Sequential Extraction Data Research Articles

Sedimentary phosphorus sequential extraction method offers new insight into soil development

Fractionation of soil phosphorus (P) by sequential extraction is one of tools to study the soil development in Earth’s critical zone for characterization of weathering pattern and soil evolution. A sequential extraction method originally developed for sediment with advantage of separating CaCO3-bound P from igneous fluorapatite has been used to quantify different forms of P in New England native forest soils. Total soil phosphorus is fractionated into exchangeable, iron-bound, CaCO3-bound, igneous fluorapatite and refractory organic P pools. Seven surface soil samples were collected from coastal, terrestrial, and lacustrine environments. Total P (TP) ranges from 11.4 to 21.5 μmol P g-1. Averaging over all sampling locations, the largest fraction is igneous fluorapatite with an average concentration of 4.9 ± 1.6 μmol P g-1, accounting for 29.2 ± 9.5 % of TP. Refractory organic P is the second largest fraction with an average concentration of 4.4 ± 1.6 μmol P g-1, accounting for 27.0 ± 9.6 % of TP. Iron-bound P is the third largest fraction with an average concentration of 3.3 ± 1.7 μmol P g-1, accounting for 20.3 ± 10.0 % of TP. CaCO3 -bound P is the second smallest fraction with an average concentration of 2.8 ± 1.4 μmol P g-1, accounting for 16.3 ± 7.5 % of TP. As usual, the smallest fraction is exchangeable P with an average concentration of 1.2 ± 0.8 μmol P g-1, accounting for 7.2 ± 4.3 % of TP. Data from this study are well fitted to a linear model based on the previous sequential extraction data compiled from global soils and sediments samples. The sequential extraction method used here offers an improved procedure that quantify the abundance of igneous fluorapatite as primary P mineral, which provides an estimate of the state and degree of weathering and soil development in the region.

Enrichment Characteristics and Ecological Risk Assessment of Heavy Metals in a Farmland System with High Geochemical Background in the Black Shale Region of Zhejiang, China

Soils derived from black shale enriched in heavy metals pose risks to the environment and human health. Eighty sets of soil–rice samples were collected in northwest Zhejiang, China. The results showed significant enrichment of As, Cd, Pb, and Zn in the studied soil. Sequential extraction data indicated that Cd had relatively high bioavailability. Thirty-four percent of the rice samples exceeded the heavy metal pollution thresholds of national food safety standards. A comprehensive evaluation of soil heavy metals using the potential ecological risk index (RI) revealed low-to-moderate-grade risk. Risk assessment code (RAC) levels decreased as follows: Cd > Ni > Zn > Cr > Cu > Pb > As > Hg. The RAC of Cd was high and very high risk, whereas those of others were no or low risk. Cd was the major contributor to the environmental risk based on the total heavy metal concentration, toxicity, and chemical fractions. The health risk to the local populace was assessed using the method recommended by the USEPA. Local people may experience both non-carcinogenic and carcinogenic health risks, and children face greater health risks than adults. As, Cd, and Pb are the most significant contributors to non-carcinogenic health risks, and Cd is the main carcinogenic risk. In conclusion, special attention should be given to heavy metal pollution in black shale-derived soils.

Revisiting the applicability and constraints of molybdenum- and uranium-based paleo redox proxies: comparing two contrasting sill fjords

Abstract. Sedimentary molybdenum (Mo) and uranium (U) enrichments are often used as redox proxies to reconstruct bottom water redox changes. However, these redox proxies may not be equally reliable across a range of coastal settings due to varying depositional environments. Fjords vary greatly in their depositional conditions, due to their unique bathymetry and hydrography, and are highly vulnerable to anthropogenic and climatic pressures. Currently, it is unknown to what extent Mo and U sequestration is affected by variable depositional conditions in fjords. Here, we use pore water and sequential extraction data to investigate Mo and U enrichment pathways in sediments of two sill fjords on the Swedish west coast with contrasting depositional environments and bottom water redox conditions. Our data suggest that sedimentary authigenic Mo and U pools differ between the two fjords. At the (ir)regularly dysoxic (oxygen = 0.2–2 mL L−1) Gullmar Fjord, authigenic Mo largely binds to manganese (Mn) oxides and to a lesser extent to iron (Fe) oxides; Mo sulfides do not play a major role due to low sulfate reduction rates, which limits the rate of Mo burial. Authigenic U largely resides in carbonates. At the (ir)regularly euxinic (oxygen = 0 mL L−1; total hydrogen sulfide ≥ 0 mL L−1) Koljö Fjord, authigenic Mo is significantly higher due to binding with more refractory organic matter complexes and Mo-Fe-sulfide phases. Uranium is moderately enriched and largely bound to organic matter. We found no direct evidence for temporal changes in bottom water redox conditions reflected in Mo and U enrichments at either Gullmar Fjord or Koljö Fjord. While sulfidic bottom waters favor Mo sequestration at Koljö Fjord, enrichment maxima reflect a combination of depositional conditions rather than short-term low-oxygen events. Our data demonstrate that secondary pre- and post-depositional factors control Mo and U sequestration in fjords to such an extent that bottom water redox conditions are either not being systematically recorded or overprinted. This explains the large variability in trace metal enrichments observed in fjords and has implications for applying Mo and U as proxies for environmental redox reconstructions in such systems.

Copper isotopes as a tool to trace contamination in mangroves from an urbanized watershed

This study investigates the chronology of copper (Cu) contamination and its stable isotopes within an emblematic Brazilian mangrove impacted by multiple urban and industrial Cu sources, deforestation, and eutrophication. In particular, it tests Cu isotopes as tracers of anthropogenic inputs into an anthropized watershed impacted by multiple sources. To do so, we used multi-isotopic approaches (δ65Cu, δ13C, and δ15N), elemental analyses (Al, Ca, Fe, P, Cu, C, and N), and selective and sequential extractions in a210Pb-dated sediment core. This geochemical "toolbox" allowed identifying two main stages of Cu evolution in the sediment core. In the first stage, before 1965, Cu isotope fingerprints responded to landscape changes, indicating a shift from marine to geogenic dominance due to the remobilization and erosion of terrestrial materials. In the second stage, after 1965, the sediment geochemical profile showed increased Cu total concentrations with a higher bioavailability (as reflected by sequential extraction data) accompanying changes in Cu isotope signatures towards anthropogenic values. The findings evidence that local industrial sources, possibly combined with diffuse urban sources, export Cu into downstream mangroves with a distinguishable isotope signature compared to natural values. This study demonstrates the applicability of Cu isotopes as new environmental forensic tools to trace anthropogenic sources in mangrove sediments. Incorporated into a robust geochemical toolbox that combines inorganic and organic proxies for sedimentary materials, this new tool provides a comprehensive understanding of Cu dynamics in mangrove ecosystems, shedding light on the historical and current sources of Cu.

Simultaneous immobilization of lead and arsenic and improved phosphorus availability in contaminated soil using biochar composite modified with hydroxyapatite and oxidation: Findings from a pot experiment

Multi-metals/metalloids contaminated soil has received extensive attention because of their adverse health effects on the safety of the food chain and environmental health. In order to provide additional insight and aid in mitigating environmental risks, a pot experiment was directed to assess the impacts of biochars derived from rice straw (BC), and modified biochars i-e., hydroxyapatite modified (HAP-BC) and oxidized biochars (Ox-BC) on the redistribution, phytoavailability and bioavailability of phosphorus (P), lead (Pb), and Arsenic (As), as well as their effects on the growth of maize (Zea mays L.) in a Lead (Pb)/Arsenic (As) contaminated soil. The results showed that HAP-BC increased the soil total and available P, compared with raw biochar and control treatment. HAP-BC improved soil properties by elevating soil pH and electric conductivity (EC). The Hedley fractionation scheme revealed that HAP-BC enhanced the labile and moderately labile P species in soil. Both HAP-BC and Ox-BC assisted in the P build-up in plant roots and shoots. The BCR (European Community Bureau of Reference) sequential extraction data for Pb and As in soil showed the pronounced effects of HAP-BC towards the transformation of labile Pb and As forms into more stable species. Compared with control, HAP-BC significantly (P ≤ 0.05) decreased the DTPA-extractable Pb and As by 55% and 28%, respectively, subsequently, resulting in reduced Pb and As plant uptakes. HAP-BC application increased the plant fresh and dry root/shoot biomass by 239%, 72%, 222% and 190%, respectively. The Pb/As immobilization by HAP-BC was mainly driven by precipitation, ion exchange and surface complexation mechanisms in soil. In general, HAP-BC application indicated a great capability to be employed as an effective alternative soil amendment for improving P acquisition in soil, simultaneously immobilizing Pb and As in the soil-plant systems.

Retention and transformation of exogenous Hg in acidic paddy soil under alternating anoxic and oxic conditions: Kinetic and mechanistic insights

To estimate the risks and developing remediation strategies for the mercury (Hg)-contaminated soils, it is crucial to understand the mechanisms of Hg transformation and migration in the redox-changing paddy fields. In present study, a Hg-spiked acidic paddy soil (pH 4.52) was incubated under anoxic conditions for 40 d and then under oxic conditions for 20 d. During anoxic incubation, the water-soluble, exchangeable, specifically adsorbed, and fulvic acid-complexed Hg decreased sharply, whereas the humic acid-complexed Hg, organic, and sulfide-bound Hg gradually increased, which were mainly ascribed to the enhanced adsorption on the surface of soil minerals with an increase in soil pH, complexation by organic matters, precipitation as HgS, and absorption by soil colloids triggered by reductive dissolution of Fe(III) oxides. By contrast, after oxygen was introduced into the system, a gradual increase in available Hg occurred with decreasing soil pH, decomposition of organic matters and formation of Fe(III) oxides. A kinetic model was established based on the key elementary reactions to quantitatively estimate transformation processes of Hg fractions. The model matched well with the modified Tessier sequential extraction data, and suggested that large molecular organic matter and humic acid dominated Hg complexation and immobilization in acidic paddy soils. The content of methylmercury increased and reached its peak on anoxic 20 d. Sulfate-reducing bacteria Desulfovibrio and Desulfomicrobium were the major Hg methylating bacteria in the anoxic stage whereas demethylating microorganisms Clostridium_sensu_stricto_1 and Clostridium_sensu_stricto_12 began to grow after oxygen was introduced. These new dynamic results provided new insights into the exogenous Hg transformation processes and the model could be used to predict Hg availability in periodically flooded acidic paddy fields.

Influence of soil physicochemical properties, particle size fractions and mineralogy on the leaching potentials of arsenic and antimony in abandoned mine soils

At abandoned mine sites, arsenic (As)- and antimony (Sb)-enriched soils are often disposed of through onsite burial or capping. In highly weathered mine sites, the mobility of As and Sb is typically controlled by iron (Fe)(III)/Fe(II) phases; thus, the suitability of such disposal methods and appropriate testing techniques are questionable. In the present study, leaching potentials of As and Sb were examined using the toxicity characteristic leaching procedure (TCLP), waste extraction test (WET), and WET-extended procedure (WET-EXT) at three abandoned mine site soils in Australia. The leached concentration of As regularly exceeded USEPA criteria (5 mg L−1). The highest leached concentrations of As and Sb were observed in the finest particle size fraction (< 0.053 mm) by WET-EXT (1 040 mg L−1 for As and 21.10 mg L−1 for Sb) followed by WET (800 mg L−1 for As and 20.90 mg L−1 for Sb). The TCLP method resulted in the lowest concentrations of leached As (0.000 9 mg L−1) and Sb (0.000 3 mg L−1). Crystalline and amorphous As-bearing Fe oxides were the main phases in the soils studied. However, the best correlations of leached As determined by TCLP (0.832), WET (0.944), and WET-EXT (0.961) were found with the non-specifically sorbed (NS1) As fraction. The mineralogical and sequential extraction data clearly indicate the dominant role of Fe geochemistry in controlling leachability of As and Sb. The TCLP method was unlikely to be suitable for assessing leachability, as it exhibited no relationship with leachable Fe and substantially lower leached As and Sb than the other two methods. Given the high to extremely high leachable As and Sb concentrations, most of the soil samples would not be recommended for placement in capping works, old shafts, or reduction systems (e.g., collection in drainage basins).

Coupling in vitro assays with sequential extraction to investigate cadmium bioaccessibility in contaminated soils

To understand how Cd in different fractions contributes to Cd bioaccessibility by in vitro assays, Cd bioaccessibility in 12 contaminated soils was determined by four assays (UBM, SBRC, IVG, and PBET) and correlated with different Cd fractions based on a sequential extraction scheme. The Cd bioaccessibility in the gastric phase (GP) was high (35–107%, averaging at 77%), implicating high risk to human health, while it decreased to 19–88% averaging at 47% in the intestinal phased (IP). From the GP to IP, the reduction of extractable Cd (0.45–48 mg kg−1) and Fe (118–3884 mg kg−1) showed significant correlation (R = 0.54–0.74) via UBM, SBRC, and IVG, suggesting co-precipitation with Fe and/or sorption onto Fe oxides maybe responsible for decrease in Cd bioaccessibility. Although Cd bioaccessibility varied among assays, their results show some consistency based on their correlation in the GP (R = 0.56–0.90) and IP (0.34–0.73, excluding UBM-IP and PBET-IP). Sequential extraction data show that Cd was primarily associated with the exchangeable fraction (E1; 7.05–72.9%, averaging 39.4%). The carbonate (C2; 6.86–44.8%, 21.9%) and Fe/Mn oxides fraction (F3; 12.5–53.6%, 28.2%) were similar, while organic (O4; 0.62–25.0%, 7.91%) and residual fraction (R5; 0.22–8.54%, 2.62%) were the lowest. Significant correlation (R = 0.59–0.88) between the first two fractions (E1+C2) and bioaccessible Cd suggest they were the main sources of bioaccessible Cd in those contaminated soils.

Sedimentary cycling and benthic fluxes of manganese, cobalt, nickel, copper, zinc and cadmium in the Peruvian oxygen minimum zone

Marine sediments are an important source and sink of bio-essential trace metals to the ocean. However, the different mechanisms leading to trace metal release or burial are not fully understood and the associated fluxes are not well quantified. Here, we present sediment, pore water, sequential extraction and benthic flux data of Mn, Co, Ni, Cu, Zn and Cd along a latitudinal depth transect across the Peruvian oxygen minimum zone at 12°S. Sediments are depleted in Mn and Co compared to the lithogenic background. Diffusive Mn fluxes from the sediments into the bottom water (−26 to −550 μmol m−2 y−1) are largely consistent with the rate of Mn loss from the solid phase (−100 to −1160 μmol m−2 yr−1) suggesting that 50% or more of the sedimentary Mn depletion is attributed to benthic efflux. In contrast, benthic Co fluxes (~ −3 μmol m−2 yr−1) are lower than the rate of Co loss from the solid phase (up to −120 μmol m−2 yr−1), implying Co dissolution in the water column. The trace metals Ni, Cu, Zn and Cd are enriched within the sediments with respect to the lithogenic background. Uptake of Ni by phytoplankton in the photic zone and delivery with organic matter to the sediment surface can account for up to 100% of the excess Ni accumulation (87 to 180 μmol m−2 y−1) in shelf sediments near the coast, whereas at greater water depth additional scavenging by Mn- and Fe-oxides may contribute to Ni accumulation. Up to 20% of excess Cu (33 to 590 μmol m−2 y−1) and generally less than 20% of excess Zn (58 to 2170 μmol m−2 y−1) and Cd (6 to 260 μmol m−2 y−1) can be explained by delivery with fresh organic matter. Sequential extraction data suggest that the discrepancies between the known sources of Cd (and Cu) and their excess accumulation may be driven by the delivery of allochthonous sulphide minerals precipitated from the water column. Additionally, Cu may be scavenged by downward sinking organic material. In contrast, precipitation of Zn sulphide chiefly takes place in the sediment. Diffusive Zn fluxes into the sediment (21 to 1990 μmol m−2 y−1) match the excess Zn accumulation suggesting that Zn delivery is mediated by molecular diffusion from bottom waters. Considering the diverse behavioural pattern of trace metals observed in this study, we argue that declining oxygen and increasing hydrogen sulphide concentrations in a future ocean will modify trace metal fluxes at the seafloor and the trace metal stoichiometry of seawater.

Field assessment of carboxymethyl cellulose bridged chlorapatite microparticles for immobilization of lead in soil: Effectiveness, long-term stability, and mechanism

Lead (Pb) contamination in soil has been a major concern. Yet, cost-effective remediation technologies have been lacking. This study pilot-tested a new type of carboxymethyl cellulose (CMC) bridged chlorapatite microparticles (CMC-CAP) for immobilization of Pb at an abandoned chemical plant site, and monitored long-term (1 year) stability of Pb under the field conditions. Concentrated CMC-CAP (18 g L−1) was prepared at the pilot scale and then used for amending the soil on the site. CMC-CAP appeared as interwoven flocks of CAP microparticles with a hydrodynamic diameter of 2442 nm, which is 2.2 times smaller than that for bare CAP. CMC-CAP at a dosage of 0.5 wt% resulted in the highest immobilization of Pb, and decreased the acid-leachable Pb in the soil from 1.46 mg L−1 to 0.008 mg L−1 after 1 day of reaction, and further to 0.005–0.006 mg L−1 when aged for 180 and 365 days under the field conditions. The long-term aging consolidated the Pb immobilization, securing the compliance with the Chinese regulatory limit (0.010 mg L−1 for Pb). CMC-CAP served as a long-term sink for leachable Pb in soil and a pH buffer to maintain an alkaline soil pH. Sequential extraction data confirmed that the CMC-CAP amendment converted the more leachable Pb fractions into the less available Pb species. The soil amendment reduced the risk assessment code from “High risk” for the untreated soil to “Low risk” after 120 days of aging. XRD and FTIR results revealed the immobilization of Pb by CMC-CAP was achieved through the formation of the highly stable pyromorphite, surface complexation, and/or ion exchange reactions. Based on the field data, the remediation cost of the CMC-CAP based technology was estimated to be $36.2/m3. This study provides important field data on the effectiveness of CMC-CAP for cost-effective immobilization of Pb in soil.

Geogenic enrichment of potentially toxic metals in agricultural soils derived from black shale in northwest Zhejiang, China: Pathways to and risks from associated crops

Agricultural soils derived from black shale are typically enriched in potentially toxic metals. This is a serious problem, both in terms of the ecological environment and human health. To assess the levels of potentially toxic metals, 90 paired soil-crops samples were collected from the Anji Country, western Zhejiang province, a typical exposed black shale area in China. Concentrations and bioavailability of potentially toxic metals in the soil-crops system were measured, and the associated potential risks were further evaluated. Results showed the enrichment of potentially toxic metals (i.e. Cd, Pb, Cu, Zn and Ni) in the soil and crop samples, especially a significant accumulation of Cd. Sequential extraction data indicated that Cd in soils derived from black shale was the second most dominant element in the exchangeable fraction (mean at 33.42%) and possessed high bioavailability, whereas Pb was mostly retained in the residual fraction (mean at 76.34%) and exhibited low mobility. The total concentration as well as mobility and bioavailability of Cd were the highest in the sampled soils. This resulted in a high potential ecological risk in areas with agricultural soils derived from black shale, which could eventually jeopardize the health of local residents through various exposure pathways. Overall, our findings provide a scientific basis for developing suitable management strategies to mitigate the exposure to potentially toxic metals in high risk areas.

Investigating the Geochemical Controls on Pb Bioaccessibility in Urban Agricultural Soils to Inform Sustainable Site Management

The solid-phase speciation of contaminants in soil plays a major role in regulating both the environmental mobility of contaminants and their bioavailability in biological receptors such as humans. With the increasing prevalence of urban agriculture, in tandem with growing evidence of the negative health impacts of even low levels of exposure to Pb, there is a pressing need to provide regulators with a relevant evidence base on which to build human health risk assessments and construct sustainable site management plans. We detail how the solid-phase fractionation of Pb from selected urban agricultural soil samples, using sequential extraction, can be utilised to interpret the bioaccessible fraction of Pb and ultimately inform sustainable site management plans. Our sequential extraction data shows that the Pb in our urban soils is primarily associated with Al oxide phases, with the second most important phase associated with either Fe oxyhydroxide or crystalline FeO, and only to a limited extent with Ca carbonates. We interpret the co-presence of a P component with the Al oxide cluster to indicate the soils contain Pb phosphate type minerals, such as plumbogummite (PbAl3(PO4)2(OH)5·H2O), as a consequence of natural “soil aging” processes. The presence of Pb phosphates, in conjunction with our biomonitoring data, which indicates the lack of elevated blood Pb levels in our gardeners compared to their non-gardening neighbours, suggests the (legacy) Pb in these soils has been rendered relatively immobile. This study has given confidence to the local authority regulators, and the gardeners, that these urban gardens can be safe to use, even where soil Pb levels are up to ten times above the UK’s recommended lead screening level. The advice to our urban gardeners, based on our findings, is to carry on gardening but follow recommended good land management and hygiene practices.

Assessing the quality of potentially reclaimed mine soils: Environmental implications for the construction of a nearby water reservoir

The cementation complex of Las Viñas (SW Spain) is a partially reclaimed abandoned mine site located in the drainage basin of a water reservoir currently under construction. The aim of this investigation was to analyze these mine soils to evaluate their potential environmental impact, especially on the final reservoir water quality. Results evidence the extremely high acidity of soils (pH of 3.4 and maximum potential acidity of 47 kg CaCO3/ton), with high concentrations of trace elements, especially As, Pb and Cu. Sequential extraction data reveal the potential release of significant quantities of Mn, Cd, Cu and other easily-soluble trace elements by rainfalls. The weathering and transport of soils to the bottom sediments of the planned reservoir could lead to the release of significant quantities of toxic trace elements to the water column if anoxic (mainly As, Sb, Cr, Ni, Cu and Pb) or oxic (mainly Hg, Pb, V, Cu and As) conditions are found in the sediments. The acidity and metals released from these soils could jeopardize the quality of the reservoir waters. Remediation measures must be therefore adopted, focused on the cleanup and liming of soils in order to promote colonization and vegetation succession, thus avoiding soil erosion and limiting metal release to the hydrosphere. This study proposes the use of different low-cost materials to improve the soil quality, limiting the metal transfer to the planned reservoir water. The information contained in this study could be of great importance in other watersheds affected by abandoned mine sites.

Spatial distribution and chemical partitioning of potentially toxic elements in soils around Khatoon-Abad Cu Smelter, SE Iran

The objective of this study was to assess the environmental impacts of Khatoon Abad Cu smelter, SE Iran, on soil contamination and to investigate the chemical partitioning of potentially toxic elements (As, Cd, Cu, Mo, Pb and Zn) in the soils. For this purpose, topsoil and subsoil samples were collected and analyzed using standard methods; dust, slag, and concentrate samples were characterized for reference. The results showed elevated concentrations of As (up to 441.8 mg kg−1), Cd (up to 11.4 mg kg−1), Cu (up to 12,611 mg kg−1), Mo (up to 178.2 mg kg−1), Pb (up to 316 mg kg−1) and Zn (up to 803 mg kg−1) in <63 μm fraction of topsoil samples. The highest recorded concentrations for these elements were in soils collected in downwind direction. The concentration of smelter driven metals in topsoil samples decreased with increasing distance from the Cu smelter and also with increasing depth of the soil samples. The granulometric distribution of the soil samples as well as the mineralogical and geochemical composition of dust sample confirms the impact of smelting activity on the surrounding soils. On the basis of sequential extraction data, the highest percentage for exchangeable, carbonate, reducible, oxidizable, and residual fractions were recorded for Cd (26.5%), Zn (35.5%), As (47.7%), Cu (28.7%) and Mo (37.8%), respectively. The anthropogenic activity (Cu smelting) was the main parameter controlling the metal chemical partitioning because the percentage of non-residual fractions of the studied elements decreased with increasing distance from the Cu smelter and also decreased with increasing depth of the soil samples. Human risk assessment indicated non-carcinogenic (hazard quotient of 1.7) risk to the population and carcinogenic (Incremental Lifetime Cancer Risk of 7.71E-04) risk of As to the children, through the ingestion pathway. The hazard quotient of dermal contact (to the children) is 1.4 for Cu at one site located around the smelter. The results of a single extraction test confirmed the higher risks of As and Cu through ingestion pathway compared with other studied elements. The results of this study show that more attention should be given to the potentially toxic elements (PTEs) pollution in Khatoon Abad area.

Selected trace-elements in alluvium and rocks, western Mojave Desert, southern California

Concentrations of twenty-seven elements, including naturally-occurring water-quality contaminants arsenic, chromium, and uranium, were measured in 217 samples of alluvium and rock from the western Mojave Desert, southern California, using portable (pXRF) and laboratory (LXRF) X-ray fluorescence. Comparison of measurements with NIST-traceable standards was good, although pXRF overestimated iron compared to LXRF. Results suggest pXRF survey data are sufficiently accurate to assess regional geochemical differences in geologic-source terrains. Principal component analysis showed rubidium and potassium were associated with alluvium eroded from felsic terrain, while iron, copper, chromium, and to a lesser extent titanium, manganese, and nickel were associated with alluvium eroded from mafic terrain. Zinc, vanadium, and arsenic were associated with alluvium eroded from hydrothermal terrain. Elemental assemblages associated with different source terrains were traced spatially to identify the source and composition of alluvium composing aquifers pumped for water supply. Changes in geologic source terrain to the Mojave River, associated with movement along the San Andreas Fault over the past one to five million years, reduced the mafic fraction and increased the felsic fraction of alluvium deposited to the regionally important floodplain aquifer along the Mojave River—lowering chromium concentrations in alluvium through geologic time. Comparison of pXRF and sequential extraction data from 40 samples showed arsenic and uranium were more abundant on the surfaces of mineral grains, while chromium and vanadium remained mostly within unweathered mineral grains—suggesting arsenic and uranium may be more readily mobilized into groundwater with changes in pH, redox, or ionic strength than chromium or vanadium.

Geochemical fractionation of metals and metalloids in tailings and appraisal of environmental pollution in the abandoned Musina Copper Mine, South Africa.

The economic benefits of mining industry have often overshadowed the serious challenges posed to the environments through huge volume of tailings generated and disposed in tailings dumps. Some of these challenges include the surface and groundwater contamination, dust, and inability to utilize the land for developmental purposes. The abandoned copper mine tailings in Musina (Limpopo province, South Africa) was investigated for particle size distribution, mineralogy, physicochemical properties using arrays of granulometric, X-ray diffraction, and X-ray fluorescence analyses. A modified Community Bureau of Reference (BCR) sequential chemical extraction method followed by inductively coupled plasma mass spectrometry/atomic emission spectrometry (ICP-MS/AES) technique was employed to assess bioavailability of metals. Principal component analysis was performed on the sequential extraction data to reveal different loadings and mobilities of metals in samples collected at various depths. The pH ranged between 7.5 and 8.5 (average ≈ 8.0) indicating alkaline medium. Samples composed mostly of poorly grated sands (i.e. 50% fine sand) with an average permeability of about 387.6m/s. Samples have SiO2/Al2O3 and Na2O/(Al2O3 + SiO2) ratios and low plastic index (i.e. PI ≈ 2.79) suggesting non-plastic and very low dry strength. Major minerals were comprised of quartz, epidote, and chlorite while the order of relative abundance of minerals in minor quantities is plagioclase > muscovite > hornblende > calcite > haematite. The largest percentage of elements such as As, Cd and Cr was strongly bound to less extractable fractions. Results showed high concentration and easily extractable Cu in the Musina Copper Mine tailings, which indicates bioavailability and poses environmental risk and potential health risk of human exposure. Principal component analysis revealed Fe-oxide/hydroxides, carbonate and clay components, and copper ore process are controlling the elements distribution.

Effect of humic and fulvic acid transformation on cadmium availability to wheat cultivars in sewage sludge amended soil.

The high nutrients and organic matter (OM) content of sewage sludge make it an excellent fertilizer to enhance soil fertility and crop production. However, the presence of adsorbed and precipitated forms of heavy metals, especially cadmium (Cd), can be a major problem for such a utilization of sludge. This pot study aims at producing safe food with minimal Cd concentrations from sewage sludge amended soils. Two wheat cultivars (NARC-11 and Shafaq-06) were sown in soil amended with sewage sludge with rates 0, 15 and 30gkg-1 soil. Application of sewage sludge resulted in enhancement of wheat grain yield while Cd concentrations in wheat grains of both cultivars remained within permissible limits (24.1 to 58.6μgkg-1 dry weight). Fourier transform infrared (FTIR) spectroscopic analysis revealed more spectral changes in fulvic acids than in humic acids, which showed a higher humification degree, making them chemically and biologically more stable for Cd retention. Sequential extraction data of Cd after NARC-11 harvest exhibited a significant decrease in mobile fractions (exchangeable and reducible fractions were reduced by 3.6 and 5.2%, respectively) and increase in immobile fraction (the oxidizable and residual fractions increased by 7 and 1.8%, respectively). It is concluded that sewage sludge application could be useful for the improvement of wheat production due to formation of stable humate complexes and decrease in Cd availability.

Distribution of phosphorous pools in western river sediments of the Urmia Lake basin, Iran.

Impact of anthropogenic loading of phosphorous (P) to an aquatic ecosystem can be qualitatively assessed by measuring the buildup and distribution of P in sediments and by differentiating bioavailable and recalcitrant P pools. Distribution of P pools in sediments is affected by the physico-chemical properties including specific elements, particle size distribution, pH, electrical conductivity (EC), and carbonate content. We applied X-ray fluorescence and scanning electron microscopy (SEM) methods to characterize sediments from western rivers in the Urmia Lake basin in Iran with a particular focus on properties that are relevant to P speciation. Phosphorous pools were sequentially extracted into operationally defined exchangeable (EXCH-P), iron and aluminum oxide-bound (Fe/Al-P), calcium-bound (Ca-P), and residual (RES-P) P pools. In river sediments, the size of P pool was found to be in the order of Ca-P > RES-P > Fe/Al-P > EXCH-P indicating small fraction of bioavailable P pool and Ca-P minerals being the most dominant P sink. Carbonate-related properties had an inverse relationship with bioavailable P pools in the river sediments studied. The principal component analysis (PCA) of the sequential extraction data with sediment properties revealed that four principal components described 82.7% of total variation. Similarly, particle size-related properties were found to have the highest eigenvalues in the first PC. Electron diffraction spectra (EDS) and X-ray fluorescence (XRF) analyses showed a largely uniform distribution of P in the upstream sediment. However, limited evidence of local enrichment of P with Fe, Al, and Ca contents was observed in the downstream river sediments. Correlation of Fe/Al-P pool size with Al2O3 and SiO2 contents indicated that P was associated with Al oxide and clay minerals in the sediment matrix. Overall, the results from this study provide insights into the variability of upstream and downstream river processes and their relationship with P pools with regard to their bioavailability. These results are expected to be useful in assessing the potential impact of P loading on the aquatic ecosystem in the Urmia Lake basin.

Metal biogeochemistry in constructed wetlands based on fluviatile sand and zeolite- and clinopyroxene-dominated lava sand

For the first time, speciation of Fe, Mn, Zn, Ni, Cu and Pb was determined along the profiles of 8 constructed wetlands (CWs) consisting of fluviatile sand (Fluv), clinopyroxene-dominated lava sand (Cl-LS) and zeolite-dominated lava sand (Ze-LS), aiming at quantifying metal behaviour in CWs and the impact caused by different filter materials. With the exception of Mn, which underwent reductive dissolution, CWs were sinks for the studied metals. Metal accumulation rates differed in the following order: Ze-LS ≥ Cl-LS > Fluv CWs, reflecting the highest metal adsorption capacity and the lowest hydraulic conductivity of Ze-LS. Sequential extraction data indicated the highest metal mobility (readily mobilised and adsorbed fractions summing up to ~60%) in Fluv CWs, implying a higher risk of metal release into adjacent environments if Fluv from CWs will be improperly disposed after usage. Zinc and Ni were transported into the deeper CW layers to a larger extent than Cu and Pb, reflecting adsorption affinity to all filter materials in the order of Pb > Cu > Zn > Ni. Therefore, understanding metal speciation and mobility in such materials is crucial when they are considered for application as filters in CWs.

Linkage between solid-phase apportionment and bioaccessible arsenic, chromium and lead in soil from Glasgow, Scotland, UK

ABSTRACTThe chemical composition of soil from the Glasgow (UK) urban area was used to identify the controls on the availability of potentially harmful elements (PHEs) in soil to humans. Total and bioaccessible concentrations of arsenic (As), chromium (Cr) and lead (Pb) in 27 soil samples, collected from different land uses, were coupled to information on their solid-phase partitioning derived from sequential extraction data. The total element concentrations in the soils were in the range &lt;0.1–135mgkg–1 for As; 65–3680mgkg–1 for Cr and 126–2160mgkg–1 for Pb, with bioaccessible concentrations averaging 27, 5 and 27% of the total values, respectively. Land use does not appear to be a predictor of contamination; however, the history of the contamination is critically important. The Chemometric Identification of Substrates and Element Distribution (CISED) sequential chemical extraction and associated self-modelling mixture resolution analysis identified three sample groupings and 16 geochemically distinct phases (substrates). These were related to iron (n=3), aluminium–silicon (Al–Si; n=2), calcium (n=3), phosphorus (n=1), magnesium (Mg; n=3), manganese (n=1) and easily extractable (n=3), which was predominantly made up of sodium and sulphur. As, Cr and Pb were respectively found in 9, 10 and 12 of the identified phases, with bioaccessible As predominantly associated with easily extractable phases, bioaccessible Cr with the Mg-dominated phases and bioaccessible Pb with both the Mg-dominated and Al–Si phases. Using a combination of the Unified Barge Method to measure the bioaccessibility of PHEs and CISED to identify the geochemical sources has allowed a much better understanding of the complexity of PHE mobility in the Glasgow urban environment. This approach can be applied to other urban environments and cases of soil contamination, and made part of land-use planning.