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This work studied the vertical migration characteristics of Cd in soil profiles from a zinc smelting site under the influence of simulated reclaimed water containing NaCl and Na 2 SO 4 . The isothermal adsorption curves of Cd in the soils of miscellaneous fill and weathered slate well fitted the Freundlich and Langmuir models, with R 2 ranging from 0.991 to 0.998. The maximum adsorption capacity of Cd in the soils decreased significantly under the salt ion treatments with NaCl and Na 2 SO 4 . After leaching, the Cd concentrations in the leachates and Cd contents in the subsoil layers of 10-60 cm followed the order NaCl treatment > Na 2 SO 4 treatment > CK (p < 0.05), suggesting that the salt ions promoted the vertical migration of exogenous Cd. The proportion of coarse particles (> 0.02 mm) decreased, while that of fine particles (< 0.02 mm) increased under salt ion treatments (p < 0.05). The morphological characterization indicated that salt ions accelerated the erosion and fragmentation of coarse particles to form fine particles. The use of reclaimed water to flush smelting sites may increase the risk of Cd migration with small-sized soil particles from the soil to groundwater., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

A sand hydroponic experiment with different concentrations of 0, 5, 10, 20, 40 mg L -1 Cd was used to study the growth and physiological response of Hylotelephium spectabile (Boreau) H. Ohba. and its phytoextraction potential for Cd. The results showed that total plant biomass under 5 mg L -1 Cd treatment was slightly affected. The content of malondialdehyde (MDA) in leaf exposed to Cd was higher, and the POD and CAT activity exhibited a positive response to the low level of Cd addition (5 mg·L -1 ). The photosynthesis pigments were slightly inhibited, and the ultrastructure of chloroplast remained intact after treatment with 10 mg L -1 Cd. The maximum leaf Cd content (603 mg·kg -1 ) was found in 5 mg L -1 Cd treatment, then decreased with the Cd level increased. The maximum Cd content in the shoots far exceeds the threshold level (100 mg kg -1 ) for a Cd-hyperaccumulator plant with the value of translocation factor (TF shoot/root ) for Cd reaching up to 5.62. In conclusion, H. spectabile showed normal growth and physiological response and high shoot Cd accumulation under 5 mg L -1 Cd stress, which made it to be a good candidate for phytoextraction of low-level Cd polluted environment.

Fast growing woody plants are proposed for potential application for phytoremediation of contaminated soil. In this study, the plant growth, physiological responses, mineral element uptake, and phytoremediation potential of the woody plant Morus alba L. were studied in different levels of Cd-contaminated soil through dynamic sampling (30, 60, 120, and 180 d). The results indicated that M. alba L. had strong physiological coordination, tolerance and detoxification capacity in response to Cd in contaminated soil. Compared with the control, the photosynthetic pigment content in M. alba L. leaves was significantly suppressed during initial cultivation (30-60 d) and the malonaldehyde (MDA) content and electrolyte leakage (EL) were increased from 30 to 120 d of cultivation. Furthermore, the uptake of Cu, Mn, and Zn in plant tissues was imbalanced throughout cultivation (30-180 d) under 55 mg·kg -1 Cd stress. However, the chlorophyll a, chlorophyll b, carotenoid, soluble protein, and soluble sugar contents and the peroxidase (POD) and ascorbate peroxidase (APX) activities in plant leaves, as well as the uptake of macronutrients (K, Ca, and Mg) in plant stems and leaves were maintained at normal levels. Furthermore, the catalase (CAT) activities in plant leaves and the Ca and Mg contents in plant roots were significantly (p < 0.05) enhanced in response to Cd stress after 180 d of cultivation. Furthermore, the biomass of M. alba L. was significantly increased with cultivation time in Cd-contaminated soil. Therefore, normal photosynthesis, antioxidant protection, and macronutrient regulation contribute to M. alba L. with high tolerance to Cd. Moreover, the uptake and total extraction amount of Cd in aboveground M. alba L. were significantly (p < 0.05) increased with both the plant growth period and soil Cd level, and the maximum amount of Cd reached up to 340.5 μg·plant -1 . Thus, M. alba L. can be regarded as a potential candidate for phytoremediation in Cd-contaminated sites., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Biodegradable chelator-assisted phytoextraction is an effective method to enhance remediation efficiency of heavy metals. A greenhouse experiment was conducted to investigate the effects of S,S-ethylenediamine disuccinic acid (EDDS), citric acid (CA), and oxalic acid (OA) application before planting on the biomass and physiological characteristics of hyperaccumulator Sedum alfredii Hance, and its cadmium (Cd), lead (Pb), and zinc (Zn) uptake. The results showed that EDDS and CA slightly inhibited the plant growth, while the 1.0 mmol kg -1 (OA-1) and 2.5 mmol kg -1 OA (OA-2.5) addition produced 55.3% and 35.2% greater shoot biomass compared with the control, which may be related to that OA can produce higher leaf chlorophyll and soluble protein contents, as well as lower concentrations of malondialdehyde. At the same time, the concentrations of Pb and Zn in leaf after OA-2.5 treatment significantly increased by 127% and 28.4%, and the Cd, Pb, and Zn uptake by shoot was obviously enhanced by 21.5%, 117%, and 44.9% for OA-1 addition and by 39.1%, 80.0%, and 58.3% for OA-2.5 addition, respectively, in comparison with the control (P < 0.05). The reductions in available contents of Cd, Pb, and Zn in soil were observed after phytoextraction by Sedum alfredii Hance when OA was treated. These findings imply that OA was suitable for facilitating Sedum alfredii Hance to remove Cd, Pb, and Zn in co-contaminated soil.

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

The effects of the continuous amendments with lime (L), lime mixed with organic manure (LO), or phosphate fertilizer (LP) on the soil bacterial community, soil available cadmium (Cd) content, and Cd accumulation in rice planted in a Cd contaminated paddy soil were determined through a four-season field experiment. The results showed that with continuous application of amendments during the four seasons, the soil pH increased significantly compared with the control, while the soil available Cd content significantly decreased by 12.9-18.2%, 13.1-17.3% and 0.09-23.2% under the L, LO, or LP treatments, and the Cd content of rice was significantly reduced by 28.5-56.2%, 37.6-53.4%, and 31.2-44.6%, respectively. The rice Cd content in each season at amendment treatments was lower than the National Food Safety Standard of China (maximum level of Cd in grains is 0.2 mg/kg). The diversity and richness of soil bacteria significantly increased after the continuous amendments in soil for four-season cropping. Soil pH and available Cd content were important factors for soil bacterial community. Lime mixed with phosphate fertilizer or organic manure had been characterized by a significant increase of Proteobacteria, Nitrospirae, and Chloroflexi and a decrease of Acidobacteria based on an Illumina Miseq sequencing analysis. The results indicate that the continuous application of lime mixed with organic manure or phosphate fertilizer is a very important measure to ensure the quality safety of rice and improve soil quality in a Cd-contaminated paddy., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The objectives of this study were to investigate the mechanism responsible for Cd and Pb immobilization by sulfate reduction to sulfide and effectiveness of decreasing Cd 2+ and Pb 2+ bioavailability in culture solution and paddy soils via sulfate-reducing bacterium (SRB1-1). The SRB1-1 strain, exhibiting high resistances to Cd 2+ and Pb 2+ , was isolated from bulk soils in the metal(loid)-contaminated paddy field. During the culture of the SRB1-1 strain, the removal percentages of Cd 2+ and Pb 2+ from culture solution reached 99.5% and 76.0% in 72 h, respectively. The surface morphology and composition of metal precipitates formed by SRB1-1 strain were analyzed by transmission electron microscopy (TEM) and further confirmed to be CdS and PbS by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). When living SRB1-1 strain was applied in Cd and Pb-contaminated soils, the SRB1-1 strain could stably colonize using its resistance to rifampicin, and showed significantly impact on the bacterial community composition. Cd and Pb contents in rice grains were decreased by 29.5% and 26.2%, respectively, while Cd and Pb contents in the roots, culms, leaves, and husk were also decreased ranging from 19.1% to 43%, respectively. Due to growth in highly Cd and Pb contaminated soils, Cd content of the rice grains did not meet the standard for limit of Cd and Pb, but safe production of rice plants may be obtained in slightly or moderately metal(loid)-contaminated soils in the presence of the living SRB1-1 strain. These results indicated that the SRB1-1 strain could effectively reduce the Cd and Pb bioavailability in soils and uptake in rice plants. Our results highlighted the possibility to develop a new bacterial-assisted technique for reduced metal accumulation in rice grains, and also showed potential for effective synergistic bioremediation of SRB1-1 strain and rice plants in metal(loid)-contaminated soils., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Cadmium (Cd) in paddy soil is one of the most harmful potentially toxic elements threatening human health. In order to study the effect of lime combined with intermittent and flooding conditions on the soil pH, Cd availability and its accumulation in tissues at the tillering, filling and maturity stages of rice, as well as enzyme activity and the microbial community in contaminated soil, a field experiment was conducted. The results showed that liming under flooding conditions is a more suitable strategy for in situ remediation of Cd-contaminated paddy soil than intermittent conditions. The availability of Cd in soils was closely related to the duration of flooding. Liming was an effective way at reducing available Cd in flooding soil because it promotes the transformation of Cd in soil from acid-extractable to reducible fraction or residual fraction during the reproductive growth period of rice. Compared with control, after liming, the concentration of Cd in brown rice was reduced by 34.9% under intermittent condition while reduced by 55.8% under flooding condition. Meanwhile, phosphatase, urease, and invertase activities in soil increased by 116.7%, 61.4% and 28.8%, and 41.3%, 46.5% and 20.8%, respectively. The high urease activity in tested soils could be used to assess soil recovery with liming for the remediation of contaminated soil. Soil microbial diversity was determined by the activities of soil acid phosphatase, urease and available Cd by redundancy analysis (RDA). The results indicated that the problem of Cd-contaminated paddy soil could achieve risk control of agricultural planting by chemical treatment such as lime, combined with various water regimes.

This study prepared immobilized Alishewanella sp. WH16-1 using alginate and lotus seed pods as a matrix and investigated the effects of its immobilization on Cd 2+ in a culture solution and in soil. Compared with the free WH16-1 strain, the immobilized WH16-1 strain possessed greater stability for long-term use and storage and higher removal ability for Cd 2+ in the culture solution. A model of Cd 2+ removal by the immobilized WH16-1 strain was proposed. The immobilized WH16-1 strain was incubated in the pot experiments of Cd-contaminated paddy soil for 120 days, and the pot experiments of Cd-contaminated paddy soil without the immobilized WH16-1 strain were used as a control. Compared with the control, the exchangeable and carbonate-bound Cd in the paddy soil incubated with the immobilized WH16-1 strain significantly decreased by 33.6% (P < 0.05) and 17.36%, respectively, and the Cd concentrations in the rice significantly decreased by 78.31% (P < 0.05). The results indicate that alginate-lotus seed pods can be used as excellent cost-effective cell carriers for the immobilization of Alishewanella sp. WH16-1 and that the immobilized WH16-1 strain may be applicable for the biological stabilization of Cd in Cd-contaminated paddy soil., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A simple mathematical model on the basis of the mass balance principle was developed to simulate the long-term changes of Cd in paddy soils. The model predicted the dynamics of cadmium concentration in soils under six alternative control scenarios, including rice straw incorporation into fields (A), removing straw from fields (B), irrigating paddies with groundwater (C), reducing atmospheric Cd deposition (D), liming (E), and integrating measures (F), which were used for Cd contaminated paddy fields in the central subtropical areas of China. The uncertainty of parameters was analyzed using Monte Carlo methods. Scenario simulation results showed that atmospheric deposition was the main external source of Cd, contributing 70% of the total inputs, and plant uptake was an important output pathway, responsible for 92% of the total outputs. Removing straw from fields was more effective than other single control scenarios, and integrating measures were more effective in lowering Cd concentration in contaminated paddy soils. The Cd concentration in soils can meet the critical value (0.3 mg kg-1) in a low-level Cd contaminated paddy field (0.68 mg kg-1) with integrating measures through 40 years of cultivation. In the same case, a high-level Cd contaminated field (1.48 mg kg-1) was converted to a low-level Cd contaminated field (0.54 mg kg-1). However, long term use of lime can increase the Cd concentration in paddy soils. Controllable factors that affected Cd accumulation in paddy soils were plant uptake factors, and the atmospheric deposition flux and irrigation water flux of Cd. Therefore, integrating measures including removing rice straw and preventing the emission of Cd into the atmosphere and irrigation water was the optimal approach to lower Cd concentration in contaminated paddy soils.

This study assessed the effectiveness of limestone-montmorillonite-rapeseed residue-Si fertilizer compound amendment on the bioavailability and crop uptake of cadmium (Cd) and enzyme activities in acidic paddy soils. Applying the compound amendment at ratios of 1%-3% increased soil pH by 0.1-1.9 units, decreased leaching ratios of soil Cd 4.0%-22%, and decreased exchangeable and carbonated Cd 42%-55% and 27%-49%, respectively. Organic matter-bound Cd increased 47%-62% (p < 0.05). Cadmium concentrations decreased in the roots, culms, leaves, and grains of rice grown in the Cd-contaminated soils by 37%-81%, 18%-73%, 29%-64% and 27%-63%, respectively, (p < 0.05). Catalase and urease activities increased 2.5%-63% and 3.9%-36%, (p < 0.05), respectively. Applying this compound amendment may significantly mitigate soil acidification and decrease the bioavailability and crop uptake of Cd in acidic Cd-contaminated paddy soils.

In a greenhouse experiment, five ornamental plants, Osmanthus fragrans (OF), Ligustrum vicaryi L. (LV), Cinnamomum camphora (CC), Loropetalum chinense var. rubrum (LC), and Euonymus japonicas cv. Aureo-mar (EJ), were studied for the ability to phytostabilization for Cd-contaminated soil. The results showed that these five ornamental plants can grow normally when the soil Cd content is less than 24.6 mg·kg -1 . Cd was mainly deposited in the roots of OF, LV, LC and EJ which have grown in Cd-contaminated soils, and the maximum Cd contents reached 15.76, 19.09, 20.59 and 32.91 mg·kg -1 , respectively. For CC, Cd was mainly distributed in the shoots and the maximum Cd content in stems and leaves were 12.5 and 10.71 mg·kg -1 , however, the total amount of Cd in stems and leaves was similar with the other ornamental plants. The enzymatic activities in Cd-contaminated soil were benefited from the five tested ornamental plants remediation. Soil urease and sucrase activities were improved, while dehydrogenase activity was depressed. Meanwhile, the soil microbial community was slightly influenced when soil Cd content is less than 24.6 mg·kg -1 under five ornamental plants remediation. The results further suggested that ornamental plants could be promising candidates for phytostabilization of Cd-contaminated soil.

The tolerance characteristics and phytostabilization potential of Platycladus orientalis grown in soil contaminated by cadmium (Cd) were studied using a greenhouse experiment. The results showed that the ornamental plant P. orientalis had high tolerance for Cd in contaminated soil at 24.6 mg·kg -1 and its physiological activities were slightly affected after 203 days (d) of cultivation. Moreover, Cd in soil at 9.6 mg·kg -1 was beneficial for P. orientalis growth, and the total biomass after 203 d cultivation was significantly (p < 0.05) increased by 35.03%, while the contents of chlorophyl a, chlorophyl b and carotenoid in leaves also increased by 20.84%, 44.06% and 28.25% compared to the control, respectively. Meanwhile, the Cd content in the tissues of P. orientalis was increased with both plant growth and the Cd content in the soil. The uptake of Cd in P. orientalis roots was greater than in shoots, with the Cd content in roots reaching 41.45 mg·kg -1 . P. orientalis, an ornamental plant, that accumulates Cd predominantly in its roots, can be suggested as a promising plant for phytostabilization in Cd-contaminated soil.

The release and form transformation of Cd, Cu, and Zn in polluted red soil and yellow red soil affected by simulated acid rains were studied through batch equilibrium experiments. The results showed that the release of test heavy metals increased significantly with decreasing pH value of simulated acid rain. Their release amount was negatively correlated to the pH value of acid rains. In polluted red soil and yellow red soil, Cd existed mainly in exchangeable form, and Cu in organically bound and Mn oxide-occluded forms. Zn existed mainly in residual and exchangeable forms in polluted red soil, and in residual and organically bound forms in polluted yellow red soil. To some extents, the release of Cd, Cu and Zn and the chemical forms of Cd and Zn in test soils were affected by soil organic matter content and CEC. The release amount of bio-available Cd and Cu in polluted red soil and yellow red soil was increased greatly with the increasing acidity of simulated acid rains, but the transformation of Zn from stable to bio-available form was not obvious.

Purpose: Crop contamination with cadmium (Cd) poses a serious health risk in some regions of the world. A field experiment involving a cropping pattern of rice (Oryza sativa L.) and rape (Brassica napus L.) was conducted over five cropping seasons, with annual application of mixed amendments, to assess the feasibility of immobilizing bioavailable Cd in soil. Materials and methods: From April 2016 to March 2018, a field trial with a rice-rape rotation was conducted. Mixed amendments, including lime + organic fertilizer (LO), lime + organic fertilizer + calcium-magnesium phosphate fertilizer (LOC), lime + organic fertilizer + sepiolite (LOS), and lime + organic fertilizer + calcium-magnesium phosphate fertilizer + sepiolite (LOCS), were added to the Cd-contaminated agricultural soil. Results: The mixed amendments significantly reduced soil Cd bioavailability and thus notably reduced Cd concentrations in brown rice by 51.5–80.2% during the years 2016–2018 with annual application. However, soil available nitrogen contents decreased by 18.5–44.6% in the third year with the amendments applied. At the same time, the grain yields significantly decreased by 37.9–57.0% for both rape and rice, except for the continual application of LOCS. Thus, LOCS is a more optimal measure to ensure the yield and quality of rice and rape in Cd-contaminated agricultural soil when mixed amendments are continuously applied. Conclusion: The mixture of organic and inorganic amendments works well for soil Cd immobilization and crop Cd reduction, while it decreases crop yields, except for LOCS. The optimal approach is to apply LOCS to Cd-contaminated soil continuously for 2 years at several-year intervals. [ABSTRACT FROM AUTHOR]

Intercropping with hyperaccumulators/accumulators is a promising alternative to enhance phytoextraction of heavy metal(loid)s in contaminated soil. In this research, a pot experiment was conducted to evaluate the influences of intercropping As hyperaccumulator Pteris vittata L. with Cd hyperaccumulator Sedum alfredii Hance or accumulator Hylotelephium spectabile (Boreau) H. Ohba on the plant growth, As and Cd phytoextraction, and rhizosphere bacterial microbiota. The results indicated that intercropping can promote the growth of plants. The total biomass of P. vittata, S. alfredii, and H. spectabile in intercropping systems was improved by 19.9–34.1%, 16.8%, and 11.5%, respectively, in comparison with corresponding plant monoculture. The As content in rhizoid and frond of P. vittata when intercropped with S. alfredii was significantly increased by 28.3% and 19.0% (P < 0.05), respectively, as compared with P. vittata monoculture, and this treatment acquired the maximum As and Cd accumulation with 2032 μg·pot−1 and 397 μg·pot−1, respectively. Intercropping enhanced the soil bacterial community diversity. The genera of Lysobacter in P. vittata rhizosphere and Massilia and Arthrobacter in S. alfredii rhizosphere had higher abundance in the intercropping system of P. vittata and S. alfredii. There were significantly positive correlation relationships between Massilia and Arthrobacter with plant Cd content and Lysobacter with plant As content, indicating that they may play important roles in As and Cd phytoextraction. The results suggested that intercropping P. vittata with S. alfredii could be a potential strategy for phytoextraction of As and Cd from co-contaminated soil. [ABSTRACT FROM AUTHOR]

In order to find an efficient and economical wetland substrate to treat mine wastewater containing various heavy metals, and effectively realize the resource utilization of water treatment residuals, in this paper, the treatment efficiency of mine wastewater containing various heavy metals was investigated using unburned ceramsite prepared from water treatment residuals (UCWTR) and clay ceramsite. The continuous dynamic test results showed that the removal rate of Pb, Cd, Cu, Zn, and Fe can reach more than 98.5% after the UCWTR-based CWs runs for 56 days, and its concentration was 30.05%, 24.85%, 20.82%, 14.63%, and 7.91% lower than that of the clay ceramsite-based CWs, respectively. SEM, XPS, and FT-IR showed that the characteristic peaks of two ceramsites were basically similar. The ceramsite undergoes ion exchange, coordination complexation, and chelation reaction with Pb, Cd, Cu, Zn, and Fe under the action of the gel of internal groups -OH, C=O, Al-OH, Si-Fe-O and C-S-H. Compared with clay ceramsite, the ion exchange reaction and chelation reaction of -OH effect and the coordination reaction of C=O effect of carboxyl group in UCWTR were enhanced. In conclusion, using UCWTR as a CWs substrate can effectively enhance the adsorption capacity of heavy metals, providing a scientific basis for the application of UCWTR-based CWs in mine wastewater treatment. [ABSTRACT FROM AUTHOR]

Atmospheric deposition of heavy metals is widely documented and has been connected to adverse ecological and health impacts. The influence of atmospheric deposition on the soil–rice system in a typical urban agglomeration region was studied continuously through a field contrast experiment for two years. The results showed that the Cd and Pb in rice grains is mainly from soil, but Cd and Pb from the atmospheric deposition should be a focus of attention. The bioavailable content of heavy metals in atmospheric deposition is higher than that in corresponding surface soil. Atmospheric deposition contributed 10.8–47.7% of the Cd and Pb in brown rice, and 13.7–60.3% of the Cd and Pb in rice leaves was from atmospheric deposition. In the traffic area, a high deposition site, the contributions of atmospheric depositions to heavy metals in rice plants were higher than those from abandoned mine area and suburban area. Atmospheric deposition also consistently decreased the pH (0.17–0.66) and increased the exchangeable Cd (27.1–62.1%) and Pb (3.3–26.1%) in surface soil. In addition, the health risk index (HRI) of rice consumption was also increased as a result of the different atmospheric depositions of heavy metals, which accounted for 40.0% and 35.5% of Cd and Pb at the high deposition site, respectively. These findings demonstrate the potential influences of atmospheric deposition on the soil–crop system and human health, and can also provide a useful reference for developing the emission control strategies. • Atmospheric deposition was an important source of heavy metal in rice. • Bioavailability of heavy metal in deposition was higher than in topsoil. • Atmospheric deposition increased bioavailable fractions of heavy metal in topsoil. • High deposition of heavy metal increased the health risk of rice consumption. [ABSTRACT FROM AUTHOR]

Abstract The changes of available forms of heavy metals would affect their corresponding ecological risks in sediments. The distribution of chemical fractions of heavy metals in sediment profiles from Chunfeng Lake estuary was investigated and then a prediction model for potential ecological risk index (PMRI) was proposed to forecast the changes of ecological risks caused by the aging process of metals in sediments. The results show that the estuarine sediments were polluted by As and Cd. The proportions of available metals were generally decreased with depth, while those of the residual forms showed an opposite trend. The aging rates of Cd and As were found to be 0.21 and 0.12%/year, respectively. The PMRI model showed that the total ecological risk of metals in sediments decreased from moderate to low risk level (<150) after 25 years, while cadmium would need 47 years in contrast to the 15 years for As. Graphical abstract Unlabelled Image Highlights • Distributions and chemical fractions of metals in the sediment profiles were studied. • The available metals were changing to unavailable forms with increasing depth. • The aging rates of Cd and As in the sediment profiles were 0.21 and 0.12%/year. • A model is proposed to predict ecological risk of metals in the sediment profiles. • The ecological risk of metals decreased from moderate to low level after 25 years. [ABSTRACT FROM AUTHOR]

Anaerobic digestion of the heavy metal-contaminated rice straw inoculated with waste activated sludge was carried out through an orthogonal array. The results indicated that the digestion process was optimized with an inoculum to substrate ratio (I/S) of 0.25, a total solid (TS) content of 5%, and an initial pH of 7.0, with corresponding total biogas and methane yields of 745.4 and 285.2 mL/g VS, respectively. Under the optimized conditions, the bioleaching percentages of Cd and As in the biomass were 13.13% and 42.90%, respectively. According to range analysis, the biogas yield, methane yield, and bioleaching percentages of Cd and As in the biomass significantly decreased with an increase in TS content from 5% to 15%. The results suggested that anaerobic digestion with waste activated sludge was feasible for achieving both biogas production and bioleaching of heavy metals from contaminated rice straw. [ABSTRACT FROM AUTHOR]

Feasibility of adsorption-pyrolysis technology to recover metals from solution using contaminated biomass phytoremediation was discussed. The technology can meet three objectives: the disposal of metals-contaminated biomass from phytoremediation, the adsorption of metals from wastewater and the reuse of metals-saturated biomass. In this study, the recovery of Cd and Cu in metals-containing solution from contaminated biomass of phytoremediation was achieved through adsorption and pyrolysis technology. The results showed that pH value of the metals-containing solution and the pyrolysis temperature for metals concentration are the key factors of the novel technology. When the pH of the metals-containing solution was 6, the content of Cd and Cu in the saturated biomass after approximately 30 min adsorption was 2.7 wt% and 1.25 wt%. Next, the saturated biomass is pyrolyzed at 450 °C, and the final content of Cd and Cu in the solid phase product was 7.13 wt% and 6.58 wt%, respectively. The concentration of metals from the adsorption-pyrolysis process for bio-ore was primarily due to the redox reaction of Cd and Cu salts and the volatilizing properties of elements. The results suggested that the adsorption-pyrolysis technology is feasible for recovery of Cd and Cu in solution. [ABSTRACT FROM AUTHOR]

Chemical washing has been carried out to remediate soil contaminated with heavy metals. In this study, the appropriate washing conditions for N , N -bis(carboxymethyl)-L-glutamic acid (GLDA) combined with ascorbic acid were determined to remove As, Cd, and Pb in the soil from the smelting site. The mechanism of heavy metal removal by the washing agent was also clarified. The results showed that heavy metals in the soil from the smelting site can be effectively removed. The removal percentages of As, Cd, and Pb in the soil from the smelting site were found to be 34.49%, 63.26%, and 62.93%, respectively, under optimal conditions (GLDA and ascorbic acid concentration ratio of 5:20, pH of 3, washing for 60 min, and the liquid-to-solid ratio of 10). GLDA combined with ascorbic acid efficiently removes As, Cd, and Pb from the soil through synergistic proton obstruction, chelation, and reduction. GLDA can chelate with iron and aluminum oxides while directly chelate with Cd and Pb. Ascorbic acid can reduce both Fe(III) to Fe(II) and As(III) to As0. The dissolution of As was promoted by indirectly preempting the binding sites of iron and aluminum in the soil while those of Cd and Pb were improved by directly interrupting the binding sites. This study suggested that GLDA combined with ascorbic acid is an effective cleanup technology to remove As, Cd, and Pb simultaneously from contaminated smelting site soils. [Display omitted] • Soil from Pb/Zn smelting site was used to cleanup As, Cd, and Pb. • GLDA combined with ascorbic acid was provided to remove As, Cd, and Pb in the soil from a Pb/Zn smelting site. • Optimal conditions for the cleanup of As, Cd, and Pb using GLDA combined with ascorbic acid were optimized. • This research validates the removal mechanism of As, Cd, and Pb by GLDA combined with ascorbic acid. [ABSTRACT FROM AUTHOR]

Exogenous application of plant-growth promoting substances in combination with chelators is a common way to enhance the phytoextraction of heavy metals. A pot experiment was used to explore the influences of indole-3-acetic acid (IAA)/gibberellin (GA 3) alone or together with oxalic acid (OA) on the growth, physiological response, and nutrient contents of hyperaccumulator Sedum alfredii Hance, and cadmium (Cd) and lead (Pb) phytoextraction efficiency. The results showed that a foliar spray of IAA/GA 3 alone or together with OA increased plant growth. The largest shoot biomass with increase by 29.7% was produced by the 50 μmol L−1 IAA combined with 2.5 mmol kg−1 OA (50I+2.5OA) treatment as compared with the control treatment (CK). The presence of IAA and GA 3 enhanced the chlorophyll a , carotenoid, and potassium contents in leaves and decreased the malondialdehyde content. The Cd content in leaf and the translocation factor (TF shoot) value from 50I+2.5OA treatment was increased by 4.29% and 21.4%, and the Pb content in stem and shoot, and the TF shoot of Pb after applying 50 μmol L-1 GA 3 combined with 2.5 mmol kg−1 OA was enhanced by 32.5%, 13.4%, and 57.6%, compared with CK, respectively. The optimal Cd and Pb phytoextraction efficiency occurred from 50I+2.5OA treatment with increase by 82.4% and 79.3% as compared with CK, respectively. Therefore, the results showed that a combined application of 50 μmol L−1 IAA and 2.5 mmol kg−1 OA could effectively enhance S. alfredii Hance phytoremediation of Cd and Pb co-contaminated soil. • IAA and GA 3 improve the photosynthetic pigments and leaf K content. • 50 GA 3 combined with OA was suitable for S. alfredii phytoextraction of Pb. • 50 IAA+2.5 OA treatment produces highest shoot biomass Cd/Pb removal efficiency. [ABSTRACT FROM AUTHOR]

• The combined amendment decreased soil cd availability and guaranteed the clean production of rice in three consecutive seasons. • The supplementary application of LS further decreased soil cd availability and cd accumulation in rice. • Health risk of consumption of rice was significantly decreased after combined amendment application. The scientific application of stabilized materials has been considered an effective method for the in situ remediation of Cd-contaminated soil. This study aimed to investigate the persistence of the effect of a combined amendment of limestone and sepiolite (LS) on soil Cd availability and accumulation in rice grown in a mildly Cd-contaminated paddy field (0.45 mg/kg of Cd) over three consecutive rice seasons. 1125–4500 kg/ha of LS was applied to the soil before the first rice planting season and 562.5–2250 kg/ha of LS was supplemented before the third rice planting season. The application of LS (1125–4500 kg/ha) increased the soil pH by 0.44–1.09, 0.18–0.53, and 0.42–0.68 in the first, second, and third season, respectively, and decreased the soil acid-extractable Cd content by 18.2–36.4%, 17.7–33.5%, and 9.6–17.6%. LS application significantly decreased the Cd contents in the rice tissues. The application of 4500 kg/ha of LS decreased the Cd content in brown rice to below the National Food Limit Standard of 0.2 mg/kg (GB 2762-2017) in the three consecutive rice seasons. However, the effect of LS on the soil-rice system was significantly weakened in the third season. The supplementary application of 562.5–2250 kg/ha of LS further decreased the Cd content in brown rice by 26.1–56.5% and decreased the health risk index by 23.7–43.8%. Therefore, it was recommended to apply 4500 kg/ha of LS in the first season and to supplement 2250 kg/ha of LS in the third season to effectively guarantee the clean production of rice in three consecutive rice seasons. [Display omitted] [ABSTRACT FROM AUTHOR]