An assessment of integrated amendments of biochar and soil replacement on the phytotoxicity of metal(loid)s in rotated radish-soya bean-amaranth in a mining acidy soil

Nano-selenium and compost vitalized morpho-physio-biochemical, antioxidants and osmolytes adjustment in soybean under tannery effluent polluted soil

The aim of this work was to investigate the impact of nano selenium (N-Se) and compost on the growth, photosynthesis, enzymes activity, compatible solutes and metals accumulation in soybean grown under tannery effluent polluted soil. The plants were exposed to compost application (no compost and compost addition) and foliar application of N-Se (0, 25, 50, and 75 mg L-1). The results showed the addition of compost in soil and foliar applied N-Se alleviated the toxic effect of tannery effluent polluted soil. Furthermore, foliar application of N-Se with basal compost supply significantly improved antoxidant enzymes activity in soybean grown in tannery effluent polluted soil. Addition of compost increased the root dry weight (46.43%) and shoot dry weight (33.50 %), relative water contents by (13.74 %), soluble sugars (15.99 %), stomatal conductance (gs) (83.33 %), intercellular CO2 concentration (Ci) (23.34 %), transpiration rate (E) (12.10 %) and decreased the electrolyte leakage (27.96 %) and proline contents by (20.34 %). The foliage application of N-Se at the rate of 75 mg L-1 showed the most promising results in control and compost amended tannery effluent polluted soil. The determined health risk index (HRI) values were recorded less than 1 for both adults and children under the application of compost and N-Se. In summary, the combined use of N-Se at 75 mg L⁻1 and basal supply of compost is an effective strategy for enhancing soybean productivity while minimizing the potential risks of metal accumulation in soybean grains grown in tannery effluent polluted soil.

Biochar and nano-hydroxyapatite combined remediation of soil surrounding tailings area: Multi-metal(loid)s fixation and soybean rhizosphere soil microbial improvement

The soil near tailings areas is relatively barren and contaminated by multi-metal(loid)s, seriously threatening the safety of crop production. Here, biochar and nano-hydroxyapatite (nHAP) were combined to improve the sterilized and unsterilized polymetallic contaminated soil, and soil incubation and soybean pot experiments were designed. Results showed that biochar and nHAP not only increased soil C, N, and P but also effectively reduced multi-metal bioavailability, wherein the combined application of the two amendments had the best effect on metal immobilization. The synergistic effect of the two amendments decreased the acid-soluble contents of Co, Cu, Fe, and Pb in rhizosphere soils up to 86.75%, 80.69%, 89.09%, and 96.70%, respectively. The ameliorant reduced the accumulation of metal(loid)s in soybean plants, and rhizosphere microorganisms inhibited the migration of soil metals to plants. Additionally, biochar and nHAP regulated the rhizosphere soil microbial community. The rhizosphere soil of the sterilization group tended to prioritize the restoration of the original dominant bacteria. As, Pb, Fe, Urease, OM, TN, and TP were the critical environmental variables affecting rhizosphere soil bacterial communities. Therefore, combining biochar and nHAP is an environmentally friendly strategy to reduce polymetallic mobility in tailings soil and crops and improve soil microbial community structure.

Human health risks of heavy metal(loid)s mediated through crop ingestion in a coal mining area in Eastern China

The heavy metal(loid)s (HMs) in soils can be accumulated by crops grown, which is accompanied by crop ingestion into the human body and then causes harm to human health. Hence, the health risks posed by HMs in three crops for different populations were assessed using Health risk assessment (HRA) model coupled with Monte Carlo simulation. Results revealed that Zn had the highest concentration among three crops; while Ni was the main polluting element in maize and soybean, and As in rice. Non-carcinogenic risk for all populations through rice ingestion was at an "unacceptable" level, and teenagers suffered higher risk than adults and children. All populations through ingestion of three crops might suffer Carcinogenic risk, with the similar order of Total carcinogenic risk (TCR): TCRAdults > TCRTeenagers > TCRChildren. As and Ni were identified as priority control HMs in this study area due to their high contribution rates to health risks. According to the HRA results, the human health risk was associated with crop varieties, HM species, and age groups. Our findings suggest that only limiting the Maximum allowable intake rate is not sufficient to prevent health risks caused by crop HMs, thus more risk precautions are needed.

Biochar amendment for reducing the environmental impacts of reclaimed polluted sediments

Dredging activities produce large amounts of polluted sediments that require adequate management strategies. Sediment reuse and relocation can involve several environmental issues, such as the release of CO2 and nitrogen compounds in the environment, the transfer of metals to plant tissues and the persistence of phytotoxic compounds. In this framework, the aim of the present work is to evaluate the use of biochar at different doses, in combination with plant growth, to reduce the environmental impacts polluted dredged sediments. Irrespective to the plant treatment, the amendment of the sediment with the lowest dose of biochar (3%) reduced by 25% the CO2 emissions of the substrate, by 89% the substrate carbon loss and by 35% the amount of nitrogen released into the environment (average values of the three plant treatments). The negative priming effect of biochar on organic matter mineralization can be responsible for the beneficial reduction of carbon and nitrogen release in the environment. The lack of similar effects observed at the higher biochar doses can depend on the low albedo of the biochar particles, causing the substrate warming (+1 °C for highest biochar dose) and accelerating the organic matter mineralization. Finally, shrub growth in combination with 3% biochar was able to offset the CO2 emission of the sediment and to reduce the amount of nitrogen lost. This work provides new insight on the potential benefit related to the biochar amendment of organic matter-rich dredged sediments, suggesting that the use of moderate dose of wood biochar in combination with shrub plantation can reduce the release of CO2 and nitrogen compounds in the environment.

Iron-modified biochar improves plant physiology, soil nutritional status and mitigates Pb and Cd-hazard in wheat (Triticum aestivum L.)

Environmental quality and food safety is threatened by contamination of lead (Pb) and cadmium (Cd) heavy metals in agricultural soils. Therefore, it is necessary to develop effective techniques for remediation of such soils. In this study, we prepared iron-modified biochar (Fe-BC) which combines the unique characteristics of pristine biochar (BC) and iron. The current study investigated the effect of pristine and iron modified biochar (Fe-BC) on the nutritional values of soil and on the reduction of Pb and Cd toxicity in wheat plants (Triticum aestivum L.). The findings of present study exhibited that 2% Fe-BC treatments significantly increased the dry weights of roots, shoots, husk and grains by 148.2, 53.2, 64.2 and 148%, respectively compared to control plants. The 2% Fe-BC treatment also enhanced photosynthesis rate, transpiration rate, stomatal conductance, intercellular CO2, chlorophyll a and b contents, by 43.2, 88.4, 24.9, 32.5, 21.4, and 26.7%, respectively. Moreover, 2% Fe-BC treatment suppressed the oxidative stress in wheat plants by increasing superoxide dismutase (SOD) and catalase (CAT) by 62.4 and 69.2%, respectively. The results showed that 2% Fe-BC treatment significantly lowered Cd levels in wheat roots, shoots, husk, and grains by 23.7, 44.5, 33.2, and 76.3%. Whereas, Pb concentrations in wheat roots, shoots, husk, and grains decreased by 46.4, 49.4, 53.6, and 68.3%, respectively. Post-harvest soil analysis showed that soil treatment with 2% Fe-BC increased soil urease, CAT and acid phosphatase enzyme activities by 48.4, 74.4 and 117.3%, respectively. Similarly, 2% Fe-BC treatment significantly improved nutrients availability in the soil as the available N, P, K, and Fe contents increased by 22, 25, 7.3, and 13.3%, respectively. Fe-BC is a viable solution for the remediation of hazardous Cd and Pb contaminated soils, and improvement of soil fertility status.

Effects of biochar on the physiology and heavy metal enrichment of Vetiveria zizanioides in contaminated soil in mining areas

The effects of biochar addition on the physiological and biochemical characteristics of Vetiveria zizanioides, and the enrichment of heavy metals, were studied herein. The aim was to provide a theoretical reference for biochar to regulate the growth of V. zizanioides in the heavy metal-contaminated soil of mining areas and the enrichment capacity of Cu, Cd, and Pb. The results showed that the addition of biochar significantly increased the contents of various pigments in the middle and late growth stages of V. zizanioides, reduced the contents of malondialdehyde (MDA) and proline (Pro) in each growth period, weakened the peroxidase (POD) activity during the entire growth period; superoxide dismutase (SOD) activity decreased in the initial stages and substantially increased in the middle and late stages. The addition of biochar reduced the enrichment of Cu in the roots and leaves of V. zizanioides, while the enrichment of Cd and Pb increased. In conclusion, it was found that biochar could reduce the toxicity of heavy metals in contaminated soil in the mining area, affect the growth of V. zizanioides and its accumulation of Cd and Pb, and is, therefore, beneficial to the restoration of contaminated soil and the overall ecological restoration of the mining area.

Improving radish phosphorus utilization efficiency and inhibiting Cd and Pb uptake by using heavy metal-immobilizing and phosphate-solubilizing bacteria

Phosphate-solubilizing bacteria play a key role in increasing plant growth as potential suppliers of soluble phosphorus and have great potential for the remediation of heavy metal-polluted soils. However, the soil and microbiological mechanisms by which phosphate-solubilizing bacteria prevent heavy metal absorption in radish have not been adequately studied. Here, the mechanisms of phosphorus solubilization, Cd and Pb immobilization, and the inhibition of heavy metal absorption by phosphate-solubilizing bacteria were studied in radish through solution adsorption and pot experiments. Two phosphate-solubilizing bacteria with high Cd and Pb removal rates (46.9-97.12 %), Klebsiella sp. M2 and Kluyvera sp. M8, were isolated. The soluble phosphorus content released by strains M2 and M8 was 265-277 mg L^-1, achieved by secreting oxalic acid, ascorbic acid, citric acid, and succinic acid in an inorganic phosphorus medium containing 3 mg L^-1 Cd and 5 mg L^-1 Pb. Furthermore, these two functional strains induced the formation of Pb₂(PO₄)₂, Cd(PO₃)₂, Fe₂Pb₃(PO₄)₂, CdS, and PbS precipitates that immobilized Cd and Pb in the solution. In general, strains M2 and M8 inhibited the absorption of Cd and Pb by radish by the following mechanisms: i) bacterial cell wall adsorption, ii) induction of Pb₂(PO₄)₂, Cd(PO₃)₂, Fe₂Pb₃(PO₄)₂, CdS, and PbS precipitation in the solution/soil, iii) increases in the Ca₂P and FeP contents in the radish rhizosphere, and iv) the promotion of bacterial community enrichment toward phosphorus-solubilizing and plant growth-promoting properties (Ramlibacter, Enterobacter, Bacillus, Gemmatimonas, and Lysinibacillusin) in the radish rhizosphere. These results provide bacterial resources and technical approaches to heavy metal pollution amelioration and efficient phosphorus fertilizer use in farmland.

Bioremediation of hazardous pollutants from agricultural soils: A sustainable approach for waste management towards urban sustainability

Soil contamination is perhaps the most hazardous issue all over the world; these emerging pollutants ought to be treated to confirm the safety of our living environment. Fast industrialization and anthropogenic exercises have resulted in different ecological contamination and caused serious dangerous health effects to humans and animals. Agro wastes are exceptionally directed because of their high biodegradability. Effluents from the agro-industry are a possibly high environmental risk that requires suitable, low-cost, and extensive treatment. Soil treatment using a bioremediation method is considered an eco-accommodating and reasonable strategy for removing toxic pollutants from agricultural fields. The present review was led to survey bioremediation treatability of agro soil by microbes, decide functional consequences for microbial performance and assess potential systems to diminish over potentials. The presence of hazardous pollutants in agricultural soil and sources, and toxic health effects on humans has been addressed in this review. The present review emphasizes an outline of bioremediation for the effective removal of toxic contaminants in the agro field. In addition, factors influencing recent advancements in the bioremediation process have been discussed. The review further highlights the roles and mechanisms of micro-organisms in the bioremediation of agricultural fields.

Recent advances in soil remediation technology for heavy metal contaminated sites: A critical review

With the increasing development of industry and urbanization, heavy metal contaminated sites have become progressively conspicuous, particularly by unreasonable emissions from electroplating, nonferrous metals smelting, mine tailing, etc. In recent years, soil remediation technologies for heavy metal contaminated sites have developed rapidly. New and effective remediation technologies have emerged successively, and more successful practical applications have appeared. Therefore, systematical summarization of the current progress is essential. As a result, in this paper, some mainstream soil remediation technologies for heavy metal contaminated sites, including physical remediation (soil thermal desorption and soil replacement), bioremediation (phytoremediation and microbial remediation), chemical remediation (chemical leaching, chemical stabilization, electrokinetic remediation-permeable reactive barrier, and chemical oxidation/reduction), as well as various combined remediation are comprehensively reviewed. The influencing factors, advantages, disadvantages, remediation mechanism, and practical applications are also deeply discussed. Besides, the corresponding remediation strategies are put forward for the remediation of heavily polluted sites such as the chemical industry, smelting, and tailing areas. Overall, this review will be beneficial for the in-depth understanding and provide references for the reasonable selection and development of soil remediation technology for heavy metal contaminated sites.

Wood vinegar facilitated growth and Cd/Zn phytoextraction of Sedum alfredii Hance by improving rhizosphere chemical properties and regulating bacterial community

Soil Cd and Zn contamination has become a serious environmental problem. This work explored the performance of wood vinegar (WV) in enhancing the phytoextraction of Cd/Zn by hyperaccumulator Sedum alfredii Hance. Rhizosphere chemical properties, enzyme activities and bacterial community were analyzed to determine the mechanisms of metal accumulation in this process. Results demonstrated that, after 120 days growth, different times dilution of WV increased the shoot biomass of S. alfredii by 85.2%-148%. In addition, WV application significantly increased soil available Cd and Zn by lowing soil pH, which facilitated plant uptake. The optimal Cd and Zn phytoextraction occurred from the 100 times diluted WV (D100), which increased the Cd and Zn extraction by 188% and 164%, compared to CK. The 100 and 50 times diluted WV significantly increased soil total and available carbon, nitrogen and phosphorus, and enhancing enzyme activities of urease, acid phosphatase, invertase and protease by 10.1-21.4%, 29.1-42.7%,12.2-38.3% and 26.8-85.7%, respectively, compared to CK. High-throughput sequencing revealed that the D 100 significantly increased the bacterial diversity compared to CK. Soil bacterial compositions at phylum, family and genera level were changed by WV addition. Compared to CK, WV application increased the relative abundances of genus with plant growth promotion and metal mobilization function such as, Bacillus, Gemmatimonas, Streptomyces, Sphingomonas and Polycyclovorans, which was positively correlated to biomass, Cd/Zn concentrations and extractions by S. alfredii. Structural equation modeling analysis showed that, soil chemical properties, enzyme activities and bacterial abundance directly or indirectly contributed to the biomass promotion, Cd, and Zn extraction by S. alfredii. To sum up, WV improved phytoextraction efficiency by enhancing plant growth, Cd and Zn extraction and increasing soil nutrients, enzyme activities, and modifying bacterial community.

Biochar in environmental friendly fertilizers - Prospects of development products and technologies

According to the circular economy concept, the production of fertilizers should be closed in a loop, which prevents excessive emissions and harmful effects to the environment. Biological wastes are problematic to collect and transport. They undergo a biological transformation that causes greenhouse gases emission and sanitary hazards. Biomass sources used for organic or organo-mineral fertilizers must be free of pathogens and rich in macro and microelements. Solid residues can be processed thermally. Biochar is a carbon produced by biomass pyrolysis without oxygen presence and has been used for many years to improve soil quality and enhance the efficiency of fertilization. There are many research works on the use of biochar in fertilization. This study is also extended by the latest developments and technologies from the patent database (recent year) and biochar-based fertilizers market. To the best of our knowledge, there is no such review currently available in scientific databases. Based on the collected data, the best method of biochar management was proposed - soil application. Biochar applied to soil has several advantages: it improves soil structure and its sorption capacity, enhances soil-nutrient retention and water-holding capacity, immobilizes contaminants from soil (sorption), reduces greenhouse gas emissions and soil nutrient leaching losses while stimulating the growth of a plant.

Effect of a Passivator Synthesized by Wastes of Iron Tailings and Biomass on the Leachability of Cd/Pb and Safety of Pak Choi (Brassica chinensis L.) in Contaminated Soil

Cadmium (Cd) and lead (Pb) carry a high heavy-metal-toxic risk for both animals and plants in soil. In this study, iron-based biochar (T-BC) was prepared by co-pyrolysis using wastes of iron tailings and biomass with urea as the functioning agents. Field-emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and toxicity-characteristic leaching procedure (TCLP) methods were employed to analyze the physicochemical characteristics of T-BC. Additionally, a pot trial was conducted to examine the effects of T-BC on the physiological characteristics of pak choi (Brassica campestris L.), the availability of heavy metals, and enzyme activities in the soils. The results show that toxic metals have been volatilized by the roasting process and immobilized within T-BC via the formation of stable metal-compounds during the co-pyrolysis process, which satisfies the requirements of a soil passivator. Incubation experiments showed that the DTPA-extractable Cd and Pb in contaminated soils decreased with an increasing amendment rate. Moreover, in the pot experiments, by adding 1% (w/w) T-BC into soils, the soils benefited from its large adsorption, complex precipitation, and immobilization capacity. Approximately 36% Cd and 29% Pb concentrations of edible parts in pak choi were reduced. The amendment proved promising for the stabilization of Cd and Pb in contaminated soils, while providing a strategy for solving the residual waste of tailings and biomass.