Mobility Of Trace Metals Research Articles

Legacy nitrate and trace metal (Mn, Ni, As, Cd, U) pollution in anaerobic groundwater: Quantifying potential health risk from “the other nitrate problem”

Denitrification in soils and aquifers sustains low nitrate concentrations in many anaerobic groundwaters despite massive inputs of N from agriculture. However, this ecosystem service sometimes comes at the cost of trace metal mobilization and concerns have been raised that denitrification in anaerobic groundwater may lead to trace metal contamination. But it remains unclear, if denitrification must necessarily result in trace metal concentrations that are potentially harmful for humans. For example, formation of iron(oxy)hydroxides after the reaction of nitrate with pyrite may reduce rather than increase the mobility of certain trace metals in aquifers. We quantified the potential health risk resulting from denitrification-associated trace metal pollution (Mn, Ni, As, Cd, U) in anaerobic groundwater with different degrees of nitrate pollution in >800 wells located in Northern Germany. Overall, observed rates of violations of legal quality standards for U, As and Cd are moderate in the study area (<10% of all wells) but elevated for Mn (>50%), which is a common contaminant under the often anaerobic conditions in the study area. However, in groundwater where denitrification had partially proceeded, the risk for drinking water standard violations was higher for Ni, Cd and U (up to a factor of 4 for Ni) as compared to anaerobic groundwater without denitrification, but lower for Mn and As. Especially poorly buffered groundwaters with pH < 5.5 are at risk of Ni and Cd contamination resulting from denitrification, while the opposite is true for Mn and U. Thus, we establish a clear linkage between nitrogen biogeochemistry and trace metal mobility and show how perturbations of groundwater redox and pH conditions by nitrate can further deteriorate groundwater quality. In addition, we find that the combination of oxygen concentrations of lower than 1 mg L−1, and nitrate concentrations above 1 mg L−1 allows for identification of denitrification (as evidenced by excess N2 in groundwater) with 90% accuracy. The methodology developed herein can be used to inform water treatment planning about potential trace metal contamination when drinking water should be produced from anaerobic aquifers beneath agricultural landscapes.

Sediments as a Source of Iron, Manganese, Cobalt and Nickel to Continental Shelf Waters (Louisiana, Gulf of Mexico)

Continental shelf sediments are a key source of trace metals to the ocean. In this study, we investigate the impact of sedimentary processes on water column concentrations of iron (Fe), manganese (Mn), cobalt (Co), and nickel (Ni) at five stations on the Louisiana continental shelf and slope, Gulf of Mexico. The highest trace metal concentrations were observed close to the seafloor at the most nearshore shelf station (water depth of 16 m), with most of the metals present in particulate form. This enrichment in the bottom water is likely the combined effect of input of trace metals in suspended matter from the Mississippi/Atchafalaya Rivers and, for Mn, Co, and Ni, benthic release from the shelf sediments. While particulate matter was the dominant carrier of Fe and Mn in bottom waters in the shelf and slope regions, Co and Ni were nearly exclusively present in dissolved form. Hence, lateral transport of Co and Ni in shelf waters is decoupled from that of Fe and Mn. Concentrations of particulate and dissolved trace metals in the water column generally decreased from the shelf to the slope, while those in the sediment increased. This suggests an increased retention of metals deposited on the sediment with distance from the coast, linked to the decrease in organic matter input and associated reductive sediment processes. The offshore decline in sediment trace metal mobilization is likely typical for river-dominated continental margins where most organic matter is deposited close to the coast.

A method to reproduce pH and Eh environmental changes due to sediment resuspension

During the last decades, metals have been released into coastal areas increasing the environmental and human health risks, however, resuspension events of trace metals polluted sediment could represent even more severe risks. Anoxic condition in the sediment is capable to stabilize the trace metals, due to the bonding with reduced anions. Although, the sediment resuspension can alter the potential redox and pH characteristics resulting in metals released from the water column. The climate change advance would impact directly on ocean chemistry, is expected the spatial increase of anoxic sites, mainly in coastal areas. Furthermore, it is mandatory and urgent to expand the knowledge over the process of sediment metals releasing in order to develop prediction and remediation tools for possible environmental impacts. This is a simple method of manipulating and simulating physicochemical alterations. The creation of microcosmos without oxygen allows the formation of a very reducible environment, common in coastal areas with low energy and high organic matter input. And further oxidation allows the assessment of the trace metals released to the water column and/or the new arrangement of these metals in different geochemical fractions.• The experimental procedure to assess trace metals mobility to potential redox and pH changes in sediment and water.• A method is suitable for a wild range of sediment characteristics.

Short-Term Seawater Inundation Induces Trace Metal Mobilisation in Freshwater and Acid Sulfate Soil Environments

Short-Term Seawater Inundation Induces Trace Metal Mobilisation in Freshwater and Acid Sulfate Soil Environments

Investigation of ICP-MS/MS for total sulfur quantification in freshwater dissolved organic matter.

Sulfur-containing functional groups in dissolved organic matter (DOM) interact with trace metals, which in turn affects trace metal mobility and bioavailability in aquatic environments. Typical methods for identification and quantification of sulfur in DOM are costly, complex, and time intensive. Triple quadrupole inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) is capable of part per billion-level sulfur quantification in environmental samples and is a more accessible analytical technique compared with other available methods. This study is the first published investigation of ICP-MS/MS for the direct quantification of sulfur in freshwater DOM. Sulfur (32 S) detection occurs at a mass-to-charge ratio of 48 as 32 S16 O+ after removal of interferences and reaction with oxygen gas. We compare three commonly used DOM preparation methods to assess variability among replicate samples. Preparation of freshwater DOM samples by solid phase extraction followed by evaporation overnight and dissolution in 2% nitric acid results in the most accurate quantification of sulfur. Analysis of sulfur in Suwannee River Fulvic Acid standard serves as method validation, measuring a carbon-normalized sulfur concentration that is ∼20% higher than previously reported methods. We apply the ICP-MS/MS analysis method to determine sulfur concentrations in DOM from nine lakes in the northern Midwest. Carbon-normalized sulfur concentrations in the selected lakes are in general agreement with previously reported percentages of sulfur-containing formulas in DOM found by Fourier transform-ion cyclotron resonance-mass spectroscopy.

Mechanistic insights into trace metal mobilization at the micro-scale in the rhizosphere of Vallisneria spiralis

Mobilization of trace metals in the rhizosphere of macrophytes is controlled by root-driven chemical changes, especially the steep gradients of O2 and pH from the rhizosphere to bulk sediments. Here, the O2 and pH dynamics, and the distribution of trace metal, in the rhizosphere of Vallisneria spiralis were obtained using planar optodes and diffusive gradients in thin films, respectively. Radial O2 loss (ROL) and acidification occurred on all visible roots of V. spiralis and exhibited highly spatiotemporal dynamics depending on the root growth and various environmental conditions. Trace metals showed different mobilization mechanisms in the rhizosphere. ROL and produced Fe(III) (oxyhydr)oxides decreased the mobility of Fe, As, Co, V and W in the rhizosphere. However, Mn, Ni and Cu exhibited greater mobility in the rhizosphere than bulk sediments as a result of the oxidation of metal sulfide and proton-induced dissolution of minerals. In particular, Co and Ni presented increased activity at the interface between rhizosphere and bulk sediment, which was attributed to the redox dissolution processes of Fe and Mn as a result of ROL and rhizosphere acidification. These results provide new insights into the roles of macrophyte root-induced O2 and pH changes in controlling trace metal mobility in sediments.

Seasonal variation and mobility of trace metals in the beach sediments of NW Borneo

Miri city has a dynamic coastal environment, mainly influenced by intensive sedimentation from the Baram River and excessive trace metal loading by the Miri River, which are significant environmental concerns. As the mobility, bioavailability, and toxicity of the trace metals in the sediments are largely controlled by their particulate speciation, the modified BCR sequential extraction protocol was applied to determine the particulate speciation of trace metals in the coastal sediments of Miri, to unravel the seasonal geochemical processes responsible for known observations, and to identify possible sources of these trace metals. The granulometric analysis results showed that littoral currents aided by the monsoonal winds have influenced the grain size distribution of the sediments, enabling us to divide the study area into north-east and south-west segments where the geochemical composition are distinct. The Cu (>84%) and Zn (82%) concentrations are predominantly associated with the exchangeable fraction, which is readily bioavailable. Pb and Cd are dominant in non-residual fractions and other metals viz., Fe, Mn, Co, Ni, and Cr are dominant in the residual fraction. Using Pearson's correlation and factor analysis, the major mechanisms controlling the chemistry of the sediments are identified as association of Cu and Zn with fine fraction sediments, sulphide oxidation in the SW segment of the study area, atmospheric fallout of Pb and Cd in the river basins, precipitation of dissolved Fe and Mn supplied from the rivers and remobilization of Mn from the coastal sediments. Based on various pollution indices, it is inferred that the coastal sediments of NW Borneo are contaminated with Cu and Zn, and are largely bioavailable, which can be a threat to the local aquatic organisms, coral reefs, and coastal mangroves.

Does the exudation of coumarins from Fe-deficient, soil-grown Brassicaceae species play a significant role in plant Fe nutrition?

The availability of iron (Fe) is highly limited for plant uptake in calcareous soils. To overcome this challenge, plants have developed different strategies of Fe mobilization. Non-gramineous species employ a reduction-based strategy (strategy I), which is assisted by the release of Fe(III)-chelating and -reducing coumarins. In this study, the coumarin release by three strategy-I plant species of the Brassicaceae family, i.e. Brassica napus L., Raphanus sativus L. and Sinapis alba L., on calcareous soil was examined using the RHIZOtest approach. With this experimental setup, the plants were first grown hydroponically in a cylindrical growth unit for 12 days, which was then subsequently brought in contact with calcareous, Fe deficient soil for another 9 days. Root exudates were collected in both experimental phases. Total carbon (C) release, coumarin exudation rates, trace metal plant uptake as well as trace metal mobilization were determined in response to Fe deficiency after 3, 6 and 9 days of soil exposure. High total C exudation rates indicated a clear stress response upon Fe deficiency during the soil contact period. Six different coumarins were detected, with scopoletin being predominantly released by all three plant species during the hydroponic stage with zero Fe supply. The exudation rate of all detected coumarins was significantly lower during soil exposure and represented only a very small fraction of the total organic compounds released. Although the role of coumarins in Fe mobilization is very complex and still not completely understood, it seems that coumarins are less important in Fe mobilization by the three investigated plant species when grown on soil compared to phytosiderophore-releasing strategy-II plants. Our data further indicate that plants growing on a Fe-deficient soil release less coumarins than in an artificial nutrient solution setup with zero Fe supply, which highlights the importance of determining root exudation rates from soil-grown plants, since data from hydroponic studies are likely not representative for soil-grown plants.

Trace metal fractions, sources, and risk assessment in sediments from Umurbey Stream (Çanakkale-Turkey).

Trace metal contamination has become a worldwide problem for aquatic systems, as sediments act as a sink for trace metals. This study was conducted to assess geochemical fractions, sources and potential risks of trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) in sediments of Umurbey stream (Çanakkale-Turkey). Sediment samples were taken from seven different locations of Umurbey stream. Aqua regia wet digestion procedure was applied to determine total contents of trace metals and BCR sequential extraction procedure was applied to determine geochemical fractions of trace metals. Trace metal total values were ordered as Zn > Pb > Cr > Cu > Ni > Cd. Just because of topography, geology, and agricultural practices, S4, S5, S6, and S7 sampling points had greater total trace metal concentrations than the other locations. Potential mobility of trace metals in sediment samples was ordered as Cd (62.1%) > Zn (60.8%) > Pb (54.8%) > Cu (46.1%) > Cr (43.0%) > Ni (29.7%). Cd, Zn, Pb, and partially Cu were encountered mostly in mobile phases. Multivariate analyses revealed that pollution in sediment samples was originated from not only anthropogenic but also natural factors. Except for Zn, trace metal concentrations were found to be at tolerable levels of biota. When the contamination factor and risk assessment code results were assessed together, it was observed that Cd, Zn, and partially Pb were weakly adsorbed onto sediments, thus might pose risks on environment in the long run.

Flow-sediment regulation regime influencing mobilization of trace metals in shallow aquifer and surface water in the Yellow River Delta, China

The Yellow River Delta (YRD) is a typical case of frequent interaction between surface water and groundwater under the seasonal flow-sediment regulation regime. A total of 40 samples (20 surface water samples, 19 groundwater samples, and 1 seawater sample), were collected during the high flow (October, 2019). Trace metals, hydrochemical indicators (EC, pH, major ion of Na+, K+, Mg2+, Ca2+, Cl−, SO4 2−, and HCO3 −) and stable isotopes (δ18O and δD) were determined. The impact of water diversion on the hydrochemistry of groundwater was significant, accounting up to a 90% of river discharge in some sites calculated by 2-component mixing model. Factor analysis indicated that Fe, Mn, Al, and B in surface water were closely correlated and were present in the dissolution phase due to sediment remobilization controlled by flow-sediment regulation; Sr was influenced by the dissolution of evaporate salt, while Ba suffered precipitation in the oxidation processes. However, the source of Sr, Mn, B, and Fe in groundwater was accompanied by hydrochemical compositions and per cent surface water, implying that the trace metals in surface water contributed to that of accumulation in the shallow aquifer; Al was influenced by plagioclase weathering, while Ba precipitated too.

Geochemical fractionation, source identification and risk assessments for trace metals in agricultural soils adjacent to a city center (Çanakkale, NW Turkey)

Agricultural lands around city centers are exposed to trace metal pollution through urbanization especially and industrialization-related human activities. This study investigates potential sources of trace metals (Cd, Cr, Cu, Ni and Pb) in agricultural lands surrounding Canakkale city center (NW Turkey) and estimates their environmental impacts with the sequential extraction procedure. Soil samples were taken from agricultural fields adjacent to the city center that represent all types of land use. The aqua regia wet digestion method was used to determine trace metal contents and the sequential extraction procedure was used to determine geochemical fractions of trace metals. Multivariate analysis was applied for source identification of trace metals. Contamination factors and risk assessment codes were used to assess current pollution. Trace metal contents were in the order: Ni > Cr > Pb > Cu > Cd. Recorded values were greater than the values specified for agricultural land. Trace metal mobility based on totals for the first three fractions was in the order: Cd (62%) > Pb (57%) > Cu (40%) > Ni (32%) > Cr (15%) and these findings indicate that Cd and Pb exist mostly in mobile phases. These mobile phases were mostly attributed to anthropogenic sources. These findings comply with the outcomes of statistical analysis. It was concluded that the soils were contaminated with Pb and Cd. While Pb poses moderate risks for the environment, Cd poses high risks. Considering the present findings, it was observed that primarily Cd and partially Pb reached soils near urban areas, exhibited accumulation and may be easily incorporated into water and plants through the mobile phases. Therefore, it is concluded that the relevant metals, especially Cd, should be controlled and monitored.

Arsenic fractionation and mobility in sulfidic wetland soils during experimental drying

In this study, two Czech wetland soils enriched in authigenic sulfide minerals (especially realgar) were collected from the saturated zone (60–100 cm), flooded with local groundwater and allowed to dry for up to 98 days. The objective was to examine the mobility of As, Fe, S and trace metals using selective chemical extractions, S isotopes and X-ray diffraction through the drying process. During the initial stage of incubation (∼20 days), the re-flooding of the soils triggered a microbially-mediated SO42− reduction, which immobilized the Co, Cu and Ni. The reductive dissolution of As-bearing Fe (oxyhydr)oxides and the release of As were documented only in the Fe-rich/organic-low soil. Over the next stage of incubation (∼75 days), the exposure and drying of the soils led to the oxidation of the Fe and As sulfides. The arsenic and trace metals released via oxidation of the sulfide phases (particularly Fe sulfides) were almost entirely sequestered by the Fe(III) (oxyhydr)oxides, but acidification during the oxidation stage of the incubation resulted in the pH-dependent release of the As and trace metals (Co, Cu, Ni) (especially in the Fe-rich/organic-low soil). These findings suggest that sulfidic soils in wetlands can be considered as long-term sources of As during major drought events.

Salinity-induced fluorescent dissolved organic matter influence co-contamination, quality and risk to human health of tube well water, southeast coastal Bangladesh

Salinity in the drinking water of coastal Bangladesh results from a severe socio-economic, environmental and human health safety crisis. In this paper, we analyzed 120 tube well water samples from southeast coastal Bangladesh for eight trace metals (TMs). Contamination, quality and risk of TMs to human health of tube well water influenced by salinity-induced fluorescent dissolved organic matter (FDOM) were assessed using multiple pollution indices, GW quality index (GWQI), traditional health risk, and PARAFAC models. The mean values of EC, Fe, Cd, Cr, and As surpassed the limit set by local and international standards with significant spatial variations. The results of the GWQI showed that 52.5% of the samples were within the moderate-poor quality range in the study region. PARAFAC modeling identified three groundwater FDOM constituents with a coupling of humic acid (HA), fulvic acid (FA), and degraded fulvic acid (DFA)-like substances. Moreover, the positive correlations among EC, TMs, HA, FA, and DFA proved that salinity-induced FDOM had significant contributions to the dissolution potential of contaminants in the aquifer, hence increased the mobilization of TMs. Health risk models suggested that children are more susceptible to the non-carcinogenic and carcinogenic risks than adults at the community level. The carcinogenic risks of Cd, As, Pb, and Cr via oral exposure pathway indicated the highest carcinogenic risks for both adults and children. The findings also indicated that the salinity-derived FDOM-TMs complex is the key driver to groundwater co-contaminations and elevated health impacts. Besides, high concentrations of Fe and As are the key causal issues for sustainable water safety. Thus, strict water management and monitoring plans require preventing these contaminants for sustainable community well-being in the coastal region.

Effect of different amendments on trace metal bioavailability in agricultural soils and metal uptake on lettuce evaluated by Diffusive Gradients in Thin Films

In this study, we have investigated the effect of two different organic amendments on trace metal transfer from soils to crops. Agricultural soils were mixed with (i) biochar (BC) at two levels (3% and 6%, w/w), and (ii) compost at one level (30%, w/w). Lettuce ( Lactuca sativa L.) was planted, and at the end of growth, trace metals (Cd, Cr, Cu, Ni, Pb and Zn) were analysed in both plants and soil. To evaluate the bioavailability and mobility of labile trace metals, different methodologies were used, such as the diffusive gradients in thin films (DGT) technique, BCR sequential extraction and pore water extraction. It has been observed that the lettuces grown in soils with added compost, the amounts of Cd, Cr, Cu and Pb was 1.7, 2.4, 1.3 and 3.7 times lower, respectively, than those found in lettuces planted in soils with no amendment. Moreover, the addition of 3% of BC reduced the uptake of Cr (24%) whereas a 6% of BC reduced Cr (55%) and Pb (50%) levels. Using the DGT technique in soils with different organic matter (OM) content, labile fractions of Cr, Cu and Pb were successfully correlated (p < 0.05) with lettuce total metal concentrations. In conclusion, BCR sequential extraction and DGT method have shown similar efficiency in front other methodologies, although it seems that DGT-methodology is faster and more cost-effective method than sequential extraction for predicting metal uptake by plants. • We tested the effect of biochar and compost applications on metal uptake by lettuce. • Uptake of Cd, Cr, Cu and Pb was 2 to 4 times lower with compost than in nonamended soils. • Biochar produces a greater weight of leaves, roots and total biomass of lettuces. • Biochar also increases leaf length and enhances significantly leaf chlorophyll content. • The effective concentration of Cr, Cu and Pb was significant correlated with metals in lettuce.

Ecological risk assessment of trace metals in sediments under reducing conditions based on isotopically exchangeable pool

Determination of potential mobility of toxic trace metals in sediments under changing redox condition is important in ecological risk assessment. Current methods are limited in risk prediction in such dynamic environment. In this study, we have discussed the general disagreement from widely used methods (sediment quality guideline (SQGs), potential ecological risk index (PERI), risk assessment code (RAC) using BCR fraction information). In addition, the stable isotopic dilution method (IDM) was also modified to quantify metal lability in a microcosm experiment mimicking river bank sediment turning into anaerobic. The isotopically exchangeable Cd, Cu, Pb, and Zn quantified by IDM (%E incub) was used in the RAC to reveal the trend of risk during this process. Strong risks from Cd are suggested by the PERI and RAC as a result of high toxicity and mobility of the element, while SQGs suggests medium risk for Cu, Pb, and Zn in certain samples. The disagreement between the results of RAC assessed by metal lability (%E dry) and by BCR metal fractionation reflects the effect of sediment properties and source of metal contamination. The RAC based on the non-residual fractions is likely to overestimate the potential risk for most metals even there is a significant change in sediment Eh. The RAC assessed by %E incub reveals that the variability in risk in response to the reducing Eh is not consistent. Large fluctuation in %E incub for Cd (28.5%, 49.5%), Pb (27.6%, 18.2%), and Cu (14.4%, 24.7%) can shift the risks to a higher level in certain range of Eh in two sediments. In sediment with lower contents of metal binding phases (e.g. mineral oxides, organic matters), the release of metals can be more significant, thus higher ecological risk in changing redox condition.

Investigation on trace metal speciation and distribution in the Scheldt estuary

The biogeochemical behavior of Cd, Co, Cr, Cu, Ni and Pb along the historically polluted Scheldt estuary (Belgium - The Netherlands) was investigated in this study. As never studied before in this area, labile trace metals were measured using the passive sampling technique of Diffusive Gradients in Thin-films (DGT), while total dissolved and particulate trace metal concentrations were assessed using classic active sampling techniques. This dual approach allowed us to highlight the variations of trace metal speciation and distribution in the estuarine surface waters, considering environmental and physicochemical gradients along the transect. The large data set obtained was then compared with literature data of historical measurements along the Scheldt (from 1980 until now), but also from other estuaries. As emphasized by our results, trace metal mobility and partitioning along the Scheldt estuary was mainly driven by biogeochemical reactions which were strongly influenced by gradients of specific estuarine physico-chemical parameters, such as salinity, turbidity, temperature and so on. Hence, all species of trace metals displayed a non-conservative behavior. More precisely, dissolved labile fractions of trace metals showed higher levels in the middle estuary, where many solubilization and remobilization processes occurred due to turbulent mixing mechanisms and an increasing salinity. Our study confirmed the decreasing trend historically observed for particulate metals along the Scheldt, as well as the rising concentrations recorded for dissolved trace metals which might also lead to an increase of their labile fraction measured by the DGT. Finally, these preliminary results suggested that a more regular monitoring of labile metal along the Scheldt estuary is essential to have an in-depth understanding of trace metal speciation and to review bioavailability of trace metals within estuarine ecosystems.

Trace metal biogeochemical responses following wood ash addition in a northern hardwood forest

Wood ash may be useful as a forest soil amendment in Canada, but trace metals can have detrimental effects if they accumulate in, or are transported from, forest ecosystems. Metal concentrations in soil water and sugar maple (Acer saccharum Marsh.) seedling tissue chemistry were measured in a north temperate hardwood forest over 4 years following a biomass boiler ash addition field trial. Twenty plots (3 m × 3 m) were established in Haliburton Forest with both fly and bottom ash treatments of 0, 4, and 8 Mg·ha−1 with four replicates, and tension lysimeters were positioned in each plot at 30, 50, and 100 cm depths. Over the 4 years, soil water metal concentrations in treated plots were not significantly different from those of the control plots. No differences in metal concentrations in foliage of sugar maple seedlings could be detected, but there were significantly higher concentrations of some metals (Al, Fe, Zn, Pb, Ni, and Sr) in roots of treated plots. Simulated drought mobilized several metals in upper mineral soil, but this mobilization occurred similarly in controls and ash-treated soils. These results suggest that doses below 8 Mg·ha−1 industrial wood ash with trace metal concentrations below Canadian regulatory limits do not cause an increase in trace metal mobility or availability in northern hardwood forests with acidic soils during the first 5 years after application.

The Solubility of Phosphogypsum and Recovery of Heavy and Radioactive Elements

The essential purpose of this paper is to illustrate and inspect the leaching characteristics of Iraqi Phosphogypsum (PG). The paper presents the results of the dissolution characteristics of heavy and radioactive elements from PG, which is a by-product result from the industry of phosphate fertilizers. Leachability of heavy and radioactive elements in deionized water that has been inspected under various states of leaching, including solid/liquid ratio (10, 20 and 50 /1g/L) and temperatures (25, 45 and 85 °C), with constant other parameters such as string speed (300 rpm) and contact time (60 minutes). For the most analysis elements, the progressive release of the metals, in addition to the major elements reflects high mobility. The mobility of trace metals in PG has been generally classified into three main degrees: (1) high mobility elements such as Pb, Zn, Mn, and Cr; (2) moderate mobility elements such as Sr, V, Ba,Y,Hg, K and Ni; and (3)l ow mobility elements like Ca,Cu,Fe, and Ag. The maximum concentrations of the most of the metals were attained from a leaching state of 10/1g/L. Regarding temperature, the experimental results revealed that the PG solubility to leaching out elements increases noticeably as the applied temperature ranges from 25 to 45 °C; after this degree, the leaching efficiency decreases. Chloride had a positive and negative effect on the solubility of phosphorus. Calcium chloride had an adverse effect on solubility and observed reduced solubility with increased chloride. While the positive effect of sodium and magnesium chloride was observed, the solubility...

Schwertmannite transformation to goethite and the related mobility of trace metals in acid mine drainage

In acid mine drainage (AMD), precipitated schwertmannite can reduce the trace metal concentration by adsorption and co-precipitation. With the geochemical changes in the water, the precipitated minerals are transformed into more stable goethite. However, no detailed systematic studies have been performed on the mobility changes of trace metals during iron-mineral transformation. The behaviors of trace metals during the transformation of schwertmannite to goethite are investigated for core samples from an AMD treatment. Schwertmannite had gradually transformed to goethite from the top to the bottom of the core samples. Among trace metals, Pb was highly retained in schwertmannite during precipitation, probably by co-precipitation with schwertmannite. Arsenate and chromate were also relatively well retained in schwertmannite, probably because of the substitution of sulfate during precipitation. Sequential extraction results showed that during the transformation of schwertmannite to goethite, most trace metals decreased their mobility by decreasing their exchangeable fraction. However, only Pb increased its mobility during transformation. Some elements, such as Cd and Co, had higher contents of exchangeable fractions compared to other metals and can be relatively easily released into water with slight geochemical changes, greatly affecting the environments of ecological systems.

Prevalence and Chemo-kinesis of Toxic Trace Metals in Environmental Samples

The aim of the study was to assess incidences, level and mobility of some toxic trace metals in environmental samples. By this, the potential impacts of anthropogenic activities on environmental and human health would be evaluated. Soil, plant and lower animal samples were randomly collected from stratified study area, labelled and taken to the laboratory for pre-treatment and analysis. Acid digestion technique was employed for the isolation of metallic contents in samples and quantitation was by Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-OES). The analytical protocol was validated through the quality assurance process which was found acceptable with quantitative metallic recoveries in the range of 85-90 %; hence considered applicable for the analyses of samples. The mean concentration of analysed metals in soil samples ranged from 53.2-2532.8 mg/kg (Cu); 59.5-2020.1 mg/kg (Zn); 1.80 –21.26 mg/kg (Cd) and 19.6-140.9 mg/kg (Pb). The mean level in grass samples ranged from 9.33 –38.63 mg/kg (Cu); 64.20-105.18 mg/kg (Zn); 0.28–0.73 mg/kg (Cd) and 0.53 -16.26 mg/kg (Pb) while the mean level in lower animal sample (beetle) varied from 9.6 -105.3 mg/kg (Cu); 134.1-297.2 mg/kg (Zn); 0.63 –3.78 (Cd) and 8.0 –29.1 mg/kg (Pb) across sample collection points (SCPs) 1-4 respectively. Metallic transfer factors (TFs) were in the order Zn &gt;Cd &gt; Cu&gt; Pb with metal Pollution Indices (MPIs) in the order SCP1 &gt; SCP2 &gt; SCP3 &gt; SCP4. About 60-70 % of analysed metals were above the Maximum Allowable Limits (MALs) in soil and plant samples using the European Economic Commission (EEC) and CODEX MALs respectively.Results obtained revealed general prevalence of analysed metals at all sampled sites with indication of metallic mobility across the food chain. This signifies dire consequences for environmental and human health. Control of pollution from source and passive environmental remediation strategies are recommended