Copper-contaminated Soil Research Articles

Biochar addition enhances remediation efficiency and rapeseed yield in copper-contaminated soil.

Soil contamination with copper (Cu) threatens ecological security and human health. Rapeseed demonstrates potential in remediating copper-contaminated soil, and biochar-assisted phytoremediation is increasingly being employed to improve remediation efficiency. However, the combined application of them has not been thoroughly studied in terms of the synergistic effects and the mechanisms of their interaction. In this regard, this study conducted a pot experiment to evaluate biochar-assisted remediation under Cu-contaminated soil with varying biochar application rates; Furthermore, the plant physiological mechanism and soil physicochemical properties involved in the biocharrapeseed system was explored. Our results showed that the exchangeable pool of copper in soil decreased by 10.0% and 12.3% with adding 5% biochar (BC1) and 10% biochar (BC2) relative to control (BC0), respectively, prior to rapeseed cultivation. The rapeseed cultivation for one season further reclaimed 4.9%, 9.0%, and 13.6% of the available copper in this soil by root extraction under the BC0, BC1, and BC2 treatments, respectively. The overall copper concentration in plants decreased by 23.7% under BC2 and 13.3% under BC1 compared to BC0. However, the plant's dry biomass at BC1 and BC2 treatments increased by 1.7-fold and 2.7-fold relative to BC0, which offset the negative impact of the decreased copper concentration on phytoremediation. Physiological analysis showed adding 10% biochar decreased the MDA content by 36% in the leaf and 49% in the root, compared to BC0. The transmission electron microscopy for cell wall ultrastructure in root tips showed that biochar addition in Cu-contaminated soil increased the mechanical strength of the celL wall, explicitly increasing the thickness of the secondary cell wall. Further cell wall components analysis revealed a remarkable increment of the pectin content in BC2 relative to BC0, increased by 56% in the leaf and 99% in the root, respectively. Additionally, 10% biochar application led to a roughly 2-fold increase in seed yield via ameliorating the soil physicochemical properties and increasing the rapeseed growth. These findings offer insights into synergistic rapeseed-biochar use for Cu-contaminated soil remediation.

Biochar improves growth and physiology of Swietenia macrophylla king in contaminated soil by copper

The production of açaí seed waste from the commercial and extractive exploitation of the Euterpe oleraceae palm tree is a serious problem that contributes to environmental contamination and production of greenhouse gases, a fact that suggests the need for an environmentally correct destination for this waste produced on a large scale. To this end, this study was conducted to evaluate the potential of acaí seed biochar (BCA) in mitigating the toxic effects of copper in Brazilian mahogany plants, analyzing biometrics and gas exchange. The experimental design was in randomized blocks, with five blocks, in a 4 × 3 factorial scheme, corresponding to the control (without Cu) and three concentration of Cu (200, 400, and 600 mg Cu kg−1) and three levels of BCA (0%, 5% and 10%) proportional to the amount of soil in the pots, totaling sixty experimental units. The use of 5% BCA in soils contaminated with up to 200 mg kg−1 Cu promoted biometric increase (height, diameter, number of leaves), maintaining gas exchange (photosynthesis, stomatal conductance, transpiration, internal carbon and internal/external carbon), and consequently, maintaining water use efficiency in plants under abiotic stress, resulting in plant growth. The findings of this study allow us to indicate the use of biochar in remediating and improving the growth of plants grown in copper-contaminated soils. The production of biochar from açaí seeds is an ecologically sustainable alternative, because it reduces its accumulation on public roads and contributes to reducing soil pollution. In the context of public policies, biochar production could be a source of income in the context of the bioeconomy and circular economy practiced in the Amazon, because it is produced in large quantities.

Exploring the Potential of Crotalaria juncea L. for Phytoremediation: Insights from Gas Exchange, Pigment Quantification, and Growth Measurements under Copper Stress

Soil contamination by trace elements is a worldwide concern that can result from several sources, such as mining, smelting, car traffic exhaust, agriculture plant protection products such as fungicides, and fertilizers. Among the metals involved, copper can cause alterations in the photosynthetic, respiratory, and enzymatic processes of plants, leading to reduced growth of roots and shoots. An alternative to dealing with metals present in the soil is phytoremediation, which consists of using plants to extract or stabilize these elements. The leguminous Crotalaria juncea is widely used as a green manure and may be advantageous due to its capacity for biological nitrogen fixation and biomass accumulation. This research aimed to evaluate the growth and physiological behaviour of C. juncea in copper-contaminated soil and its potential use as a phytoremediation plant. For the fresh and dry mass of shoots and roots, compared with 30 mg.dm−3 of Cu, there was a decrease in values with the increase in concentrations up to a dose of 480 mg.dm−3. The roots were less sensitive to increased Cu concentrations than the shoots. The tolerance index decreased as copper concentrations in the soil increased. From 60 mg.dm−3, its vegetative growth decreased, but C. Juncea was able to tolerate and accumulate copper in the root system, presenting high potential as a phytostabilizing species.

Macronutrients dynamics in copper-contaminated soils: Implications for hemp growth and its phytoremediation potential

Fibrous plants with higher biomass, particularly industrial hemp, have ability to withstand and accumulate significant quantities of heavy metals from contaminated environments. The present study aimed to evaluate the dynamics of different levels (ratios) of macronutrients nitrogen, phosphorus and potassium (NPK) viz., NPK1NPK (1:1:1); NPK2NPK (2:1:1); NPK3NPK (3:1:2); NPK4NPK (4:1:2) on hemp growth and Cu contents under various levels of Cu stress (100, 400 and 800 mg kg−1 on dry soil basis using CuSO4·5H2O). Results revealed that by increasing the Cu stress, growth and biomass decreased linearly and lipid per oxidation and enzymatic antioxidants increased. Balanced application of NPK improved the biomass and decreased the membrane damage by the modulation of malonaldehyde contents. Maximum concentration of Cu in roots (377.47 ± 4.90 mg kg−1), shoots (137.45 ± 5.60 mg kg−1) and (150.07 ± 3.57 mg kg−1) was recorded at Cu3NPK2 treatment as compared to control. Maximum translocation factor (TF) and bioaccumulation coefficients (BAC) in the shoots and leaves of hemp plant were noticed where Cu stress was applied at the rate of 100 mg kg−1. However, BAC and TF were below 1. The NPK2 treatment enhanced biomass and increase Cu content both in leaves and stems, rather than the roots. Our study suggests that balanced application of NPK is a practicable approach to alleviate Cu stress and improve biomass production of industrial hemp plant. These findings indicate that optimum nutrient supply, under Cu stress, can maximize the growth potential and overall health of industrial hemp, making it a viable option for phytoremediation and sustainable agriculture on contaminated soils.

Effects of phosphorus fertilizer on kenaf growth physiology and copper absorption in copper-contaminated soil

Effects of phosphorus fertilizer on kenaf growth physiology and copper absorption in copper-contaminated soil

Nighttime Warming Reduced Copper Concentration and Accumulation in Wheat Grown in Copper-Contaminated Soil by Affecting Physiological Traits

The changes in biomass (including yield), copper (Cu) concentration, and the accumulation of wheat (Triticum aestivum. L) in response to soil Cu pollution under nighttime warming had still not been explored. Hence, this study was carried out, and these variations were analyzed from a physiological perspective. Pot trials were performed at two levels of ambient temperatures (no-warming (NT) and average nighttime warming of 0.28 °C (WT)) and two levels of soil Cu concentrations (control check without Cu application (CK) and 100 mg/kg Cu application (Cu)). Soil was collected from the carbonate cinnamon soil region of central China. The warming effects of the passive nighttime warming system were prominent, and the average increment was 0.28 °C. Antioxidant enzyme activities were promoted by warming (p < 0.05) and Cu. The highest yield was achieved in NT-Cu, mainly attributed to relatively strong root activity and photosynthesis caused by supplemental Cu, but the Cu concentration in its grains was close to the threshold (10 mg/kg) for Cu concentration in foodstuff and could present a potential food safety risk. Though nighttime warming did not increase the total biomass and yield of wheat, it decreased the Cu accumulation of wheat grown in Cu-contaminated soil, especially in grains. Moreover, WT-CK and WT-Cu increased the Cu concentration in the roots and glumes and reduced the Cu concentration in grains by 13.09% and 55.84%, respectively, probably because of a lower transpiration rate. Among them, the Cu concentration of grains in WT-Cu was the lowest and significantly lower than other applications. Our findings reveal that nighttime warming has the potential to reduce the Cu risk of grains in wheat grown in the Cu-contaminated carbonate cinnamon soil region of central China and could then provide a theoretical reference for risk assessment of food quality for wheat subjected to dual stress from nighttime warming and Cu pollution.

Multifunctional 3D-printed composites based on biopolymeric matrices and tomato plant (Solanum lycopersicum) waste for contextual fertilizer release and Cu(II) ions removal

The production of tomatoes faces significant challenges, including the high amount of waste generated during the harvest stage and copper-contaminated soil due to pesticide use. To address these issues and to promote a more sustainable agriculture, innovative biodegradable green composites for contextual controlled soil fertilization and Cu removal were produced by 3D-printing technology. These composites were made by incorporating NPK fertilizer flour and tomato plant waste particles (SLP) into three different biodegradable polymeric matrices: polylactic acid (PLA); a commercial blend of biodegradable co-polyesters (Mater-Bi®, MB) and their blend (MB/PLA, 50:50). Rheological characterization suggested the potential processability of all of the composites by FDM. Morphological analysis of printed samples confirmed the good dispersion of both filler and fertilizer, which also acted as reinforcement for MB and MB/PLA composites. SLP and NPK moduli were evaluated by powder nanoindentation and, for almost composites, the theoretical Halpin-Tsai model satisfactorily fitted the actual tensile moduli. The decrease in NPK fertilizer release rate and the increase in Cu(II) removal efficiency were achieved using whole 3D-printed composites. By selecting the appropriate matrix and incorporating SLP particles, it was possible to tune the NPK release rate and achieve copper absorption efficiency. Notably, MB samples containing SLP particles displayed the fastest release and the highest Cu(II) removal efficiency.Graphical abstract

Insights into tolerance mechanisms of earthworms (Eisenia fetida) in copper-contaminated soils by integrating multi-omics analyses

Earthworms can resist high levels of soil copper (Cu) contamination and play an essential role in absorbing them effectively. However, the molecular mechanisms underlying Cu tolerance in earthworms are poorly understood. To address this research gap, we studied alterations of Eisenia fetida in antioxidant enzymes, gut microbiota, metabolites, and genes under varying levels of Cu exposure soils (0, 67.58, 168.96, 337.92 mg/kg). Our results revealed a reduction in antioxidant enzyme activities across all treatment groups, indicating an adaptive response to alleviate Cu-induced oxidative stress. Analysis of gut microbiota revealed a significant increase in the abundance of bacteria associated with nutrient uptake and Cu2+ excretion under Cu stress. Furthermore, metabolomic analysis discovered an increase in certain metabolites associated with energy metabolism, such as pyruvic acid, L-malic acid, and fumaric acid, as Cu concentration escalated. These results suggested that enhanced energy supply contributes to the elevated tolerance of E. fetida towards Cu. Additionally, transcriptome analysis not only identified crucial detoxification genes (Hsp70, CTSL, GST, CHAC, and GCLC), but also confirmed the critical role of glutathione metabolism as a key pathway in E. fetida Cu detoxification processes. These findings provide a new perspective on the molecular mechanisms of Cu tolerance in earthworms.

Zinc shields against copper phytotoxicity in a contaminated soil

While zinc protects plants from copper in hydroponics, its behavior in soil remains unclear. We investigated the potential of zinc sulfate to protect ryegrass from copper toxicity in contaminated soil. Twelve soil treatments combined varying levels of copper oxide (CuO) and zinc sulfate (ZnSO4). Increasing CuO significantly stunted ryegrass, but adding ZnSO4 mitigated the effects at each CuO level. ZnSO4 had no effect in unpolluted conditions. These results, supported by the Terrestrial Biotic Ligand Model, indicate that zinc competes with copper for binding sites, reducing copper uptake by ryegrass and mitigating its toxicity. Application of zinc sulfate to copper-contaminated soils appears promising for ryegrass growth, although field studies are critical to confirm real-world efficacy.

Phytoremediation of copper-contaminated soils by rapeseed (Brassica napus L.) and underlying molecular mechanisms for copper absorption and sequestration

High levels of copper released in the soil, mainly from anthropogenic activity, can be hazardous to plants, animals, and humans. The present research aimed to estimate the suitability and effectiveness of rapeseed (Brassica napus L.) as a possible soil remediation option and to uncover underlying adaptive mechanisms A pot experiment was conducted to explore the effect of copper stress on agronomic and yield traits for 32 rapeseed genotypes. The copper-tolerant genotype H2009 and copper-sensitive genotype ZYZ16 were selected for further physiological, metabolomic, and transcriptomic analyses. The results exhibited a significant genotypic variation in copper stress tolerance in rapeseed. Specifically, the ratio of seed yield under copper stress to control ranged from 0.29 to 0.74. Furthermore, the proline content and antioxidant enzymatic activities in the roots were greater than those in the shoots. The accumulated copper in the roots accounted for about 50% of the total amount absorbed by plants; thus, the genotypes possessing high root volumes can be used for rhizofiltration to uptake and sequester copper. Additionally, the pectin and hemicellulose contents were significantly increased by 15.6% and 162%, respectively, under copper stress for the copper-tolerant genotype, allowing for greater sequestration of copper ions in the cell wall and lower oxidative stress. Comparative analysis of transcriptomes and metabolomes revealed that excessive copper enhanced the up-regulation of functional genes or metabolites related to cell wall binding, copper transportation, and chelation in the copper-tolerant genotype. Our results suggest that copper-tolerant rapeseed can thrive in heavily copper-polluted soils with a 5.85% remediation efficiency as well as produce seed and vegetable oil without exceeding food quality standards for the industry. This multi-omics comparison study provides insights into breeding copper-tolerant genotypes that can be used for the phytoremediation of heavy metal-polluted soils.

The downside of copper pesticides: An earthworm's perspective.

The widespread use of copper-based pesticides, while effective in controlling plant diseases, has been identified as a major source of copper contamination in soils. This raises concerns about potential adverse effects on earthworms, key players in soil health and ecosystem function. To inform sustainable pesticide practices, this study aimed to establish copper toxicity thresholds for earthworm avoidance in agricultural soils impacted by copper-based pesticides. We collected 40 topsoil samples (0-5cm) from orchards and vineyards in the O'Higgins Region of central Chile, and 10 additional soils under native vegetation as background references. A standardized avoidance bioassay using Eisenia fetida assessed the impact of copper-based pesticides on the soils. Total copper concentrations ranged between 23 and 566mgkg-1, with observed toxic effects on earthworms in certain soils. The effective concentration at 50% (EC50) for total soil copper, determined by Eisenia fetida's avoidance response, was 240mgkg-1, with a 95% confidence interval of 193-341mgkg-1. We further compared our EC50 values with existing data from agricultural soils impacted by mining activities. Interestingly, the results revealed a remarkable similarity between the thresholds for earthworm avoidance, regardless of the source of copper contamination. This observation underscores the universality of copper toxicity in agricultural ecosystems and its potential impact on soil biota. This study provides novel insights into copper toxicity thresholds for earthworms in real-world, pesticide-contaminated soils.

Remediation of copper-contaminated soils and growth enhancement of Pakchoi (B. chinensis L.) via biofertilizers composed of new Bacillus amyloliquefaciens SYNU1

BackgroundExcessive copper contaminants are harmful to soil, microbes, plants and humans and can be remediated by biosorption. Applying biofertilizers to remediate copper-contaminated soil is an environmentally friendly way.ResultsIn this study, we identified a new strain, Bacillus amyloliquefaciens SYNU1, based on morphological, biochemical, physiological and phylogenetic analyses. It has been cultured on Luria–Bertani (LB) medium and absorbs soluble Cu2+ from pH 3.5–5 and 25–40 °C at Cu2+ concentrations of 100 mg L−1. The results showed that the maximum adsorption capacity of copper by strain SYNU1 is 53.09% w/w. Furthermore, microbe fertilizers were made based on strain SYNU1, these fertilizers were allowed to ferment for 15 days, and they were used for remediation of copper-contaminated soil and growth tests of Pakchoi (B. chinensis L) in pot experiments. The results showed that the growth of Pakchoi planted in copper-contaminated soil at concentrations ranging from 50 to 200 mg kg−1 was inhibited, and its growth indices, such as plant height, fresh weight and dry weight, decreased significantly with increasing copper concentration. Compared with the control, the increases in plant height, fresh weight and dry weight of Pakchoi treated with biofertilizer were 10.37, 65.3 and 67.78%, respectively, indicating that biofertilizer could significantly promote the growth of Pakchoi.ConclusionsBacillus amyloliquefaciens SYNU1 is useful for the bioremediation of Cu2+-contaminated soil in Northeast China.

Co-Composting of Hop Bines and Wood-Based Biochar: Effects on Composting and Plant Growth in Copper-Contaminated Soils

Decades of intensive use of copper-based fungicides against downy mildew in hops has led to considerable accumulation of copper in topsoil, resulting in toxic effects on plants. Due to its high sorption capacity, the application of co-composted biochar compost might reduce copper toxicity, whereby a synergistic effect of the composting process is supposed to occur. Furthermore, biochar addition might improve the composting process itself. Therefore, hop bines were co-composted without as well as with 5 and 20 vol% biochar, respectively. During composting, the temperature and concentration of O2, CO2, H2S, CH4 and NH3 in the compost heaps were regularly recorded. The biochar-free compost as well as the two composts with the biochar addition were characterized with regard to their plant-growing properties and were mixed into soils artificially spiked with different amounts of copper as well as into copper-polluted hop garden and apple orchard soils. The respective soil without the compost addition was used as the control, and further treatments with biochar alone and in combination with biochar-free compost were included in a plant response test with Chinese cabbage. The biochar addition increased the temperature within the compost heaps by about 30 °C and extended the duration of the thermophilic phase by almost 30 days, resulting in a higher degree of hygienization. Furthermore, the application of co-composted biochar composts significantly improved plant biomass by up to 148% and reduced the copper concentration, especially of roots, by up to 35%. However, no significant differences in the biochar-free compost were found in the artificially copper-spiked soils, and the effect of co-composted biochar compost did not differ from the effect of biochar alone and in combination with biochar-free compost. Nevertheless, the co-composting of hop bines with biochar is recommended to benefit from the positive side effect of improved sanitization in addition to reducing copper toxicity.

Deciphering the effect mechanism of chromosome doubling on the biomass increase in Elsholtzia splendens

Elsholtzia splendens is an ideal plant species for remediating copper-contaminated soils. However, its application range is regrettably hindered by its generally low biomass and rather narrow range of suitable growing conditions. Polyploid technique is a shortcut to enhance biomass and environmental adaptability of plant, which may become an important breakthrough to improve application value of E. splendens. In this study, tetraploid E. splendens (2n = 4x = 32) was successfully obtained from wild E. splendens (2n = 2x = 16) using a primary meristem processing technique for the first time, exhibiting a huge biomass advantage. In order to find out the underlying mechanism for its huge biomass advantage, a series of difference assessments between two ploidy-level E. splendens were performed, including morphological, anatomical, physiological, photosynthesis, transcriptome and endogenous hormones experiments. All the results consistently showed that enhanced photosynthesis and alterated cell differentiation function drove significant biomass increase. During the process of excavating molecular mechanism deeply, five hub genes (regulating Rubisco, light-harvesting chlorophyII a/b-binding protein 2 (Lhcb2), photosystem I subunit PsaO (PsaO), magnesium protoporphyrin IX methyltransferase (ChlM) and lateral organ boundaries (LOB) domain (LBD)) were found to play extremely vital roles in biomass increase regulation. Especially, LOB may be the most key factor resulting in the transformation of E. splendens from a single plant to a cluster, ultimately leading to biomass multiplication. Finally, a responsive model was proposed to elucidate the regulatory mechanisms of huge biomass in the tetraploid E. splendens. The present findings provide new evidence for understanding the complex regulatory networks responsible for remarkable biomass increase in polyploid plants.

Complex resistivity spectrum of pollutant soils with low-concentration heavy metals

Soil contamination by heavy metals occurs globally, with varying degrees of severity, especially in agricultural fields. Investigating the frequency response characteristics of different types of heavy metal pollutants through induced polarization can provide valuable evidence for surveys based on this method. Soil specimens with varying low concentrations of copper (Cu), chromium (Cr), cadmium (Cd), and lead (Pb) heavy metals were prepared for this study, and parameters including complex resistivity, amplitude-frequency, and resistivity phase were measured. Our findings reveal the following trends: Complex resistivity decreases as heavy metal concentrations increase, demonstrating significant shifts within lower concentration ranges but presenting limitations for assessing pollution in high-concentration areas. Conversely, amplitude-frequency increases with higher heavy metal concentrations, displaying excellent performance in high-concentration scenarios. The differences in complex resistivity and amplitude-frequency among different types of heavy metal pollutants are distinct. In contrast, the absolute phase decreases with rising heavy metal concentrations. The resistivity phase spectra for various heavy metal pollutants exhibit unique patterns. For example, copper-contaminated soil exhibits phase peaks in the frequency range of 8–32 Hz, whereas chromium-contaminated soil shows phase peaks at 16–64 Hz. Cadmium-contaminated soil displays phase peaks ranging from 0.25 Hz to 2 Hz, while lead-contaminated soil exhibits phase peaks within the 0.5 Hz–4 Hz range. Leveraging the frequency range corresponding to phase peaks as an identification method for heavy metal pollution types proves effective. The frequency response characteristics of induced polarization vary significantly among different types and concentrations of heavy metal pollutants, providing important foundations for the application of induced polarization method in the field of heavy metal pollution detection.

Impacts of Bamboo Biochar Amendment on Growth, Morphological Traits, and Biomass Allocation of Bambusa balcooa under Copper-Contaminated Soil Conditions

The accumulation of heavy metals in water streams and soil is considered a grave environmental threat that impacts plants and animals. Biochar has recently been widely used to overcome the effects of heavy metal contamination in plants and remediate the soil. A pot-trial study assessed the morphological traits of Bambusa balcooa under copper contamination. Each pot (twenty-four earthen pots) was filled with 7.0 kg of soil and spiked with copper sulfate of 0, 300, 600, and 1200 mg kg-1. Of the total, twelve pots were amended with 7% (w/w of soil) bamboo biochar. Plant samples were harvested after one year (365 days) of treatment for biomass estimation. Data was recorded for different growth and morphological traits such as the number of clums, nodes, leaves, internode length, plant height, leaf area, root length, and dry biomass of root, shoot, and leaf to evaluate the impact of copper with or without bamboo biochar on Bambusa balcooa. The results indicated that the higher concentration of copper suppressed growth parameters such as shoot length, internode length, number of leaves, and leaf area; therefore, growth increment was significantly reduced at ) mg Kg‑1 copper-added soil. Biochar diminishes the impact of Cu stress on plants to some extent as at higher concentrations (600 and 1200 mg kg-1) was enhanced root dry biomass (51 and 148%), shoot dry biomass (42 and 57%), and leaf dry biomass (38 and 48%). Thus, results confirm that biochar amendment under Bambusa balcooa reduces the impact of copper contamination on the plant and increases plant growth by improving soil health, suggesting that bamboo biochar application was effective in metal stabilization, thereby, reducing the bioavailability and phytotoxicity of Cu and can help to restore copper-contaminated soil.

Growth, nodulation, and anatomical characterization of Calopogonium mucunoides Desv., a tropical legume, in copper-contaminated soil

Growth, nodulation, and anatomical characterization of Calopogonium mucunoides Desv., a tropical legume, in copper-contaminated soil

Iron-Based Amorphous Alloy Enhanced Electrokinetic Method for Remediation of Copper-Contaminated Soil

Iron-Based Amorphous Alloy Enhanced Electrokinetic Method for Remediation of Copper-Contaminated Soil

Enhancing Soil Remediation of Copper-Contaminated Soil through Washing with a Soluble Humic Substance and Chemical Reductant

The bioavailability and mobility of copper (Cu) in soil play a crucial role in its toxicity and impact on soil organisms. Humic substances, with their abundant functional groups and unique pore structure, have demonstrated the ability to effectively mitigate the toxic effects of heavy metals in soil. This study explores the potential of a soluble humic substance (HS) derived from leonardite for Cu removal from contaminated soils. The effects of various washing conditions, such as concentration and washing cycles, on removal efficiency were assessed. The results showed that a single washing with HS solution achieved an optimal removal efficiency of 37.5% for Cu in soil, with a subsequent reuse achieving a removal efficiency of over 30.5%. To further enhance Cu removal efficiency, a two-step soil washing approach using a chemical reductant NH2OH·HCl coupled with an HS solution (NH2OH·HCl + HS) was employed, resulting in an increased removal efficiency to 53.0%. Furthermore, this approach significantly reduced the plant availability and bioaccessibility of Cu by 13.6% and 11.4%, respectively. Compared to a single washing with NH2OH·HCl, both HS and NH2OH·HCl + HS increased the soil pH and organic matter content. These findings suggest that the two-step soil-washing approach using NH2OH·HCl + HS effectively removed Cu from polluted soil. This study demonstrates the potential of humic substances as environmentally friendly materials for remediating heavy metal-polluted soil, promoting green and sustainable applications in soil remediation practices.

Phytoremediation of copper-contaminated soils by drip or sprinkling irrigation coupled with intercropping.

Intercropping improves the phytoremediation of soil trace metal contamination. Dripping irrigation could further promote the phytoremediation of trace metals by influencing their speciation and total amount in soil. However, there is currently insufficient information elucidating this synergistic effect. In this study, the combined effect of drip irrigation and intercropping on the phytoremediation of Cu-contaminated soil was testified by investigating the changes of Cu spatial distribution and speciation in soil irrigated by dripping or sprinkling methods, as well as Cu bioconcentration factor and translocation factor by plants. Results showed that after a 30-day drip irrigation, the Cu level in soils near the drip outlet decreased by 4.7% and that in Triticum aestivum L. (T. aestivum) roots intercropped with Helianthus annuus L. (H. annuus) and Zea mays L. (Z. mays) dropped by 53.2% and 25.1%, respectively, relative to sprinkler irrigation. Meanwhile, the total Cu and exchangeable Cu levels in soils 6cm away from the drip outlet increased by 10.8% and 20.4% after 30days of drip irrigation, leading to 41.1% and 40.0% increases of Cu content in remediation plants H. annuus and Z. mays seedlings as compared to the values by sprinkler irrigation. Therefore, the drip irrigation enhanced the effect of intercropping on Cu phytoremediation.