Use of a hyperaccumulator and biochar to remediate an acid soil highly contaminated with trace metals and/or oxytetracycline

Intraspecific variation in tomato: Impact on production quality and cadmium phytoremediation efficiency in intercropping systems with hyperaccumulating plant

Intercropping with hyperaccumulators can facilitate the safe utilization of cadmium-contaminated soil. However, the effectiveness of this approach is influenced by plant species and varieties, which necessitates research on optimal plant consortia. In this study, 8 tomato varieties (3 cherry tomatoes and 5 common large-fruit tomatoes) were intercropped with Sedum alfredii in a moderately Cd-contaminated vegetable field. The results showed that the Cd concentration in the fruits of common large-fruit tomato varieties under monoculture was 1.03-1.50 mg/kg, while that in the fruits of cherry tomato varieties was 0.67-0.71 mg/kg. After intercropping with S. alfredii, the fruit Cd concentrations of Hangza 501, Hangza 503, and Hangza 108 decreased by 16.42 %, 19.72 %, and 6.76 %, respectively, while those of the other varieties significantly increased, except for those of Hangza 8. In contrast, the shoot Cd concentration of cherry tomatoes was greater than that of large-fruit tomatoes under monoculture. Furthermore, a significant increase in the shoot Cd concentration was noted in the Hangza 501, Hangza 503 and Hangza 603 plants following intercropping. Additionally, intercropping with S. alfredii increased the concentration of soluble sugars in the fruits of Hangza 8, Hangza 501, Hangza 503 and Hangza 603 by 4.66 %, 17.91 %, 10.60 % and 17.88 %, respectively. Intercropping with tomatoes resulted in a decrease in both the biomass and Cd uptake of S. alfredii. Interestingly, the inhibitory effect on S. alfredii was less pronounced when intercropped with cherry tomatoes than when intercropped with large-fruit tomatoes. Among the intercropping treatments, S. alfredii exhibited the greatest total Cd accumulation (0.06 mg/plant) when intercropped with Hangza 503. In conclusion, the cherry tomato variety Hangza 503 was the most suitable for intercropping with S. alfredii and can be used safely for vegetable production and simultaneous phytoremediation of polluted soil. Our findings suggest that strategic selection of tomato varieties can optimize the effectiveness of "phytoextraction coupled with agro-safe production" technology for managing soil Cd concentrations.

Hydrochar reduces oxytetracycline in soil and Chinese cabbage by altering soil properties, shifting microbial community structure and promoting microbial metabolism

The efficient remediation of antibiotic-contaminated soil is critical for agroecosystem and human health. Using the cost-effective and feedstock-independent hydrochar with rich oxygen-containing functional groups as a soil remediation material has become a hot concern nowadays. However, the feasibility and effectiveness of hydrochar amendment in antibiotic-contaminated soil still remain unknown. Therefore, this study investigated the remediation effect and potential mechanisms of different hydrochars from cow manure (H-CM), corn stalk (H-CS) and Myriophyllum aquaticum (H-MA) at two levels (0.5% and 1.0%) in oxytetracycline (OTC)-contaminated soil using a pot experiment. Results showed that compared with CK, OTC content in the soils amended with H-CM and H-MA was decreased by 14.02-15.43% and 9.23-24.98%, respectively, whereas it was increased by 37.03-42.64% in the soils amended with H-CS. Additionally, all hydrochar amendments effectively reduced the OTC uptake in root and shoot of Chinese cabbage by 10.41-57.99% and 31.92-65.99%, respectively. The response of soil microbial community to hydrochar amendment heavily depended on feedstock type rather than hydrochar level. The soil microbial metabolism (e.g., carbohydrate metabolism, amino acid metabolism) was enhanced by hydrochar amendment. The redundancy analysis suggested that TCA cycle was positively related to the abundances of OTC-degrading bacteria (Proteobacteria, Arthrobacter and Sphingomonas) in all hydrochar-amended soils. The hydrochar amendment accelerated the soil OTC removal and reduced plant uptake in soil-Chinese cabbage system by altering soil properties, enhancing OTC-degrading bacteria and promoting microbial metabolism. These findings demonstrated that the cost-effective and sustainable hydrochar was a promising remediation material for antibiotic-contaminated soil.

Comparative efficacy of Parthenium hysterophorus (L.) derived biochar and iron doped zinc oxide nanoparticle on heavy metals (HMs) mobility and its uptake by Triticum aestivum (L.) in chromite mining contaminated soils

In this study we investigated the efficacy of a novel material parthenium weed (Parthenium hysterophorus L.) biochar (PBC), iron doped zinc oxide nanoparticles (nFe-ZnO), and biochar modified with nFe-ZnO (Fe-ZnO@BC) to adsorb heavy metals (HMs) and reduce their uptake by wheat (Triticum aestivum L.) in a highly chromite mining contaminated soil. The co-application of the applied soil conditioners exhibited a positive effect on the immobilization and restricted the HMs uptake below their threshold levels in shoot content of wheat. The maximum adsorption capacity was because of large surface area, cation exchange capacity, surface precipitation, and complexation of the soil conditioners. The scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) showed porous smooth structure of parthenium weed derived biochar that helped in HMs adsorption, increase the efficiency of soil fertilizers and nutrients retention which help in the enhancement soil condition. Under different application rates the highest translocation factor (TFHMs) was obtained at 2 g nFe-ZnO rate followed the descending order: Mn > Cr > Cu > Ni > Pb. The overall TFHMs was found <1.0 indicating that low content of HMs accumulation in roots from soil slight transferred to shoot, thus satisfying the remediation requirements.

Manganese-modified biochar promotes Cd accumulation in Sedum alfredii in an intercropping system

Intercropping of crops with hyperaccumulators is a sustainable method to remediate contaminated soil without impeding agro-production. However, the function of engineered biochar in intercropping systems and its possible influence on cadmium (Cd) accumulation in hyperaccumulators remain unknown. A root box experiment on celery and Sedum alfredii with and without root separation was conducted in this study. Pristine and KMnO₄-modified biochar (BC_Mn) were used to investigate the effects of different biochars on plant growth and Cd uptake in an intercropping system, as well as the influence of engineered biochar on Cd accumulation in hyperaccumulators. The results demonstrated that soil pH did not significantly vary with biochar application in the root separation treatment. However, BC_Mn significantly increased soil pH and thus reduced available Cd when the plant roots were not separated. Intercropping (no separation treatment) led to a 34% higher and 24% lower aboveground biomass of celery and S. alfredii, respectively, regardless of biochar addition. Compared with aboveground plant parts, plant roots exhibited more significant responses to biochar. Interestingly, intercropping may favour the phytoextraction of Cd by S. alfredii. In particular, the Cd uptake by S. alfredii roots substantially increased (118-187%), whereas that of celery roots decreased (51-71%) with BC_Mn addition, compared with other treatments. Moreover, after BC_Mn addition the accumulation of Cd in aboveground S. alfredii in the no separation treatment was 136% higher than that in the separation treatment. This was possibly related to the interaction of manganese (Mn) with Cd as well as the roots of S. alfredii. These findings provide new insights into the application of engineered biochar for phytoextraction, which is important for the efficient remediation of Cd-contaminated soils.

Global perspectives for biochar application in the remediation of heavy metal-contaminated soil: a bibliometric analysis over the past three decades

Herein, 7,308 relevant documents on biochar application for the remediation of heavy metal (HM)-contaminated soil (BARHMCS) from 1991 to 2020 were extracted from the Web of Science Core Collection and subjected to bibliometric and knowledge mapping analyses to provide a global perspective. The results showed that (1) the number of publications increased over time and could be divided into two subperiods, i.e., the slow growth period (SGP) and rapid growth period (RGP), according to whether the annual publication number was ≥300. (2) A total of 126 countries, 741 institutions, and 1,021 scholars have contributed to this field. (3) These studies are mainly published in Science of the Total Environment, Chemosphere, etc., and are mainly based on the categories of environmental science, soil science, and environmental engineering. (4) The top five keyword clusters for the SGP were biochar, biochar, sorption, charcoal, and HMs, and those for the RGP were adsorption, black carbon, nitrous oxide, cadmium, and pyrolysis. (5) The main knowledge domains and the most cited references during the SGP and RGP were discussed. (6) Future directions are related to biochar application for plant remediation, the mitigation of climate change through increased carbon sequestration, biochar modification, and biochar for HMs and multiple organic pollutants.

Reactive effects of pre-sowing magnetic field exposure on morphological characteristics and antioxidant ability of Brassica juncea in phytoextraction

As magnetic fields constantly act on living and biochemical processes, it is reasonable to hypothesize that magnetic field treatment of plant seeds would enhance the uptake capacity of non-essential elements. To verify this hypothesis, seeds of Brassica juncea were treated with 50, 100, 150, 200, and 400 mT fields, and the dry weight, Cd uptake capacity, ferritin content, antioxidant enzyme activity, and phytoremediation effects of the plant were compared at the end of the experiment. Relative to the control, low- and moderate-intensity fields (50-200 mT) enhanced the dry weight of plant leaves by 15.1%, 24.5%, 35.8%, and 49.1%, respectively, whereas the high-intensity field (400 mT) decreased the biomass yield by 18.9%. The content of Cd in the above-ground tissues of B. juncea enhanced with the increasing field intensity, accompanied by an increase in oxidative damage. The activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased with exposure to low (50 and 100 mT) and moderate (150 and 200 mT) intensities, followed by a reduction at a high intensity (400 mT). Catalase activity (CAT) and ferritin content exhibited an increasing trend with increasing intensity. The Cd decontamination index of B. juncea increased with the increasing magnetic field intensity until it reached a peak at 150 mT, after which the values remained constant. Considering the phytoremediation effect and energy consumption, 150 mT was the optimal scheme for magnetic-field-assisted phytoremediation using B. juncea. This study suggests that a suitable magnetic field can be regarded as an ecologically friendly physical trigger to improve the phytoextraction effect of B. juncea.

Influence of DOM and its subfractions on the mobilization of heavy metals in rhizosphere soil solution

Long-term industrial pollution, wastewater irrigation, and fertilizer application are known factors that can contribute to the contamination of heavy metals (HMs) in agricultural soil. In addition, dissolved organic matter (DOM) plays key roles in the migration and fate of HMs in soil. This study investigated the effects of amending exogenous DOM extracted from chicken manure (DOMc), humus soil (DOMs), rice husk (DOMr), and its sub-fractions on the mobilization and bio-uptake of Cd, Zn, and Pb. The results suggested that the exogenous DOM facilitate the dissolution of HMs in rhizosphere soil, and the maximum solubility of Zn, Cd, and Pb were 1264.5, 121.3, and 215.7 μg L^-1, respectively. Moreover, the proportion of Zn-DOM and Cd-DOM increased as the DOM concentration increased, and the highest proportions were 97.5% and 86.9%. However, the proportion of Pb-DOM was stable at > 99% in all treatments. In addition, the proportion of hydrophilic acid (Hy) and Pb/Cd in the rhizosphere soil solution were 17.5% and 8.3%, respectively. This finding suggested that the Hy-metals complex has a vital influence on the mobilization of metals, besides its complexation with fulvic acid and humic acid. Furthermore, the elevated DOM addition contributed to an increment of HMs uptake by Sedum alfredii, in the following order, DOMc > DOMs > DOMr. This study can provide valuable insights to enhance the development of phytoremediation technologies and farmland manipulation. Since the risk that exogenous DOM would increase the uptake of HMs by crops, it is also needed to evaluate this case from an agricultural management perspective.

Solar-Driven Soil Remediation along with the Generation of Water Vapor and Electricity

As a renewable energy source, solar energy has become an important part of human energy use. However, facilities utilizing solar energy are often complex and technically difficult, and preparation equipment and materials are expensive, while these equipment and materials often cause new environmental pollution. Soil, which exists in large quantities on the earth’s surface, is an inexhaustible natural material with loose and stable properties. Due to the specificity of its composition and microscopic form, the soil has an inherent advantage as a medium for solar thermal and photovoltaic conversion. Here, we built an integrated solar energy utilization system, the Integrated Soil Utilization Module (ISUM), integrating multi-functions into one hybrid system, which enables solar-driven water vapor and electricity generation and soil remediation. The evaporation rate of the soil represented by the rocky land was 1.2 kg·m⁻²·h⁻¹ under 1-sun irradiation with evaporation induced voltage of 0.3 V. With only seven days of continuous exposure to sunlight, the removal of heavy metal ions from the soil reached 90%, while the pH was raised to near neutral. The combined application of readily available natural soil with solar energy not only demonstrates the potential of a soil for solar desalination and power generation, but in addition, solar-driven interfacial evaporation provides an energy-efficient, environmentally friendly, and sustainable method for purifying heavy metal and acid-contaminated soil.

Recent advances in nanoremediation: Carving sustainable solution to clean-up polluted agriculture soils

Agriculture is one of the foremost significant human activities, which symbolizes the key source for food, fuel and fibers. This activity results in a lot of ecological harms particularly with the excessive usage of chemical fertilizers and pesticides. Different agricultural practices have remained industrialized to advance food production, due to the growth in the world population and to meet the food demand through the routine use of more effective fertilizers and pesticides. Soil is intensely embellished by environmental contamination and it can be stated as "universal incline." Soil pollution usually occurs from sewage wastes, accidental discharges or as byproducts of chemical residues of unrestrained production of numerous materials. Soil pollution with hazardous materials alters the physical, chemical, and biological properties, causing undesirable changes in soil fertility and ecosystem. Engineered nanomaterials offer various solutions for remediation of contaminated soils. Engineered nanomaterial-enable technologies are able to prevent the uncontrolled release of harmful materials into the environment along with capabilities to combat soil and groundwater borne pollutants. Currently, nanobiotechnology signifies a hopeful attitude to advance agronomic production and remediate polluted soils. Studies have outlined the way of nanomaterial applications to restore the eminence of the environment and assist the detection of polluted sites, along with potential remedies. This review focuses on the latest developments in agricultural nanobiotechnology and the tools developed to combat soil or land and or terrestrial pollution, as well as the benefits of using these tools to increase soil fertility and reduce potential toxicity.

Strategy for Mitigating Antibiotic Resistance by Biochar and Hyperaccumulators in Cadmium and Oxytetracycline Co-contaminated Soil

The global prevalence of antibiotic resistance genes (ARGs) is of increasing concern as a serious threat to ecological security and human health. Irrigation with sewage and farmland application of manure or biosolids in agricultural practices introduce substantial selective agents such as antibiotics and toxic metals, aggravating the transfer of ARGs from the soil environment to humans via the food chain. To address this issue, a hyperaccumulator (Sedum plumbizincicola) combined with biochar amendment was first used to investigate the mitigation of the prevalence of ARGs in cadmium and oxytetracycline co-contaminated soil by conducting a pot experiment. The addition of biochar affected the distribution of ARGs in soil and plants differently by enhancing their prevalence in the soil but restraining transmission from the soil to S. plumbizincicola. The planting of S. plumbizincicola resulted in an increase in ARGs in the soil environment. A structural equation model illustrated that mobile genetic elements played a dominant role in shaping the profile of ARGs. Taken together, these findings provide a practical understanding for mitigating the prevalence of ARGs in this soil system with complex contamination and can have profound significance for agricultural management in regard to ARG dissemination control.

Nutrient alterations following biochar application to a Cd-contaminated solution and soil

Biochars, when applied to contaminated solutions or soils, may sequester potentially toxic elements while releasing necessary plant nutrients. This purpose of this study focused on quantifying both phenomenon following wheat straw (Triticum aestivum L.) biochar application (0, 5, and 15% by wt) to a Cd containing solution and a Cd-contaminated paddy soil using 240-day laboratory batch experiments. Following both experiments, solid phases were analyzed for elemental associations using a combination of wet chemical sequential extractions and synchrotron-based X-ray absorption spectroscopy (XAS). When wheat straw biochar was applied at 15% to Cd containing solutions, Cd and Zn concentrations decreased to below detection in some instances, Ca and Mg concentrations increased by up to 290%, and solution pH increased as compared to the 5% biochar application rate. Similar responses were observed when biochar was added to the Cd-contaminated paddy soil, suggesting that this particular biochar has the ability to sequester potentially toxic elements while releasing necessary plant nutrients to the soil solution. When significant, positive correlations existed between nutrient release over time, while negative correlations were present between biochar application rate, potentially toxic element sorption and pH. The latter suggests that potentially toxic elements were sorbed by a combination of organic functional groups or mineral precipitation based on whether pH was above or below ~ 7. In support of this contention, the wet chemical sequential extraction procedure in conjunction with previously observed Cd or current Zn XAS showed that biochar application promoted the formation of layered double hydroxides, sorption to (oxy)hydroxides, and organically bound to biochar as Zn species. As a multifunctional material, biochar appears to play an important role in sequestering Cd while releasing essential plant nutrients. These findings suggest that biochar may be a 'win-win' for improving environmental quality in potentially toxic element contaminated agroecosystems.

Effects of biochar on the migration and transformation of metal species in a highly acid soil contaminated with multiple metals and leached with solutions of different pH

A number of recent studies have been conducted on soil metal immobilization by biochars but there is little information on the migration and transformation of metal species in soils contaminated with multiple metals as affected by biochar and acid rain. Here, a column study investigated the effects of biochar derived from maize straw pyrolyzed at 600 °C on metal (Cu, Pb, Zn and Cd) mobility in a highly acid soil during leaching with simulated acid rain. All four metals examined were released at early stages of the leaching process and the percentages of the metals leached followed the sequence Zn > Cd > Cu > Pb. Acid rain with high acidity resulted in larger amounts of metals leached, particularly at the later stages of leaching. This enhancement of leaching by highly acidic leaching solutions was eliminated by amendment with biochar. However, the effects of biochar on metal mobility depended on metal species, with significant immobilization of soil Cu, Zn and Pb (>90%, 26% and 72%, respectively) but with no effect on soil Cd. Overall, simulated acid rain enhanced soil metal mobility and biochar reduced soil metal mobility and also alleviated the effects of acid rain. More emphasis is needed on metal speciation in the use of biochars for soil metal immobilization in areas with acid rain. The use of biochars in phytoremediation may decrease the toxicity of soil metals to the hyperaccumulator plant.

Heavy metals in soil-vegetable system around E-waste site and the health risk assessment

Investigating the farmland quality around electronic waste (E-waste) dismantling site and taking positive measures to ensure local food safety are urgent. Eleven types of vegetables (n = 184) and their corresponding soils were collected from vegetable fields in a city with famous historical e-waste activities in China. Nemerow integrated pollution indices analysis revealed that local vegetable fields suffered from heavy metal pollution to a certain extent, especially with regards to Cd, Cu, and Zn. The human health risk models provided by USEPA have been used to evaluate the non-carcinogenic and carcinogenic risks associated with the consumption of vegetables by local residents. Results indicated that both adults and children were suffering potential health risks. And the consumption of lettuce and sweet potato caused the greatest health risk, whereas cabbage and cowpea were relatively safe. The bioaccumulation factors (BAF) of heavy metals in various vegetables were calculated, and different vegetables showed huge variance in metal accumulation. Considering both contamination status and health risk assessment, cabbage and cowpea were selected as low accumulators of heavy metals. This study reveals the need for adjusting plantation structure and applying amendments to current protocols to alleviate the adverse effects caused by soil pollution.

Analysis of the effect of cadmium stress on root exudates of Sedum plumbizincicola based on metabolomics

Root exudates are the most direct manifestation of the response of plants changes in the external environment. Therefore, based on non-targeted gas chromatography-time-of-flight mass spectrometry and metabolomics, the response of Sedum plumbizincicola root exudates to Cd stress was used to reveal the possible mechanism of resistance to or accumulation of Cd. The results showed that Cd significantly changed the composition and contents of S. plumbizincicola root exudates. A total of 155 metabolites were identified in S. plumbizincicola root exudates, among which 33 showed significant differences under Cd stress, including organic acids, amino acids, lipids, and polyols. Cd stress suppressed organic acid metabolism and lipid metabolism in S. plumbizincicola and significantly affected amino acid metabolism. There were 16 metabolic pathways related to Cd stress, among which arginine and proline metabolism, valine, leucine, and isoleucine biosynthesis, glycine, serine, and threonine metabolism, glutathione metabolism, and purine metabolism were the key pathways with the highest correlation, and were closely related to the stress resistance of S. plumbizincicola.

Effect of cornstalk biochar on phytoremediation of Cd-contaminated soil by Beta vulgaris var. cicla L

Cadmium (Cd) contamination is the most common and extensive heavy metal pollution in the farmland of China. Phytoremediation is considered as a promising measure for Cd-contaminated soil remediation, but the remediation efficiency still needs to be enhanced. Biochar as an effective amendment medium is widely manufactured and studied for the soil remediation of heavy metals. In this study, a greenhouse pot trial was conducted to investigate the effects of cornstalk biochar on Cd accumulation of Beta vulgaris var. cicla L. (Beta vulgaris) in Cd contaminated soil. The Cd availability, speciation and nutrients in soil, biomass and Cd chemical forms in the Beta vulgaris root were studied to explore the mechanism that how the cornstalk biochar promoted Cd accumulation in Beta vulgaris. Biochar amendment reduced the DTPA-extractable Cd concentration and stimulated the growth of root. Compared to the Beta vulgaris without biochar treatment, the results of 5% biochar amendment showed that the root dry weight of Beta vulgaris increased to 267%, Cd accumulation in Beta vulgaris increased to 206% and the Cd concentration in leaves and roots increased by 36% and 52%, respectively. Additionally, after 5% biochar was applied to soil, the total content of organic matter-bound Cd and residual Cd increased by 38%, while the content of Fe-Mn oxides-bound Cd decreased by 40%. Meanwhile, Cd may mainly bind to the root cell wall and the ratio of NaCl-extracted Cd to HAc-extracted Cd increased to 166% with 5% biochar amendment. According to our study, Cd in soil can be removed by Beta vulgaris and phytoremediation efficiency can be improved with biochar amendment. The combination of phytoremediation and biochar amendment is a promising strategy for the Cd-contaminated soil remediation.

Acid buffering capacity of four contrasting metal-contaminated calcareous soil types: Changes in soil metals and relevance to phytoextraction

Four different metal-contaminated calcareous soil types, Carbonati-Perudic Cambosols (CPC), Fe-accumuli-Stagnic Anthrosols (FSA), Ochri-Aquic Cambosols (OAC) and Calci-Orthic Aridosols (COA), were investigated. The acid buffering capacity and metal-releasing behaviors of the soils were explored using an acid extraction method. Soil incubation and pot experiments were conducted to investigate changes in soil metal speciation and the enhancement of phytoextraction by soil acidification. There were several to tens of times differences in acid buffering capacities between soils. Soil calcium content may represent the major buffering system as indicated by significant linear correlations between the amount of Ca²⁺ released and H⁺ addition, and metal release into solution with H⁺ addition showed three stages, i.e. little release, slow release and rapid release stages. Soil carbonate-bound and Fe/Mn oxide-bound Cd and Zn decreased with the addition of H⁺ to all four soils, but organic matter-bound and residual metals remained unchanged. Based on the intensity of acidification, the efficiency Cd and Zn phytoextraction increased substantially with the addition of H⁺ in the case of the CPC but not the FSA which had a higher acid buffering capacity than the CPC. Hence, it may be concluded that the acid buffering capacity and changes in soil metal fractions with acidification of contaminated calcareous soil types should be determined before phytoextraction of these soils is attempted.

Biochar-assisted phytoextraction of Cd and Zn by Noccaea caerulescens on a contaminated soil: A four-year lysimeter study

Amendments of biochar, the residual solid of biomass pyrolysis, have been shown to enhance metal phytoextraction from contaminated soils with hyperaccumulating plants in specific situations. In order to investigate this phenomenon over successive harvests in field conditions, two identical undisturbed soil cylinders (1-m² section × 1.85-m height) were excavated from a contaminated agricultural plot and monitored with instrumented lysimeters. Wood-derived biochar was added at a rate of 5% (w/w) in the first 30 cm of one of the two lysimeters. The Cd/Zn-hyperaccumulator Noccaea caerulescens was then grown for the next four years on both lysimeters. Our results showed that the hyperaccumulating plant was able to remove about 2 g m^-2 of Cd and 12-16 g m^-2 of Zn within four years, representing about 40% and 4% of the initial Cd and Zn soil contamination, respectively. Biochar amendment improved plant germination and survival and increased root surface density. However, no significant effect of biochar on shoot metal content of N. caerulescens was observed. Mass balances suggested that up to 10% the metal contamination moved from the disturbed Ap horizon to the deeper horizons, particularly in the biochar-amended soil profile. Furthermore, shoot Cd and Zn concentration generally decreased over the successive harvests, together with soil metal availability. Depending on the way to account for this progressive decrease in efficiency, our estimations of the time necessary to remove the excess of metals in the topsoil in these conditions ranged from 11 to 111 years for Cd and from 97 years to an infinite time for Zn. In conclusion, the simultaneous use of N. caerulescens and biochar amendment can lead to a significant removal of specific metallic elements from the topsoil, but the risk of metal movement down the soil profile and the observed decrease in phytoextraction efficiency over time deserve further investigations.

Cd uptake by Phytolacca americana L. promoted by cornstalk biochar amendments in Cd-contaminated soil

Cadmium (Cd) contamination is the most extensive pollution in China farmland. A greenhouse pot trial was conducted to investigate the effects of cornstalk biochar on Cd accumulation by Phytolacca americana L. (pokeweed) in Cd-contaminated soil. The Cd concentration increased in leaves, shoots, and roots of plants amended with 5% biochar by 79%, 113%, and 32%, respectively, compared with the pokeweed without biochar. The Cd availability, soil Cd speciation, soil fertility, root biomass, and Cd chemical forms in root were investigated to explore the mechanism by which Cd uptake increased in presence of biochar. The extractability of Cd by DTPA decreased in presence of biochar by 30% compared with that of soil without biochar. The increases occurred with dose of biochar increased in available phosphorus, labile organic carbon, and C/N atom ratio. Although, the dry weight of the aboveground part of the pokeweed decreased by 38.5%, however, the weight of roots increased by 20.8%. Root biomass and microbial activity reached maximum in the treatment that recieved 5% biochar. Cd forms extracted by NaCl and acetic acid (HAc) were predominant in root. When 5% biochar applied to soil, HAc-extracted Cd took up maximum of the increase in root.

Combining phytoextraction by Brassica napus and biochar amendment for the remediation of a mining soil in Riotinto (Spain)

Soil contamination in mining areas is an important environmental concern. In these areas, phytoremediation is often impeded because of the low fertility and pH. Assisted phytoremediation is increasingly being used in polluted areas. Biochar could assist plant growth via enhanced soil fertility. An experiment was performed in a mining soil (RIII) from the mining area of Riotinto (Spain) contaminated with Cu, Pb, Zn and As in order to study: (i) The effects of biochar on soil fertility; (ii) Biochar temperature of preparation effect and (iii) Effect of biochar on phytoremediation potential. A mesocosm experiment was designed using Brassica napus as test specie. Soil (RIII) was treated with rabbit manure biochars prepared at 450 °C (BM450) and 600 °C (BM600) at a rate of 10% in mass and incubated for 60 days with or without Brassica napus. Results showed that the combination of BM450 or BM600 with Brassica napus growth decreased the amount of As, Cu, Co, Cr, Se and Pb in the soil. Values of bioaccumulation factor (BAF) for Cd were particularly elevated (>10) in the unamended soil and reached values higher than 1 for other elements, indicating the potential of Brassica napus to accumulate several heavy metals. Translocation Factor (TF) was reduced for Co, Cr, Cd, Cu, Ni, Zn, Pb and As after biochar addition indicating root accumulation of these metals. In all cases, biochar addition increased biomass production. Finally, the addition of BM450 increased GMea index indicating also an improvement on soil quality.

Phytoextraction potential of soils highly polluted with cadmium using the cadmium/zinc hyperaccumulator Sedum plumbizincicola

A three-crop repeated phytoextraction experiment was conducted using four soils (S1-S4) highly polluted with cadmium (Cd) and two enhanced phytoextraction pot experiments using the most polluted soil (S4) to investigate the feasibility of Cd removal from highly polluted soils using the Cd/zinc (Zn)-hyperaccumulator Sedum plumbizincicola. Shoot biomass showed no significant difference during the repeated phytoextraction experiment on the four test soils and shoot Cd content showed a decreasing trend with the three consecutive crops in soils S1, S2, and S3 but not in soil S4. The Cd removal rates in soils S1, S2, S3, and S4 were 84.5, 81.6, 45.3, and 32.4%, respectively. Rice straw application increased Cd extraction efficiency by 42.6% but the addition of ethylenediaminedisuccinic acid, biochar or nitrogen had no effect on Cd remediation. Shoot Cd content increased significantly (1.57 and 1.71 times, respectively) at low (S₀-1) and high (S₀-2) sulfur addition rates. Soil extractable-Cd in S₀-1 after the experiment showed no significant difference from the control but was 2.43 times higher in S₀-2 than in the control. These results indicate that S. plumbizincicola shows good prospects for the phytoextraction of Cd from highly polluted soils and that the process can be enhanced by adding straw and/or sulfur to the soil.