Labile Trace Elements Research Articles

Landscape, Soil, Lithology, Climate and Permafrost Control on Dissolved Carbon, Major and Trace Elements in the Ob River, Western Siberia

In order to foresee possible changes in the elementary composition of Arctic river waters, complex studies with extensive spatial coverage, including gradients in climate and landscape parameters, are needed. Here, we used the unique position of the Ob River, draining through the vast partially frozen peatlands of the western Siberia Lowland and encompassing a sizable gradient of climate, permafrost, vegetation, soils and Quaternary deposits, to assess a snap-shot (8–23 July 2016) concentration of all major and trace elements in the main stem (~3000 km transect from the Tom River confluence in the south to Salekhard in the north) and its 11 tributaries. During the studied period, corresponding to the end of the spring flood-summer baseflow, there was a systematic decrease, from the south to the north, of Dissolved Inorganic Carbon (DIC), Specific Conductivity, Ca and some labile trace elements (Mo, W and U). In contrast, Dissolved Organic Carbon (DOC), Fe, P, divalent metals (Mn, Ni, Cu, Co and Pb) and low mobile trace elements (Y, Nb, REEs, Ti, Zr, Hf and Th) sizably increased their concentration northward. The observed latitudinal pattern in element concentrations can be explained by progressive disconnection of groundwaters from the main river and its tributaries due to a northward increase in the permafrost coverage. A northward increase in bog versus forest coverage and an increase in DOC and Fe export enhanced the mobilization of insoluble, low mobile elements which were present in organo-ferric colloids (1 kDa—0.45 µm), as confirmed by an in-situ dialysis size fractionation procedure. The chemical composition of the sampled mainstream and tributaries demonstrated significant (p < 0.01) control of latitude of the sampling point; permafrost coverage; proportion of bogs, lakes and floodplain coverage and lacustrine and fluvio-glacial Quaternary deposits of the watershed. This impact was mostly pronounced on DOC, Fe, P, divalent metals (Mn, Co, Ni, Cu and Pb), Rb and low mobile lithogenic trace elements (Al, Ti, Cr, Y, Zr, Nb, REEs, Hf and Th). The pH and concentrations of soluble, highly mobile elements (DIC, SO4, Ca, Sr, Ba, Mo, Sb, W and U) positively correlated with the proportion of forest, loesses, eluvial, eolian, and fluvial Quaternary deposits on the watershed. Consistent with these correlations, a Principal Component Analysis demonstrated two main factors explaining the variability of major and trace element concentration in the Ob River main stem and tributaries. The DOC, Fe, divalent metals and trivalent and tetravalent trace elements were presumably controlled by a northward increase in permafrost, floodplain, bogs, lakes and lacustrine deposits on the watersheds. The DIC and labile alkaline-earth metals, oxyanions (Mo, Sb and W) and U were impacted by southward-dominating forest coverage, loesses and eluvial and fertile soils. Assuming that climate warming in the WSL will lead to a northward shift of the forest and permafrost boundaries, a “substituting space for time” approach predicts a future increase in the concentration of DIC and labile major and trace elements and a decrease of the transport of DOC and low soluble trace metals in the form of colloids in the main stem of the Ob River. Overall, seasonally-resolved transect studies of large riverine systems of western Siberia are needed to assess the hydrochemical response of this environmentally-important territory to on-going climate change.

Observation of the deep Indonesian throughflow using helium isotopes

Helium isotopes in the ocean are very useful tracers of hydrothermal input and deep-sea circulation. Unlike labile trace elements, noble gases are inert and do not react with other substances in the water column. Previous studies in the Indian Ocean showed that helium isotopes in the region were discharged mainly from the central Indian midocean ridge, convergent boundaries, and the Pacific Ocean via currents that flow through the Indonesian archipelago. These Indonesian waters then exit out as the Indonesian Throughflow (ITF) into the Indian Ocean through shallow sills. The ITF plays a significant role in global climate, because it serves as the main pathway of thermocline waters between the Pacific Ocean and Indian Ocean. We present new helium isotope data from International Indian Ocean Expedition (IIOE-2) at the east Indian Ocean in December 2018. Helium isotopes were measured using a Noble Gas Mass Spectrometer at the Atmosphere and Ocean Research Institute, The University of Tokyo. We compare our data with those from previous expeditions and discuss the source and distribution of helium isotopes near Java. Waters with high excess 3He from the ITF were observed at 1000 m. Application of two-components mixing model enabled us to estimate ITF fraction in the observed area and to clarify the ITF flow in the deep layer. Moreover, flow rate of the deep ITF from Savu sill to Indian Ocean was estimated to be ~ 0.8–1.6 Sv. Based on stations near the Java coast, there could be a deep current or hydrothermal source at 3000 m that advects water enriched in 3He southwards along the Java Island.

Sub-millimeter distribution of labile trace element fluxes in the rhizosphere explains differential effects of soil liming on cadmium and zinc uptake in maize

Trace element concentrations in the rhizosphere were quantified to better understand why soil liming often fails to reduce cadmium (Cd) uptake by plants. Maize seedlings were grown on a soil with natural background levels of Cd and zinc (Zn). Soil liming increased soil pH from 4.9 to 6.5 and lowered the soil solution free ion activities by factor 7 (Cd) and 9 (Zn). In contrast, shoot Cd concentrations were unaffected by liming while shoot Zn concentrations were lowered by factor 1.9. Mapping of labile soil trace elements using diffusive gradients in thin films (DGT) in combination with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) revealed an almost complete depletion of Cd in the rhizosphere in all soil treatments, showing that Cd uptake is controlled by diffusion. The flux of Cd from soil to the DGT, with direct contact between the soil and the binding gel, was unaffected by liming whereas it decreased by factor 3 for Zn, closely mimicking the contrasting effects of liming on Cd and Zn bioavailability. This evidence, combined with additional flux data of freshly spiked Cd and Zn isotopes in soil and with modelling, suggests that the diffusive transport of Cd in unsaturated soil is more strongly controlled by the labile adsorbed metal concentration than by its concentration in solution. This is less the case for Zn because of its inherently slower desorption compared to Cd.

Assessment of the DGT technique in digestate to fraction twelve trace elements

This study proposes an evaluation of the diffusive gradients in thin films technique (DGT) for studying trace elements in digested sewage sludge samples. Twelve elements were monitored by Chelex (Al, Cd, Co, Cr (III), Cu, Fe, Mn, Ni, Pb) and zirconia-DGT (As, Mo, Se) samplers exposed from 4 h to 9 days. Twenty-four hours’ deployment time was suitable for most of the studied elements. However, short deployment led to insufficient element accumulation or non-establishment of steady state while long deployment (from 18 to 144 h depending on the element) led to saturation of the binding gels and/or competing effects with other major elements. In addition, this study showed that the matrix of the digested sewage sludge lowers the accumulation of some trace elements in the DGT samplers, leading to labile concentrations underestimation of roughly 10–30% (depending on the element). Moreover, compared to the conventional total dissolved elements measurement, DGT technique allowed to quantify 7 out of 12 labile elements whereas only 3 out of 12 dissolved elements were quantified. These results highlight the potential of DGT technique to assess labile trace elements in digestate samples, provided a careful adaptation of the deployment time as well as an evaluation of the matrix effect is performed.

Chemical association and mobility of trace elements in 13 different fuel incineration bottom ashes

The release of trace elements from waste incineration bottom ash is problematic during utilization/landfilling. Thirteen bottom ashes (from various waste fuels and wooden/mixed wooden fuel) were investigated with respect to the total content, leaching behaviour by standard leaching procedure (EN 12457-3), and chemical association of trace elements by sequential extraction. Results showed that the content of trace elements in household/or industrial waste bottom ashes were of high level in comparison to in wooden/mixed wooden fuel/mixed wooden waste ashes. Type of fuel being treated greatly impacts the total inventory of trace elements. On average, trace element content in 13 ashes followed the decreasing order; Cu>Zn>Pb>Cr>Ni>Sb>As. In this study the average total content of Zn, Pb, Cu and Cr was higher in grate bottom ash treating household/industrial waste in comparison to fluidized boilers ash using same waste, however, there were too few data points and variation in data was large. By Standard leaching procedure, an excessive amount (more than disposal limit) of leached Cr, Pb, Sb and Cu (mostly in household/industrial waste ash) was observed in 6, 5, 5 and 4 of the 13 samples, respectively. Correlation coefficients (r) found between total and water leachable contents for Cu, Sb and As were 0.8, 0.7 and 0.6 respectively. Sequential extraction indicated that residual was the major fraction mostly, however, considerable amounts of trace elements had the potential to leach out. A large fraction of arsenic (57% based on average values) in 5 samples (mostly in waste/virgin wood and mixed wooden waste/fuel) and Zn (49% based on average values) in 4 of 13 samples (mostly household/or industrial) were found in the fractions that are easily available (acid soluble and exchangeable). Further, a considerable amount of Cu in 4 samples were found associated with the organic-bound phase. Dissolved organic matter might play an important role in leaching of Cu during utilization/landfilling. Moreover, principal component analysis (PCA) showed that fuel type affects the association of trace elements in bottom ash. Amounts of labile trace elements in wooden/mixed wooden fuel/waste bottom ashes were comparatively lower than other fuel bottom ashes. None of the samples exceeded the limit of disposal with respect to DOC leaching while chlorine in two and sulphate in three samples (household/industrial) exceeded limit. LOI (550°C) values were higher for bottom ash from grate facilities probably due to no-pre-treatment of the waste fuel. While comparatively low values of LOI (1000°C) in few samples implies that the oxidation might have outweighed the loss of carbonates.

Effect of organic fertilizers on soil organic carbon and risk trace elements content in soil under permanent grassland

Karabcova H., Pospisilova L., Fiala K., Skarpa P., Bjelkova M. (2015): Effect of organic fertilizers on soil organic carbon and risk trace elements content in soil under permanent grassland. Soil & Water Res., 10: 228–235. The effect of different kinds of organic matter inputs on elemental composition, content, and quality of humic sub stances was studied on permanent grassland during 2008–2013. The experiment included two organic fertilizer types – compost and slurry, both with the range of stocking rates 0.9, 1.4, and 2.0 livestock units (LU)/ha (corresponding to 54, 84, and 120 kg N/ha, respectively), and control without any fertilizer. The soil was sandy-loam, of Cambisol type, with semi natural permanent grassland. Labile forms and total contents of selected trace elements (Co, Cu, Zn, Cd) and macroelements (Ca, Mg, K, P, and N) were measured. Soil organic matter parameters such as total organic carbon (C ox ), humic substances (HS), humic acid (HA), fluvic acid (FA), and labile carbon forms ( hot-water extractable carbon ( C hws ), cold water extractable carbon ( C cws )) were determined. Results showed that the greatest content of P, Ca, Mg, and N in the soil was detected by the CO 2.0 treatment. Furthermore, the positive effect of compost on C ox , C hws , HA, FA, HS, N and macronutrients was observed. The elemental analysis of humic acids showed lower carbon content and higher oxygen content in HA molecule, which indicated young humic acids, with a lower condensation degree. The content and quality of humic substances strongly influenced the total and labile trace elements content in the soil. Additionally, hot water soluble carbon significantly correlated with plant available forms of Zn, Cu, and Cd.

Assessment of trace element phytoavailability in compost amended soils using different methodologies

This study evaluates the effects of two soil amendments and the growth of two plant species on labile trace element (TE) fractions in two different contaminated soils. We studied the effects of two organic amendments (biosolid compost and alperujo compost) and two plant species (Medicago polymorpha and Poa annua) on pH, total organic carbon (TOC), and TE availability, by three extraction methods (CaCl2 aqueous solution, soil pore water (SPW), and diffusive gradient in thin film (DGT)), in two contaminated soils with contrasting pH values (Aznalcazar, 6.53, and Vicario, 3.48) in a 118-day pot experiment. The effects of the composts on labile TE fractions were compared with element concentrations in plants. No relevant effects of amendments and plants were found on the physical and chemical characteristics of the Aznalcazar soil. However, the addition of amendments was essential for plant species growing in the acid Vicario soil. In this soil, amendments and plant growth increased pH and TOC and reduced substantially TE bioavailability. Although absolute values of bioavailable TE contents obtained by the three methods were very different and followed the trend CaCl2 extraction > SPW > DGT, these values follow a similar behavior in the two studied soils and for the two species. The results demonstrate that the application of organic amendments are suitable for remediating acid TE-contaminated soils, for the establishment of a vegetation cover on previously bare soils for reducing wind and water erosion and for reducing labile TE fractions to prevent leaching of pollutants into subsoil or groundwater layers. Moreover, the results obtained in this study pointed out that under microcosm conditions, the three methods tested (CaCl2 extraction, SPW, and DGT) to predict TE bioavailability were highly correlated.

Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice.

In wetland-adapted plants, such as rice, it is typically root apexes, sites of rapid entry for water/nutrients, where radial oxygen losses (ROLs) are highest. Nutrient/toxic metal uptake therefore largely occurs through oxidized zones and pH microgradients. However, the processes controlling the acquisition of trace elements in rice have been difficult to explore experimentally because of a lack of techniques for simultaneously measuring labile trace elements and O2/pH. Here, we use new diffusive gradients in thin films (DGT)/planar optode sandwich sensors deployed in situ on rice roots to demonstrate a new geochemical niche of greatly enhanced As, Pb, and Fe(II) mobilization into solution immediately adjacent to the root tips characterized by O2 enrichment and low pH. Fe(II) mobilization was congruent to that of the peripheral edge of the aerobic root zone, demonstrating that the Fe(II) mobilization maximum only developed in a narrow O2 range as the oxidation front penetrates the reducing soil. The Fe flux to the DGT resin at the root apexes was 3-fold higher than the anaerobic bulk soil and 27 times greater than the aerobic rooting zone. These results provide new evidence for the importance of coupled diffusion and oxidation of Fe in modulating trace metal solubilization, dispersion, and plant uptake.

Petrographic, chemical and spectroscopic evidence for thermal metamorphism in carbonaceous chondrites I: CI and CM chondrites

We present a comprehensive description of petrologic, chemical and spectroscopic features of thermally metamorphosed CI-like and CM (and CM-like) chondrites. Only two such CI chondrites have so far been discovered i.e. Y-86029 and Y-82162. Thermal metamorphism in these chondrites is apparent in their low contents of H2O, C and the most thermally labile trace elements, partial dehydration of matrix phyllosilicates and abundance of thermally decomposed Ca–Mg–Fe–Mn carbonates, which apparently resulted from heating of Mg–Fe carbonate precursors.The CM chondrites exhibit a wide range of aqueous and thermal alteration characteristics. This alteration was almost complete in Y-86720 and Y-86789, which also escaped alternating episodes of oxidation and sulfidization experienced by the others. Thermal metamorphism in the CM chondrites is apparent in loss of thermally labile trace elements and also in partial to almost complete dehydration of matrix phyllosilicates: heating was less uniform in them than in CI chondrites. This dehydration is also evident in strength and shapes of integrated intensities of the 3μm bands except in PCA 91008, which experienced extensive terrestrial weathering. Tochilinite is absent in all but Y-793321 probably due to heating. Textural evidence for thermal metamorphism is conspicuous in blurring or integration/fusion of chondrules with matrix in the more extensively heated (⩾600°C) CM chondrites like PCA 91008 and B-7904. TEM and XRD analyses reveal that phyllosilicate transformation to anhydrous phases proceeds via poorly crystalline, highly desiccated and disordered ‘intermediate’ phases in the least and moderately heated (400–600°C) carbonaceous chondrites like WIS 91600, PCA 91008 and Y-86029. These findings are significant in that they confirm that these phases occur in meteorites as well as terrestrial samples.Thermal alteration in these meteorites can be used to identify other carbonaceous chondrites that were thermally metamorphosed in their parent bodies. Combining RNAA trace element data for experimentally heated Murchison CM2 samples with petrographic and spectroscopic data, these thermally metamorphosed carbonaceous chondrites can be ordered by severity of open system heating as 400°C⩽Y-793321<WIS91600=EET90043=A881655<PCA91008<B-7904=Y-86029<Y-82162<Y-86720=Y-86789⩾700°C. Nearly all heated carbonaceous chondrites discovered so far have been found in Antarctica, which is known to have sampled the flux of near-Earth material for much longer than exemplified by current falls.

H/L chondrite LaPaz Icefield 031047 – A feather of Icarus?

Antarctic meteorite LAP 031047 is an ordinary chondrite composed of loosely consolidated chondritic fragments. Its petrography, oxygen isotopic composition and geochemical inventory are ambiguous and indicate an intermediate character between H and L chondrites. Petrographic indicators suggest LAP 031047 suffered a shock metamorphic overprint below ∼10 GPa, which did not destroy its unusually high porosity of ∼27 vol%. Metallographic textures in LAP 031047 indicate heating above ∼700 °C and subsequent cooling, which caused massive transformation of taenite to kamacite. The depletion of thermally labile trace elements, the crystallization of chondritic glass to microcrystalline plagioclase of unusual composition, and the occurrence of coarsely crystallized chondrule fragments is further evidence for post-metamorphic heating to ∼700–750 °C. However, this heating event had a transient character because olivine and low-Ca pyroxene did not equilibrate. Nearly complete degassing up to very high temperatures is indicated by the thorough resetting of LAP 031047’s Ar–Ar reservoir ∼100 ± 55 Ma ago. A noble gas cosmic-ray exposure age indicates it was reduced to a meter-size fragment at <0.5 Ma. In light of the fact that shock heating cannot account for the thermal history of LAP 031047 in its entirety, we test the hypothesis that this meteorite belonged to the near-surface of an Aten or Apollo asteroid that underwent heating during orbital passages close to the Sun.

Size-fractionated labile trace elements in the Northwest Pacific and Southern Oceans

Photosynthesis by marine phytoplankton requires bioavailable forms of several trace elements that are found in extremely low concentrations in the open ocean. We have compared the concentration, lability and size distribution (< 1 nm and < 10 nm) of a suite of trace elements that are thought to be limiting to primary productivity as well as a toxic element (Pb) in two High Nutrient Low Chlorophyll (HNLC) regions using a new dynamic speciation technique, Diffusive Gradients in Thin-film (DGT). The labile species trapped within the DGT probes have a size that is smaller or similar than the pore size of algal cell walls and thus present a proxy for bioavailable species. Total Dissolvable trace element concentrations (TD concentration) varied between 0.05 nM (Co) and 4.0 nM (Ni) at K2 (Northwest Pacific Ocean) and between 0.026 nM (Co) and 4.7 nM (Ni) in the Southern Ocean. The smallest size fractionated labile concentrations (< 1 nm) observed at Southern Ocean sampling stations ranged between 0.002 nM (Co) and 2.1 nM (Ni). Moreover, large differences in bioavailable fractions (ratio of labile to TD concentration) were observed between the trace elements. In the Northwest Pacific Ocean Fe, Cu and Mn had lower labile fractions (between 10 and 44%) than Co, Cd, Ni and Pb (between 80 and 100%). In the Southern Ocean a similar trend was observed, and in addition: (1) Co, Cd, Ni and Pb have lower labile fractions in the Southern Ocean than in the Northwest Pacific and (2) the ratios of < 1 nm to dissolvable element concentrations at some Southern Ocean stations were very low and varied between 4 and16%.

Seasonality of particle-associated trace element fluxes in the deep northeast Atlantic Ocean

In the framework of the German contribution to the Joint Global Ocean Flux Study (JGOFS), deep-water fluxes of particle-associated trace elements were measured in the northeast Atlantic Ocean. The sinking particles were collected almost continuously from 1992 to 1996 at three time-series stations, L1 (33°N/22°W), L2 (47°N/20°W), and L3 (54°N/21°W), using sediment traps. The focus of the present study is the temporal variability of the particle-associated elemental fluxes of Al, Ca, Cd, Co, Cu, Fe, Mn, Ni, P, Pb, Ti, V, and Zn at a depth of 2000 m. A clear seasonality of the fluxes that persisted for several years was documented for the southernmost station (L1) at stable oligotrophic conditions in the area of the North Atlantic Subtropical Gyre East (NASTE). At L2 and L3, an episodic nature of the elemental fluxes was determined. Mesoscale eddies are known to frequently cause temporal and spatial variability in the flux of biogenic components in that area. These events modified the simple seasonal pattern controlled by the annual cycle at L2, in the North Atlantic Drift Region (NADR), and at L3, which was influenced by the Atlantic Arctic province (ARCT). All stations were characterized by an additional episodic lithogenic atmospheric supply reaching the deep sea. The integrated annual fluxes during the multi-year study revealed similar flux magnitudes for lithogenic elements (Al, Co, Fe, Ti, and V) at L2 and L3 and roughly twofold fluxes at L1. Biogenic elements (Cd, P, and Zn) showed the opposite trend, i.e., two to fourfold higher values at L2 and L3 than at L1. For Mn, Ni, and Cu, the spatial differences were smaller, perhaps because of the intermediate behavior, between lithogenic and biogenic, of these elements. Similarly, among the three study sites, there were no noticeable differences in the total annual flux of Pb. The respective lithogenic fractions of the deep-sea fluxes of Cd, Co, Cu, Mn, Ni, V, and Zn were subtracted based on the amount of Al, with the average composition of the continental crust as reference. This procedure allowed estimation of the labile trace element fraction (TE exc) of the particles, i.e., TE taken up or scavenged during particle production and sedimentation. The ratios of TE exc/P clearly demonstrated an enrichment of TE over labile P from biogenic surface material to the deep sea for Zn (factor 4–6), Mn (12–27), Ni (3–5), and Cu (9–25); an intermediate status for Co (0.5–2.2); and depletion for Cd vs. P (0.2–0.4). Surprisingly, the recycling behavior of excess Co was found to be similar to that of P. Hence, Co exc behaved like a biogenic element; this is in contrast to total Co, which is dominated by the refractory lithogenic fraction. Moreover, it is argued that these excess elemental fluxes caused a loss of the dissolved elements in upper waters, since their transport reaches the deep-sea waters at 2000 m, a depth far below of deep-winter mixing and upwelling. The annual amount of excess TE exported from surface waters was estimated to be 1.3×10 9 mol Zn y −1, 4.4×10 9 mol Mn y −1, 4.9×10 8 mol Ni y −1, 2.2×10 7 mol Cd y −1, 7.4×10 8 mol Cu y −1, and 2.7×10 7 mol Co y −1 for the whole North Atlantic Ocean. Important primary sources that could replenish these losses are the aeolian and fluvial supply processes.

Labile trace elements in basaltic achondrites: Can they distinguish between meteorites from the Moon, Mars, and V‐type asteroids?

Abstract— We report data for 14 mainly labile trace elements (Ag, Au, Bi, Cd, Cs, Ga, In, Rb, Sb, Se, Te, Tl, U, and Zn) in eight whole‐rock lunar meteorites (Asuka [A‐] 881757, Dar al Gani [DaG] 262, Elephant Moraine [EET] 87521, Queen Alexandra Range [QUE] 93069, QUE 94269, QUE 94281, Yamato [Y‐] 793169, and Y‐981031), and Martian meteorite (DaG 476) and incorporate these into a comparative study of basaltic meteorites from the Moon, Mars, and V‐type asteroids. Multivariate cluster analysis of data for these elements in 14 lunar, 13 Martian, and 34 howardite, eucrite, and diogenite (HED) meteorites demonstrate that materials from these three parents are distinguishable using these markers of late, low‐temperature episodes. This distinguishability is essentially as complete as that based on markers of high‐temperature igneous processes. Concentrations of these elements in 14 lunar meteorites are essentially lognormally distributed and generally more homogeneous than in Martian and HED meteorites. Mean siderophile and labile element concentrations in the 14 lunar meteorites indicate the presence of a CI‐equivalent micrometeorite admixture of 2.6% When only feldspathic samples are considered, our data show a slightly higher value of 3.4% consistent with an increasing micrometeorite content in regolith samples of higher maturity. Concentrations of labile elements in the 8 feldspathic samples hint at the presence of a fractionated highly labile element component, possibly volcanic in origin, at a level comparable to the micrometeorite component. Apparently, the process(es) that contributed to establishing lunar meteorite siderophile and labile trace element contents occurred in a system open to highly labile element transport.

The Fe/Na ratio, a framework for modelling trace element distributions in Jamaican soils

The trace element geochemistry of Jamaican soils (&lt;150 μm) is extremely variable due to their development on diverse parent materials, varying maturity (ages range from recent to &gt;5 Ma) and the variety of soil-forming processes. It is demonstrated that the Fe/Na ratio of the soils forms a useful quantitative framework for studying trace element distributions. The ratio varies 2.5 orders of magnitude from &lt;2 in newly developed inceptisols to &gt;500 in oxisols and terra rossas that have been developing for &gt;5 Ma. The form of the trace element distributions with respect to Fe/Na ratio may be interpreted in the context of mineralogy of the parent material, removal of labile trace element fractions during soil development, sequestration in stable secondary forms, and ultimate concentration of stable primary resistate and secondary minerals by terra rossa soil formation processes that lead to elevated Fe and Al levels and the depletion of silica and base cations, Ca 2+ , Mg 2+ , Na + and K + . As examples, the distributions of U and As are modelled as functions of the Fe/Na ratio. Use of robust regression procedures identifies individual soil samples that exhibit divergent patterns of trace element concentration. Some of these can be linked to local bedrock sources, while others are more likely related to exotic volcanic ash-fall material from Central America deposited on proto-Jamaica in the late Miocene.

Chemical studies of H chondrites‐10: Contents of thermally labile trace elements are unaffected by late heating

Abstract— We have used radiochemical neutron activation analysis (RNAA) to determine 15 trace elements, including 10 moderately to highly volatile ones—Rb, Ag, Se, Cs, Te, Zn, Cd, Bi, Tl, In (in increasing volatility order), in 6 H chondrite falls with low‐3He contents. These (plus prior RNAA data) provide a compositional database of 92 H4‐6 chondrite falls. Three suites of samples can be identified from their noble gas contents: 44 with “normal” contents and, therefore, “normal” orbits and cosmic‐ray exposure histories; 8 that lost radiogenic gases, presumably by shock late in their histories; and 17 that lost cosmogenic gases by heating during close solar approach. We used the standard multivariate statistical techniques of linear discriminant analysis and logistic regression to compare contents of the 10 moderately and highly volatile trace elements, listed above, in these three suites. We found no significant differences. This contrasts sharply with similar comparisons involving random falls and H4‐6 chondrites that landed on Earth at specific time intervals. Apparently, contents of volatile trace elements in H4‐6 chondrites were established early in their histories, and they are so retentively sited that loss during later heating episodes did not occur.

Acidification Effects on Trace Element Chemistry in Agricultural Evaporation Pond Sediments

Evaporation ponds have been used to dispose of saline agricultural drainage waters in the western San Joaquin Valley of California for approximately 20 yr. Through evaporation, high concentrations of trace elements have accumulated in pond waters, evaporite minerals, and bottom sediments resulting in a toxicity hazard to wildlife. Acidification of pond waters (pH 4-5) is proposed as a means of inhibiting biological productivity, thereby discouraging wildlife from using these ponds as a feeding ground. This investigation uses a pH-stat equilibration (72 h) of pond sediment suspensions to evaluate the effectiveness of sulfuric acid (H 2 SO 4 ) and FeSO 4 as acid sources and the effect of these acid treatments on soluble trace element concentrations at pH 4 and 5. Acid extraction of pond sediments with 1 M HCl showed the following release of potentially labile trace elements: AlFe>>B >Mn>>As,Cu,Mo,Zn>>Se. Titration of brine/sediment suspensions to pH 4.0 showed that the buffering capacity of the brine water and sediments were about equal. During a 72 h pH stat, minor acid additions were required to maintain the target pH of 4.0. Relative to non-acidified controls, soluble trace element concentrations in the pH 4 H 2 SO 4 treatment increased for Fe, Mn, Al, Zn, B, and As, remained constant for Cu, Se, and Zn, and decreased for Mo. Similar results were shown for the FeSO 4 treatment at pH 4 with the exception of small increases for Cu and Zn and a decrease of Se. The effect of a brine matrix on trace element release/retention showed only minor differences compared to deionized water. The FeSO 4 treatment was the most effective acidifying agent and resulted in the lowest soluble concentrations of the most potentially hazardous trace elements (As, Mo, and Se).

Chemical studies of H chondrites — 7. Contents of Fe3+ and labile trace elements in Antarctic samples

Abstract— Linear discriminant analysis and logistic regression have been applied to concentration data for 10 labile trace elements (Rb, Ag, Se, Cs, Te, Zn, Cd, Bi, Tl and In) in 33 Antarctic H4–6 chondrites. The proportion of bulk Fe in the Fe3+ state, Fe3+/Fe, of these same chondrites permit their assignment to less‐ and more‐weathered suites. Wherever the division between these suites is placed, the results are identical and consistent with the null hypothesis that the suites sample a single preterrestrial compositional population. Hence, no evidence exists that preterrestrial contents of labile trace elements in Antarctic H4–6 chondrites have been significantly altered by weathering as quantified by Fe3+/Fe or the A‐B‐C weathering index.

Meteoroid streams: Evidence from meteorites recovered on Earth

The flux of small meteoroids, originating primarily from comets, consists of sporadic, random objects and others whose orbits are related. Here, we summarize data relevant to the question of whether the flux of large meteoroids of asteroidal origin (recoverable as meteorites) also consists of objects with random orbits, as well as coorbital objects. After reviewing some relevant properties of planetary materials, applications of two nuclear techniques - radiochemical neutron activation analysis (RNAA) and accelerator mass spectrometry (AMS) - to this question are discussed. Contents of ten thermally labile trace and ultratrace elements determined by RNAA (Ag, Bi, Cd, Cs, In, Rb, Se, Te, Tl, Zn) act as thermometers for thermal metamorphism in parent sources. These data, together with spectral reflectivity information, establish the nature of surfaces on abundant C-, G-, B- and F-class asteroids. Data for these ten cosmothermometers in H4-6 type ordinary chondrites, when treated by multivariate statistical techniques, demonstrate that a suite chosen by one set of criteria (the circumstances of their fall in May, between 1855 and 1895) is distinguishable by another set, i.e. compositionally, from all other such falls analyzed. Hence, this suite, H Cluster 1, has an average thermal history distinguishable from those of all other falls, demonstrating that near-Earth source regions for H chondrite falls changes rapidly. AMS measurements of cosmogenic36Cl (301 kyr half-life), quantify nominal terrestrial ages for Antarctic H chondrites whose contents of thermometric trace elements were also established by RNAA. While multivariate statistical analysis of RNAA data from Antarctic H chondrites with nominal terrestrial ages ≤50 kyr are not distinguishable from those of falls, older Antarctic H chondrites are compositionally distinguishable from falls. Assertions that these highly significant compositional differences reflect terrestrial or methodologic causes are refutable. This result argues that near-Earth source regions of H chondrites have changed over a long time, as well. Thus, the Earth receives a highly biased sampling of planetary objects in the Solar System in any one time-period.

An H chondrite stream: Identification and confirmation

Fall data indicate that a significant, elongate cluster of co‐orbital H chondrite falls in May between 1855 and 1895 (H Cluster 1) records encounters with two or three closely spaced and probably related meteoroid stream components, each of which was met near its perihelion. Although meteorites included in the Cluster vary widely in petrographic type (3–6), shock facies (a‐d), and 21Ne exposure age (&lt;5 to 50 Ma), they have a distinct labile trace element signature that confirms a common thermal history and, thus, a common source region within an H chondrite parent body. Hence, meteorites selected by one criterion (fall parameters) as distinguishable from all other H chondrites, are distinguished from them by another completely different criterion (contents of labile trace elements).

Chemical studies of differentiated meteorites: I. Labile trace elements in Antarctic and non-Antarctic eucrites

We report data for Ag, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Sb, Se, Te, Tl, U, and Zn determined by RNAA in 25 Antarctic and 9 non-Antarctic eucrites (including the cumulate eucrites Moore Co. and Serra de Magé). Compositional variations for a given element in a population range from <10% for Ga to ~200× for Ag, Au, Bi, In, or Tl. Highly incompatible, refractory elements like U are well known to exceed Cl levels in eucrites because of their igneous origin. Surprisingly, contents of highly labile elements can also be quite high, sometimes at 0.1 × Cl, I.E., levels more like chondritic. However, a carbonaceous chondrite pattern (the most likely admixture possibility) is not apparent since Cl-normalized trace element data for a given eucrite sample do not match the flat trends known for carbonaceous chondrites. The Unormalized contents of most elements indicate a thermal (vapor/solid) process accompanied in the case of lithophiles Rb and Cs by a geochemical fractionation. For these, or Ag, Bi, Cd, or Tl (elements with ionic radii and charges resembling those of incompatible elements), Antarctic and non-Antarctic noncumulate eucrites lie on the same trend line, indicating that all derive from the same parent. The thermal process responsible for the U-normalized trend could involve devolatilization of eucrite parent material or, as we prefer because of other data, condensation of volcanic emanations to differing degrees on preexisting eucrite (and diogenite and howardite) parent rocks. Antarctic eucrites have different—usually higher—contents of labile elements, particularly Tl, than do non-Antarctic eucrites. The difference seems not to be due to the terrestrial history of the samples but, rather, is preterrestrial in origin. By our preferred scenario, Antarctic eucrites received a greater average complement of mobile elements, hence, were presumably cooler (and nearer the surface of the eucrite parent body) than were non-Antarctic eucrites.