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Long-term pig manure addition has been widely applied in red soil to improve soil fertility. However, the influence of combined utilization of pig manure and effective microbes (EM) on soil organic carbon (SOC) and Cd are not well understood. This study conducted a 23-year (1996-2019) long-term fertilization field trial to investigate the changes of different fractions of SOC and Cd under chemical fertilization (CF), pig manure (PM), and pig manure with effective microbes (PM + EM) treatments in an agricultural soil of Jiangxi Province, South China. The results showed that the pig manure addition significantly enhanced the contents of SOC and Cd in the soils compared with the CF treatments. Furthermore, with the increment of SOC, the PM + EM treatment significantly increased the contents of soil microbial biomass carbon, dissolved organic carbon and easily oxidizable carbon compared with the pig manure application alone. Meanwhile, compared with the CF treatments, the EM addition significantly enhanced the exchangeable and oxidizable fractions of Cd, thus the potential Cd environment risk due to pig manure application should be carefully assessed.

The rhizosphere microbiome plays an important role in plant growth and behavior during phytoremediation. This work aims to explore how hyperaccumulating plant performance (shoot biomass and Cd uptake) and rhizosphere bacterial community are driven by plant development under a Cd concentration gradient and their relationship during plant growth. A pot experiment was conducted using the Cd hyperaccumulator Sedum plumbizincicola grown in soil spiked with 0, 5 and 20 mg Cd kg−1 for 13 weeks. Plant performance (shoot biomass and Cd uptake) was determined and the rhizosphere bacterial community was examined by weekly Illumina sequencing. Biomarker genera were identified by the Random Forest model and the functions were predicted by PICRUSt2. The rhizospheres bacterial community tended to stabilize from the 6th or 7th week regardless of the soil Cd concentration, coinciding with the vigorous growth stage of the hyperaccumulator. Biomarker genera Paenibacillus and Streptacidiphilus enriched in the stable stage showed significant positive correlations with Cd uptake. In addition, some predicted gene abundances of enzymes related to plant growth promotion by the rhizosphere bacterial community were influenced to various degrees by plant development and soil Cd concentration. There exists a stable bacterial community in the rhizosphere of S. plumbizincicola during phytoremediation and biomarker taxa enriched at this stage were positively correlated with Cd uptake. Selecting microorganisms that match the developmental stages might further enhance phytoremediation. This provides some theoretical basis for modulating rhizosphere microbes at the appropriate time during phytoextraction to optimize the phytoremediation technique.

Particulate cadmium (Cd) and zinc (Zn) are ubiquitous in agricultural soils of Pb-Zn mining regions. Water management serves as an important agronomic measure altering the bioavailability of Zn and Cd in soils, but how this affects particulate Cd and Zn and the underlying mechanisms remain largely unknown. Microcosm soil incubation combined with spectroscopic and microscopic characterization was conducted. During a two-year-long incubation period we observed that the concentrations of soil CaCl

Chemical weathering of carbonate-hosted Pb-Zn mines via acid-promoted or oxidative dissolution generates metal-bearing colloids at neutral mine drainage sites. However, the mobility and bioavailability of the colloids associated with metals in nearby soils are unknown. Here, we monitored the mobility of metal(loid)s in soils affected by aeolian deposition and river transport in the vicinity of a carbonate-hosted Pb-Zn mine. Using chemical extraction, ultrafiltration, and microscopic and spectroscopic analysis of metals we find that contamination levels of the soil metals cadmium (Cd), lead (Pb) and zinc (Zn) were negatively correlated with metal extractability. However, nano-scale characterization indicates that colloid-metal(loid) interactions induced potential mobilization and increased risk from metal(loid)s. Dynamic light scattering (DLS) and HRTEM-EDX-SAED analysis further indicate that organic matter (OM)-rich nano-colloids associated with calcium (Ca), silicon (Si) and iron (Fe) precipitates accounted for the majority of the dissolved metal fractions in carbonate-hosted Pb-Zn mine soils. More stable nano-crystals (ZnS, ZnCO

Remediation of farmland soils contaminated with high levels of multiple heavy metals near PbZn smeltery is still a great challenge. It is of great significance to find cost-effective green remediation technologies for stabilization of multiple heavy metals in soil and reduce metal accumulation in crops with ensured yield. In this study, we demonstrated that bone char (BC) is an effective heavy metal stabilizer which can substantially increase residual fractions of heavy metals and reduce metal accumulation in pea (Pisum sativum) with its enhanced growth. We chose the soils contaminated with high levels of Pb, Zn, Cu and Cd near the Baiyin PbZn smeltery as the tested soil. After 2 months of BC application, the relative mobile fractions (non-residual fractions) of Cu, Zn, Pb and Cd in the contaminated soil decreased while the residual fraction increased significantly. The leachability of Cu, Zn, Pb and Cd decreased by 91.2%, 38.6%, 67.6% and 54.3%, respectively compared with the control. BC application remarkably promoted pea growth and reduced accumulation of heavy metals in shoots. The mechanisms for stabilization of multiple heavy metals BC include ion exchange, surface complexation and subsequent mineralization, accompanied with release of Ca and phosphate. The immobilization of heavy metals led to their reduced toxicity to plant, and thus increased pea growth. The results show that BC is a cost-effective and sustainable heavy metal stabilizer with phosphate fertilization function. It can simultaneously immobilize multiple heavy metals in soil and facilitate crop production.

The status of essential and potentially toxic trace elements in soils and crops can be affected by long-term fertilization practices. This study aimed to investigate changes in peanut (Arachis hypogaea L.) yield and kernel quality, and changes in copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) concentrations in soil and peanut kernels after 16 years of continuous cropping with different fertilization treatments. Five fertilization treatments were applied at a red soil site in Southeast China: chemical fertilizer (F) containing nitrogen, phosphorus, and potassium, F + trace elements (FT), pig manure (M), M + effective microorganisms (MB), and MB + trace elements (MBT). Properties of soil and pig manure, heavy metal contents in soil and peanut kernels, and the compositions of amino and fatty acids in kernels were determined. Application of pig manure significantly increased peanut biomass, kernel yield, and crude protein and total amino acid contents in kernels, but led to higher amounts of Cu, Zn, and Cd in soil and higher amounts of Zn and Cd in peanut kernels compared with that of chemical fertilizer. There should be greater concern about potential kernel Cd and Zn contaminations resulting from long-term application of pig manure contaminated with potentially toxic metals as an organic fertilizer.

Cadmium (Cd)-bearing sphalerite and smithsonite ore particles are ubiquitous in soils near metal-mining areas. Previous studies indicate that smithsonite is more readily dissolved in acidic waters and soils than sphalerite but the mobility of Cd and zinc (Zn) derived from these ores in soils is unknown. Using microcosm incubation experiments and microscopic and spectroscopic analysis, we found that the mobility of Cd and Zn derived from smithsonite is higher than from sphalerite. The mobilization rates of Cd (16.6%) and Zn (13.7%) released from smithsonite in soils after 30-day incubation experiments were higher than those from sphalerite (Cd, ~ 1.42%; Zn, ~ 0.75%). Moreover, the percentages of Cd

Improving phytoremediation techniques requires a thorough understanding of the mechanisms of plant uptake and the replenishment of the bioavailable pool of the target element, and this may be effectively explored using stable isotope methods. A repeated phytoextraction experiment over five successive crops of cadmium (Cd) and zinc (Zn) hyperaccumulator Sedum plumbizincicola X.H. Guo et S.B. Zhou ex L.H. Wu (Crassulaceae) was conducted using four agricultural soils differing in soil pH and clay content. The isotopic composition of total Zn and NH4OAc-extractable Zn in soils before phytoextraction and after the fifth crop were determined, together with Zn in shoot samples in the first crop. S. plumbizincicola preferentially took up light Zn isotopes from the NH4OAc-extractable pool (Δ66Znshoot-extract = −0.42 to −0.16‰), indicating the predominance of Zn low-affinity transport. However, after long-term phytoextraction NH4OAc-extractable Zn became isotopically lighter than prior to phytoextraction in three of the soils (Δ66Znextract: P5-P0 = −0.39 to −0.10‰). This was resulted from the equilibrium replenishment of Zn bound to iron (Fe) and manganese (Mn) oxides based on Zn isotopic and chemical speciation analysis. Zinc showed opposite fractionation patterns to Cd in the same plant-soil system with heavy Cd isotope enrichment in S. plumbizincicola (Δ114/110Cdshoot-extract = 0.02–0.17‰) and in the NH4OAc-extractable pool after repeated phytoextraction (Δ114/110Cdextract: P5-P0 = 0.07–0.18‰). This indicates different mechanisms of membrane transport (high-affinity transport of Cd) and supplementation of the bioavailable pool in soil (Cd supplied mainly through complexation with root-derived organic ligands) of the two metals. The combination of chemical speciation and stable Zn isotope ratios in the plant and the bioavailable soil pool reveal that the Zn pool related to Fe and Mn oxides became increasingly bioavailable with increasing crop generations. Capsule: Stable isotope analysis indicates that soil Fe- and Mn-oxide bound Zn replenishment boosted Zn uptake by the hyperaccumulator Sedum plumbizincicola during long-term remediation.

Soil cadmium (Cd) contamination threatens food safety and human health. Increasing Cd phytoextraction efficiency by hyperaccumulators and growing safe products during remediation remain challenges. A pot experiment was conducted to explore the effects of different rates of sulfur (S) associated with alternating drying and wetting on a Sedum plumbizincicola-Oryza sativa rotation in Cd-contaminated neutral and calcareous soils. The oxidation of added S under aerobic conditions significantly decreased soil solution pH and increased soluble sulfate (SO42−), Cd and iron (Fe) concentrations in both soils. During the rice growing season the soil solution redox (Eh) decreased to < −200 mV and the solution pH increased to neutral during the first few days of flooding. Soluble SO42− and Cd in the S treatments decreased significantly with increasing duration of flooding. Sulfur addition promoted shoot Cd concentrations of S. plumbizincicola by 1.7–5.5 times on calcareous soil and 1.7–2.3 times on neutral soil compared to the controls. Rice yields increased but Cd concentrations decreased at suitable S addition rates. Appropriate sulfur amendment combined with water management can be a feasible strategy to enhance the Cd remediation efficiency of the hyperaccumulator and reduce the accumulation of Cd in the rice grains in this rotation.

A three-crop repeated phytoextraction experiment was conducted using four soils (S1-S4) highly polluted with cadmium (Cd) and two enhanced phytoextraction pot experiments using the most polluted soil (S4) to investigate the feasibility of Cd removal from highly polluted soils using the Cd/zinc (Zn)-hyperaccumulator Sedum plumbizincicola. Shoot biomass showed no significant difference during the repeated phytoextraction experiment on the four test soils and shoot Cd content showed a decreasing trend with the three consecutive crops in soils S1, S2, and S3 but not in soil S4. The Cd removal rates in soils S1, S2, S3, and S4 were 84.5, 81.6, 45.3, and 32.4%, respectively. Rice straw application increased Cd extraction efficiency by 42.6% but the addition of ethylenediaminedisuccinic acid, biochar or nitrogen had no effect on Cd remediation. Shoot Cd content increased significantly (1.57 and 1.71 times, respectively) at low (S0-1) and high (S0-2) sulfur addition rates. Soil extractable-Cd in S0-1 after the experiment showed no significant difference from the control but was 2.43 times higher in S0-2 than in the control. These results indicate that S. plumbizincicola shows good prospects for the phytoextraction of Cd from highly polluted soils and that the process can be enhanced by adding straw and/or sulfur to the soil.

In this study, different dosages of calcium polysulphide (CaS(x)) were used as an amendment to investigate effects on the immobilizing of Cd in a wetland soil by pot experiment. In addition to chemical analysis (pH and bioavailable Cd concentration), changes in soil enzyme activities, microbial carbon utilization capacity, metabolic and community diversity were examined to assess dynamic impacts on soil environmental quality and toxicity of Cd resulting from ameliorant dosing. Soil pH increased immediately upon CaS(x) amendment compared to the unamended control (CK), and then declined slowly to a level lower than CK. Diethylenetriamine pentaacetic acid (DTPA) extractable Cd concentration was determined to characterize the bioavailability of Cd in the soil. The CaS(x) dose-dependent effect observed that with increasing CaS(x) dosage, the immobilizing efficiency decreased. Soil urease and catalase activity assays and Biolog EcoPlate assay indicated that early stage addition of CaS(x) significantly inhibited soil microbial activities. However, mid and late stage time periods showed the inhibition effects were alleviated, and the microbial activities could be recovered in 1% and 2% CaS(x) treatments. Moreover, with increasing incubation time, microbial community diversity and richness were significantly recovered in 1% and 2% CaS(x) treatments compared to the CK. No considerable changes were observed in the 5% CaS(x) treatment. Conclusively, the 1% CaS(x) amendment was an efficient and safe dosage for the stabilization of Cd contaminated wetland soil. This study contributes to the development of in situ remediation ameliorants and technologies for heavy metal polluted wetland soils.

Most studies on the phytoextraction of cadmium (Cd) and zinc (Zn) by the hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) have been conducted in metal contaminated acidic and neutral soils. However, little information is available on phytoremediation of calcareous soils. Two experiments were conducted to investigate the phytoextraction efficiency of S. plumbizincicola in a contaminated calcareous soil in He'nan province, north China. In a field experiment there was no significant decrease in shoot biomass production or metal (Cd and Zn) concentration in the shoots after three successive repeated phytoextractions. Repeated phytoextraction had no significant effect on the percentage distribution of Cd or Zn fractions in the soil even though the soil total Cd and Zn concentrations decreased by 32.8 and 19.7%, respectively. In a pot experiment the shoot biomass production and Zn and Cd uptake by S. plumbizincicola increased significantly with growth in metal contaminated calcareous soil amended with organic fertilizer, perlite and vermiculite. The results indicate that S. plumbizincicola can maintain sustainable uptake of Cd and Zn from the calcareous soil and enhancement of soil fertility and structure will significantly increase the phytoextraction efficiency.

Rapid and safe treatment of harvested fresh biomass of hyperaccumulators is essential for phytoremediation of metal-contaminated soils. Here, an electro-Fenton (EF) process was used to remove cadmium (Cd) and chemical oxidation demand (COD) from waste liquor from the dewatering of biomass of the hyperaccumulator

Agricultural soil contaminated with potentially toxic metals poses great health risk to humans and it requires long-term remediation. Here, we investigate the remediation of metal-polluted agricultural soil by combining chemical washing with repeated phytoextraction. The polluted field was initially washed with 40 mmol L

Analysis of stable metal isotopes can provide important information on biogeochemical processes in the soil-plant system. Here, we conducted a repeated phytoextraction experiment using the cadmium (Cd) hyperaccumulator Sedum plumbizincicola X. H. Guo et S. B. Zhou ex L. H. Wu (Crassulaceae) in four different Cd-contaminated agricultural soils over five consecutive crops. Isotope composition of Cd was determined in the four soils before and after the fifth crop, in the plant shoots harvested in all soils in the first crop, and in the NH4OAc extracts of two contrasting soils with large differences in soil pH (5.73 and 7.32) and clay content (20.4 and 31.3%) before and after repeated phytoextraction. Before phytoextraction NH4OAc-extractable Cd showed a slight but significant negative isotope fractionation or no fractionation compared with total Cd (Δ114/110Cdextract-soil = -0.15 ± 0.05 (mean ± standard error) and 0.01 ± 0.01‰), and the extent of fractionation varied with soil pH and clay content. S. plumbizincicola preferentially took up heavy Cd from soils (Δ114/110Cdshoot-soil = 0.02-0.14‰), and heavy isotopes were significantly depleted in two soils after repeated phytoextraction (Δ114/110Cdsoil:P5-soil:P0 = -0.15 ± 0.02 and -0.12 ± 0.01‰). This provides evidence for the existence of specific Cd transporters in S. plumbizincicola, leading to positive isotope fractionation during uptake. After phytoextraction by five sequential crops, the NH4OAc-extractable Cd pool was significantly enriched in heavy isotopes (Δ114/110Cdextract:P5-extract:P0 = 0.07 ± 0.02 and 0.18 ± 0.05‰) despite the preferential uptake of heavy isotopes, indicating the occurrence of root-induced Cd mobilization in soils, which is supposed to favor heavy Cd in the organo-complexes with root exudates. Our results demonstrate that Cd is taken up by S. plumbizincicola via specific transporters, partly after active mobilization from the more strongly bound soil pool such as iron/manganese (hydr)oxide-bound Cd during repeated phytoextraction. This renders S. plumbizincicola a suitable plant for large-scale field phytoremediation.

Washing using low-molecular-weight organic acid is an effective and eco-friendly technique to permanently remove heavy metals from soil. There is still lack of evaluation of the application modes and the recovery methods, as well as the variations of heavy metal and nutrients fractions on a pilot-scale during washing. Here, we developed a simple combined solubilization and eluent drainage system in a pilot-scale washing box using industrial grade citric acid with feasible waste eluent treatment method to remove cadmium (Cd) and copper (Cu) from agricultural soil. The removal rates of Cd and Cu after sequential two-stage citric acid-water washing reach up 68.9% and Cu 41.4%, which was 7.5% and 10.0% higher than single citric acid. The removed the heavy metals were mainly in exchangeable and reducible fractions. The heavy metals at different soil depth were dissolved more effectively by citric acid-water washing with wheat straw as underdrain filling material than that of crushed stone. The potential risks of Cd in soils all decreased by approximately 75% from considerable to low risk. The two-stage citric acid-water washing significantly mitigated the effect of soil acidification. The average contents of soil organic matter, available ammonium N-NH4 and available phosphorus increased by 40.9%, 57.3%, 32.0% after citric acid-water washing under wheat straw filling. The waste eluent can be efficiently recovered by clam powder, which removed 78.7% of Cd and 57.5% of Cu. The regenerated citric acid showed similar removal efficiencies for Cd and Cu compared to the fresh citric acid. These results indicate that the combination of washing, drainage and flocculation can effectively remove Cd and Cu from contaminated agricultural soil and realize the recycling of waste eluent.

To explore the effects of some chemical amendments on the plant growth and phytoextraction efficiencies of cadmium (Cd)/zinc (Zn) hyper accumulator Sedum plumbizincicola in acid soils with high aluminum (Al) toxicity, a greenhouse pot experiment was conducted. Different kinds and dosages of amendments including calciummagnesium-phosphorus fertilizer (CMP), magnesium carbonate (MgCO₃), potassium dihydrogen phosphate (KH₂POPO₄ ) were added. The results showed that CMP and MgCO₃ increased soil pH and decreased soil exchangeable Al concentration to some extent, while KH₂PO₄ reduced soil exchangeable Al concentration but had little effect on increasing soil pH. Proper application (9.39 mg/kg) of CMP could improve the biomass and Cd and Zn phytoextraction efficiencies by S. plumbizincicola but it would inhibit plant growth and phytoextraction performance when exceeding 9.39 mg/kg. MgCO₃ addition enhanced plant metal uptake while KH₂PO₄ presented an opposite effect. It suggests that using CMP and MgCO₃ could alleviate Al toxicity to S. plumbizincicola in acid soils and maintain relatively high metal extraction efficiency.为探究不同改良剂对酸性土壤铝 (Al) 胁迫条件下镉 (Cd) 锌 (Zn) 超积累植物伴矿景天Sedum plumbizincicola 生长以及镉和锌吸取修复效率的影响，分别添加不同种类改良剂 (钙镁磷肥 (CMP)、MgCO₃、KH₂PO₄) 和不同浓度CMP 进行温室盆栽试验。结果表明，CMP 能够一定程度上提高土壤pH 值并降低土壤交换性Al 的浓度，MgCO₃ 能够显著提高土壤pH 值和降低土壤交换性Al 的浓度，KH₂PO₄ 能够降低土壤中交换性Al浓度但未改变土壤pH 值。施用适量的CMP (9.39 mg/kg) 能够提高伴矿景天生物量和Cd、Zn 吸取修复效率，用量过高会抑制伴矿景天生长和Cd、Zn 修复效率；施用MgCO₃ 可增大伴矿景天生物量和Cd、Zn 修复效率，施用KH₂PO₄ 反而抑制了伴矿景天生长。酸性土壤上施用适量的CMP 和MgCO₃ 能够缓解伴矿景天的铝毒作用，维持较高的重金属吸收效率。.

The robustness of in vitro bioaccessibility assays to predict oral relative bioavailability (RBA) of multiple metals in contaminated soils requires validation using additional soil samples. In this study, 11 contaminated soils from mining/smelting areas were analyzed for As-, Cd-, and Pb-RBA using a mouse bioassay and metal bioaccessibility via the UBM gastric phase assay. Metal-RBA varied considerably among soils, with As-RBA (2.5–23%, mean 12%) being generally lower than Cd-and Pb-RBA (3.4–88 and 3.3–59%, mean 42 and 28%), due to higher proportions of As in the residual fractions. Metal-RBA generally decreased with increasing metal concentrations probably due to reduced labile metal fractions. In addition, strong negative correlations were observed between total Fe with As-, Cd-, and Pb-RBA (R2 = 0.46–0.77), suggesting the role of Fe in controlling metal-RBA in soils. Like RBA, metal bioaccessibility by the UBM assay also varied among samples. However, strong in vivo-in vitro correlations (IVIVCs) were observed between metal-RBA and bioaccessibility (R2 = 0.52–0.81). Further, there were little differences when As-, Cd-, and Pb-IVIVCs established using soils from this study and soils pooled from literature were compared, suggesting the robustness of the UBM assay to predict metal-RBA in contaminated soils. Keywords: Heavy metals, Mouse model, Bioavailability, In vitro assay, Bioaccessibility

Soil contamination with cadmium (Cd) represents a substantial threat to human health and environmental quality. Long-term effectiveness and persistence of remediation are two important criteria for the evaluation of amendment techniques used to remediate soils polluted with potentially toxic metals. In the current study, we investigated the remediation persistence of a natural sepiolite bearing material (NSBM, containing 15% sepiolite) and ground limestone (equivalent to > 98.0% CaO) on soil pH, Cd bioavailability, and Cd accumulation by pak choi (Brassica chinensis L.) during the growth of four consecutive crops in a Cd-contaminated acid soil with different amounts of NSBM (0, 0.2, 0.5, 1, 2, and 5%). Soil pH levels ranged from 5.21 to 7.76 during the first crop, 4.30 to 7.34 during the second, 4.23 to 7.80 during the third, and 4.33 to 6.98 during the fourth, and increased significantly with increasing the application rate of NSBM. Soil CaCl2-Cd and shoot Cd concentrations decreased by 8.11 to 99.2% and 6.58 to 94.5%, respectively, compared with the control throughout the four cropping seasons. A significant negative correlation was found between soil CaCl2-Cd and soil pH. Combined use of 0.1% lime and NSBM showed greater effects than NSBM alone, especially, when the application rate of NSBM was ˂ 2%. Moreover, pak choi tissue Cd concentrations in the treatments with NSBM addition alone at ≥ 2% or at ≥ 1% NSBM combined with 0.1% lime met the maximum permissible concentration (MPC) over the four crops, allowed by the Chinese and European regulations. Based on the present study, safe crop production in the test soil is possible at a soil pH > 6.38 and CaCl2-Cd

Soil particulate organic matter (POM) has rapid turnover and metal enrichment, but the interactions between organic matter (OM) and metals have not been well studied. The present study aimed to investigate changes in the OM concentration and composition of the POM fraction and their corresponding effects on metal distribution and extractability in long-term polluted paddy soils. Soil 2000–53 μm POM size fractions had higher contents of C–H and C=O bonds, C–H/C=O ratios and concentrations of fulvic acid (FA), humic acid (HA), cadmium (Cd) and zinc (Zn) than the bulk soils. Cadmium and Zn stocks in soil POM fractions were 24.5–27.9% and 7.12–16.7%, respectively, and were more readily EDTA-extractable. Compared with the control soil, the 2000–250 μm POM size fractions had higher organic carbon concentrations and C/N ratios in the polluted soils. However, there were no significant differences in the contents in C–H and C=O bonds or C–H/C=O ratios of POM fractions among the control, slightly and highly polluted soils. In accordance with the lower contents of C=O bonds and FA and HA concentrations, the Cd and Zn concentrations in 250–53 μm POM size fractions were lower than those in 2000–250 μm POM size fractions. Enrichment of Cd in POM fractions increased with increasing soil pollution level. These results support the view that changes in the OM concentration and the size and composition of POM fractions play a key role in determining the distribution of Cd and Zn in paddy soils.

Induction of the antioxidant enzymes catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) and the avoidance of potentially toxic metals in soil by Folsomia candida were investigated. Both laboratory-spiked and field-polluted agricultural soils were used. Cadmium (Cd) concentrations in body tissues, animal avoidance behaviour and physico-chemical properties of the field soils were also determined. In laboratory Cd-spiked soils, the CAT and SOD activities in the Cd treatments were 71.1-94.7 and 1.31-4.55 times higher than in the control, respectively. In field-polluted agricultural soils, the CAT and POD activities generally increased with increasing pollution index (PI Nemerow ) of soil Cd, Cu, Pb and Zn. The CAT, POD and SOD activities at different PI Nemerow were 65.7-128, 30.1-180 and 36.5-95.8% higher than in the control, respectively. In line with the enzyme activities, Cd concentrations in the animal bodies were 8.31-15.1 and 3.21-10.0 times higher than in the control in spiked and field-polluted soils, respectively. Avoidance behaviour also increased with increasing metal concentrations in both soils. The effects of metals on CAT, POD or SOD activity were influenced by soil properties such as soil texture and pH. These results indicate that the antioxidant enzymes activities of F. candida can be induced by heavy metals and potentially used to assess the toxicity, and also that soil properties must be considered in the analysis of enzyme activities in different types of field soils.

Recent research on the rhizosphere microbiome indicates that plants may benefit more from microbial communities than from individual members in a community. The link between soil microbiome and plant performance remains poorly understood during trace metal phytoremediation by hyperaccumulator plants. The effect of different microbiomes on the cadmium (Cd)/zinc (Zn) phytoextraction efficiency of Sedum plumbizincicola was therefore explored. Different microbiomes were set up using γ-irradiation and vancomycin addition and a pot experiment was conducted. The microbial communities were characterized using high-throughput sequencing and their functions were predicted. Plant Cd and Zn contents in the vancomycin-amended treatment were about 38–46% and 35%–53% respectively lower than those in the other treatments. Bacterial composition and diversity were substantially changed by γ-irradiation and vancomycin addition but plant trace metal accumulation did not change subsequently. The bacterial functional profiles were very different following treatment with vancomycin compared with the other treatments at KEGG orthology hierarchy level 3. Genes related to up-regulated biofilm formation and down-regulated siderophore synthesis may partly contribute together to the low plant trace metal accumulation following vancomycin treatment. Specific bacterial community function rather than bacterial community diversity and composition may affect trace metal uptake by hyperaccumulator plants.

Highly precise and reliable determination of heavy metals in soil micro-arthropod tissues remains a challenge because of the small size of the animals and their typical low abundance in metal-contaminated agricultural soils. The present study sought to develop a method for cadmium (Cd) determination in soil micro-arthropods by optimizing the sample digestion procedure, reducing sample weight, modifying sample pre-treatment and validating the methodology with field samples. The optimized digestion conditions comprised a sample mass of 50-150 mu g, digestion reagent of nitric acid:hydrogen peroxide (3:1), digestion temperature of 105 degrees C, digestion period of 3 h and digestion volume of 30 mu L. Defecation of the standatd Collembola Folsomia candida (92 h) and the indigenous Collembola Onychiurus yodai (42 h) and ultrasonic cleaning of F. candida increased the accuracy of Cd determination. The recovery of Cd using the refined procedure was 98.9% and the limits of detection and quantification were 0.002 and 0.008 mu g L-1, respectively. The within-batch precision values were < 3%. The Cd concentrations in the tissues of the Collembola Isotoma sp. collected from a range of metal-contaminated fields determined by the improved method were consistent with the Cd concentrations in the field soils. The results indicate that the optimized method can be used for more accurate or reliable determination of Cd concentrations in soil micro-arthropod tissues.

The source-area weathering and pedogenesis processes in the alluvial soil profiles might affect depth distribution of heavy metals. Red clay horizon (RCH) with a thickness of 5–50 cm in a 1 m soil profile has been found ubiquitously in the Yellow River Delta (YRD). The occurrence of this RCH was supposed to be related with the frequent shifting of the Yellow River tail channel in the Yellow River Delta (YRD). The geochemical features of the RCH were distinct from its upper or lower yellow silt horizon (YSH). The average median grain size of the RCH (10.5 μm) was almost three times lower than that of the YSH (29.9 μm). Meanwhile, the RCH was characterized of higher chemical index of alteration (CIA), magnetic susceptibility ( χ lf ) and frequency-dependent magnetic susceptibility ( χ fd ) values than the YSH, which implied a stronger source-area weathering and pedogenesis intensity of the RCH. Besides the distinctive characteristics of the RCH, it also accumulated significantly ( p χ lf and χ fd , however, such a correlation was not found except for Pb in the YSH. In addition, result of BCR sequential extraction indicated that a higher percentage of Fe–Mn oxides associated fraction was in the RCH than in the YSH for the heavy metals of Pb and Co. Cadmium was observed at higher percentage of exchangeable fraction in the RCH than in the YSH, implying a higher environmental risk of the Cd in the RCH.

Pentachloronitrobenzene (PCNB) is a toxic chlorinated nitroaromatic compound. However, only a few bacteria have been reported to be able to utilize PCNB. In the present study, one pentachloronitrobenzene (PCNB)-degrading bacterium, Cupriavidus sp. YNS-85, was isolated from a contaminated Panax notoginseng plantation. The strain co-metabolized 200 mg L−1 PCNB in aqueous solution with a removal rate of 73.8% after 5 days. The bacterium also degraded PCNB effectively under acid conditions (pH 4–6) and showed resistance to toxic trace elements (arsenic, copper, and cadmium). Its ability to utilize proposed PCNB intermediates as sole carbon sources was also confirmed. The soil microcosm experiment further demonstrated that bacterial bioaugmentation enhanced the removal of PCNB (37.8%) from soil and the accumulation of pentachloroaniline (89.3%) after 30 days. Soil enzyme activity and microbial community functional diversity were positively influenced after bioremediation. These findings indicate that Cupriavidus sp. YNS-85 may be a suitable inoculant for in situ bioremediation of PCNB-polluted sites, especially those with acid soils co-contaminated with heavy metal(loid)s.

Wheat is one of several cereals that is capable of accumulating higher amounts of Cd in plant tissues. It is important to understand the Cd2+ transport processes in roots that result in excess Cd accumulation. Traditional destructive technologies have limited capabilities in analyzing root samples due to methodological limitations, and sometimes may result in false conclusions. The mechanisms of Cd2+ uptake into the roots of wheat seedlings (Triticum aestivum L.) were investigated by assessing the impact of various inhibitors and channel blockers on Cd accumulation as well as the real-time net Cd2+ flux at roots with the non-destructive scanning ion-selective electrode technique. The P-type ATPase inhibitor Na3VO4 (500 μM) had little effect on Cd uptake (p

Effects of cadmium (Cd) on predator-prey relationships and soil ecological function are poorly understood and there are few methods available to measure soil functional change. Thus, we structured a soil-dwelling food chain containing the predatory mite Hypoaspis aculeifer and its collembolan prey Folsomia candida to study the effects of Cd exposure for eight weeks in a spiked soil aged for five years. The 15N labeled litter was added as food to analyze the change in nitrogen (N) transfer content. H. aculeifer reproduction and growth and the survival and reproduction of F. candida were all negatively affected by Cd exposure, and H. aculeifer reproduction was the most sensitive parameter. The sensitivity responses of F. candida and H. aculeifer were different from those using the previous single species test. The results suggest that predator–prey interactions might influence the toxicity of Cd by predation and food restriction. Cadmium lethal body concentrations of adults and juveniles of F. candida and H. aculeifer juveniles were 500–600, 180–270 and 8–10 μg g−1, respectively. The content of N transfer from litter to animals in the food chain decreased significantly with increasing soil Cd concentration between 100 and 400 mg kg−1. The results suggest that the 15N labeled litter addition method is potentially useful for quantitative assessment of soil functional change for further risk assessment purposes.

Measuring specific ion fluxes from different regions of the root under practical physiological conditions is crucial for understanding metal uptake mechanisms by plants. We developed and tested a neutral carrier-based liquid-membrane Pb2+ and Cu2+ ion selective microelectrode (ISME) to investigate ion-transport processes along the roots of three common wetland plant species. The Pb2+ and Cu2+ ISME exhibited a Nernstian response with Pb2+ and Cu2+ activities as low as 1.0 nM and 1.0 μM in deionized water and simulated soil solution, respectively. Phragmites australis had a region of Cu2+ release for approximately the first 200 μm, while it exhibited Pb2+ and Cd2+ outward net flux up to the first 500 μm. Although in older sections of the root of Phragmites australis there were areas of influx of Cu2+, Pb2+ and Cd2+, the overall influx was much smaller than that of Typha latifolia or Canna indica. Such a reduced uptake and/or an increased efflux of metal ions across the root-cell plasma-membrane might explain the higher resistance of Phragmites australis to metals, at least in part. The Pb2+ and Cu2+ ISMEs are shown to permit detailed investigation of heavy-metal ion transport in plant roots, especially for plants used for phytoremediation.

Effects of cadmium (Cd) on collembolans and predatory mites have been well studied but Cd accumulation and biological transfer and the relationship between Cd trophic transfer and nitrogen (N) isotope fractionation and transfer in soil micro-arthropod food chains remain poorly understood. Here, we investigated the biological transfer and trophic toxicity of Cd and the effects of dietary Cd exposure on 15N fractionation in animal tissues and N transfer from food in a soil collembolan (Folsomia candida)-predatory mite (Hypoaspis aculeifer) food chain using experiments conducted in plate and soil systems. Synchronized F. candida were fed yeast or wheat spiked with 0 (Control), 50 (Cd50), 100 (Cd100) or 200 (Cd200) μg Cd g−1 food for two weeks and were then offered to synchronized H. aculeifer as prey for two weeks. Cadmium concentrations in tissues of both the collembolan and its predator increased as the Cd concentrations in the food yeast or wheat increased in both the plate and soil systems, and the Cd concentrations in the food and the animals were all significantly and positively correlated. Except for the controls, the Cd bioaccumulation factor (BAF) between adults of predatory mites and consumer collembolans (0.20–1.13) was 2.5–14 times higher than that from food yeast/wheat to consumer collembolans (0.02–0.08). Cadmium transfer has not altered the reproduction of the filial generation collembolans but the reproduction of the predatory mite declined by 34.3% with the Cd concentration in its juveniles reaching 5.94 μg g−1, suggesting that Cd transfer from the spiked food can present a higher toxicity to the predator H. aculeifer. Food spiked with Cd decreased the N content in the collembolan tissues assimilated from the food and enriched the 15N fraction (δ15N) in their tissues by affecting their metabolic turnover and growth rates. The Cd trophic transfer between collembolans and predatory mites from spiked food can directly increase the δ15N value of predatory mites and restrict the movement of N from collembolans to predatory mites. The δ15N of soil animals has considerable potential as a biomarker of Cd stress, 15N isotope application may be limited in Cd polluted soil ecosystems, and the N transfer function of soil food webs may be more vulnerable in polluted ecosystems.

Deducing soil cadmium (Cd) safety thresholds should be different for rice cultivars with different capacities to accumulate Cd to guarantee safe rice production in China. This study developed prediction models based on soil properties and deduced soil safety thresholds for Cd translocation from thirty-three paddy soils by two contrasting rice cultivars, Yelicanghua (high Cd accumulator, HCd) and Longhuamaohu (low Cd accumulator, LCd). A total of 330 paired field validation samples were used to examine the accuracy of prediction models and soil safety thresholds. The average soil Cd concentration was 0.26 (range 0.057–0.72) mg kg−1. The average brown rice Cd concentrations were 0.14 (0.043–0.55) mg kg−1 in HCd and 0.024 (0.007–0.15) mg kg−1 in LCd in 2017, with corresponding values of 0.16 (0.016–0.66) and 0.027 (0.009–0.10) mg kg−1 in 2018. Soil total Cd and pH were the two most important variables exhibiting direct effects on Cd concentrations in HCd, explaining 66% of the variance across the 33 soils. Soil total Cd, pH and organic carbon (OC) were the three most important variables in LCd, explaining 75% of the variance. Soil safety thresholds ranged from 0.27 to 1.00 mg kg−1 for HCd and from 4.52 to 46.9 mg kg−1 for LCd with pH ranging from 4.5 to 8.0. The validation results suggest ∼60% for HCd or the current soil quality standard (SQS) and 88% for LCd of the validation samples were suitable to meet the food quality standard (FQS), with 6.4% and 12%, respectively, of the validation soils unsuitable for rice cultivation. The current Chinese SQS is too strict for LCd which may be grown safely in moderately polluted soils and the derivation of soil thresholds should therefore consider the abilities of different cultivars to accumulate Cd.

Metal contamination in soil, dust, and food matrices impacts the health of millions of people worldwide. During the past decades, various animal bioassays have been developed to determine the relative bioavailability (RBA) of As, Pb, and Cd in contaminated soils, dust, and foods, which vary in operational approaches. This review discusses the strengths and weaknesses of different animal models (swine and mice), dosing schemes (single gavage dose, repeated gavage dose, daily repeated feeding, and free access to diet), and end points (blood, urine, and tissue) in metal-RBA measurement; compares metal-RBA obtained using mouse and swine bioassays, different dosing schemes, and different end points; and summarizes key findings on As-, Pb-, and Cd-RBA values in contaminated soils, dust, and foods. Future directions related to metal-RBA research are highlighted, including (1) comparison of metal-RBA determinations between different bioassays and different laboratories to ensure robust bioavailability data, (2) enhancing the metal-RBA database for contaminated dust and foods, (3) identification of physiological and physicochemical mechanisms responsible for variability in metal-RBA values, (4) formulation of strategies to decrease metal-RBA values in contaminated soils, dust, and foods, and (5) assessing the impacts of cocontaminants on metal-RBA measurement. Refereed/Peer-reviewed

Rapid industrialization and urbanization have accelerated the contamination of paddy soils with potentially toxic elements (PTEs). However, the status and the key factors responsible for the geographical variation in PTE concentrations in rice remain poorly understood. Here, a total of 113 pairs of soil and rice plant samples were collected from 19 provinces in four major rice producing areas of China to assess the geographical variation in total arsenic (As), cadmium (Cd) and lead (Pb) concentrations in the soil-rice system. Average total concentrations of As, Cd and Pb were 11.8, 0.45 and 25.7 mg kg−1, respectively, in the soils and 0.089, 0.087 and 0.036 mg kg−1 in the polished rice. The national maximum allowable concentrations of total soil As and Cd were exceeded in 6.19 and 33.6% of soils and that of Cd was exceeded in 7.96% of polished rice and no polished rice exceed the Pb limit. The As, Cd and Pb concentrations of rice were significantly and positively correlated (p

A three-crop repeated phytoextraction experiment was conducted using four soils (S1-S4) highly polluted with cadmium (Cd) and two enhanced phytoextraction pot experiments using the most polluted soil (S4) to investigate the feasibility of Cd removal from highly polluted soils using the Cd/zinc (Zn)-hyperaccumulator

Differences in growth conditions in the glasshouse and in the field may affect the consistency of phytoextraction results. Two crops of the hyperaccumulator Sedum plumbizincicola were grown in six contrasting soils in pot experiments under three different sets of growth conditions (glasshouse, polytunnel and field) to compare the phytoextraction of cadmium (Cd) and zinc (Zn). The total shoot biomass of two crops in the glasshouse was significantly smaller than in the polytunnel or field. However, in general there were no significant differences in total shoot metal uptake of two crops per pot among three sets of growth conditions. And greater decreases in soil metal than plant uptake in the polytunnel and field in an acid soil indicate high leaching losses of soil metals in the polytunnel and field, and this was confirmed by analysis of metal concentrations in soil profiles. This brings into question on the validity of estimating the practical applicability of phytoextraction based only on plant metal uptake in glasshouse conditions. It is advisable to examine leaching losses in acid soils in the field when estimating the duration of phytoextraction.

Four heavy metals (Cd, Cu, Pb and Zn), two metalloids (As and Sb) and two rare metals (In and Tl) were selected as target elements to ascertain their concentrations and accumulation in the soil-plant system and their effects on the structure of the soil microbial community in a typical area of rare metal smelting in south China. Twenty-seven soil samples 100, 500, 1000, 1500 and 3000 m from the smelter and 42 vegetable samples were collected to determine the concentrations of the target elements. Changes in soil micro-organisms were investigated using the Biolog test and 454 pyrosequencing. The concentrations of the eight target elements (especially As and Cd) were especially high in the topsoil 100 m from the smelter and decreased markedly with increasing distance from the smelter and with increasing soil depth. Cadmium bio-concentration factors in the vegetables were the highest followed by Tl, Cu, Zn, In, Sb, Pb, and then As. The concentrations of As, Cd and Pb in vegetables were 86.7, 100 and 80.0 %, respectively, over the permissible limits and possible contamination by Tl may also be of concern. Changes in soil microbial counts and average well colour development were also significantly different at different sampling distances from the smelter. The degree of tolerance to heavy metals appears to be fungi > bacteria > actinomycetes. The 454 pyrosequencing indicates that long-term metal contamination from the smelting activities has resulted in shifts in the composition of the soil bacterial community.

Appropriate disposal of hyperaccumulator biomass is a problem inhibiting the widespread use of phytoremediation technology. In the present study, kinetic analysis of the pyrolysis process of Sedum plumbizincicola, the behaviour of heavy metals and bio-oil composition were studied. The kinetic analysis of the pyrolysis process shows that activation energy (E) changed from 150 to 186 kJ mol−1 and the frequency factor (A) changed from 1.34 × 1011 to 8.99 × 1015 s−1. At temperatures of 450–750 °C more than 66.3 % of zinc (Zn) remained in the char. More than 87.6 % of the cadmium (Cd) was found in the bio-oil. Pyrolysis at 650 °C led to the highest yield of alkanes with low-oxygen compounds found in the bio-oil. Pyrolysis at 650 °C can likely offer a valuable processing method for S. plumbizincicola and recovery of Zn from the char and recovery of Cd from the bio-oil will be attempted in future research.

Phytoextraction is one of the most promising technologies for the remediation of metal contaminated soils. Changes in soil metal availability during phytoremediation have direct effects on removal efficiency and can also illustrate the interactive mechanisms between hyperaccumulators and metal contaminated soils. In the present study the changes in metal availability, desorption kinetics and speciation in four metal-contaminated soils during repeated phytoextraction by the zinc/cadmium hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) over three years were investigated by chemical extraction and the DGT-induced fluxes in soils (DIFS) model. The available metal fractions (i.e. metal in the soil solution extracted by CaCl2 and by EDTA) decreased greatly by >84% after phytoextraction in acid soils and the deceases were dramatic at the initial stages of phytoextraction. However, the decreases in metal extractable by CaCl2 and EDTA in calcareous soils were not significant or quite low. Large decreases in metal desorption rate constants evaluated by DIFS were found in calcareous soils. Sequential extraction indicated that the acid-soluble metal fraction was easily removed by S. plumbizincicola from acid soils but not from calcareous soils. Reducible and oxidisable metal fractions showed discernible decreases in acid and calcareous soils, indicating that S. plumbizincicola can mobilize non-labile metal for uptake but the residual metal cannot be removed. The results indicate that phytoextraction significantly decreases metal availability by reducing metal pool sizes and/or desorption rates and that S. plumbizincicola plays an important role in the mobilization of less active metal fractions during repeated phytoextraction.

Alternating flooding and drainage conditions have a strong influence on redox chemistry and the solubility of trace metals in paddy soils. However, current knowledge of how the effects of water management on trace metal solubility are linked to trace metal uptake by rice plants over time is still limited. Here, a field-contaminated paddy soil was subjected to two flooding and drainage cycles in a pot experiment with two rice plant cultivars, exhibiting either high or low Cd accumulation characteristics. Flooding led to a strong vertical gradient in the redox potential (Eh). The pH and Mn, Fe, and dissolved organic carbon concentrations increased with decreasing Eh and vice versa. During flooding, trace metal solubility decreased markedly, probably due to sulfide mineral precipitation. Despite its low solubility, the Cd content in rice grains exceeded the food quality standards for both cultivars. Trace metal contents in different rice plant tissues (roots, stem, and leaves) increased at a constant rate during the first flooding and drainage cycle but decreased after reaching a maximum during the second cycle. As such, the high temporal variability in trace metal solubility was not reflected in trace metal uptake by rice plants over time. This might be due to the presence of aerobic conditions and a consequent higher trace metal solubility near the root surface, even during flooding. Trace metal solubility in the rhizosphere should be considered when linking water management to trace metal uptake by rice over time.

In two long-term field experiments the zinc (Zn)/cadmium (Cd) hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) was examined to optimize the phytoextraction of metal contaminated soil by two agronomic strategies of intercropping with maize (Zea mays) and plant densities. Soil total Zn and Cd concentrations decreased markedly after long-term phytoextraction. But shoot biomass and Cd and Zn concentrations showed no significant difference with increasing remediation time. In the intercropping experiment the phytoremediation efficiency in the treatment "S. plumbizincicola intercropped with maize" was higher than in S. plumbizincicola monocropping, and Cd concentrations of corn were below the maximum national limit. In the plant density experiment the phytoremediation efficiency increased with increasing plant density and 440,000 plants ha(-1) gave the maximum rate. These results indicated that S. plumbizincicola at an appropriate planting density and intercropped with maize can achieve high remediation efficiency to contaminated soil without affecting the cereal crop productivity. This cropping system combines adequate agricultural production with soil heavy metal phytoextraction.

Excessive aluminum (Al) in acid soils or Al released due to acidification during repeated phytoextraction might impair the phytoextraction efficiency of hyperaccumulators but this is often neglected. Here, we investigate for the first time the toxicity of Al to the cadmium (Cd) and zinc (Zn) hyperaccumulator Sedum plumbizincicola with hydroponics experiments both in the long (7 weeks) and short terms (72 h), and in soil conditions in a pot experiment. In the long-term hydroponics experiment, observable toxic effects of Al were found even at100 μM Al at pH 5.00 (soluble Al: 8.74 μM) which lowered shoot Cd uptake by 39.3% compared with the Al-free treatment. The scanning ion-selective electrode technique shows that root Cd

Excessive inputs of potentially toxic elements (PTEs) into the surface environment as a consequence of atmospheric deposition, imposes long-term burdens on agricultural ecosystems. Studying the spatial and temporal variation in PTEs in atmospheric deposition and their effects on plant shoot accumulation are important in understanding the sources and contributions of PTEs in soils and agricultural products. Here, the spatial and temporal variations in cadmium (Cd) concentration and atmospheric deposition fluxes were investigated in five rice-producing areas of the urbanized Chang-Zhu-Tan region over two years. Then, the effects of simulated wet precipitation on the uptake of Cd in rice seedlings in hydroponic culture was explored. The results showed substantial spatial variability in Cd concentrations and atmospheric deposition fluxes in this region. The Cd concentration of atmospheric deposition ranged from 0.07 to 114 μg L−1, and the annual Cd fluxes in the industrial area reached 61.0 g ha−1 but all were

Estimating the bioavailability and predicting the uptake of metals to hyperaccumulators is very important in developing the field application of phytoextraction. A pot experiment was conducted using 108 agricultural soils covering a wide range of soil properties by the cadmium (Cd) hyperaccumulator Sedum plumbizincicola . The contributions of a range of soil properties to Cd uptake were quantified. Soil total, soluble, CaCl 2 -extractable and diffusive gradients in thin films (DGT)-extractable Cd concentrations (Cd total , Cd soln , Cd CaCl 2 and Cd DGT ) were used to estimate Cd bioavailability and predict shoot Cd concentration (Cd shoot ) using a piecewise function. Cd total and pH were the two major contributors to Cd uptake. Cd shoot showed a logarithmic increase with Cd total from 0.30 to 10.0 mg kg −1 but no further increase when Cd levels exceeded 10 mg kg −1 . Soil pH had a discernible negative effect on Cd bioavailability from pH 5.5 to 7.5 but a weak influence at pH 7.5. This indicates that the optimum pH for phytoextraction with S . plumbizincicola was ~5.5 and lower pH produced little increase in shoot Cd uptake. DGT gave the best estimation of Cd bioavailability across all the data. When Cd total > 10 mg kg −1 , none of the four measures was accurate enough to predict Cd shoot but when pH > 7.5 all the four measures were well correlated with Cd shoot . Piecewise equations in different ranges of Cd total or pH significantly improved the prediction of Cd shoot compared with the global equations derived from all the data. Compared with the piecewise equations, when pH > 7.5 Cd shoot was greatly overestimated with the global equation of Cd total . Our study provides useful information on the soils in which phytoextraction with S . plumbizincicola is feasible in the field. Capsule Cd availability to S . plumbizincicola was estimated by a piecewise function in soils with wide ranges of total Cd concentration and pH.

Sedum plumbizincicola (Crassulaceae), a new Sedum species, was originally discovered in 2005 in Zhejiang Province, eastern PR China. It was identified as a Cd-Zn hyperaccumulator in 2007. During the past decade, great efforts have been made to understand its metal-accumulating capacities, physiological mechanisms for metal hypertolerance and hyperaccumulation, enhancing measures of phytoextraction, field application phytoremediation practice, and disposal of harvested biomass. This chapter provides a brief review of the progress on phytoremediation of Cd- and Zn-contaminated soils using this species. Agronomic measures to enhance Cd and Zn phytoextraction efficiency by S. plumbizincicola were studied, including cultivation management, intercropping with other plant species, and nutrient management. Changes in soil and plant metal uptake were investigated during long-term and repeated phytoextraction of Cd- and Zn-contaminated soils using S. plumbizincicola. Field assessment results confirm that phytoextraction using S. plumbizincicola is a promising technique for the remediation of slightly Cd-polluted soils without the need to halt normal agricultural production.

A plant growth-promoting bacterial (PGPB) strain SC2b was isolated from the rhizosphere of Sedum plumbizincicola grown in lead (Pb)/zinc (Zn) mine soils and characterized as Bacillus sp. based on (1) morphological and biochemical characteristics and (2) partial 16S ribosomal DNA sequencing analysis. Strain SC2b exhibited high levels of resistance to cadmium (Cd) (300 mg/L), Zn (730 mg/L), and Pb (1400 mg/L). This strain also showed various plant growth-promoting (PGP) features such as utilization of 1-aminocyclopropane-1-carboxylate, solubilization of phosphate, and production of indole-3-acetic acid and siderophore. The strain mobilized high concentration of heavy metals from soils and exhibited different biosorption capacity toward the tested metal ions. Strain SC2b was further assessed for PGP activity by phytagar assay with a model plant Brassica napus. Inoculation of SC2b increased the biomass and vigor index of B. napus. Considering such potential, a pot experiment was conducted to assess the effects of inoculating the metal-resistant PGPB SC2b on growth and uptake of Cd, Zn and Pb by S. plumbizincicola in metal-contaminated agricultural soils. Inoculation with SC2b elevated the shoot and root biomass and leaf chlorophyll content of S. plumbizincicola. Similarly, plants inoculated with SC2b demonstrated markedly higher Cd and Zn accumulation in the root and shoot system, indicating that SC2b enhanced Cd and Zn uptake by S. plumbizincicola through metal mobilization or plant-microbial mediated changes in chemical or biological soil properties. Data demonstrated that the PGPB Bacillus sp. SC2b might serve as a future biofertilizer and an effective metal mobilizing bioinoculant for rhizoremediation of metal polluted soils.

Long-term application of sewage sludge resulted in soil cadmium (Cd) and zinc (Zn) contamination in a pot experiment conducted to phytoextract Cd/Zn repeatedly using Sedum plumbizincicola and Apium graceolens in monoculture or intercropping mode eight times. Shoot yields and soil physicochemical properties changed markedly with increasing number of remediation crops when the two plant species were intercropped compared with the unplanted control soil and the two monoculture treatments. Changes in soil microbial indices such as average well colour development, soil enzyme activity and soil microbial counts were also significantly affected by the growth of the remediation plants, especially intercropping with S. plumbizincicola and A. graveolens. The higher yields and amounts of Cd taken up indicated that intercropping of the hyperaccumulator and the vegetable species may be suitable for simultaneous agricultural production and soil remediation, with larger crop yields and higher phytoremediation efficiencies than under monoculture conditions.

A horizontal tube furnace was designed to test the disposal of ground hyperaccumulator biomass. X-ray diffraction (XRD), thermodynamic analysis and chemical extraction were used to characterise the heavy metals. The recoveries of Zn, Pb, and Cd in bottom ash decreased with increasing incineration temperature but increased in fly ash. The recoveries of Zn, Pb, and Cd fluctuated with increasing air flow rate and most of the metals were found in the fly ash. Cd, Pb, and Zn occurred during the combustion process in the form of elementary substances and their oxides. During reduction in the thermal process both Pb and Cd formed metal complexes such as Ca0.75Cd0.25O and Pb2O3.333 or their mixtures and more of the bottom ash Zn under the reducing conditions was present as pure metal, crystalline oxides, sulphides or complex compounds combined with other metals. (C) 2014 Elsevier B.V. All rights reserved.

Pot and field experiments were conducted to investigate the effects of water regimes on the speciation and accumulation of arsenic (As) and cadmium (Cd) in Brazilian upland rice growing in soils polluted with both As and Cd. In the pot experiment constant and intermittent flooding treatments gave 3–16 times higher As concentrations in soil solution than did aerobic conditions but Cd showed the opposite trend. Compared to arsenate, there were more marked changes in the arsenite concentrations in the soil solution as water management shifted, and therefore arsenite concentrations dominated the As speciation and bioavailability in the soil. In the field experiment As concentrations in the rice grains increased from 0.14 to 0.21 mg/kg while Cd concentrations decreased from 0.21 to 0.02 mg/kg with increasing irrigation ranging from aerobic to constantly flooding conditions. Among the various water regimes the conventional irrigation treatment produced the highest rice grain yield of 6.29 tons/ha. The As speciation analysis reveals that the accumulation of dimethylarsinic acid (from 11.3% to 61.7%) made a greater contribution to the increase in total As in brown rice in the intermittent and constant flooding treatments compared to the intermittent-aerobic treatment. Thus, water management exerted opposite effects on Cd and As speciation and bioavailability in the soil and consequently on their accumulation in the upland rice. Special care is required when irrigation regime methods are employed to mitigate the accumulation of metal(loid)s in the grain of rice grown in soils polluted with both As and Cd. © 2014 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

The aim of this study was to determine Zn/Cd accumulation ability and cellular distribution in Sedum plumbizincicola from a mine area. Spatial localization of S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn and Cd in frozen-hydrated sections of S. plumbizincicola was quantitatively determined using cryo-micro-PIXE. The shoots of S. plumbizincicola hyperaccumulated up to 1,470 mg kg−1 of Cd and 14,600 mg kg−1 of Zn (dry weight) in field-grown plants. Micro-PIXE analyse shows that in roots Zn was concentrated in the cortex. In stems Zn was preferentially accumulated in the epidermis (5,090 mg kg−1 wet weight) and in vascular bundles and neighbouring parenchyma cells. Interestingly, some vascular bundles of the stem were depleted in Zn. Taking tissue area into account, 22.1, 46.2 and 31.8 % of total Zn and 17.1, 71.6 and 11.3 % of total Cd in the stem were present in the epidermis, cortex and central cylinder, respectively. In the leaves, 81.3 % of total Cd and 55.2 % of total Zn were distributed in the mesophyll. The parenchyma cells, e.g. cortex in stem and mesophyll in leaf, play more important roles in Cd storage and detoxification than Zn in S. plumbizincicola.