Simultaneous in-situ remediation and fertilization of Cd-contaminated weak-alkaline farmland for wheat production

Influence of conditioner and straw on the herbaceous plant-based phytoremediation copper tailings: a field trial at Liujiagou tailings pond, China

A field trial was performed to carry out an enhanced phytoremediation technique for multi-metal contaminated copper tailings by Sudan grass (Sorghum Sudanese), ryegrass (Lolium perenne L.), and Bermuda grass (Cynodon dactylon), using conditioner (TH-LZ01) and straw combination into composite amendments as soil amendments, aimed to obtain the maximum of phytoremediation effect. The results showed that compared with untreated herbaceous plants, the application of conditioner and straw planted with herbaceous plants reduced the pH and conductivity and increased the organic matter and water content of the copper tailings to different degrees. With the addition of conditioner and straw, the DTPA-Cd, DTPA-Cu, DTPA-Pb, and DTPA-Zn contents in the copper tailings showed a decreasing trend compared with the untreated group. The herbaceous plants were promoted to reduce the percentage contents of acid soluble fractions Cd, Cu, Pb, and Zn and to increase the percentage contents of reducible, oxidizable, and residual fractions heavy metals (Cd, Cu, Pb, and Zn) in the copper tailings to different degrees. The contents of Cd, Cu, Pb, and Zn in the underground part of herbaceous plants were higher than those in the aboveground part, and the contents of Cd, Cu, Pb, and Zn in the aboveground part and underground part decreased after adding conditioner and straw, which indicated that the conditioner and straw inhibited the transport of heavy metals in the plant. Furthermore, the principal component analysis showed that the application of conditioner and straw with planting ryegrass had more potential for improving the physicochemical properties of copper tailings and reducing heavy metal toxicity, followed by Bermuda grass and Sudan grass.

Extraction of heavy metals from copper tailings by ryegrass (Lolium perenne L.) with the assistance of degradable chelating agents

Heavy metal contamination is an urgent ecological governance problem in mining areas. In order to seek for a green and environmentally friendly reagent with better plant restoration effect to solve the problem of low efficiency in plant restoration in heavy metal pollution soil. In this study, we evaluated the effects of three biodegradable chelating agents, namely citric acid (CA), fulvic acid (FA) and polyaspartic acid (PASP), on the physicochemical properties of copper tailings, growth of ryegrass (Lolium perenne L.) and heavy metal accumulation therein. The results showed that the chelating agent application improved the physicochemical properties of copper tailings, increased the biomass of ryegrass and enriched more Cu and Cd in copper tailings. In the control group, the main existing forms of Cu and Cd were oxidizable state, followed by residual, weak acid soluble and reducible states. After the CA, FA or PASP application, Cu and Cd were converted from the residual and oxidizable states to the reducible and weak acid soluble states, whose bioavailability in copper tailings were thus enhanced. Besides, the chelating agent incorporation improved the Cu and Cd extraction efficiencies of ryegrass from copper tailings, as manifested by increased root and stem contents of Cu and Cd by 30.29-103.42%, 11.43-74.29%, 2.98-110.98% and 11.11-111.11%, respectively, in comparison with the control group. In the presence of multiple heavy metals, CA, FA or PASP showed selectivity regarding the ryegrass extraction of heavy metals from copper tailings. PCA analysis revealed that the CA-4 and PASP-7 treatment had great remediation potentials against Cu and Cd in copper tailings, respectively, as manifested by increases in Cu and Cd contents in ryegrass by 90.98% and 74.29% compared to the CK group.

Effects of Priestia aryabhattai on Phosphorus Fraction and Implications for Ecoremediating Cd-Contaminated Farmland with Plant-Microbe Technology

The application of phosphate-solubilizing bacteria has been widely studied in remediating Cd-contaminated soil, but only a few studies have reported on the interaction of P and Cd as well as the microbiological mechanisms with phosphate-solubilizing bacteria in the soil because the activity of phosphate-solubilizing bacteria is easily inhibited by the toxicity of Cd. This paper investigates the phosphorus solubilization ability of Priestia aryabhattai domesticated under the stress of Cd, which was conducted in a soil experiment with the addition of Cd at different concentrations. The results show that the content of Ca2-P increased by 5.12-19.84%, and the content of labile organic phosphorus (LOP) increased by 3.03-8.42% after the addition of Priestia aryabhattai to the unsterilized soil. The content of available Cd decreased by 3.82% in the soil with heavy Cd contamination. Priestia aryabhattai has a certain resistance to Cd, and its relative abundance increased with the increased Cd concentration. The contents of Ca2-P and LOP in the soil had a strong positive correlation with the content of Olsen-P (p < 0.01), while the content of available Cd was negatively correlated with the contents of Olsen-P, Ca2-P, and LOP (p < 0.05). Priestia aryabhattai inhibits the transport of Cd, facilitates the conversion of low-activity P and insoluble P to Ca2-P and LOP in the soil, and increases the bioavailability and seasonal utilization of P in the soil, showing great potential in ecoremediating Cd-contaminated farmland soil with plant-microbe-combined technology.

Mercapto-palygorskite efficiently immobilizes cadmium in alkaline soil and reduces its accumulation in wheat plants: A field study

Cadmium (Cd) contamination in wheat fields has become a major environmental issue in many regions of the world. Mercapto-palygorskite (MPAL) is a high-performance amendment that can effectively immobilize Cd in alkaline wheat soil. However, MAPL as an in-situ Cd immobilization strategy for alkaline wheat soil remains to be evaluated on a field-scale and the underlying mechanisms requires further evaluation. Here, MPAL were used as soil amendment to evaluate their immobilization efficiency on Cd-contaminated alkaline soil in the field experiments. The field experiments showed that MPAL application significantly reduced wheat grain Cd concentration from 0.183 mg/kg to 0.056 mg/kg, with Cd concentration in wheat grain treated with MPAL all falling below the limit value of 0.1 mg/kg as defined in China's food safety standard (GB 2762-2022). The maximal immobilization efficiency of MPAL on soil Cd figured out by diethylenetriaminepentaacetic acid (DTPA) extraction was 61.5%. The mechanisms involved in Cd immobilization by MPAL were mainly related to the enhanced sorption of Cd onto Fe oxides, and the removal of amorphous or free Fe oxides from soil had a substantial impact on Cd immobilization efficiency by MPAL. Furthermore, the antagonistic effect between Mn and Cd uptake may also contribute to the reduction of wheat Cd accumulation after MPAL application. The current research can provide theoretical and technical support for the large-scale application of MPAL in Cd-contaminated wheat fields.

Immobilization of cadmium in paddy soil using a novel active silicon-potassium amendment: a field experimental study

The rapid development of industrialization and agriculture has led to extensive environmental issues worldwide such as cadmium (Cd) pollution of paddy soils, posing a potential threat to environmental safety and food health. Therefore, there is an urgent need to reduce the Cd contents in paddy soils. In this study, a newly active silicon-potassium amendment was first prepared from potassium hydroxide-assisted potassium feldspar at a low temperature, and then was used to remediate a contaminated paddy soil by Cd over a long period. The obtained results demonstrated the effectiveness of the applied active silicon-potassium in promoting rice growth in the experimental field. In addition, soil pH values increased to 6.89-7.03, thus decreasing the bioavailability of Cd bioavailability by 8.61-13.7%. The soil enzyme activities and available nutrients (Si, Ca, Mg, N, and P) were also significantly increased. In particular, the Cd contents in the rice grains decreased from 0.279 to 0.179-0.194 mg/kg following the application of the active silicon-potassium amendment, reaching the food crop standard level of China (< 0.2 mg/kg). The detailed remediation mechanisms of the Cd-contaminated paddy soil involved several processes, including ion exchange, ligand complexation, electrostatic attraction, and precipitation. Overall, the active silicon-potassium material is a promising amendment for achieving effective control of Cd-contaminated paddy soils.

Soil pH restricts the ability of biochar to passivate cadmium: A meta-analysis

Soil acidification is the main cause for aggravation of soil cadmium (Cd) pollution. Biochar treatment can increase the soil pH and decrease the Cd availability in soils. However, there is limited information in literature on the comprehensive assessment of the response of Cd fractions to biochar. Therefore, in the present meta-analysis study, we evaluate the response of Cd fractions to biochar application in soils with different pH and to further examine the effect of physicochemical properties of biochar on Cd. Results from the overall analysis indicated that biochar treatment increased the soil pH by 7.0%, thereby decreasing the amount of available Cd (37.3%). In acidic soil, biochar significantly reduced the acid-soluble fraction (Acid-Cd) of Cd by 36.8%, while Oxidizable fraction of Cd (Oxid-Cd, 20.9%) and Residual fraction of Cd (Resid-Cd, 22.2%) were significantly increased. In neutral soils, only Acid-Cd was significantly reduced (33.0%) in the presence of biochar. In alkaline soils, biochar caused significant reduction in Acid-Cd of 12.4% and an increase in Oxid-Cd and Resid-Cd of 26.6% and 47.8%, respectively. Further, our findings showed that biochar with cation exchange capacity >100 cmol⁺/kg effectively decreased Acid-Cd (32.4%), while biochar with the percentage of hydrogen <2% was more contributory in increasing Resid-Cd (64.3%). These results demonstrate the importance of soil pH in regulating the biological effectiveness of Cd in soil and the complexation between the functional groups of biochar and Cd, and provide key information for the remediation of Cd pollution in soils with different pH by biochar.

Hidden risks from potentially toxic metal(loid)s in paddy soils-rice and source apportionment using lead isotopes: A case study from China

Pyrite is a typical sulfide mineral which contains various potentially toxic metal(loid)s (PTMs). The pyrite smelting and subsequent industrial utilization activities usually release numerous amounts of PTMs into nearby ecosystem, which may be enriched in the nearby farmland soils and crops, leading to hidden but irreversible harm to human health via the food chain. Herein, the distribution pattern, source apportionment, and potential health risks of Pb, Zn, Cu, Cd and multiple seldom monitored PTMs (Ag, Bi, Sb, Sr, Th, U, W, and V) in the paddy soils and different organs of the rice plants from ten various sites in a typical industrial zone were investigated, where pyrite ores were used for the production of sulfuric acid and subsequent cement over several decades. The results showed that the contents of Cd, Pb and Zn in studied paddy soils generally exceeded the maximum permissible level (MPL) in China, and the contents of Sb and V were approaching the MPL. Moreover, the rice is easier to bioaccumulate Cd, Cu, and Zn than the other studied elements. The hazard quotient (HQ) calculations indicate that the rice containing such multiple elements may cause a high potential non-carcinogenic and carcinogenic health risk for residents, particularly for the senior group. The Pb isotope tracing method combined with PCA (principal component analysis) further uncovered that the pyrite industrial utilization contributed 18.58-55.41 % to the highly enriched PTMs in paddy soils. All these findings indicate that the paddy soil system has been contaminated by the pyrite industrial activities and certain distances or areas should be rigidly forbidden from rice cultivation in the proximity of the pyrite smelting and related industrial sites.

Prediction of Cd Accumulation in Wheat (Triticum aestivum L.) and Simulation Calculation of Lime or Zn Fertilizer Remediated Soil

Soil Cd contamination to wheat raise wide concerns over food safety. It is essential to find the key factors affecting Cd accumulation in wheat and to establish a predictive model. The effects of pH, Zn, Ca, and DOM on the accumulation of Cd in wheat were investigated using hydroponic experiments. The results showed that Zn was the most important factor inhibiting Cd uptake in wheat. Models were developed to predict the Cd contents in wheat tissues based on the ion concentration. Meanwhile, the available Cd contents in soil were predicted using a geochemical multi-surface model (MSM) which is suitable for various soils and conditions. The combination of the hydroponic accumulation model and MSM exhibits good predictions of wheat-Cd (R² = 0.822-0.862, RMSE = 0.317-0.533). The results of this study can quantitatively predict the accumulation of Cd in wheat and provide a reference for soil remediation and safe wheat production.

Technical solutions for minimizing wheat grain cadmium: A field study in North China

The minimization of Cd pollution in wheat is urgently needed in many parts of the world. Thus, the aims of the present study were to evaluate the feasibility of popular technologies (i.e., soil amendment and low-Cd wheat cultivar) at sites with different Cd risk levels (high and low) and to propose a risk-based strategy for safe grain production. At a high-Cd site, wheat variety JM22 yielded significantly lower grain Cd than SX828, regardless of soil amendment (biochar, sepiolite, and microbial agent YZ1). Neither biochar nor sepiolite amendment reduced grain Cd, DTPA-Cd, or bioconcentration factors, possibly due to low dosage. Metagenomic sequencing and quantitative PCR showed that YZ1 colonization had little effect on rhizospheric fungal community structure and could not be sustained through winter. At a low-Cd site, significantly lower grain Cd was observed in JM22, LX99, and JM262, which could be used as low-Cd cultivars in the study area. Interestingly, the grain Cd of JM22 was linearly correlated with soil Cd (R² = 0.84), which allowed the inference of a soil Cd threshold of 1.55 mg·kg^-1, below which JM22 alone was capable of producing safe grain. Cost-benefit analysis also indicated that the use of low-Cd cultivars is promising for pollution control. This study provides viable technical solutions for minimizing the grain Cd of wheat grown in northern China.

Effects of exogenous additives on wheat Cd accumulation, soil Cd availability and physicochemical properties in Cd-contaminated agricultural soils: A meta-analysis

Cadmium (Cd) contamination in wheat is a serious issue. The application of exogenous additives can effectively inhibit Cd bioavailability in soil and decrease Cd accumulation in wheat. However, a comprehensive and quantitative analysis of how additives affect wheat Cd accumulation, wheat yield, soil Cd availability, and soil properties is lacking. We conducted a meta-analysis of 65 peer-reviewed papers published before April 2021 to investigate how additives application affects Cd accumulation in wheat and soil Cd availability. The results indicated that most additives application decreased the diethylenetriaminepentaacetic acid extractable-Cd content (5.27-56.33%) in the soil, and wheat grain and root Cd concentrations (0.03-129.87% and 0.42-52.84%, respectively); the pH values of wheat-grown soil and the properties of the additives affected the reduction percentage. Overall, most wheat-grown soils were calcareous soil (42 peer-reviewed papers); in calcareous soil, the magnitude of the Cd reduction in wheat grain was the highest under treatments with clay minerals (129.87%) due to clay modification, followed by composite (75.36%) and phosphorus materials (73.55%). Moreover, most additives application increased wheat grain yield by 0.03-51.84%, which was attributed to the positive effects of additives on wheat antioxidant capacity, photosynthesis, respiration, and nutrient uptake. Additives application increased the pH value of acidic wheat soil, and positively affected the electrical conductivity, cation exchange capacity, and organic carbon content of the wheat grown soil. In addition, regression analysis showed that soil available Cd was negatively correlated with the pH value with additives application in acidic soil (r² = 0.43), while a non-significant correlation was observed in neutral and calcareous wheat soils (r² = 0.017 and 0.016, respectively). The results of this study can assist in the selection, modification, and utilisation of additives to remediate Cd-contaminated wheat soils.

Cadmium adsorption by thermal-activated sepiolite: Application to in-situ remediation of artificially contaminated soil

Soils contamination with Cd result in detriment to the environmental quality. In-situ immobilization methods by applying clay minerals have been gaining prominence. The effects on sepiolite of thermal activation at different temperatures (300-750 °C), for removing Cd from aqueous solutions were evaluated, in order to consider their further application for soil remediation. The influence of activation temperature was investigated using XRD, SEM, and N₂ adsorption-desorption measurements. The S-600 exhibited the maximum adsorption capacity (21.28 mg/g), despite its lower SSA, and Langmuir model described the adsorption isotherms better than the Freundlich equation. TCLP was used to quantify the remediation effects of thermal-activated sepiolite on simulated soils artificially polluted with Cd. The results indicated that the mobility of Cd in soil was effectively reduced after treating with thermal-activated sepiolite and the use of S-600 was the most efficient, reducing the TCLP-Cd by approximately 73% compared with the control test. The main remediation mechanism was considered as the cation exchange of Cd by Mg at the edges of octahedral sheet. This study showed that thermal-activated sepiolite could be promising amendments for remediation of Cd-contaminated soil.

Experimental study on treatment of heavy metal-contaminated soil by manganese-oxidizing bacteria

There are many studies on the treatment of heavy metals by manganese-oxidizing bacteria and the reaction is good; the problem of compound pollution of heavy metals in soil has been difficult to solve. In this study, the application of manganese-oxidizing bacteria in soil was studied. The tolerance of manganese-oxidizing strains (Pseudomonas taiwanensis) to environmental conditions and the treatment effect of heavy metals As, Pb, and Cd in aqueous solution were investigated, and the effect of iron-manganese ratio on the treatment effect was discussed. The results showed that the suitable pH conditions for the growth of P. taiwanensis were 5-9, and the salt tolerance was 6% (by sodium chloride). The tolerant concentrations for heavy metals As(V) and Mn(II) were 500 mg L^-1 and 120 mg L^-1, respectively. The strains were enriched by nutrient broth medium. After the logarithmic phase, the bacterial suspension was mixed with ATCC#279 medium at a ratio of 1:10, and a certain amount (10 mg L^-1) of Mn(II) was added. The results of As, Pb, and Cd removal in the composite polluted water phase were 22.09%, 30.75%, and 35.33%, respectively. The molar ratio of manganese and iron affected the removal efficiency of single arsenic, the highest efficiency is 68%, and the ratio of iron to manganese is 1:5. However, when the soil was treated by the same method, the results showed that not all metals were passivated, such as Cu. At the same time, for As, Pb, and Cd, the treatment effects in soil were worse than those in water, perhaps more consideration should be given to environmental conditions, such as soil moisture and temperature, when manganese-oxidizing bacteria are used to treat soil.

Comparative effects of Tagetes patula L. extraction, mercapto-palygorskite immobilisation, and the combination thereof on Cd accumulation by wheat in Cd-contaminated soil

Phytoextraction and in situ immobilisation are two of the most commonly used remediation techniques for Cd-contaminated farmland. In theory, phytoextraction followed by immobilisation can reduce the total Cd and available Cd contents of the soil, making it suitable for the remediation of heavily Cd-contaminated alkaline soil. However, the real remediation efficiency is uncertain, and it is also unknown whether phytoextraction affects subsequent wheat Cd accumulation. In this study, two seasonal pot experiments were conducted to determine the effects of S,S-ethylenediamine disuccinic acid (EDDS)-assisted Tagetes patula L. (T. patula) extraction, mercapto-palygorskite (MPAL) immobilisation, and the combination thereof on subsequent Cd accumulation in wheat. EDDS application significantly increased the Cd content in the subsequent-soil solution, but the EDDS-activated Cd could not be absorbed by wheat roots. T. patula extraction decreased the subsequent soil pH value by 0.1-0.2 pH units, increased the available Cd content by 0.19 mg/kg, but had no effect on subsequent wheat Cd accumulation. The Cd absorption capacity of wheat roots and the Cd translocation capacity of wheat stems to grains of high-Cd wheat were higher than that of low-Cd wheat cultivar. The application of MPAL had no effect on soil pH value, but significantly decreased soil available Cd and exchangeable Cd contents by 17.78-36.76% and 21.13-52.63%; it also increased the Fe/Mn oxide-bound Cd fraction by 14.02-64.00%. MPAL application decreased the wheat grain Cd concentrations from 0.51 to 0.13 mg/kg (high-Cd wheat) and 0.35 to 0.05 mg/kg (low-Cd wheat), but had no negative effect on Fe, Mn, Cu, and Zn elements. Compared with the single MPAL application treatments, the combination treatments had no inhibition effect on Cd accumulation in wheat. MPAL is an efficient amendment, and considering the remediation efficiency, stability, and time of these methods, the combination of MPAL application with a low-Cd accumulation wheat cultivar represents a suitable proposal to ensure the safe production of wheat in Cd-contaminated alkaline soil.

Phytoexclusion of heavy metals using low heavy metal accumulating cultivars: A green technology

Heavy metal (HM) pollution of farmland is a serious problem worldwide and consumption of HM-contaminated food products poses significant public health risks. Phytoexclusion using low HM accumulating cultivars (LACs) is a promising and practical technology to mitigate the risk of HM contamination of agricultural products grown in polluted soils, and does not alter cultivation practices, is easy to apply, and is economical. This review provides an overview of the major scientific advances accomplished in the field of LACs worldwide. The LACs concept and identification criteria are presented, and the known LACs among currently cultivated grain crops and vegetables are re-evaluated. The low HM accumulation by LACs is affected by crop ecophysiological features and soil physicochemical characteristics. Taking low Cd accumulating cultivars as an example, it is known that they can efficiently exclude Cd from entering their edible parts in three ways: 1) decrease in root Cd uptake by reducing organic acids secretion in the rhizosphere and transport protein production; 2) restriction of Cd translocation from roots to shoots via enhanced Cd retention in the cell wall and Cd sequestration in vacuoles; and 3) reduction in Cd translocation from shoots to grains by limiting Cd redirection and remobilization mediated through nodes. We propose an LAC application strategy focused on LACs and optimized to work with other agronomic measures according to the classification of HM risk level for LACs, providing a cost-effective and practical solution for safe utilization of large areas of farmland polluted with low to moderate levels of HMs.

Hydroxyapatite as a passivator for safe wheat production and its impacts on soil microbial communities in a Cd-contaminated alkaline soil

The remediation of Cd-contaminated alkaline soil plays a critical role in safe wheat production. In this study, hydroxyapatite (HAP), a functional environmental remediation material, was selected to investigate the effects of HAP on cadmium accumulation in winter wheat (Triticum aestivum L.), Cd bioavailability in alkaline soil moderately polluted with Cd (2.46 mg kg^-1) and the soil bacterial community via pot experiments. The results showed HAP effectively inhibited Cd accumulation in the grains of two investigated wheat cultivars by hindering root uptake. The Cd concentrations decreased by 49.9-81.9%, and 35.7-92.4% in the grains of Zhoumai-30 and Zhengmai-7698, respectively. HAP increased the soil pH and reduced the bioavailability of Cd. 16S rRNA sequencing analysis indicated that the changes of soil physicochemical properties changed the diversity and composition of the bacterial community by increasing the relative abundance of beneficial soil bacteria. These results demonstrated the application of 2.5% HAP combined with planting Zhengmai-7698 treatment was a potential remediation method for safe wheat production, and also benefited soil P and N cycling by increasing the relative abundance of beneficial bacteria. The good performance of HAP in inhabiting Cd accumulation in wheat grains indicated it is a promising material for safe wheat production.

Simultaneous reduction of arsenic and cadmium bioavailability in agriculture soil and their accumulation in Brassica chinensis L. by using minerals

In situ immobilization of heavy metal cations in contaminated soil using natural minerals is an attractive remediation technique. However, little research has focused on the remediation of arsenic (As) and cadmium (Cd) co-contaminated. In this work, three different crystal structures and chemical compositions minerals, zeolite; bentonite; and dolomite, were applied to simultaneously reduce the uptake of As and Cd in Brassica chinensis L., and the mechanism on reducing As and Cd bioavailability in soil were also investigated. The results showed that the three minerals decreased the bioavailability of As and Cd and restrained their uptake by Brassica chinensis L. with the order followed bentonite > zeolite > dolomite. Particularly, bentonite decreased the exchangeable As and Cd by 4.05% and 32.5% and the concentrations of As and Cd in shoots of Brassica chinensis L. by 36.2% and 64.6%, as compared with the controls. Moreover, with the addition of minerals increased, the dry biomass of Brassica chinensis L. and the rhizosphere microbial functional diversity increased significantly, and the highest biomass increased by 289% at 4.0% addition of bentonite. Correlation analysis indicated that the uptake of As and Cd was positive with the available Cd and As in soil, and was negative with soil pH and available N. Furthermore, the Scanning Electron Microscopy-Energy Dispersive Spectroscopy and Fourier Transform Infrared Spectroscopy analysis illustrated the interaction between minerals and Cd mainly involved ion-exchange and adsorption, while As was mainly immobilized by calcium and magnesium through forming precipitation. In conclusion, this present study implied that the bentonite can be recommended as the more effective amendment to immobilize metal (loid)s in soil and thereby reduce the exposure risk of metal (loid)s associated with grains consumption.

Effects of EDDS on the Cd uptake and growth of Tagetes patula L. and Phytolacca americana L. in Cd-contaminated alkaline soil in northern China

Phytoextraction has been considered an effective and environment-friendly method for removing heavy metals from contaminated soil. However, the efficiency, mechanism, and adaptability of phytoextraction by hyperaccumulators in Cd-polluted weakly alkaline soil have not been investigated in detail. In this study, pot experiments were conducted to evaluate the enhanced effects of S,S-ethylenediamine disuccinic acid (EDDS) on phytoextraction in alkaline soil by measuring the degradation kinetic characteristics of EDDS and Cd absorption dynamics of Tagetes patula L. (T. patula) and Phytolacca americana L. (P. americana) for a period of 55 days. Results showed that the half-life of EDDS varied from 4.20-7.07 days and 3.35-4.36 days for T. patula and P. americana, respectively. EDDS-activated Cd reached saturation at a low dosage (1 mM) and a single application of EDDS was found to be better than double applications. The activation of EDDS on Cd applied before 45 days of harvest was better than that before 15 days of harvest, and disappeared after a 35-day application. Correspondingly, the Cd concentration in P. americana and T. patula leaves increased significantly after 3 days of the EDDS application. However, T. patula had a biomass 2.57 times and Cd absorption capacity 10.06 times higher than P. americana. EDDS showed almost no influence on the stem and leaf biomass of T. patula; however, the root weight decreased by 9.44-71.77%. The Cd concentration in T. patula leaves of all the treatments was 1.00-1.81 times that of the control group. In comparison with other treatments, the EDDS application (3 mM) before 15 days of harvest extracted the highest amount of Cd (601.45 μg/pot) in T. patula shoots, reaching 1.40 times that in the control group. Therefore, T. patula might be a more suitable phytoremediator for Cd-polluted alkaline soil than P. americana; the most effective method was the EDDS application (3 mM) before 15 days of harvest.