Total Elemental Analysis Research Articles

Biorefinery solid cake waste to biocrude via hydrothermal treatment: optimization of process parameters using statistical approach

Conversion of Pongammia de-oiled seed cake to liquid biofuel at hydrothermal conditions is reported in this work. The main objectives were to identify an approach that would enable us to understand and optimize the relationships between process parameters. In this work, estimation of the optimized conditions for the maximization of two responses namely biocrude yield and transportation grade fuel (TGF) selective has been reported. Plackett–Burman design was used for parameter screening on seven different process parameters for biocrude yield. Further, centre composite design and response surface methodology approach were used to develop the quadratic models to study the effect of individual and combined interactions on the biocrude yield as well as TGF selectivity on four parameters. Quadratic models were modified for the significant (p < 0.05) individual, quadratic, and interaction terms. Based on the statistical results, it is concluded that temperature is the most significant individual parameter for biocrude yield, whereas for TGF selectivity, all four parameters, considered for statistical analysis, are important. Temperature with pressure and temperature with time are the major interaction with p ≤ 0.05 for biocrude yield. In the case of TGF selectivity, temperature and pressure are the only significant interaction. Superimposed contour plots and predicted model confirmed 400 °C (temperature), 25 kg/cm2 (pressure), 35 min (reaction time) and 2 W/B ratio as optimal conditions for the maximum biocrude yield (~38.9 %) and TGF selectivity (~29.6 %). Verification experiments confirmed the validity of the predicted model. The predicted and experimentally obtained yields for biocrude and TGF selectivity were comparable with an error of ±12.5 and ±8.5 %, respectively. TGF fraction obtained at these conditions was characterized by silica gel adsorption chromatography, calorific value, total acidic number elemental composition and FTIR analysis, which showed a high percentage of oxygenated compounds.

Pretreatment and Integrated Analysis of Spectral Data Reveal Seaweed Similarities Based on Chemical Diversity

Extracting useful information from high dimensionality and large data sets is a major challenge for data-driven approaches. The present study was aimed at developing novel integrated analytical strategies for comprehensively characterizing seaweed similarities based on chemical diversity. The chemical compositions of 107 seaweed and 2 seagrass samples were analyzed using multiple techniques, including Fourier transform infrared (FT-IR) and solid- and solution-state nuclear magnetic resonance (NMR) spectroscopy, thermogravimetry-differential thermal analysis (TG-DTA), inductively coupled plasma-optical emission spectrometry (ICP-OES), CHNS/O total elemental analysis, and isotope ratio mass spectrometry (IR-MS). The spectral data were preprocessed using non-negative matrix factorization (NMF) and NMF combined with multivariate curve resolution-alternating least-squares (MCR-ALS) methods in order to separate individual component information from the overlapping and/or broad spectral peaks. Integrated analysis of the preprocessed chemical data demonstrated distinct discrimination of differential seaweed species. Further network analysis revealed a close correlation between the heavy metal elements and characteristic components of brown algae, such as cellulose, alginic acid, and sulfated mucopolysaccharides, providing a componential basis for its metal-sorbing potential. These results suggest that this integrated analytical strategy is useful for extracting and identifying the chemical characteristics of diverse seaweeds based on large chemical data sets, particularly complicated overlapping spectral data.

Recent Advances in the Measurement of Arsenic, Cadmium, and Mercury in Rice and Other Foods.

Trace element analysis of foods is of increasing importance because of raised consumer awareness and the need to evaluate and establish regulatory guidelines for toxic trace metals and metalloids. This paper reviews recent advances in the analysis of trace elements in food, including challenges, state-of-the-art methods, and use of spatially resolved techniques for localizing the distribution of arsenic and mercury within rice grains. Total elemental analysis of foods is relatively well-established, but the push for ever lower detection limits requires that methods be robust from potential matrix interferences, which can be particularly severe for food. Inductively coupled plasma mass spectrometry (ICP-MS) is the method of choice, allowing for multi-element and highly sensitive analyses. For arsenic, speciation analysis is necessary because the inorganic forms are more likely to be subject to regulatory limits. Chromatographic techniques coupled to ICP-MS are most often used for arsenic speciation, and a range of methods now exist for a variety of different arsenic species in different food matrices. Speciation and spatial analysis of foods, especially rice, can also be achieved with synchrotron techniques. Sensitive analytical techniques and methodological advances provide robust methods for the assessment of several metals in animal- and plant-based foods, particularly for arsenic, cadmium, and mercury in rice and arsenic speciation in foodstuffs.

Metallomics and NMR-based metabolomics of Chlorella sp. reveal the synergistic role of copper and cadmium in multi-metal toxicity and oxidative stress.

Industrial wastewaters often contain high levels of metal mixtures, in which metal mixtures may have synergistic or antagonistic effects on aquatic organisms. A combination of metallomics and nuclear magnetic resonance spectroscopy (NMR)-based metabolomics was employed to understand the consequences of multi-metal systems (Cu, Cd, Pb) on freshwater microalgae. Morphological characterization, cell viability and chlorophyll a determination of metal-spiked Chlorella sp. suggested synergistic effects of Cu and Cd on growth inhibition and toxicity. While Pb has no apparent effect on Chlorella sp. metabolome, a substantial decrease of sucrose, amino acid content and glycerophospholipid precursors in Cu-spiked microalgae revealed Cu-induced oxidative stress. Addition of Cd to Cu-spiked cultures induced more drastic metabolic perturbations, hence we confirmed that Cu and Cd synergistically influenced photosynthesis inhibition, oxidative stress and membrane degradation. Total elemental analysis revealed a significant decrease in K, and an increase in Na, Mg, Zn and Mn concentrations in Cu-spiked cultures. This indicated that Cu is more toxic to Chlorella sp. as compared to Cd or Pb, and the combination of Cu and Cd has a strong synergistic effect on Chlorella sp. oxidative stress induction. Oxidative stress is confirmed by liquid chromatography tandem mass spectrometry analysis, which demonstrated a drastic decrease in the GSH/GSSG ratio solely in Cu-spiked cultures. Interestingly, we observed Cu-facilitated Cd and Pb bioconcentration in Chlorella sp. The absence of phytochelatins and an increment of extracellular polymeric substances (EPS) yields in Cu-spiked cultures suggested that the mode of bioconcentration of Cd and Pb is through adsorption of free metals onto the algal EPS rather than intracellular chelation to phytochelatins.

The Study of Phosphate Rock Forming Minerals (Francolite) of Iran through the EDX-SEM to Assessment of Compositions in Nano-scale

In this work, the fine grains of Phosphate rocks forming minerals (francolite-Ca5(PO4,CO3)3F,OH) which belong to the geological formation of phosphate rocks of Zagros mountains in IRAN were detected, analyzed and interpreted by SEM-EDX in nano-scale. Moreover, the results are compared with the results of XRD analysis and straight observations of samples through the polarized microscope. Finding the composition of elements in minerals is the best path finder and also is very important in many geological investigations. The fine grain Phosphate minerals perform as traps which attract some kinds of elements. But sometimes these minerals are very fine and it is too difficult to determine and separate them for further studies. For instance, interpretation and investigation of the composition of fine minerals in Nano-scale by using single crystal X-ray Diffraction (Single-crystal XRD) analysis is impossible. Due to variety of minerals phases in a rock sample, the interpretations of the results of total elemental analysis, for example XRF, ICP, are not so real. Therefore, the best method for determination of elements in fine grain rock forming minerals is the study of minerals by the Scanning Electron Microscopy (SEM), with Energy Dispersive X-Ray Analysis (EDX).

Elemental and mineral composition of salts from selected natural and mine-affected areas in the Poopó and Uru-Uru lakes (Bolivia)

The environmental effects of extensive mineral extractions have been the focus of recent remediation efforts in the Poopó and Uru-Uru lakes (Bolivia). Our study determined the chemical and mineral composition of salt and water samples collected in mine areas (MA) and natural sites [basin and lakes (BL), Salar de Uyuni (SU)] in the Oruro mining district. The laboratory techniques that we used included X-ray diffraction, scanning electron microscopy and total elemental analysis. Results revealed that salt samples in SU sites were dominated by halite, while thenardite, halite and konyaite were observed in BL. Sites in MA had >15 species of sulphates, oxides, hydroxides and other minerals. Metals such as Au, Ba, Cd, Co, Cr, Cu, Li, Ni, Pb, Sn, Sc, and Zn were elevated in salt samples in MA sites compared to BL and SU sites. Salts in MA sites had lower pH (3.2) than BL (pH=9.6) and SU (pH=8.0). In MA sites, dissolution of minerals during the rainy season may mobilize metals from terrestrial (e.g., tailing deposits) to aquatic environments. We can conclude that mining activities combined with some natural metal mobilization events such as dissolution of salt efflorescence on rainy days and oxidation of pyrites may degrade the quality of water and land in the region.

Nutrient Analysis, Decomposition, and Nitrogen Mineralization of Various Organic Amendments Used for Pechay Production

Farmers are increasingly using alternative fertilizer inputs such as manures and composts due to the high cost of inorganic fertilizers. However, different organic amendments have varied characteristics and thus also their effects on soil properties and the growth and yield of crops. The study was conducted to determine the characteristics and nutrient content of organic amendments, evaluate the decomposition rate and nitrogen mineralization rate of the various organic amendments, and examine the effects of different organic amendments on pechay. Four organic amendments used include swine manure, chicken dung, mudpress, and vermicast. These were analyzed for total elemental analysis, microbial decomposition, and nitrogen mineralization rate. A pot experiment was carried out to test the effects of these amendments on the growth and yield of pechay. Results showed that organic amended soil significantly increased the rates of microbial decomposition and nitrogen mineralization, organic material content, and the growth and yield of pechay. In terms of total elemental analysis, chicken dung had the highest content of essential nutrients such as P, K, Ca, and Cl as compared to mudpress, vermicast, swine manure, hence, has good potential as source of organic fertilizer for vegetable production. High amounts of heavy metals such as lead, strontium, nickel, copper, and zinc were detected in the swine manure.

Pedogenesis, weathering status and mineralogy of the soils on ironstone plateaux (laterites), Sokoto Nigeria

Soils on four ironstone plateau near kalalawa, Adarawa, Bissalam and Tureta in Sokoto State were studied with the aim of a ascertaining their genesis, weathering status and soil mineral content. Morphological studies, total elemental analysis and X-ray diffraction were conducted for this purpose. The soils were found to have formed on weathered geological materials overlain by indurated ironstone crust. The geological weathered materials are Gwandu/kalambaina, Gwandu, Dange/Wurno and Gundumi formation on kalambaina, Adarawa, Bissalam and Tureta ironstone plateau respectively. The soils have good structural development and pronounced textural differentiation. The soils are well developed in terms of pedogenic processes (humification, mineralization, lessivation, homogenization and leaching) that have operated and are still operating to form the soils. Result of the silt/clay ratio, sesquioxide ratio and total Potassium, revealed a low weathering potential of the soils making them moderately weathered soils. The dominant mineral identified in the soils is quartz with kaolinite, feldspar and chlorite in trace amounts.

The Concentration and Partitioning of Heavy Metals in Surface Sediments of the Maharlu Lake, SW Iran

In this study, an assessment is made of the environmental impacts of heavy metal concentration and fractionation in bed sediments of the saline Maharlu Lake, SW Iran. Total elemental analysis indicated that sediments were highly enriched in Pb and Cd. Sequential extraction analysis revealed that salt of the lake is probably highly contaminated with Cd, Pb, and Co. Due to the oxidizing conditions of the lake, the organic matter fraction of the elements was not significant. In all sediments, Cd, Pb, Co, Mn, and Zn were strongly associated with exchangeable plus carbonate fractions, with mean percentage of 76.4%, 65.3%, 56%, 40.9%, and 34.3%, respectively. On average, the percentage of Ni associated with the sum of the exchangeable and carbonate fractions was 19.8%. Cr, Fe, and Cu fractionation indicated that these metals are environmentally inert and immobile. Statistical relationships among metal fractions and sediment properties showed that Cd, Pb, Zn, Ni, Co, and Mn were mainly from recent anthropogenic sources, while such sources were less important for Cr, Cu, and Fe. The latter metals represented natural geochemical levels.

Sulfur, sulfides, oxides and organic matter aggregated in submarine hydrothermal plumes at 9°50′N East Pacific Rise

Deep-sea hydrothermal plume particles are known to sequester seawater trace elements and influence ocean-scale biogeochemical budgets. The relative importance of biotic versus abiotic oxidation–reduction and other particle-forming reaction, however, and the mechanisms of seawater trace element sequestration remain unknown. Suspended particulate material was collected from a non-buoyant hydrothermal plume by in situ filtration at 9°50′N East Pacific Rise during a 3-day, 24 sample, time-series. Twenty-three samples were digested for total elemental analysis. One representative sample was selected for particle-by-particle geochemical analyses including elemental composition by X-ray fluorescence, speciation of Fe, S, and C by 1s X-ray absorption near edge structure spectroscopy, and X-ray diffraction. Consistent with past studies, positive linear correlations were observed for P, V, As, and Cr with Fe in the bulk chemistry. Arsenic was associated with both Fe oxyhydroxides and sulfides but not uniformly distributed among either mineral type. Particle aggregation was common. Aggregates were composed of minerals embedded in an organic matrix; the minerals ranged from <20nm to >10μm in diameter. The speciation of major mineral forming elements (Fe, Mn, S) was complex. Over 20 different minerals were observed, nine of which were either unpredicted by thermodynamic modeling or had no close match in the thermodynamic database. Sulfur-bearing phases consisted of polysulfides (S6, S8), and metal sulfides (Fe, Cu, Zn, Mn). Four dominant species, Fe oxyhydroxide, Fe monosulfide, pyrrhotite, and pyrite, accounted for >80% of the Fe present. Particulate Mn was prevalent in both oxidized and reduced minerals. The organic matrix was: (1) always associated with minerals, (2) composed of biomolecules, and (3) rich in S. Possible sources of this S-rich organic matter include entrained near vent biomass and in situ production by S-oxidizing microorganisms. These results indicate that particle aggregation with organic material is prevalent in dispersing hydrothermal plume fluxes, as well as in sinking particulate matter at this site. Particle aggregation and organic coatings can influence the reactivity, transport, and residence time of hydrothermal particles in the water column. Thus a biogeochemical approach is critical to understanding the net effect of hydrothermal fluxes on ocean and sedimentary trace element budgets.

Comparison of Wet-Digestion and Dry-Ashing Methods for Total Elemental Analysis of Biochar

Total elemental analyses of biochars presents challenges during digestion because of biochars' high chemical recalcitrance and widely varied composition. Three biochars were chosen with contrasting properties: corn stover pyrolyzed at 300 °C, oak wood at 600 °C, and poultry manure with sawdust at 600 °C. Recovery of phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), and zinc (Zn) from poultry manure biochar was 10 to 100 times less with published wet- or dry-digestion methods than when using improved methods. The published dry-digestion method returned significantly (P < 0.05) more sodium (Na), suggesting contamination from borosilicate glassware. A modified dry-ashing (MDA) method was the most precise method, demonstrating a relative standard deviation within 3.7% of the most precise method for recovery of P, K, S, Ca, Mg, and Zn from both corn and oak biochars. The MDA method is comparatively safe and effective for preparing biochar for elemental analysis.

Detection of metals and metalloproteins in the plasma of stroke patients by mass spectrometry methods

Stroke is the leading cause of adult disability, worldwide. Metalloproteins and metals play key roles in epigenetic events in living organisms, including hypertension, the most important modifiable risk factor for stroke. Thus, metalloproteins may be important target biomarkers for disease diagnosis. The primary goal of this study was to assess metal containing proteins in blood plasma, detected by ICP-MS, followed by ESIMS for peptide/protein identification. We then compared the relative concentration differences between samples from patients with ischemic stroke, hemorrhagic stroke and stroke mimics. In 29 plasma samples (10 stroke mimics, 10 ischemic stroke and 9 hemorrhagic stroke patients) previously collected from patients who presented to the University of Cincinnati Emergency Department within 12 hours of symptom onset for a plasma banking project. For the metal associated protein study, Mg, Mn, Cu, Se concentrations were statistically different when compared between stroke mimics vs. ischemic stroke patients and ischemic stroke patients vs. hemorrhagic stroke patients. Pb concentrations were statistically different when compared between stroke mimics vs. ischemic stroke patients and Mo levels were statistically the same among the three groups. In addition, we also report concentration levels and preliminary correlation studies for total elemental analysis among the three sets of patients. This pilot study demonstrates that mass spectrometry methods may be highly valuable in detecting novel stroke biomarkers in blood plasma. Expanded studies are warranted to confirm these findings.

TOENAIL ARSENIC CONCENTRATIONS AMONG RESIDENTS OF A COAL MINING AREA OF THE APPALACHIAN MOUNTAINS OF THE UNITED STATES: A PILOT STUDY.

Background and Aims: Arsenic is an established lung carcinogen. Lung cancer rates in the Appalachian region of Kentucky are about twice the national rates in the U.S.A. The high rates of smoking in the area do not explain all the elevation in lung cancer risk. This area is also characterized by extensive coal mining activity. This pilot study explored a comparison of toenail arsenic concentrations in Appalachian Kentucky and another distant region of the state. Methods:Toenail samples were collected for a population - based case-control study in Kentucky. A sub-group of the samples were selected and analyzed for trace elements, based on location of the study participants, who were included if they lived in the East Kentucky Coal counties in Appalachian Kentucky, or in the largest urban center of Jefferson County. For the assessment of population-based exposure, only the controls of the original study were included. Total elemental analyses were performed using inductively-coupled plasma-mass spectrometry. There were a considerable number of samples with arsenic concentrations below the method detection limit, due in part to inadequate sample mass. Therefore, a reverse Kaplan-Meier method was used for the statistical analysis of the left-censored data. Results: A total of 88 toenail samples from Appalachian Kentucky and 155 from Jefferson County were analyzed for arsenic concentrations. The reverse Kaplan-Meier estimation indicated that the arsenic concentrations in the Appalachian counties were significantly higher than in Jefferson (75th and 90th percentiles were 0.13 vs. 0.03 and 0.29 vs. 0.04 ug/g, respectively). Conclusions: The results of this study suggest that residents of the selected Appalachian Kentucky counties with high coal mining activity have higher exposure to arsenic than those in an urban, non-coal mining region of the same state. However, further studies are needed to elucidate the source of the arsenic exposure.

Changes in the Chemical and Mineralogical Properties of Mt. Talang Volcanic Ash in West Sumatra during the Initial Weathering Phase

Eruptions from Talang volcano on 12 April 2005 distributed volcanic ash over portions of the Solok District of West Sumatra, Indonesia. Unleached and leached pristine volcanic ash were collected immediately after the eruption, and the third sample was collected after 2 years. The mineralogy and chemical properties of pristine volcanic ash and volcanic ash deposits that were weathered for 2 years from the 2005 eruption of Mt. Talang, Sumatra, were studied to characterize the volcanic ash, identify the primary minerals present, and determine its chemical properties. Results showed that the volcanic ash contained 30% noncrystalline minerals (or volcanic glass); the remaining ash is composed of crystalline minerals such as labradorite, hypersthene, augite, hornblende, olivine, opaque ferromagnetic minerals, and rock fragments. Notable differences in pH values were observed as the pH tended to become more acidic from the unleached, leached, and weathered volcanic ash, but the ash did not give much response to the sodium fluoride (NaF) test. Total sulfur gradually decreased from 3.28% in unleached ash to 1.93% after 2 years. Available phosphorus (P) in the unleached volcanic ash was 68 mg kg−1, and this value was decreased by 15 % after 2 years of being exposed to the atmosphere, while phosphate retention ranged between 52.8% and 66.8%. Cation exchange capacity (CEC) was low with the value of 10 cmolc kg−1 although base saturation was high, exceeding 75%. The low acid oxalate–extractable silicon (Si), aluminum (Al), and iron (Fe) values of 0.07%, 0.25% and 1.17%, respectively, show the scarcity of secondary amorphous compounds in the ash. Total elemental analysis indicated that no differences were found in total silica oxide (SiO2) content of all samples, with a value about 56%, and this volcanic ash can be classified as basaltic andesite. We observed that removal of chemical elements by leaching was large for calcium oxide (CaO), magnesium oxide (MgO), and sodium oxide (Na2O) as the values decreased in time. Solid-state 29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) studies indicated that Al occurred in both tetrahedral and octahedral forms. Silicon was not present in the tetrahedral layer. An intense peak at −92 ppm was indicative of the presence of aluminosilicates.

Low temperature oxidation of a coking plant soil organic matter and its major constituents: An experimental approach to simulate a long term evolution

In contaminated soils, several natural processes (biodegradation, oxidation, etc.) can induce degradation of organic pollutants. The aim of this work was to evaluate the impact of an abiotic low-temperature oxidation on a coking plant soil and its main organic constituents (coal, coke, coal tar and road asphalts) in order to understand its long term evolution. This natural process was experimentally reproduced by oxidizing the soil and isolated organic matrices at 100 °C during 180 days. The samples were analyzed by total organic carbon measurements and elemental analyses, and the solvent-extractable organic matter was quantified by GC–MS (gas chromatography–mass spectrometry). Oxidation experiments on coal, coal tar and coking plant soil samples lead to the decrease in polycyclic aromatic hydrocarbon (PAH) concentrations correlated to an incorporation of oxygen evidenced by the production of oxygenated PAHs. The increasing amount of polar macromolecules and the decrease in solvent-extractable organic matter suggest a molecular growth through ether/ester cross-linking. The chemical environment of organic compounds and the presence of a reactive mineral fraction are important parameters that improve the efficiency of oxidation. This work reveals that abiotic low temperature oxidation, can strongly contribute to pollutant removal especially by a stabilization process and should be considered in the long term evolution of a soil.

Sand and clay mineralogy of sal forest soils of the Doon Siwalik Himalayas

The peteromineralogical characterization of the soil was carried out for the 12 soil profiles exposed in the Shorea robusta dominated forests of the Siwalik forest division, Dehradun. The quartz was observed as the dominating light mineral fraction (64–80%) in all the profiles studied. Biotite, hornblende, zircon, tourmaline, rutile and opaques comprising of iron minerals constituted the heavy mineral fraction (20%). The mineralogy of both the sand and clay fractions revealed a mixed mineralogy. The clay minerals in the order of their dominance were vermiculite, illite, kaolinite and mixed layer minerals. The presence of vermiculite and illite in appreciable quantities indicates that these were synthesized from the K-rich soil solution, as orthoclase and micas were present in significant quantities in the sand minerals. The mineral suites identified in the study shows that the geological, climatological and topographical factors of the region collectively played a dominant role in their formation and transformation. After critical appraisal of the results, it may be deduced that the mineralogical composition, physicochemical properties and total elemental analysis of the soils do not show any deficiency of the bases and other plant nutrients in general. The inherent fertility of the soil is good as indicated by the sand and clay mineralogy of the soil and the biotite and feldspar together with the mica is an important source of nutrients for the vegetation in the soils of the Doon valley.

Determination of the geochemical weathering indices and trace elements content of new volcanic ash deposits from Mt. Talang (West Sumatra) Indonesia

Since the Indonesian archipelago is part of the very active and dynamic Pacific Ring of Fires, the volcanic eruptions occur from time to time. Immediately after the eruption of Mount Talang in West Sumatra (April 12, 2005), volcanic ashes, both unleached and leached were collected. The deposits from Mt. Talang were andesitic to basaltic in composition. The volcanic ash consisted of volcanic glass, plagioclase feldspar in various proportions, orthopyroxene, clinopyroxene, olivine, amphibole, titanomagnetite. We conducted the total elemental analysis of the bulk samples of the volcanic ash. The contents of major, trace and rare elements as well as heavy metals were determined by wet chemical methods and x-ray fluorescence (XRF) analyses. Although the volcanic ash of Mt. Talang are still very new, an evaluation of the geochemical weathering indices was performed with the objective of showing the volcanic ash condition at the early stage of weathering. Eight weathering indices were evaluated. The results showed that the unleached volcanic ash has higher Ruxton Ratio (R), Weathering Index of Parker (WIP), Product of Weathering Index (PWI) and Silica Titanium Index (STI) values compared to the leached ash, while the leached ash exhibited higher Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Vogt’s Residual Index (VO), and Plagioclase Index of Alteration (PIA). These weathering indices can be used to quantify the condition of the volcanic ashes at the initial stage of weathering, to evaluate their fertility, to provide a better understanding of element mobility during weathering, and predict the source of soil nutrients as well as determine the products of primary minerals alteration.

Adjustment of weak partial extraction data assuming metal ion adsorption: examples using bulk cyanide leach

ABSTRACT Geochemical analysis of soils using partial extractions, purported to detect only a fraction of elements mobilized during dispersion, represents a useful exploration tool. Interpretation of partial extraction data is, however, subject to uncertainty because the effects of changing soil or sediment properties on extraction are poorly defined. In particular, soil properties which are known to affect the retention of metal ions (e.g. clay content, organic carbon content, pH) may provide useful parameters against which to calculate adjusted total and partial assay values and thereby enhance anomaly contrast in geochemical exploration. Bulk cyanide leach (BCL), a commonly-used weak partial extraction technique, reduces the nugget effect for Au and can provide higher anomaly contrast than total elemental analyses. For a range of elements (Ag, Au, Cd, Co, Cu, Mo, Ni, Pd and Zn), we conducted BCL determinations, measured the same elements by NAA, XRF or aqua regia digest, and determined a range of soil chemical properties for traverses at 10 exploration prospects in Australia and Namibia. Raw total and BCL data were compared with (i) concentration : soil parameter ratios, and (ii) adjusted BCL values based on a simple model of trace element speciation in soils. Anomaly contrasts for raw and normalized or adjusted data were compared using an estimate of anomalism based on both quantitative and heuristic criteria. At prospects with soils containing detectable carbonate, normalization of total and BCL assays to carbonate content significantly improved multi-element anomaly contrast. Normalization to amorphous Fe or Mn oxide content, or total Al, K or Mg also significantly improved anomaly contrast at fewer prospects. Adjusting BCL values using a simple adsorption model also showed limited success in improving anomaly contrast, and represents a useful framework for interpreting weak partial extraction data. Supplementary material: Data tables relating to study are available at http://www.geolsoc.org.uk/SUP18409.

Distribution and potential source evaluation of heavy metals in prominent soils of Accra Plains, Ghana

Environmental contamination by heavy metals remains a major threat to health and agricultural productivity, particularly in developing countries. This study evaluated the distribution, controlling variables, and potential sources of heavy metals in the soils of the Legon hill catena, prominent soils of Accra Plains, Ghana, West Africa. Soil samples were collected from the profiles of five dominant soil series, comprising four Alfisols and one Vertisol, developed on different physiographic positions. Samples were characterized for various soil properties including total elemental analysis. Variations in major physical and chemical characteristics among the soils were chiefly attributed to physiographic position and parent materials. Dominant heavy metals and concentration ranges observed were Co (22.0–260 mg kg − 1 ), Cu (9.80–72.9 mg kg − 1 ), Ni (22.8–201 mg kg −1), Pb (9.30–45.0 mg kg − 1 ), and Zn (5.80–69.8 mg kg − 1 ), with averages of 76.8, 35.5, 66.3, 26.0, and 44.0 mg kg − 1 , respectively. Except in a few occasions, the concentrations of these metals generally increased with depth. All the soils were dominated by SiO 2, Al 2O 3, and Fe 2O 3. Copper and Zn were positively correlated with Fe 2O 3 ( R 2 ≥ 0.67, P < 0.001), but negatively correlated with SiO 2 ( R 2 ≥ 0.71, P < 0.001). Principal component and correlation analyses suggested that Cu, Pb, and Zn contents of this region could be of similar lithogenic origin, while Co and Ni were attributed to a different geogenic source. Evidence gathered from this study further suggested that the metal contents of these soils were generally below the maximum allowable limits set by most countries.

Phosphorus biogeochemistry across a precipitation gradient in grasslands of central North America

Soil P transformations and distribution studies under water limited conditions that characterize many grasslands may provide further insight into the importance of abiotic and biotic P controls within grass-dominated ecosystems. We assessed transformations between P pools across four sites spanning the shortgrass steppe, mixed grass prairie, and tallgrass prairie along a 400-mm precipitation gradient across the central Great Plains. Pedon total elemental and constituent mass balance analyses reflected a pattern of increased chemical weathering from the more arid shortgrass steppe to the more mesic tallgrass prairie. Soil surface A horizon P accumulation was likely related to increased biocycling and biological mining. Soluble P, a small fraction of total P in surface A horizons, was greatest at the mixed grass sites. The distribution of secondary soil P fractions across the gradient suggested decreasing Ca-bound P and increasing amounts of occluded P with increasing precipitation. Surface A horizons contained evidence of Ca-bound P in the absence of CaCO 3, while in subsurface horizons the Ca-bound P was associated with increasing CaCO 3 content. Calcium-bound P, which dominates in water-limited systems, forms under different sets of soil chemical conditions in different climatic regimes, demonstrating the importance of carbonate regulation of P in semi-arid ecosystems.