Enrichment Factors Range Research Articles

The application of CuGA MOF in a food safety monitoring procedure specialized for parsley juice with no dilution via extraction and preconcentration of its pesticides

In this study, a specialized analytical method for the safety assessment of parsley juice is introduced for monitoring its pesticide content. Also, CuGA metal–organic framework (synthesized using three green materials including copper, gallic acid, and deionized water) was applied in the developed method as a sorbent. The high compatibility of the developed method with parsley juice proves that no dilution was required to proceed with the approach. The extraction procedure began with the addition of the metal–organic framework into the parsley juice and its vortexing for adsorption. This step separated the pesticides from the juice and also performed a cleanup process to dwindle the matrix effect. After the settlement of the sorbent via centrifugation, methanol was used as an eluent to desorb the analytes through vortexing. For the conduction of a preconcentration procedure moreover to extraction, the methanolic phase was mixed with 1,2-dibromo ethane as an extractant and injected into deionized water. Centrifugation settled the extractant droplets from the milky solution and an aliquot of it was injected into a gas chromatograph equipped with a flame ionization detector. The enrichment factors range was 206–322. Extraction recovery values were in the range of 41–64%. Limits of detection and quantification were in the ranges of 0.40–2.65 and 1.32–8.74 μg L−1, respectively. By successfully detecting oxadiazon in parsley juice at the concentration of 35 ± 3 µg L−1 by performing the method, the developed approach seems highly applicable.

Polystyrene-based nanospheres with controllable microstructures for exceptional solid phase microextraction of organic pollutants

Systematic investigation on the adsorption performance of polystyrene-based nanospheres towards persistent organic pollutants (POPs) is of great importance to the design of high-capacity adsorbent and the toxicological risk assessment of nano plastic. In this study, a series of polystyrene-based nanospheres with controllable microstructures, have been constructed successfully as model adsorbents, by the strategies of emulsion polymerization, hyper-crosslinking and direct carbonization. In the form of Solid phase microextraction (SPME) coatings, the impacts of microstructures on the adsorption performance of constructed nanospheres have been highlighted, by employing benzene series, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) as target adsorbates. Moreover, it is surprisingly found that the grafted F atoms make PS demonstrate better enrichment effects towards PCBs than the Cl atoms, mainly due to stronger sigma (σ)-hole interactions between F atoms and PCBs. In consideration of the most outstanding performance, the F-functionalized nanospheres (xFFNs)-coated SPME fiber is employed for the enrichment of PCBs from water samples, and the enrichment factors range from 1500 to 10030. After coupling the xFFNs-coated fiber with gas chromatography-mass spectrometry (GC-MS), highly sensitive analytical method is developed with detection limits of 0.08–0.89 ng L−1, realizing precise quantifications of trace PCBs in treated sewage samples.

A hydrogel composite prepared from alginate, an amino-functionalized metal-organic framework of type MIL-101(Cr), and magnetite nanoparticles for magnetic solid-phase extraction and UHPLC-MS/MS analysis of polar chlorophenoxy acid herbicides.

A regenerable hydrogel composite isdescribed that iscomprised of alginate, amino-functionalized metal-organic framework (MIL-101(Cr)-NH2) and magnetite nanoparticles. The composite was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, vibrating-sample magnetometry and Brunauer-Emmett-Teller measurement. The material was applied to the magnetic solid-phase extraction of six polar chlorophenoxy acid (CPA) herbicides. Specifically, the herbicides clofibric acid, 4-chlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, 2,4,5-trichlorophenoxyacetic acid and 2-(2,4,5-trichlorophenoxy)propionic acid were extracted from environmental aqueous samples and analyzed by ultra-HPLC-tandem mass spectrometry. The abundance of hydroxyl and carboxyl groups on the natural polymer renders alginate a superior hydrophilic coating. It brings the polar acidic herbicides into closer proximity to the porous metal-organic framework. When integrated with MIL-101(Cr)-NH2, the composite material combines the favorable attributes of high hydrophilicity and large adsorption capacity. An orthogonal array design matrix was employed for the optimization of the extraction parameters. Under the most favorable conditions, the method displays a wide linear response and low limits of detection (0.43-16ng⋅L-1). Precision and reproducibility (with relative standard deviations of ≤13%) are satisfactory. Enrichment factors range between 27 and 107. The composite was applied to the extraction of CPA herbicides from lake and pond water samples. A markedly improved sorbent-based extraction procedure and performance (compared to previous methods) is found. Graphical abstract Schematic of the magnetic solid-phase extraction of polar herbicides using a hydrogel composite as sorbent. The amino-functionalized MIL-101(Cr) and hydrophilic alginate work in synergy resulting in a material which possess favorable attributes of both components that are beneficial for extraction.

A regenerable sorbent composed of azeolite imidazolate framework(ZIF-8), Fe3O4 and graphene oxide for enrichment of atorvastatin and simvastatin prior to their determination by HPLC.

Graphene oxide (GO), nanosized Fe3O4 and zeolite imidazolate framework-8 (ZIF-8) were hybridized as a multifunctional sorbent for use in microextraction. The sorbent was characterized by SEM, TEM, XRD and FTIR. The composite is porous, has a high specific surface (> 600m2·g-1) and is paramagnetic. The GO sheets are shown to act as carriers for the Fe3O4 nanoparticles and ZIF-8. The composite is a viable material for the preconcentration of atorvastatin and simvastatin from urine prior to their determination by HPLC with PDA detection. The limits of detection are 116 and 387pg·mL-1, respectively. Recoveries from spiked urine samples range between 84.7 and 95.7%, with relative standard deviation of ≤4.5%. Enrichment factors range from 169 to 191. The method was successfully applied to the determination of atorvastatin in urine. Moreover, this sorbent is regenerable and recyclable for at least seven times without obvious decrease in performance. Graphical abstract A composite sorbent composed of a zeolite imidazolate framework, Fe3O4 and graphene oxide was applied to the extraction of statins in urine prior their determination by HPLC.

New data for geology and geochemistry of the Rodion gold–quartz deposit, northeastern Russia

This paper is focused on the new data for geology, mineralogy, and geochemistry of stockworks consisting of steep and gentle quartz veins and veinlets forming a complex multilevel structure at the Rodion deposit. These stockworks range from 25 to 150 m in thickness. Average gold grade is 1.8 g/t. Ore minerals pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, and native gold are predominantly concentrated on the vein and veinlet walls. Thermal metamorphism caused by the intrusion of the Ulakhan granodiorite pluton is the important singularity of the deposit. The deposit ore is enriched in chalcophile microelements Au, Ag, As, Sb, Cu, Pb, Zn, and Bi as compared to the average composition of the upper crust and hosting Permian sequences. The enrichment factors range from a few to hundreds of times. Bi, W, Pb, Ag, and Na2O are positively correlated between each other and with Au. The highest correlation coefficient 0.59 is between Au and Bi. Au is negatively correlated with Ba, Li, Co, Ni, Mn, Ti, and Be. The stockwork ores were formed involving homogeneous low-saline (9.4–4.3 wt % NaCl equiv) substantially aqueous bicarbonate-chloride fluid at 275–330°C and 300–1840 bar fluid pressure. Fluid has a high concentration of CO2 (up to 349 g/kg of water) and is reductive (СО2/СН4 = 17–37.3). Na and Ca are the major cations in the fluid, whereas K and Mg are minor. In addition, many microelements were detected in the fluid: As, Li, Rb, Cs, Mo, Ag, Sb, Cu, Zn, Cd, Pb, U, Ga, Ge, Ti, Mn, Fe, Co, Ni, V, Cr, Y, Zr, Sn, Ba, W, Au, Hg, and REE. The results obtained are consistent with the metamorphic–magmatic formation model of orogenic gold–quartz deposits within the Yana–Kolyma belt.

Vortex- and Shaker-Assisted Liquid–Liquid Microextraction (VSA-LLME) Coupled with Gas Chromatography and Mass Spectrometry (GC-MS) for Analysis of 16 Polycyclic Aromatic Hydrocarbons (PAHs) in Offshore Produced Water

A simple, cost-effective, and efficient pretreatment method, namely, vortex- and shaker-assisted liquid–liquid microextraction (VSA-LLME) coupled with gas chromatography and mass spectrometry (GC-MS), is developed for determining 16 trace-level polycyclic aromatic hydrocarbons (PAHs) in offshore produced water. The parameters affecting the VSA-LLME performance including solvent volume, ion strength, shaking time, and centrifuge speed were optimized. Under the optimized condition, the enrichment factors range between 68 and 78. The method linearities (R 2) for all 16 PAHs were above 0.99 at concentration range between 10 and 200 ng/L. The recoveries of the method were 74–85 %, and the limits of detection were as low as 2 to 5 ng/L. The relative standard deviations (RSD%) were 6~11 %. The developed method was also validated in industrial wastewater sample and showed good capability in determination of 16 PAHs in offshore produced water. The developed method offers advantages including simplicity of operation, low cast, and high sensitivity.

Deep-sea redox across the Paleocene-Eocene thermal maximum

Large amounts of 13C-depleted carbon were released to the oceans and atmosphere during a period of abrupt global warming at the Paleocene-Eocene thermal maximum (PETM) (∼55 Ma). Investigations of qualitative sedimentologic and paleontologic redox proxies such as bioturbation and benthic assemblages from pelagic and hemipelagic sections suggest transient reductions in bottom water oxygen during this interval, possibly on a global scale. Here, we present bulk sediment manganese (Mn) and uranium (U) enrichment factors (EF) in Atlantic and Pacific deep-sea cores to constrain relative paleoredox changes across the PETM. Mn EF range from 1 to 9 in Atlantic sites, 1 to 35 in Southern Ocean sites, and are at crustal averages (EF = 1) in Pacific sites. U EF range from 1 to 5 in Atlantic sites, 1 to 90 in Southern Ocean sites, and are at crustal averages in Pacific sites. Our results indicate suboxic conditions prior to, during, and in the recovery from the PETM at intermediate depth sites in the Atlantic and Southern Ocean while the Pacific sites remained relatively oxygenated. The difference in oxygenation between the Atlantic and Pacific sites leads us to suggest the source for isotopically light carbon release during the PETM was in the Atlantic.

Emulsification-based dispersive liquid microextraction and HPLC determination of carbazole-based explosives

We have developed a method for liquid-liquid microextraction of the explosives trinitrocarbazole (TrNC), tetranitrocarbazole (TNC) and carbazole from water samples. It is based on the use of a solvent mixture that contains appropriate amounts of the extraction solvent (chloroform) and an aqueous solution of didecyl dimethyl ammonium bromide as disperser. This mixture is rapidly injected into the water sample upon which a cloudy microemulsion is formed which extracts the analytes. After centrifugation and phase separation, the sedimented phase is used for the determination of the analytes by HPLC with UV detection. Under the optimized conditions, the calibration plot is linear in the range from 0.35 to 351 ng mL−1 for TNC, 0.30 to 305 ng mL−1 for TrNC, and 2.1–421 ng mL−1 for carbazole. The limits of detection, at a signal-to-noise ratio of 3, range from 0.08 to 0.10 ng mL−1, the relative standard deviations (at n = 6) for the extraction of TNC (3.5 ng mL−1), TrNC (3.0 ng·mL−1) and carbazole (3.2 ng mL−1) vary between 5.3 and 6.1 %, and the enrichment factors range from 264 to 295.

Simultaneous determination of carbazole-based explosives in environmental waters by dispersive liquid—liquid microextraction coupled to HPLC with UV-Vis detection

Dispersive liquid-liquid microextraction as a rapid, simple and efficient method coupled with high performance liquid chromatography-UV-Vis detection was used for sample preparation and subsequent determination of carbazole, tri nitro carbazole (TrNC) and tetra nitro carbazole in water samples. The influence of several important variables on the extraction efficiency has been evaluated. The methods works best with chloroform as an extractant and acetonitrile as the dispersive solvent. Under optimum conditions, the calibration curve is linear in the range from 0.007 to 1.75 μg mL−1 for TNC, 0.006 to 1.52 μg mL−1 for TrNC, and 0.008–2.10 μg mL−1 for carbazole. The limits of detection (LODs; at a signal-to-noise ratio of 3), range from 1.7 to 1.1 ng mL−1, for TNC, TrNC and carbazole. Also, the relative standard deviations (RSD, n = 6) for the extraction of TNC (at 174 ng mL−1), TrNC (at 151 ng mL−1) and carbazole (at 84 ng mL−1) vary between 4.1 and 5.2%. The enrichment factors range from 179 to 186. The method was successfully applied to the determination of TNC, TrNC and carbazole in environmental samples.

Extraction of phthalate esters from water and beverages using a graphene-based magnetic nanocomposite prior to their determination by HPLC

We have developed a highly sensitive microextraction method for the preconcentration of some phthalate esters such as diethyl phthalate, di-n-propylphthalate, di-n-butyl-phthalate, dicyclohexyl-phthalate, and diethyl-hexyl phthalate prior to their determination by HPLC. It is based on a magnetic graphene nanocomposite as an effective adsorbent. The effects of the amount of the extractant composite employed, extraction time, pH values, salt concentration and desorption conditions were investigated. Under the optimum conditions, the enrichment factors range from 1574 to 2880. Response is linear in the concentration range from 0.1 to 50 ng mL−1. The limits of detection (at S/N = 3) were between 0.01 and 0.04 ng mL−1. The method was successfully applied to the determination of five phthalate esters in water and beverage samples.

Application of ultrasound-assisted ionic liquid dispersive liquid-phase microextraction followed high-performance liquid chromatography for the determination of fungicides in red wine

A new method was developed for the determination of fungicides in red wine using ultrasound-assisted ionic liquid dispersive liquid–phase microextraction followed by high-performance liquid chromatography. The ionic liquid, 1-hexyl-3-methylimidazolium hexafluorophosphate (IL) was quickly disrupted by ultrasonication and dispersed in wine as fine droplets. At this stage, the analytes were extracted into the fine droplets of IL. After centrifugation, the concentration of the enriched fungicides in the sedimented phase was determined. Extraction conditions including the type of extraction solvent, the extraction solvent volume, ultrasonication time, centrifugation time and sample pH were optimized. The performance of the method was studied in terms of linearity, precision, and recovery. Quantitative recoveries (>70%) except for pyrimethanil were obtained, and method precision was also satisfactory (RSD < 10%). Enrichment factors range from 100 to 200, and the limits of detection are at the low μg per liter level for most of the target compounds.

Low toxic dispersive liquid–liquid microextraction using halosolvents for extraction of polycyclic aromatic hydrocarbons in water samples

A low toxic dispersive liquid–liquid microextraction (LT-DLLME) combined with gas chromatography–mass spectrometry (GC–MS) had been developed for the extraction and determination of 16 polycyclic aromatic hydrocarbons (PAHs) in water samples. In normal DLLME assay, chlorosolvent had been widely used as extraction solvents; however, these solvents are environmental-unfriendly. In order to solve this problem, we proposed to use low toxic bromosolvent (1-bromo-3-methylbutane, LD 50 6150 mg/kg) as the extraction solvent. In this study we compared the extraction efficiency of five chlorosolvents and thirteen bromo/iodo solvents. The results indicated that some of the bromo/iodo solvents showed better extraction and had much lower toxicity than chlorosolvents. We also found that propionic acid is used as the disperser solvent, as little as 50 μL is effective. Under optimum conditions, the range of enrichment factors and extraction recoveries of tap water samples are ranging 372–1308 and 87–105%, respectively. The linear range is wide (0.01–10.00 μg L −1), and the limits of detection are between 0.0003 and 0.0078 μg L −1 for most of the analytes. The relative standard deviations (RSD) for 0.01 μg L −1 of PAHs in tap water were in the range of 5.1–10.0%. The performance of the method was gauged by analyzing samples of tap water, sea water and lake water samples.

Isotopic evidence and quantification assessment of in situ RDX biodegradation in the deep unsaturated zone

Abstract Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is an explosive compound whose extensive use has resulted in significant contamination of soils and groundwater worldwide. We studied its in situ biodegradation along the unsaturated zone beneath an explosives wastewater lagoon using compound-specific isotope analysis (CSIA) of RDX in the unsaturated zone, together with biodegradation slurry experiments under anaerobic conditions. We found the highest degradation potential of RDX and its nitroso derivatives in the upper part of the soil profile while in the lower parts, RDX-degradation potential was lower and the nitroso derivatives tended to persist. This was also observed in the field, as reflected by the isotopic composition of RDX along the profile. We also found a correlation between biodegradation potential and clay content: biodegradation was further enhanced in layers characterized by high-clay content or in those influenced by the high-clay layers. In addition, in the presence of high organic matter content, further enhancement of biodegradation was observed. We obtained different isotopic enrichment factors ( ɛ ) for RDX biodegradation in different sections of the unsaturated profile and suggest that different degradation pathways exist simultaneously in situ , in variable proportions. Using the range of enrichment factors, we were able to assess the biodegradation extent of RDX at different sampling points along the profile, which ranged between 30 and 99.4%. The novel application of CSIA together with slurry experiments provides better insight into degradation processes that are otherwise difficult to detect and assess.

Seasonal changes and temperature-dependent accumulation of polycyclic aromatic hydrocarbons in high-altitude soils

Polycyclic Aromatic Hydrocarbons (PAHs) are a major group of pollutants whose occurrence in the environment is mainly of anthropogenic origin. In this paper, we examine the effect of topographical slope exposure on PAH contamination and seasonal change in PAH concentrations in soils. We collected soil samples on three dates in 2007 (early May, end of July and beginning of November) from south- and north-facing aspects at 1900 m a.s.l. in the central Italian Alps. We found greater PAH contamination in soils from a north-facing slope than in those from a south-facing slope at all seasons. We calculated North–South Enrichment Factors as the ratio between the concentrations measured in soils from northern and southern aspects. These ratios ranged from 1.4 to 1.9 for lighter PAHs (from 2 to 4 rings). These values are consistent with theoretical calculations based on temperature-specific octanol-air partition coefficients (predicted North-South Enrichment Factors range from 1.6 to 2.0). For heavier PAHs (from 5 to 6 rings), smaller differences were observed between soils from northern and southern aspects, due to the gas/particle distribution of these compounds. We also found consistent differences in normalised PAH concentrations across the three sampling periods. The majority of compounds showed a significant decreasing trend from the beginning of May to the end of July, due to the annual cycles of physical processes (deposition vs. volatilisation) and biological processes (uptake and/or biotransformation). Only a few compounds showed different trends, presumably due to season-specific local emission sources.

Size dependent elemental composition of road-associated particles

Stormwater particles often provide transport for metals and other contaminants, however only larger particles are effectively removed by typical best management practices. Fine particles and their associated constituents are more likely to reach receiving waters; this merits further investigation regarding the metal contribution of fine ( d p < 10 µm) and very fine ( d p < 1.5 µm) particles. Road associated particles were collected by vacuuming a road surface and by collecting highway stormwater runoff. A cell sorter was employed to sort road associated particles into four size ranges: 0.1–0.3, 0.3–0.5, 0.5–1.0, and 1.0–1.5 µm. These very fine particles, along with six particle size ranges (total range < 2–63 µm) separated using a settling column, were analyzed for Al, Mn, Fe, Cr, Ni, Cu, Zn, and Pb using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Enrichment factors (EFs), calculated using Al as a basis to represent crustal contributions, were similar for the vacuumed road dust and the stormwater runoff. Fe and Mn were minimally depleted (0.1 ×) or near unity for all size ranges (Fe EF range 0.01–3.7; Mn EF range 0.02–10.6). Cr, Ni, Cu, Zn, and Pb were moderately (10 ×) to considerably (> 100 ×) enriched for most size ranges; these metals were most enriched in the very fine fractions (max EF ~ 4900 in Zn, 0.1–0.3 µm). Based on this preliminary study, a cell sorter is an acceptable means of fractionating aqueous particles of diameter 0.1–1.5 µm. In spite of their minimal relative mass contribution, the very fine particles are environmentally relevant due to their mobility and enrichment in potentially toxic metals.

Stable Carbon Isotope Fractionation of Chloroethenes by Dehalorespiring Isolates

Stable carbon isotope fractionation during the reductive dechlorination of chloroethenes by two bacterial strains that dechlorinate to ethene, Dehalococcoides ethenogenes 195 and Dehalococcoides sp. strain BAV1 as well as Sulfurospirillum multivorans and Dehalobacter restrictus strain PER-K23, isolates that do not dechlorinate past DCE, are reported. Fractionation by a Dehalococcoides-containing enrichment culture is also measured for comparison to the isolates. All data adequately fit the Rayleigh model and results are presented as enrichment factors. For strain 195, the measured enrichment factors were -9.6 +/- 0.4, -21.1 +/- 1.8, and -5.8 +/- 0.5 when degrading TCE, cDCE, and 1,1-DCE, respectively. Strain BAV1 exhibited enrichment factors of -16.9 +/- 1.4, -8.4 +/- 0.3, -21.4 +/- 0.9, and -24.0 +/- 2.0 for cDCE, 1,1-DCE, tDCE, and VC, respectively. The surprisingly large differences in enrichment factors caused by individual reductases (RDases) reducing different chloroethenes is likely the result of chemical structure differences among the chloroethenes. For TCE reduction, S. multivorans and D. restrictus strain PER-K23 exhibited enrichment factors of -16.4 +/- 1.5 and -3.3 +/- 0.3, respectively. While all of the organisms studied here utilize RDases that require corrinoid cofactors, the biotic TCE enrichment factors varied widely from those reported for the abiotic cobalamin-catalyzed reaction, indicating that additional factors affect the extent of fractionation in these biological systems. The enrichment factors measured for the Dehalococcoides-containing enrichment culture did not match well with those from any of the isolates, demonstrating the inherent difficulties in predicting fractionation factors of undefined communities. Although compound-specific isotope fractionation is a powerful tool for evaluating the progress of in situ bioremediation in the field, given the wide range of enrichment factors associated with functionally similar and phylogenetically diverse organisms, caution must be exercised when applying enrichment factors for the interpretation of dechlorination data.

Evaluation of Isotopic Enrichment Factors for the Biodegradation of Chlorinated Ethenes Using a Parameter Estimation Model: Toward an Improved Quantification of Biodegradation

A model was developed to predict the concentrations of chlorinated ethenes and ethene during sequential reductive dechlorination of tetrachloroethene (PCE) from stable carbon isotope values using Rayleigh model principles and specified isotopic enrichment factors for each step of dechlorination. The model was tested using three separate datasets of concentration and isotope values measured during three experiments involving the degradation of PCE to vinyl chloride (VC), trichloroethene (TCE) to ethene, and cis-1,2-dichloroethene (cDCE) to ethene. The model was then coupled to a parameter estimation method to estimate values for the isotopic enrichment factors of TCE, cDCE, and VC when they are intermediates in the dechlorination to ethene. The enrichment factors estimated for TCE and cDCE when they were intermediates in biodegradation experiments were close to or within the published range of enrichment factors determined from experiments where TCE or cDCE were the initial substrates. In contrast, the enrichment factors determined by parameter estimation for experiments in which VC was an intermediate in biodegradation experiments were consistently more negative (by approximately 10 per thousandth) than the most negative published enrichment factor determined from experiments where VC was the initial substrate. This finding suggests that the range of enrichment factors for VC dechlorination may not be as narrow as previously suggested (-21.5 per thousandth to -26.6 per thousandth) and that fractionation during VC dechlorination when VC is an intermediate compound may be significantly larger than when VC is the initial substrate. These findings have important implications both for the current practice of extrapolating laboratory-derived isotopic enrichment factors to quantify biodegradation of chlorinated ethenes in the field and for understanding the details of enzymatic reductive dechlorination.

Estimating denitrification in a large constructed wetland using stable nitrogen isotope ratios

Nitrate losses and their relationships to nitrogen isotope fractionation were evaluated in a wetlands environment in southern California. This paper reports the first study to follow isotope ratio changes in a large natural system with extensive macrophyte growth. As NO 3 concentrations decreased during flow through the wetlands, progressive enrichment in 15NO 3 was found. This increase corresponded to an enrichment value of −2.5‰, a value much lower that those reported for laboratory studies of denitrification (−17 to −29‰), but closer to the range of enrichment factors attributed to denitrification in studies of groundwaters (−3.5 to −16‰). By considering a laboratory derived value of −17‰ as the enrichment factor strictly due to denitrification, 10–23% of the Prado losses could be attributed through isotope enrichment to denitrification. Other studies at Prado, using a mass balance approach which considered macrophyte growth, concluded that bacterial denitrification was the major loss mechanism (89–95%). A similar, but somewhat smaller discrepancy between estimates of denitrification was found in nearby wetlands with large shallow water bodies with dense phytoplankton growth but negligible macrophytes. These discrepancies suggest that enrichment or fractionation factors derived under laboratory conditions where all nitrogen losses are attributable to denitrification cannot be used directly as the denitrification end-member in field situations where organic matter decomposition and nitrogen recycling are occurring simultaneously or sequentially with denitrification. Further studies which consider entire growing and decomposition cycles in macrophyte-rich wetlands are needed to resolve the discrepancy in the various methods of estimating dentrification in natural wetlands.

Metal redistribution during fluid exsolution and migration in the Middle Banded series of the Stillwater Complex, Montana

Olivine-bearing zones III and IV (OB-III and -IV) of the Stillwater Complex, MT preserve evidence of fluid migration particularly in the variation of apatite compositions. This feature, coupled with the lack of evidence of the addition of substantial amounts of primitive magma, allows these zones to be used to test the importance of volatile fluids in redistributing metals. The concentrations of Cu, Au, Ag, and As all show marked increases at and/or below the levels inferred to represent the top of the fluid migration front in the crystal pile. However, no significant sulfide enrichment is associated with the maximum metal enrichments. The Au concentration peak is much sharper and offset stratigraphically above that of Cu and corresponds with the maximum Cl content of interstitial apatite. These concentration profiles are modeled numerically, assuming fluid transport and chromatographic concentration of the metals. Mass-balance calculations indicate that cumulates significantly below the level of the inferred fluid-saturation front lost Cu while those at or immediately below gained Cu. We conclude that Cl-rich fluids redistributed the background metal concentrations. Although no dramatic enrichments are observed (enrichment factors range from two to three), the results demonstrate the potential importance of fluids in redistributing and concentrating metals in layered intrusions.

Trace element geochemistry of volcanic gases and particles from 1983–1984 eruptive episodes of Kilauea Volcano

Compositional data have been obtained for volcanic gases and particles collected from fume emitted at the Pu'u O'o vent on the east rift zone of Kilauea volcano. The samples were collected by pumping fume through a filter pack system consisting of a front stage particulate filter followed by four base‐treated filters (7LiOH). Particles and condensed phases are trapped on the particulate filter, and acidic gases are collected on the treated filters. The filters are analyzed for 30 elements by instrumental neutron activation analysis. Fume samples were collected from the Pu'u O'o vent for two eruptive episodes: (1) 7 days after episode 11 (cooling vent samples) and (2) the waning stage of episode 13 (active vent samples). Additional samples were collected by aircraft from the gas plume released during the lava fountaining phase of episode 17 (aircraft samples). Element concentrations in the vent gases were &gt; 104 μg m−3 for S, Cl, and F. Enrichment factors (EFs) for the volcanic fume versus the source magma were calculated using the volatile element Br as the reference element for normalization and the U.S. Geological Survey standard BHVO‐1 as the magma standard. This removes the ash dilution effect obtained by using an ash constituent (Al, Sc, or Mg) as the reference element. Bromine‐normalized EFs (× 105) range from 101 to 102 for Na, K, and Cu; 102 to 105 for Zn, W, Sb, In, Ir, Ag, F, and As; and &gt; 105 for Au, Cd, Re, Cl, Se, and S. The highest enrichment factors are for aircraft samples collected during the most gas‐rich phase of an eruption cycle. Metal and volatile‐element data form two groups: (1) elements showing little or no variation in abundance ratios with sample type (group 1: Cl, Br, and Re) and (2) elements that show significant variation in abundance ratios by sample type (group 2: Zn, W, Sb, In, Ir, Au, and Cd). Bivariate plots of elements of the first group versus elements of the second group separate by sample type. The separation corresponds to samples collected during eruptive activity versus samples collected during repose periods. Monitoring trace metal ratios in volcanic fume could provide an additional tool for predicting volcanic eruptions. The F/Cl ratio of cooling vent samples is higher than those of active vent or aircraft samples, and the ratio is inversely correlated with EFs for most volatile metals.