Floodplain soils across Central Elbe River (CER), Germany, vary considerably in potentially toxic element (PTE) content. However, there has never been a comprehensive study that links PTE levels with ...human health risk for children and adults. Our objective was to determine the contamination of 13 PTEs in 94 soil profiles along CER and assess the associated health risk via diverse indices for adults and children. Of 94 soil profiles, we measured soil properties and total content of arsenic, barium, chromium, copper, nickel, lead, rubidium, tin, strontium, vanadium, zinc, and zirconium using x-ray fluorescence spectrometer (XRF). We calculated the Contamination Factor and the Pollution Load Index (PLI), and assessed the health risk for male and female adults as well as for children. Topsoil median contents of Cr (84 mg kg−1), Cu (42), Ni (33), and Zn (195) exceeded the Precautionary Values for sandy soils according to the German Federal Soil Protection and Contaminated Sites Ordinance, while As, Pb, and V were 32, 73, and 77 mg kg−1, respectively. Median topsoil PLI was 1.73, indicating elevated multi-element contamination, with 90th percentile and maximum values being 3.20 and 4.31, respectively. All PTE concentrations were higher in top- compared to subsoils. Also at the 50th percentile the most enriched elements were Sn and As, followed by Zr and Rb, while in the 90th percentile Sn and As were followed by Zn, Pb and Cu. Median children's hazard index (HI) was higher than unity (HI = 2.27) and the 90th percentile was 5.53, indicating elevated health risk. Adult median HIs were 0.18 for male and 0.21 for female persons. Arsenic was found to be the primary contributor to total risk, accounting of 57.4% of HI in all three-person groupings, with Cr (17.3%) being the second, and V (10.2%) the third. Children's health is at dramatically higher risk than that of adults; also As, Cr, Pb, and V have a predominant role in contamination-related health risks. The presence of V, a less-expected element, among those of major risk contribution, reveals the necessity of monitoring areas at large scale. Our results demonstrate that our study may serve as a model for similar works studying multi-element-contaminated areas in future.
•Tin had the highest enrichment in soil based on all studied contamination indices.•Tin was followed by As, Zn, Pb and Cu at 90th percentile.•Zirconium and Rb seem to originate from non-anthropogenic inputs.•Hazard Index for children was higher than unity, showing significant health risks.•Risk assessment indicated As as the predominant risk factor, followed by Cr, V, Pb.•The study is a model for works addressing contamination risks in extended areas.
Knowledge on the redox geochemistry of Ni is behind in comparison to other heavy metals. Hence, this article reviews the direct and indirect impact of redox potential (EH) on mobilization and release ...dynamics of Ni in soils and sediments across the world. Nickel can show a different behavior in response to EH. Mobilization of Ni increased at low EH in various soils; however, oxic conditions can lead to an increased mobilization of Ni in other soils. Those differences occur because the mobilization of Ni is often indirectly affected by EH, e.g. through EH-dependent pH changes, co-precipitation with iron (Fe) and manganese (Mn) (hydr)oxides, complexation with soil organic carbon, similar position of Ni and magnesium (Mg) in the soil solid phase, and/or precipitation as sulphides. Dissolved concentrations of Ni showed a similar pattern like Fe and increased at low EH in many soils, which might be explained by the reductive dissolution of Fe (hydr)oxides and the release of the co-precipitated/sorbed Ni. Few other studies indicated that Ni might be associated with Mn oxides rather than with Fe oxides. Additionally, the formation of soluble complexes with dissolved organic carbon may contribute to a mobilization of Ni at low EH. Nickel and Mg are similarly affected by redox changes especially in serpentine soils. This review summarizes the recent knowledge about the redox chemistry of Ni and contributes thus to a better understanding of the potential mobilization, hazard, and eco-toxicity of Ni in frequently flooded soils and sediments as agricultural ecosystems.
•The impact of redox potential (EH) on mobilization of Ni in soils was reviewed.•Mobilization of Ni increased under reducing conditions in various soils.•Oxic conditions can lead to an increase mobilization of Ni in other soils.•Mobilization of Ni in soils is indirectly affected by EH-dependent pH changes.•Dynamics of Ni were controlled mainly by the chemistry of Fe, Mn, Mg, and DOC.
Soil contamination by potentially toxic elements (PTEs) has led to adverse environmental impacts. In this review, we discussed remediation of PTEs contaminated soils through immobilization techniques ...using different soil amendments with respect to type of element, soil, and amendment, immobilization efficiency, underlying mechanisms, and field applicability. Soil amendments such as manure, compost, biochar, clay minerals, phosphate compounds, coal fly ash, and liming materials are widely used as immobilizing agents for PTEs. Among these soil amendments, biochar has attracted increased interest over the past few years because of its promising surface properties. Integrated application of appropriate amendments is also recommended to maximize their use efficiency. These amendments can reduce PTE bioavailability in soils through diverse mechanisms such as precipitation, complexation, redox reactions, ion exchange, and electrostatic interaction. However, soil properties such as soil pH, and clay, sesquioxides and organic matter content, and processes, such as sorption/desorption and redox processes, are the key factors governing the amendments' efficacy for PTEs immobilization in soils. Selecting proper immobilizing agents can yield cost-effective remediation techniques and fulfill green and sustainable remediation principles. Furthermore, long-term stability of immobilized PTE compounds and the environmental impacts and cost effectiveness of the amendments should be considered before application.
Display omitted
•Comprehensive review on immobilization of potentially toxic elements by soil amendments•Immobilization efficiency with respect to type of soil and amendment is reviewed.•Combined application of appropriate amendments maximizes their use efficiency.•Immobilization mechanisms, field applicability, and future research are discussed.
Display omitted
•P-rich biochar was more effective in immobilizing Pb than raw and Fe-rich biochars.•Raw and Fe-rich green waste biochars were more feasible for Cd fixation than Pb.•Fe modification ...decreased the efficacy of green waste biochar for Pb stabilization.•Green waste biochars could immobilize Cd under both anoxic and oxic conditions.•Raw and Fe-rich green waste biochars immobilized Pb under Eh ≤ -300 mV.
Functionalized biochar has gained extensive interests as a sustainable amendment for an effective remediation of paddy soils contaminated with heavy metals (HMs). We examined the efficiency of pig carcass-derived biochar (P-rich biochar, total P = 8.3%) and pristine (raw biochar, total Fe = 0.76%) and Fe-modified (Fe-rich biochar, total Fe = 5.5%) green waste-derived biochars for the immobilization of cadmium (Cd) and lead (Pb) in a paddy soil under pre-defined redox conditions (Eh, from -400 to +300 mV). Average concentrations (μg L-1) of dissolved Cd increased under reducing conditions up to 10.9 in the control soil, and decreased under oxidizing conditions to below the detection limit (LDL = 2.7) in the raw and Fe-rich biochar treated soils. Application of the raw biochar decreased the concentrations of dissolved Cd by 43–59% under Eh ≤ -100 mV, compared to the non-treated control, which was more effective than the Fe-rich biochar (31–59%) and the P-rich biochar (8–19%). The immobilization of Cd under low Eh might be due to its precipitation with sulfide (S2-), whereas its immobilization under high Eh might be due to the associated increase of pH. Concentrations (μg L-1) of Pb ranged from 29.4 to 198.2 under reducing conditions, and decreased to LDL (12.5) under oxidizing conditions. The P-rich biochar was more effective in immobilizing Pb than the raw and Fe-rich biochars, particularly under Eh ≤ 0 mV (55–82%), which might be due to the retention of Pb by phosphates. The raw and Fe-rich biochars immobilized Pb under low Eh (≤ -300 mV), but both biochars, particularly the Fe-rich biochar mobilized Pb under Eh higher than -200 mV, especially at +100 mV, due to the decrease of pH at this point (pH = 6.0 to 6.5). These results improved our understanding of using P-rich and Fe-rich functionalized biochars for the immobilization of Cd and Pb in a paddy soil under stepwise redox changes. The amendment of P-rich pig carcass-derived biochar to paddy soils could be a promising approach for mitigating the risk of Pb for human health and the environment. The raw and Fe-rich green waste-derived biochars can be used for immobilizing Cd and mitigating its risk in paddy soils under both reducing and oxidizing conditions.
Display omitted
•Transportation and pathways of Cd in soil-rice systems have been reviewed.•Cd accumulation in rice can be controlled by water, fertilizer and rice variety.•Transporters are critical ...to Cd uptake by rice root through the symplast pathway.•Phytoremediation can achieve the aims of green and sustainable remediation of Cd.•Low-Cd rice cultivars with modified transporters are expected to avoid Cd uptake.
Cadmium (Cd) contamination in paddy fields is a serious health concern because of its high toxicity and widespread pollution. Recently, much progress has been made in elucidating the mechanisms involved in Cd uptake, transport, and transformation from paddy soils to rice grains, aiming to mitigate the associated health risk; however, these topics have not been critically reviewed to date. Here, we summarized and reviewed the (1) geochemical distribution and speciation of Cd in soil-rice systems, (2) mobilization, uptake, and transport of Cd from soil to rice grains and the associated health risks, (3) pathways and transformation mechanisms of Cd from soil to rice grains, (4) transporters involved in reducing Cd uptake, transport, and accumulation in rice plants, (5) factors governing Cd bioavailability in paddy, and (6) comparison of remediation approaches for mitigating the environmental and health risks of Cd contamination in paddy fields. Briefly, this review presents the state of the art about the fate of Cd in paddy fields and its transport from soil to grains, contributing to a better understanding of the environmental hazards of Cd in rice ecosystems. Challenges and perspectives for controlling Cd risks in rice are thus raised. The summarized findings in this review may help to develop innovative and applicable methods for controlling Cd accumulation in rice grains and sustainably manage Cd-contaminated paddy fields.
Coal fly ash (CFA), a by-product of coal combustion has been regarded as a problematic solid waste, mainly due to its potentially toxic trace elements, PTEs (e.g. Cd, Cr, Ni, Pb) and organic ...compounds (e.g. PCBs, PAHs) content. However, CFA is a useful source of essential plant nutrients (e.g. Ca, Mg, K, P, S, B, Fe, Cu and Zn). Uncontrolled land disposal of CFA is likely to cause undesirable changes in soil conditions, including contamination with PTEs, PAHs and PCBs. Prudent CFA land application offers considerable opportunities, particularly for nutrient supplementation, pH correction and ameliorating soil physical conditions (soil compaction, water retention and drainage). Since CFA contains little or no N and organic carbon, and CFA-borne P is not readily plant available, a mixture of CFA and manure or sewage sludge (SS) is better suited than CFA alone. Additionally, land application of such a mixture can mitigate the mobility of SS-borne PTEs, which is known to increase following cessation of SS application. Research analysis further shows that application of alkaline CFA with or without other amendments can help remediate at least marginally metal contaminated soils by immobilisation of mobile metal forms.
CFA land application with SS or other source of organic carbon, N and P can help effectively reclaim/restore mining-affected lands. Given the variability in the nature and composition of CFA (pH, macro- and micro-nutrients) and that of soil (pH, texture and fertility), the choice of CFA (acidic or alkaline and its application rate) needs to consider the properties and problems of the soil. CFA can also be used as a low cost sorbent for the removal of organic and inorganic contaminants from wastewater streams; the disposal of spent CFA however can pose further challenges.
Problems in CFA use as a soil amendment occur when it results in undesirable change in soil pH, imbalance in nutrient supply, boron toxicity in plants, excess supply of sulphate and PTEs. These problems, however, are usually associated with excess or inappropriate CFA applications. The levels of PAHs and PCBs in CFA are generally low; their effects on soil biota, uptake by plants and soil persistence, however, need to be assessed. In spite of this, co-application of CFA with manure or SS to land enhances its effectiveness in soil improvements.
•Opportunities and challenges in the use of coal fly ash (CFA) for soil improvement reviewed.•CFA nutrients and contaminants examined for biomass production and contamination.•CFA can be a useful resource for soil improvement when used strategically.•CFA co-application with sewage sludge provides best soil improvement outcomes.•CFA can be used for remediation of contaminated soils and wastewaters.
Trace elements (TEs) may have toxic effects to plants and humans; thus, countries and organizations impose maximum allowable regulation limits of their concentrations in soils. Usually such limits ...are placed in different categories according to soil use, soil properties or based on both attributes. However, some countries have regulation limits irrespective of differentiation in soil properties. In this review, we aimed at collecting TE regulation limits in soils from major countries and organizations around the globe, and critiquing them by assessing potential human health risks in the case of soils attaining the maximum allowable values. We explored the soil-to-human pathway and differentiated among three major exposures from TEs, i.e., residential, industrial and agricultural. We observed the existence of problems concerning TE regulation limits, among which the fact that limits across countries do not regulate the same TEs, not even a minimum number of TEs. This indicates that countries do not seem to agree on which regulation limits of TEs pose a high risk. Also, these regulation limits do not take into account TE mobility to neighbouring environment interphases such as plant, especially edible, and water matrices. Moreover, limits for same TEs are vastly diverse across countries; this indicates that those countries have conflicting information concerning TE-related health risks. Subsequently, we addressed this problem of diversity by quantifying resultant risks; we did that by calculating human health risk indices, taking into consideration the cases in which the highest allowable TE limits are attained in soil. Arsenic limits were found to generate a relatively high hazard quotient (HQi, accounting for human intake over the maximum allowable oral reference dose for that same TE), indicating that its risk tends to be underestimated. Other TE limits, such as those of Cd, Cu, Ni, Pb, and Zn typically result in low HQi, meaning that limits in their cases are rather overprotective. Our approach reveals the need of reducing diversity in regulation limits by drafting soil legislations of worldwide validity, since risks are common across countries. We suggest that new directions should strategically tend to (a) reduce limits of TEs with underestimated contribution to health risk (such as As), (b) cautiously increase limits of TEs that currently cause minor health risks, (c) quantify TE risks associated with uptake to edible plants and potable water, and (d) consider multi-element contamination cases, where risks are cumulatively enhanced due to TE synergism.
Display omitted
•Trace element (TE) regulation limits around the globe are highly diverse.•Regulation limits across countries regulate different trace elements.•Arsenic limits generate high hazard quotients (HQ), thus they must be reconsidered.•Cadmium, Cu, Ni, Pb and Zn limits result in low HQ—thus they are overprotective.•Risks associated with uptake to edible plants and potable water must be implemented.
Poor brain penetration of tarenflurbil (TFB) was one of the major reasons for its failure in phase III clinical trials conducted on Alzheimer's patients. Thus there is a tremendous need of developing ...efficient delivery systems for TFB. This study was designed with the aim of improving drug delivery to brain through intranasally delivered nanocarriers. TFB was loaded into two different nanocarriers i.e., poly (lactide-co-glycolide) nanoparticles (TFB-NPs) and solid lipid nanoparticles (TFB-SLNs). Particle size of both the nanocarriers (<200nm) as determined by dynamic light scattering technique and transmission electron microscopy, assured transcellular transport across olfactory axons whose diameter was ≈200nm and then paving a direct path to brain. TFB-NPs and TFB-SLNs resulted in 64.11±2.21% and 57.81±5.32% entrapment efficiencies respectively which again asserted protection of drug from chemical and biological degradation in nasal cavity. In vitro release studies proved the sustained release of TFB from TFB-NPs and TFB-SLNs in comparison with pure drug, indicating prolonged residence times of drug at targeting site. Pharmacokinetics suggested improved circulation behavior of nanoparticles and the absolute bioavailabilities followed this order: TFB-NPs (i.n.)>TFB-SLNs (i.n.)>TFB solution (i.n.)>TFB suspension (oral). Brain targeting efficiency was determined in terms of %drug targeting efficiency (%DTE) and drug transport percentage (DTP). The higher %DTE (287.24) and DTP (65.18) were observed for TFB-NPs followed by TFB-SLNs (%DTE: 183.15 and DTP: 45.41) among all other tested groups. These encouraging results proved that therapeutic concentrations of TFB could be transported directly to brain via olfactory pathway after intranasal administration of polymeric and lipidic nanoparticles.
Display omitted
Knowledge about the behavior and reactions of separate soil components with trace elements (TEs) and their distribution coefficients (Kds) in soils is a key issue in assessing the mobility and ...retention of TEs. Thus, the fate of TEs and the toxic risk they pose depend crucially on their Kd in soil. This article reviews the Kd of TEs in soils as affected by the sorption system, element characteristics, and soil colloidal properties. The sorption mechanism, determining factors, favorable conditions, and competitive ions on the sorption and Kd of TEs are also discussed here. This review demonstrates that the Kd value of TEs does not only depend on inorganic and organic soil constituents, but also on the nature and characteristics of the elements involved as well as on their competition for sorption sites. The Kd value of TEs is mainly affected by individual or competitive sorption systems. Generally, the sorption in competitive systems is lower than in mono-metal sorption systems. More strongly sorbed elements, such as Pb and Cu, are less affected by competition than mobile elements, such as Cd, Ni, and Zn. The sorption preference exhibited by soils for elements over others may be due to: (i) the hydrolysis constant, (ii) the atomic weight, (iii) the ionic radius, and subsequently the hydrated radius, and (iv) its Misono softness value. Moreover, element concentrations in the test solution mainly affect the Kd values. Mostly, values of Kd decrease as the concentration of the included cation increases in the test solution. Additionally, the Kd of TEs is controlled by the sorption characteristics of soils, such as pH, clay minerals, soil organic matter, Fe and Mn oxides, and calcium carbonate. However, more research is required to verify the practical utilization of studying Kd of TEs in soils as a reliable indicator for assessing the remediation process of toxic metals in soils and waters.
MS: Mono-sorption system; CS: competitive sorption system; Fluvial: fluvial soil (Entisols); Lacus: Lacustrine soil (Entisols); Marine: sandy soil (Entisols); Aridis: Aridisols; Entis: Entisols; Vertis: Vertisols; Mollis: Mollisols; Histos: Histosols; Alfis: Alfisols.
Effect of soil types on Cd and Zn distribution coefficient, Kd medium (Lkg−1) under mono-metal and competitive sorption system. Display omitted
•Distribution coefficient (Kd) of trace elements (TEs) in soils has been reviewed.•Proves the link between Kd and sorption system, element types, and soil properties•The element Kd in competitive sorption is lower than in mono-metal system.•Strongly sorbed TEs (Pb, Cu) are less affected by competition than mobile elements (Cd, Ni, Zn).•Values of Kd decreased with an increase of the added concentration in the test solution.
In this study, we examined the sorption of arsenite (As(III)) and arsenate (As(V)) to Japanese oak wood-derived biochar (OW-BC) in aqueous solutions, and determined its efficiency to remove As from ...As-contaminated well water. Results revealed that, among the four sorption isotherm models, Langmuir model showed the best fit to describe As(III) and As(V) sorption on OW-BC, with slightly greater sorption affinity for As(V) compared to As(III) (QL=3.89 and 3.16mgg−1; R2=0.91 and 0.85, respectively). Sorption edge experiments indicated that the maximum As removal was 81% and 84% for As(III)- and As(V)-OW-BC systems at pH7 and 6, respectively, which decreased above these pH values (76–69% and 80–58%). Surface functional groups, notably OH, COOH, CO, CH3, were involved in As sequestration by OW-BC, suggesting the surface complexation/precipitation and/or electrostatic interaction of As on OW-BC surface. Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy indicated that 36% of the added As(III) was partially oxidized to As(V) in the As(III) sorption experiment, and in As(V) sorption experiment, 48% of As(V) was, albeit incompletely, reduced to As(III) on OW-BC surface. Application of OW-BC to As-contaminated well water (As: 27–144μgL−1; n=10) displayed that 92 to 100% of As was depleted despite in the presence of co-occurring competing anions (e.g., SO42−, CO32−, PO43−). This study shows that OW-BC has a great potential to remove As from solution and drinking (well) water. Overall, the combination of macroscopic sorption data and integrated spectroscopic and microscopic techniques highlight that the fate of As on biochar involves complex redox transformation and association with surface functional moieties in aquatic systems, thereby providing crucial information required for implication of biochar in environmental remediation programs.
Display omitted
•Arsenic removal efficiency of Japanese oak wood biochar (OW-BC) was explored.•Langmuir model provided the best fit, with a greater QL for arsenate than arsenite.•XANES spectroscopy indicated redox transformation of arsenite⇔arsenate on OW-BC.•FTIR spectra revealed arsenite/arsenate association with functional groups on OW-BC.•OW-BC efficiently removed As (92 to 100%) from drinking well water.
PDF
