Preferentially Removed Research Articles

Preferential elimination of negatively charged micropollutants in water over cerium-based metal–organic frameworks

In this study, three groups of harmful chemicals at trace amounts (μg/L) in water with extremely high environmental risk were preferentially removed over cerium-based UiO-66 and MOF-808, including nonsteroidal anti-inflammatory drugs (NSAIDs), quinone antibiotics, and perfluoroalkyl carboxylic acids (PFCAs). Results found that cerium-oxygen clusters with oxygen vacancies and larger pore sizes effectively adsorbed targets by both chemical and physical mechanisms. Remarkably, log Kow of five PFCAs (PFPeA, PFHxA, PFOA, PFNA, PFDA) with increasing lengths of alkyl chains strongly correlated (R2 = ∼0.99) with ln (v0) and Qe. In contrast, Ce-MOFs rapidly adsorbed NSAIDs and quinone antibiotics, ranking the excellent adsorbents reported so far (e.g., Qe, OFC = 419.8 mg/g on MOF-808). Hydrophobic, diffusion, and electrostatic interaction mechanism were systematically studied using mathematic models, including pseudo first/second-order, Elovich, and Weber-Morris intraparticle diffusion ones. Thanks to the generation of reactive species (e.g., •OH, 1O2, •O2– and oxygen vacancies) over cerium-oxygen clusters under the irradiation of solar light, aromatic NSAIDs were completely decomposed (>99 %) within 60 min. This study offers helpful guidance for the preferential removal of ECs in water.

Preferential removal of phthalic esters by photocatalysis on selective TiO2

Endowing traditional photocatalysis with selectivity for a class of characteristic pollutants is important in environmental science. Using PAEs-TiO2 as a selective photocatalyst, 302.5 μg L−1 of 11 phthalic esters (PAEs) were preferentially removed to 4.94 μg L−1 in the presence of 10 mg L−1 of natural organic matter via specific hydrogen bonds or cation-π interactions. Further, degradation of PAEs is a lower risk pathway for PAEs-TiO2. The in-situ photocatalytic electron paramagnetic resonance initially revealed that PAEs-TiO2 facilitated the ring opening and mineralization of PAEs, resulting in nearly 100 % detoxification. In actual wastewater, PAEs were not detected after treatment with PAEs-TiO2. Further, the energy cost was reduced by 48.1 %, reaching discharge standard. This study offers new sights into selective photocatalysis of a class of pollutants with similar molecular structure.

Preferential and simultaneous removal of chlorophenoxy herbicide pollutants via double molecular imprinted TiO2 single crystalline surface

A double molecular imprinted (DMI) two-dimensional {001} facet oriented TiO2 single crystal photoelectrocatalytic surface was constructed for the preferential and simultaneous removal of two pollutants, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-(2,4-dichlorophenoxy) propionic acid (2,4-DP). The fabricated photoelectrode showed enhanced removal and selectivity for the targeted pollutants. In a three-component system with 2,4-D, 2,4-DP and natural organic matters, both of the targeted pollutants could be preferentially removed over 90% while the oxidation for non-targeted substances was severely prohibited (only ∼ 66% removal). Furthermore, the detailed adsorption processes of 2,4-D and 2,4-DP on different imprinted electrodes were systematically investigated by both in situ Raman and IR spectroelectrochemical measurements suggesting that the preferential removal originated from the specific adsorption for the targeted molecules with DMI enhancement. This work provides new thoughts for the application of multi-templates molecular imprinted photelectrodes on preferential removal of several highly toxic contaminants with similar structures in complicated coexisting aqueous systems.

Characterization of DBP precursor removal by magnetic ion exchange resin using spectroscopy and high-resolution mass spectrometry

The characteristics of dissolved organic matter (DOM) play an important role in the formation and speciation of carcinogenic disinfection byproducts. This study investigated changes in the characteristics and reactivity of DOM caused by the magnetic ion exchange resins, MIEX® DOC and MIEX® GOLD, using fluorescence excitation-emission matrix (EEM) with parallel factor (PARAFAC) analysis and Orbitrap mass spectrometry (Orbitrap MS) with unknown screening analysis. A five-component PARAFAC model was developed and validated from 208 EEMs of raw and MIEX®-treated water samples. The two resins exhibited preferential removal of the humic-like components (67–87% removal) and successfully removed protein-like components to a lesser extent (5–61% removal). Unknown screening analysis indicated removal of most condensed aromatic structures and lignin-like features that had high O/C values and refractory characteristics of lipid-like features by MIEX® treatments. MIEX® preferentially removed DOM molecules with more oxidized and shorter CH2 chains. The two resins had similar performance in trihalomethanes formation potential removal, but MIEX® GOLD achieved greater haloacetonitriles formation potential removal owing to its larger pore opening. Over 100 CHOCl DBP features were commonly found in all the samples while tens of CHOCl DBPs were uniquely formed in the samples with and without pre-treatments by MIEX®. Treatments by MIEX® before chlorination resulted in more intermediate CHOCl DBPs formed after chlorination compared to chlorinated raw waters. By optical spectroscopic analysis together with Orbitrap MS molecular characterization, we were able to confirm both quantitative and qualitative changes in DOM properties by MIEX® treatment related to DBP formation.

Bitumens from Tell Yarmuth (Israel) from 2800 BCE to 1100 BCE: A unique case history for the study of degradation effects on the Dead Sea bitumen

Twenty-one archaeological samples (2800 BCE-1100 BCE) from Tell Yarmuth (Israel) and two samples (700–800 BCE) from Tall Dhiban (Jordan) were analyzed by geochemical techniques. Dead Sea bitumen was identified in all samples.The sample set affords a unique opportunity to study the effects of weathering on Dead Sea bitumen. Lumps of pure bitumen were compared to bitumens which coat the interior face of potsherds. Bitumen on potsherds was recognized as more altered than lumps of pure bitumen.Saturates of potsherd bitumens were enriched in both 2H and 13C. Resins and asphaltenes were depleted in 2H. Resin was the only fraction depleted in 13C. The δ13C of asphaltenes was almost unchanged: −29.3 ± 0.07 (‰/VPDB) compared to an average −29.3 ± 0.16 (‰/VPDB) for present day Dead Sea asphalt. This stability confirms the δ13C of asphaltenes as a reliable parameter for tracing the sources of archaeological bitumens. Both resins and asphaltenes were enriched in 15N. Biodegradation and oxidation proceed through the cleavage of the N-C bond with preferential removal of 14N.Steranes and terpanes were also affected by degradation. C27steranes were preferentially removed. C30αβ hopane was degraded. 18α-22,29,30-trisnorneohopane (Ts) /17α-22,29,30-trisnorhopane (Tm) and Gammacerane/C31αβHopane ratios increased due to the selective biodegradation of the αβ hopane family. Significant changes were recorded among phenanthrenes, dibenzothiophenes and also in triaromatic steroids.

Preferential removal of benzene, toluene, ethylbenzene, and xylene (BTEX) by persulfate in ethanol-containing aquifer materials.

The effective approaches to eliminate impacts of ethanol on the biodegradation of benzene, toluene, ethylbenzene, and xylene (BTEX) are concerned in the bioremediation of groundwater contaminated with ethanol-blended gasoline. In situ chemical oxidation (ISCO) is a common technique widely used for the remediation of contaminated groundwater. However, the selectivity of ISCO for BTEX and ethanol removal is poorly understood. Therefore, a batch experiment was performed with different aquifer materials, including calcareous soil, basalt soil, granite soil, dolomite, and sand. Gasoline was used to provide dissolved BTEX and ethanol reagent was used as additive to improve the quality of gasoline and to reduce the possibility of air pollution caused by gasoline. Persulfate (PS) was used as a chemical oxidant to oxidize organic contaminants. The target concentrations of BTEX and ethanol were 20mg/L and 1000mg/L, respectively. The results showed that ethanol could be preferentially degraded in the absence of PS and inhibit BTEX biodegradation. However, BTEX could be preferentially removed prior to ethanol in all aquifer materials used at ambient temperature, when PS was added at a PS/BTEX molar ratio of 150. Over 94% BTEX in sand, dolomite, and granite soil was preferentially removed with the first-order decay rate constants of 0.890-2.703day-1 within the first ~ 10days, followed by calcareous and basalt soil at the constants of 0.123-0.371day-1. Ethanol could compete with BTEX for sulfate radical at the first-order decay rate constants of 0.005-0.060day-1 for the first 25days, which was slower than that of BTEX. The pH quickly decreased to < 2.5 in dolomite, sand, and granite soil, but maintained > 6.2 in calcareous soil. Rich organic matter in calcareous and basalt soil had an inhibition effect on BTEX oxidation by PS. The pH buffer in calcareous soil may imply the potential of PS oxidation combined with bioremediation in carbonate rock regions.

Sunlight-induced changes in naturally stored reclaimed water: Dissolved organic matter, micropollutant, and ecotoxicity

Natural sunlight is a vital environmental element and plays a significant role in the ecological storage of reclaimed water (RW), but its impacts on RW quality are poorly understood. In this study, sunlight-induced changes in RW with a focus on dissolved organic matter (rDOM) and 52 residual micropollutants were investigated in the field during the summer and winter seasons. The results indicated that sunlight exposure led to the dissipation of chromophoric DOM (CDOM) in the summer (55% loss) and winter (19% loss) after 14 consecutive sunny days. During open storage of RW, CDOM absorption in UVC regions was preferentially removed in the summer, while during the winter there was preferential removal of CDOM in UVA regions. The results also showed higher fluorescent DOM (FDOM) removal in summer than in winter (49% and 28%, respectively). Results in both seasons indicated that humic acid-like compounds were the most photolabile fractions and were preferentially removed under sunlight exposure. Sunlight also induced attenuation of micropollutants in the summer and winter at reductions of 66% and 24% from the initial values, respectively. Significant attenuation (>75%) was only observed for endocrine-disrupting chemicals, pharmaceuticals, and sunscreens in the summer, but they accounted for 76% of the total concentrations. Vibrio fischeri toxicity tests demonstrated that sunlight constantly decreased the luminescent bacteria acute toxicity of RW, which was estimated to be caused mainly by the sunlight-induced changes of FDOM and CDOM, while the detected micropollutants could only explain 0.02%–2% of acute toxicity. These findings have important implications regarding our understanding of the ecological storage of reclaimed water and the contribution of management strategies.

Fluorescent compounds retained by ultrafiltration membranes for water reuse

Ultrafiltration (UF) membranes are increasingly being applied in water treatment and reuse processes because they provide effective removal of microorganisms, suspended solids, and high molecular weight compounds. However, membrane fouling necessitates backwashing and periodic chemical cleaning and, as a result, causes an increase in the amount of energy and overall cost for operation. Dissolved organic matter (DOM) has been identified as one of the major causes of biofilm formation and fouling during membrane ultrafiltration. Yet there is still much to be understood regarding how DOM interacts with biofilms, with some studies suggesting that labile DOM fractions may be preferentially removed by biogeochemical interactions with the biofilm. In this study, we evaluated the effects of biofilm formation on the retention of different organic compounds by measuring dissolved organic carbon, total dissolved nitrogen, DOM fluorescence peak intensities, and also performed parallel factor analysis (PARAFAC) modeling of fluorescent components to characterize the feed, permeate, and backwash during UF membrane fouling. We used a pilot scale, inside-out flow, UF membrane with a 0.03 μm pore size and different synthetic wastewater solutions as feed water. To evaluate the role of biofilms in preferential removal of DOM, unsterilized and sterilized synthetic wastewater solutions were run for several cycles. Results indicate that ultrafiltration for both solutions preferentially removed the biologically labile tryptophan-like components compared to the humic-like components. The similar percentage of removal of tryptophan-like components in both experiments suggest that the membrane biofilm on polyethersulfone membranes has little influence on the removal of biodegradable organic constituents. These findings also demonstrate that fluorescence spectroscopy can be a valuable tool to discriminate between different DOM fractions retained and passing through UF membrane filters.

Uranium and molybdenum isotope evidence for an episode of widespread ocean oxygenation during the late Ediacaran Period

To improve estimates of the extent of ocean oxygenation during the late Ediacaran Period, we measured the U and Mo isotope compositions of euxinic (anoxic and sulfidic) organic-rich mudrocks (ORM) of Member IV, upper Doushantuo Formation, South China. The average δ238U of most samples is 0.24±0.16‰ (2SD; relative to standard CRM145), which is slightly higher than the average δ238U of 0.02±0.12‰ for restricted Black Sea (deep-water Unit I) euxinic sediments and is similar to a modeled δ238U value of 0.2‰ for open ocean euxinic sediments in the modern well-oxygenated oceans. Because 238U is preferentially removed to euxinic sediments compared to 235U, expanded ocean anoxia will deplete seawater of 238U relative to 235U, ultimately leading to deposition of ORM with low δ238U. Hence, the high δ238U of Member IV ORM points to a common occurrence of extensive ocean oxygenation ca. 560 to 551 Myr ago.The Mo isotope composition of sediments deposited from strongly euxinic bottom waters ([H2S]aq >11μM) either directly records the global seawater Mo isotope composition (if Mo removal from deep waters is quantitative) or represents a minimum value for seawater (if Mo removal is not quantitative). Near the top of Member IV, δ98Mo approaches the modern seawater value of 2.34±0.10‰. High δ98Mo points to widespread ocean oxygenation because the preferential removal of isotopically light Mo to sediments occurs to a greater extent in O2-rich compared to O2-deficient marine environments. However, the δ98Mo value for most Member IV ORM is near 0‰ (relative to standard NIST SRM 3134=0.25‰), suggesting extensive anoxia. The low δ98Mo is at odds with the high Mo concentrations of Member IV ORM, which suggest a large seawater Mo inventory in well-oxygenated oceans, and the high δ238U. Hence, we propose that the low δ98Mo of most Member IV ORM was fractionated from contemporaneous seawater. Possible mechanisms driving this isotope fractionation include: (1) inadequate dissolved sulfide for quantitative thiomolybdate formation and capture of a seawater-like δ98Mo signature in sediments or (2) delivery of isotopically light Mo to sediments via a particulate Fe–Mn oxyhydroxide shuttle.A compilation of Mo isotope data from euxinic ORM suggests that there were transient episodes of extensive ocean oxygenation that break up intervals of less oxygenated oceans during late Neoproterozoic and early Paleozoic time. Hence, Member IV does not capture irreversible deep ocean oxygenation. Instead, complex ocean redox variations likely marked the transition from O2-deficient Proterozoic oceans to widely oxygenated later Phanerozoic oceans.

Improving on SUVA254 using fluorescence-PARAFAC analysis and asymmetric flow-field flow fractionation for assessing disinfection byproduct formation and control

Several challenges with disinfection byproduct (DBP) control stem from the complexity and diversity of dissolved organic matter (DOM), which is ubiquitous in natural waters and reacts with disinfectants to form DBPs. Fluorescence parallel factor (PARAFAC) analysis and asymmetric flow-field flow fractionation (AF4) were used in combination with free chlorine DBP formation potential (DBPFP) tests to study the physicochemical DOM properties and DBP formation in raw- and alum-coagulated waters. Enhanced coagulation with alum became more effective at removing DBP-precursors as the pH decreased from 8 to 6. AF4-UV254 fractograms indicated enhanced coagulation at pH 6 preferentially removed larger DOM, whereas no preferential size removal occurred at pH 8. Fluorescence-PARAFAC analysis revealed the presence of one protein-like and three humic-like fluorophore groups; stronger linear correlations were found between chloroform and the maximum intensity (FMAX) of a humic-like fluorophore (r2 = 0.84) than with SUVA254 (r2 = 0.51). This result indicated that the fluorescence-PARAFAC approach used here was an improvement on SUVA254, i.e., fluorescence-based measurements were stronger predictors of chloroform formation.

Inherited drainage - paleochannels and preferential groundwater flow

It is suggested that in a localized remnant of Kalahari sand at Dufuya, central Zimbabwe, groundwater flows in an integrated pattern inherited from the paleochannel network of the underlying gneiss. Contact springs occur at discrete localities along the Kalahari sand/gneiss boundary and are associated with spring sapping and land surface subsidence. Subsidence is presumed to be due to preferential solute removal by leaching and dissolution as a result of concentration of groundwater flow within the buried paleochannel network and the location of the springs is presumed to occur where the paleochannel network intersects the Kalahari sand/gneiss boundary. Over time the surficial Kalahari sand is preferentially removed along these buried drainage lines by spring sapping and headwards erosion, exposing the gneiss. Multi-electrode direct current resistivity profiling and radar have been used to map the sub-surface, revealing the topography of the basement and nature of the Kalahari cover. Coincidence of gneiss basement depressions with the spring sites, leached sands and subsidence zones suggests inheritance of the gneiss fluvial paleochannel network pattern by the present day groundwater flow. Washed sand and gravel intersected in shallow boreholes in these areas provides further evidentiary support for the concept of inherited drainage.

Preferential removal of dissolved carbohydrates during estuarine mixing in the Bay of Saint Louis in the northern Gulf of Mexico

Water samples were collected from the Bay of Saint Louis (BSL) estuary in the northern Gulf of Mexico to investigate the abundance, distribution, and mixing behavior of dissolved organic carbon (DOC) and total dissolved carbohydrates (TCHO). Laboratory experiments were also conducted to examine the removal mechanisms of DOC and TCHO during estuarine mixing. Both DOC and TCHO concentrations decreased with increasing salinity, showing a non-conservative behavior in the BSL with considerable removal of DOC (43%) and TCHO (63%). The ratio of TCHO to DOC varied from 0.31 in riverwater to ∼ 0.10 in coastal waters, decreasing with increasing salinity within the estuary. The TCHO was higher in the > 1 kDa colloidal fraction, ranging from 53% to 73% as quantified using an ultrafiltration permeation model compared to the bulk DOC that had a colloidal fraction of 40–63%. Coastal waters also had a slightly elevated CHO/DOC ratio in the colloidal phase, suggesting in situ production of CHO. Results from laboratory experiments showed that physical mixing resulted in a removal of 5–10% TCHO, while microbial processes accounted for a removal of up to 25–30% of TCHO during incubation experiments, suggesting that microbial degradation was the primary mechanism responsible for the removal of CHO in the BSL. However, physical removal combined with microbial degradation accounted for only 30–40% of the removal of DOC and TCHO in the BSL, indicating that the removal might be overestimated and/or other processes are also important in the removal of DOC and CHO in the estuarine environment. Both field observations and laboratory experiments demonstrated consistently greater removal of CHO compared to bulk DOC, supporting our hypothesis that carbohydrates are a more active organic component and could be preferentially removed during estuarine mixing.

The surface chemistry of multi-oxide silicates

The surface chemistry of natural wollastonite, diopside, enstatite, forsterite, and albite in aqueous solutions was characterized using both electrokinetic techniques and surface titrations performed for 20 min in batch reactors. Titrations performed in such reactors allow determination of both proton consumption and metal release from the mineral surface as a function of pH. The compositions, based on aqueous solution analysis, of all investigated surfaces vary dramatically with solution pH. Ca and Mg are preferentially released from the surfaces of all investigated divalent metal silicates at pH less than ∼8.5–10 but preferentially retained relative to silica at higher pH. As such, the surfaces of these minerals are Si-rich and divalent metal poor except in strongly alkaline solutions. The preferential removal of divalent cations from these surfaces is coupled to proton consumption. The number of protons consumed by the preferential removal of each divalent cation is pH independent but depends on the identity of the mineral; ∼1.5 protons are consumed by the preferential removal of each Ca atom from wollastonite, ∼3 protons are consumed by the preferential removal of each Mg or Ca atom from diopside or enstatite, and ∼4 protons are consumed by the preferential removal of each Mg from forsterite. These observations are interpreted to stem from the creation of additional ‘internal’ adsorption sites by the preferential removal of divalent metal cations which can be coupled to the condensation of partially detached Si. Similarly, Na and Al are preferentially removed from the albite surface at 2 > pH > 11; mass balance calculations suggest that three protons are consumed by the preferential removal of each Al atom from this surface over this entire pH range. Electrokinetic measurements on fresh mineral powders yield an isoelectric point (pH IEP) 2.6, 4.4, 3.0, 4.5, and <1, for wollastonite, diopside, enstatite, forsterite, and albite, respectively, consistent with the predominance of SiO 2 in the surface layer of all of these multi-oxide silicates at acidic pH. Taken together, these observations suggest fundamental differences between the surface chemistry of simple versus multi-oxide minerals including (1) a dependency of the number and identity of multi-oxide silicate surface sites on the aqueous solution composition, and (2) the dominant role of metal–proton exchange reactions on the reactivity of multi-oxide mineral surfaces including their dissolution rate variation with aqueous solution composition.

Adsorption of natural organic matter from waters by iron coated pumice

Natural pumice particles were used as granular support media and coated with iron oxides to investigate their adsorptive natural organic matter (NOM) removal from waters. The impacts of natural pumice source, particle size fraction, pumice dose, pumice surface chemistry and specific surface area, and NOM source on the ultimate extent and rate of NOM removal were studied. All adsorption isotherm experiments were conducted employing the variable-dose completely mixed batch reactor bottle-point method. Iron oxide coating overwhelmed the surface electrical properties of the underlying pumice particles. Surface areas as high as 20.6 m 2 g −1 were achieved after iron coating of pumice samples, which are above than those of iron coated sand samples reported in the literature. For all particle size fractions, iron coating of natural pumices significantly increased their NOM uptakes both on an adsorbent mass- and surface area-basis. The smallest size fractions (<63 μm) of coated pumices generally exhibited the highest NOM uptakes. A strong linear correlation between the iron contents of coated pumices and their Freundlich affinity parameters ( K F) indicated that the enhanced NOM uptake is due to iron oxides bound on pumice surfaces. Iron oxide coated pumice surfaces preferentially removed high UV-absorbing fractions of NOM, with UV absorbance reductions up to 90%. Control experiments indicated that iron oxide species bound on pumice surfaces are stable, and potential iron release to the solution is not a concern at pH values of typical natural waters. Based on high NOM adsorption capacities, iron oxide coated pumice may be a promising novel adsorbent in removing NOM from waters. Furthermore, due to preferential removal of high UV-absorbing NOM fractions, iron oxide coated pumice may also be effective in controlling the formation of disinfection by-products in drinking water treatment.

Evaluation of the performance of tight-UF membranes with respect to NOM removal using effective MWCO, molecular weight, and apparent diffusivity of NOM

Concepts for the effective MWCO of tight-UF membranes, and apparent diffusion coefficients for NOM, were introduced to determine the mechanisms influencing NOM removal and to explain the various behaviors of NOM removal by UF membranes with different hydrophobicities, permeability, and surface charges. Colloidal NOM (COM) and non-colloidal hydrophobic NOM (NCD HP) constituents were chosen for the evaluation of two different UF membranes. For a relatively hydrophobic, relatively high permeability, and less negatively charged UF membrane, the hydrophobic fractions of COM were preferentially removed and were also removed by a size exclusion mechanism (i.e., both hydrophobic interaction and size exclusion mechanisms). The NCD HP exhibited no such preferential removal of the hydrophobic fractions, but could be removed by a size exclusion mechanism (i.e., only size exclusion mechanism). With a relatively hydrophilic, relatively low permeability, and more negatively charged UF membrane, COM exhibited no preferential removal of the hydrophobic fractions, but could be removed by a size exclusion mechanism (i.e., only size exclusion mechanism). Whereas the hydrophobic fractions of the NCD HP were preferentially removed, these could not be removed by a size exclusion mechanism (i.e., only hydrophobic interaction mechanism). The apparent diffusion coefficients of NOM, as determined from NOM diffusion experiments using a diffusion cell equipped with a regenerated cellulose membrane, were much lower than those calculated by the Stokes-Einstein relation. The diffusion coefficient of NOM is expected to be used to predict and explain NOM transport behaviors in tight-UF membranes.

Particle geochemistry in the Rainbow hydrothermal plume, Mid-Atlantic Ridge

We report the analysis of 18 large volume (500–1500 L) in situ filtered samples of particulate material from the largest hydrothermal plume on the Mid-Atlantic Ridge, overlying the ultramafic-hosted Rainbow hydrothermal field at 36° 14′N. Measured particulate iron concentrations reach 614 nM. High concentrations of particulate Fe oxyhydroxides result from the extremely high Fe concentration (∼24 mM) and Fe/H 2S ratio (∼24) of the vent fluids, and persist to at least 10 km away from the vent site due to the advection of plume material with the ambient along-axis flow. Two of the nine pairs of pump deployments appear to have intercepted the buoyant or otherwise very young portion of the hydrothermal plume. These samples are characterized by anomalously (compared to neutrally buoyant plume samples) high concentrations of Mg, U, and chalcophile elements, and low concentrations of Mn, Ca, V, Y, and the rare earth elements (REE). Within the neutrally buoyant plume, elemental distributions are largely consistent with previously observed behaviors: preferential removal of chalcophile elements, conservative behavior of oxyanions (P, V, and U), and continuous scavenging of Y and the REE. This consistency is particularly significant in light of the underlying differences in fluid chemistry between Rainbow and other studied sites. Chalcophile elements are preferentially removed from the plume in the order Cd>Zn>Co>Cu. Phosphorus/iron and vanadium/iron ratios for the neutrally buoyant plume are consistent with global trends with respect to the concentration of dissolved phosphate in ambient seawater. Comparison of buoyant and neutrally buoyant plume ratios with data from hydrothermal sediments underlying the Rainbow plume (Cave et al., 2002) indicates, however, that while P/Fe ratios are indeed constant V/Fe ratios increase progressively from early stage plume particles to sediments. REE distributions in the buoyant and neutrally buoyant plume appear most consistent with a continuous scavenging process during dispersion through the water column.

Applicability of solid-state 13C CP/MAS NMR analysis in Spodosols: chemical removal of magnetic materials

The presence of magnetic species, Fe in particular, decreases the effectiveness of nuclear magnetic resonance (NMR) analysis of soil organic matter (SOM), especially in Spodosols. This study was conducted to evaluate the utility of dithionite, stannous chloride, and hydrofluoric acid (HF) extraction for Fe removal and solid-state 13C NMR spectral enhancement in forested Spodosols. Extraction with 2% HF resulted in the greatest removal of Fe (45%–99%), while 4% (w/v) dithionite extraction was the least effective in removing Fe from the same soils (8%–54%). The 2% HF treatment also removed the largest proportion of total C (12%–67%) and total N (19%–66%). In five of the 10 mineral horizon soils studied, the C/N ratios changed more than 25% after HF treatment, suggesting that some alteration of bulk chemical composition occurred. The treatment had little effect on low-Fe samples because the quality of NMR spectra was similar between untreated and chemically treated organic horizon (Oa) soil samples. For soils high in Fe, as is typical in Spodosol mineral horizons, the 2% HF and the 0.05 M SnCl 2 treatment showed some spectral improvement but the results were inconsistent. 13C NMR spectra for soil HF extracts indicated that carbohydrate and carboxyl C groups were preferentially removed in the extraction. Some quantitative changes of C distribution among various structures were observed after HF treatment, possibly indicating the alteration of organic matter during extraction. Several factors may contribute to the differences in the determination of various C groups by 13C NMR spectroscopy before and after chemical treatment, including poor signal-to-noise ( S/ N) ratios, interactions between paramagnetic ions and different C moieties, preferential removal of some C groups by different chemicals, sideband interference, mass loss, and perhaps other factors. Based on our results, it seems premature to recommend routine chemical pretreatment as a means of improving 13C NMR spectral quality.

Aspects of the differences in the erodibility of the waste rock dump and natural surfaces, Ranger Uranium Mine, Northern Territory, Australia

Small-scale flume experiments on the waste rock dump of Ranger Uranium Mine, Northern Territory, Australia, show that the unmanaged surface of the dump is 10–100 times more erodible than adjacent natural hillslopes. Silt and clay are preferentially removed and their proportion of the total sediment load is enhanced over their content in surface sediment. There is strong evidence that a low threshold of erosion does not exist and that even the smallest of flows across the waste rock dump can erode and transport some surface material. The erodible dump surface and the preferential removal of silt-clay could degrade ecosystems both on the dump and off-site. Rehabilitation of the waste rock dump will require special attention to erosion and its management.

Advances in our Knowledge of Biodegradation of Hydrocarbons in Reservoirs

Biodegradation of hydrocarbons in reservoirs is a widespread phenomenon that is currently observed by petroleum organic geochemists in most sedimentary basins. This basic phenomenon is responsible for the occurrence of large, heavy oil deposits referred to as tar mats or tar belts. Biodegradation of crude oils takes place in reservoirs in which oil-eating bacteria may thrive. For this reason, effective and present biodegradation effects are not observed at subsurface temperatures higher than 70-80[degrees]C. Significant compositional changes, especially at a molecular level, still remain linked to the aerobic biodegradation of crude oils. Under favorable circumstances, both alkanes and aromatics are degraded, but when nutrients (N, P, O[sup 2]) are impoverished, aromatics seem to be preferentially removed. Biodegradation extends also to sulfur-bearing aromatics with a preferential removal of alkylated structures. Changes in molecular patterns are used to assess degrees of biodegradation in crude oils. The most bacterially resistant structures are polycyclic alkanes and aromatics. The in-reservoir biodegradation of hydrocarbons does not generate new hydrocarbons, e.g., 25-norhopanes as proposed by several authors. In fact, the selective removal of less resistant structures concentrates preexisting minor families that were not detected on the unaltered crude due to their low absolute concentration. Consequently, the molecular spectrummore » found in severely biodegraded oils may be considered as highly diagnostic of a part of the primary genetic spectrum of each oil. In outcrop samples, biodegradation is associated with other complementary phenomena such as photooxidation, oxidation, inspissation, evaporation, water washing, etc. Of particular importance are weathering effects linked to oxidation, which entail drastic compositional changes, with neogenesis of resins, asphaltenes, and even insoluble residue.« less

Metabolism of two forms of apolipoprotein B of VLDL by rat liver

Apolipoprotein B (apoB) is composed of metabolically distinct fractions of higher molecular weight (apoBh) and lower molecular weight (apoBl). When 125I-labeled very low density lipoprotein (VLDL) prepared from recirculating liver perfusates was injected into rats, labeled apoBl was preferentially removed from the plasma and apoBh entered low density lipoprotein (LDL). The time-related movement of labeled apoBh into higher density fractions was independent of that of labeled apoBl. When 125I-labeled triglyceride-rich lipoprotein (TRL) prepared from sucrose-fed rats was incubated with plasma from rats injected with heparin and then studied in a recirculating liver perfusion, apoBl was preferentially removed compared to apoBh. Thus, the loss of apoBl of hepatic VLDL in vivo was similar to the loss of apoBl of lipase-treated TRL in vitro. In control perfusions where TRL was incubated with heat-treated postheparin plasma, not only was there less initial hepatic clearance of apoB but the early phase of preferential apoBl removal during 30 min of perfusion was not observed. ApoE removal from perfusates was the same whether or not the TRL had been treated with heparin-releasable lipases. Apoprotein degradation, as indicated by the appearance in the perfusate of labeled degradation products, occurred 30 min after the preferential phase of apoBl removal. These results suggest that hepatic clearance of VLDL and TRL remnants is favored by lipolysis and by the presence of apoBl on the particle that enhances their hepatic binding and degradation.