DTPA-extractable Cd Research Articles

Effects of Bacillus thuringiensis HC-2 Combined with Biochar on the Growth and Cd and Pb Accumulation of Radish in a Heavy Metal-Contaminated Farmland under Field Conditions.

The objective of this study was to explore the effect of heavy metal-resistant bacteria and biochar (BC) on reducing heavy metal accumulation in vegetables and the underlying mechanism. We tested Bacillus thuringiensis HC-2, BC, and BC+HC-2 for their ability to immobilize Cd and Pb in culture solution. We also studied the effects of these treatments on the dry weight and Cd and Pb uptake of radish in metal-contaminated soils under field conditions and the underlying mechanism. Treatment with HC-2, BC, and BC+HC-2 significantly reduced the water-soluble Cd (34–56%) and Pb (31–54%) concentrations and increased the pH and NH4+ concentration in solution compared with their vales in a control. These treatments significantly increased the dry weight of radish roots (18.4–22.8%) and leaves (37.8–39.9%) and decreased Cd (28–94%) and Pb (22–63%) content in the radish roots compared with the control. Treatment with HC-2, BC, and BC+HC-2 also significantly increased the pH, organic matter content, NH4+ content, and NH4+/NO3− ratio of rhizosphere soils, and decreased the DTPA-extractable Cd (37–58%) and Pb (26–42%) contents in rhizosphere soils of radish. Furthermore, BC+HC-2 had higher ability than the other two treatments to protect radish against Cd and Pb toxicity and increased radish biomass. Therefore, Bacillus thuringiensis HC-2 combined with biochar can ensure vegetable safety in situ for the bioremediation of heavy metal-polluted farmland.

Cadmium accumulation, availability, and rice uptake in soils receiving long-term applications of chemical fertilizers and crop straw return.

Fertilization and straw return have been widely adopted to maintain soil fertility and increase crop yields, but their long-term impacts on the accumulation and availability of cadmium (Cd) in paddy soils are still unconfirmed. Therefore, this study was undertaken in central China to investigate the accumulation, availability, and subsequent uptake of Cd by rice (Oryza sativa L.) in two adjacent field trials (P1 and P2, lasting for 10 and 12years, respectively) under long-term straw return or in combination with chemical fertilizers. Obvious Cd accumulation, probably due to the notable Cd input from irrigation and traffic exhaust in the bulk soil (0-20cm) of P1, was observed. The bulk soil of P2 received homogeneous straw return and chemical fertilizers, as did that of P1; however, the P2 soil almost showed Cd balance. Long-term straw return increased the portion of soil DTPA-extractable Cd to the total pool for both sites, but only P1 showed significant differences when compared to the controls. However, the highest Cd concentrations and the maximum bioconcentration factors in rice straw and grain were obtained using solo application of chemical fertilizers at both sites. Continuous additional applications of crop straw, in contrast, resulted in slightly decreased Cd uptake in rice straw, but not in grain. These findings demonstrate that neither long-term straw return nor fertilization leads directly to notable Cd accumulation, but that the promotion effects of long-term chemical fertilizer applications on Cd uptake in rice need more attention.

Characterization of phosphorus engineered biochar and its impact on immobilization of Cd and Pb from smelting contaminated soils

Biochar has been used as an amendment to immobilize toxic metals (TMs) and increase nutrient content in the contaminated soil. In this study, Ca(H2PO4)2-engineered swine manure biochar (PSMB) and swine manure biochar (SMB) were prepared and investigated to evaluate their effects on the availability of toxic metals (Cd and Pb) and soil nutrient content in Fengxian (FX)- and Kunming (KM)-contaminated soils through incubation experiment. The soil samples were collected at 0–20 cm depth from two contaminated farmlands close to abandoned Pb smelters, which are located in FX and KM. Swine manure was obtained from the rural hog lot in Yangling, China. Each biochar (SMB and PSMB) was mixed with the air-dried soil samples (FX and KM) at a dosage of 1% and 3% w/w, respectively. Then, a portion of 3 kg of the mixture was placed in plastic pots and incubated for 30 days in a greenhouse. After the soil incubation experiment, pot experiments were performed in a greenhouse of Northwest A&F University, Yangling, China. Adding PSMB at a rate of 3% maximally decreased the concentrations of DTPA-extractable Cd (34.02 and 47.73%) and Pb (18.70 and 24.58%) in FX and KM soil. The BCR data revealed that the percentage of acid-soluble Cd and Pb fraction in FX and KM soils remarkably decreased whereas the percentages of residual Cd fraction and reducible Pb fraction in FX and KM soils significantly increased in all the biochar-amended soils compared with control. To confirm these results, a pot experiment was conducted to investigate the effects of amendments on growth and uptake of toxic metals in Chinese cabbage (Brassica rapa L. spp. pekinensis). The results showed that the addition of PSMB3% significantly (P < 0.05) increased the biomass of plants and reduced the absorption of toxic metals in plant. The results revealed that the dry biomass increased and the absorption of toxic metals decreased in plants. All treatments of biochar were beneficial and application of PSMB 3% was most effective in enhancing plant biomass and reducing the accumulation of toxic metals in the plants.

A field experiment on stabilization of Cd in contaminated soils by surface-modified nano-silica (SMNS) and its phyto-availability to corn and wheat

Cd-contaminated soil is a common environmental problem. Stabilization is an effective way of in situ remediation for Cd contamination in soils, but there is a lack of information about the influences of the amendments on soil ecosystems and Cd uptake by crops, especially under field conditions. In this study, surface-modified nano-silica (SMNS) was used to stabilize a Cd-contaminated soil under field condition within one year. SMNS was mixed with Cd-contaminated soil at the dosage of 0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1%, respectively. After that, corn and wheat were sown within one year. DTPA extraction and sequential extraction were used to evaluate stabilization efficiency of SMNS to Cd. The influences of SMNS on crop yield, soil enzyme activities, and Cd accumulation in crops were also analyzed. The DTPA-extractable Cd in soil was reduced by 61.14% when the dosage of SMNS was 1%. SMNS transferred Cd to more stable fractions, with the organic-bound and residual Cd increased 148.11% and 90.52%, respectively. The addition of SMNS decreased soil dehydrogenase slightly, but its influences on soil urease, catalase, and yields of corn and wheat were negligible. More importantly, at the dosage of 1%, SMNS reduced 42.87% and 47.95% of Cd contents in corn and wheat grains, respectively. SMNS was effective in reducing the mobility of Cd in contaminated soils. These results suggest that SMNS has a great potential in the remediation of Cd-contaminated agricultural soils.

Effects of crop straw and its derived biochar on the mobility and bioavailability in Cd and Zn in two smelter-contaminated alkaline soils

In this study, comparative investigations on the effects of crop straw and its derived biochars on soil Cd and Zn mobility and availability were conducted. Crop straws (i.e. maize straw, rapeseed straw, and wheat straw) and their derived biochars were incubated with two contaminated alkaline soils (FX and TG soils) at 2.5% (w/w). The changes of soil properties like pH, EC, organic matter content, and dissolved organic matter content were investigated along with metal mobility, speciation distribution, and accumulation in ryegrass (Lolium multiflorum Lam.). Results indicated biochar, especially those were high in pH, enhanced soil pH (>0.2 units, p < 0.05), whereas a continuous reduction of soil pH was observed among treatments with crop straws. Both soil EC and the organic matter content increased with the application of both crop straws and biochars. In term of metals, Cd and Zn mobility were reduced with 6–14%/1–5% and 6–27%/7–15% reduction in the DTPA extractable Cd and Zn contents in TG and FX soil treatments, respectively. Moreover, distinct changes of metals in different fractions were also observed (acid soluble and reducible fraction → oxidizable fraction in straw treatments; acid soluble fraction → reducible soluble fraction in biochar amendments). Furthermore, the biological analysis revealed that the growth of ryegrass was promoted, but the accumulation of metals in ryegrass shoots was reduced, especially in MS700 treatment. Apart from the amendments, metal immobilization efficiencies were negatively correlated with the contamination status. Despite that, a higher rate of biochar application (>10%) could dramatically reduce the amount of available metal in soil extracts, except for Zn in FX soil treatments. This present work demonstrated that biochars, especially those produced at a higher temperature, are superior to crop straws to immobilize metals in soils. However, the remediation efficiencies were strongly restricted by soil pH and contamination status.

Use of soil amendments to reduce cadmium accumulation in rice by changing Cd distribution in soil aggregates

The objectives of this study were to investigate the response of cadmium (Cd) distribution and stability in soil aggregates as affected by applying different amendments and to understand the relationship between changes in soil aggregates and alleviation of Cd phytotoxicity to rice after amendment application. In the present study, rice (Oryza sativa L.) was cultivated on a Cd-polluted soil. Five soil amendments were applied, which are as follows: rice husk biochar (BC), Fe-added rice husk biochar (Fe-BC), attapulgite-based mixture (AM), zeolite-based mixture (ZM), and cow manure-based mixture (MM). The effect on Cd redistribution in soil and Cd accumulation in rice plant was evaluated. The results showed that the five amendments applied at the rate of 3% (w/w) significantly increased soil pH and decreased Cd mobility in soil and Cd accumulation in rice plants. The reduction rate of Cd content in rice grains ranged from 41 to 62% after amendment application. The remediation efficiency of the different amendments for decreasing Cd accumulation in rice tissues followed the order of Fe-BC > MM > BC > ZM > AM. Adding amendments promoted the formation of large aggregates (0.2-2.0mm) with more mass loading of Cd and enhanced aggregate stability. Comparatively, Fe-BC was more effective than others for remediation of acid Cd-polluted paddy soil, as a significantly decreased Cd concentration in rice grain after its application was observed. Structural equation modeling (SEM) analysis revealed that DTPA-extractable Cd in small aggregates was the main factor affecting Cd accumulation in rice grain; soil pH directly affected aggregate stability; and aggregate stability was closely related to Cd availability in different size soil particles. These results indicated that the applied amendments were effective in reducing Cd bioavailability, most likely through raising the soil pH, improving aggregate stability, and re-distributing Cd from smaller soil aggregates to larger ones.

Effect of biochars on the bioavailability of cadmium and di-(2-ethylhexyl) phthalate to Brassica chinensis L. in contaminated soils

Soil co-contamination of potentially toxic elements (PTEs) and phthalate esters has become prominent due to its potential adverse effect on human food supply. There is limited information on using wood- and animal-derived biochars for the remediation of co-contaminated soils. Therefore, a pot experiment was conducted using Brassica chinensis L. as a bio-indicator plant to investigate the effect of P. orientalis biochar and pig biochar application on the bioavailability of cadmium (Cd) and di-(2-ethylhexyl) phthalate (DEHP) and on plant physiological parameters (malondialdehyde, proline and soluble sugars). Biochar materials were applied to two soils containing low (LOC) and high (HOC) organic carbon content at rates of 0, 0.5, 1, 2, and 4%. To better understand the influence of biochar, physicochemical properties and X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), Fourier transform-infrared spectrometry (FTIR), scanning electron microscopy (SEM) were characterized. Biochar application increased soil pH, organic carbon content, and available phosphorus content. Increasing biochar application rates decreased DTPA-extractable Cd and extractable DEHP concentrations in both soils. Biochar application reduced the plant uptake of both Cd and DEHP from co-contaminated soils; the maximum reduction of Cd (92.7%) and DEHP (52.0%) was observed in 2% pig biochar-treated LOC soil. The responses of plant physiological parameters to increased biochar applications indicated that less Cd and DEHP were taken up by plants. Pig biochar was more effective (P < 0.05) at reducing the bioavailability of Cd and DEHP in both soils than P. orientalis biochar; therefore, pig biochar had greater potential for improving the quality of the crop. However, the highest application rate (4%) of pig biochar restricted plant seed germination. Key factors influencing the bioavailability of Cd and DEHP in soils were soil organic carbon content, biochar properties (such as surface alkalinity, available phosphorus content and ash content) and biochar application rates.

Effects of CO2 application coupled with endophyte inoculation on rhizosphere characteristics and cadmium uptake by Sedum alfredii Hance in response to cadmium stress

Comparative impact of CO2 application and endophyte inoculation was investigated on the growth, rhizosphere characteristics, and cadmium (Cd) absorption of two ecotypes of Sedum alfredii Hance in response to Cd stress under hydroponic or rhizo-box culture conditions. The results showed that both CO2 application and endophyte inoculation significantly (P < 0.05) promoted plant growth (fresh weight and dry weight), improved root morphological properties (SRL, SRA, SRV, ARD and RTN) and exudation (pH, TOC, TN, soluble sugar and organic acids), changed Cd uptake and distribution of both ecotypes of S. alfredii. Meanwhile soil total and DTPA extractable Cd in rhizo-box decreased by biofortification treatments. Superposition biofortification exhibits utmost improvement for the above mentioned parameters, and has potential for enhancing phytoremediation efficiency of hyperaccumulator and sustaining regular growth of non-hyperaccumulator in Cd contaminated soils.

Effects of mixed amendments on the phytoavailability of Cd in contaminated paddy soil under a rice-rape rotation system.

A field experiment was performed to study the effects of mixed amendments, namely lime + organic fertilizer (LO), lime + organic fertilizer + calcium-magnesium phosphate fertilizer (LOC), lime + organic fertilizer + sepiolite (LOS), and lime + organic fertilizer + calcium-magnesium phosphate fertilizer + sepiolite (LOCS), on the availability and uptake of Cd from contaminated paddy soil under a rice-rape (Oryza sativa L. and Brassica napus L.) rotation system. The results showed that the grain yields of rice and rape with mixed amendment-treated were slightly influenced, in that the soil pH significantly increased while the DTPA-extractable Cd content of the soil and Cd uptake by the rice and rape were significantly reduced. The uptake of Cd by brown rice decreased significantly (p < 0.05), by 55.9-59.3% and 69.6-75.5% in the 2016 and 2017 crops, respectively, compared with that of the control (CK). The Cd uptake by rapeseeds during the 2017 season observably (p < 0.05) decreased by 38.2 and 29.6% under LO and LOC treatments, respectively. The Cd concentrations in rapeseeds were 0.11-0.18mgkg-1 under all the treatments except LOCS treatment, which is lower than the National Standard of Pollutants in Food of China (GB 2762-2017, 0.2mgkg-1). From both economic and food safety standpoints, rape is recommended for Cd-contaminated soil because it has a low Cd accumulation ability. The results showed that the rice-rape rotation combined with LO or LOC application was useful for reducing the Cd content in both rice and rape in Cd-contaminated soil and the effects could be sustained at least for three crop seasons.

Soil liming effects on CH4, N2O emission and Cd, Pb accumulation in upland and paddy rice

Keeping in view the expanding environmental pollution and irrigation water deficit, a pot experiment was performed for the upland (Huyou2, Hanyou737) and paddy rice cultivars (Taigeng8; Yixiang2292), to study soil liming effects on methane (CH4) and nitrous oxide (N2O) emission, bioavailability and accumulation of Cd, Pb in upland and paddy rice. Upland rice reduced 90% of soil CH4 emission as compared to paddy conditions. Soil CH4 emission decreased by 45% and 39% with dolomite, and it reduced by 35% and 33% with lime treatment both in upland and paddy conditions, respectively. Soil N2O emission decreased by 44% and 52% with dolomite, and with the lime application, it was reduced by 37% and 44% for both upland and paddy conditions respectively. Reduction in soil DTPA-extractable Cd was between 37-53% and 43–80% with dolomite and 16–37% and 24–72% Cd decreased with lime application in upland and paddy conditions respectively. Soil DTPA-extractable Pb reduced by 27–44% and 25–53% with dolomite and 16–40% and 11–42% with soil-applied lime in upland and paddy conditions, respectively. Cd accumulation in rice grain was decreased by 47–88% and 62–79% with dolomite and 31–86% and 45–52% reduction by lime application in upland and paddy rice respectively. Rice grain Pb reduced by 58–91% and 66–78% with dolomite application and 32–71% and 44–71% with lime in upland and paddy rice, respectively. Our results showed that soil liming significantly reduced soil N2O and CH4 emission and Cd, Pb accumulation in rice grain, but dolomite was more effective as compared to lime. Altogether, results of this study suggest that upland rice can be cultivated in CdPb polluted soils with least soil CH4 emission. Cd and Pb toxicity, accumulation, and N2O emission in upland rice can be minimized by soil liming of 3 g kg−1 and optimizing the nutrients composition of the soil.

Role of compost biochar amendment on the (im)mobilization of cadmium and zinc for Chinese cabbage (Brassica rapa L.) from contaminated soil

This study aims to assess the effect of amendment of an alkaline Zn, Cd-contaminated soil with compost of wheat straw biochar (CB) (4, 8, 12, and 18%) and sludge and different dosages of nitrogen. In addition, this study aimed to substantially mitigate the bioavailability of Zn and Cd for Chinese cabbage (Brassica rapa L.) from smelter-contaminated soils. This study was based on Chinese cabbage (B. rapa L.) growth for phytoremediation of soil toxic metals (TMs) (Zn and Cd) in different dosages of CB nitrogen (50, 150, 250, and 300 kg ha−1) and soil (T1) alone as well as different nitrogen dosages (50-T18, 150-T19, 250-T20, and 300-T21 kg ha−1) of chemical fertilizer (CF). The total and bioavailability of Zn and Cd were measured in shoot and root dry weight biomass, and soil in initial and after harvesting of Chinese cabbage. The chlorophyll content, pH, electrical conductivity, cation exchange capacity, and dissolved organic carbon content were measured to understand their role for plant growth and bioavailability of Zn and Cd. The phytoremediation of Zn and Cd was estimated by diethylene triamine pentaacetic acid (DTPA)-extractable method using smelter-contaminated soils amended with four different dosages of biochar. The CB application considerably reduced the DTPA-extractable Zn from contaminated soils, while in comparison to the control and CF treatment evidently mobilized the Zn in soil by approximately 4.17%. The maximum solubility of Zn of 23.46 and 26.78% was obtained with the control and CF-applied treatments in soils, respectively. The DTPA-extractable Cd concentration became elevated with increasing CB dosage, and a significantly higher Cd concentration was recorded in T6 compared to the control and chemical fertilizer-applied treatments. In the cases of higher dosages of CB, the Zn translocation in plants from soil was evidently reduced, but a lower CB amendment increased Zn levels by 5.15% in the shoot and 4.78% in the root, respectively. The changes in the soil EC, pH, and CEC by the amendment of CB could be the main reasons for the (im)mobilization of TMs in contaminated soil. Finally, the results confirmed that the CB amendment, especially with 300 kg ha−1 nitrogen, could reduce maximum bioavailability of Zn and Cd and the ecological risk of contaminated soil with TMs.

Spatial distribution of smelter emission heavy metals on farmland soil.

This work was conducted to explore heavy metal pollution in soils in an area near lead smelters in Jiyuan City, which is one of the main lead production areas in China. Altogether, 88 topsoil samples (0-20cm) were collected from farmlands near the Yuguang lead smelting facilities; the sampling sites were 1570 to 6388m to the main stack of the Yuguang. Analysis of the samples indicated that (i) the ranges of total Cd and Pb concentrations were 0.81-4.30 and 64.5-435mgkg-1, respectively, mean pollution indices (concentration in soil/background value, PI) were 32.8 and 9.11, respectively, and the concentrations of total Cu, Zn, and Ni were slightly higher than the background values. Mean concentrations of DTPA-extractable Cd and Pb were 0.752 and 58.7mgkg-1, respectively. (ii) The total concentrations of Cd, Pb and Pb/Cd ratios of samples decreased as the distance to the main stack of the Yuguang increased. Abnormal variations of these trends suggested these parameters of certain samples were affected by pollution sources other than the Yuguang. (iii) Judged by the results of this work, the area of the heavy metal-polluted land in Jiyuan was much greater than 115km2, a value reported by an earlier investigation. These results indicate that the soil in the study area was polluted by Cd and Pb emissions from more than one polluting sources, the variation of Cd, Pb concentration and Pb/Cd ratios of samples to the distance of the pollution source can be potentially used for pollution source identification.

Comparative efficacy of organic and inorganic amendments for cadmium and lead immobilization in contaminated soil under rice-wheat cropping system

Field experiments were conducted in two consecutive rice-wheat cropping seasons on a yellow clay soil to assess the efficacy of organic and inorganic amendments for cadmium (Cd) and lead (Pb) immobilization. Amendments were applied alone and in combinations to compare their efficacy for metals immobilization. Composite amendment of GSA-4 (Green Stabilizing Agent) and biochar resulted in higher biomass and grains yield for both rice (Oryza sativa L.) and wheat (Triticum aestivum L.). Liming, DEK1 (Di Kang No. 1) or GSA-4 amendment increased soil pH from 6.34 to 7.35, 7.20 and 7.15, respectively. Soil amendments significantly reduced DTPA extractable Cd and Pb in soil at wheat harvest. Cadmium and Pb fractionation showed a significant decrease in the extractable fractions by the amendment of biochar (34% and 25%) or GSA-4 (35% and 26%, respectively). GSA-4 and biochar amendment enhanced metals immobilization and reduced their uptake by plant and subsequent accumulation in the grains of rice and wheat, particularly with GSA-4. These results indicate that GSA-4 and biochar, especially their combination, have great potential for application to remediate Cd and Pb contaminated soils.

Effectiveness of simultaneous applications of lime and zinc/iron foliar sprays to minimize cadmium accumulation in rice

Due to the large area of Cd-contaminated paddy soils worldwide, low-cost measures to reduce the accumulation of Cd in rice plant are necessary. A field experiment was therefore conducted to investigate the reducing effect of lime combined with foliar applications of Zn (ZnSO4) or Fe (EDTA·Na2Fe) on Cd concentrations in brown rice on a Cd-contaminated paddy soil. The results indicated that liming alone or in combination with foliar sprays of Zn or Fe increased the soil pH by 0.27–0.63 units. However, limited effects of lime or lime combined with foliar applications of Zn/Fe on soil DTPA-extractable Cd, rice grain and rice straw biomass were observed. Liming alone significantly reduced the Cd concentration in brown rice and rice straw by 31.8% and 42.3%, respectively. The Cd concentrations in brown rice decreased by 25.5% and 65.4% and in rice straw by 53.0% and 68.1% after liming combined with foliar applications of Fe and Zn, respectively. In contrast, liming combined with foliar spraying of Fe significantly increased the transfer ratio of Cd from the rice straw to the grain. As a low-cost technique, lime application combined with foliar application of ZnSO4 could be recommended for the remediation of Cd-contaminated paddy soils.

Evaluation of cadmium transfer from soil to leafy vegetables: Influencing factors, transfer models, and indication of soil threshold contents

Food chain contamination by soil cadmium (Cd) through leafy vegetable consumption poses a threat to human health. It is imperative to understand the relationship between Cd phytoavailability in soils and its uptake in common leafy vegetables. A large-scale field survey in Zhejiang Province, southeast China, was conducted to develop models to evaluate the Cd phytoavailability to leafy vegetables based on soil properties and to establish soil Cd thresholds based on food safety. The empirical models developed in this study explained the combined effects of soil properties and diethylenetriaminepentaacetic acid (DTPA)-extractable Cd content on Cd phytoavailability to leafy vegetables. The Cd accumulation in celery, pak choi, and amaranth was quantitatively predicted by measurement of DTPA-extractable soil Cd and soil pH, organic matter, cation exchange capacity and clay content. For predicting Cd accumulation, the DTPA-extractable Cd, pH and clay content had a major influence in lettuce; and for water spinach, the DTPA-extractable Cd, pH, and cation exchange capacity had a major influence. Soil DTPA-extractable Cd was suitable to be used as Cd thresholds in soils cultivating celery, amaranth, pak choi, lettuce, and water spinach, with values of 0.24, 0.13, 0.23, 0.32, and 0.37 mg kg−1, respectively. However, the threshold values of soil total Cd were 0.26, 0.34, and 0.83 mg kg−1 for amaranth, celery, and pak choi fields, indicating that the current soil quality standard (GB 15618-1995) for soils cultivating different types of vegetables could be overestimated or underestimated for Cd contamination and the associated risk. This study will provide a useful reference for controlling Cd contamination in common leafy vegetables and developing sustainable production of leafy vegetables.

Effect of sulfur-iron modified biochar on the available cadmium and bacterial community structure in contaminated soils

Cadmium contamination in paddy soils has aroused increasing concern around the world, and biochar has many positive properties, such as large specific surface areas, micro porous structure for the heavy metal immobilization in soils. However there are few studies on sulfur-iron modified biochar as well as its microbiology effects. The purpose of this study was to evaluate the Cd immobilization effects of sulfur or sulfur-iron modified biochar and its related microbial community changes in Cd-contaminated soils. SEM-EDX analysis confirmed that sulfur and iron were loaded on the raw biochar successfully. Sulfur-modified biochar (S-BC) and sulfur-iron modified biochar (SF-BC) addition increased pH value and the content of soil organic matter, and also decreased DTPA-extractable Cd. There was a negative significant correlation between organic matter content and the available Cd (P < 0.05). During a 45-d incubation period, the fractions of Cd are mainly with the exchangeable (25.16–35.79%) and carbonate (22.01–25.10%) fractions. Compared with the control, the concentrations of exchangeable Cd in soil were significantly (P < 0.05) decreased by 12.54%, 29.71%, 18.53% under the treatments of BC, S-BC, SF-BC respectively. The S-BC and SF-BC treatments significantly (P < 0.05) increased Chao1, observed, Shannon and Simpson diversity indices compared with the control and biochar treatments. Meanwhile, the relative abundance of Proteobacteria, Bacteroidetes, and Actinobacteria increased, whereas the abundance of Acidobacteria and Germmatimonadetes decreased.Capsule: Sulfur-modified and sulfur-iron modified biochar applications decreased the available Cd and changed the microbial community.

Metal-immobilizing Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 increase biomass and reduce heavy metal accumulation of radish under field conditions

In this study, metal-tolerant bacteria Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 were compared for their Cd and Pb immobilization in solution and impacts on biomass and Cd and Pb uptake in a radish in metal-contaminated soils under field conditions. Strains CL-1 and X30 significantly reduced water-soluble Cd and Pb concentrations (45–67%) and increased the pH in solution compared to the controls. These strains significantly increased the biomass (25–99%) and decreased edible tissue Cd and Pb uptake in the radish (37–81%) and DTPA-extractable Cd and Pb contents (18–44%) of the rhizosphere soil compared to the un-inoculated controls. Strain CL-1 had higher potential to reduce edible tissue Cd and Pb uptake in the radish and DTPA-extractable Cd content than strain X30. Also, these strains significantly increased Cd translocation factor and strain CL-1 also significantly increased Pb translocation factor of the radish. Furthermore, strain CL-1 significantly increased the ratio of small soil aggregates (< 0.25 mm and 0.25–0.50 mm) of the rhizosphere soil. The results showed that these strains reduced the edible tissue Cd and Pb uptake through decreasing Cd and Pb availability in the soil and increasing Cd or Pb translocation from the roots to the leaves of the radish. The results also suggested the bacteria-related differences in reduced heavy metal uptake in the radish and the mechanisms involved under field conditions.

Effect of Calcium Silicate-biological Humus Fertilizer Composite on Uptake of Cd by Shallots from Contaminated Agricultural Soil

The safety of vegetable production is a key link in reducing cadmium consumption through the food chains. Field experiments were conducted to investigate the effects of composite materials (calcium silicate-biological humus fertilizer) on the growth of shallots and the uptake of Cd by shallots from contaminated agricultural soil. Four treatments (T1: 0.5% calcium silicate+0.5% biological humus fertilizer; T2: 0.5% calcium silicate+1.0% biological humus fertilizer; T3: 1.0% calcium silicate+0.5% biological humus fertilizer; and T4: 1.0% calcium silicate+1.0% biological humus fertilizer) and a control group (CK) were adopted. The changes in soil pH, DTPA-extractable Cd, biomass of shallots, and cadmium concentrations in shallots over time under different treatments were analyzed. The results show that the application of composite amendments decreased the concentrations of DTPA-extractable Cd in the soil. In particular, after T3 treatment, the concentrations of soil DTPA-extractable Cd decreased by 60.71%, 49.54%, 44.63%, and 58.94% after 14, 28, 42, and 56 d, respectively. The biomass of the shallots aboveground increased significantly by 107.99% and 107.19% after T3 and T4 treatment, respectively. The composite amendments exhibited different effects on the uptake of Cd by the shallots from the soil, and the T4 treatment was the most effective in immobilizing Cd and inhibiting translocation of Cd into the shallots. The cadmium concentration in the shallots decreased by 43.80% after 56 d with the T4 treatment. In conclusion, T4 is the optimum treatment for soil cadmium immobilization.

Increased biomass and reduced rapeseed Cd accumulation of oilseed rape in the presence of Cd-immobilizing and polyamine-producing bacteria

Two Cd-immobilizing and polyamine-producing bacteria Serratia liquefaciens CL-1 and Bacillus thuringiensis X30 were characterized for their effects on Cd immobilization, pH, and polyamine production in the solution and the rapeseed biomass and Cd uptake of Brassica napus Qinyou-10 in Cd-contaminated soil. These strains significantly increased pH and reduced water-soluble Cd concentration (25–76%) compared to the controls. Furthermore, strain CL-1 produced more polyamine (71–192%) in the solution than strain X30. Cell surface absorbed Cd content was increased by 23-56% in the presence of strain CL-1 compared to strain X30. The strains significantly increased the rapeseed biomass (12–32%), pH, polyamine content (70–244%), and relative abundance (21-49%) of arginine decarboxylase-producing bacteria (ADPB) of the rhizosphere soils but decreased DTPA-extractable Cd content and rapeseed Cd uptake compared to the controls. Notably, strain CL-1 had higher ability to reduce the rapeseed Cd and DTPA-extractable Cd contents and increase the abundance of ADPB than strain X30. Our results showed the distinct impact of these strains on the rapeseed Cd uptake and available Cd content and suggested that these strains reduced the available Cd and rapeseed Cd uptake by increasing the cell adsorption of Cd, abundance of ADPB, polyamine production, and pH in the rhizosphere soils.

Effects of biochar and nitrogen addition on nutrient and Cd uptake of Cichorium intybus grown in acidic soil

ABSTRACTBiochar is an organic amendment used for soil remediation, there are only a few studies documenting the effects of nitrogen on the role of biochar in contaminated soils. A pot experiment was conducted to investigate the impacts of biochar (0%, 1%, and 2.5%, w/w) and nitrogen (0, 100, and 200 mg N kg−1) on plant growth, nutrient and cadmium (Cd) uptake of Cichorium intybus. N, P, Ca, Mg, and Cd concentrations increased with N level in 0% and 1% biochar treatments. In plants treated with 2.5% biochar, 200 mg N kg−1 addition caused significant reductions of N, P, Ca, Mg, and Cd concentrations in comparison to 100 mg N kg−1 treatments. Nitrogen promoted shoot biomass at all biochar treatments, while biochar had no effect on shoot biomass in 0 and 200 mg N kg−1 addition treatments. Nitrogen also significantly increased N, P, K, Ca, Mg, and Cd contents in the 0% and 1.5% biochar addition treatments. Although soil DTPA-extractable Cd concentration showed the lowest values in 1% biochar in combination with 100 and 200 mg N kg−1 addition treatments, lowest shoot Cd concentration, and relatively high shoot biomass occurred in the 2.5% biochar + 200 mg N kg−1 treatment. Based on these results, biochar application at its highest rate (2.5%) in combination with high N supply (200 mg N kg−1) contributed to both crop yield and agricultural product safety. N input alone might increase the risk of human health, and the optimum N dose should be determined during phytostabilization process.