Effects of BC on metal uptake by crops (availability) and the vertical migration behavior in soil: A 3-year field experiments of crop rotation.

Biochar (BC) has been substantiated to effectively reduce the available content of heavy metals (HMs) in soil-plant system; however, the risk of biochar (BC)derived dissolved organic matter (DOM) induced metal vertical migration has not been well documented, especially in the long-term field conditions. Therefore, this study investigated HM vertical migration ecological risks and the long-term effectiveness of the amendment of biochar in the three successive years of field trials during the rotation system. The results revealed that biochar application could increase soil pH and DOM with a decrease in soil CaCl2 extractable pool for Pb, Cu, and Cd. Furthermore, the results indicated a significant decrease in acid phosphatase activities and an increase in urease and catalase activities in the soil. Cucumber was shown to be safe during a three-year rotation system in the field. These results suggest that BC has the potential to enhance soil environment and crop yields. BC derived DOM-specific substances were identified using parallel factor analysis of excitation-emission matrix in deep soil (0-60 cm). The study incorporated HM concentration fluctuations in deep soils, providing an additional interpretation of DOM and co-migration of HMs.The environmental risk associated with the increase in DOM hydrophobicity should not be ignored by employing BC for soil HM remediation applications. The study enhances understanding of biochar-derived DOM's migration and stabilization mechanisms on heavy metals, providing guidelines for its use as a soil amendment.

Three-year field experiments revealed the immobilization effect of natural aging biochar on typical heavy metals (Pb, Cu, Cd).

Biochar has been widely used for the remediation of heavy metal contaminated soil, while the long-term field aging on its properties and the performance in the ability of metal immobilization must not be overlooked. In this study, the stability of immobilized heavy metals (Cd, Cu, Pb) on biochar during a 3-year remediation for soil in the field was investigated through desorption experiments. The results indicated that the application of biochar and its aging in the field both remarkably increased the immobilization of the 3 metal ions in the field under 3-year remediation. The cumulative desorption of the 3 metals decreased with biochar aging, and the desorption rate of Pb2+, Cu2+ and Cd2+ in T3 (Application of 30 t·hm-2 of biochar) for the third year was 0.08 %, 0.20 % and 13.15 %. Meanwhile, both the desorption rates and extents exhibited significant difference with the order of Pb2+ < Cu2+ < Cd2+. The increased soil pH, the enhancement of O/C ratio (Increase from 0.30 for fresh BC to 0.61 for aged BC(S3)) and oxygen-containing functional groups in biochar, and the accretion of organo-mineral micro-agglomerates on biochar surfaces and in pores during field aging process jointly contributed the immobilization of metals in soils mainly through co-precipitation and complexation. Our results provide new insights into the practical application of biochar in soils contaminated with multiple heavy metals from the perspective of long-term effects, which suggests that the potential release risk of metals become slighter over time.

The adsorption affinity of N-doped biochar plays a crucial role in peroxydisulfate activation and bisphenol A oxidative degradation.

Metal-free biochar to activate persulfate and degrade organic contaminants has attracted great attention in advanced oxidation processes, while the role of biochar adsorption in the activation and oxidative decomposition process still needed to be further clarified. In this study, nitrogen-doped porous biochar derived from a waste litchi branch was prepared as a peroxydisulfate (PDS) activator for bisphenol A (BPA) degradation, in which the regulation behavior of biochar adsorption was evaluated on the basis of phase distribution and PDS activation mechanism. N-doped biochar obtained at 800 °C with urea and sodium bicarbonate added presented a high specific surface area (821 m2/g), abundant nanopores, and a graphitic structure, and showed the best adsorption capacity and catalytic activity toward BPA. At a dosage of 0.15 g/L NBC-800, 95% BPA can be completely degraded within 60 min with an apparent rate constant (kobs) of 0.0483 min-1. The identified active sites and reactive oxygen species as well as electrochemical tests suggested that both free radicals O2•- and •OH and nonradical pathways including 1O2 originated from C = O and surface electron-transfer mechanisms were involved in BPA decomposition. The experiments and activation mechanisms all confirmed that BPA adsorption on the NBC-800 surface was an extremely crucial step for BPA oxidative degradation.

Field-scale fluorescence fingerprints of biochar-derived dissolved organic matter (DOM) provide an effective way to trace biochar migration and the downward co-migration of Pb, Cu and As in soil.

Although the benefits of biochar amendment for heavy metal(loid) immobilization in soil have been widely recognized, its migration in soil and the resultant effects on the risk of downward migration of metal(loid)s are still poorly understood. In this study, based on biochar derived dissolved organic matter (DOM), excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) technique was employed to trace biochar migration within one year in 0-100 cm soil profiles in the field. The vertical co-migration of Pb, Cu and As was also analyzed. With biochar amended, DOM, humification index (HIX) and biological index (BIX) in 0-60 cm soil profiles increased significantly, while pH only increased in the topsoil. The identified water-extracted DOM components showed that biochar could enhance the content of fulvic acids and humic acids in soil DOM and biochar might migrate downward to 60 cm soil profiles. Furthermore, toluene/methanol-extracted DOM also confirmed the migration extent of biochar, which was more suitable to trace biochar migration because of its high resistance to the long-term ageing in the field. Moreover, we found that biochar reduced the content of Cu in 0-60 cm soil profiles, but increased the available Pb and As in the 20-40 cm soil layers. The Pearson's correlation study confirmed a strong correlation (0.568**≤R ≤ 0.803**) between the content of heavy metal(loid)s and humic-like components of soil DOM, which suggested that biochar co-migrated with Pb, Cu and As, and the potential environmental risks of biochar should be fully evaluated while it was applied for soil metal(loid) remediation.

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.

Knowledge is insufficient on feasible remediation techniques to agricultural soils contaminated by multiple heavy metal(loid)s with elevated concentrations and extreme acidy from acid mine drainages (AMD). We aimed to elucidate the effect of integrated biochar (BC) and soil replacement on improving the mining soil properties and then alleviating the phytotoxicity of As, Pb, Cd, Cu, and Zn on radish (Raphanus sativus L.)-soya bean (Glycine max Merr.) -amaranth (Amaranthus tricolor L.) rotation and the potential risk of crops to human health. Biochar and soil replacement showed outstanding effects on improving soil properties by increasing soil pH values, reducing available metal(loid)s, and enhancing the activity of catalase, urease and acid phosphatase. Also, the integrated technique regulated the physiological disorders of crops caused by metal(loid)s, specifically increasing chlorophyll content and reducing malondialdehyde (MDA) in the three crops, and reducing the content of metal(loid)s in edible parts of plants. The combination of biochar and soil replacement exhibited better remediation effect than the single application of biochar or soil replacement, which played different roles in remediating mining farmland. Biochar exhibited efficacy in soil pH amelioration, metal stabilization and soil enzyme activity enhancement, while soil replacement alleviated metal(loid)s stress through the dilution effect. Among the 8 treatments, only biochar combined with 35% (S35BC) and 50% (S50BC) of replaced soil could achieve the safe production of the three crops under the three-season crop rotation.

Immobilization of heavy metal(loid)s in acid paddy soil by soil replacement-biochar amendment technology under normal wet condition.

The remediation of agricultural soil contaminated by acid mine drainages (AMD) with extreme acidity and elevated concentrations of metal(loid)s still remains to be solved. In the present study, the combination of soil replacement-biochar (BC) amendment was adopted in 270-day incubation experiments to evaluate the effect on the metal(loids) (As, Pb, Cu, Cd, and Zn) immobilization and soil properties (pH, dissolved organic carbon (DOC), redox potential (Eh), and soil water holding capacity (SWC)). The incubation study showed that soil replacement-biochar amendment improved soil health by changing soil properties, which in turn exhibited significant effects on CaCl2-extracted metal(loid)s. The combination of soil replacement and biochar amendment exhibited positive effect on the immobilization of Pb, Cu, Cd, and Zn, while, the risk of As and Cd mobility induced by biochar in the ageing process should be paid attention. Further laboratory seed germination study suggested that soil replacement-biochar amendment could effectively alleviate the stress of metal(loid)s, with the treatment of S50BC achieving the best remediation results. The results of this study suggested that soil replacement-biochar amendment was a promising remediation technology for agricultural soil contaminated by AMD. Graphical abstract.

Assessing biochar application to immobilize Cd and Pb in a contaminated soil: a field experiment under a cucumber-sweet potato-rape rotation.

Cd and Pb are common toxic contaminants prevailing in agricultural soils contaminated by mining activities. In this study, biochar was used to stabilize Cd and Pb contaminated soil for safe with three crops rotation condition within one year. Field experiments were carried out to investigate the effect of Litchi branch biochar (BC), pyrolyzed at 600 °C and applied at 4 rates [(0 t ha-1 (T0), 10 t ha-1 (T1), 20 t ha-1 (T2) and 30 t ha-1 (T3)]) on remediation of Cd and Pb in agricultural soil near Dabaoshan Mine in South China under a cucumber-sweet potato-rape rotation. The results showed that the application of BC can significantly increase the pH, cation exchange capacity and soil organic matter. After cultivation of crops, the pH values decrease gradually, with the biggest drop of 0.45 pH units in T3 treatment after rape cultivation. BC application increased the yield of three crops up to onefold to twofold in T3 treatment as compared to the control. The uptake of Cd and Pb in all three crops decreases with the increase in BC doses, which is mainly related to the decrease in bioavailable metals in their respective soil treatments. Under 1-year crops rotation, the remediation ability of BC still remains, while Cd and Pb can exhibit different risk to different crops. The data of this study can provide scientific suggestions for the selection of suitable crops and proper BC amount in remediation of heavy metal contaminated soil.