Assessing simultaneous immobilization of lead and improvement of phosphorus availability through application of phosphorus-rich biochar in a contaminated soil: A pot experiment

Relief effect of biochar on continuous cropping of tobacco through the reduction of p-hydroxybenzoic acid in soil

Biochar application to soil has proven to be an excellent approach for decreasing the concentration of auto-toxic compounds and promoting plant growth in continuous-cropping fields. However, the mechanisms underlying the action pathway among biochars, auto-toxic compounds and tobacco remain unknown. In this study, we conducted an experiment tracking the incidence rate of black rot and auto-toxic compounds for a 3-year continuous-cropping tobacco pot trial in response to biochar treatment intensity compared with that of non-biochar treatment. Biochar inhibited the incidence of black rot. Using ultra-high-performance liquid chromatography-mass spectrometry (UPLC‒MS/MS), we revealed that biochar can effectively decrease the concentration of p-hydroxybenzoic acid (PHA), which is associated with the incidence rate of black rot (R2 = 0.890, p < 0.05). The sorption kinetics and isotherm of PHA sorption on biochar indicate that the coexistence of heterogeneous and monolayer sorption plays an important role in the adsorption process. Using Molecular dynamics (MD), Density functional theory (DFT) and Independent gradient model (IGM) analyses, we provide evidence that van der Waals force (vdW), π-π bonds and H-bonds between biochar and PHAs are the dominant factors that affect adsorption capacity. Moreover, the molecular adsorption rate (Nbiochar: NPHAs = 1:4) was theoretically calculated. In contrast, biochar dramatically increased nutrient retention capacity and improved soil properties, further enhancing tobacco quality, including its agronomic and physiological traits. Therefore, we considered that biochar not only relieved continuous cropping but also improved soil properties suitable for tobacco growth. Together, we demonstrate that the action of biochar in continuously cropped soil improves soil traits and alleviates auto-toxic compound toxicity. These data contribute to the direction of modified biochar application to improve continuous-cropping soil.

Impact of coconut-fiber biochar on lead translocation, accumulation, and detoxification mechanisms in a soil-rice system under elevated lead stress

Biochar, an environmentally friendly material, was found to passivate lead (Pb) in contaminated soil effectively. This study utilized spectroscopic investigations and partial least squares path modeling (PLS-PM) analysis to examine the impact of coconut-fiber biochar (CFB) on the translocation, accumulation, and detoxification mechanisms of Pb in soil-rice systems. The results demonstrated a significant decrease (p < 0.05) in bioavailable Pb concentration in paddy soils with CFB amendment, as well as reduced Pb concentrations in rice roots, shoots, and brown rice. Synchrotron-based micro X-ray fluorescence analyses revealed that CFB application inhibited the migration of Pb to the rhizospheric soil region, leading to reduced Pb uptake by rice roots. Additionally, the CFB treatment decreased Pb concentrations in the cellular protoplasm of both roots and shoots, and enhanced the activity of antioxidant enzymes in rice plants, improving their Pb stress tolerance. PLS-PM analyses quantified the effects of CFB on the accumulation and detoxification pathways of Pb in the soil-rice system. Understanding how biochar influences the immobilization and detoxification of Pb in soil-rice systems could provide valuable insights for strategically using biochar to address hazardous elements in complex agricultural settings.

Biochar co-pyrolyzed from peanut shells and maize straw improved soil biochemical properties, rice yield, and reduced cadmium mobilization and accumulation by rice: Biogeochemical investigations

Biochar is an eco-friendly amendment for the remediation of soils contaminated with cadmium (Cd). However, little attention has been paid to the influence and underlying mechanisms of the co-pyrolyzed biochar on the bioavailability and uptake of Cd in paddy soils. The current study explored the effects of biochar co-pyrolyzed from peanut shells (P) and maize straw (M) at different mixing ratios (1:0, 1:1, 1:2, 1:3, 0:1, 2:1 and 3:1, w/w), on the bacterial community and Cd fractionation in paddy soil, and its uptake by rice plant. Biochar addition, particularly P1M3 (P/M 1:3), significantly elevated soil pH and cation exchange capacity, transferred the mobile Cd to the residual fraction, and reduced Cd availability in the rhizosphere soil. P1M3 application decreased the concentration of Cd in different rice tissues (root, stem, leaf, and grain) by 30.0%- 49.4%, compared to the control. Also, P1M3 enhanced the microbial diversity indices and relative abundance of iron-oxidizing bacteria in the rhizosphere soil. Moreover, P1M3 was more effective in promoting the formation of iron plaque, increasing the Cd sequestration by iron plaque than other treatments. Consequently, the highest yield and lowest Cd accumulation in rice were observed following P1M3 application. This study revealed the feasibility of applying P1M3 for facilitating paddy soils contaminated with Cd.

Remediation options to reduce bioaccessible and bioavailable lead and arsenic at a smelter impacted site - consideration of treatment efficacy

In this study, smelter contaminated soil was treated with various soil amendments (ferric sulfate [Fe2(SO4)3], triple superphosphate [TSP] and biochar) to determine their efficacy in immobilizing soil lead (Pb) and arsenic (As). In soils incubated with ferric sulfate (0.6M), gastric phase Pb bioaccessibility was reduced from 1939 ± 17 mg kg-1 to 245 ± 4.7 mg kg-1, while intestinal phase bioaccessibility was reduced from 194 ± 25 mg kg-1 to 11.9 ± 3.5 mg kg-1, driven by the formation of plumbojarosite. In TSP treated soils, there were minor reductions in gastric phase Pb bioaccessibility (to 1631 ± 14 mg kg-1) at the highest TSP concentration (6000 mg kg-1) although greater reductions were observed in the intestinal phase, with bioaccessibility reduced to 9.3 ± 2.2 mg kg-1. Speciation analysis showed that this was primarily driven by the formation of chloropyromorphite in the intestinal phase following Pb and phosphate solubilization in the low pH gastric fluid. At the highest concentration (10% w/w), biochar treated soils showed negligible decreases in Pb bioaccessibility in both gastric and intestinal phases. Validation of bioaccessibility outcomes using an in vivo mouse assay led to similar results, with treatment effect ratios (TER) of 0.20 ± 0.01, 0.76 ± 0.11 and 1.03 ± 0.10 for ferric sulfate (0.6M), TSP (6000 mg kg-1) and biochar (10% w/w) treatments. Results of in vitro and in vivo assays showed that only ferric sulfate treatments were able to significantly reduce As bioaccessibility and bioavailability with TER at the highest application of 0.06 ± 0.00 and 0.14 ± 0.04 respectively. This study highlights the potential application of ferric sulfate treatment for the immobilization of Pb and As in co-contaminated soils.

Immobilization effects of co-pyrolyzed neem seed mixed with poultry manure on potentially toxic elements in soil and the phytoremediation potentials of native Manihot esculenta and Jatropha curcas in ensuring sustainable land use

This study evaluated the effects of neem seed biochar, poultry manure, and their combinations at varying rates of 15 and 25% (w/w) on potentially toxic elements (PTEs) in soils. Afterward, the suitability of Manihot esculenta and Jatropha curcas in removing Cd, As, Zn, Pb, and Hg from mine spoils were appraised in a 270-day outdoor pot experiment. Using ICP-Mass Spectrometry, the elemental contents of target PTE in the shoot, root, and soil specimens were determined for each treatment. The obtained average values were further subjected to a nonparametric test of samples using IBM SPSS Statistic 29. The applied organic amendments resulted in significant differences p < 0.05 in PTE availability for plant uptake after the Independent-Samples Kruskal-Wallis Test was made. Nonetheless, applying a 25% (w/w) mixture of neem seed biochar and poultry manure was efficient in immobilizing more PTEs in soils which caused lower PTEs presence in plants. Organic amendments further significantly enhanced the fertility of the mine soils leading to about a 6- 25.00% increase in the biomass yield (p < 0.05) of both plants. No significant difference (p > 0.05) was however observed between the phytoremediation potentials of both plants after the Independent-Sample Mann-Whitney U test. Even that, Manihot esculenta was averagely more efficient in PTE uptake than Jatropha curcas. Larger portions of the bioaccumulated PTEs were stored in the roots of both plants leading to high bioconcentration factors of 1.94- 2.47 mg/kg and 1.27- 4.70 mg/kg, respectively, for Jatropha curcas and Manihot esculenta. A transfer factor < 1 was achieved for all PTEs uptake by both plants and indicated their suitability for phytostabilization. Techniques for easy cultivation of root-storing PTEs are required to enhance their large-scale use as their biomass could further be used in clean energy production.

Chitin and crawfish shell biochar composite decreased heavy metal bioavailability and shifted rhizosphere bacterial community in an arsenic/lead co-contaminated soil

Sustainable management of ever-increasing organic biowaste and arable soil contamination by potentially toxic elements are of concern from both environmental and agricultural perspectives. To tackle the waste issue of crawfish shells and simultaneously minimize the threat of arsenic (As) and lead (Pb) to human health, a pot trial was conducted using chitin (CT), crawfish shell biochar (CSB), crawfish shell powder (CSP), and CT-CSB composite to compare their remediation efficiencies in As/Pb co-contaminated soil. Results demonstrated that addition of all amendments decreased Pb bioavailability, with the greatest effect observed for the CT-CSB treatment. Application of CSP and CSB increased the soil available As concentration, while significant decreases were observed in the CT and CT-CSB treatments. Meanwhile, CT addition was the most effective in enhancing the soil enzyme activities including acid phosphatase, α-glucosidase, N-acetyl-β-glucosaminidase, and cellobiohydrolase, whereas CSB-containing treatments suppressed the activities of most enzymes. The amendments altered the bacterial abundance and composition in soil. For instance, compared to the control, all treatments increased Chitinophagaceae abundance by 2.6-4.7%. The relative abundance of Comamonadaceae decreased by 1.6% in the CSB treatment, while 2.1% increase of Comamonadaceae was noted in the CT-CSB treatment. Redundancy and correlation analyses (at the family level) indicated that the changes in bacterial community structure were linked to bulk density, water content, and As/Pb availability of soils. Partial least squares path modeling further indicated that soil chemical property (i.e., pH, dissolved organic carbon, and cation exchange capacity) was the strongest predictor of As/Pb availability in soils following amendment application. Overall, CT-CSB could be a potentially effective amendment for simultaneously immobilizing As and Pb and restoring soil ecological functions in contaminated arable soils.

Crawfish shell- and Chinese banyan branch-derived biochars reduced phytoavailability of As and Pb and altered community composition of bacteria in a contaminated arable soil

Globally, soil contamination with arsenic (As) and lead (Pb) has become a severe environmental issue. Herein, a pot experiment was conducted using pak choi (Brassica chinensis L.) to investigate the effects of biochars derived from crawfish (Procambarus clarkia) shells (CSB) and Chinese banyan (Ficus microcarpa) branches (CBB) on the phytoavailability of As and Pb, and bacterial community composition in soils. Our results showed that the application of CSB and CBB decreased the concentrations of DTPA-extractable Pb in soils ranging from 26.8 % to 28.8 %, whereas CSB increased the concentration of NH₄H₂PO₄-extractable As in soils, compared to the control. Application of both biochars reduced the uptake of As and Pb in the edible part of pak choi. In addition, application of CBB significantly (P < 0.05) increased the activities of α-glucosidase, β-glucosidase, cellobiohydrolase, and acid phosphomonoesterase by 55.0 %, 54.4 %, 195.1 %, and 76.7 %, respectively, compared to the control. High-throughput sequencing analysis revealed that the predominant bacteria at the phyla level in both biochar-treated soils were Firmicutes, Proteobacteria, and Actinobacteriota. Redundancy and correlation analyses showed that the changes in bacterial community composition could be related to soil organic carbon content, As availability, and nutrient availability in soils. Overall, the Chinese banyan branch biochar was more suitable than the crawfish shell biochar as a potential amendment for the remediation of soils co-contaminated with As and Pb.

Potential of hydrochar/pyrochar derived from sawdust of oriental plane tree for stimulating methanization by mitigating propionic acid inhibition in mesophilic anaerobic digestion of swine manure

VFAs accumulation in anaerobic digestion systems can lead to disturbance of the acid base balance, which has brought major challenges for methane production. Meanwhile, less research explored the potential of biochar derived from wood wastes of oriental plane tree (Platanus orientalis L.) for stimulating methanization in mesophilic anaerobic digestion. In this study, the effects of pyrochar and hydrochar derived from sawdust of oriental plane tree on mesophilic anaerobic digestion of swine manure were compared for the first time. Fourier infrared transform analysis indicated that more functional groups existed on the surface of hydrochar, whereas higher ash content and BET specific surface area were found in pyrochar. The maximum methane production rate during anaerobic digestion was observed in the pyrochar treatment, which increased by 59.5% compared with the control without biochar. Although stimulative effects on dissolved organic carbon and volatile fatty acids production were both observed in the pyrochar and hydrochar treatments, the pyrochar treatment was much easier to trigger multipath methanogenesis and direct interspecific electron transport and subdue propionic acid accumulation compared to the hydrochar treatment. Moreover, redundancy analysis indicated that the variations in acetic acid and dissolved organic carbon were mostly associated with microbial succession. These results suggest that pyrochar has better promoting effects than HC in terms of methane generation and propionic acid inhibition alleviation owing to its special porous structures, functional groups (e.g., C=O, C-O and O-H), and physicochemical properties. These excellent properties play a greater role in recruiting functional archaea and bacteria to regulate the levels of volatile fatty acids and dissolved organic carbon to enhance the methane yield of anaerobic digestion. This study provides novel and valuable information for further engineering applications of pyrochar and hydrochar derived from sawdust of oriental plane tree in energy production and environmental waste treatment.

Multiple-functionalized biochar affects rice yield and quality via regulating arsenic and lead redistribution and bacterial community structure in soils under different hydrological conditions

Rice grown in soils contaminated with arsenic (As) and lead (Pb) can cause lower rice yield and quality due to the toxic stress. Herein, we examined the role of functionalized biochars (raw phosphorus (P)-rich (PBC) and iron (Fe)-modified P-rich (FePBC)) coupled with different irrigation regimes (continuously flooded (CF) and intermittently flooded (IF)) in affecting rice yield and accumulation of As and Pb in rice grain. Results showed that FePBC increased the rice yield under both CF (47.4%) and IF (19.6%) conditions, compared to the controls. Grain As concentration was higher under CF (1.94-2.42 mg kg^-1) than IF conditions (1.56-2.31 mg kg^-1), whereas the concentration of grain Pb was higher under IF (0.10-0.76 mg kg^-1) than CF (0.12-0.48 mg kg^-1) conditions. Application of PBC reduced grain Pb by 60.1% under CF conditions, while FePBC reduced grain As by 12.2% under IF conditions, and increased grain Pb by 2.9 and 6.6 times under CF and IF conditions, respectively, compared to the controls. Therefore, application of the multiple-functionalized biochar can be a promising strategy for increasing rice yield and reducing the accumulation of As in rice grain, particularly under IF conditions, whereas it is inapplicable for remediation of paddy soils contaminated with Pb.

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.