A novel and recyclable silica gel-modified biochar to remove cadmium from wastewater: Model application and mechanism exploration.

Water pollution caused by heavy metals is a major environmental problem, threatening water production, food safety, and human health. Cadmium (Cd) pollution is particularly serious because of food-chain biomagnification at toxic concentrations. Modified biochar is promising for heavy metal removal; however, efficient adsorbents for Cd removal are lacking. In the present study, a novel adsorbent, silica gel-modified biochar (SGB), was prepared and applied to treat sewage polluted by Cd. Through the batch adsorption experiments, it is known that SGB possessed outstanding Cd removal ability and recycleability. Furthermore, the adsorption behavior and mechanisms were analyzed by the application of kinetic and isotherm models. The maximum Cd2+ adsorption capacity of SGB was 38.08 mg g-1, and after five recycling processes, the Cd2+ removal rate was still 86.89 %. When the pH of the solution was 7.0, SGB showed the strongest Cd2+ adsorption capacity (29.06 mg g-1). When competitive ions existed, biochar also had high Cd removal efficiency, although the effect of Pb2+ was greater than those of Cu2+ and Zn2+, indicating that SGB was applicable to complex polluted water. Additionally, the main Cd2+ adsorption mechanisms by SGB were electrostatic interactions, π-π interactions, complexation, and co-precipitation. These results showed that SGB can effectively treat Cd-contaminated wastewater as a new adsorbent.

Effects of the three amendments on NH3 volatilization, N2O emissions, and nitrification at four salinity levels: An indoor experiment.

The marked salinity and alkaline pH of coastal saline soil profoundly impact the nitrogen conversion process, leading to a significantly reduced nitrogen utilization efficiency and substantial gaseous nitrogen loss. The application of soil amendments (e.g. biochar, manure, and gypsum) was proved to be effective for the remediation of saline soils. However, the effects of the three amendments on soil nitrogen transformation in soils with various salinity levels, especially on NH3 volatilization and N2O emission, remain elusive. Here, we reported the effects of biochar, manure, and gypsum on NH3 volatilization and N2O emission under four natural salinity gradients in the Yellow River Delta. Also, high-throughput sequencing and qPCR analysis were performed to characterize the response of nitrification (amoA) and denitrification (nirS, nirK, and nosZ) functional genes to the three amendments. The results showed that the three amendments had little effect on NH3 volatilization in low- and moderate-salinity soils, while biochar stimulated NH3 volatilization in high-salinity soils and reduced NH3 volatilization in severe-salinity soils. Spearman correlation analysis demonstrated that AOA was significantly and positively correlated with the NO3--N content (r = 0.137, P < 0.05) and N2O emissions (r = 0.174, P < 0.01), which indicated that AOA dominated N2O emissions from nitrification in saline soils. Structural equation modeling indicated that biochar, manure, and gypsum affected N2O emission by influencing soil pH, conductivity, mineral nitrogen content, and functional genes (AOA-amoA and nosZ). Two-way ANOVA further showed that salinity and amendments (biochar, manure, and gypsum) had significant effects on N2O emissions. In summary, this study provides valuable insights to better understand the effects of gaseous N changes in saline soils, thereby improving the accuracy and validity of future GHG emission predictions and modeling.

Effects of a novel Cd passivation approach on soil Cd availability, plant uptake, and microbial activity in weakly alkaline soils.

Heavy metal pollution, including that caused by cadmium (Cd), is a matter of increasing concern. Although in situ passivation remediation has been widely used to treat heavy metal-polluted soils, most studies have focused on acidic soils, while studies on alkaline soil conditions are scarce. In this study, the effects of biochar (BC), phosphate rock powder (PRP), and humic acid (HA) on Cd2+ adsorption were examined alone and in combination to choose an appropriate Cd passivation approach for weakly alkaline soils. Additionally, the combined impact of passivation on Cd availability, plant Cd absorption, plant physiology indexes, and soil microbial community was elucidated. BC had a higher Cd adsorption capacity and removal rate than those of PRP and HA. Moreover, HA and PRP enhanced the adsorption capacity of BC. A combination of biochar and humic acid (BHA), and biochar and phosphate rock powder (BPRP) significantly affected soil Cd passivation. BHA and BPRP decreased the plant Cd content and soil Cd-DTPA (diethylenetriaminepentaacetic acid) by 31.36 %, 20.80 %, 38.19 %, and 41.26 %, respectively; however, they increased the fresh weight by 65.64-71.48 % respectively, and dry weight by 62.41-71.35 %, respectively. Notably, only BPRP increased the node and root tip number in wheat. Total protein (TP) content increased in BHA and BPRP, with BHA showing lower TP than BPRP. BHA and BPRP showed a reduction in glutathione (GSH), malondialdehyde (MDA), H2O2, and peroxidase (POD); BHA showed a significantly lower GSH than BPRP. Additionally, BHA and BPRP increased soil sucrase, alkaline phosphatase, and urease activities, with BPRP showing considerably higher enzyme activity than BHA. Both BHA and BPRP increased the number of soil bacteria, altered the community composition, and critical metabolic pathways. The results demonstrated that BPRP could be used as a highly effective, novel passivation technique for the remediation of Cd-contaminated soil.

Biochar mitigation of soil acidification and carbon sequestration is influenced by materials and temperature.

The alleviation effects on soil acidification by different raw materials and pyrolysis temperatures can broaden the utilization of biochar. In this study, nine types of biochar produced from three raw materials, namely fruit tree branch, peanut shell, and cow dung, at three pyrolysis temperatures (300, 450, and 600 °C) were used to amend acidified brown soil; the rape growth, physiology character, soil chemical and microbial, along with soil organic carbon mineralization were also investigated. The results showed that application of biochar increased soil pH by 8.48-79.25% and reduced exchangeable acidity, exchangeable Al, and exchangeable H by 56.94-94.95%, 34.38-95.66%, and 58.72-93.27%, respectively. Biochar alleviated oxidative stress in plants, reduced malondialdehyde and glutathione content in leaves, promoted rape growth, and increased microbial community diversity and the relative abundances of Acidobacteria and Olpidiomycota in the acidic soil. Moreover, biochar reduced the mineralization rate of organic carbon and the proportion of mineral-bonded organic carbon. Overall, biochar application is an effective strategy to ameliorate soil acidification and enhance rape production and carbon sequestration. The mitigation effect of branch biochar and cow dung biochar on soil acidification was superior to that of peanut shell biochar. The effects of biochar depended on the pyrolysis temperature; the positive effects of biochar samples pyrolyzed at 450 and 600 â„ƒ were stronger than those pyrolyzed at 300 â„ƒ. In this study, the optimum biochar materials and carbonization temperature for acidified soil improvement, as well as the effects of biochar application on soil microbial and carbon mineralization were clarified, which provides a new potential strategy for acidified soil improvement and expand the application range of biochar.

Effective utilization of weak alkaline soils with Cd-contamination by wheat and rape intercropping.

Recently, there has been increasing concern about the health hazards of heavy metal-polluted farmlands. Recent findings suggest that intercropping could be effective remediation strategy for agricultural soils without affecting crop biomass yield. However, there are concerns on the heavy metal accumulation in plant organs in phytoremediation, emphasizing the need to develop an effective intercropping remediation model. In this study, we evaluated the effects of intercropping rape and wheat with different accumulation characteristics of cadmium (Cd), and crop growth and physiological characteristics. Intercropping significantly reduced the Cd content of rape shoot and root, with the rape-low Cd-accumulating wheat intercropping system yielding the best results. However, intercropping had no significant effect on Cd accumulation in wheat. Additionally, intercropping affected the root system configuration and structure, photosynthetic indicators, chlorophyll content, crop enzyme content, and rhizosphere enzyme activity of both species, but did not significantly affect the biomass of wheat and rape. Overall, our findings showed that intercropping rape with a low Cd-accumulating wheat variety could be an effective model for safe production of wheat and rape in weak alkaline soils without compromising biomass yield. The study demonstrates that similar innovative, effective, and judicious intercropping strategy can enrich the theory of contaminated soil remediation.

Precise Monitoring of Soil Salinity in China's Yellow River Delta Using UAV-Borne Multispectral Imagery and a Soil Salinity Retrieval Index.

Monitoring salinity information of salinized soil efficiently and precisely using the unmanned aerial vehicle (UAV) is critical for the rational use and sustainable development of arable land resources. The sensitive parameter and a precise retrieval method of soil salinity, however, remain unknown. This study strived to explore the sensitive parameter and construct an optimal method for retrieving soil salinity. The UAV-borne multispectral image in China's Yellow River Delta was acquired to extract band reflectance, compute vegetation indexes and soil salinity indexes. Soil samples collected from 120 different study sites were used for laboratory salt content measurements. Grey correlation analysis and Pearson correlation coefficient methods were employed to screen sensitive band reflectance and indexes. A new soil salinity retrieval index (SSRI) was then proposed based on the screened sensitive reflectance. The Partial Least Squares Regression (PLSR), Multivariable Linear Regression (MLR), Back Propagation Neural Network (BPNN), Support Vector Machine (SVM), and Random Forest (RF) methods were employed to construct retrieval models based on the sensitive indexes. The results found that green, red, and near-infrared (NIR) bands were sensitive to soil salinity, which can be used to build SSRI. The SSRI-based RF method was the optimal method for accurately retrieving the soil salinity. Its modeling determination coefficient (R2) and Root Mean Square Error (RMSE) were 0.724 and 1.764, respectively; and the validation R2, RMSE, and Residual Predictive Deviation (RPD) were 0.745, 1.879, and 2.211.

Pollution assessment, source identification, and health risks of heavy metals: a case study in a typical wheat-maize rotation area of eastern China.

Winter-wheat-summer-maize rotations are important cropping patterns in China, and the quality of the food produced from these systems can affect human health. However, the effects of heavy metal pollution on both crops remain unclear. We analyzed soil-wheat and soil-maize samples from eastern China for their Cd, Cu, Zn, Cr, Ni, and Pb contents. The concentrations of these metals in the soils analyzed were found to be lower than those recommended by the national guidelines, but the Cd, Cr, Cu, and Ni concentrations were higher than the natural soil background values in China. Quality indices showed that subpollution was predominant in wheat/maize (95.00%/81.25%) samples. Positive matrix factorization model data revealed that the contributions from natural sources, agricultural activities, and traffic to the heavy metal pollution levels were 30.40-43.07%, 34.67-26.63%, and 34.92-30.27%, respectively, in the wheat-maize rotations. Although the health hazard quotient values for wheat were higher than those for maize, there were no health risks for children or adults.

Effect of phosphorus supplementation on growth, nutrient uptake, physiological responses, and cadmium absorption by tall fescue (Festuca arundinacea Schreb.) exposed to cadmium.

Cadmium is a common heavy metal pollutant. In some plants, its absorption is inhibited by exogenous phosphorus. Here, the effect of P supplementation on the growth of tall fescue exposed to Cd was evaluated in a hydroponic culture experiment. Plants were exposed to five concentrations of P (0, 0.25, 0.5, 0.75, and 1.0 mmol L-1) and three concentrations of Cd (50, 100, and 150 mg L-1), and plant growth, Cd content, absorption, physiological characteristics, and nutrient accumulation were investigated. P supplementation significantly reduced the Cd content, Cd translocation factor (TF), Cd removal efficiency, plant P absorption, chlorophyll content, glutathione levels, glutathione reductase levels, and superoxide dismutase (SOD) activity in tall fescue under Cd stress (P < 0.05). Moreover, it increased the vertical growth rate and biomass of tall fescue. At a constant P concentration, the biomass and vertical growth rate significantly decreased with an increasing Cd concentration, and the shoot Cd content, SOD activity, and TF significantly increased (P < 0.05). High P supplementation (0.75 and 1.0 mmol L-1) ameliorated the damage caused by 150 mg L-1 Cd stress, and the biomass, vertical shoot and vertical root growth rates were increased by 72.06-82.06%, 250.00-316.67%, 300.00-312.00%, respectively. In the plants subjected to 50 mg L-1 Cd stress, 0.5 mmol L-1 P supplementation enhanced biomass, vertical shoot and vertical root growth rates by 29.99%, 20.41%, and 21.43%, respectively, and reduced the Cd content in shoots (45.85%) and roots (9.71%). Except for the total potassium content and catalase activity, different concentrations of Cd negatively affected all parameters tested. Such negative effects were limited by P supplementation. Optimizing the nutrient composition and concentrations could minimize the potential negative impacts of Cd on plant growth.

Spermidine application alleviates salinity damage to antioxidant enzyme activity and gene expression in alfalfa.

We investigated whether spermidine (Spd) application alleviates salinity-induced damage in alfalfa (Medicago sativa L), and explored defence mechanisms associated with stress-related ion balance, antioxidant metabolism, and gene expression. We examined the response of 30-day-old alfalfa maintained in hydroponic culture tests for 7 days and subjected to one of six treatments: half-strength Hoagland solution (control); 1% NaCl; 10 µM Spd + 1% NaCl; 20 µM Spd + 1% NaCl; 40 µM Spd + 1% NaCl; and 60 µM Spd + 1% NaCl. In salinity-stressed plants, chlorophyll b, chlorophyll a + b, and total protein showed significant decreases, while marked increases were detected in relative electrolyte leakage, H2O2 content, glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione reductase (GR) activity, the Na+/K+ ratio, and APX1, APX2, GR, and SOD gene expression levels. Chlorophyll a and total protein content markedly increased under exogenous application of 20 µM Spd, while H2O2 content, GSH, SOD, CAT, POD, GR activity, the Na+/K+ ratio, and APX2, GR, and SOD expression levels all decreased. These results indicated that exogenous application of 20 µM spermidine effectively alleviates salinity-induced damage in alfalfa. These findings could benefit alfalfa cultivation and promote the development and utilization of saline-alkali soil.

Characterization of three Pb-resistant fungi and their potential Pb2+ ions adsorption capacities.

Bioremediation is preferred in heavy metal remediation, and the high-performance microbe is of prime importance. In the present research, three Pb-resistant microbes were isolated and growth characteristics and adsorption capacities were evaluated. The results showed that R. oryzae SD-1, T. asperellum SD-5, and M. irregularis SD-8 can grow well under 100 mg L-1 Pb2+ ions stress. There is a higher minimum inhibitory concentration (MIC) of Pb but lower MICs of Cd and Zn in T. asperellum SD-5. However, there were similar MICs of Cu among the three microbes. R. oryzae SD-1 exhibited a higher adsorption capacity and removal rate relative to the other two microbes under various Pb2+ ion levels. The Langmuir equation was fitted for the adsorption capacity of T. asperellum SD-5 and M. irregularis SD-8, and their maximum adsorption capacities were approximately 456.62 mg g-1 and 93.62 mg g-1. Moreover, the Elovich equation and the double constant equation can describe the adsorption process of Pb2+ ions in Pb-resistant microbes well. The strongest adsorption capacity under lower Pb2+ ion level was observed in M. irregularis SD-8, while the strongest adsorption capacities under higher Pb2+ ion levels were seen in R. oryzae SD-1 and T. asperellum SD-5. Therefore, three novel Pb-resistant microbes may be used as efficient, easily cultivated materials for Pb-contaminated soil remediation.

Straw and phosphorus applications promote maize (Zea mays L.) growth in saline soil through changing soil carbon and phosphorus fractions.

Introduction: Straw return has been widely recognized as an important carbon (C) enhancement measure in agroecosystems, but the C-phosphorus (P) interactions and their effects on plants in saline soils are still unclear. Methods: In this study, we investigated the effects of straw return and three P application levels, no P fertilizer (Non-P), a conventional application rate of P fertilizer (CP), and a high application rate of P fertilizer (HP), on maize growth and soil C and P fractions through a pot experiment. Results and discussion: The results revealed that the dry matter weight of maize plant was no difference between the two straw return levels and was 15.36% higher under HP treatments than under Non-P treatments. Plant nutrient accumulations were enhanced by straw addition and increased with increasing P application rate. Straw application reduced the activities of peroxidase (POD), superoxide dismutase (SOD), catalase, and the content of malondialdehyde (MDA) in maize plants by 31.69%, 38.99%, 45.96% and 27.04%, respectively. P application decreased SOD, POD activities and MDA content in the absence of straw. The contents of easily oxidized organic carbon (EOC), particulate organic carbon (POC) and the ratio of POC/SOC in straw-added soils were 10.23%, 17.00% and 7.27% higher, respectively, than those in straw-absent soils. Compared with Non-P treatments, HP treatments led to an increase of 12.05%, 23.04% in EOC, POC contents respectively, while a decrease of 18.12% in the contribution of MAOC to the SOC pool. Straw return improved the P status of the saline soil by increasing soil available P (14.80%), organic P (35.91%) and Ca2-P contents (4.68%). The structural equation model showed that straw and P applications could promote maize growth (indicated by dry matter weight, P accumulation, antioxidant enzyme activity and MDA content) through improving soil C and P availabilities. Conclusion: This study provides evidence that straw return together with adequate P supply in saline soil can promote crop nutrient accumulation, attenuate the oxidation damage on crop growth, and be beneficial for SOC turnover and soil P activation.

The Complete Genome Sequence of Bacillus toyonensis Cbmb3 with Polyvinyl Chloride-Degrading Properties.

The accumulation of high amounts of plastic waste in the environment has raised ecological and health concerns, particularly in croplands, and biological degradation presents a promising approach for the sustainable treatment of this issue. In this study, a polyvinyl chloride (PVC)-degrading bacterium was isolated from farmland soil samples attached to waste plastic, utilizing PVC as the sole carbon source. The circular chromosome of the strain Cbmb3, with a length of 5,768,926 bp, was subsequently sequenced. The average GC content was determined to be 35.45%, and a total of 5835 open reading frames were identified. The strain Cbmb3 was designated as Bacillus toyonensis based on phylogenomic analyses and genomic characteristics. The bioinformatic analysis of the Cbmb3 genome revealed putative genes encoding essential enzymes involved in PVC degradation. Additionally, the potential genomic characteristics associated with phytoprobiotic effects, such as the synthesis of indole acetic acid and secondary metabolite synthesis, were also revealed. Overall, the present study provides the first complete genome of Bacillus toyonensis with PVC-degrading properties, suggesting that Cbmb3 is a potential strain for PVC bioremediation and application.

Improved Denitrification Performance of Polybutylene Succinate/Corncob Composite Carbon Source by Proper Pretreatment: Performance, Functional Genes and Microbial Community Structure.

Blending biodegradable polymers with plant materials is an effective method to improve the biodegradability of solid carbon sources and save denitrification costs, but the recalcitrant lignin in plant materials hinders the microbial decomposition of available carbon sources. In the present study, corncob pretreated by different methods was used to prepare polybutylene succinate/corncob (PBS/corncob) composites for biological denitrification. The PBS/corncob composite with alkaline pretreatment achieved the optimal NO3--N removal rate (0.13 kg NO3--N m-3 day-1) with less adverse effects. The pretreatment degree, temperature, and their interaction distinctly impacted the nitrogen removal performance and dissolved organic carbon (DOC) release, while the N2O emission was mainly affected by the temperature and the interaction of temperature and pretreatment degree. Microbial community analysis showed that the bacterial community was responsible for both denitrification and lignocellulose degradation, while the fungal community was primarily in charge of lignocellulose degradation. The outcomes of this study provide an effective strategy for improving the denitrification performance of composite carbon sources.

Reinforced Bioremediation of Excessive Nitrate in Atrazine-Contaminated Soil by Biodegradable Composite Carbon Source.

Bioremediation is a good alternative to dispose of the excessive nitrate (NO3-) in soil and alleviate the secondary salinization of soil, but the presence of atrazine in soil interferes with the bioremediation process. In the present study, the biodegradable composite carbon source with different dosages was added to the atrazine-contaminated soil to intensify the bioremediation of excessive NO3-. The atrazine-contaminated soil with a 25 g/kg composite carbon source achieved the optimal NO3- removal performance (92.10%), which was slightly higher than that with a 5 g/kg composite carbon source (86.15%) (p > 0.05). Unfortunately, the negative effects of the former were observed, such as the distinctly higher emissions of N2O, CO2 and a more powerful global warming potential (GWP). Microbial community analysis showed that the usage of the composite carbon source clearly decreased the richness and diversity of the microbial community, and greatly stimulated nitrogen metabolism and atrazine degradation (p < 0.05). To sum up, the application of a 5 g/kg composite carbon source contributed to guaranteeing bioremediation performance and reducing adverse environmental impacts at the same time.

The Microbiome and Antibiotic Resistome in Soil under Biodegradable Composite Carbon Source Amendment.

The decomposition of biodegradable composite carbon sources generates a large amount of biodegradable microplastics, which may not only furnish microbial denitrification, but might also pose potential environmental risks. In the present study, the effects of different dosages of a biodegradable composite carbon source on the microbial communities, the nitrogen metabolic pathways and the antibiotic resistome were explored through Illumina MiSeq sequencing analysis and metagenomic analysis. The results of partial least-square discriminant analysis (PLS-DA) and analysis of similarity (ANOSIM) demonstrated that the response of the bacterial community to a biodegradable composite carbon source was more obvious than the fungal community. The application of biodegradable microplastics diminished the complexity of the microbial communities to some extent and obviously stimulated denitrification. Antibiotics resistance gene (ARG) dispersal was not evidently accelerated after the addition of biodegradable composite carbon source. Lysobacter, Methylobacillus, Phyllobacterium, Sinorhizobium, Sphingomonas from Proteobacteria and Actinomadura, Agromyces, Gaiella and Micromonospora from Actinobacteria were the major ARG hosts. Overall, the addition of a biodegradable composite carbon source shaped microbial communities and their antibiotic resistance profiles in this study.

A novel phytoremediation technology for polluted cadmium soil: Salix integra treated with spermidine and activated carbon.

A variety of plants have been used as phytoremediation materials to remove Cd from polluted soil. However, the disadvantages of using plants for decontamination include low biomass, low uptake, and inefficiency. We conducted experiments to determine the effects of spermidine and activated carbon treatments of Salix integra on Cd removal. The results showed that exogenous spermidine and activated carbon increased plant growth and root development compared with the CK. The increased dry mass (39.65-92.95%) with the combined spermidine and activated carbon treatments was higher than that with either single treatment (14.79-62.80%). The root length, surface area, root volume, and root diameter with the combined spermidine and activated carbon treatments (53.51-189.35%, 113.08-207.62%, 111.71-499.27%, and 32.51-106.62%, respectively) were higher than those of the lone application treatments (19.35-132.23%, 52.33-111.57%, 35.08-297.07%, and 24.22-81.38%, respectively). In addition, spermidine and activated carbon application reduced the toxicity of Cd to S. integra by improving the antioxidant capacity, thereby increasing the accumulation of Cd. The application of spermidine and activated carbon also changed the distribution of Cd in each part of S. integra. There was increased accumulation of Cd in the shoots and better absorption by the S. integra shoots, thereby improving their Cd remediation efficiency. The combined 0.8 mM spermidine and 0.5 g kg-1 activated carbon were most effective on removing Cd from the soil. The Cd removal efficiency was 78.11-120.86% higher than that of the CK. Our results may provide foundational information for understanding the mechanisms for the sustainable remediation of Cd-contaminated soil using a combination of spermidine and activated carbon.

Transcriptome Analysis Reveals Molecular Mechanisms under Salt Stress in Leaves of Foxtail Millet (Setaria italica L.).

Foxtail millet (Setaria italica L.) is an important cereal for managing future water scarcity and ensuring food security, due to its strong drought and salt stress resistance owing to its developed root system. However, the molecular responses of foxtail millet leaves to salt stress are largely unknown. In this study, seeds of 104 foxtail millet accessions were subjected to 0.17 mol·L-1 NaCl stress during germination, and various germination-related parameters were analyzed to derive 5 salt-sensitive accessions and 13 salt-tolerant accessions. Hong Gu 2000 and Pu Huang Yu were the most salt-tolerant and salt-sensitive accessions, respectively. To determine the mechanism of the salt stress response, transcriptomic differences between the control and salt-treated groups were investigated. We obtained 2019 and 736 differentially expressed genes under salt stress in the salt-sensitive and salt-tolerant accessions, respectively. The transcription factor families bHLH, WRKY, AP2/ERF, and MYB-MYC were found to play critical roles in foxtail millet's response to salt stress. Additionally, the down-regulation of ribosomal protein-related genes causes stunted growth in the salt-sensitive accessions. The salt-tolerant accession alleviates salt stress by increasing energy production. Our findings provide novel insights into the molecular mechanism of foxtail millet's response to salt stress.

Biochar Alleviates Phytotoxicity by Minimizing Bioavailability and Oxidative Stress in Foxtail Millet (Setaria italica L.) Cultivated in Cd- and Zn-Contaminated Soil.

Soil contamination with multiple heavy metals is a global environmental issue that poses a serious threat to public health and ecological safety. Biochar passivation is an efficient and economical technology to prevent heavy metal contamination of Cd; however, its effects on compound-contaminated and weakly alkaline soil remain unclear. Further, the mechanisms mediating the immobilization effects of biochar have not been evaluated. In this study, three biochar treated at different pyrolytic temperatures [300°C (BC300), 400°C (BC400), and 500°C (BC500)] were applied to Cd-/Zn-contaminated soils, and their effects on plant growth, photosynthetic characteristics, Cd/Zn accumulation and distribution in foxtail millet were evaluated. Further, the effect of biochar application on the soil physicochemical characteristics, as well as the diversity and composition of the soil microbiota were investigated. Biochar significantly alleviated the phytotoxicity of Cd and Zn. DTPA (diethylenetriamine pentaacetic acid)-Cd and DTPA-Zn content was significantly reduced following biochar treatment via the transformation of exchangeable components to stable forms. BC500 had a lower DTPA-Cd content than BC300 and BC400 by 42.87% and 39.29%, respectively. The BC500 passivation ratio of Cd was significantly higher than that of Zn. Biochar application also promoted the growth of foxtail millet, alleviated oxidative stress, and reduced heavy metal bioaccumulation in shoots, and transport of Cd from the roots to the shoots in the foxtail millet. The plant height, stem diameter, biomass, and photosynthetic rates of the foxtail millet were the highest in BC500, whereas the Cd and Zn content in each organ and malondialdehyde and hydrogen peroxide content in the leaves were the lowest. Moreover, biochar application significantly increased the abundance of soil bacteria and fungi, as well as increasing the fungal species richness compared to no-biochar treatment. Overall, biochar was an effective agent for the remediation of heavy metal-contaminated soil. The passivation effect of biochar exerted on heavy metals in soil was affected by the biochar pyrolysis temperature, with BC500 showing the best passivation effect.

Treatment of cadmium and zinc-contaminated water systems using modified biochar: Contaminant uptake, adsorption ability, and mechanism.

Cd and Zn contamination in water occurs frequently that threatens water supply, human health, and food production. MnFeB, a novel absorbent biochar modified using KMnO4 and hematite, was prepared and used for the treatment of Cd2+ and Zn2+solutions. MnFeB exhibits a rough surface structure, large specific surface area, higher total pore volume, massive functional groups, and abundant iron oxide, all of which contribute to higher Cd2+ and Zn2+ adsorption capacity. In single metal systems, maximum Cd2+ and Zn2+ adsorption capacities of MnFeB were 1.88 and 1.79 times higher than those of unmodified biochar (CSB). The maximum Cd2+ and Zn2+ adsorption capacities of MnFeB were 2.73 and 2.65 times higher than CSB in the binary metal system. Key adsorption mechanisms of Cd2+ and Zn2+ by MnFeB included electrostatic interaction, co-precipitation, π-π interaction, complexation, and ion exchange. Thus, MnFeB can be used as a novel absorbent to treat Cd and Zn-polluted water.

Individual and combined contamination of oxytetracycline and cadmium inhibited nitrification by inhibiting ammonia oxidizers.

Introduction: The large-scale development of animal husbandry and industrialization lead to more and more serious co-contamination from heavy metals and antibiotics in soils. Ecotoxic effects of residues from antibiotics and heavy metals are of increasing concern. Materials and Methods: In this study, oxytetracycline (OTC) and cadmium (Cd) were selected as target pollutants to evaluate the individual and combined effects on nitrification process using four different soil types sampled from North to South China through a 56-day incubation experiment. Results and Discussion: The results demonstrated that the contaminations of OTC and Cd, especially combined pollution had significant inhibitory effects on net nitrification rates (NNRs) as well as on AOA and AOB abundance. The toxic effects of contaminants were greatly enhanced with increasing OTC concentration. AOB was more sensitive than AOA to exogenous contaminants. And the interaction effects of OTC and Cd on ammonia oxidizers were mainly antagonistic. Furthermore, Cd contaminant (with or without OTC) had indirect effects on nitrification activity via inhibiting mineral N and AOA/AOB, while OTC alone indirectly inhibited nitrification activity by inhibiting ammonia oxidizers. The results could provide theoretical foundation for exploring the eco-environmental risks of antibiotics and heavy metals, as well as their toxic effects on nitrification processes.