Bioavailability Of Cd Research Articles

Combined effects of zinc oxide nanoparticles and melatonin on wheat growth, chlorophyll contents, cadmium (Cd) and zinc uptake under Cd stress

Zinc oxide nanoparticles (ZnONPs) and melatonin (MT) have been known to regulate heavy metal toxicities in plants in some studies, the effect of their combined use on cadmium (Cd) uptake by wheat (Triticum aestivum L.) and underlying mechanisms is largely unknown. Thus, plant growth, uptake and translocation of Cd mediated by soil applied ZnONPs and foliar applied MT were investigated in wheat grown in Cd polluted soil under ambient conditions. The results depicted that ZnONPs stimulated the growth, chlorophyll contents, and yield of wheat in a dose additive way and this effect was further increased with foliar application of MT. 100 mg/kg of ZnONPs alone enhanced the grain yield by 60.5 % and this increase was about 177.5 % under combined ZnONPs and 100 μM MT treatment. ZnONPs treatments decreased Cd concentration whereas increased zinc (Zn) concentrations in shoots, roots, husks and grains and the effect was further increased with exogenous MT combined with NPs in a dose-additive way. 50 and 100 mg/kg ZnONPs treatments alone decreased grain Cd by 6.5 %, and 20 % and increased the Zn concentration by 20.1 % and 24 % than control. 100 mg/kg ZnONPs +100 μM MT treatment decreased the grain Cd by 63.5 % and increased grain Zn by 51 % than control treatment. Total Cd uptake (tissues biomass × Cd concentration in respective tissues) in shoots, roots, husks and grains increased with ZnONPs alone or combined with MT than control whereas soil post-harvest bioavailable Cd concentration decreased with treatments than control. The Cd reduction in grains was due to increase in biomass and Zn concentration thereby decreasing bioavailable Cd in soil and its accumulation in plants. This study suggested that combined use of ZnONPs and MT may provide new approaches for minimizing Cd and biofortification of Zn in edible parts of plants.

Polyethylene and poly (butyleneadipate-co-terephthalate)-based biodegradable microplastics modulate the bioavailability and speciation of Cd and As in soil: Insights into transformation mechanisms

Microplastics (MPs) that enter the soil can alter the physicochemical and biochemical properties of soil and affect speciation of heavy metals (HMs), thereby perturbing the bioavailability of HMs. However, the mechanisms underlying these effects are not understood. Therefore, we investigated the effects of MPs from poly (butyleneadipate-co-terephthalate)-based biodegradable mulch (BM) and polyethylene mulch (PM) in Cd- or As-contaminated soil on soil properties and speciation of HMs. MPs were characterised using Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The addition of MPs reduced the bioavailability of HMs in soil and promoted the transformation of HMs into inert fractions. The mechanisms underlying the reduction of the bioavailability of HMs in soils could be as follows: (1) the entry of MPs into the soil changed its properties, which reduced the bioavailability of HMs; (2) FTIR and XPS analyses revealed that the hydroxyl and carboxyl groups and benzene ring present on the surface of aged MPs stabilized complexes (As(V)-O) with As(V) may have directly reduced the bioavailability of As(V) in soil; (3) aged BM exposed more amounts and types of reactive functional groups and was more effective in stabilising soil HMs than PM. Overall, this study provides new insights regarding the complexation mechanisms of soil HMs by MPs from different plastic mulch sources.

Characteristics and DGT Based Bioavailability of Cadmium in the Soil-Crop Systems from the East Edge of the Dongting Lake, China.

Contamination of heavy metals (including the cadmium, Cd) in agricultural soils has become an increased issue, posing a threat to the crop safety and human health. In order to evaluate the contamination characteristics and bioavailability of Cd in the soil−crop systems from the East edge of the Dongting Lake, four kinds of agricultural products for typical crops (rice, peanut, sweet potato, and corn) and corresponding rhizosphere soils were collected and analyzed for the Cd concentrations. The technique of diffusive gradients in thin-films (DGT) was applied to evaluate the Cd bioavailability in the rhizosphere soils. Concentrations of Cd ranged from 0.04 to 2.95 mg/kg (average 0.24 mg/kg) with 73.9% sites above the background levels, especially for paddy soils. Cd concentrations in the agricultural products ranged from 0.01 to 2.19 mg/kg (average 0.18 mg/kg), with Cd enrichment observed in the peanut samples. No obvious correlations (R2 < 0.25) were observed between the Cd concentrations in the agricultural products and total Cd concentrations in the rhizosphere soils, this indicated that the total Cd concentrations in the soils cannot predict the concentrations in the agricultural products of crops. While the DGT measured Cd concentrations showed good correlations (R2 = 0.64−0.90) with the concentrations in the most agricultural products of crops, which may be used to evaluate the safety of the soil and further safety of the agricultural products of crops. Overall, DGT showed a good potential for prediction of heavy metal bioavailability in soil since the DGT technique can simulate the sustained supply of heavy metals from solid to liquid in the soils.

Enhanced removal of arsenic and cadmium from contaminated soils using a soluble humic substance coupled with chemical reductant

Soil washing is an efficient, economical, and green remediation technology for removing several heavy metal (loid)s from contaminated industrial sites. The extraction of green and efficient washing agents from low-cost feedback is crucially important. In this study, a soluble humic substance (HS) extracted from leonardite was first tested to wash soils (red soil, fluvo-aquic soil, and black soil) heavily contaminated with arsenic (As) and cadmium (Cd). A D-optimal mixture design was investigated to optimize the washing parameters. The optimum removal efficiencies of As and Cd by single HS washing were found to be 52.58%–60.20% and 58.52%–86.69%, respectively. Furthermore, a two-step sequential washing with chemical reductant NH2OH•HCl coupled with HS (NH2OH•HCl + HS) was performed to improve the removal efficiency of As and Cd. The two-step sequential washing significantly enhanced the removal of As and Cd to 75.25%–81.53% and 64.53%–97.64%, which makes the residual As and Cd in soil below the risk control standards for construction land. The two-step sequential washing also effectively controlled the mobility and bioavailability of residual As and Cd. However, the activities of soil catalase and urease significantly decreased after the NH2OH•HCl + HS washing. Follow-up measures such as soil neutralization could be applied to relieve and restore the soil enzyme activity. In general, the two-step sequential soil washing with NH2OH•HCl + HS is a fast and efficient method for simultaneously removing high content of As and Cd from contaminated soils.

The Status and Research Progress of Cadmium Pollution in Rice- (Oryza sativa L.) and Wheat- (Triticum aestivum L.) Cropping Systems in China: A Critical Review.

The accumulation of cadmium in rice (Oryza sativa L.) and wheat (Triticum aestivum L.) is a serious threat to the safe use of farmland and to the health of the human diet that has attracted extensive attention from researchers. In this review, a bibliometric analysis was performed using a VOS viewer (1.6.18, Netherlands) to investigate the status of cadmium contamination in rice and wheat growing systems, human health risks, mechanisms of Cd uptake and transport, and the corresponding research hotspots. It has a certain reference value for the prevention and control of cadmium pollution in rice and wheat planting systems in China and abroad. The results showed that the Cd content in rice and wheat planting systems in the Yangtze River Basin was significantly higher than that in other areas of China, and the Cd content in rice and wheat grains and the hazard quotient (HQ) in Hunan Province was the highest. The average Cd concentration exceeded the recommended limit by about 62% for rice and 81% for wheat. The main reasons for the high Cd pollution in rice and wheat growing areas in Hunan are mining activities, phosphate fertilizer application, sewage irrigation, and electronic equipment manufacturing. In this review, we demonstrate that cadmium toxicity reduces the uptake and transport of essential elements in rice and wheat. Cadmium stress seriously affected the growth and morphology of plant roots. In the shoots, Cd toxicity was manifested by a series of physiological injuries, such as decreased photosynthesis, soluble protein, sugar, and antioxidant enzyme activity. Cadmium that accumulates in the shoots is transferred to grains and then passes up the food chain to people and animals. Therefore, methods for reducing cadmium content in grains of rice and wheat are urgently needed, especially in Cd-contaminated soil. Current research on Cd pollution in rice and wheat planting systems focuses on the bioavailability of Cd, soil rhizosphere changes in wheat and rice, and the role of antioxidant enzyme systems in alleviating heavy metal stress in rice and wheat.

Combined toxicity of Cd and 2,4-dichlorophenoxyacetic acid on the earthworm Eisenia andrei under biochar amendment.

Due to anthropogenic activities, various pollutants can be found in agricultural soil, such as cadmium (Cd) and 2,4-dichlorophenoxyacetic acid (2,4-D). They are highly toxic and can have a negative impact on soil fertility. For remediation strategies, biochar has acquired considerable attention due to its benefits for agriculture. However, we should recognize the ecological risk posed by biochar use. In addition, little is known about its non-desirable effects on soil organisms such as earthworms, especially in the case of soil remediation. In this study, earthworms (Eisenia andrei) were exposed to soil contaminated with Cd (0.7mg/kg), (2,4-D) (7mg/kg), and a mixture of the two in the presence and absence of biochar (2%). A 7- and 14-day incubation experiment was carried out for this purpose. Cd and 2,4-D uptakes in earthworms' tissues, oxidative stress, cytotoxic response, DNA damage, histopathological changes, and gene expression level were assessed. Results suggested that biochar increased the bioavailability of Cd and 2,4-D and the frequency of micronuclei (MNi) and decreased the lysosomal membrane stability (LMS) in earthworms. Also, histopathological examination detected numerous alterations in animals exposed to the contaminants without any amelioration when biochar was added. The biochemical response of earthworms in terms of oxidative stress demonstrates that in the presence of biochar, animals tend to alleviate the toxicity of Cd and 2,4-D. This was also supported by transcriptomic analyses where expression gene levels related to oxidative stress were upregulated in earthworms exposed to Cd and 2,4-D + biochar. The present investigation brought new insights concerning the use of biochar in agriculture.

Catalytic modification of corn straw facilitates the remediation of Cd contaminated water and soil

Turning postharvest residue into high-value-added products is crucial for agricultural waste management and environmental remediation. In this proof-of-concept study, nanosized Pt/TiO2 was used as a model catalyst to modify corn straw (CS) materials through a simple low-temperature oxidation process. This method was demonstrated to be self-sustainable, waste-free, and with high yields. At an optimal temperature of 220 °C, O2 treatment with 1 wt% Pt/TiO2 greatly changed ultra-micropore and mesopore structures, dissolved organic carbon, aromatic contents and surface oxygen (O)-containing functional groups in CS products. This treatment resulted in an approximately 5-fold increase of cadmium (Cd) adsorption from aqueous solution and immobilization rate of 43.1% at 7d for bioavailable Cd in soil. Spectroscopic and linear regression analysis demonstrated that both acidic and basic functional groups in CS contributed to Cd adsorption, suggesting chemical adsorption. According to the d-band theory, the unexpected role of catalysts in CS modification could be associated with dissociative adsorption of molecular O2 on the Pt surface. These results provide insights for the development of economic and sustainable technologies to reutilize agricultural waste biomass for water and soil remediation.

Enhancing the effect of biochar ageing on reducing cadmium accumulation in Medicago sativa L

Biochar (BC) application to farmland soil can reduce the mobility and bioavailability of Cd. Nevertheless, BC is prone to natural ageing in soil, which alters its structure, physicochemical properties, thereby affecting the immobilisation of Cd. We used dry–wet and freeze–thaw cycles to mimic the natural ageing of BC, and used adsorption experiments to explore the changes of Cd adsorption capacity of BC and aged BC (ABC). We conducted a pot experiment to investigate the effects of BC and ABC on soil biotic and abiotic factors, alfalfa growth, and Cd accumulation in agricultural soils with high and low Cd concentrations. The increase of specific surface area, pore size, oxygen containing functional groups and mineral composition leads to better adsorption capacity of ABC. The adsorption of Cd(II) by BC and ABC is mainly by monolayer adsorption and chemical adsorption. Applying BC and ABC to Cd-contaminated soil significantly increased the aboveground biomass and decreased the Cd accumulation by reducing the Cd bioconcentration factor in alfalfa. At high Cd levels, adding BC and ABC reduced the Cd content in alfalfa shoots by 32.8 % and 35.1 %, respectively; the fixing effect of ABC was better than that of BC. Adding BC and ABC significantly increased the microbial biomass and geometric mean of enzymes. BC addition increased soil pH by 0.32–0.36 units and cation exchange capacity (CEC) by 15.5 %. Adding BC and ABC significantly increased soil organic matter (SOM) by 5.7 % and 6.2 %, respectively. Random forest analysis showed that SOM, total organic carbon, and fluorescein diacetate hydrolase were important variables for Cd content in alfalfa shoots. Structural equation modelling showed that BC indirectly affected the Cd content in alfalfa shoots by affecting soil pH, CEC, SOM, microbial biomass, and microbial metabolic activity. BC has a long-term effect on alleviating Cd pollution in farmland.

Impacts of magnetic biochar from reed straw on anaerobic digestion of pigment sludge: Biomethane production and the transformation of heavy metals speciation

The effects of magnetic biochar (MBC) on the anaerobic digestion efficiency of pigment sludge and the passivation of heavy metals Cd, Pb were investigated. MBC participated in the dual direct interspecies electron transfer effects of biochar and Fe3O4, improved the anaerobic digestion efficiency. Compared with the control group, the maximum volatile fatty acids (VFAs) concentration, the VS (volatile solids) removal rate, cumulative methane production, average daily methane production, and average daily methane production rate increased by 51.4 %, 37.8 %, 56.3 %, 56.3 %, 37.2 %, respectively. Moreover, MBC addition signally reduced the distribution rate of the bioavailable state of heavy metals in the pigment sludge and improved the passivation efficiency. Compared with the feedstock, the mass ratios of exchangeable and reducible Cr were reduced by 43.6 % and 61.6 %, and the corresponding ratios of Pb were reduced by 41.0 % and 59.2 %, respectively. The results indicate MBC could improve the efficiency of the anaerobic digestion of pigment sludge and reduce the bioavailability of heavy metals Cd and Pb.

Heavy metals speciation in surface sediments of the Cross River Estuary, Gulf of Guinea, South East Nigeria.

The speciation of heavy metals (Ni, Cr, Cu, Zn, Pb, and Cd) was studied in surface sediments of the Cross River Estuary (CRE), Gulf of Guinea, South East Nigeria. Pb (~56%), Cd (~71%), Zn (~67%), and Cr (~76%) were mainly available in non-residual phases, suggesting potential bioavailability. High contents of Ni and Cu in residual phase indicated immobilization of these metals in aluminosilicate minerals. Cd was the most polluted heavy metal with the highest bioavailability risk. Bayesian Network model results revealed that sedimentary organic carbon (OC) from terrestrial C3 plants controlled the contents and variability of Pb and Zn, while the input of terrestrial soil OC strongly influenced Cu and Ni. However, Cd and Cr were dominantly influenced by sediment pH, while Ni was mainly influenced by sediment salinity. Strong interdependency between Cd and total nitrogen (TN) suggested that nitrogen might increase Cd bioavailability upon release from sediments.

Pinus halepensis in Contaminated Mining Sites: Study of the Transfer of Metals in the Plant-Soil System Using the BCR Procedure.

The study aimed at evaluating the geochemical fractions of Zn, Pb, Cd and their bioavailability in soil in-depth and around the root of Pinus halepensis grown on heavily contaminated mine tailing in south-western Sardinia, Italy. The contaminated substrates were partly investigated in a previous study and are composed of pyrite, dolomite, calcite, quartz, gypsum, barite, iron-sulfate and iron-oxide. The geochemical fractions and bioavailability of Zn, Pb and Cd were measured through the BCR extractions method. Cadmium in the superficial contaminated substrates was mainly found in the exchangeable BCR fraction. Zinc and lead were often found in the residual BCR fraction. PCA confirmed that the uppermost alkaline-calcareous layers of mine waste were different with respect to the deeper acidic layers. We demonstrated that Pb and Zn were less present in the exchangeable form around the roots of P. halepensis and in soil depth. This can be due to uptake or other beneficial effect of rhizospheres interaction processes. Further studies will shed light to confirm if P. halepensis is a good candidate to apply phytostabilization in mine tailing.

Effects of stabilizing materials on soil Cd bioavailability, uptake, transport, and rice growth

Cadmium, a widespread toxic heavy metal in farmland soils, is harmful to human health. A field experiment was conducted to investigate the effects of biochar and biochar-based fertilizers on soil pH, organic matter, and available Cd, as well as rice Cd uptake and translocation. The results showed that rice biomass was significantly increased after both the application of biochar and high rate of biochar-based fertilizers at the tillering stage. The biomass and plant height of rice were improved at filling and maturity stages. Soil pH was significantly increased with the application of biochar but not with the biochar-based fertilizer. The amendments of biochar and biochar-based fertilizers had no significant (p &amp;lt; 0.05) influence on soil organic matter content. The concentration of available Cd in soil and the concentration of Cd in rice were decreased with the application of different amounts of biochar and biochar-based fertilizers in the mature stage. However, this effect was much greater under biochar amendment. Compared to the control, the concentration of available Cd in soil was reduced by 33.09% with the low application rate of biochar, while that was reduced by 18.06% with the high application rate of biochar. The lowest bioaccumulation factor was due to the high concentration of biochar and biochar-based fertilizers. It is concluded that biochar and biochar-based fertilizers particularly at a high addition rate are appropriate for decreasing Cd mobility and improve soil quality for contaminated paddy soils. The study showed a method for the safe production of rice in Cd-polluted farmlands by using a high application rate of biochar or carbon-based fertilizers.

Different nanobubbles mitigate cadmium toxicity and accumulation of rice (Oryza sativa L.) seedlings in hydroponic cultures

Cadmium (Cd) contamination can pose a severe threat to food production and human health. The accumulation of Cd in rice will decrease rice biomass, photosynthetic activity, and antioxidant capacity, affecting crop yield. The effects of different nanobubbles on the growth and Cd accumulation of rice seedlings under hydroponic conditions were investigated in this study. The results showed that the biomass, photosynthetic pigment content, and antioxidant enzyme activity of rice seedlings decreased when treated with Cd alone and that Cd induced lipid peroxidation in rice seedlings. However, when different types of nanobubbles were introduced into the nutrient solution, the bioavailability of Cd in the solution was reduced. As a result, the Cd content in rice was significantly decreased compared to treatment with Cd alone. Nanobubbles increased the biomass of rice, enhanced photosynthesis, and improved the antioxidant capacity of rice by increasing antioxidant enzyme activities to alleviate Cd-induced oxidative stress. At the same time, nanobubbles increased the Fe content in rice, which decreased the Cd content, as Cd is antagonistic to Fe. In conclusion, these results suggested that nanobubbles are a potential method of mitigating Cd stress that may help to improve rice yield and could be further explored in production.

Effects of landscape restoration on migration of lead and cadmium at an abandoned mine site

Abandoned lead and zinc (Pb/Zn) mining wastes represent a serious environmental hazard because heavy metals (e.g., Pb and Cd) are continuously released into the environment, threatening ecological and human health. This study was devoted to investigate the stability of Pb and Cd in the soil at an abandoned Pb/Zn mine site after landscape restoration by five-year monitoring. Chemical extraction was applied to measure the distribution of metals. The results showed that the bioavailability of Pb and Cd in soil increased, during the accumulation of soil organic matter of about seven g/kg, and that the soil pH value decreased from 4.82 to 4.44. Soil organic matter and soil pH significantly affected the distribution of metals. Long-term afforestation can lead to continuous soil acidification. There was a significant negative correlation between the carbonate-bound state distribution and soil pH. With the decrease in pH, the decomposition of carbonates was promoted, and relative abundances of Pb and Cd in the distribution associated with the fulvic and humic complex of organic matter increased by 0.54% and 3.17%, respectively. Pb and Cd showed different migration behavior in pine. Compared with Cd, Pb was more concentrated in roots. These results have important implications for the long-term sustainable management of forests formed by the phytostabilization of contaminated soil.

Effectiveness of Passivator Amendments and Optimized Fertilization for Ensuring the Food Safety of Rice and Wheat from Cadmium-Contaminated Farmland

The effect of various soil amendments on cadmium (Cd)-contaminated farmland was evaluated in terms of effectiveness, safety, economics, and simplicity. Experiments were conducted in May 2020, on Cd-contaminated land in Tong Ling, An Hui, China. The efficacy of optimized fertilization and heavy metal passivators—gypsum, bamboo charcoal, lime, and a compound passivator (mixture of bamboo charcoal, silicon fertilizer, gypsum, furfural residue, plant ash, and chicken manure)—was evaluated as amendments to reduce the uptake of Cd in rice. The results indicate that all treatments reduced the Cd bioavailability in Cd-contaminated soil and rice grain Cd accumulation to levels that meet national food safety standards. Moreover, the rice yield increased by 4.80 to 14.27% and the Cd content in rice grains decreased by 23.53 to 36.83%. The efficacy of Cd reduction in rice was as follows: optimized fertilization &gt; lime &gt; compound passivator &gt; bamboo charcoal &gt; gypsum powder. Wheat was planted after the rice season to test the effect of the soil amendment measures implemented during the rice season on crop growth in the next season. Wheat yield improved by 3.46 to 10.96%, and the grain Cd content decreased by 6.47 to 41.03%. The efficacy of Cd reduction in wheat was as follows: lime &gt; compound passivator &gt; optimized fertilization &gt; gypsum powder &gt; bamboo charcoal. Following the lime treatment, the wheat grain Cd content met national food safety standards. A comprehensive comparison was conducted to evaluate the safe utilization and economic effect of the passivator and optimized fertilization. The results reveal that optimized fertilization was the most effective treatment. The findings from this study provide a scientific basis for safe rice–wheat rotation systems on mildly Cd-contained farmland (0.3 mg/kg &lt; Cd &lt; 1.0 mg/kg) in the Yangtze River Basin.

Assessment of Bacillus subtilis applied in rice-crayfish coculture system on physicochemical properties, microbial sulfur cycling, Cd accumulation and bioavailability

Bacillus subtilis is frequently used commercially in rice-crayfish coculture system (RCCS) to modify the physicochemical characteristics of soil and water. However, given the intensification of cadmium (Cd) contamination in RCCS and potential implications for food safety, the impacts of this modulation on the Cd bioavailability and accumulation need to be more thoroughly assessed. Here, B. subtilis was inoculated into RCCS containing different levels of soil Cd through an outdoor mesocosm experiment. Results showed that the abundance of B. subtilis in the soil was highest on the 1st day after inoculation and appeared the second peak on the 2nd week. 40–128-fold increase in B. subtilis abundance in crayfish intestines was found in the B. subtilis added groups compared to the non-B. subtilis added groups. Additionally, the Cd accumulation in crayfish and rice tissues rose significantly when the soil Cd content raised. However, with the improvement of soil pH, oxidation-reduction potential (ORP), nitrification potential (NP), acid volatile sulfide (AVS) and sulfur reducing bacteria abundance, and the decrease of organic matter (OM) at 2 W and 8 W, the addition of B. subtilis into RCCS with various Cd contents significantly reduced the Cd accumulation and the soil Cd bioavailability. The low bioavailability of Cd was characterized by the reduction of exchangeable Cd (EXC-Cd) and the grows of Fe–Mn oxides bound Cd (FeMnOx-Cd) and residual Cd (RES-Cd). Specifically, the soil EXC-Cd was negatively correlated with soil pH (−0.647), OPR (−0.663) and NP (−0.811). In short, the obtained results demonstrated that B. subtilis was able to stabilize the physicochemical properties of soil and water in RCCS, while mineralizing Cd and attenuating Cd accumulation in the crayfish and rice, suggesting that B. subtilis can be used as a cleaning probiotic applied in rice and aquatic animals coculture system.

Optimal remediation strategies for simultaneously immobilizing arsenic and cadmium using combination of vermicompost and zero-valent iron in two soil types

Arsenic and cadmium co-contamination has attracted extensive attention in agriculture, application of organic–inorganic combined amendments has been proven as an effective mean of remediation. But research about the effective remediation strategy for different soils is limited. In this study, mixture of vermicompost (VC) and zero-valent iron (Fe 0 ) in different ratios (1:1,V1F1; 2:1, V2F1; 5:1, V5F1) were selected as amendments to reduce bioavailability of As and Cd in paddy soil and laterite through the water spinach ( Ipomoea aquatica Forsk) pot experiments. The untreated soil and soil treated with individual VC and Fe 0 were designed as controls. Application of the combined amendments simultaneously decreased the soil available As and Cd by 15.5%–30.6% in paddy soil and 17.4%–21.7% in laterite. As- and Cd-absorbance in shoot of water spinach decreased by 43.5%–72.0% in paddy soil and 29.3%–47.6% in laterite. The combined amendments also significantly improved the soil properties (pH, OM, CEC, enzyme activity) and promoted the plant growth (biomass, height, SPAD values). Structural equation modelings (SEMs) revealed that Fe 0 played a more important role in lowering As bioavailability by directly reducing migration and availability of soil As, while VC played a more important role in lowering Cd bioavailability by improving soil properties and yield. Calculating from SEMs, in the combined amendments, the total effects of Fe 0 on reducing shoot As was −0.84 and −0.28, the total effects of VC on reducing shoot Cd was −0.67 and −0.93, in paddy and laterite, respectively. Taken together these observations, V1F1 was effective in the remediation of paddy soil with high As concentration, V2F1 was effective in the remediation of laterite with high Cd concentration and acidic property. This work provide clear remediation strategies for different As and Cd co-contaminated soils, but large scale field experiments are still needed to verify the strategies in the future. • Combination of VC and Fe 0 were used as amendment agents. • The effectiveness of VC and Fe 0 on As and Cd phytotoxicity were quantified by SEMs. • VC and Fe 0 affected the migration of As and Cd through different pathways. • V1F1 was optimal for paddy soil with high As concentration. • V2F1 was optimal for laterite with high Cd concentration and acidic nature.

Remediation of Cadmium and Lead in contaminated soils by a newly modified fly ash material: The possibility and safety

Heavy metal (HM) contamination in soils harms the organisms through the food chain. A large number of methods have been used to alleviate soil pollution. However, there is a lack of information about soil security after amendments. A new material, modified fly ash (MFA), was developed by a low-temperature and alkali calcination technology, and explored the possibility and safety for remediation of lead (Pb) and Cadmium (Cd) contaminated soils. The remediation efficiency was studied through pots experiments. To ensure accuracy, soils were collected in three different areas; a similar material, zeolite (ZO), known for its good remediation of HMs, was introduced for comparison. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Brunauer–Emmett–Teller (BET) were introduced to better understand the repair mechanism; the soil pH, the concentration of Cd and Pb in soil and plant, soil enzyme activity were detected to explore the possible and safety of MFA. The main remediation mechanisms may be ion exchange, surface affinity and complexation. The MFA reduces the concentrations of bio-available Cd (53.44%–92.01%) and Pb (28.96%–35.56%) in soils. Then their concentration in Solanum nigrum L. ( S. nigurm ) also be decreased (in the root and above-ground (stems and leaves): 44.58%–66.44% and 53.87%–73.28% for Cd, 21.01%–53.63% and 15.91%–33.27% for Pb.). Besides, the activities of urease (URE), alkaline phosphatase (ALP), and protease (PRE) were 3.12–5.28, 1.09–1.69, and 7.08–47.80 times of those in the initial phase of the experiment, respectively. Consequently, MFA has excellent remediation ability for contaminated soils in different areas and soil quality has been improved. • MFA can be successfully prepared by low-temperature and NaOH fusion. • MFA can reduce the bio-available of Cd and Pb in soil. • The application of MFA can reduce the enrichment of Cd and Pb in S.nigrum • The activities of URE, ALP and PRE were improved with the MFA application. • Remediation mechanisms is Ion exchange, surface affinity and complexation.

Effect of pyrolysis temperature of biochar on Cd, Pb and As bioavailability and bacterial community composition in contaminated paddy soil

To further investigate the effect of pyrolysis temperature on bioavailable Cd, Pb and As, as well as the bacterial community structure in multi-metal(loid) contaminated paddy soil, six types of biochar derived from wood sawdust and peanut shell at 300 °C, 500 °C and 700 °C were prepared and incubated with Cd, Pb and As contaminated paddy soil for 45 days. The results showed that adding biochar decreased bioavailable Cd by 31.3%− 42.9%, Pb by 0.61–56.1%, while bioavailable As changed from 9.68 mg kg−1 to 9.55–10.84 mg kg−1. We found that pyrolysis temperature of biochar had no significant effect on Cd bioavailability while Pb bioavailability decreased obviously with pyrolysis temperature raising. Biochar reduced the proportion of soluble and exchangeable Cd from 45.0% to 11.2–15.4% in comparison with the control, while no significant effect on the speciation of Pb and As. Wood sawdust biochar (WSBs) had more potential in decreasing bioavailable Cd and Pb than peanut shell biochar (PSBs). Although high-temperature biochar resulted a larger increase in bacterial species than low-and mid- temperature biochar, feedstock played a more important role in altering soil bacterial diversity and community composition than pyrolysis temperature. PSBs increased the diversity of soil bacteria through elevating soil dissolved carbon (DOC). Biochar altered soil bacterial community structure mainly by altering the level of soil electricity conductivity, DOC and bioavailable Cd. In addition, applying high-temperature PSBs increased the genus of bacteria that relevant to nitrogen cycling, such as Nitrospira, Nitrosotaleaceae and Candidatus_Nitrosotalea.

Effects of sepiolite and biochar on the photosynthetic and antioxidant systems of pakchoi under Cd and atrazine stress

Sepiolite and biochar effectively immobilize Cd and atrazine in vegetable soils. This study further investigated the effects of sepiolite and biochar on the photosynthetic and antioxidative defence systems of pakchoi under Cd and atrazine stress. The results showed that after adding sepiolite and biochar to contaminated soil, the chlorophyll content was restored and the photosynthetic rate increased, whereas the soluble sugar content of pakchoi decreased. In the antioxidant system of the plants, the activities of peroxidase, ascorbate peroxidase, and superoxide dismutase decreased, while the activity of catalase increased. The content of malondialdehyde, glutathione, and O2 ·− increased, but the content of H2O2 decreased. In general, remediation materials reduced the bioavailability of Cd and atrazine, reduced the stress on pakchoi, and restored and improved the rate of photosynthesis and function of antioxidants.