Influence of biochar remediation on Eisenia fetida in Pb-contaminated soils

The interaction between biochar and earthworms: Revealing the potential ecological risks of biochar application and the feasibility of their co-application

Biochar's interaction with soil-dwelling organisms, particularly earthworms, is crucial in ensuring the effective and secure utilization of biochar in the soil. This review introduces the application of biochar in soil, summarizes how earthworms respond to biochar-amended soil and the underlying factors that can influence their response, discusses the synergistic and antagonistic impacts of earthworm activity on the efficacy of biochar, and considers the feasibility of applying them together. A review of existing research has identified uncertainty in the effect of biochar exposure on earthworms, with biochar derived from animal wastes, produced at higher pyrolysis temperatures, and used at higher doses of biochar having more negative effects on earthworms. Habitat modification, toxicity release, particle effects, and contaminant immobilization are underlying factors in how biochar affects earthworm indicators. While biochar in contaminated soils may alleviate the stress of pollutants on earthworms by decreasing their bioaccumulation, this remedial effect is not always effective. Additionally, earthworm bioturbation can enhance the migration, fragmentation, and oxidation of biochar, while also stimulating extracellular enzymes that convert biochar into 'vermichar'. Earthworms and biochar can synergize well to improve soil fertility and remediate soil organic pollution, yet exhibit contrasting roles in soil C sequestration and immobilizing heavy metals in soil. These findings highlight both the advantages and risks of their co-application. Therefore, when considering the use of biochar alone or with earthworms, it is crucial to thoroughly assess its potential ecotoxicity on earthworms and other soil organisms, as well as the influence of bioturbation, such as that caused by earthworms, on the effectiveness of biochar.

Removal of Pb pollution using alginate-coupled magnetic sludge biochar: Solidification and stabilization behavior and electron promotion mechanisms

Environmental and human health problems caused by Pb pollution have attracted much attention, and solidification and stabilization are effective means for its remediation. Improving the ability of biochar to remediate heavy metals through modification is the focus of current biochar research. This study used calcium-alginate gel (GB) and Fe3+ (magnetic) to encapsulate and improve sludge biochar (SB), and explored the adsorption behavior and passivation mechanism of Pb2+ on it from outside to inside. The magnetic-biochar (MB) in magnetic-biochar-gel microspheres (MBGB) showed a homogeneous dispersion and part of the Fe ion was detached from the MB into the three-dimensional pores of the gel. The results of kinetic, isothermal and pH adsorption experiments showed that the MBGB has 108.4 % and 200 % higher Pb2+ adsorption capacity and rate than SB and can be applied to pH 3-9. The adsorption of Pb2+ by MBGB is a multilayer adsorption with both physical and chemical mechanisms. Mineralogical and electrochemical results demonstrate that the cross-linking of the gel with magnetic-biochar (MB) can provide a directional diffusion channel for Pb2+ from the outside to the inside. The electron transfer rate of MBGB was significantly higher than that of SB (222.2 %) after the reaction. The dissolved cations and electrons on the MB guide Pb2+ from the MBGB surface to the internal MB quickly via accelerating the electron transfer and migration rate between Pb2+ and MB. Subsequently, the abundance of PO43- on the MB ensures stable mineral precipitation (Pyromorphite). Moreover, four-step extraction analysis confirmed that most of Pb2+ in MBGB was stable (36.2 % acid-soluble and 47.6 % non-bioavailable). Meanwhile, the Pb adsorption efficiency of MBGB was still >93.0 % after three cycles of adsorption-desorption. Excellent reuse performance and stability guarantee the environmental security of MBGB. The results of the study provide theoretical support for the efficient treatment of Pb2+ polluted water assisted by gel materials.

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.

Biochar and organic fertilizer drive the bacterial community to improve the productivity and quality of Sophora tonkinensis in cadmium-contaminated soil

Excessive Cd accumulation in soil reduces the production of numerous plants, such as Sophora tonkinensis Gagnep., which is an important and widely cultivated medicinal plant whose roots and rhizomes are used in traditional Chinese medicine. Applying a mixture of biochar and organic fertilizers improved the overall health of the Cd-contaminated soil and increased the yield and quality of Sophora. However, the underlying mechanism between this mixed fertilization and the improvement of the yield and quality of Sophora remains uncovered. This study investigated the effect of biochar and organic fertilizer application (BO, biochar to organic fertilizer ratio of 1:2) on the growth of Sophora cultivated in Cd-contaminated soil. BO significantly reduced the total Cd content (TCd) in the Sophora rhizosphere soil and increased the soil water content, overall soil nutrient levels, and enzyme activities in the soil. Additionally, the α diversity of the soil bacterial community had been significantly improved after BO treatment. Soil pH, total Cd content, total carbon content, and dissolved organic carbon were the main reasons for the fluctuation of the bacterial dominant species. Further investigation demonstrated that the abundance of variable microorganisms, including Acidobacteria, Proteobacteria, Bacteroidetes, Firmicutes, Chloroflexi, Gemmatimonadetes, Patescibacteria, Armatimonadetes, Subgroups_ 6, Bacillus and Bacillus_ Acidiceler, was also significantly changed in Cd-contaminated soil. All these alterations could contribute to the reduction of the Cd content and, thus, the increase of the biomass and the content of the main secondary metabolites (matrine and oxymatrine) in Sophora. Our research demonstrated that the co-application of biochar and organic fertilizer has the potential to enhance soil health and increase the productivity and quality of plants by regulating the microorganisms in Cd-contaminated soil.

Eisenia fetida impact on cadmium availability and distribution in specific components of the earthworm drilosphere

Although the potential of vermiremediation for restoring metal-contaminated soils is promising, the effects of earthworms on the availability of soil metals are still debatable. Most previous studies considered the soil as a "whole black box." Mobilization or immobilization of metals are affected by earthworm activities within drilosphere hotspots under different soil conditions, which has not been specifically studied. Therefore, an improved 2D terrarium was designed to study the impact of earthworm activities on cadmium (Cd) fate in the drilosphere hotspots (burrow wall soils, burrow casts, and surface casts) of different artificially spiked Cd treatments (CK: 0 mg kg-1; LM: 1 mg kg-1; and HM: 5 mg kg-1) with different organic amendments (2% and 10%). The results revealed that Cd increased earthworm activities with the highest cast production in HM and the highest burrow length in LM. Earthworms exhibited a stronger tendency to reduce total Cd concentration by 4.48-13.58% in casts of LM soils, while 3.37-5.22% in burrow walls under HM treatments. Overall, earthworms could increase the availability of Cd in casts under all conditions (55.46-121.01%). The organic amendments decreased the total Cd concentration and increased the availability of Cd in the disturbed soil. A higher amount of organic amendment significantly decreased total Cd concentration of the drilosphere by 1.16-5.83% in LM and HM treatments, while increasing DTPA-Cd concentrations in all components by 23.13-55.20 %, 14.63-35.11%, and 3.30-11.41% in CK, LM, and HM treatments, respectively, except for earthworm non-disturbed soil and no-earthworm soil in HM treatments. Redundancy analysis (RDA) revealed that the moisture, pH, and total carbon contents in soil are the main factors affecting Cd bioavailability. In this study, we decoded the "black box" of soil by making it relatively simple to better understand the effects and mechanisms of earthworm activities on soil metal availability and consequently provided comprehensive insights for using earthworms in soil vermiremediation.

Remediating thiacloprid-contaminated soil utilizing straw biochar-loaded iron and manganese oxides activated persulfate: Removal effects and soil environment changes

Thiacloprid (THI) has accumulated significantly in agricultural soil. Herein, a novel approach to removing THI was explored by straw biochar-loaded iron and manganese oxides (FeMn@BC) to activate the persulfate (PS). The factors influencing the removal of 5 mg kg-1 THI from the soil by FeMn@BC/PS were investigated, including FeMn@BC dosing, PS dosing, temperature, and soil microorganisms. The feasibility was demonstrated by the 75.22% removal rate of THI with 3% FeMn@BC and 2% PS at 7 days and a 92.50% removal rate within 60 days. Compared to the THI, NH4+-N and available potassium were 3.96 and 3.25 times, and urease and phosphatase activities were increased by 22.54% and 33.28% in the FeMn@BC/PS at the 15 days, respectively. THI was found to seriously alter the structure of the genus in the 15 days by 16 S rRNA analysis; however, the FeMn@BC/PS group alleviated the damage, compared to the THI with 658 more operational taxonomic units. Actinobacteriota accounted for 51.48% of the microbial community in the FeMn@BC/PS group after 60 days, possibly converting transition products of THI into smaller molecules. This article provides a novel insight into advanced oxidative remediation of soils.

High performance self-assembled nano-chlorapatite in the presence of lactonic sophorolipid for the immobilization of cadmium in polluted sediment

A novel lactonic sophorolipid (LS) self-assembled nano-chlorapatite (LS-nClAP) was prepared for the immobilization of severe cadmium (Cd) in sediment. The experimental results indicated that the introduction of LS not only improved the dispersed performance of chlorapatite, but also brought massive hydroxyl and carboxyl groups, which significantly improved the immobilization efficiency of Cd and reduced its eco-toxicity in sediment. LS can significantly increase the effective utilization rate of phosphorus in chlorapatite, and reduce the content of available phosphorus (AP) by half after remediation compared with ClAP. Additionally, the participation of LS possessed a significant impact on the enzyme activities in the sediment, especially for urease, which was closely related to the effective stability of Cd and the introduction of LS. All experimental results of this study provided new insights into the possible effects of Cd immobilization by chlorapatite in contaminated sediments, demonstrating great application potential for sediment remediation in the future.

Influences of lithium on soil properties and enzyme activities

Lithium is an emerging environmental contaminant under the current sustainable energy strategy, but little is known about its contamination characteristic in soil. In this study, soil properties and enzyme activities in soils treated with 10-1280 mg kg^-1 lithium were measured. The results showed that the content of ammonium nitrogen, total nitrogen, and exchangeable potassium significantly increased by 64.39%-217.73%, 23.06%-131.86%, and 4.76%-16.10%, while electric conductivity and available phosphorus content in lithium treated soils was respectively as 1.10-fold-13.44-fold and 1.27-fold-6.66-fold comparing to CK value. Soil pH and cation exchange capacity slightly declined and increased, respectively, and there was no significant variation in total organic carbon. However, nitrate nitrogen and sulfate content significantly decreased under higher lithium stress. On the other hand, lower lithium treatment level of 10, 20, 40, or 80 mg kg^-1 selectively promoted the activities of sucrase, urease, aryl sulfatase, and peroxidase, while the protease, neutral phosphatase, phytase, and lipase were significantly inhibited under all lithium levels, indicating a weaken geochemical cycling of carbon, nitrogen, phosphorus, and sulfur. Then, lithium's 10% and 50% ecological dose (ED10 and ED50) was respectively fitted as 21.18 and 1408.67 mg kg^-1 basing on Geometric Mean Index. The influences of lithium on soil were adverse. This study provided important insights into understanding the characteristics of lithium contamination, informing risk assessment and guiding remediation.

Chromium Contamination and Health Risk Assessment of Soil and Agricultural Products in a Rural Area in Southern China

With the rapid development of industry, chromium (Cr) pollutants accumulate constantly in the soil, causing severe soil Cr pollution problems. Farmland Cr pollution hurts the safety of agricultural production and indirectly affects human health and safety. However, the current situation of Cr pollution in farmland soil and crops has not been detailed enough. In this study, the evaluation of Cr potential risk in soil-crop systems was conducted in a rural area that was affected by industry and historic sewage irrigation. Ten different crops and rhizosphere soils were sampled from four fields. The results showed that Cr contents in farmland soil exceeded the national standard threshold in China (>21.85%), and the Cr content in edible parts of some agricultural products exceeded that too. According to the PCA and relation analysis, the Cr accumulation in edible parts showed a significant correlation with soil Cr contents and available potassium contents. Except for water spinach, the target hazard quotient (THQ) of the other crops was lower than 1.0 but the carcinogenic health risks all exceeded the limits. The carcinogenic risks (CR) of different types of crops are food crops > legume crops > leafy vegetable crops and root-tuber crops. A comprehensive assessment revealed that planting water spinach in this area had the highest potential risk of Cr pollution. This study provided a scientific and reliable approach by integrating soil environmental quality and agricultural product security, which helps evaluate the potential risk of Cr in arable land more efficiently and lays technical guidelines for local agricultural production safety.

A critical review on biochar-assisted free radicals mediated redox reactions influencing transformation of potentially toxic metals: Occurrence, formation, and environmental applications

Potentially toxic metals have become a viable threat to the ecosystem due to their carcinogenic nature. Biochar has gained substantial interest due to its redox-mediated processes and redox-active metals. Biochar has the capacity to directly adsorb the pollutants from contaminated environments through several mechanisms such as coprecipitation, complexation, ion exchange, and electrostatic interaction. Biochar's electron-mediating potential may be influenced by the cyclic transition of surface moieties and conjugated carbon structures. Thus, pyrolysis configuration, biomass material, retention time, oxygen flow, and heating time also affect biochar's redox properties. Generally, reactive oxygen species (ROS) exist as free radicals (FRs) in radical and non-radical forms, i.e., hydroxyl radical, superoxide, nitric oxide, hydrogen peroxide, and singlet oxygen. Heavy metals are involved in the production of FRs during redox-mediated reactions, which may contribute to ROS formation. This review aims to critically evaluate the redox-mediated characteristics of biochar produced from various biomass feedstocks under different pyrolysis conditions. In addition, we assessed the impact of biochar-assisted FRs redox-mediated processes on heavy metal immobilization and mobility. We also revealed new insights into the function of FRs in biochar and its potential uses for environment-friendly remediation and reducing the dependency on fossil-based materials, utilizing local residual biomass as a raw material in terms of sustainability.