Search Results (58)

Heavy metal contamination of soils represents a persistent environmental challenge, for which in situ immobilization has emerged as a cost-effective and technically viable alternative to conventional invasive remediation technologies. This review comparatively evaluates three distinct categories of soil amendments—biochar, zeolite and attapulgite—within a unified analytical framework integrating extractable fractions (TCLP, DTPA, and CaCl₂) and geochemical fractionation approaches (BCR and Tessier). The novelty of this study lies in the systematic assessment of the dominant immobilization mechanisms associated with each amendment in relation to soil properties and the chemical speciation of the target metal, as well as in distinguishing between an apparent reduction in metal extractability and a genuine shift toward more stable geochemical fractions. The findings identify ion exchange as the primary immobilization mechanism in zeolites (NaA zeolite, 1–5% w/w, 96% reduction in TCLP-extractable Pb and 91% reduction in TCLP-extractable Cd), the synergistic action of adsorption, complexation, and precipitation in biochar systems (manure-derived biochar, 0–5% w/w, 97.4% reduction in the exchangeable Pb fraction according to the Tessier scheme), and the critical role of surface modification in attapulgite-based amendments (C-ATP, 4% w/w, 95.1% and 74.3% reductions in TCLP-extractable Pb and Cd, respectively). Because these efficiencies were obtained using different extraction protocols, they are not directly comparable. At the same time, cases of adverse responses were identified, including increased As extractability following the application of phosphate-modified biochar and the redistribution of Pb and Cd after amendment with natural zeolite in industrially contaminated soil. These observations highlight that amendment performance is not an intrinsic property of the material itself, but rather the outcome of specific geochemical interactions occurring within the soil system. Increased soil pH emerged as the principal common factor promoting metal stabilization across all amendment categories, whereas substantial variability in amendment dosage, incubation period, and analytical methodology limited direct quantitative comparisons among studies. Consequently, the selection of an appropriate soil amendment should be based on the integrated evaluation of soil physicochemical properties, contaminant speciation, and the intended scale of application, supported by long-term monitoring under field conditions. Full article

Thallium (Tl) and cadmium (Cd) are highly toxic heavy metals that frequently co-occur in sulfide ores, posing a serious food safety risk through accumulation in rice. Although calcium-based (Ca-based) amendments have been widely applied to remediate heavy metal-contaminated soils, their effectiveness in Tl–Cd co-contaminated paddy soils remains unclear. A pot experiment was conducted to evaluate four Ca-based amendments—limestone powder, dolomite powder, hydrated lime, and oyster shell powder—on Tl and Cd bioavailability and uptake in paddy soil near a mining area. Ca-based amendments effectively reduced Tl and Cd bioavailability, with DTPA-Tl reducing by 11.2–17.2% and DTPA-Cd by 8.9–21.3%. These reductions were attributed to increased soil pH and decreased DOC, Fe, and Mn in the pore water. Additionally, Ca-based amendments shifted Tl and Cd from acid-extractable to residual fractions, reducing mobility. Additionally, Ca-based amendments promoted Fe/Mn plaque formation on rice roots, reducing Tl and Cd uptake. Consequently, Tl and Cd concentrations in brown rice decreased by over 14%, with the lowest levels observed under oyster shell powder. However, Cd concentrations still exceeded the maximum permissible limit, indicating that, although Ca-based amendments show considerable potential for in situ remediation of Tl–Cd co-contaminated paddy soils, further optimization and additional measures are required to achieve safe production. Full article

The increasing accumulation of microplastics (MPs) in soils necessitates a better understanding of their effects on soil chemistry and trace element behavior. This study examined the influence of three MPs—low-density poly(ethylene) (LDPE), polypropylene (PP), and poly(ethylene terephthalate) (PET)—on cadmium (Cd) and copper (Cu) mobility in four clayey–sandy soils with similar organic matter content but differing pH, representing acidic and alkaline terrestrial matrices. Soils were incubated with 1% (w/w) MPs at 60% water-holding capacity for 30 and 90 days. Total Cd and Cu concentrations remained largely unaffected; however, time-dependent changes in metal availability and distribution were observed. Extractability (CaCl₂ and DTPA), sequential BCR fractionation, and environmental risk indices (CF, Igeo, RAC, MF, and PLI) indicated slight increases in Cd availability after 30 days, which became more pronounced after 90 days, particularly in acidic soils (pH 5.5). The magnitude of the MP effect followed the trend PET > PP > LDPE in all cases. Among the two target metals, Cd exhibited substantially higher mobility than Cu, as reflected by RAC and MF values. Specifically, Cd RAC (6–35%) and Cd MF (28–63%) values were considerably higher than those of Cu (1.1–3.8% and 15–28%, respectively). Overall, although the general pollution indices remained relatively stable, MPs altered the extractability and geochemical partitioning of the examined heavy metals—particularly Cd—indicating their potential role as vectors in soil environments. These results demonstrate that incubation time, polymer type, and soil pH jointly regulate MP-induced change in Cd and Cu mobility, with important implications for soil ecosystem risk. Full article

Application of CFA-treated biosolids (NVS) offers multiple benefits to agricultural soils, including fertilizer replacement, soil rehabilitation, and disinfection. It also poses a heavy metal(loid)s threat to the agro-environment. NVS (and CFA to some extent) was tested in lysimeter and field trials, using soils differing in physicochemical properties and a large selection of crops. Consistently, As, Pb, and Cd concentrations in leachate were at or below detection limit, and these and other heavy metal(loid)s (and P) were within the permitted range in plant tissue. Foliage Mo (occasionally also Se, P) concentrations often increased significantly, especially in crops (legumes, potatoes) grown on marginal soils, which also displayed significantly higher yields. CFA and NVS reduced lettuce and legumes foliage Mn (and occasionally Zn) concentrations, which remained, however, adequate. NVS (214 and 642 mT ha⁻¹), digested sewage sludge (ADS) and its compost (24 and 72 mT ha⁻¹), temporarily increased the DTPA-extractability of some elements (NVS: B, Cr; ADS: Cu, Ni, Zn; Compost: Zn) 10–30-fold. The extractabilities of Fe and P increased by up to six times. These increases vanished soon after additive application, supporting the hypothesis of ‘self-attenuation’ by applied biosolids. Our data indicate that long-term application of NVS (and CFA) to calcareous soils poses no heavy metal(loid)s-related threat to the agro-environment. Full article

The current investigation involved preliminary laboratory research regarding the accumulation capacity of three types of hyperaccumulator plants when specific soil factors are altered during their cultivation. Three different plants participated in this experiment, namely, milk thistle (Silybum marianum (L.) Gaerth), industrial hemp (Cannabis sativa L.), and tobacco (Nicotiana tabacum L.), which were cultivated in two soils with different pH values, yet containing similar levels of metal pollutants. ABC fire extinguisher powder (FP), which had been tested in the past and found to cause a significant change in nutrient availability, was added to the soils. The FP was added at 1% v/v and, in order to facilitate its fast incorporation into the soil, the soil moisture was maintained at 60–65%. The experiment was conducted in pots where the plants were grown in contaminated soils, with and without the FP addition. The pseudo-total (after extraction with Aqua Regia), available (after extraction with DTPA), and water-soluble concentrations (after extraction with CaCl₂ solution) of Cd, Cr, and Cu were determined in the soils. The plants completed their growth cycle (in 112, 128, and 139 days, respectively), were harvested, and the metal concentrations were assessed after extraction with Aqua Regia, both in the underground and above-ground parts. FP addition caused a significant decrease in the availability of each of the three metals, yet mainly Cr, as it caused a maximum reduction of 19.6% and 16.0% in the rate of water-soluble and available (after extraction with DTPA) Cr, respectively, in relation to the total Cr concentration in acidic soil, revealing the decisive role played by soil reaction in metal availability. FP addition caused a significant Cd reduction in accumulation in the above-ground parts of cultivated plants in the order of hemp > thistle > tobacco. FP use appears to significantly alter the plant-to-soil metal transfer, affecting the plants’ ability to accumulate Cd, Cr, and Cu. Apparently, this material, disposed of in the environment, could be a useful and low-cost soil conditioner, in line with the principles of the circular economy. Full article

Addressing the threat of heavy metal contamination in agriculture, this study evaluated the efficacy of crab shell biochar (CB) and compost (CO) in immobilizing copper (Cu), zinc (Zn), and lead (Pb). The objective was to determine the impact of solitary and combined applications of CB and CO on soil physicochemical properties, nutrient availability, HMs bioavailability, subsequent growth, and oxidative stress responses in spinach plants. The experiment involved two soil types (clay loam and sandy clay loam) with differing initial properties, which were simultaneously spiked with 300 mg kg⁻¹ Cu, 500 mg kg⁻¹ Zn, and 400 mg kg⁻¹ Pb, aged for 30 days, and then treated with varying doses of CB and CO (e.g., 1% and 1.5% w/w). Key results demonstrated that the combined application of 1.5% CB + 1.5% CO was most effective, significantly (p < 0.05) increasing soil pH and reducing DTPA-extractable Cu (by 53–64%), Zn (42–50%), and Pb (57–59%) in both soil types. This treatment also led to a pronounced decrease in the bioaccumulation factor (BF) of HMs in spinach, coupled with improved plant growth parameters (height, fresh/dry weight, chlorophyll content) and reduced oxidative stress (as indicated by lower levels of MDA and antioxidant enzymes). We conclude that the synergistic interaction between CB and CO creates a multi-mechanistic immobilization system, offering a highly effective strategy for the remediation of heavy metal-contaminated soils and the safe cultivation of crops. Full article

Organic amendments application has been proposed as an efficient method for remediation of heavy metals-contaminated soils. This study evaluated the performance of the water-insoluble organic material polyvinylpolypyrrolidone on decontaminating water and soil polluted by heavy metals Cu, Cd and Zn via batch trials, soil incubation and pot experiments with oilseed rape. The adsorption process of Cu, Cd and Zn by polyvinylpolypyrrolidone included a rapid step which achieved 92%, 76% and 87% of adsorption capacities within 10 min, followed with a slow step before reaching equilibrium which varied from 4 to 24 h among the three heavy metals. The maximum adsorption capacities were 327, 330 and 186 mg g⁻¹ for Cu, Cd and Zn, respectively. With application doses of polyvinylpolypyrrolidone ranging from 10 to 60 g kg⁻¹, the DTPA-extracted Cu, Cd and Zn showed 59–96%, 27–93% and 13–83% reduction compared to no addition. Moreover, the uptake of Cu, Cd and Zn by oilseed rape were significantly inhibited with polyvinylpolypyrrolidone amendments, and the effects improved with the accrual of polyvinylpolypyrrolidone. Intriguingly, the application of polyvinylpolypyrrolidone showed insignificant influences on nutrients taken up by oilseed rape. Results of the present study indicated that polyvinylpolypyrrolidone is a promising organic amendment for heavy metal (Cu, Cd and Zn) stabilization in polluted water and soil. Full article

It is well known that physico-chemical soil parameters can influence, or even determine, the concentrations of heavy metals in soil. Moreover, in recent decades, there has been growing concern about the role of climatic variables such as temperature fluctuations, drought, or extreme rainfall in affecting heavy metal availability. To examine the combined influence of soil properties and climatic changes on pollution levels, a 10-year study was conducted in an intensively cultivated region of central Greece. This work builds on an earlier study that established predictive relationships for Aqua Regia (Aq-Re)-extracted (pseudo)-total Fe and toxic Cd levels from a set of soil parameters, macronutrients or coexisting metals. The present investigation extends this approach by including DTPA-extracted metal concentrations and additional climatic predictors. The updated methodology applies Linear and Quadratic Regression models as well as Linear and Quadratic Mixed-Effects Models to account for the temporal variation driven by climate. The models were trained and validated on continuous, decade-long measurements. In many cases, this led to substantial revisions of the previously established correlations. Incorporating climate-related variables improved the predictive power of the models, revealing a more complex soil–metal dynamic than previously considered. The newly developed models demonstrated more accurate estimations of both total and available metal concentrations, even under the extreme weather conditions observed in autumn 2020. Given the importance of the Thessaly plain to the Greek agricultural sector, these models serve as a valuable tool for monitoring and risk assessment. Quantifying nutrient and toxic element availability under climate shifts is key to safeguarding Mediterranean soil health and addressing the broader impacts of the climate crisis in agroecosystems. Full article

The increasing demand for lithium-ion batteries (LIBs) and their limited lifespan emphasize the urgent need for sustainable recycling strategies. This study investigates the application of tetrabutylphosphonium-based ionic liquids (ILs) as alternative leaching agents for recovering critical metals, Li(I), Co(II), Ni(II), and Mn(II), from spent NMC cathode materials. Initial screening experiments evaluated the leaching efficiencies of nine tetrabutylphosphonium-based ILs for Co(II), Ni(II), Mn(II), and Li(I), revealing distinct metal dissolution behaviors. Three ILs containing HSO₄⁻, EDTA²⁻, and DTPA³⁻ anions exhibited the highest leaching performance and were selected for further optimization. Key leaching parameters, including IL and acid concentrations, temperature, time, and solid-to-liquid ratio, were systematically adjusted, achieving leaching efficiencies exceeding 90%. Among the tested systems, [TBP][HSO₄] enabled near-complete metal dissolution (~100%) even at room temperature. Furthermore, an aqueous biphasic system (ABS) was investigated utilizing [TBP][HSO₄] in combination with ammonium sulfate, enabling the complete extraction of all metals into the salt-rich phase while leaving the IL phase metal-free and potentially suitable for reuse, indicating the feasibility of integrating leaching and extraction into a continuous, interconnected process. This approach represents a promising step forward in LIB recycling, highlighting the potential for sustainable and efficient integration of leaching and extraction within established hydrometallurgical frameworks. Full article

Soil heavy metal contamination poses critical challenges to ecological sustainability in mining regions, particularly in acidic soils from copper sulfide mines. This study developed a sustainable remediation strategy using a carbonyl iron powder–biochar composite (CIP@BC) derived from agricultural waste (rice husk) and industrial byproducts. The composite was synthesized through an energy-efficient mechanical grinding method at a 10:1 mass ratio of biochar to carbonyl iron powder, aligning with circular economy principles. Material characterization revealed CIP particles uniformly embedded within biochar’s porous structure, synergistically enhancing surface functionality and redox activity. CIP@BC demonstrated exceptional Cu²⁺ immobilization capacity (910.5 mg·g⁻¹), achieved through chemisorption and monolayer adsorption mechanisms. Notably, the remediation process concurrently improved key soil health parameters. Soil incubation trials demonstrated that 6% CIP@BC application elevated soil pH from 4.27 to 6.19, reduced total Cu content by 29.43%, and decreased DTPA-extractable Cu by 67.26%. This treatment effectively transformed Cu speciation from bioavailable to residual fractions. Concurrent improvements in electrical conductivity (EC), cation exchange capacity (CEC), soil organic matter (OM), and soil water content (SWC) collectively highlighted the composite’s multifunctional remediation potential. This study bridges environmental remediation with sustainable land management through an innovative waste-to-resource approach that remediates acidic mine soils. The dual functionality of CIP@BC in contaminant immobilization and soil quality restoration provides a scalable solution. Full article

Heavy metal (HMs) toxicity has severely impacted wheat production and is considered an emerging threat to human health due to bioaccumulation. The application of organic and inorganic amendments has proven effective in mitigating HM’s phytotoxicity by limiting their mobility in soil and plants. A pot experiment was conducted to evaluate the efficiency of biochar (BC), bentonite (BN), and rock phosphate (RP), both individually and in combination, in alleviating lead (Pb) toxicity and enhancing wheat growth, and physiological attributes. The present investigation revealed that BC, BN, RP, and their combined mineral biochar amendments (MBAs) at 1.5% level significantly enhanced wheat growth along with reducing DTPA-extractable Pb in soil by 30.0–49.8% and Pb uptake in roots by 15.7–37.5% and in shoots by 34.5–48.5%. Antioxidant enzymatic activities were improved, and stress indicators were reduced in roots and shoots of wheat under Pb stress, including hydrogen peroxide (H₂O₂) by 50.7 and 81.0%, malondialdehyde (MDA) levels by 16.0 and 74.9%, and proline content by 34.5 and 64.0%, respectively. The effectiveness of the treatments is described in descending order viz. MBA-1 > MBA-3 > MBA-2 > BC > RP > BN under Pb stress. In conclusion, the integration of biochar, bentonite, and rock phosphate is a promising strategy for sustainable and cleaner cereal crop production under heavy metal stress conditions. Full article

Simultaneously stabilizing cadmium, lead, and arsenic in contaminated soils is challenging due to their significant differences in physical and chemical properties. This study developed a composite material by modifying hydrochar with iron (Fe), phosphorus (P), and sulfur (S) to address this issue. The iron–phosphorus–thiol-modified Trachycarpus fortunei hydrochar (H-PAL-Fe2-P-T) effectively stabilized these metals. Experimental results showed that the H-PAL-Fe2-P-T achieved over 90% stabilization for DTPA-extracted cadmium, lead, and arsenic. Characterization by XRD, SEM, and FTIR revealed structural and functional changes in the hydrochar. Column leaching tests simulating acid rain showed that the composite material maintained stable stabilization effects, with the fluctuations in the stabilization rates remaining below 20%. Additionally, the composite-modified hydrochar enhanced the stabilization of water-soluble, DTPA-extracted, and TCLP-extracted heavy metals in soil, demonstrating good stability and durability for long-term use. These findings suggest that Fe-, P-, and S-modified hydrochar is a promising and sustainable approach for the remediation of soils contaminated with cadmium, lead, and arsenic. Full article

The concept of metal bioavailability in soils is increasingly becoming the key to addressing potential risks. Yet, space–time variations of heavy metal concentrations in salt-affected soils is still vague. The current work, therefore, is the first attempt to address spatial and seasonal analyses of heavy metals in a Mediterranean arid agroecosystem. This study was conducted in a coastal area in northeastern Egypt as an example. The DTPA-extractable concentrations of Cr, Co, Cu, Fe, Pb, Mn, Ni, and Zn in addition to the main properties of 70 georeferenced soil samples (0–30 cm) were determined during the wet (March) and dry (September) seasons. The results revealed that except for Cu, the concentrations of all the determined metals stood below the safe limits. On average, the concentrations of Cu were 4.1- and 5-fold the acceptable limit of 0.20 mg kg⁻¹, respectively. The statistical analysis indicated that seasonal variations greatly affect the concentrations of Mn, Ni, and Zn. Compared with the wet season, significant increases of 1.25, 1.50, and 1.28-fold in the concentrations of these metals occurred during the dry season, respectively. The principal component analysis affirmed that the presence of Cr, Co, Fe, and Ni was closely related to geogenic factors; meanwhile, agronomic practices were likely the main inputs of Cu, Pb, and Zn. The geostatistical analysis illustrated that the geographic variability of Cr, Fe, Mn, and Zn was due to interactions of natural and stochastic processes. Farming practices controlled the spatial variability of Ni, Pb (in the wet period), and Co (in the dry period). The effect of natural processes during the wet period was evident for Cu, which showed strong spatial variability. The kriged maps showed that the concentrations of Co, Fe, and Ni tended to increase seaward and were found to be affected by pH, salt ions, and exchangeable Na⁺. Moreover, both silt and organic matter content had profound impacts on the spatial distribution of Cr, while the distributions of Cu, Pb, and Zn were linked to that of CaCO₃ content. The suggested mechanisms governing metal bioavailability were sorption and complexation with ligands (for Co, Fe, and Ni), redox potential (for Cr), dissolution–precipitation (for Mn), and ion exchange (for Cu, Pb, and Zn). The results of this study affirm that drying–wetting cycles and spatial distribution affect the bioavailability of heavy metals in coastal salt-affected soils of arid regions. These findings imply that seasonality (wet and dry) and spatiality should be considered for monitoring and rehabilitation of degraded soils under similar ecological conditions. Full article

The origin and bioavailability of nickel (Ni), chromium (Cr), and cobalt (Co) have been assessed in the Čemernica River basin among the following soil types: Leptosol on serpentinite and Fluvisol, Vertisol, and Leptosol on sandstone. Alongside the impact of serpentine rocks, part of the region also displays significant anthropogenic activity. A sequential analysis following the modified BCR procedure identified four fractions of heavy metals: F1—exchangeable and acid-soluble, F2—bound to Fe and Mn oxides, F3—bound to organic matter, and F4—residual. The overall content of Ni, Cr, and Co in the soil increases in the following order: Leptosol on sandstone, and Vertisol, Fluvisol, Leptosol on serpentinite. In most samples, the values exceed the maximum allowable concentrations in legal regulations, while in some samples, particularly in serpentine soils, they also exceed the remediation thresholds. The average contribution of nickel in the overall content decreases as follows: F4 > F2 > F3 > F1, chromium as F4 > F3 > F2 > F1, and cobalt in the most samples as F2 > F4 > F1 > F3. The percentage of Ni, Cr, and Co in the fractions of different soil types is similar to that in serpentine soils, though the absolute contents vary significantly, indicating a common origin, which is mostly geochemical. According to the Risk Assessment Code, most samples exhibit a low bioavailability risk. Full article

Slow pyrolysis was carried out in biosolids under three different temperatures (400, 500 and 600 °C) and two different carrier gases (CO₂ and N₂) on a fluidized bed reactor. The total concentration, chemical fractionation, and plant availability of the heavy metals in biochar were assessed by standard methods. The total concentration of Fe, Zn, Cu, Mn, Cr, Ni and Pb increased with the conversion of biosolids to biochar and with increasing pyrolysis temperature. The community’s Bureau of Reference (BCR) sequential extraction identified the migration of metals from toxic and bioavailable to potentially stable available or non-available forms at higher pyrolysis temperatures. Diethylenetriamine penta-acetic acid (DTPA)-extractable metals (Cu, Zn, Cd, Cu, Fe and Pb) were significantly lower in biochar compared to biosolids. By replacing N₂ with CO₂, the total metal concentration of heavy metals was significantly different for Mn, Ni, Cd, Pb and As. There were larger amounts of metals in the residual and oxidizable fractions compared to when N₂ was used as a carrier gas. Consequently, the biochar produced at higher temperatures (500 and 600 °C) in the N₂ environment exhibited lower potential ecological risks than in CO₂ environments (69.94 and 52.16, respectively, compared to values from 75.95 to 151.38 for biochars prepared in N₂). Overall, the results suggest that the higher temperature biochar can support obtaining environmentally safe biochar and can be effective in attenuating the ecological risks of biosolids. Full article