Mobility Of Potentially Toxic Elements Research Articles

Potential influence mechanism of mineral–organic matter (OM) interactions on the mobility of toxic elements in Pb/Zn smelter contaminated soils

To date, how complex mineral–organic matter (OM) interactions affect the migration and mobility of potentially toxic elements (PTEs) in soils is highly understudied. This work mainly focused on the occurrence characteristics of PTEs and their close association with the composition characterization of mineral elements and dissolved OM (DOM) molecules. The results revealed that quartz (20.20%), albite (15.60%) and biotite (14.37%) were the dominant minerals in soils. CHO molecules were most abundant, accounting for 58.41%. The unsaturated hydrocarbons with both low and high O/C ratios were the dominant organic compounds, accounting for 21.56% and 36.73%, respectively. Sequential extraction results indicated that most Cd was hosted in carbonate minerals, while considerable amounts of As, Cu, Mn, Pb and Zn were bound to Fe/Mn oxyhydroxides. The elemental distribution characteristics displayed the coexistence of As, Cd, Cu, Mn, Pb and Zn with O, S, Al, Si, Ca and Fe. Fe oxyhydroxides might preferentially retain the unsaturated hydrocarbons with low O/C ratio and phenols. Furthermore, Fe oxide–organic composites had more significant impacts on Mn than As, Cd, Cu, Pb and Zn mobility. Overall, these findings would provide important insights into how mineral–OM interactions played the key roles on PTEs mobility in soils.

Assessment of potentially toxic and mineral elements in paddy soils and their uptake by rice (Oryza sativa L.) with associated health hazards in district Malakand, Pakistan

Rice, a primary food source in many countries of the world accumulate potentially harmful elements which pose a significant health hazard to consumers. The current study aimed to evaluate potentially toxic and mineral elements in both paddy soils and rice grains associated with allied health risks in Malakand, Pakistan. Rice plants with intact root soil were randomly collected from paddy fields and analyzed for mineral and potentially toxic elements (PTEs) through inductively coupled plasma optical emission spectrometry (ICP‒OES). Through deterministic and probabilistic risk assessment models, the daily intake of PTEs with allied health risks from consumption of rice were estimated for children and adults. The results of soil pH (< 8.5) and electrical conductivity (EC > 400 μs/cm), indicated slightly saline nature. The mean phosphorus concentration of 291.50 (mg/kg) in soil samples exceeded FAO/WHO permissible limits. The normalized variation matrix of soil pH with respect to Ni (0.05), Ca (0.05), EC (0.08), and Mg (0.09), indicated significant influence of pH on PTEs mobility. In rice grains, the mean concentrations (mg/kg) of Mg (463.81), Al (70.40), As (1.23), Cr (12.53), Cu (36.07), Fe (144.32), Mn (13.89), and Ni (1.60) exceeded FAO/WHO safety limits. The transfer factor >1 for K, Cu, P and Zn indicated bioavailability and transfer of these elements from soil to rice grains. Monte Carlo simulations of hazard index >1 for Cr, Zn, As, and Cu with certainties of 89.93% and 90.17%, indicated significant noncarcinogenic risks for children and adults from rice consumption. The total carcinogenic risk (TCR) for adults and children exceeded the USEPA acceptable limits of 1×10−6 to 1×10−4, respectively. The sensitivity analysis showed that the ingestion rate was a key risk factor. Arsenic (As) primarily influenced total cancer risk (TCR) in children, while chromium (Cr) significantly impacted adults. Deterministic cancer risk values slightly exceeded probabilistic values due to inherent uncertainties in deterministic analysis. Rice consumption poses health risks, mainly from exposure to Cr, Ni and As in the investigated area.

Evaluation of potentially toxic elements in soils developed on limestone and lead-zinc mine sites in parts of southeastern Nigeria

The present study investigated the distribution of elements and potentially toxic elements (PTEs) in soil profiles in the southeastern region of Nigeria, where unrefined and primitive mining practices are common. Soil samples were collected from mine and non-mine sites in Ameka and Nkalagu and analyzed for total elemental concentration using portable X-ray fluorescence (pXRF). The results showed that the Ameka mine-affected soils were heavily polluted, while the Ameka non-mine-affected soils were moderately polluted. The Nkalagu mine and non-mine-affected soils were also moderately polluted. The potential ecological risk (PER) was high in the Ameka mine-affected site due to elevated As, Cu, and Pb levels, while the Ameka non-mine-affected site had a low PER. The enrichment factor (EF) values indicated more enrichment of PTEs in the mine-affected sites compared to the non-mine-affected sites. The geoaccumulation index (Igeo) showed moderate to extreme contamination in the Ameka mine-affected site with Cu, Zn, As, and Pb. In contrast, the Nkalagu mine-affected site had considerably lower contamination. The regression model showed that site characteristics alone were insufficient to explain elements and PTEs distribution, emphasizing the importance of considering soil properties in understanding their spatial patterns. The study highlights the higher concentrations of As, Cu, and Pb in the mine-affected sites compared to the non-mine areas and recommends remediation strategies for these elements and PTEs, especially in the vicinity of mine sites. Further laboratory analysis is recommended to understand the mobility of PTEs with depth for better remediation approaches.

Mobility and Fate of Potentially Toxic Elements in Soil Environment

AbstractSoil pollution, caused by potentially toxic elements (PTEs), is a significant problem worldwide. This study has investigated the key factors that control the mobility and fate of six PTEs (Pb, Cd, Cr, Cu, Zn, and Ni) which are frequently detected in contaminated soils. The findings of this study demonstrate that smaller particles present in soil show stronger adsorption capacity compared to larger particles because of the higher specific surface area. Moreover, soil with higher organic matter content (e.g., humic acid) exhibits stronger adsorption capacity due to the presence of abundant functional groups namely hydroxyl (─OH) and carboxyl (─COOH). Notably, these functional groups possess high affinity for Pb adsorption, followed by Cd &gt; Cu &gt; Cr &gt; Zn &gt; Ni. The adsorption of most of the PTEs by soil with and without humic acid is better described by the Langmuir isotherm model and pseudo‐second‐order kinetic model. Overall, the experimental results illustrate that soil with high contents of humic acid can restrict the mobility of PTEs. This mechanistic evaluation predicts how soils with different organic matter contents respond to PTEs pollution. This study outcome will be helpful in developing sustainable remediation strategies to tackle pollution caused by PTEs in the soil environment.

Mixing Compost and Biochar Can Enhance the Chemical and Biological Recovery of Soils Contaminated by Potentially Toxic Elements.

Biochar and compost are able to influence the mobility of potentially toxic elements (PTEs) in soil. As such, they can be useful in restoring the functionality of contaminated soils, albeit their effectiveness can vary substantially depending on the chemical and/or the (micro)biological endpoint that is targeted. To better explore the potential of the two amendments in the restoration of PTE-contaminated soils, biochar, compost (separately added at 3% w/w), and their mixtures (1:1, 3:1, and 1:3 biochar-to-compost ratios) were added to contaminated soil (i.e., 2362 mg kg-1 of Sb and 2801 mg kg-1 of Zn). Compost and its mixtures promoted an increase in soil fertility (e.g., total N; extractable P; and exchangeable K, Ca, and Mg), which was not found in the soil treated with biochar alone. All the tested amendments substantially reduced labile Zn in soil, while biochar alone was the most effective in reducing labile Sb in the treated soils (-11% vs. control), followed by compost (-4%) and biochar-compost mixtures (-8%). Compost (especially alone) increased soil biochemical activities (e.g., dehydrogenase, urease, and β-glucosidase), as well as soil respiration and the potential catabolic activity of soil microbial communities, while biochar alone (probably due to its high adsorptive capacity towards nutrients) mostly exhibited an inhibitory effect, which was partially mitigated in soils treated with both amendments. Overall, the biochar-compost combinations had a synergistic effect on both amendments, i.e., reducing PTE mobility and restoring soil biological functionality at the same time. This finding was supported by plant growth trials which showed increased Sb and Zn mineralomass values for rigid ryegrass (Lolium rigidum Gaud.) grown on biochar-compost mixtures, suggesting a potential use of rigid ryegrass in the compost-biochar-assisted phytoremediation of PTE-contaminated soils.

Potentially Toxic Elements: A Review on Their Soil Behavior and Plant Attenuation Mechanisms against Their Toxicity

The presence of potentially toxic elements (PTEs) can induce phytotoxicity and growth inhibition in plants. These elements are bioaccumulated and biomagnified in the food chain due to their high stability and resistance to biodegradation. The availability and mobility of PTEs in soil depend on certain physicochemical procedures. Many scientific studies on PTEs have provided valuable information about the processes, environmental fate, effects and remediation techniques. However, there is a need for gathering and presenting all up-to-the-date information concerning mechanisms and processes of PTE mobility in the soil-plant interface. More specifically, soil chemical reactions and processes need to be discussed under the light of PTE potential uptake by plants, as well as the physiological mechanisms at plant molecular level of PTE attenuation when plants are subjected to PTE stress. Thus, in this study we discuss the important soil processes that influence the bioavailability of PTEs for plant uptake. We also elucidate the mechanisms such as phytochelation and antioxidant defense through which plants can mitigate PTE toxicity, enhance their tolerance, and promote their survival in contaminated soils. Moreover, we discuss the major mechanisms of reactive oxygen species (ROS) production and the strategies for ROS scavenging which involve enzymes and non-enzymatic compounds that demonstrate antioxidant effects. In conclusion, this review provides a comprehensive understanding regarding PTE toxicity, utilization and transportability. It could be used by the scientific community and soil end-users towards a better understanding of the mechanisms that plants use to alleviate PTE toxicity, significantly affecting the potential use of plants in soil remediation programs and their capacity to grow in PTE-contaminated soils.

Yedoma Permafrost Releases Organic Matter with Lesser Affinity for Cu2+ and Ni2+ as Compared to Peat from the Non-Permafrost Area: Risk of Rising Toxicity of Potentially Toxic Elements in the Arctic Ocean.

Pollution of the Arctic Ocean by potentially toxic elements (PTEs) is a current environmental problem. Humic acids (HAs) play an important role in the regulation of PTE mobility in soil and water. The permafrost thaw releases ancient organic matter (OM) with a specific molecular composition into the Arctic watersheds. This could affect the mobility of PTEs in the region. In our study, we isolated HAs from two types of permafrost deposits: the Yedoma ice complex, which contains pristine buried OM, and the alas formed in the course of multiple thaw-refreezing cycles with the most altered OM. We also used peat from the non-permafrost region as the recent environmental endmember for the evolution of Arctic OM. The HAs were characterized using 13C NMR and elemental analysis. Adsorption experiments were conducted to assess the affinity of HAs for binding Cu2+ and Ni2+. It was found that Yedoma HAs were enriched with aliphatic and N-containing structures as compared to the much more aromatic and oxidized alas and peat HAs. The adsorption experiments have revealed that the peat and alas HAs have a higher affinity for binding both ions as compared to the Yedoma HAs. The obtained data suggest that a substantial release of the OM from the Yedoma deposits due to a rapid thaw of the permafrost might increase the mobility of PTEs and their toxicity in the Arctic Ocean because of much lesser "neutralization potential".

Impact of the change in irrigation practices from untreated to treated wastewater on the mobility of potentially toxic elements (PTEs) in soil irrigated for decades

PurposeLong-term agricultural irrigation with untreated wastewater has resulted in metals and metalloids accumulation in soil. Little information is available on the consequences of a change to irrigation with treated water on the mobility of these potentially toxic elements (PTEs).Materials and methodsThe potential mobility of PTEs was assessed using sequential extractions performed on soil irrigated with untreated wastewater for a century in Mexico. The possible effects of change in irrigation practices on PTEs mobility was evaluated through batch experiments, simulating a decrease in pH, an increase in salinity, and in chlorine of the irrigation water. Geochemical modeling allowed predicting the speciation of mobilized PTEs.Results and discussionSoils irrigated with untreated water were mainly enriched with PTEs in surface horizons. Only Cd and As were found in the soluble or exchangeable fractions (< 20%). Cu and Pb were mainly associated with soil organic matter (OM), whereas As and Zn were bound to iron oxides, and Cr with refractory minerals. Batch experiments revealed that acidification resulted in the increased solubility of Cu, Zn, and Cd for surface samples, and As in deep horizons. In contrast, increased salinity only mobilized Zn, Cd, and Cr. Water chlorination mobilized higher amount of Zn, Pb, and Cd compared to the other experiments. As was not mobilized for these two experiments.ConclusionA change in irrigation practices could increase the mobility of PTEs if water treatment is not adapted to the soil type. The mobilization of PTEs, especially As and Cd, could affect both crops and groundwater quality. It is essential to monitor this mobility to avoid future risks to human health.

Mobility of Potentially Toxic Elements (Pb, Zn, Cd, As, Sb) in Agricultural Carbonated Soils Contaminated by Mine Tailings (Northern Tunisia): A New Kinetic Leaching Approach with Organic Acids

The present study was carried out to show the potential of root exudates to mobilize potentially toxic elements (PTE) present in rhizospheric carbonated soils. Five different contaminated rhizospheric soils were collected from five former mining districts of northern Tunisia (Jebel Hallouf (H3), Sidi-Bouaouane (B1), Jebel Ghozlane (G7), Hammam Zriba (Z2) and Jalta (J2)). The abundant minerals in these soils are quartz, calcite and clays. These soils contain significant PTE amounts compared to the local geochemical background (LGB). The important concentrations of Pb, Zn, Cd, As and Sb are, respectively, in the order of 17,350 mg·kg−1 in B1, 37,000 mg·kg−1 in G7, 205 mg·kg−1 in G7, 683 mg·kg−1 in B1 and 145 mg·kg−1 in B1. Kinetic leaching tests were conducted with a mixture of low molecular weight organic acids (LMWAOs) for increasing times up to 16 h (initial pH = 2.8) to study the mobility of PTE in the rhizospheric soils. The results showed an increase in the pH of the solution (2.8) to values up to neutrality together with the increase in Ca and Mg concentrations in the leachate, resulting from the dissolution of carbonates (calcite and dolomite). Additionally, leaching tests showed important extractions of Cd and Zn (25% for Cd and 11% for Zn). Pb was also mobilized but to a lesser extent (5%). The extractability of metalloids (As and Sb) was, in contrast, relatively low, except for Jebel Hallouf and Sidi Bouaouane soils, with an extraction percentage of no more than 1% for Sb and 0.1% for As, respectively. The mobility of Zn, Pb and Cd was thought to be controlled by both the solubility of their host minerals (e.g., sphalerite, hemimorphite, cerussite and jordanite) and the high pH. In contrast, As and Sb mobility was dependent on secondary carrier phases such as iron oxyhydroxides.

Changes in potentially toxic element concentration and potential ecological risk in topsoil caused by sewage sludge application on forestland: A 3-year field trial

Sewage sludge (SS) application on forest plantation soils as a fertilizer/soil amendment is increasingly becoming a forestry management measure. However, the potential risk of SS-derived potentially toxic elements (PTEs) is still a cause for concern. This research was carried out to evaluate PTEs behavior in SS applied as an amendment for forestland application purposes. Speciation and transformation perspectives on residual effects during a 3-year field experiment were evaluated. Sewage sludge was applied to soils under Eucalyptus urophylla S.T. Blake, Schima superba Gardn. et Champ, and Pinus elliottii Engelm plantations at 30 Mg·ha−1 (dry weight). We investigated the total concentrations of Cu, Zn, Pb, Cd, and Ni, as well as their concentrations of five fractions: exchangeable (F1), bound to carbonates (F2), Fe–Mn oxides (F3), organic matter (F4), and residual (F5) along with the 0–10 cm of a surface A horizon (topsoil) one day, one, two, and three years after SS application, respectively. Sewage sludge caused significant increase in PTEs total concentrations and proportion of fraction F1 or F2. The mobility index and potential ecological risk confirmed that the risk was linked to the presence of these PTEs, especially for Cd. The total concentration and corresponding ecological risks of PTEs in most cases decreased, suggesting a potential loss of PTEs from the topsoil system. The percentage of all PTEs in fractions F1–F4 decreased and that in F5 increased with time. These results illustrate that the residual and mobility of PTEs in the topsoil during SS utilization was lower than expected and more attention should be paid to the risk of PTEs transferring to other environments.

Influence of biochar and soil properties on soil and plant tissue concentrations of Cd and Pb: A meta-analysis

The application of biochar to soils contaminated with potentially toxic elements (PTEs) has received particular attention due to its ability to reduce PTE uptake by the plants. Therefore, we conducted a meta-analysis to identify Cd and Pb concentrations in plant shoots and roots in response to biochar application and soil properties. We collected data from 65 peer-reviewed journal articles published from 2009 to 2020 in which 66% of manuscripts were published from 2015 to 2020. The data were processed using OpenMEE software. The results pinpointed that addition of biochar to soil caused a significant decrease in shoot and root Cd and Pb concentrations as compared to untreated soils with biochar (control), and the reduction rate was affected by plant types and both biochar and soil properties. The biochar size less than 2 mm, biochar pH higher than 10, pyrolysis temperature of 401–600 °C, and the application rate higher than 2% appeared to be effective in reducing shoot and root Cd and Pb concentration. Soil properties such as pH, SOC, and texture influenced the efficiency of biochar for reducing plant Cd and Pb uptake. Biochar application increased SOC (54.3%), CEC (48.0%), pH (0.08), and EC (59.4%), and reduced soil extractable Cd (42.1%) and Pb (47.1%) concentration in comparison to control. A detailed study on the rhizosphere chemistry and uptake mechanism will help to underpin the biochar application rates and their efficiency reducing PTE mobility and plant uptake.

Source patterns of potentially toxic elements (PTEs) and mining activity contamination level in soils of Taltal city (northern Chile).

Mining activities are among the main sources of potentially toxic elements (PTEs) in the environment which constitute a real concern worldwide, especially in developing countries. These activities have been carried out for more than a century in Chile, South America, where, as evidence of incorrect waste disposal practices, several abandoned mining waste deposits were left behind. This study aimed to understand multi-elements geochemistry, source patterns and mobility of PTEs in soils of the Taltal urban area (northern Chile). Topsoil samples (n = 125) were collected in the urban area of Taltal city (6km2) where physicochemical properties (redox potential, electric conductivity and pH) as well as chemical concentrations for 35 elements were determined by inductively coupled plasma optical emission spectrometer. Data were treated following a robust workflow, which included factor analysis (based on ilr-transformed data), a new robust compositional contamination index (RCCI), and fractal/multi-fractal interpolation in GIS environment. This approach allowed to generate significant elemental associations, identifying pool of elements related either to the geological background, pedogenic processes accompanying soil formation or to anthropogenic activities. In particular, the study eventually focused on a pool of 6 PTEs (As, Cd, Cr, Cu, Pb, and Zn), their spatial distribution in the Taltal city, and the potential sources and mechanisms controlling their concentrations. Results showed generally low baseline values of PTEs in most sites of the surveyed area. On a smaller number of sites, however, higher values concentrations of As, Cd, Cu, Zn and Pb were found. These corresponded to very high RCCI contamination level and were correlated to potential anthropogenic sources, such as the abandoned mining waste deposits in the north-eastern part of the Taltal city. This study highlighted new and significant insight on the contamination levels of Taltal city, and its links with anthropogenic activities. Further research is considered to be crucial to extend this assessment to the entire region. This would provide a comprehensive overview and vital information for the development of intervention limits and guide environmental legislation for these pollutants in Chilean soils.

Effects of natural zeolites on ryegrass growth and bioavailability of Cd, Ni, Pb, and Zn in an Albanian contaminated soil

The use of eco-friendly and cost-effective adsorbent materials in the remediation of soils contaminated by potentially toxic elements (PTE) is a sustainable way of reducing the transfer of these elements into the food chain. However, an evaluation of the potential of natural zeolites to immobilize toxic elements in contaminated soils was required to enable their efficient use. The effect of natural zeolite (Stilbite-Stellerite) from the Munella area (Northern Albania), added at rates ranging from 1.25 to 10 % w/w on a contaminated soil was investigated in a greenhouse pot experiment with ryegrass (Lolium multiflorum L.) and by selective extractions. PTE availability for plants was assessed either as their accumulation in plant tissue or by DTPA-extraction. Oral bio-accessibility was estimated by the in vitro PBET method and the mobility and consequent potential risk of leaching by the USEPA TLCP method. The effect of zeolites on soil properties (pH, electrical conductivity-EC, organic C, and total N) was also investigated. A five steps sequential extraction procedure (SEP) was applied to investigate the immobilization mechanism. The addition of 2.5% w/w of natural zeolites caused a significant decrease of PTE mobility, but to observe a significant reduction of DTPA-extractable metals, it was necessary to reach 10% addition rate. In contrast, plant growth showed a gradual increase with addition rate and a corresponding decrease of concentration of PTE in plant tissue. Correlation between DTPA-extractable PTE and their concentration in both root and shoot plant tissue was rather poor. Human hazard due to soil ingestion (PBET method) changed only for Cu and Zn in the gastric phase with 1.25 and 5% addition rate respectively, whereas decreased for Cu and Zn at 5% rate in the Intestinal phase. The results of SEP support the hypothesis that the main mechanism involved in metals fixation are as follows: (1) insolubilization by pH rise, (2) adsorption on Fe/Mn oxides (3) increase of cation exchange retention, (4) organic complexation. The results of this work suggest that the addition of natural zeolites from the Munella area (AL) is a sustainable practice to reduce the environmental impact of PTE contaminated soils, but an assessment on the longevity of their immobilization need to be evaluated in the long-term perspectives.

Chemical mobility of inorganic elements in stream sediments of a semiarid zone impacted by ancient mine residues

Water availability is a worldwide issue, particularly in semiarid zones. Therefore, it is necessary to know the geochemical processes involved in the mobility of contaminant sources to ensure adequate quality for this resource. Some mining areas of México are of economic importance; however, they are also the sources of large quantities of mine residues, such as the site included in this study. As an important aspect of understanding contaminant mobility in sediments and water, a thorough mineralogical characterization is paramount to identify sources and sinks for relevant elements, in this case, potentially toxic elements (PTEs) such as arsenic (As), lead (Pb) and cadmium (Cd); hence, scanning electron microscopy (SEM), X-ray diffraction (XRD) and chemical analysis were used. The total geochemical distribution was established by means of a modified selective sequential extraction procedure. The results showed that sediments constitute an effective attenuation substrate for mobilized PTEs to groundwater. Hence, arsenic and cadmium were stabilized in the sediments and/or the vadose zone, and although Pb and Zn were identified in groundwater with concentrations above the background values, they were below drinking water standards. Sulfate and total hardness concentrations in the groundwater confirmed the impact of acid mine drainage (AMD) infiltration. Considering that similar sites in Mexico are found along the Sierra Madre Oriental, the methodology of this study could be applied to understand the mobility of PTEs in the sediments and waters of semiarid environments.

Application of pyrogenic carbonaceous product for immobilisation of potentially toxic elements in railway sleepers and polluted soil

In the last decades, there is a growing concern about soils polluted with potentially toxic elements (PTE) and their negative impact on the ecosystems. In the recent year, biochar is intensively investigated not only for carbon sequestration or soil productivity enhancement but also like a new sorbent for polluted soils’ remediation. The aim of this work is: (1) to assess the effect of two pine wood biochar types (produced at 450 and 700 °C temperatures) on the PTE mobility in the solution of the former sewage sludge soil; (2) to make risk assessment of pyrogenic carbonaceous product made from railway sleepers and (3) to assess pine wood biochar (700 °C) impact on the PTE uptake to oat (Avena sativa L.). Three different experiments were done: (1) incubation; (2) leaching and (3) bioaccumulation. Incubation experiment showed that both pine wood biochar types showed good immobilisation efficiency in the case of Cd (> 85%), but lower temperature biochar (450 °C) had higher efficiency used in the immobilisation of Zn (78%) and Cu (76%) in multi-polluted soil. Leaching experiment showed that both biochar types well retained Pb (> 99%), but lower temperature biochar had greater retention efficiency in the case of Cu (93%).

Controlled burn and immediate mobilization of potentially toxic elements in soil, from a legacy mine site in Central Victoria, Australia

Conducting controlled burns in fire prone areas is an efficient and economic method for forest management, and provides relief from the incidence of high severity wild fires and the consequent damage to human property and ecosystems. However, similar to wild fires, controlled burns also affect many of the physical and biogeochemical properties of the forest soil and may facilitate remobilization of potentially toxic elements (PTEs) sequestered in vegetation and soil organic matter. The objective of the current study is to investigate the mobilization of PTEs, in Central Victorian forest soils in Australia after a controlled burn. Surface soil samples were collected two days before and after the controlled burn to determine the concentration of PTEs and to examine the physicochemical properties. Results show that As, Cd, Mn, Ni and Zn concentrations increased 1.1, 1.6, 1.7, 1.1 and 1.9 times respectively in the post-burn environment, whereas the concentrations of Hg, Cr and Pb decreased to 0.7, 0.9 and 0.9 times respectively, highlighting considerable PTE mobility during and after a controlled burn. Whilst these results do not identify very strong correlations between physicochemical properties of soil and PTEs in the pre- and post-burn environments, PTEs themselves demonstrated very strong and significant correlations. The mobilization of As, Hg and other toxic elements raise potential health concerns as the number of controlled burns are projected to increase in response to climate change. Due to this increased level of PTE release and remobilization, the use of any kinds of controlled burn must be carefully considered before being used as a forest management strategy in mining-affected landscapes which include areas with high PTE concentrations.

Effect of mycorrhizal inoculation on metal accumulation by poplar leaves at phytomanaged sites

Phytotechnologies for the management of lands contaminated with potentially toxic elements (PTEs) are considered as gentle alternatives to conventional remediation techniques. During the last few years, phytotechnologies have progressively shifted to phytomanagement, a concept that includes the valorization of the plant biomass produced on the contaminated site. This study aimed at evaluating the mid-term effect of ecto- and endomycorrhizal inoculation on the reduction of PTE mobility in soils and foliar accumulation by two poplar clones, Skado (Populus trichocarpa x P. maximowiczii) and I-214 (P. deltoides x P. nigra), dedicated to bioenergy purposes. The effects of inoculation were investigated in two large scale trials of 1ha each. Poplars grown on highly contaminated soils accumulated excessive Cd and Zn in leaves compared with those planted on less contaminated soils, and the I-214 clone generally accumulated less PTEs than the Skado clone. Interestingly, the filtering capacity of mycorrhizal fungi was significant for Zn, Cu, Pb and Cr in Skado leaves only at the most contaminated areas after two growing seasons. These foliar concentrations were not correlated with Ca(NO3)2-extractable concentrations in soils, suggesting that mycorrhizal fungi limited PTE translocation from roots to leaves without impacting PTE mobility in soils. Therefore, the reduction of PTE accumulation in poplar leaves may be optimized by selecting appropriate combinations of cultivars and inocula at specific PTE levels and soil conditions. Because Cd and Zn may pose a risk after leaf abscission and wood harvest, further research is needed to efficiently reduce Cd and Zn concentrations in poplar tissues. Otherwise, the phytomanagement of metal contaminated sites with poplars should include options to safely manage both leaves and wood.

Transfer processes of potentially toxic elements (PTE) from rocks to soils and the origin of PTE in soils: A case study on the island of Santiago (Cape Verde)

The understanding of rock-soil geochemical fluxes provides an important tool for evaluating natural environmental risk. In this research we compare the geochemical composition of soils (n=249) collected on Santiago Island (Cape Verde) with their parent rocks (n=96). Basalt and basanites units and overlying soils are relatively rich in Co, Sc, Mg, Ca, Fe, V, Ti, Ni, Cr, and Cu, whilst phonolitic-trachytic units and overlying soils are relatively rich in Zn, P, Sr, Mn, Ba, La, As, Th and Pb. An enrichment of potentially toxic elements (PTE; As, Cd, Co, Cr, Cu, Fe, La, Mn, Ni, Pb, Sc, Th, V) was observed in soils relative to their parent rocks. This enrichment of PTE in Santiago soils results mainly from the removal of mobile elements that are common in primary minerals (e.g., Ca, Na, Mg, K) and coprecipitation and/or adsorption by Fe-oxy-hydroxides and clay minerals (mostly smectite and palygorskyte) under the influence of high pH values. Potentially toxic element contents were found to increase with weathering; oxidation is a major weathering mechanism under a semi-arid climate, and a high correlation between Fe and PTE was found, suggesting that the mobility of PTE is controlled by the iron phases. The level of enrichment of PTE in a specific site does not reflect the bulk concentration and so is not a good indicator of the actual geochemical environmental quality. The extent of contamination is not limited to the vicinity of the source, as contaminated material may be physically remobilized, particularly in high runoff conditions, causing dispersion of geo-pollutants over many kilometres from the source. The geochemical flux clarify the lithological origin of these elements, refuting the hypothesis of an anthropogenic contamination, as the PTE enrichment in Santiago soils is not a local phenomenon, but, on the contrary, occurs over the entire island.

Contamination status and assessment of urban and non-urban soils in the region of Sulaimani City, Kurdistan, Iraq

Soil contamination, especially in urban areas, is a globally increasing threat. Yet, knowledge on the status of urban soils in recently and rapidly developing regions and semiarid areas is still scarce. In this study, soils were investigated from Sulaimani city that underwent rapid growth and urbanization in past decades. Properties and contamination of 91 topsoils from 11 areas of different anthropogenic impact were determined. Differences between urban and non-urban soils were attributed by principal component analysis to differences in contents of pedogenic oxides, carbonate, organic nitrogen and carbon, pH and CEC. Also total contents of potentially toxic elements (PTE) were higher; mean contents of Cd, Pb, Cu and Zn in urban soils were 0.35, 51.8, 78.6 and 163.0 mg kg−1. The PTE contents increased with traffic volume and industrial emissions. The anthropogenic origin of contamination was further evidenced by significant enrichment of PTE in the top 0–5 cm compared to deeper topsoil layers. Additionally, mobility of PTEs was low in the clayey, alkaline soils. Contamination was substantially lower compared to many other cities, being explained by the short history of urban development in Sulaimani. Correspondingly, contents of polycyclic aromatic hydrocarbons were mostly not detectable. Contamination with PTEs was assessed using pollution indices and classified as ‘moderate’ to ‘considerable’ in roadside soils and significant’ to ‘very high’ in soils from industrial areas, depending on the single element. Toxicity indices >0.5 revealed that adverse effects on ecosystem functions must be expected at several urban and especially industrial sites.

The role of cassiterite controlling arsenic mobility in an abandoned stanniferous tailings impoundment at Llallagua, Bolivia

The surface water contamination by potentially toxic elements (PTE) leached from mine tailings is a major environmental concern. However, the formation of insoluble solid phases can control the mobility of PTE, with subsequent decrease of the risk that tailings suppose to the environment. We characterized the tailings from a tin inactive mine in Llallagua, Bolivia in order to assess the risk for surface water quality. These tailings contain high concentrations of PTE, with up to 94,344mg/kg Fe, 9135mg/kg Sn, 4606mg/kg As, 1362mg/kg Cu, 1220mg/kg Zn, 955mg/kg Pb and 151mg/kg Cd. Oxidation of sulfide minerals in these tailings generates acid leachates (pH=2.5–3.5), rich in SO42− and dissolved PTE, thereby releasing contaminants to the surface waters. Nevertheless, the concentrations of dissolved Sn, As and Pb in acid leachates are low (Sn<0.01mg/L; As=0.25–2.55mg/L; Pb<0.05mg/L). This indicates that, for the most part, Sn, As and Pb are being retained by the solid phases in the impoundment, so that these elements are not reaching the surface waters. Fe-bearing cassiterite—an insoluble and weathering-resistant oxide mineral—is abundant in the studied tailing deposits; it should be the main solid phase controlling Sn and As mobility in the impoundment. Additionally, jarosite and plumbojarosite, identified among the secondary minerals, could also play an important role controlling the mobility of As and Pb. Taking into account (a) the low solubility constants of cassiterite (Ksp=10−64.2), jarosite (Ksp=10−11) and plumbojarosite (Ksp=10−28.66), and (b) the stability of these minerals under acidic conditions, we can conclude that they control the long-term fate of Sn, As and Pb in the studied tailings.