Bioavailability Of Potentially Toxic Elements Research Articles

Effect of biological sewage sludge and its derived biochar on accumulation of potentially toxic elements by corn (Zea mays L.)

The land application of sewage sludge can cause different environmental problems due to the high content of potentially toxic elements (PTEs). The objective of this study was to compare the effect of urban biological sewage sludge (i.e. the waste of activated sludge process) and its derived biochar as the soil amendments on the bioavailability of PTEs and their bioaccumulation by corn (Zea mays L.) under two months of greenhouse conditions. The soil was treated by adding biochar samples at 0 (control), 1, 3, 5% w/w. The diethylenetriamine pentaacetic acid (DTPA)-extractable concentrations of PTEs including Zn, Pb, Cd, Cr, Ni, Fe, and Cu in soil and their accumulation by plant shoot and root were measured. Conversion of the biological sewage sludge into the biochar led to decrease the PTEs bioavailability and consequently decreased their contents in plant tissues. The DTPA extractable metal concentrations of produced biochar in comparison to the biological sewage sludge reduced 75% (Cd), 65% (Cr), 79% (Ni and Pb), 76% (Zn), 91% (Cu) and 88% (Fe). Therefore, the content of Ni, Fe, Zn and Cd in corn shoot was decreased 61, 32, 18 and 17% respectively in application of 5% biochar than of raw sewage sludge. Furthermore, the application of 5% biochar enhanced the physiological parameters of the plants including shoot dry weight (twice) and wet weight (2.25 times), stem diameter (1.70 times), chlorophyll content (1.03 times) in comparison to using 5% raw sewage sludge. The results of the study highlight that application of the biochar derived from urban biological sewage sludge in soil could decrease the risk of PTEs to the plant.

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.

Environmental bioavailability of arsenic, nickel and chromium in soils impacted by high geogenic and anthropogenic background contents

High arsenic, chromium and nickel in soils can pose a hazard to the ecosystem and/or human health. Large areas can be affected by elevated potentially toxic elements (PTE) background contents, entailing a significant effort for managing the potential risk. Assessing the environmental hazard associated to PTE-contaminated soils requires the determination of soil PTE environmental bioavailability, which reflects the capacity of these elements to be transferred to living organisms. Here we assess the environmental bioavailability of As, Cr and Ni in topsoils from the Liège basin and Belgian Lorraine, two areas in Wallonia, Belgium, affected by elevated As, Cr and Ni background contents. The source of soil As, Cr and Ni differs in Liège and Lorraine: anthropogenic in the former location and geogenic in the latter. The environmental bioavailability of PTE was determined using two complementary approaches: (1) by chemical fractionation with the Community Bureau of Reference (BCR) three-step sequential extraction protocol and (2) by estimating the phytoavailability using a plant-based biotest (Lolium multiflorum as plant model). The results show that total As (6–130 mg·kg−1), Cr (15–268 mg·kg−1), and Ni (8–140 mg·kg−1) contents in the Liège and Lorraine soils frequently exceed the soil clean-up standards. However, no positive correlation was found between the total contents and BCR extraction results or rye-grass contents, except for As in Liège soils. Total As, Cr or Ni contents surpassing soil standards do not necessarily result in elevated mobile, potentially mobilizable and phytoavailable contents. In general, environmental bioavailability of As, Cr and Ni is higher in soils from Liège basin compared to those sampled in Belgian Lorraine. The mobile and potentially mobilizable fractions of As, Cr and Ni account for <30 % of their total contents following the BCR extractions. Our study provides valuable information for sustainable management at the regional scale of soils containing high PTE contents.

Biochar from animal manure: A critical assessment on technical feasibility, economic viability, and ecological impact

AbstractAnimal manure has been used to manage soil fertility since the dawn of agriculture. It provides plant nutrients and improves soil fertility. In the last decades, animal husbandry has been significantly expanded globally. Its economics were optimized via the (international) trade of feed, resulting in a surplus of animal manure in areas with intensive livestock farming. Potentially toxic elements (PTEs), pathogenic microorganisms, antibiotic residues, biocides, and other micropollutants in manure threaten animal, human, and environmental health. Hence, manure application in crop fields is increasingly restricted, especially in hotspot regions with intensive livestock activities. Furthermore, ammonia volatilization and greenhouse gas (GHG) emissions during manure storage, field application, and decomposition contribute to air pollution and climate change. Conventional manure management scenarios such as composting and anaerobic digestion partially improve the system but cannot guarantee to eliminate sanitary and contamination risks and only marginally reducing its climate burden. Hence, this review discusses the potential of pyrolysis, the thermochemical conversion under oxygen‐limited conditions as an alternative treatment for animal manure providing energy and biochar. Manure pyrolysis reduces the bioavailability of PTEs, eliminates pathogenic microorganisms and organic micropollutants, and reduces GHG emissions. Pyrolysis also results in the loss of nitrogen, which can be minimized by pretreatment, that is, after removing soluble nitrogen fraction of manure, for example, by digestion and stripping of ammonia–nitrogen or liquid–solid separation. However, conclusions on the effect of manure pyrolysis on crop yield and fertilization efficiencies are hampered by a lack of nutrient mass balances based on livestock unit equivalent comparisons of manure and manure biochar applications. Hence, it is essential to design and conduct experiments in more practically relevant scenarios and depict the observations based on the amount of manure used to produce a certain amount of biochar.

Characterization and risk assessment of soil around waste rock heaps affected by acid rock drainage in an abandoned pyrite mining area

Acid rock drainage (ARD) is one of the most serious and potentially lasting environmental issues for the mining industry. Many researchers investigated the impact of ARD on downstream farmland, but few focused on the soil properties change around waste rock heaps. In this study, a total of 119 soil samples were taken around the 35 waste rock heaps which are scattered in 12 mining sites in an abandoned pyrite mining area (Baihe County, Northwest China). Both rainy and dry seasons of ARD were collected from the discharge outlet of each mining site. The bulk levels of potentially toxic elements (PTEs), including As, Cd, Cu, Ni, Cr, Zn, Pb, Fe, Mn, and F, in waste rock, soil, and ARD samples were analyzed. Leaching concentration and chemical speciation of these PTEs in soils were further investigated. The results show that the ARD had very high pollution loads of PTEs both in the rainy season and dry season, continuously exporting pollutants to the surrounding soils. More than 70% of the soil samples were acidic (pH&amp;lt;5.5). The bulk of As in 17 soil surface samples exceeded the risk control limit specified in China (60 mg/kg), while the leaching concentrations of As and other PTEs in soil were far below the regulated limits. According to the sequential extraction results, the residual fraction of As, Cr, Cu, Zn, and Ni in the soil accounted for over 90%, indicating these metals were possibly retained by the silicate matrix. Considering the relatively low bioavailability of PTEs and limited exposure routes, the human health risk of the soil surrounding the waste heap is generally acceptable. This research work provides a more comprehensive understanding of the properties and effects of ARD in the pyrite mining area which is conducive to the development of a sustainable control strategy of environmental pollution in typical mining regions.

Accumulation patterns and health risk assessment of potentially toxic elements in the topsoil of two sloping vineyards (Tokaj-Hegyalja, Hungary)

PurposeIn agricultural soils, accumulation and bioavailability patterns of potentially toxic elements (PTEs) are key ecological and health risk issues, especially in metal-based crop protection systems such as those applied in vineyards. However, PTE levels in the topsoils of historical wine-growing regions of Hungary have been scarcely studied so far. The specific goals of this research were to assess the accumulation tendencies and bioavailability of PTEs complemented with human health risk assessment in two sloping vineyards with pH-contrasted soils in Tokaj-Hegyalja, Hungary, and under different farming practices.MethodsComposite topsoil (< 20 cm) and borehole samples were collected from two vineyards and local forests. The total and bioavailable PTE contents (Zn, Pb, Co, Ni, Cr, Cu) were analyzed following digestion in aqua regia and extraction with a strong chelating agent (0.05 M Na2-EDTA). Enrichment factors (EFs) were calculated based on Fe as a reference element and the local uncultivated soil. The hazard indexes (HIs) for outdoor workers, children, and adults living in residential areas near the vineyards were calculated to assess the health risks associated with the target PTEs.ResultsHigher PTE contents were observed in the organic vineyard (near Tokaj) compared to the conventional one (near Tállya), except for Cu and Pb. The EFs confirmed that the duration of Cu-fungicide applications mainly determines the soil-bound Cu levels, with an average of 2.6 in the 28-year-old organic vineyard and 9.6 in the more than 100-year-old conventional vineyard. The PTEs predominantly accumulated at the top of the hillslope in Tállya, while in Tokaj, a general trend of downslope accumulation of PTEs can be noticed. Bioavailable Cu reached a maximum of 50% of total Cu at the top of the hillslope (Tállya) and positively correlated with soil organic matter content. Iron/Mn oxides, total Ca content, and soil pH show a significant correlation with the PTE total contents (other than Cu); meanwhile, their bioavailability is mainly influenced by Mn oxides. The calculated HIs are less than 1, indicating no elevated health risk. Total Cr is the major contributor to the HI in both vineyards, reaching 79.0% (Tokaj) and 49.7% (Tállya).ConclusionOverall, the accumulated Cu contents mainly depended on the vineyard age, while farming practices and terrain morphology play a minor role in its spatial distribution. The further accumulation of PTEs, especially in high-metal hotspots within the vineyards, may ultimately cause toxicity to re-planted grapevines, soil biota, and, in the longer term, farmers and residents.

Insights into bioaccumulation and bioconcentration of potentially toxic elements in marine sponges from the Northwestern Mediterranean coast of Morocco

The present research aimed to investigate the concentrations and patterns of six potentially toxic elements (PTEs) in three common sponge species collected along the Moroccan Mediterranean coast, as well as their levels in ambient seawater and sediments. Distinct inter-species variability in PTEs bioaccumulation was observed among the three species, suggesting that sponges have distinct selectivity for assimilating PTEs from the surrounding environment. C. crambe had a higher enrichment capacity for Cu, As, Cr and Ni, while P. ficiformis and C. reniformis exhibited the highest concentration of Cd and Pb, respectively. Interestingly, a similar spatial distribution patterns of PTEs was observed in the three media, with high values occurring in Tangier and Al-Hoceima locations. Overall, our results confirm that sponges reliably reflect the bioavailability of PTEs in their immediate environment, especially C. crambe, whose PTE tissue contents were highly and positively correlated with the contents of all PTEs in the sediments.

Phytoremediator Potential of Ipomea asarifolia in Gold Mine Waste Treated with Iron Impregnated Biochar

Growing environmental pollution in recent decades has been generating potentially toxic elements (PTE) which pose an ongoing threat to terrestrial and aquatic ecosystems and human health, especially in mining areas. Biochar and PTE-tolerant species have been used in soil remediation as they are environmentally friendly alternatives. This study aimed to assess the influence of açaí seed biochar (Euterpe oleracea Mart), impregnated with iron (BFe) or not (BC), on the bioavailability of PTEs, in a multi-contaminated soil from a gold (Au) mining area in the Amazon, using Ipomea asarifolia as a plant test since it was naturally growing on the tailings. BC increased the soil pH while BFe reduced. Biochars increased PTEs in the oxidizable fraction (linked to soil organic matter). The use of BC and BFe improved the immobilization of PTEs and BC increased arsenic (As) in the easily soluble fraction in the soil. Moreover, plants grown with biochars showed lower dry matter yield, higher concentrations of PTEs and lower nutrient content than the control treatment. According to the phytoextraction and translocation factors, Ipomea asarifolia can be classified as a species with potential for phytostabilization of Zn and tolerant to other PTEs, mainly As.

Biosurfactant-assisted phytoremediation of potentially toxic elements in soil: Green technology for meeting the United Nations Sustainable Development Goals

Biosurfactants are biomolecules produced by microorganisms, low in toxicity, biodegradable, and relatively easy to synthesize using renewable waste substrates. Biosurfactants are of great importance with a wide and versatile range of applications, including the bioremediation of contaminated sites. Plants may accumulate soil potentially toxic elements (PTEs), and the accumulation efficacy may be further enhanced by the biosurfactants produced by rhizospheric microorganisms. Occasionally, the growth of bacteria slows down in adverse conditions, such as highly contaminated soils with PTEs. In this context, the plant's phytoextraction capacity could be improved by the addition of metal-tolerant bacteria that produce biosurfactants. Several sources, categories, and bioavailability of PTEs in soil are reported in this article, with the focus on the cost-effective and sustainable soil remediation technologies, where biosurfactants are used as a remediation method. How rhizobacterial biosurfactants can improve PTE recovery capabilities of plants is discussed, and the molecular mechanisms in bacterial genomes that support the production of important biosurfactants are listed. The status and cost of commercial biosurfactant production in the international market are also presented.

Abandoned Mine Lands Reclamation by Plant Remediation Technologies

Abandoned mine lands (AMLs), which are considered some of the most dangerous anthropogenic activities in the world, are a source of hazards relating to potentially toxic elements (PTEs). Traditional reclamation techniques, which are expensive, time-consuming and not well accepted by the general public, cannot be used on a large scale. However, plant-based techniques have gained acceptance as an environmentally friendly alternative over the last 20 years. Plants can be used in AMLs for PTE phytoextraction, phytostabilization, and phytovolatilization. We reviewed these phytoremediation techniques, paying particular attention to the selection of appropriate plants in each case. In order to assess the suitability of plants for phytoremediation purposes, the accumulation capacity and tolerance mechanisms of PTEs was described. We also compiled a collection of interesting actual examples of AML phytoremediation. On-site studies have shown positive results in terms of soil quality improvement, reduced PTE bioavailability, and increased biodiversity. However, phytoremediation strategies need to better characterize potential plant candidates in order to improve PTE extraction and to reduce the negative impact on AMLs.

Steel mill waste application in soil: dynamics of potentially toxic elements in rice and health risk perspectives

Potentially toxic elements (PTEs) are of great concern in steel mill wastes. Therefore, in order to use them as potential fertilizers in soil, risk assessments are needed. Three steel mill wastes were tested as possible amendments for soils at seven different doses (0, 0.5, 1, 2, 4, 8, 16 t ha-1): phosphate mud (PM), metallurgical press residue (MPR), and filter press mud (FPM) during rice cultivation in a pot experiment in a Haplic Gleisol. Analysis on rice tissues, including roots, shoots, husk, and grains, were conducted and contents of Cu, Cd, Ni, Zn, Mn, and Pb were assessed. Translocation and bioaccumulation factors were calculated for each element. In general, PTEs are more accumulated in roots and greater contents of Zn and Mn were found, while the lowest ones were found for Pb, probably due to its lack of functional roles during plants development. Higher translocation was observed for Mn, which is associated to the redox conditions of rice cultivation and the high mobility of this element under this condition. Application of steel mill wastes can increase PTE bioavailability and translocation factors, especially PM, but all of the wastes reveal a high hazard index.

Innovative amendments derived from industrial and municipal wastes enhance plant growth and soil functions in potentially toxic elements-polluted environments

Potentially toxic elements (PTE), e.g. As, Sb, Cd, Cu, Pb, Zn, can severely impact soil element cycling, organic matter turnover and soil inhabiting microbiota. Very often this has dramatic consequences for plant growth and yield which are greatly restricted in PTE-contaminated soils. The use of innovative amendments to reduce the labile pool of such soil contaminants, can result as a feasible and sustainable strategy to improve the fertility and functionality of PTE-contaminated soils as well as to exploit these latter from an agronomic point of view. Water treatment residuals (WTR), red muds (RM), organic-based materials originating from the waste cycle, e.g. municipal solid waste compost (MSWC) and biochar (BCH), have emerged in the last decades as promising amendments. In this paper, we report a synthesis of the lessons learned from research carried out in the last 20 years on the use of the above-mentioned innovative amendments for the manipulation of soil fertility and functionality in PTE-contaminated soils. The amendments considered possess physico-chemical properties useful to reduce labile PTE in soil (e.g. alkaline pH, porosity, Fe/Al phases, specific functional groups and ionic composition among the others). In addition, they contain organic and inorganic nutrients which can contribute to improve the soil chemical, microbial and biochemical status. This is often reflected by a higher organic matter content in amended soils and/or an increase of the cation exchange capacity, available P and total N and/or dissolved organic C. As a result, soil microbial abundance, in particular heterotrophic fungi and bacteria, and enzyme activities (e.g. dehydrogenase, urease and β-glucosidase) are commonly enhanced in amended soils, while plant growth can be significantly stimulated. Overall, the obtained results suggest that the studied amendments can be used to reduce PTE bioavailability in polluted soils, improve soil microbial status and functionality, and enhance the productivity of different crops. This can offer a precious opportunity for the productive recovery of PTE-polluted soils.&#x0D; Highlights - Water treatment residuals, red muds, municipal solid waste compost and biochar can reduce labile PTE in contaminated soils. - When used as amendments, WTR, RM, MSWC and BCH improve soil chemical fertility of PTE-polluted soils. - WTR, RM, MSWC and BCH stimulate soil enzyme activity and heterotrophic bacterial abundance in PTE-polluted soils. - WTR, RM, MSWC and BCH can be used as strategic amendments to enhance plant growth in environments polluted by PTE.

Potentially toxic element accumulation in badgers (Meles meles): a compositional approach

Potentially Toxic Elements (PTEs) in Badgers (Meles meles), otherwise known as heavy metals, are unique amongst environmental pollutants occurring, both naturally and anthropogenically. PTEs have a broad range of negative health and environmental effects, therefore identifying their sources and pathways through the environment is imperative for public health policy. This is difficult in terrestrial systems due to the compositional nature of soil geochemistry. In this study, a compositional statistical approach was used to identify how PTEs accumulate in a terrestrial carnivorous mammal, Eurasian Badgers (Meles meles). Compositional principal component analysis (PCA) was used on geochemical data from the Tellus survey, the soil baseline and badger tissue data to map geo-spatial patterns of PTEs and show accumulative trends measured in time. Mapping PCs identified distinct regions of PTE presence in soil and PTE accumulation in badger tissues in Northern Ireland. PTEs were most elevated in liver, kidney and then muscle tissues. Liver and kidney showed the most distinct geo-spatial patterns of accumulation and muscle was the most depleted. PC1 and 2 for each type were modelled using generalised additive mixed models (GAMM) to identify trends through time. PC1 for the liver and muscle were associated with rainfall and ∂N15 in the liver, showing a link to diet and a bioaccumulation pathway, whilst PC2 for both tissues was associated with mean temperature, showing a link to seasonal activity and a bioaccessibility pathway. However, in kidney tissue these trends are reversed and PC1 was associated with bioaccessibility and PC2 with bioaccumulation. Combined these techniques can elucidate both geo-spatial trends in PTEs and the mechanisms by which they move in environment and in future may be an effective tool for assessing PTE bioavailability in environmental health surveys.

Identification of spatial patterns, geochemical associations and assessment of origin-specific health risk of potentially toxic elements in soils of Armavir region, Armenia

The study of soil potentially toxic elements (PTE) contents and establishment of the geochemical characterization of areas which have never been studied is of great concern. In 2019, soil survey of the Armavir region (Armenia) was conducted in order to investigate the spatial pattern of PTE, reveal PTE geochemical associations and assess the origin-specific health risks. The application of compositional data analysis and geospatial mapping allowed to identify two clusters of samples. The first cluster was spatially located on volcanic rocks and was represented by Fe, Co, Mn, Ti, Zn, Ba, Pb suggesting a natural origin of PTE in these areas. The second cluster was allocated on the alluvial, deluvial, and proluvial sediments and represented by As, Cu, Cr, Ni. Such combination of elements in the same group indicates the anthropogenic introduction of some quantities of PTE. The latter is confirmed by the presence of outliers and extreme values for As, Cu and Ni, as well as by the spatial colocation of Fe, Mn, Co, Pb, Zn outliers and extreme contents. The health risk assessment showed that for children the multi-elemental non-carcinogenic risk was detected, while for the adults the non-carcinogenic risk and carcinogenic risk were below the allowable level. The detailed study of the risk levels showed that in first cluster comparatively higher risk were observed for Pb, V, Ba, Zn while in the second cluster: Fe, Co, Mn, As, Cr, Cu, Ni. The results indicated the necessity of additional in-depth studies with special focus on bioavailability of PTE.

Health Risk Assessment in Agricultural Soil Potentially Contaminated by Geogenic Thallium: Influence of Plant Species on Metal Mobility in Soil-Plant System

In agricultural soils, thallium (Tl) of geogenic origin may represent a potential risk for human health, mainly via ingestion of food crops. In this work, a pot experiment was carried out to evaluate (1) the bioavailability of Tl and other potentially toxic elements (PTEs) in an agricultural soil with naturally occurring Tl; (2) the uptake and accumulation of PTEs in Lactuca sativa L. var. acephala, Diplotaxis tenuifolia L. DC and Silene latifolia Poir; (3) the health risks arising from plant and soil ingestion by different subpopulations and dermal contact of soil by farmers. In soil, only Tl and Pb pseudototal contents were above Italian screening values. Nevertheless, the promptly bioavailable contents of all PTEs were always below internationally recognized trigger values. Plants affected PTE bioavailability in soil by their rhizodepositions and accumulated PTEs in their shoots. Acceptable risks (hazard index &lt; 1) arose from dietary intake of both L. sativa L., D. tenuifolia L. and dermal contact of soil by farmers. Significant health risks can derive from the intake of S. latifolia Poir. (accumulating high Tl concentrations), in particular by children (HI = 74). In conclusion, an adequate management and crop selection are needed to profitably exploit soils with geogenic Tl for agricultural purposes.

Potentially Toxic Element Availability and Risk Assessment of Cadmium Dietary Exposure after Repeated Croppings of Brassica juncea in a Contaminated Agricultural Soil

Phytoextraction of potentially toxic elements (PTEs) is eco-friendly and cost-effective for remediating agricultural contaminated soils, but plants can only take up bioavailable forms of PTEs, thus meaning that bioavailability is the key for the feasibility of this technique. With the aims to assess the phytoextraction efficiency on an agricultural soil contaminated by Cr, Zn, Cd, and Pb and the changes induced by plants in PTE bioavailability and in human health risk due to dietary exposure, in this work we carried out a mesocosm experiment with three successive croppings of Brassica juncea, each followed by Rocket salad as bioindicator. Brassica juncea extracted more Zn and Cd than Cr and Pb, significantly reducing, after three repeated croppings, the bioavailable element concentrations in soil as a result of plant uptake and soil pH changes. For Cd, this reduction did not bring the bioavailable amounts obtained by soil extraction with NH4NO3 below the trigger value of 0.1 mg kg−1 set by some European countries. Nevertheless, the Hazard Quotient for Cd in Rocket salad decreased across three repeated croppings of Brassica juncea. This indicated the beginning of a re-equilibration process between soil PTE forms of different bioavailability, that are in a dynamic equilibrium, thus stressing the need to monitor the possible regeneration of the most readily bioavailable pool.

Enrichment of potentially toxic elements in the fine fraction of soils from Iraq and Kuwait

The fine fraction of soils in arid and semi-arid regions can be readily suspended into the atmosphere by winds and transported long distances, carrying potentially toxic elements (PTEs) associated with these source materials. In this study, environmentally available PTE loadings for As, Cd, Cr, Cu, Ni, Pb, V, and Zn were measured in the fine fraction (< 75 μm) of 19 bulk soil samples collected in 2007 from 4 sites in Iraq and 15 sites in Kuwait. Soil samples were mechanically sieved and particle size distribution in the fine fraction was measured using laser diffraction particle sizing. Major and minor element composition was determined in the soil fine fraction using energy-dispersive X-ray fluorescence. Sub-samples were digested using strong acids and analyzed using high-resolution inductively coupled mass spectrometry to assess the maximum environmental availability of PTEs in each fine fraction of each soil sample. Measured environmentally available PTE loadings were normalized to soluble iron to allow for an assessment of soil contamination at and between sites that included weathering effects and was more focused on the mobile fraction of the total PTE load. Physiologically based fluid extractions were also performed on select samples to assess potential bioavailability of PTEs through ingestion and inhalation. Results show significant PTE loadings and anthropogenic contamination in the fine fraction of soils from Iraq and Kuwait. All sites showed moderate-to-high Ni contamination but loadings and contamination levels for all PTEs varied among sites in Iraq and Kuwait as a function of weathering, local geology, and inputs from non-local and/or anthropogenic sources. PTE contamination tended to be higher in the fine fraction of soil collected at the sites in Iraq, and the lowest overall PTE loadings were found at sites in northern Kuwait where the mean measured particle diameter was largest. Potential bioavailability of PTEs via inhalation was generally low (< 10% of loading) but a significant portion of the PTE load for As, Cu, and Pb (and V and Zn at select sites) was available via ingestion. The fine fraction of soils collected from Iraq and Kuwait in this study had significant environmentally available PTE contamination. Sites from Lower Mesopotamia in Iraq were the most impacted. PTE loadings and contamination were strongly influenced by local-scale weathering and geology, proximity to urban PTE sources, and inputs from non-local and/or anthropogenic sources. Sites with a smaller mean particle diameter had the greatest levels of PTE contamination. Potential bioavailability of PTEs was generally low.

Bioaccumulation of Potentially Toxic Elements in Cereal and Legume Crops: A Review

Contamination of soil and water with potentially toxic elements (PTEs) has become a global environmental concern that could pose potential risks to human health and agriculture. The major anthropogenic sources of PTEs contamination include coal combustion processes, leather tanning operations, mining, smelting activities, and use of sewage water for irrigation. Scattered studies are available in the literature that determines the sources, bioavailability, and potential hazards due to PTEs contamination to crop plants and, ultimately, to human beings. This article reviews how solid‐ and solution‐phase chemistry of soil and existing plant species influence the bioavailability of PTEs to cereal and legume plants, along with the mechanisms involved in the uptake and accumulation. This article also describes the phytotoxic effects of PTEs and strategies to overcome these toxic effects by identifying highly tolerant cereals and legumes. Moreover, this article also summarizes recent advances in the field application and discusses perspectives to reduce PTEs accumulation in cereal and legume crops.

Biochars mitigate greenhouse gas emissions and bioaccumulation of potentially toxic elements and arsenic speciation in Phaseolus vulgaris L.

Anthropogenic and natural activities can lead to increased greenhouse gas emissions and discharge of potentially toxic elements (PTEs) into soil environment. Biochar amendment to soils is a cost-effective technology and sustainable approach used to mitigate greenhouse gas emissions, improve phytoremediation, and minimize the health risks associated with consumption of PTE-contaminated vegetables. Greenhouse pot experiments were conducted to investigate the effects of peanut shell biochar (PNB) and sewage sludge biochar (SSB) on greenhouse gas (GHG) emissions, plant growth, PTE bioaccumulation, and arsenic (As) speciation in bean plants. Results indicated that amendments of PNB and SSB increased plant biomass production by increasing soil fertility and reducing bioavailability of PTEs. Addition of biochars also increased soil pH, total nitrogen (TN), total carbon (TC), dissolved organic carbon (DOC), and ammonium-nitrogen (NH4-N) but decreased available concentrations of PTEs such as cadmium (Cd), lead (Pb), and As. The concentration of nitrate-nitrogen (NO3--N) was also decreased in biochar-amended soils. In addition, PNB and SSB amendments significantly (P<0.01) reduced the bioaccumulation of chromium (Cr), As, Cd, Pb, and nickel (Ni) in stalks, leaves, and fruits of Phaseolus vulgaris L. Similarly, PNB and SSB amendments significantly (P≤0.05) reduced inorganic As species like arsenite (As (III)) and arsenate (As (V)). Greenhouse gases such as carbon dioxide (CO2) and methane (CH4) emissions were significantly (P<0.01) reduced but nitrous oxide (N2O) emissions first increased and then decreased amended with both biochars. Current findings demonstrate that SSB and PNB are two beneficial soil amendments simultaneous mitigating greenhouse gas emissions and PTE bioaccumulation as well as arsenic speciation in P. vulgaris L.

Study on the mobility and bioavailability of PTEs in soils from Urban Forest Parks in Sofia, Bulgaria

Forest parks in many urbanized areas are affected by the anthropogenic pollution as demonstrated by the poor health status of many trees. The concentrations of harmful agents like Potentially Toxic Elements (PTEs) can be very high in urban soils and their availability is an important issue for biological components in these environments. This study focuses on the mobile forms of PTEs extracted by 1М NH4OAc at pH=7 in relation to determining their bioavailability for forest trees in oak ecosystems in urban areas. The area studied is along an urban–rural gradient from the Sofia region, Bulgaria. The NH4OAc extracts mainly “biologically active” fraction of elements in soils comprising primarily the soluble and exchangeable forms and in some cases showed good positive correlation with PTE accumulation in trees. Four experimental forest park sites (U1, U2, U3 and U4) created on Hortic/Technic Anthrosols were selected along the urban gradient in the Sofia region. The control sites located in rural zones with natural soils Cambisols and Luvisols (R1, R2, R3 and R4) were used as reference. Strong correlations were found between mobile forms of Cu, Zn, Pb, Cd in urban soils and a number of soil parameters (pH, CEC and texture). The mobility is related to soil pH and with more acidic soils a higher mobility is shown, which is statistically significant for Pb. The element Cu is less mobile in the soil and is localized in the top layer, where it is mainly associated with soil organic matter. The mobile (NH4OAc extractable) portions of Cu, Zn, Pb, and Cd (mg/kg soils) in Urban Soils ranged between: 0.74 and 2.61; 2.94 and 3.29; 1.34 and 3.28; and 0.02 and 0.16, respectively and those in Natural Soils ranged between: 0.73 and 1.65; 1.20 and 5.29; 1.10 and 6.80; and 0.02 and 0.07. The significance of the mobile proportion was greatest for Cd in urban soils where it reached 33.3% of the total content. Despite the determined correlation between mobile forms of Pb and Cd with their total content in leaves of oak trees there is no clear visible effect on the tree health characteristics using parameters as defoliation and decoloration of crowns.