The compound effects of biochar and iron on watercress in a Cd/Pb-contaminated soil

Effect of biochar, zeolite and bentonite on physiological and biochemical parameters and lead and zinc uptake by maize (Zea mays L.) plants grown in contaminated soil

Heavy metals (HMs) are common contaminants with major concern of severe environmental and health problems. This study evaluated the effects of organo-mineral amendments (mesquite biochar (MB), zeolite (ZL) and bentonite (BN) alone and in combination) applied at different rates to promote the maize (Zea mays L.) growth by providing essential nutrient and improving the soil physio-chemical properties under zinc (Zn) and lead (Pb) contamination. Result revealed that the incorporation of organo-mineral amendments had significantly alleviated Pb and Zn contamination by maize plants and improved the physiological and biochemical attributes of plants. Combined application of organo-mineral amendments including BMA-1, BMA-2 and BMA-3 performed excellently in terms of reducing Pb and Zn concentrations in both leaves (19-60%, 43-75%, respectively) and roots (24-59%, 42-68%, respectively) of maize. The amendments decreased the extractable, reducible, oxidisable and residual fractions of metals in soil and significantly reduced the soil DTPA-extractable Pb and Zn. BMA-1 substantially improved antioxidant enzyme activities in metal-stressed plants. This study indicated that combined use of organo-mineral amendments can effectively reduce the bioavailability and mobility of Pb and Zn in co-contaminated soils. Combined application of organo-mineral amendments could be viable remediation technology for immobilization and metal uptake by plants in polluted soils.

Persistent effects of swine manure biochar and biogas slurry application on soil nitrogen content and quality of lotus root

Using swine manure biochar and biogas slurry in agriculture proves to be an effective strategy for soil improvement and fertilization. In this study, a pot trial on the growth of lotus root was conducted to investigate the persistent effects of applying 350°C swine manure biochar (1% and 2%) and biogas slurry (50% and 100%) on soil nitrogen nutrient and lotus root quality. The results showed that compared to chemical fertilizer alone (A0B0), swine manure biochar significantly increased soil nitrogen content after one year of application. The contents of total nitrogen (TN), alkali-hydrolyzed nitrogen (AHN), ammonium nitrogen (NH4 +-N), and nitrate nitrogen (N O 3 -   - N ) increased by 17.96% to 20.73%, 14.05% to 64.71%, 17.76% to 48.68% and 2.22% to 8.47%, respectively, during the rooting period. When swine manure biochar was present, the application of biogas slurry further elevated soil nitrogen content. The co-application of swine manure biochar and biogas slurry significantly increased soil nitrogen content, and the 100% nitrogen replacement with biogas slurry combined with 2% swine manure biochar (A2B2) treatment exhibited the most significant enhancement effect during whole plant growth periods. Soil enzyme activities, including soil protease (NPT), leucine aminopeptidase (LAP), b-glucosidase (β-GC) and dehydrogenase (DHA), showed a tendency to increase and then decrease with the prolongation of lotus root fertility period, reaching the maximum value during the rooting period. Compared to A0B0, the treatment with 2% swine manure biochar had the most significant effect on enzyme activities and increased the lotus root's protein, soluble sugar, and starch contents. Nitrate content decreased with the application of 2% swine manure biochar as the amount of biogas slurry increased. In conclusion, swine manure biochar effectively improved soil nitrogen content, enzyme activity, and lotus root quality. Even after one year of application, 2% swine manure biochar had the best enhancement effect.

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.

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.

A state-of-the-art review on cadmium uptake, toxicity, and tolerance in rice: From physiological response to remediation process

Cadmium (Cd), a major contaminant of concern, has been extensively reviewed and debated for its anthropogenic global shifts. Cadmium levels in rice grains raise wide food safety concerns. The aim of this review is therefore to capture the dynamics of Cd in paddy soil, translocation pathways of Cd from soil to consumption rice, and assess its bio-accessibility in human consumption. In crop plants, Cd reduces absorption of nutrients and water, triggers oxidative stress, and inhibits plant metabolism. Understanding the mechanisms and behaviour of Cd in paddy soil and rice allows to explain, predict and intervene in Cd transferability from soil to grains and human exposure. Factors affecting Cd movement in soil, and further to rice grain, are elucidated. Recently, physiological and molecular understanding of Cd transport in rice plants have been advanced. Morphological-biochemical characteristics and Cd transporters of plants in such a movement were also highlighted. Ecologically viable remediation approaches, including low input cost agronomic methods, phytoremediation and microbial bioremediation methods, are emerging.

Iron-modified phosphorus- and silicon-based biochars exhibited various influences on arsenic, cadmium, and lead accumulation in rice and enzyme activities in a paddy soil

Contamination of paddy soils with potentially toxic elements (PTEs) has become a severe environmental issue. Application of functionalized biochar for rice cultivation has been proposed as an effective means to reduce environmental risks of these PTEs in paddy soils. This work was undertaken to seek the positive effects of a rice husk-derived silicon (Si)-rich biochar (Si-BC) and a pig carcass-derived phosphorus (P)-rich biochar (P-BC), as well as their Fe-modified biochars (Fe-Si-BC and Fe-P-BC) on the enzyme activity and PTE availability in an As-Cd-Pb-contaminated soil. A rice cultivation pot trial was conducted using these functionalized biochars as soil amendments for the alleviation of PTE accumulation in rice plants. Results showed that Si-BC decreased the concentrations of As in rice grain and straw by 59.4 % and 61.4 %, respectively, while Fe-Si-BC significantly (P < 0.05) enhanced plant growth, increasing grain yield (by 38.6 %). Fe-Si-BC significantly (P < 0.05) elevated Cd and Pb accumulation in rice plants. P-BC enhanced the activities of dehydrogenase, catalase, and urease, and reduced grain-Pb and straw-Pb by 49.3 % and 43.2 %, respectively. However, Fe-P-BC reduced plant-As in rice grain and straw by 12.2 % and 51.2 %, respectively, but increased plant-Cd and plant-Pb. Thus, Fe-modified Si- and P-rich biochars could remediate paddy soils contaminated with As, and enhance the yield and quality of rice. Application of pristine P-rich biochar could also be a promising strategy to remediate the Pb-contaminated paddy soils and limit Pb accumulation in rice.

Sodium alginate-based composite microspheres for controlled release of pesticides and reduction of adverse effects of copper in agricultural soils

Excessive copper (Cu) concentrations pose significant health risks to both plants and humans. In this study, sodium alginate (SA)-gelatin (GEL)-polyvinyl pyrrolidone (PVP)- embedded dinotefuran (DIN) microspheres were prepared using spray-drying technology. The loading content and encapsulation efficiency of optimal microspheres determined by physical modifications were 19.77% and 99.32%, respectively. In addition, the microspheres showed variable stimuli-responsive controlled release capacities in different temperatures and types of soil, as well as showed better control efficiency of larvae of Protaetia brevitarsis at pesticide application in the early stage, with the potential ability to control pest outbreaks at high temperatures. In addition, blank microspheres improved the growth and physiological activity of cucumber seedlings, reduced copper content in leaves, increased soil nutrient content, and prevented soil acidification. Further, the use of blank microspheres increased the relative abundance of soil beneficial functional bacteria communities, which mediate heavy metal (HM) immobilization/tolerance and promote plant growth. Redundancy analysis (RDA) and Spearman correlation analysis showed that these beneficial functional bacteria were mainly positively correlated with soil EC, A-N, and N-N. In summary, this study showed that the technique of combining physically modified carrier materials with pesticides has the potential to reduce Cu contamination in the surrounding agricultural soil during pesticide application, thereby reducing Cu uptake by crops.

Responses of aquatic vegetables to biochar amended soil and water environments: a critical review

Aquatic vegetables, including lotus root, water spinach, cress, watercress and so on, have been cultivated as commercial crops for a long time. Though aquatic vegetables have great edible and medicinal values, the increasing demands for aquatic vegetables with high quality have led to higher requirements of their soil and water environments. Unfortunately, the soil and water environment often face many problems such as nutrient imbalance, excessive fertilization, and pollution. Therefore, a new cost-effective and eco-friendly solution for addressing the above issues is urgently required. Biochars, one type of pyrolysis product obtained from agricultural and forestry waste, show great potential in reducing fertilizer application, upgrading soil quality and remediating pollution. Application of biochars in aquatic vegetable cultivation would not only improve the yield and quality, but also reduce its edible risk. Biochars can improve the soil micro-environment, soil microorganism and soil enzyme activities. Furthermore, biochars can remediate the heavy metal pollution, organic pollution and nitrogen and phosphorus non-point source pollution in the water and soil environments of aquatic vegetables, which promotes the state of cultivation conditions and thereby improves the yield and quality of aquatic vegetables. However, the harmful substances such as heavy metals, PAHs, etc. derived from biochars can cause environmental risks, which should be seriously considered. In this review, the application of biochars in aquatic vegetable cultivation is briefly summarized. The changes of soil physicochemical and biological properties, the effects of biochars in remediating water and soil environmental pollution and the impacts of biochars on the yield and quality of aquatic vegetables are also discussed. This review will provide a comprehensive overview of the research progress on the effects of biochars on soil and water environments for aquatic vegetable cultivation.

Effects of biochar on the transformation of cadmium fractions in alkaline soil

To investigate the chemical properties in the biochar-mediated transformation of soil cadmium (Cd) fractions, the effects of biochar applied at different pyrolysis temperatures on soil Cd-fractions, pH value, and soil organic matter (SOM) were studied through an in-lab incubation experiment on contaminated soil. The results showed that the dissolved organic carbon (DOC) of CsBC300 (biochar prepared at 300 °C) was significantly higher (up to 1.31 times) than that of CsBC600 (biochar prepared at 600 °C). However, CsBC600 was more aromatic. Due to the difference in pyrolysis temperatures, the Cd deactivation mechanism of CsBC300 and CsBC600 was mainly to provide a large amount of organic matter and aromatic functional groups to the soil, respectively. The addition of these two biochar types significantly reduced the acid-extracted Cd content, by 76.56-83.52% and 70.48-76.81%, respectively. Contrastingly, it increased the residual Cd content by 2.26-2.36 and 2.08-2.29 times, respectively, which promoted the Cd transformation from the unstable to the stable state. However, CsBC300 had slightly better deactivation effect than CsBC600 on the 120th day, which was due to the decrease of soil pH and the increased SOM content. These study results can provide a theoretical reference for the remediation of Cd-contaminated alkaline soil.

Study on the physicochemical properties changes of field aging biochar and its effects on the immobilization mechanism for Cd2+ and Pb2

It has been widely reported that biochar can be used as a cost-effective amendment to immobilize of heavy metal contaminants in soil. While less research has been conducted on effect of biochar long-term field aging on its properties and the adsorption capability. In this study, the characteristics of aged biochar were investigated by comprehensive characterization to elucidate its mechanism transformation for heavy metal immobilization. Our results showed that, compared to fresh biochar, the relative content of C of aged biochar was reduced by 34.12%, while O was increased by 8.79%. Additionally, the specific surface area, pore volume, pore size and oxygen-containing functional groups of aged biochar were significantly increased compared to the fresh biochar. Batch adsorption experiment indicated that the maximum adsorption for Cd2+ (Qm = 32.157 mg/g) and Pb2+ (Qm = 39.216 mg/g) on aged biochar surface was much larger than that of Cd2+ (Qm = 7.573 mg/g) and Pb2+ (Qm = 8.134 mg/g) on fresh biochar. The underlying adsorption mechanisms for Cd2+ and Pb2+ on fresh biochar were dominated by coprecipitation, cation exchange and cation-π interaction, whereas surface complexation and cation exchange appeared to be more vital for aged biochar, as more active adsorption sites and Oxygen-containing functional groups were formed on its surface during aging, which was well explained by BET, XPS, FTIR and Elemental Analysis. Our study found that the physicochemical properties of biochar changed significantly during field aging. Although these changes increased the adsorption of heavy metals by biochar, the reduced stability of biochar to passivated heavy metal ions.

The effects of a combined amendment on growth, cadmium adsorption by five fruit vegetables, and soil fertility in contaminated greenhouse under rotation system

Cadmium (Cd) exposure is related to a multitude of adverse health outcomes because food crops grown on Cd-polluted soil are widely consumed by the public. The present study investigates the different application techniques of a combined amendment (lime + zeolite + biochar + compost, LZBC) for soil Cd immobilization effect on growth performance, Cd uptake by the second season crops, and soil quality in greenhouse vegetable production (GVP) under a rotation system. Five fruit vegetables were cultivated as the second season crop in the same plots which have been used for pakchoi as the first season crop (with or without LZBC application). The results indicated that LZBC with the consecutive application (T3) promoted crops biomass and fruit yield the most, followed by LZBC with the second crop application (T2) and LZBC with the first crop application (T1). LZBC application showed increasing rhizosphere soil pH and improvement in soil fertility of all crops including available nitrogen, available phosphorus, available potassium, organic matter, and cation exchange capacity. LZBC had positive influences on soluble sugar, soluble protein, and vitamin C in edible parts of 5 vegetables. Cd contents in fruit, shoot, and root of eggplant, pimento, cowpea, and tomato except cucumber were reduced by adding LZBC. As for the economic performance, T3 had the highest output/input ratio in general. Overall, these results demonstrated that T3 was dramatically more effective for minimizing health risk, increasing production, and facilitating sustainable utilization of soil under the Cd-contaminated GVP system.

Immobilization of cadmium and lead using phosphorus-rich animal-derived and iron-modified plant-derived biochars under dynamic redox conditions in a paddy soil

Functionalized biochar has gained extensive interests as a sustainable amendment for an effective remediation of paddy soils contaminated with heavy metals (HMs). We examined the efficiency of pig carcass-derived biochar (P-rich biochar, total P = 8.3%) and pristine (raw biochar, total Fe = 0.76%) and Fe-modified (Fe-rich biochar, total Fe = 5.5%) green waste-derived biochars for the immobilization of cadmium (Cd) and lead (Pb) in a paddy soil under pre-defined redox conditions (Eh, from -400 to +300 mV). Average concentrations (μg L^-1) of dissolved Cd increased under reducing conditions up to 10.9 in the control soil, and decreased under oxidizing conditions to below the detection limit (LDL = 2.7) in the raw and Fe-rich biochar treated soils. Application of the raw biochar decreased the concentrations of dissolved Cd by 43-59% under Eh ≤ -100 mV, compared to the non-treated control, which was more effective than the Fe-rich biochar (31-59%) and the P-rich biochar (8-19%). The immobilization of Cd under low Eh might be due to its precipitation with sulfide (S^2-), whereas its immobilization under high Eh might be due to the associated increase of pH. Concentrations (μg L^-1) of Pb ranged from 29.4 to 198.2 under reducing conditions, and decreased to LDL (12.5) under oxidizing conditions. The P-rich biochar was more effective in immobilizing Pb than the raw and Fe-rich biochars, particularly under Eh ≤ 0 mV (55-82%), which might be due to the retention of Pb by phosphates. The raw and Fe-rich biochars immobilized Pb under low Eh (≤ -300 mV), but both biochars, particularly the Fe-rich biochar mobilized Pb under Eh higher than -200 mV, especially at +100 mV, due to the decrease of pH at this point (pH = 6.0 to 6.5). These results improved our understanding of using P-rich and Fe-rich functionalized biochars for the immobilization of Cd and Pb in a paddy soil under stepwise redox changes. The amendment of P-rich pig carcass-derived biochar to paddy soils could be a promising approach for mitigating the risk of Pb for human health and the environment. The raw and Fe-rich green waste-derived biochars can be used for immobilizing Cd and mitigating its risk in paddy soils under both reducing and oxidizing conditions.

Passivation and remediation of Pb and Cr in contaminated soil by sewage sludge biochar tubule

Currently, numerous studies have carried out to research the effect of biochars remediation soil heavy metals (HMs) contaminated, but there have been fewer explorations of the effect of biochars tubule on soil HMs remediation. This work aimed to study the effect of passivation and remediation of lead (Pb) and chromium (Cr) contaminated soil after insert sewage sludge biochar (SSB) tubule. The results showed that the high risky fractions of Pb and Cr could be transformed into more stable fractions; also, Pb and Cr total contents are significantly decreased by SSB tubule. The mechanisms include adsorption, ion exchange, complexation, and precipitation which are concluded from the characteristic analysis. Detailly, the passivation of Pb and Cr is better when the moisture is 25% and 35%, respectively [Pb: exchangeable (F1), carbonate bound (F2) decreased by 25.1%, 16.8%, Fe-Mn oxides bound (F3) increased by 18.5%; Cr: F1 decreased by 73.0%, F2, F3, organic matter bound (F4) increased by 13.2%, 23.9%, 30.8%), respectively]. The remediation of Pb and Cr is better when the moisture is 25% and 35%, respectively, (Pb: decreased by 23.3%; Cr: decreased by 38.4%, respectively). The findings showed that the SSB tubule is effective when used for soil HMs contaminated.