The storm loading rate of coliform from the San Diego Creek watershedthe largest watershed draining into Newport Bayappears to be unaffected by the dramatic shift away from agricultural land-use that occurred in the watershed over the study period. Further, the peak loading of coliform during storms is larger than can be reasonably attributed to sources of human sewage, suggesting that nonhuman fecal pollution and/or bacterial regrowth contribute to the coliform load. Summer time measurements of coliform exhibit interannual trends, but these trends are site specific, apparently due to within-Bay variability in land-use, inputs of dry-weather runoff, and tidal mixing rates. Overall, these results suggest that efforts to improve water quality in Newport Bay will likely have greater efficacy during dry weather summer periods. Water quality during winter storms, on the other hand, appears to be dominated by factors outside of local management control namely, virtually unlimited nonhuman sources of coliform in the watershed and global climate patterns, such as the El Nino Southern Oscillation, that modulate rainfall and stormwater runoff in southern California.

Identifying Pollutant Sources in Tidally Mixed Systems: Case Study of Fecal Indicator Bacteria from Marinas in Newport Bay, Southern California
  • Youngsul Jeong ,
  • Stanley B. Grant ,
  • Scott Ritter ,
  • Abhishek Pednekar ,
  • Linda Candelaria , and
  • Clinton Winant

This study investigates the contribution of several marinas to fecal indicator bacteria impairment in Newport Bay, a regionally important tidal embayment in southern California. Three different fecal indicator bacteria groups were assayed, including total coliform, Escherichia coli, and enterococci bacteria, all measured using the IDEXX Colilert and Enterolert system. To document temporal variability in the fecal indicator bacteria signal, water column samples (n = 4132) were collected from two marinas over time scales ranging from hours to months. To document spatial variability of the fecal indicator bacteria signal, water column and sediment samples were collected from a number of sites (n = 11 to 36, depending on the study) in and around the two marinas, over spatial scales ranging from meters to kilometers. To identify the dominant temporal and spatial patterns in these data a statistical approachEmpirical Orthogonal Function analysiswas utilized. Finally, to clarify the transport pathways responsible for the observed temporal and spatial patterns, fecal indicator bacteria data were compared to simultaneous measurements of tidal flow, temperature, and salinity. The results of this field effort collectively implicate runoffboth dry weather runoff at sampling sites located near some storm drains and wet weather runoff at all sitesas a primary source of fecal indicator bacteria in the water column and subtidal sediments. The results and analysis presented here reinforce the growing body of evidence that management of fecal indicator bacteria impairment in the coastal waters of southern California will require developing long-term strategies for treating nonpoint sources of both dry weather and stormwater runoff.

Chemical Heterogeneity of Organic Soil Colloids Investigated by Scanning Transmission X-ray Microscopy and C-1s NEXAFS Microspectroscopy
  • Marc Schumacher ,
  • Iso Christl ,
  • Andreas C. Scheinost ,
  • Chris Jacobsen , and
  • Ruben Kretzschmar

Colloid release and deposition in soils and sorption of inorganic and organic pollutants to soil colloids are strongly influenced by the composition and chemical heterogeneity of colloidal soil particles. To investigate the chemical heterogeneity of organic soil colloids at the particle scale, we used synchrotron scanning transmission X-ray microscopy (STXM) and C-1s near-edge X-ray absorption fine structure (NEXAFS) spectroscopy on 49 individual particles isolated from the surface horizons of three forest soils. Stacks of 130 images of each particle were collected at different X-ray energies between 280 and 310 eV. From these image arrays, NEXAFS spectra were obtained for each pixel and analyzed by principle component analysis and cluster analysis (PCA-CA) to characterize the intraparticle heterogeneity of the organic components. The results demonstrate that the organic matter associated with water-dispersible soil colloids is chemically heterogeneous at the single-particle scale. PCA-CA identified at least two distinct regions within single particles. However, the spectral variations between these regions were much smaller than the variations of averaged NEXAFS spectra representing different particles from the same soil horizon, implying that interparticle heterogeneity is much larger than intraparticle heterogeneity. Especially the contents of aromatic and carboxyl carbon exhibited a large variability. Overall, the NEXAFS spectra of water-dispersible soil colloids were similar to the NEXAFS spectrum of the humic acid fraction, but differed clearly from the fulvic acid and dissolved organic matter fractions extracted from the same soil horizon using conventional techniques.

Perfluorinated Compounds in the Plasma of Loggerhead and Kemp's Ridley Sea Turtles from the Southeastern Coast of the United States
  • Jennifer M. Keller ,
  • Kurunthachalam Kannan ,
  • Sachi Taniyasu ,
  • Nobuyoshi Yamashita ,
  • Rusty D. Day ,
  • Michael D. Arendt ,
  • Al L. Segars , and
  • John R. Kucklick

Perfluorinated compounds (PFCs) have been measured in blood of humans and wildlife and are considered globally distributed contaminants. We examined 12 PFCs in the plasma of 73 loggerhead sea turtles (Caretta caretta) and 6 Kemp's ridley sea turtles (Lepidochelys kempii) captured from inshore waters of Core Sound, North Carolina (NC), and offshore waters of South Carolina, Georgia, and Florida (SC−FL). Perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA) were the dominant compounds, with respective mean concentrations of 11.0 ng/mL and 3.20 ng/mL for loggerhead turtles and 39.4 ng/mL and 3.57 ng/mL for Kemp's ridley turtles. Mean PFOS concentrations were 2- to 12-fold higher than typical mean ΣPCB concentrations (∼5 ng/g wet mass) measured previously in sea turtle blood. More than 79% of the samples had detectable levels of perfluorocarboxylates (PFCAs) with 8−12 carbons, whereas only 17% or less of samples had detectable levels of PFCAs with 6 or 7 carbons. No samples had detectable levels of PFCAs with 4 or 5 carbons. In loggerhead turtles, ΣPFC concentrations were not influenced by sex (p > 0.05), but were higher in turtles captured from inshore waters of NC than in turtles from offshore waters of SC−FL (p = 0.009). A backward stepwise multiple regression model showed that ΣPFC concentrations were (1) significantly higher in Kemp's ridley turtles than loggerhead turtles (p < 0.0001), (2) higher in larger turtles (p = 0.018 carapace length used as a proxy for age), and (3) higher in turtles captured toward the north (p = 0.006). These findings suggest that bioaccumulation of PFCs in sea turtles is influenced by species, age, and habitat.

Source Diagnostics of Polycyclic Aromatic Hydrocarbons Based on Species Ratios: A Multimedia Approach
  • X. L. Zhang ,
  • S. Tao ,
  • W. X. Liu ,
  • Y. Yang ,
  • Q. Zuo , and
  • S. Z. Liu

Often, the sources of polycyclic aromatic hydrocarbons (PAHs) in environmental media can be identified by comparing the ratios of concentrations of selected pairs of PAH congeners in the source emissions to the ratios in the contaminated environmental media. However, these ratios can be altered significantly due to differences in the transport of the PAH compounds in a multimedia environment. To examine such changes, a fugacity model was applied to PAH ratios in a model environment. A linear relationship between the rate of emission and the bulk media concentration was identified for each PAH compound in an environmental medium at steady state and was quantified by a receptor-to-source ratio (RRS). It was demonstrated that the RRS values of the two congeners usually differ significantly. Consequentially, PAH ratios changed remarkably from the source emissions to various environmental media. A site-specific rectification factor (RF) was defined as the ratio of the two RRS values of the paired congeners for a specific PAH ratio in a given medium, which can be applied to account for the ratio changes in a multimedia environment. The PAH ratio changes were further verified with the surface soil data collected from Tianjin, China, and the observed changes of PAH ratios were compared favorably with the model predictions. The sensitivity analysis revealed that PAH ratios of the low molecular weight compounds were less stable. The most influential parameters controlling PAH ratios were those pertaining to dry precipitation, surface-to-air diffusion, degradation in air and water, and exchange between water and sediment.

Passive and Active Air Samplers as Complementary Methods for Investigating Persistent Organic Pollutants in the Great Lakes Basin

Data obtained using passive air samplers (PAS) are compared to active high-volume air sampling data in order to assess the feasibility of the PAS as a method, complementary to active high-volume air sampling (AAS), for monitoring levels of organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) in the Laurentian Great Lakes. PAS were deployed at 15 of the Integrated Atmospheric Deposition Network (IADN) sites on a quarterly basis between July 2002 and June 2003, and PAS and AAS results are compared. Levels for the OC pesticides are typically highest in agricultural areas, with endosulfan I dominating air concentrations with values ranging between 40 and 1090 pg·m-3, dieldrin values between 15 and 165 pg·m-3, and γ-HCH values between 13 and 100 pg·m-3. α-HCH was seen to be relatively uniform across the Great Lakes Basin with values ranging between 15 and 73 pg·m-3. Large urban centers, such as Chicago and Toronto, have the highest levels of PCBs and PBDEs that range between 400 and 1200 pg·m-3 and 10 and 70 pg·m-3, respectively. Comparison of the AAS and the PAS data collected during this study shows good agreement, within a factor of 2 or 3, suggesting that the two sample methods produce comparable results. It is suggested that PAS networks, while providing data that are different in nature from AAS, can provide a cost-effective and complementary approach for monitoring the spatial and temporal trends of persistent organic pollutants.

Spectroscopic Study of Carbaryl Sorption on Smectite from Aqueous Suspension
  • Maurilio Fernandes de Oliveira ,
  • Cliff T. Johnston ,
  • G. S. Premachandra ,
  • Brian J. Teppen ,
  • Hui Li ,
  • David A. Laird ,
  • Dongqiang Zhu , and
  • Stephen A. Boyd

Sorption of carbaryl (1-naphthyl-N-methyl-carbamate) from aqueous suspension to smectite was studied using Fourier transform infrared (FTIR), high-performance liquid chromatography (HPLC) (for batch sorption), and quantum chemical methods. The amount of carbaryl sorbed was strongly dependent on the surface-charge density of the smectite with more sorption occurring on the two “low” surface-charge density smectites (SHCa-1 and SWy-2) compared to that of the high surface-charge SAz-1 smectite. In addition, the amount of carbaryl sorbed was strongly dependent on the nature of the exchangeable cation and followed the order of Ba ∼ Cs ∼ Ca > Mg ∼ K > Na ∼ Li for SWy-2. A similar trend was found for hectorite (SHCa-1) of Cs > Ba > Ca > K ∼ Mg > Na ∼ Li. Using the shift of the carbonyl stretching band as an indicator of the strength of interaction between carbaryl and the exchangeable cation, the observed order was Mg > Ca > Ba ∼ K > Na > Cs. The position of the carbonyl stretching band shifted to lower wavenumbers with increasing ionic potential of the exchangeable cation. Density functional theory predicted a cation-induced lengthening of the CO bond, resulting from the carbonyl group interacting directly with the exchangeable cation in support of the spectroscopic observations. Further evidence was provided by a concomitant shift in the opposite direction by several vibrational bands in the 1355−1375 cm-1 region assigned to stretching bands of the carbamate N−Ccarbonyl and Oether−Ccarbonyl bonds. These data indicate that carbaryl sorption is due, in part, to site-specific interactions between the carbamate functional group and exchangeable cations, as evidenced by the FTIR data. However, these data suggest that hydrophobic interactions also contribute to the overall amount of carbaryl sorbed. For example, the FTIR data indicated that the weakest interaction occurred when Cs+ was the exchangeable cation. In contrast, the highest amount of carbaryl sorption was observed on Cs-exchanged smectite. Of all the cations studied, Cs has the lowest enthalpy of hydration. It is suggested that this low hydration energy provides the carbaryl with greater access to the hydrophobic regions of the siloxane surface.

Quantification of Particle Number Emission Factors for Motor Vehicles from On-Road Measurements
  • Lidia Morawska ,
  • Milan Jamriska ,
  • Stephen Thomas ,
  • Luis Ferreira ,
  • Kerrie Mengersen ,
  • Darren Wraith , and
  • Fraser McGregor

The database on particle number emission factors has been very limited to date despite the increasing interest in the effects of human exposure to particles in the submicrometer range. There are also major questions on the comparability of emission factors derived through dynamometer versus on-road studies. Thus, the aims of this study were (1) to quantify vehicle number emission factors in the submicrometer (and also supermicrometer) range for stop−start and free-flowing traffic at about 100 km h-1 driving conditions through extensive road measurements and (2) to compare the emission factors from the road measurements with those obtained previously from dynamometer studies conducted in Brisbane. For submicrometer particles the average emission factors for Tora Street were estimated at (1.89 ± 3.40) × 1013 particles km-1 (mean ± standard error n = 386) for petrol and (7.17 ± 2.80) × 1014 particles km-1 (diesel n = 196) and for supermicrometer particles at 2.59 × 109 particles km-1 and 1.53 × 1012 particles km-1, respectively. The average number emission factors for submicrometer particles estimated for Ipswich Road (stop−start traffic mode) were (2.18 ± 0.57) × 1013 particles km-1 (petrol) and (2.04 ± 0.24) × 1014 particles km-1 (diesel). One implication of the conclusion that emission factors of heavy duty diesel vehicles are over 1 order of magnitude higher than emission factors of petrol-fueled passenger cars is that future control and management strategies should in particular target heavy duty vehicles, as even a moderate decrease in emissions of these vehicles would have a significant impact on lowering atmospheric concentrations of particles. The finding that particle number emissions per vehicle-km are significantly larger for higher speed vehicle operation has an important implication on urban traffic planning and optimization of vehicle speed to lower their impact on airborne pollution. Additionally, statistical analysis showed that neither the measuring method (dynamometer or on-road), nor data origin (Brisbane or elsewhere in the world), is associated with a statistically significant difference between the average values of emission factors for diesel, petrol, and vehicle fleet mix. However, statistical analyses of the effect of fuel showed that the mean values of emission factors for petrol and diesel are different at a 5% significance level.

Fate and Effects of Enrofloxacin in Aquatic Systems under Different Light Conditions
  • C. W. Knapp ,
  • L. A. Cardoza ,
  • J. N. Hawes ,
  • E. M. H. Wellington ,
  • C. K. Larive , and
  • D. W. Graham

The fate and effects of fluoroquinolone antibacterials (FQ) in the environment is of significance because of apparent increased FQ resistance in environmental and clinical organisms. Here we simultaneously assessed the fate and effects of enrofloxacin (enro), an FQ often used in agriculture, on the chemistry and in situ microbial communities in receiving waters. We added enro to 25 μg/L in nine outdoor mesocosms maintained under three light conditions (in triplicate): full sunlight typical of the upper epilimnion (100% full-light exposure, FLE), partial shading typical of the lower epilimnion (28% FLE), and near-complete shading typical of the hypolimnion (0.5% FLE). Enro disappearance and ciprofloxacin (cipro) formation were monitored over time using LC/MS, and water chemistry and ambient microbial communities (using denaturing gradient gel electrophoresis DGGE) were characterized. Enro half-lives were 0.8, 3.7, and 72 days for the 100%, 28%, and 0.5% FLE treatments, respectively, creating three distinct FQ exposure scenarios. Although FQ exposures ranged from ∼6 μg/L for 24 h to ∼21 μg/L for 30 days, no statistically significant exposure effects were noted in water quality or microbial communities (as indicated by whole-community 16S rDNA DGGE analysis and specific amplification of the QRDR region of gyrase A). Small changes in water chemistry were noted over time however, changes could not be specifically attributed to FQs. In general, enro addition had minimal effect on water column conditions at the levels and durations used here however, further investigation is needed to assess effects in aquatic sediments.

EXAFS Analysis of Arsenite Adsorption onto Two-Line Ferrihydrite, Hematite, Goethite, and Lepidocrocite
  • Georges Ona-Nguema ,
  • Guillaume Morin ,
  • Farid Juillot ,
  • Georges Calas , and
  • Gordon E. Brown

The modes of As(III) sorption onto two-line ferrihydrite (Fh), hematite (Hm), goethite (Gt), and lepidocrocite (Lp) have been investigated under anoxic condition using X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure spectroscopy (XANES) indicates that the absence of oxygen minimized As(III) oxidation due to Fenton reactions. Extended X-ray absorption fine structure spectroscopy (EXAFS) indicates that As(III) forms similar inner-sphere surface complexes on two-line ferrihydrite and hematite that differ from those formed on goethite and lepidocrocite. At high surface coverage, the dominant complex types on Fh and Hm are bidentate mononuclear edge-sharing (2E) and bidentate binuclear corner-sharing (2C), with As−Fe distances of 2.90 ± 0.05 and 3.35 ± 0.05 Å, respectively. The same surface complexes are observed for ferrihydrite at low surface coverage. In contrast, As(III) forms dominantly bidentate binuclear corner-sharing (2C) sorption complexes on Gt and Lp [d(As−Fe) = 3.3−3.4 Å], with a minor amount of monodentate mononuclear corner-sharing (1V) complexes [d(As−Fe) = 3.5−3.6 Å]. Bidentate mononuclear edge-sharing (2E) complexes are virtually absent in Gt and Lp at the high surface coverages that were investigated in the present study. These results are compared with available literature data and discussed in terms of the reactivity of iron(III) (oxyhydr)oxide surface sites.

Oxidation of Gaseous Elemental Mercury to Gaseous Divalent Mercury during 2003 Polar Sunrise at Ny-Alesund
  • Francesca Sprovieri ,
  • Nicola Pirrone ,
  • Matthew S. Landis , and
  • Robert K. Stevens

The springtime phenomenon, termed as the mercury depletion event (MDE), during which elemental gaseous mercury (Hg0) may be converted to a reactive form that accumulates in polar ecosystems, first noted in the Arctic, has now been observed at both poles and results in an important removal pathway for atmospheric mercury. An intensive international springtime mercury experiment was performed at Ny-Alesund, Spitsbergen, from 19 April to 13 May 2003 to study the atmospheric mercury chemistry in the Arctic environment and, in particular, the MDEs which occurred in the arctic boundary layer after polar sunrise. Automated ambient measurements of Hg0, divalent reactive gaseous mercury (RGM) and fine particulate mercury (<2.5 μm) (Hg(p)) were made at the Zeppelin Mountain Station (ZMS). During the experiment mercury concentrations in the lower atmosphere varied in synchrony with ozone levels throughout the Spring. Hg0 concentrations ranged from background levels (∼1.6 ng m-3) to undetectable values (<0.1 ng m-3) during the first and major MDE, while RGM data showed an opposite trend during the sampling period with concentrations increasing dramatically to a peak of 230 pg m-3, synchronous with the depletion of Hg0. The results of a meteorological transport analysis indicate the MDEs observed at ZMS were primarily due to air masses being transported in from open water areas in the Arctic Ocean that were already depleted of Hg0 when they arrived and not due to in-situ oxidation mechanisms.

Sorption of the Antimicrobial Ciprofloxacin To Aluminum and Iron Hydrous Oxides

Solution chemistry (pH, ionic strength (I), and sorbate-to-sorbent ratio) effects on ciprofloxacin sorption to hydrous oxides of Al (HAO) and Fe (HFO) were investigated using macroscopic and spectroscopic analyses. Sorption to both HAO and HFO showed a strong pH-dependent behavior, following the fraction of zwitterionic species over the entire pH range studied. Increase in I from 0.01 to 0.5 M had an insignificant effect on the extent of ciprofloxacin sorption, and isotherms were well-described by the Langmuir model. HFO possessed a higher sorption capacity (0.066 mmol kg-1) than HAO (0.041 mmol kg-1). Ligand-promoted dissolution of hydrous oxides, more pronounced for HAO, was observed in the presence of ciprofloxacin, but at a fairly high initial concentration (0.5 mM). Attenuated total reflectance Fourier transform infrared spectroscopy analysis indicated that different types of ciprofloxacin surface complexes are formed with HAO and HFO while a monodentate mononuclear complex (with −COO-) appears likely between ciprofloxacin and HAO, keto O and one O from COO- seem to be involved in the formation of a six-membered ring with Fe on the HFO surface. The study results are expected to increase our understanding of the environmental reactivity of fluoroquinolones, an important class of antimicrobial compounds.

Controls on Arsenic Speciation and Solid-Phase Partitioning in the Sediments of a Two-Basin Lake
  • J. A. Jay ,
  • N. K. Blute ,
  • K. Lin ,
  • D. Senn ,
  • H. F. Hemond , and
  • J. L. Durant

Arsenic (As) regeneration from sediments of Spy Pond, a two-basin lake near Boston, MA, continues to result in seasonally elevated As levels despite the several decades that have elapsed since the pond's historical contamination by a pulse input of As. Solid-phase speciation and partitioning of As in the sediments appear to be primary determinants of both potential As regeneration rate and, conversely, the rate at which long-term burial of the pond's As burden will occur. Although iron (Fe) chemistry often controls As speciation in lakes, a higher rate of As regeneration in the south basin, accompanied by the absence of a correlation between regenerated As and Fe in this basin, suggest that additional factors operate to control As cycling in this lake. Solid-phase As speciation was remarkably similar between sediments of the two basins of this lake, about 40% of sedimentary As in upper sediments being in relatively labile (ionically bound and strongly adsorbed) fractions and a larger fraction of As being associated with recalcitrant minerals, likely sulfides. Extraction, X-ray fluorescence, and acid-volatile sulfide data collectively suggest that sedimentary As cycling in both basins is largely controlled by the formation of sulfide minerals. An accounting of the size of sulfur (S) pools supports this conclusion, showing that sufficient S exists in the north basin to control both Fe and As, while the south basin has lower S levels resulting in seasonal accumulation of Fe in the porewater.

Photosensitizer Method to Determine Rate Constants for the Reaction of Carbonate Radical with Organic Compounds
  • Silvio Canonica ,
  • Tamar Kohn ,
  • Marek Mac ,
  • Francisco J. Real ,
  • Jakob Wirz , and
  • Urs von Gunten

Carbonate radical (CO3•-) is a powerful oxidant that is present in sunlit surface waters and in waters treated by advanced oxidation processes. The production of CO3•- in aqueous solution through oxidation of carbonate anion by excited triplet states of aromatic ketones was investigated in this study to provide new methods for the determination of rate constants and to explore a possible photoinduced pathway of CO3•- formation in the aquatic environment. Rate constants for triplet quenching by carbonate anion of up to 3.0 × 107 M-1 s-1 and CO3•- yields approaching unity, determined using laser flash photolysis, allowed us to conclude that such a formation mechanism might be significant in sulit natural waters. Kinetic methods based on either flash photolysis or steady-state irradiation and on the use of aromatic ketones as photosensitizers gave bimolecular rate constants in the range of 4 × 106 to 1 × 108 M-1 s-1 for the reaction of CO3•- with several s-triazine and phenylurea herbicides. For various anilines and phenoxide anions, rate constants determined by these methods agreed well with published values. Moreover, it could be shown for the first time by a direct method that dissolved natural organic matter (DOM) reduces the lifetime of CO3•- and a second-order rate constant of (280 ± 90) (mg of C/L)-1 s-1 was obtained for Suwannee River fulvic acid.

Effects of Microbially Mediated Redox Conditions on PAH−Soil Interactions

The impacts of microbially mediated redox conditions on the bioavailability of persistent polycyclic aromatic hydrocarbons (PAHs) in soils and sediments have received little study, despite the fact that most water-saturated soils and sediments spend a significant portion of the time under reduced conditions. To address this need an uncontaminated surface soil was incubated under various redox conditions (aerobic, nitrate-reducing, sulfate-reducing, and methanogenic). Depending on redox conditions, different quantities of fulvic and humic acids were liberated as dissolved organic matter (DOM) from the soil during incubation. The DOM released under highly reduced conditions was more nonpolar, aromatic, and polydisperse, of higher molecular weight, and had a higher sorption capacity for pyrene compared to that obtained from relatively oxic incubations. The soil-phase organic matter incubated under reduced conditions also became relatively more aromatic, containing nonpolar organic molecules of lower oxygen contents and exhibiting higher capacity and more nonlinear and hysteric sorption/desorption behavior for pyrene. These observations support the hypothesis that reduced environments established by indigenous soil microbes alter soil organic matter in a matter similar to diagenetic processes. Such humification-like alteration occurred principally in relatively more labile fractions of soil organic matter. These findings are important for assessing the ultimate fate and exposure risk of hydrophobic organic contaminants in soils and sediments where living microorganisms play a significant role in formation and evolution of soil/sediment organic matter.

Effect of Precipitation on Low Frequency Electrical Properties of Zerovalent Iron Columns

We conducted column studies to investigate the application of a noninvasive electrical method to monitor precipitation in Fe0 columns using (a) Na2SO4 (0.01 M, dissolved oxygen (DO) = 8.8 ppm), and (b) Na2CO3 (0.01 M, DO = 2.3 ppm) solutions. An increase in complex conductivity terms (maximum 40% in sulfate column and 23% in carbonate column) occurred over 25 days. Scanning electron microscopy (SEM) identified mineral surface alteration, with greater changes in the high DO sulfate column relative to the low DO carbonate column. X-ray diffractometry (XRD) identified reduced amounts of hematite/maghemite in both columns, precipitation of goethite/akaganeite in the sulfate column, and precipitation of siderite in the carbonate column. Nitrogen adsorption measurements showed increases in specific surface area of iron minerals (27.5% for sulfate column and 8.2% for carbonate column). As variations in electrolytic conductivity and porosity were minimal, electrical changes are attributed to (1) higher complex interfacial conductivity due to increased surface area and mineralogical alteration and (2) increased electronic conduction due to enhanced electron transfer across the iron−fluid interface. Our results show that electrical measurements are a proxy indicator of Fe0 surface alteration.

Phosphorus Composition of Sheep Feces and Changes in the Field Determined by 31 P NMR Spectroscopy and XRPD
  • Charles A. Shand ,
  • Grace Coutts ,
  • Stephen Hillier ,
  • David G. Lumsdon ,
  • Alexander Chudek , and
  • Jan Eubeler

Information on the P species in sheep feces is lacking. Such information is required to understand P-cycling in grazed ecosystems. The P composition of feces from sheep grazing grass in Scotland was assessed on freeze-dried samples by 31P MAS (magic angle spinning) NMR (nuclear magnetic resonance) spectroscopy and XRPD (X-ray powder diffraction). The 31P MAS NMR spectrum showed resonances and sidebands consistent with dicalcium phosphate dihydrate (brushite) and ammonium magnesium phosphate hexahydrate (struvite). XRPD confirmed the result and allowed quantification of these minerals, which accounted for 63% of the P. To determine transformations in the field, sheep feces were collected and reapplied to sheep-free pasture in synthetic patches during late summer. The dry weight decreased with time and the feces disappeared between 84 and 112 days following heavy rainfall. The concentration of P in the feces recovered at intervals up to 84 days changed little with time but the contribution from brushite and struvite decreased and within 1 week <50% remained indicating conversion into other forms. Solution-phase 31P NMR spectra of NaOH/EDTA extracts of the feces were dominated by the inorganic orthophosphate with minor amounts of organic P that were attributed to phosphate esters and polyphosphates.

Acceleration and Quenching of the Photolysis of PCB in the Presence of Surfactant and Humic Materials

The photodecay of a polychlorobiphenyl (PCB) congener, 2,3,4,5-tetrachlorobiphenyl (TeCB), in a surfactant-aided soil-washing process was investigated. The surfactant was found to be a useful hydrogen source in improving the TeCB photodecay via photoreduction process, while the light attenuation effect resulted from the nontarget compounds in the solution, and the impact of humic materials that co-extracted from the soil played important roles in the process of photolytic destruction of TeCB. A well-defined sediment, EPA-11, was used as the source of humic materials in examining the acceleration and quenching effects in the photolysis process. Experimental results indicated that the low dose of humic materials mainly acted as a supplementary hydrogen source to improve the photodegradation rate, while at a higher dose its amphoteric property of being a photochemical quencher become perceptible gradually, thus retarding the reaction. These effects were inspected and the dominant rate constants were quantified through the examination of possible sub-reactions in the assistant of proposed linear models in this study. The models under three different conditions at zero, low, and high humic levels associated with a light attenuation model were successfully developed to solve the dominant rate constants of the process. The good correlations between the experimental data and the models verify that the proposed reaction mechanisms of rate acceleration (resulting from the hydrogen source characteristics of the surfactant and humic material) and rate retardation (high levels of humic materials) coexist in the process.

Iron(II)-Catalyzed Oxidation of Arsenic(III) in a Sediment Column
  • Kevin J. Bisceglia ,
  • Kevin J. Rader ,
  • Richard F. Carbonaro ,
  • Kevin J. Farley ,
  • John D. Mahony , and
  • Dominic M. Di Toro

Arsenic contamination in aquatic systems is a worldwide concern. Understanding the redox cycling of arsenic in sediments is critical in evaluating the fate of arsenic in aquatic environments and in developing sediment quality guidelines. The direct oxidation of inorganic trivalent arsenic, As(III), by dissolved molecular oxygen has been studied and found to be quite slow. A chemical pathway for As(III) oxidation has been proposed recently in which a radical species, Fe(IV), produced during the oxidation of divalent iron, Fe(II), facilitates the oxidation of As(III). Rapid oxidation of As(III) was observed (on a time scale of hours) in batch systems at pH 7 and 7.5, but the extent of As(III) oxidation was limited. The Fe(II)-catalyzed oxidation of As(III) is examined in a sediment column using both computational and experimental studies. A reactive-transport model is constructed that incorporates the complex kinetics of radical species generation and Fe(II) and As(III) oxidation that have been developed previously. The model is applied to experimental column data. Results indicate that the proposed chemical pathway can explain As(III) oxidation in sediments and that transport in sediments plays a vital role in increasing the extent of As(III) oxidation and efficiency of the Fe(II) catalysis.

Oxidative Degradation of Glyphosate and Aminomethylphosphonate by Manganese Oxide

Glyphosate (N−(phosphonomethyl)glycine), the most commonly used herbicide worldwide, degrades relatively rapidly in soils under most conditions, presumably by microbial processes. The most frequently detected degradation product in soil and water is AMPA (aminomethylphosphonic acid). We report the first evidence for an abiotic pathway of glyphosate and AMPA degradation under environmentally realistic conditions. Both glyphosate and AMPA degraded at 20 °C in dilute aqueous suspensions of birnessite, a manganese oxide common in soils, as evidenced by the accumulation of orthophosphate in solution over a period of several days. It is concluded that the abiotic degradation involved C−P bond cleavage at the Mn oxide surface, although evidence for C−N bond cleavage in the case of glyphosate and sarcosine, a likely degradation product of glyphosate, was found. The degradation of glyphosate was faster than that of AMPA, and higher temperature (50 °C) resulted in faster degradation of both glyphosate and AMPA. The addition of sulfate to the solution had no marked effect on the reaction rate, although Cu2+ addition inhibited degradation. As this metal ion complexes strongly with glyphosate, the inhibition can be attributed to the ability of Cu2+ to limit glyphosate coordination to reactive oxidation sites at the Mn oxide surface. Using a similar experimental design, we were unable to detect glyphosate degradation in an equimolar solution of MnCl2 (0.5 mM). However, we demonstrated that the oxidation of Mn2+ is enhanced both in solution and on an inert surface, in the presence of glyphosate (4:1 Mn−glyphosate molar ratio). This result suggests that the oxidative breakdown of glyphosate in the presence of Mn2+ may ultimately occur following the spontaneous oxygen-mediated oxidation of manganese.

Products and Mechanism of Secondary Organic Aerosol Formation from Reactions of n-Alkanes with OH Radicals in the Presence of NOx

Secondary organic aerosol (SOA) formation from reactions of n-alkanes with OH radicals in the presence of NOx was investigated in an environmental chamber using a thermal desorption particle beam mass spectrometer for particle analysis. SOA consisted of both first- and higher-generation products, all of which were nitrates. Major first-generation products were δ-hydroxynitrates, while higher-generation products consisted of dinitrates, hydroxydinitrates, and substituted tetrahydrofurans containing nitrooxy, hydroxyl, and carbonyl groups. The substituted tetrahydrofurans are formed by a series of reactions in which δ-hydroxycarbonyls isomerize to cyclic hemiacetals, which then dehydrate to form substituted dihydrofurans (unsaturated compounds) that quickly react with OH radicals to form lower volatility products. SOA yields ranged from ∼0.5% for C8 to ∼53% for C15, with a sharp increase from ∼8% for C11 to ∼50% for C13. This was probably due to an increase in the contribution of first-generation products, as well as other factors. For example, SOA formed from the C10 reaction contained no first-generation products, while for the C15 reaction SOA was ∼40% first-generation and ∼60% higher-generation products, respectively. First-generation δ-hydroxycarbonyls are especially important in SOA formation, since their subsequent reactions can rapidly form low volatility compounds. In the atmosphere, substituted dihydrofurans created from δ-hydroxycarbonyls will primarily react with O3 or NO3 radicals, thereby opening reaction pathways not normally accessible to saturated compounds.

Relationship between Mercury Accumulation in Young-of-the-Year Yellow Perch and Water-Level Fluctuations

A three-year (2001−2003) monitoring effort of 14 northeastern Minnesota lakes was conducted to document relationships between water-level fluctuations and mercury bioaccumulation in young-of-the-year (YOY) yellow perch (Perca flavescens) collected in the fall of each year at fixed locations. Six of those lakes are located within or adjacent to Voyageurs National Park and are influenced by dams on the outlets of Rainy and Namakan lakes. One site on Sand Point Lake coincides with a location that has nine years of previous monitoring suitable for addressing the same issue over a longer time frame. Mean mercury concentrations in YOY yellow perch at each sampling location varied significantly from year to year. For the 12-year monitoring site on Sand Point Lake, values ranged from 38 ng gww-1 in 1998 to 200 ng gww-1 in 2001. For the 14-lake study, annual mean concentrations ranged by nearly a factor of 2, on average, for each lake over the three years of record. One likely factor responsible for these wide variations is that annual water-level fluctuations are strongly correlated with mercury levels in YOY perch for both data sets.

Use of the Chiral Pharmaceutical Propranolol to Identify Sewage Discharges into Surface Waters

The discharge of relatively small volumes of untreated sewage is a source of wastewater-derived contaminants in surface waters that is often ignored because it is difficult to discriminate from wastewater effluent. To identify raw sewage discharges, we analyzed the two enantiomers of the popular chiral pharmaceutical, propranolol, after derivitization to convert the enantiomers to diastereomers. The enantiomeric fraction (the ratio of the concentration of one of its isomers to the total concentration) of propranolol in the influent of five wastewater treatment plants was 0.50 ± 0.02, while after secondary treatment it was 0.42 or less. In a laboratory study designed to simulate an activated sludge municipal wastewater treatment system, the enantiomeric fraction of propranolol decreased from 0.5 to 0.43 as the compound underwent biotransformation. In a similar system designed to simulate an effluent-dominanted surface water, the enantiomeric fraction of propranolol remained constant as it underwent biotransformation. Analysis of samples from surface waters with known or suspected discharges of untreated sewage contained propranolol with an enantiomeric fraction of approximately 0.50 whereas surface waters with large discharges of wastewater effluent contained propranolol with enantiomeric fractions similar to those observed in wastewater effluent. Measurement of enantiomers of propranolol may be useful in detecting and documenting contaminants related to leaking sewers and combined sewer overflows.

Automated Speciated Mercury Measurements in Michigan

Automated speciated mercury measurements were made at a rural (Dexter, MI) and an urban (Detroit, MI) site in Michigan during selected times from 1999 to 2002 to assess the concentrations of elemental (Hg0), reactive gaseous (RGM), and particulate mercury (Hgp) in these environments. Here we present the first-ever reported values for RGM in Michigan. Median RGM concentrations were 2.21−2.93 pg m-3 at Dexter and were 3−11 times higher in Detroit at 6.41−22.0 pg m-3. Maximum RGM concentrations of 38.7 pg m-3 and 270 pg m-3 were observed in Dexter and Detroit, respectively. Measured RGM/Hg0 ratios were in the range of 0.04−11.60% indicating that at times RGM comprises greater than the currently held view of 5% of total gaseous mercury in the air. Well-pronounced diurnal patterns of RGM were observed at the rural site, whereas the urban site exhibited patterns that were influenced by nighttime emissions and regional transport. An analysis of RGM/Hgp ratios at the urban site when combined with trajectory analysis suggests that the site receives mercury inputs from both local and regional sources. Episodes of elevated ozone concentrations which were accompanied by increases in RGM concentrations were observed to occur in the late afternoon and overnight. These may be evidence of advection of ozone and RGM over long distances to the site.

Removal and Inactivation of Waterborne Viruses Using Zerovalent Iron

A daunting challenge facing the water industry and regulators is how to simultaneously control microbial pathogens, residual disinfectant, and disinfection byproducts in drinking water, and to do so at an acceptable cost. Of the different pathogens, viruses are especially problematic due to their small size, high mobility, and resistance to chlorination and filtration. In the past decade, zerovalent iron has been used to treat a wide variety of organic and inorganic contaminants from groundwater. However, iron has not been tested against biological agents. This study examined the effectiveness of commercial zerovalent iron to remove two viruses, φX174 and MS-2, from water. Removal of these viruses by iron granules in batch reactors was first-order, and the rate was likely controlled by external mass transfer. Most of the viruses removed from solution were either inactivated or irreversibly adsorbed to iron. In a flow-through column containing zerovalent iron (with 20 min of iron contact time), the removal efficiency for both viruses was 4-log in an initial pulse test, and over 5-log in the second pulse test after passage of 320 pore volumes of artificial groundwater. We assume that the improved efficiency was due to continuous formation of new iron (oxyhydr)oxides which served as virus adsorption sites. To our knowledge, this is the first demonstration of biological agent removal from water by zerovalent iron. Results of this study suggest zerovalent iron may be potentially useful for disinfecting drinking water and wastewater, thereby reducing our dependence on chlorine and reducing the formation of disinfection byproducts.

Sequential Electrolytic Oxidation and Reduction of Aqueous Phase Energetic Compounds

Contamination of soils and groundwater with energetic compounds has been documented at many former ammunition manufacturing plants and ranges. Recent research at Colorado State University (CSU) has demonstrated the potential utility of electrolytic degradation of organic compounds using an electrolytic permeable reactive barrier (e-barrier). In principle, an electrolytic approach to degrade aqueous energetic compounds such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) or 2,4,6-trinitrotoluene (TNT) can overcome limitations of management strategies that involve solely oxidation or reduction, through sequential oxidation−reduction or reduction−oxidation. The objective of this proof-of-concept research was to evaluate transformation of aqueous phase RDX and TNT in flow-through electrolytic reactors. Laboratory experiments were conducted using six identical column reactors containing porous media and expanded titanium−mixed-metal-oxide electrodes. Three columns tested TNT transformation and three tested RDX transformation. Electrode sequence was varied between columns and one column for each contaminant acted as a no-voltage control. Over 97% of TNT and 93% of RDX was transformed in the reactors under sequential oxidation−reduction. Significant accumulation of known degradation intermediates was not observed under sequential oxidation−reduction. Removal of approximately 90% of TNT and 40% of RDX was observed under sequential reduction−oxidation. Power requirements on the order of 3 W/m2 were measured during the experiment. This suggests that an in-situ electrolytic approach may be cost-practical for managing groundwater contaminated with explosive compounds.

Decomposition of 2,4,6-Trinitrotoluene (TNT) by Gamma Irradiation

The purpose of this study was to evaluate the potential of gamma irradiation to decompose 2,4,6-trinitrotoluene (TNT) in an aqueous solution the concentration range of the TNT solution was 0.11−0.44 mmol/L. The decomposition rate of TNT by gamma irradiation was pseudo-first-order kinetic over the applied initial concentrations. The dose constant was strongly dependent on the initial concentration of TNT. Increasing the concentration of dissolved oxygen in the solution was more effective on the decomposition of TNT as well as its mineralization. The required irradiation dose to remove 90% of initial TNT (0.44 mmol/L) was 58, 41, 32, 28, and 25 kGy at the dissolved oxygen concentration of 0.025, 0.149, 0.3, 0.538, and 0.822 mmol/L, respectively. However, TOC still remained as 30% of the initial TOC (3.19 mmol/L) when 200 kGy irradiation dose was applied to the TNT solution (0.44 mmol/L) containing dissolved oxygen of 0.822 mmol/L. The removal of the TNT was more efficient at a pH below 3 and at a pH above 11 than at neutral pH (pH 5−9). The required irradiation dose to remove over 99% of the initial TNT (0.44 mmol/L) was 39, 76, and 10 kGy at pH 2, 7, and 13, respectively. The dose constant was increased 1.6-fold and over 15.6-fold at pH 2 and 13, respectively, compared to that at pH 7. When an irradiation dose of 200 kGy was applied, the removal efficiencies of the TOC (initial concentration 3.19 mmol/L) were 91, 46, and 53% at pH 2, 7, and 13, respectively. Ammonia and nitrate were detected as the main nitrogen byproducts of TNT, and glyoxalic acid and oxalic acid were detected as organic byproducts.

Reductive Biotransformation of Tetrachloroethene to Ethene during Anaerobic Degradation of Toluene: Experimental Evidence and Kinetics

Reductive biotransformation of tetrachloroethene (PCE) to ethene occurred during anaerobic degradation of toluene in an enrichment culture. Ethene was detected as a dominant daughter product of PCE dechlorination with negligible accumulation of other partially chlorinated ethenes. PCE dechlorination was linked to toluene degradation, as evidenced by the findings that PCE dechlorination was limited in the absence of toluene but was restored with a spike of toluene again in the cultures. PCE was effectively dechlorinated in cultures amended with a wide range of concentrations of PCE and toluene. PCE dechlorination can be described by a Monod-like equation but followed a zero-order kinetic at high levels of PCE. In addition to toluene, benzoate and lactate were also able to be used as sole electron donors for reductive dechlorination of PCE in the cultures. In terms of dechlorination rates, lactate was the best electron donor followed by benzoate and then toluene. The kinetic characteristics of PCE dechlorination were retained in the cultures regardless of electron donors used, but the kinetic constant values were unique to each electron donor. The dechlorination rate was found to be closely correlated with the level of H2 produced during fermentation of the three organic compounds. Nitrate and sulfate were observed to be favorable electron acceptors in this culture, and their presence completely blocked electron flow to PCE. However, the presence of nitrate and sulfate did not destroy the capability of PCE dechlorination by the culture. PCE dechlorination was immediately reestablished after depletion of nitrate and sulfate in the culture. This anaerobic process provides an opportunity for concurrent remediation of chlorinated solvents and certain fuel hydrocarbons, and recognition of this process is also important in understanding the subsurface fate and transport of these contaminants under natural conditions.

Chemical Pathway and Kinetics of Phenol Oxidation by Fenton's Reagent
  • J. A. Zazo ,
  • J. A. Casas ,
  • A. F. Mohedano ,
  • M. A. Gilarranz , and
  • J. J. Rodríguez

Phenol oxidation by Fenton's reagent (H2O2 + Fe2+) in aqueous solution has been studied in depth for the purpose of learning more about the reactions involved and the extent of the oxidation process, under various operating conditions. An initial phenol concentration of 100 mg/L was used as representative of a phenolic industrial wastewater. Working temperatures of 25 and 50 °C were tested, and the initial pH was set at 3. The H2O2 and the Fe2+ doses were varied in the range of 500−5000 and 1−100 mg/L, respectively, corresponding to 1−10 times the stoichiometric ratio. A series of intermediates were identified, corresponding mainly to ring compounds and short-chain organic acids. Most significant among the former were catechol, hydroquinone, and p-benzoquinone the main organic acids were maleic, acetic, oxalic, and formic, with substantially lower amounts of muconic, fumaric, and malonic acids. Under milder operating conditions (H2O2 and Fe2+ at lower concentrations), a great difference was found between the measured total organic carbon (TOC) and the amount of carbon in all analyzed species in the reaction medium. This difference decreased as the doses of H2O2 and Fe2+ increased, indicating that the unidentified compounds must correspond to oxidation intermediates between phenol and the organic acids. To establish a complete oxidation pathway, experiments were carried out using each of the identified intermediates as starting compounds. Dihydroxybenzenes were identified in the earlier oxidation stages. Muconic acid was detected in catechol but not in the hydroquinone and p-benzoquinone oxidation runs the last two compounds were oxidized to maleic acid. Oxalic and acetic acid appeared to be fairly refractory to this oxidation treatment. A detailed knowledge of the time evolution of the oxidation intermediates is of environmental interest particularly in the case of hydroquinone and p-benzoquinone because their toxicities are several orders of magnitudes higher than that of phenol itself. The time evolution of the intermediates and TOC was fitted to a simple second-order kinetic equation, and the values of the kinetic constants were determined. This provides a simplified approach useful for design purposes.

Reaction of Nonaqueous Phase TCE with Permanganate

Oxidative treatment of trichloroethylene (TCE) in the form of dense nonaqueous-phase liquid (DNAPL) by potassium permanganate (KMnO4) was investigated in a series of batch tests. The study focused on understanding the fundamental mechanisms of oxidative removal of DNAPL TCE by permanganate oxidation. Dissolution experiment for DNAPL TCE has been performed as a control experiment in the absence of KMnO4. DNAPL TCE dissolved into the aqueous phase until it reached the saturation concentration of 1200 mg/L (9.16 × 10-3 M) at 20 °C. The rate of dissolution of DNAPL TCE was proportional to the volume of the DNAPL. In the presence of KMnO4, the experimental results showed that the amount of TCE oxidized during the reaction was increased continuously as [MnO4-] decreased even though the rate decreased as [MnO4-] decreased. It was apparent that more DNAPL TCE was removed with a faster rate for higher initial permanganate concentration. At high permanganate concentration, the aqueous concentration of TCE was kept low and practically constant by the chemical reaction between aqueous TCE and MnO4-. However, as MnO4- was consumed in the system, the aqueous concentration started to increase until it reached solubility. From experimental observation, 1.56−1.78 mol of MnO4- was consumed per mole of TCE oxidized. Furthermore, 2.85−2.98 mol of Cl- was released to the solution per mole of TCE oxidized. Since the complete mineralization of TCE requires 2.0 mol of MnO4- and releases 3 mol of Cl- per mol of TCE oxidized, the observed stoichiometric factors indicated incomplete mineralization of TCE, but nearly complete dechlorination. Enhancement factor due to chemical reaction was quantified experimentally. The enhancement factor was shown to be a function of the molar ratio of MnO4- to TCE in the system, and hence varied during the reaction period.

Mineralogy of Air-Pollution-Control Residues from a Secondary Lead Smelter: Environmental Implications
  • Vojtěch Ettler ,
  • Zdenek Johan ,
  • Alain Baronnet ,
  • Filip Jankovský ,
  • Christian Gilles ,
  • Martin Mihaljevič ,
  • Ondřej Šebek ,
  • Ladislav Strnad , and
  • Petr Bezdička

The mineralogy and solubility of air-pollution-control (APC) residues from a secondary lead (Pb) smelter have been studied on samples from the Příbram smelter, Czech Republic, recycling car batteries, with the emphasis on their potential environmental effect. The presence of dominant anglesite (PbSO4) and laurionite (Pb(OH)Cl) was observed in a sintered residue from after-burning chambers (800−1000 °C). In contrast, low-temperature Pb-bearing phases, such as KCl·2PbCl2 and caracolite (Na3Pb2(SO4)3Cl), were detected in the major APC residue from bag-type fabric filters. Metallic elements, zinc (Zn), cadmium (Cd), and tin (Sn) were found homogeneously distributed within this residue. The formation of anglesite, cotunnite (PbCl2), (Zn,Cd)2SnO4, and (Sb,As)2O3 was observed during the sintering of this APC residue at 500 °C in a rotary furnace. The 168 h leaching test on filter residue, representing the fraction that may escape the flue gas treatment system, indicated rapid release of Pb and other contaminants. Caracolite and KCl·2PbCl2 are significantly dissolved, and anglesite and cotunnite form the alteration products, as was confirmed by mineralogical analysis and PHREEQC-2 modeling. The observed Pb-bearing chlorides have significantly higher solubility than anglesite and, following emission from the smelter stack, can readily dissolve, transferring Pb into the environmental milieu (soils, water, inhabited areas).

Push−Pull Tests to Quantify In Situ Degradation Rates at a Phytoremediation Site
  • Mark T. Pitterle ,
  • Rikke G. Andersen ,
  • John T. Novak , and
  • Mark A. Widdowson

Nine push−pull tests (PPTs) were performed to determine in-situ aerobic respiration rates at a creosote-contaminated site and to assess the contribution of hybrid poplar trees to the remediation of polynuclear aromatic hydrocarbons (PAH) in groundwater. PPTs were conducted by injecting a solution containing dissolved oxygen and naphthalene (reactive tracers) with bromide (nonreactive tracer) into wells constructed in a shallow unconfined aquifer. The objective of this study was to determine seasonal variation and spatial differences (contaminated versus uncontaminated areas and treed versus untreed areas) in the rate of consumption of dissolved oxygen. First-order aerobic respiration rates varied from 0.0 (control well) to 1.25 hr-1, which occurred at a planted area in early summer (June). Rates measured in winter at treed areas were greater by a factor of 3−5 when compared to winter rates determined at nontreed areas of the site. Rates at treed regions were found to increase by over 4 times in summer relative to winter at the same location.

Improvement of the Desulfurization and Regeneration Properties through the Control of Pore Structures of the Zn−Ti-based H2S Removal Sorbents
  • Suk Yong Jung ,
  • Hee Kwon Jun ,
  • Soo Jae Lee ,
  • Tae Jin Lee ,
  • Chong Kul Ryu , and
  • Jae Chang Kim

To improve the sulfur removing capacity of the conventional Zn−Ti-based H2S removal sorbents, a new Zn−Ti based sorbent (ZT-cp) was prepared by the coprecipitation method and tested in a packed bed reactor at middle temperature conditions (H2S absorption at 480 °C, regeneration at 580 °C). The new Zn−Ti-based sorbent showed excellent sulfur removing capacity without deactivation, even after 10 cycles of absorption and regeneration. The conventional Zn−Ti-based sorbents (ZT-700, ZT-1000), however, that were prepared by physical mixing, were continuously deactivated. In particular, the initial sulfur removing capacity of the ZT-cp sorbent showed a very high absorption value (0.22 g S/g sorbent), which corresponded to 91.6% of theoretical absorption amount. These results can be explained by the difference in physical properties such as pore volume, surface area, and particle size. It was also found that the sulfides formed from the ZT-cp and ZT-1000 sorbents with spinel structure were easily regenerated even at 580 °C. Those from the ZT-700 sorbent, with separated ZnO and TiO2 structures, needed a temperature higher than 610 °C for regeneration.

Determination of Kinetic Law for Toxic Metals Release during Thermal Treatment of Model Waste in a Fluid-Bed Reactor
  • Jing Liu ,
  • S. Abanades ,
  • D. Gauthier ,
  • G. Flamant ,
  • Chuguang Zheng , and
  • Jidong Lu

Accumulation of toxic metals generated by thermal treatment of municipal solid waste presents a serious threat to the environment. A study was carried out to investigate the kinetic law of toxic metal release from municipal solid waste during their thermal treatment. Both direct and inverse models were developed in transient conditions. The direct mathematical model of the fluid-bed reactor is based on Kunii and Levenspiel's two-phase flow model for Geldart Group B particles. The inverse model intends to predict the metal's rate of vaporization from its concentration in the outlet gas. The derived models were found to predict reasonably well the experimental observations. A method to derive the kinetic law of toxic metals release during fluidized bed thermal treatment of model waste from the global model and the experimental measurements is derived and illustrated. A first-order law was fitted for the mineral matrix, and a second-order law (simplified) was fitted for the realistic model waste. The kinetic law obtained in this way could be integrated in a global model of combustion of municipal solid waste in order to simulate the effects of operating parameters on the metal's behavior.

Effect of Hydroxypropyl-β-cyclo- dextrin on the Degradation of Pentachlorophenol by Potassium Monopersulfate Catalyzed with Iron(III)−Porphyrin Complex

A novel biomimetic catalytic system containing a supramolecular complex between iron(III)−tetrakis(p-sulfonatophenyl)porphyrin [Fe(III)−TPPS] and hydroxypropyl-β-cyclodextrin (HP-β-CD) was examined for the potassium monopersulfate catalyzed oxidation of pentachlorophenol (PCP). In the absence of HP-β-CD, the percentage of PCP disappearance and the numbers of chlorine atoms released from PCP increased to 50% and 1.5 for a 1-day reaction period, respectively. However, in the presence of HP-β-CD, the PCP completely disappeared and the number of chlorine atoms from PCP was increased to 3.1. o-Tetrachloroquinone, 2- and 4-hydroxyl-nonachlorodiphenyl ethers, and octachlorodibenzo-p-dioxin were detected among the oxidation products. In the absence of HP-β-CD, the percentage of PCP conversion to oxidation products increased and then reached plateau. In the presence of HP-β-CD, the amount of oxidation products produced initially increased for the first 10 min and thereafter decreased gradually. These results suggest that the addition of HP-β-CD results in the further degradation of oxidation products. In addition, the mineralization of PCP to CO2 was investigated using 14C6-labeled PCP. After a 1-day reaction period, 24% of the 14C6-labeled PCP was converted to 14CO2 in the presence of HP-β-CD, although significant 14CO2 generation was not observed in its absence. The effect of HP-β-CD on the facilitation of PCP degradation can be attributed to the fact that the self-oxidation of Fe(III)−TPPS is prevented by the formation of a stable supramolecular complex between HP-β-CD and Fe(III)−TPPS.

Modeling Cryptosporidium parvum Oocyst Inactivation and Bromate Formation in a Full-Scale Ozone Contactor
  • George Tang ,
  • Kwabena Adu-Sarkodie ,
  • Dooil Kim ,
  • Jae-Hong Kim ,
  • Susan Teefy ,
  • Hiba M. Shukairy , and
  • Benito J. Mariñas

The inactivation of Cryptosporidium parvum oocysts and the formation of bromate were assessed simultaneously by performing experiments with a full-scale ozone bubble-diffuser contactor used for drinking water disinfection. Fluorescence-dyed polystyrene microspheres were used as surrogates for C. parvum oocysts. Semi-batch ozonation experiments were performed to determine the fluorescence-intensity decay of individual microspheres, which was measured by flow cytometry. The results obtained with the microspheres were correlated to the inactivation kinetics of C. parvum oocysts by choosing an appropriate threshold fluorescence intensity below which microspheres were considered to be equivalent to nonviable oocysts. A mathematical model was then used to predict the inactivation efficiency and bromate formation. The contactor hydrodynamics were characterized by running tracer tests, and the kinetic parameters for ozone decomposition and bromate formation were obtained by performing batch experiments. Model predictions were in good agreement with full-scale experimental results. Additional model simulations revealed that ozone contactors should be designed with the lowest possible backmixing so that the target inactivation efficiency can be achieved with the lowest possible formation of bromate.

Inhibition of Biohydrogen Production by Undissociated Acetic and Butyric Acids

Glucose fermentation to hydrogen results in the production of acetic and butyric acids. The inhibitory effect of these acids on hydrogen yield was examined by either adding these acids into the feed of continuous flow reactors (external acids), or by increasing glucose concentrations to increase the concentrations of acids produced by the bacteria (self-produced). Acids added to the feed at a concentration of 25 mM decreased H2 yields by 13% (acetic) and 22% (butyric), and 60 mM (pH 5.0) of either acid decreased H2 production by >93% (undissociated acid concentrations). H2 yields were constant at 2.0 ± 0.2 mol H2/mol glucose for an influent glucose concentration of 10−30 g/L. At 40 g glucose/L, H2 yields decreased to 1.6 ± 0.1 mol H2/mol glucose, and a switch to solventogenesis occurred. A total undissociated acid concentration of 19 mM (self-produced acids) was found to be a threshold concentration for significantly decreasing H2 yields and initiating solventogenesis. Hydrogen yields were inhibited more by self-produced acids (produced at high glucose feed concentrations) than by similar concentrations of externally added acids (lower glucose feed concentrations). These results show the reason hydrogen yields can be maximized by using lower glucose feed concentrations is that the concentrations of self-produced volatile acids (particularly butyric acid) are minimized.

Avian Toxicity Reference Values for Perfluorooctane Sulfonate

Toxicity reference values (TRVs) and predicted no effect concentrations (PNECs) were derived for perfluorooctane sulfonate (PFOS) based on the characteristics of a top avian predator. On the basis of the protective assumptions used in this assessment, the benchmarks are protective of avian populations and were based on acute and chronic dietary exposures of northern bobwhite quail and mallard. Toxicological endpoints included mortality, growth, feed consumption, and histopathology. Reproductive endpoints included egg production, fertility, hatchability and survival, and growth of offspring. On the basis of the U. S. Environmental Protection Agency Great Lakes Initiative methodology, and a lowest observable adverse effect concentration (LOAEC) of 10 mg PFOS kg-1 feed, an uncertainty factor of 36 was derived. The TRV based on PFOS dietary intake was 0.021 mg PFOS kg-1 body weight day-1, while for serum, liver, and egg, TRVs were 1.7 μg PFOS mL-1, 0.6 μg PFOS g-1 wet weight, and 1.7 μg PFOS mL-1, respectively. On the basis of the European Commission methodology, a correction factor of 2 (for lowest observed effect level to no observable effect level) and an assessment factor of 30, for a total adjustment of 60, were used to derive PNECs. PNECs based on dietary, mean serum, liver, and egg PFOS concentrations were 0.013 mg PFOS kg-1 body weight day-1, 1.0 μg PFOS mL-1, 0.35μg PFOS g-1 wet weight, and 1.0 μg PFOS mL-1, respectively.

Uptake of Aqueous and Dietary Metals by Mussel Perna viridis with Different Cd Exposure Histories

The influences of different Cd pre-exposure regimes (route, concentration, and duration of Cd exposure) on the bioavailability of Cd, Ag, Hg, and Zn to the green mussels Perna viridis were quantified in this study. Following pre-exposing the mussels to Cd, we measured the mussel's tissue Cd concentration and clearance rate, as well as the metal dietary assimilation efficiency (AE) and the influx rate from the dissolved phase of the four studied metals. Differences in the route (aqueous and dietary pathways) and the history of pre-exposure (combined Cd concentration and duration) did not significantly affect the subsequent Cd dietary and aqueous uptake. The Cd dietary AEs increased following both the dissolved and dietary Cd pre-exposure. There was a significant correlation between the Cd AE and the accumulated Cd body concentration in the mussels. Dietary assimilation of Hg and Zn also increased slightly (but not significantly) after Cd pre-exposure, but the AEs of Ag remained constant. Except for the significant decrease in the dissolved uptake of Hg, Cd pre-exposure did not apparently affect the uptake of the other three metals from the solution. Metal−metal interactions are likely to be affected by the specificity of metallothionein induction. Our study demonstrated that the Cd body concentration as well as the environmental Cd concentration instead of the history of pre-exposure was more important in affecting the Cd accumulation in the mussels. Such factors need to be considered in interpreting metal body concentrations in biomonitors.

Oxide Nanoparticle Uptake in Human Lung Fibroblasts: Effects of Particle Size, Agglomeration, and Diffusion at Low Concentrations
  • Ludwig K. Limbach ,
  • Yuchun Li ,
  • Robert N. Grass ,
  • Tobias J. Brunner ,
  • Marcel A. Hintermann ,
  • Martin Muller ,
  • Detlef Gunther , and
  • Wendelin J. Stark

Quantitative studies on the uptake of nanoparticles into biological systems should consider simultaneous agglomera tion, sedimentation, and diffusion at physiologically relevant concentrations to assess the corresponding risks of nanomaterials to human health. In this paper, the transport and uptake of industrially important cerium oxide nanoparticles, into human lung fibroblasts is measured in vitro after exposing thoroughly characterized particle suspensions to a fibroblast cell culture for particles of four separate size fractions and concentrations ranging from 100 ng g-1 to 100 μg g-1 of fluid (100 ppb to 100 ppm). The unexpected findings at such low but physiologically relevant concentrations reveal a strong dependence of the amount of incorporated ceria on particle size, while nanoparticle number density or total particle surface area are of minor importance. These findings can be explained on the basis of a purely physical model. The rapid formation of agglomerates in the liquid is strongly favored for small particles due to a high number density while larger ones stay mainly unagglomerated. Diffusion (size fraction 25−50 nm) or sedimentation (size fraction 250−500 nm) limits the transport of nanoparticles to the fibroblast cells. The biological uptake processes on the surface of the cell are faster than the physical transport to the cell at such low concentrations. Comparison of the colloid stability of a series of oxide nanoparticles reveals that untreated oxide suspensions rapidly agglomerate in biological fluids and allows the conclusion that the presented transport and uptake kinetics at low concentrations may be extended to other industrially relevant materials.

Watch the video: Electron flow in sulfur chemolithotrophic bacteria (January 2022).