Availability Of Heavy Metals Research Articles

Enhanced fertilizer utilization and heavy metals immobilization by ball-milling bentonite with NH4Cl: Experiments and DFT calculations

Over-application of nitrogen fertilizer induces soil acidification, which activates heavy metals availability and poses significant challenge to crop production and food safety. In this study, we prepared a clay-based material by ball-milling bentonite with NH4Cl (NH4Cl@bentonite) and assessed its synergistic performance in enhancing nitrogen fertilizer utilization efficiency, immobilizing heavy metals, and improving crop yield and safety. The results showed that the optimal performance of NH4Cl@bentonite was achieved by milling bentonite with NH4Cl at a 4:1 mass ratio for 9 h. NH4Cl@bentonite significantly improved soil water holding and retention capacity by 1.6 and 4.3 times, respectively. In comparison to NH4Cl alone, NH4Cl@bentonite led to a 22.3% increase in N-use efficiency and a 1.5 times enhancement in crop yield. The Pb and Cd content in water spinach shoots decreased by 55.3% and 57.5%, respectively, attributed to the transformation of heavy metals into lower bioavailability states by NH4Cl@bentonite. Experiments and Density Functional Theory (DFT) calculations indicated that NH4Cl@bentonite could immobilize Pb and Cd through processes such as cation exchange, surface adsorption, complexation, and enhancement of soil pH. This work proposes a simple and efficient method for improving cropland fertilizer utilization while ensuring healthy and sustainable development. Environmental implicationSoil acidification, caused using chemical fertilizers, especially nitrogen-based ones, threatens crop production and food safety by damaging soil structure, speeding up nutrient loss, and increasing the solubility of heavy metals. To tackle this problem, we made a clay material by mixing bentonite with NH4Cl (NH4Cl@bentonite) in a ball mill. NH4Cl@bentonite increased N-use efficiency by 22.3%, boosted crop yield by 1.5 times, and reduced the Pb and Cd levels in water spinach shoots by 55.3% and 57.5%, respectively. This work suggests a simple and effective way to enhance fertilizer use in croplands while ensuring healthy and sustainable development.

Effect of different calcium salts on phosphorus availability and immobilization of heavy metals in municipal sludge derived biochar

Transforming municipal sludge (MS) into biochar via co-pyrolysis with calcium salts enhances phosphorus (P) recovery and reduces the risk of heavy metal contamination. In this study, the performance and mechanism of bioavailable P conversion and heavy metal stabilization were systematically compared under co-pyrolysis of MS with CaCO3, CaO, and CaCl2 at mass ratios of 2.5–10 % at 700 °C. The results showed that CaCl2 had the best ability to convert P from non-apatite inorganic P to apatite P, followed by CaO and then CaCO3. CaO and CaCO3 addition induced more Ca5(PO4)3OH formation, while CaCl2 induced more Ca2PO4Cl and Ca5(PO4)3Cl formation. The degree of stabilization of heavy metals (e.g., Cd, Cr, Cu, Ni, Pd, and Zn) was significantly improved after co-pyrolysis of MS with these salts, thus reducing the potential environmental risk. In particular, because of the dual action mechanism of chloride ions and calcium ions, co-pyrolysis with CaCl2 exhibited the lowest risk of heavy metal contamination compared with CaCO3 and CaO. These findings suggest that addition of 2.5 % CaCl2 can optimize the production of bioavailable P and the stabilization of heavy metals in biochar. This treatment is recommended for the safe utilization of P resources derived via MS pyrolysis.

The impact of olive mill wastewater on soil properties, nutrient and heavy metal availability – A study case from Syrian vertisols

Olive oil mill wastewater (OMW) is an environmental concern in olive oil producers' regions due to its use in agricultural soils as an organic amendment. However, OMW can also be used as organic fertilizer due to their high organic matter and nutrient levels, but its use, when it occurs without environmental management, can cause serious environmental implications for soils and waters. This work evaluated the impact of different OMW levels on a set of physicochemical parameters from an agricultural vertisol where wheat grew (Triticum aestivum L var. Douma 1). A set of physicochemical parameters were conducted before adding different levels of OMW (0, 5, 10 and 15 L m−2) at two soil depths (0–30 and 30–60 cm) and for the two growing seasons to determine: i) the effect of OMW treatments on the studied physicochemical soil properties (bulk density, soil porosity, soil pH, electrical conductivity and organic matter), ii) available primary (N, P, K) and secondary macronutrients (Ca, Mg and Na), ii) micronutrients (Cu Fe, Mn and Zn), and iv) available heavy metals (Cd and Pb). The results indicated that soil physicochemical parameters were slightly improved, mainly due to improvement in organic matter, macro- and micronutrients, usually proportionally to the olive mill wastewater dose. Cadmium and Pb were within the permissible limits. The increased OMW had different behaviour on the soil nutritional balances of different elements, leading to nutrient imbalances, although in some cases, they were improved. However, the plant growth was not affected, and it was improved under 10 L m−2 and 15 L m−2 doses. The results offer valuable data about the use of OMW as organic fertilizer for crops and their potential impact on soil properties.

Assessment of heavy metals availability and its health risk on Zea mays and Sorghum grown on agricultural soil, Southern Borno, Nigeria

Heavy metals are deleterious due to their long biological half-lives, non-biodegradable nature, and their ability to accumulate in different body parts. Heavy metals emanating from anthropogenic sources are more dangerous because of their instability and solubility leading to high bioavailability. Heavy metals uptake by plants is generally the first step of their entry into the agricultural food chain. The present study aimed at assessing the availability of heavy metals on cereals crops (Zea mays and Sorghum) grown on agricultural soil hence their health risk index. Soil and cereals crops were digested analyzed for Cr, Cd, Cu, Pb, Ni and Zn using Atomic Absorption Spectroscopy (Buck scientific model 210GP) while transfer factor (TF), daily intake of metals (DIM) and health risk index (HRI) were evaluated. The concentration of Cd in all the three soil samples had mean values of 10.7±2.32 mg/kg while Zea mays and Sorghum had mean values of 2.12±0.09 and 2.75±0.03 mg/kg respectively. The decrease in concentrations of the metals in Zea mays and Sorghum samples across sampling locations followed this order Cd > Cu > Cr > Pb > Ni > Zn. The trend of heavy metal transfer factor from soil to Zea mays and Sorghum grown in Askira Uba, Southern Adamawa were in the order of Cd > Ni > Cu > Pb > Cr > Zn. The HRI values of Cd (1.00, 2.70) in both zea mays and sorghum were higher than other studied heavy metals. The finding of this study with respect to DIM and HRI showed that the consumption of Zea mays and Sorghum grown in Askira Uba, Southern Borno were nearly free of risks at all sites for all assessed heavy metals except Cd. Even though the values of HRI for other metals were nearly one, the long term consumption of these crops may lead to serious health risk.

Rice straw biochar and lime regulate the availability of heavy metals by managing colloid-associated- but dissolved-heavy metals

Heavy metal (HM) pollution has extensively spread in agricultural soils, posing potential threats to food safety and human health. Biochar and lime are two amendments used to remediate the soils contaminated with HMs. However, colloids have been shown to increase the mobility of HMs in paddy soils. Nevertheless, limited investigations have been made into the impact of biochar and lime on the formation of colloid-associated (colloidal) HMs in paddy soils. In this study, column and microcosm incubation experiments were conducted to examine how biochar and lime affected the availability of HMs (arsenic, cadmium, copper, iron, manganese, lead, and zinc) in different layers of paddy soils. The results revealed that biochar significantly inhibited the formation of colloidal HMs in the soil flooding phase, whereas the lime increased the colloidal HMs. These colloids containing HMs were identified as poorly dissolved metal sulfides. When the soil was drained, colloidal HMs transformed into dissolved forms, thereby improving the availability of HMs. Biochar decreased HM availability by reducing colloidal- but dissolved- HMs, whereas lime had the opposite effect. Hence, biochar demonstrated a stable and reliable remediation ability to decrease HM availability in paddy soil during flooding and drainage processes. In conclusion, this study highlighted that biochar efficiently reduced HM availability by mitigating the formation of colloidal HMs during flooding and their transformation into dissolved HMs during drainage in paddy soils.

Increasing phosphorus plant availability from P-rich ashes and biochars by acidification with sulfuric acid

Biochars and ashes derived from thermal treatment of P-rich wastes could be used as bio-based fertilizers to improve P recycling. However, thermal treatments often result in low plant P availability. Acidification of these materials before soil application could potentially increase plant P availability. Based on the water-extractable P levels obtained in titration experiments, sulfuric acid concentrations between 2.5 M and 10 M were applied to digestate solids char and ash (DS-C, DS-A), poultry litter ash (PL-A), insect frass char (IF-C), sewage sludge char and ash (SS-C, SS-A) and meat and bone char (MB-C). Acidified and untreated materials were applied in a pot experiment with maize in 33P labeled soil to determine fertilizer P uptake. The acidification resulted in a significant increase in P solubility. The amount of acid required depended on the materials’ buffer capacity and P speciation. Based on XRD analysis, we assume that mainly Ca-associated P was solubilized. In the pot experiment, acidified materials outperformed untreated materials and the unfertilized control in terms of biomass and P uptake. The P recovery from the acidified materials ranked in the order DS-C > SS-A > PL-A > IF-C > DS-A > SS-C > MB-C. The acidification did not significantly decrease soil pH, nor was there an effect on plant heavy metal availability. In conclusion, acidification increased plant growth and P uptake without affecting plant heavy metal uptake and soil pH. Therefore, acidification to increase the P fertilizer value of ashes and chars is a promising approach to facilitate P recycling.

Characterization of Technosols for Urban Agriculture

Soil characterization is essential for planning activities in urban areas in order to detect potential risks and understand the possible impacts derived from those activities. Nine soils located in Alicante (southeast of Spain) developed over construction debris were studied. Soil characteristics including mineralogy, elemental composition and metal availability were analyzed in two consecutive years, 2019 and 2020. These soils were similar to forest soils in the same area, with no evidence of asbestos clays or excess harmful elements. However, the use of DTPA extraction revealed high levels of Mn and Zn in some soils. Organic carbon and metals extracted with DTPA differed in 2019 and 2020, but no relationship between metal-DTPA and organic carbon content was observed. In general, organic matter content was higher in 2019, and elements extracted with DTPA were lower. The above-average rainfall in 2019 could have led to the washing away of dissolved materials and fine soil particles, decreasing elemental availability on the one hand, while promoting the development of natural vegetation, increasing soil organic matter, and immobilizing elements in living organisms on the other hand. The fact that the metal mobility varies depending on weather and soil characteristics is important when planning. Despite the demonstrated advantages of increasing urban green areas from an environmental and social point of view, we should not forget the materials on which urban soils are developed. Therefore, it is essential to establish annual plans for monitoring variations in the availability of heavy metals. This is of the most relevance when the plants are for human consumption. It is therefore also necessary to control the vegetables that grow on these soils and, in the event of possible problems, use the soil for gardening.

Occurrence and Health Risk Assessment of Heavy Metals in Lychee (Litchi chinensis Sonn., Sapindaceae) Fruit Samples

This study aimed to assess the occurrence of eight heavy metals in lychee (Litchi chinensis Sonn.) fruit samples collected from orchards of the Dehradun and Haridwar districts in Uttarakhand, India. Lychee fruit samples were collected from ten (10) sampling locations from May to June 2023 and analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). Results showed that lychee fruit samples showed varying levels of selected heavy metals, i.e., Cd (0.009–0.095 mg/kg), Cr (0.079–0.960 mg/kg), Cu (0.095–0.258 mg/kg), Fe (0.254–0.531 mg/kg), Pb (0.000–0.011 mg/kg), Mn (0.862–1.903 mg/kg), Ni (0.166–0.310 mg/kg), and Zn (0.076–0.149 mg/kg). It was observed that lychee fruit sampling sites near urban and industrial areas had higher concentrations of heavy metals as compared to those in rural and agricultural areas. In addition, principal component analysis (PCA) and clustered heatmap dendrogram results showed that several sites had significant similarities in terms of heavy metal availability. Overall, the levels of all heavy metals were below the safe limits as suggested by health risk studies. The selected indices such as daily intake of metals (DIM), health risk index (HRI), and target hazard quotient (THQ) did not exceed the standard limit which indicated consumption of lychee fruit was safe at all sampling sites. The results of this study emphasize the need to regularly monitor lychee heavy metal levels and implement sustainable agricultural and environmental practices to reduce contamination sources.

Effects of an assistive electric field on heavy metal passivation during manure composting

Composting is one of main technologies for treating and thus utilizing livestock manure and sludge. However, heavy metals are major concerns in compost utilization due to their potential environmental hazards and health risks. This study aimed to investigate the effects of electric field-assisted composting on the variations of heavy metals and the affecting factors. The results showed that electric field significantly reduced the contents of bioavailable heavy metals including Mn, Zn, Cu, Ni, and Cd, with their bioavailable concentrations decreasing by 61.7, 63.8, 64.9, 83.7, and 63.8 %, respectively. The heavy metals being transformed into stable states were increased, indicating that the electric field also passivated these heavy metals and reduced their biological toxicity and stabilized their forms. Spearman's correlation analysis revealed that the changes in substances, temperature, and organic matter were the dominant environmental factors affecting the forms of heavy metals. Microbial community analysis indicated an increase in the abundance of metal-resistant bacteria such as Pseudomonas and Bacillus during electric field-assisted composting, with their relative abundances being increased to 2.66 % and 15.63 % in the pile of electric field-assisted composting, respectively, compared to the values of 1.88 % and 4.36 % respectively in the conventional composting. The current study suggests that electric field-assisted composting can significantly reduce the availability of heavy metals in the compost, and thus mitigate the health risks associated with its application.

The Vital Roles of Parent Material in Driving Soil Substrates and Heavy Metals Availability in Arid Alkaline Regions: A Case Study from Egypt

Despite studies focusing on soil substrates (carbon and nitrogen) and heavy metal availability, the impact of diversified parent materials in arid alkaline regions has received little attention. To reveal the influence of parent material, we investigated four different parent materials: fluvio-marine, Nile alluvial, lacustrine, and aeolian deposits. We assessed the effect of soil parent materials through selected soil physical and chemical properties, such as clay content, bulk density, pH, and available phosphorus (AP). The Tukey HSD test (SPSS ver. 23) was used to assess the soils derived from these different sediments. Using the R “glmulti” package, we examined this effect in a model of mixed-effects meta-regression. The sum of Akaike weights for models that contained each element was used to estimate the importance of each factor. The average contents of soil organic carbon (SOC) and total N in alluvial deposits were greater (p < 0.001) than those of marine, aeolian, and lacustrine deposits. A multivariate analysis in arid regions revealed that parent material, soil pH, and the availability of P had the greatest effects on SOC concentration, whereas clay content, available P, soil pH, parent material, and bulk density had the greatest effects on soil total nitrogen. The average content of Fe in the aeolian deposits was greater (p < 0.001) than those of marine, alluvial, and lacustrine deposits, without any significant differences between the latter two deposits. We found that the highest average contents of zinc (Zn), manganese (Mn), and copper (Cu) were recorded in alluvial deposits, with significant differences between other deposits. Soil parent material was the major factor impacting soil iron (Fe) content, along with clay content and soil pH. However, soil bulk density was the most important factor controlling soil Zn and Mn contents, while SOC drove Cu content. This study will help in developing a more accurate model of the dynamics of soil substrates and availability of heavy metals by considering readily available variables, such as parent materials, soil pH, soil bulk density, and clay content.

Microplastics drive microbial assembly, their interactions, and metagenomic functions in two soils with distinct pH and heavy metal availability

Microplastics (MPs) have emerged as widely existing global environmental concerns in terrestrial ecosystems. However, the mechanisms that how MPs are affecting soil microbes and their metagenomic functioning is currently uncertain. Herein, we investigated the response mechanisms of bacterial and fungal communities as well as the metagenomic functions to the addition of MPs in two soils with distinct pH and heavy metals. In this study, the acidic soil (Xintong) and the neutral soil (Huanshan) contaminated by heavy metals were incubated with Polyvinyl Chloride (PVC) MPs at ratios of 2.5% and 5% on 60 and 120 days. We aimed to evaluate the responding, assembly, and interactions of the metagenomic taxonomy and function. Results showed that only in the acidic soil, PVC MPs significantly increased soil pH and decreased CaCl2-extractable heavy metals, and also reduced bacterial alpha diversity and interaction networks. The relative proportions of Proteobacteria and Bacteroidota in bacteria, and Mortierellomycota in fungi, were increased, but Chloroflexi and Acidobacteriota in bacteria, Ascomycota and Basidiomycota in fungi, were significantly decreased by PVC MPs. Metagenomic functions related to C cycling were repressed but the nutrient cycles were enriched with PVC MPs. In conclusion, our study suggests that the addition of PVC MPs could shift soil microbial community and metagenomic functioning, as well as increasing soil pH and reduced heavy metal availability.

Synergistic interplay between ABA-generating bacteria and biochar in the reduction of heavy metal accumulation in radish, pakchoi, and tomato

Heavy metal (HM) contamination is an environmental concern that threatens the agricultural product safety and human health. To address this concern, we developed a novel strategy involving the synergistic application of Azospirillum brasilense, a growth-promoting rhizobacterium which produces abscisic acid (ABA), and biochar to minimize HM accumulation in the edible parts of vegetable crops. Compared to A. brasilense or biochar alone, the concentrations of Cd, Ni, Pb, and Zn in radish (Raphanus sativus L.), pakchoi (Brassica chinensis L.), and tomato (Lycopersicon esculentum L.) decreased by 18–63% and 14–56%, respectively. Additionally, the synergistic treatment led to a 14–63% decrease in the bioconcentration factor. The biomass of the edible parts of the three crops increased by 65–278% after synergistic treatment, surpassing the effects of single treatments. Furthermore, the synergistic application enhanced the SPAD values by 1–45% compared to single treatments. The MDA concentrations in stressed plants decreased by 16–39% with the bacteria-biochar co-treatment compared to single treatments. Co-treatment also resulted in increased soluble protein and sugar concentrations by 8–174%, and improvements in flavonoids, total phenols, ascorbic acid, and DPPH levels by 2–50%. Pearson correlation analysis and structural equation modeling revealed that the synergistic effect was attributed to the enhanced growth of A. brasilense facilitated by biochar and the improved availability of HMs in soils. Notably, although ABA concentrations were not as high as those achieved with A. brasilense alone, they were maintained at relatively high levels. Overall, the synergistic application of A. brasilense-biochar might have remarkable potential for reducing the accumulation of HMs while promoting growth and improving nutritional and antioxidant qualities in tuberous, leafy, and fruit crops.

Heavy metals concentration and availability of serpentine soils in southwestern Turkey

Heavy metals concentration and availability of serpentine soils in southwestern Turkey

Effects of biochar, zeolite and mycorrhiza inoculation on soil properties, heavy metal availability and cowpea growth in a multi-contaminated soil

Heavy metal pollution of agricultural soil has become a major serious concern. The development of suitable control and remediation strategies for heavy metal contaminated soil has become critical. The outdoor pot experiment was conducted to investigate the effect of biochar, zeolite, and mycorrhiza on the bioavailability reduction of heavy metals and its subsequent effects on soil properties and bioaccumulation in plants as well as the growth of cowpea grown in highly polluted soil. Zeolite, biochar, mycorrhiza, zeolite with mycorrhiza, biochar with mycorrhiza, and soil without any modifications were the six treatments used. The experiment was conducted with a completely randomized design and four replications. The results indicated that the combination of biochar with mycorrhiza had the highest values of root and shoot dry weight and the lowest heavy metal concentrations in root and shoot as well as bioconcentration and translocation factors for all heavy metals. The highest significant reductions in the availability of heavy metals over the control were found with biochar with mycorrhiza, which were 59.1%, 44.3%, 38.0%, 69.7%, 77.8%, 77.2% and 73.6% for Cd, Co, Cr, Cu, Ni, Pb and Zn, respectively. The application of biochar and zeolite either alone or in combination with mycorrhiza increased significantly soil pH and EC compared to mycorrhiza treatment and untreated soil. It can be concluded that the combination of biochar and mycorrhizal inoculation has great potential as a cost-effective and environmentally technique for enhancing heavy metal immobilization, lowering heavy metal availability and plant uptake, and improving cowpea plant growth.

Empirical and Mechanistic Modeling of Release Kinetics of Heavy Metals and Their Chemical Distribution in the Rhizosphere and Non-rhizosphere Soils Under Vegetable Cultivation.

Biochemical processes in the rhizosphere affect the availability and distribution of heavy metals (HMs) in various forms. Rhizosphere soil (RS) and non-rhizosphere soil (NRS) samples were collected from 10 fields under tarragon(Artemisia dracunculus L.) cultivation to investigate the release kinetics and distribution of HMs including cadmium (Cd), cobalt (Co), copper (Cu), iron (Fe), and zinc (Zn) in five fractions. The cumulative amounts of Cu and Fe released after 88h were in the following ranges, respectively: 1.31-2.76 and 3.24-6.35mgkg-1 in RS and 1.41-2.72 and 3.15-5.27mgkg-1 in NRS. The parabolic diffusion and pseudo-second-order equations provided the best fit to the release kinetics data of Cu and Fe, respectively. The cation exchange model (CEM) based on Gaines-Thomas selectivity coefficients implemented in the PHREEQC program could well simulate the release of Cu and Fe suggesting that cation exchange was the dominant mechanism in the release of Fe and Cu from soils by 0.01 MCaCl2. Cadmium was predominantly found in fraction F2, while other HMs were mainly present in fraction F5. According to the risk assessment code, there was a very high risk for Cd, a medium risk for Co and Cu, a very low risk for Fe, and a low risk for Zn. Correlation analysis showed that soil physicochemical properties were effective in the distribution and transformation of HMs. Significant positive correlations between five fractions indicated that different forms of HMs can potentially transform into each other.

Effects of α-Fe2O3 modified chicken manure biochar on the availability of multiple heavy metals and soil biochemical properties

The problem of increasingly severe soil heavy metals contamination is of great concern worldwide. Herein, chicken manure and potassium ferrocyanide were used as raw materials to prepare a α-Fe2O3 loaded biochar (Fe2O3/BC) composite material through a simple calcination method. We found Fe2O3/BC obtained at 350 ℃ (Fe2O3/BC-350) exhibited excellent immobilization efficiency on multiple heavy metals in soil. And then density functional theory (DFT) calculations explained the reason of Fe2O3/BC-350 exhibited better remediation performance than the Fe2O3/BC-250 and Fe2O3/BC-550. When cultured for 90 days, the passivation effect of the 1% Fe2O3/BC-350 dosage treatment achieved the highest with the immobilization rates for Cu(II), Cd(II) and Pb(II) reaching 62.5%, 45.56% and 42.56%, respectively. The composite material increased soil pH and cation exchange capacity (CEC), and promoted the transformation of Cu(II), Cd(II) and Pb(II) ions from acid-soluble to more stable forms through ion exchange, precipitation and complexation. The soybean pot experiment further verified that Fe2O3/BC-350 could reduce the phytoavailable fractions of heavy metal soil remediation material. In addition, Fe2O3/BC-350 increased the activity of soil urease and sucrase. Meanwhile, the diversity and richness of the soil microbial community were improved. These results demonstrated that Fe2O3/BC-350 not only had an excellent immobilization effect on heavy metals in the soil, but also Fe2O3/BC-350 exhibited environmentally friendly in soil. As a result, Fe2O3/BC can serve as a promising remediation agent for multiple heavy metal polluted soils.

Differences between total amount of heavy metals and their occurrence form contents in the wastelands of a molybdenum mine area

In a single sample plot, the total amount of heavy metals in the soil could not necessarily reflect the contents of their effective states. This must be considered when attempting to determine the degree of soil heavy-metal pollution in an area. In the present study, the soil around the molybdenum mining area in Huludao, China, was surveyed and sampled to evaluate soil heavy-metal pollution using the Nemerow multifactor pollution index method. The Tessier continuous extraction method was used to analyze the distribution of heavy-metal forms’ and their content changes in the soil of this area. Thus, the bioactivity of heavy metals in the soil, the absorption of heavy metals by plants, and the distribution of heavy metals in plants were explored to provide data supporting the use of phytoremediation technology to treat the heavy-metal pollution in the molybdenum mining area and develop ecological restoration strategies for the area’s wastelands. The pollution index results indicate that heavy-metal pollution in the soil around the tailings pond is severe, mainly due to Pb and Zn heavy metals. Heavy-metal pollution in the surrounding land is mainly due to Cd and Zn. Content analysis of the heavy-metal forms/states in soils shows that exchangeable forms, which are most effective and toxic to plants, of the following metals are highest in the following areas: Cd, Cu, and Zn in the mountains around the stope; Zn, Mo, and Cu in the cultivated land around the dump; and Cd, Zn, and Mo in the cultivated land around the tailings pond. The pollution index analysis provides a basic overview of soil heavy-metal pollution across the entire mining area. However, content analysis of heavy-metal forms/states better reflects the relationship between the availability of heavy metals in the soil and the effectiveness of plants. Thus, the latter analysis can help ensure that phytoremediation strategies are adequately targeted, science-based, and effective.

The effect of pH on heavy metals availability on crude oil remediated and non-remediated soil, Nkeleoken Community Eleme, Rivers State, Nigeria

This study was aimed at examining the influence of pH on heavy metals availability in polluted and non-polluted soils. The findings showed that metal availability depends on soil solution which is pH dependent. The values of pH in Nkeleoken remediated soil (RSENa, RSENb, RSENc) in dry season were 6.01, 5.87, 5.78 and 6.64, 5.77, 5.68 in wet season with mean values of 5.89±0.05 and 6.03±0.53 while the pH of the contaminated soil ranged between 4.31 – 4.41. The mean values of heavy metals in Nkeleoken remediated soil are; Se (318±9.88; 326±11.6 mg/kg), Cd (3.65; 3.82±1.09 mg/kg), V (1095±71.05; 1189±149 mg/kg), Ba (8.98±1.53; 9.40±1.89 mg/kg), Cu (8.19±0.08; 8.84±0.14 mg/kg), Ni (0.02±0.01 mg/kg), As (5.52±2.35; 10.3±2.38mg/kg), Pb (1.73±0.32; 2.70±1.38 mg/kg) and Cr (23.1±4.05; 23.1±4.05 mg/kg). The results revealed that V and Se had the highest concentration level followed by As while the least concentrations were observed in Cd, Ba, Pb and Cr in both dry and wet season. The concentrations of heavy metals in the non-remediated soil ranged from 866 – 868 mg/kg, 1356 – 6332 mg/kg, 211 – 218 mg/kg, 73.6 – 79.0, and 866 – 868 mg/kg for Se, V, Ba Pb and as in dry and wet seasons. However, Cr concentrations ranged from 6.03 – 7.02 mg/kg. The concentrations of V and Se in the non-remediated soils (NRSENx - NRSENz) during dry and wet seasons were higher than their corresponding in the remediated soils likewise the recommended values set by DPR (2012).

Remediation of Cd and Cu Contaminated Agricultural Soils near Oilfields by Biochar Combined with Sodium Humate-Wood Vinegar

Soil contaminations by heavy metals near oilfields have been widely reported and are causing great concern. Thus, it is highly desirable to develop cost-effective materials and methods to avoid heavy metal residues contaminating soil and food. An effective, environmentally friendly, and inexpensive remediation material for heavy metal-polluted soil was designed and prepared using biochar (BC) combined with humic acid (HA) resulting from sodium humate (NaHA) simply reacting with wood vinegar (BHW). After adding BHW, the chemical fractions of copper and cadmium in the soil undergo larger changes. Meanwhile, the availability of heavy metals decreases. The maximum adsorption capacity of copper and cadmium in the soil using the BHW is larger than that only using biochar. The adsorption kinetics ensures that the adsorption process of Cd2+ and Cu2+ ions on BHW is chemical adsorption, which is best fitted using the pseudo-second-order rate equation. The thermodynamics guarantees that the metal ions adsorb on the heterogeneous surface of BHW in multilayer, which is credited to the enhancement of oxygen-containing groups in the biochar combined with the humic acid. The remediation material BHW holds promise for the immobilization of heavy metal in the soils and could be recommended based on its economic feasibility, high efficacy, and environmental safety.

Biochar application on heavy metal immobilization in unsaturated soil with vegetation: a review

ABSTRACT Biochar, a type of soil amendment, is widely used in heavy metal–polluted soil. It is also effective in enhancing plant performance. However, how biochar affects the soil heavy metal toxicity considering the plant–soil interactions is not well summarized. Therefore, this paper aims to review and summarize the effects of biochar on heavy metal availability in vegetated unsaturated soil. First, this review summarizes the effects of biochar on key parameters of unsaturated soil, including pore size distribution, water permeability, water retention curve, nutrient cycling and soil biota. Then, the mechanism of biochar for managing heavy metals in soil with vegetation is discussed, with a focus on both physical and biochemical aspects. Additionally, the impact of biochar-induced plant growth on the availability of heavy metals in the plant–soil system is explored. Finally, suggestions for future research and applications of biochar are provided. This paper supplies novel outlooks for further study and practice.