Cadmium phytoremediation potential of Houttuynia cordata: Insights from growth, uptake, and rhizosphere mechanisms.

Cadmium (Cd) pollutes 7.0 % of China's land area. This study examined the potential of Houttuynia cordata for Cd phytoremediation because of its ability to accumulate Cd in its growth matrix. H. cordata were planted in plastic pots filled with paddy field soils having low (LCd), medium (MCd), and high (HCd) Cd levels of 0.19, 0.69, and 2.91 mg/kg, respectively. After six months of growth, harvested plant parts were evaluated for Cd uptake and tolerance mechanisms. Metabolomics and metagenomics approaches were employed to investigate the soil rhizosphere mechanism. Results showed that the average plant biomass increased as soil Cd increased. The biomass Cd contents surpassed the allowable Cd limits for food (≤ 0.2 mg/kg) and medicinal uses (≤ 0.3 mg/kg). Cd contents were higher in H. cordata roots (30.59-86.27 mg/kg) than in other plant parts (0.63-2.90 mg/kg), with significantly increasing values as Cd soil level increased. Phenolic acids, lipids, amino acids and derivatives, organic acids, and alkaloids comprised the majority (69 in MCd vs HCd and 73 % in LCd vs HCd) of the shared upregulated metabolites. In addition, 13 metabolites specific to H. cordata root exudates were significantly increased. The top two principal metabolic pathways were arginine and proline metabolism, and beta-alanine metabolism. H. cordata increased the abundance of Firmicutes and Glomeromycota across all three Cd levels, and also stimulated the growth of Patescibacteria, Rozellomycota, and Claroideoglomus in HCd. Accordingly, H. cordata demonstrated potential for remediation of Cd-contaminated soils, and safety measures for its production and food use must be highly considered.

Degradation and humification of steroidal estrogens in the soil environment: A review.

Emerging pollutants are toxic and harmful chemical substances characterized by environmental persistence, bioaccumulation and biotoxicity, which can harm the ecological environment and even threaten human health. There are four categories of emerging pollutants that are causing widespread concern, namely, persistent organic pollutants, endocrine disruptors, antibiotics, and microplastics. The distribution of emerging pollutants has spatial and temporal heterogeneity, which is influenced by factors such as geographical location, climatic conditions, population density, emission amount, etc. Steroidal estrogens (SEs) discussed in this paper belong to the category of endocrine disruptors. There are generally three types of fate for SEs in the soil environment: sorption, degradation and humification. Humification is a promising pathway for the removal of SEs, especially for those that are difficult to degrade. Through humification, these difficult-to-degrade SEs can be effectively transferred or fixed, thus reducing their impact on the environment and organisms. Contrary to the well-studied process of sorption and degradation, the role and promise of the humification process for the removal of SEs has been underestimated. Based on the existing research, this paper reviews the sources, classification, properties, hazards and environmental behaviors of SEs in soil, and focuses on the degradation and humification processes of SEs and the environmental factors affecting their processes, such as temperature, pH, etc. It aims to provide references for the follow-up research of SEs, and advocates further research on the humification of organic pollutants in future studies.

Phytoextraction and Migration Patterns of Cadmium in Contaminated Soils by Pennisetum hybridum.

This study was conducted to identify soil cadmium (Cd) removal pathways and their contribution rates during phytoremediation by Pennisetum hybridum, as well as to comprehensively assess its phytoremediation potential. Multilayered soil column tests and farmland-simulating lysimeter tests were conducted to investigate the Cd phytoextraction and migration patterns in topsoil and subsoil simultaneously. The aboveground annual yield of P. hybridum grown in the lysimeter was 206 ton·ha-1. The total amount of Cd extracted in P. hybridum shoots was 234 g·ha-1, which was similar to that of other typical Cd-hyperaccumulating plants such as Sedum alfredii. After the test, the topsoil Cd removal rate was 21.50-35.81%, whereas the extraction efficiency in P. hybridum shoots was only 4.17-8.53%. These findings indicate that extraction by plant shoots is not the most important contributor to the decrease of Cd in the topsoil. The proportion of Cd retained by the root cell wall was approximately 50% of the total Cd in the root. Based on column test results, P. hybridum treatment led to a significant decrease in soil pH and considerably enhanced Cd migration to subsoil and groundwater. P. hybridum decreases Cd in the topsoil through multiple pathways and provides a relatively ideal material for phytoremediation of Cd-contaminated acid soils.

[Effectiveness and Mechanisms of Chemical Leaching Combined with Electrokinetic Technology on the Remediation of Heavy Metal Contaminated Soil].

In this study, chemical leaching and electrokinetic technology were used to remediate heavy metal contaminated soil to elucidate its effectiveness and mechanisms. Chemical leaching agents of FeCl3, Fe(NO3)3, KCl, KNO3, and HCl solutions were selected, and the effects of Fe3+, K+, H+, and Cl- on four heavy metal (Cd, Pb, Cu, and Zn) removals were compared and analyzed. Then, the influence of the speciation of heavy metals in soil after chemical leaching on the electrokinetic remediation efficiency was studied. The results showed that Fe3+, K+, H+, and Cl- had different effects on the four heavy metal removals; for Cd and Zn, the removal effect of H+was the most effective, but for Pb and Cu, the effect of Fe3+ was the most obvious. On the whole, FeCl3 and Fe(NO3)3 showed the best removal effect for Cd, Pb, and Cu. For the removal of Zn from the soil, the difference in the removal effect of the five leaching agents was not obvious. In comparison with that of FeCl3 and Fe(NO3)3, the HCl solution had a moderate removal effect on the four heavy metals in the soil, and the neutral salts KCl and KNO3 had little removal effect on the four heavy metals. Especially for Cd and Cu, KCl and KNO3 addition significantly increased the removal of heavy metals through the subsequent electrokinetic remediation. After the chemical leaching, electrokinetic remediation could make heavy metals in the topsoil (0-10 cm) migrate downward and enrich the 10-20 cm and 20-30 cm soil layers, which requires further studies to resolve.

Field experiments to assess the remediation efficiency of metal-contaminated soil by flushing with ferric chloride followed by applying amendments.

The Cd, Cu, Pb, and Zn removal efficiencies achieved by flushing with FeCl3 were determined in a field experiment using soil contaminated with multiple metals. Soil was first flushed with FeCl3 and then with FeCl3 or a mixture of chelators. Flushed soil was amended with lime and organic matter to revitalize the soil, then the soil was used to grow Zea mays and Brassica juncea. The heavy metal concentrations in groundwater were determined to assess the risks of leaching caused by soil flushing. The Cd, Cu, Pb, and Zn removal efficiencies were 70%, 40%, 33%, and 17%, respectively, when FeCl3 (25 mmol (kg topsoil)-1) was applied. The second washing generally did not significantly decrease the heavy metal contents of the soil but the second FeCl3 washing did decrease the Pb content. Pb leached from topsoil was partly retained by the subsoil 20-40 cm deep. The Zea mays yields were significantly lower but the Brassica juncea yields were significantly higher after the combined soil flushing and amendment treatment than after only the amendment treatment. This indicated that soil flushing only negatively affected growth of deep-rooted Z. mays. The Cd, Cu, Pb, and Zn concentrations in Z. mays grains and the edible parts of B. juncea grown in remediated soil were below the Chinese tolerable limits for contaminants in food. Washing with FeCl3 did not increase groundwater contamination during the study. The results indicated that flushing soil with FeCl3 and subsequent amendments is a technically feasible method for remediating agricultural soil contaminated with Cd.

Green remediation of cadmium-contaminated soil by cellulose nanocrystals.

Cellulose nanocrystals (CNC) were used as a novel, green eluent to remediate Cd-contaminated soil in this study. The influence of washing conditions on the removal of Cd, including CNC concentration, pH value, liquid/solid (L/S) ratio, contact time and temperature were investigated. The effect of CNC remediation of Cd-contaminated soil on soil health and the possible remediation mechanism were also explored. The results showed that CNC concentration, pH value and contact time had a significant effect on the removal efficiency of Cd. CNC rapidly removed heavy metals in soil within 30 min. When the pH value of the eluent was 9.0, the removal efficiency of Cd could reach 86.3 %. The eluent mainly removed exchangeable and reducible fractions of Cd, which could effectively reduce the bioavailability of heavy metals. CNC washing had no negative effects on seed growth, species abundance and Shannon index. C-O, -COO- groups on CNC played an important role in the reaction between CNC and soil Cd, and other oxygen-containing functional groups on CNC could also assist in adsorption, ion exchange and chemical complexation processes. Therefore, cellulose nanocrystals had the potential to remediate heavy metal-contaminated soils in a green and efficient manner.

Oxy-fuel co-combustion dynamics of phytoremediation biomass and textile dyeing sludge: Gas-to-ash pollution abatement.

The environmental pressures of major wastes in the circular economies can be abated leveraging the complementarity and optimal conditions of their co-combustion. The oxy-fuel co-combustion of phytoremediation biomass of Sedum alfredii Hance (SAH) and textile dyeing sludge (TDS) may be a promising choice for sustainable CO2 capture and a waste-to-energy conversion. This study characterized and quantified their co-combustion performances, kinetics, and interactions as a function of blend ratio, atmosphere type, and temperature. With a focus on the characteristic elements of SAH (Ca, K, Zn, and Cd) and TDS (Al and S), changes in the mineral phases and ash melting and slagging trends of K2O-Al2O3-SiO2 and CaO-Al2O3-SiO2 systems were quantified. The Zn and Cd residual rates of the co-combustion of 75% SAH and 25% TDS rose by 58.52% and 5.93%, respectively, in the oxy-fuel atmosphere at the 30% oxygen concentration, relative to the mono-combustion of SAH in the air atmosphere. The co-combustion in the oxy-fuel atmosphere at the 20% oxygen concentration delayed the release peaks of SO2, C2S, and H2S, while the Ca-rich SAH captured S in TDS through the formation of CaSO4. Our findings provide new and practical insights into the oxy-fuel co-combustion toward the enhanced co-circularity.

Evaluation of manganese application after soil stabilization to effectively reduce cadmium in rice.

In order to produce safe rice from cadmium (Cd) contaminated soils, a special pot experiment in the field was proposed to facilitate the study of multiple remediation measures. In the field experiments, four treatments were selected for the first half of the year: rice without soil treatment (R); rice with zeolite stabilization (RZ); oilseed rape phytoremediation (OR); and inter-cropping Sedum alfredii and maize phytoremediation (IC). As the early rice with zeolite stabilization still contained elevated Cd, manganese (Mn) fertilizer was added in the late rice with a special pot experiment in the field. Results showed that, in the first crops, the grains of maize and oilseed rape contained Cd below the food standard limit, while Cd in rice grain exceeded the limit of 0.2 mg/kg. The RZ treatment did not reduce Cd in rice but decreased significantly Mn in rice straw. In the late rice, Mn fertilizer additionally reduced Cd in rice grain to 0.12 mg/kg in combination with the RZ treatment. Mn accumulation in rice straw was enhanced by Mn fertilizer. These results indicate that the pot experiment in the field provides a useful tool to further evaluate effective treatment combinations to reduce Cd in rice.

Effect of mixed chelators of EDTA, GLDA, and citric acid on bioavailability of residual heavy metals in soils and soil properties.

Soil washing is an effective technology for the remediation of multi-metal contaminated soils. However, bioavailability of residual heavy metals in soils and soil properties could be changed during washing processes. This study investigated the effects of EDTA, FeCl3 and mixed chelators (MC) on bioavailability of residual heavy metals in soils and soil biological properties after soil washing. The results showed that soil washing by chelators successfully decreased the total concentration of heavy metals in soils, while it did not effectively decrease the exchangeable fraction of heavy metals, especially for calcareous contaminated soil. The toxic effects of the washed soils seemed to exhibit higher correlations with the changes in the soil properties such as soil pH and nutrient concentrations. As compared with FeCl3 and EDTA, MC tended to moderately change soil properties (e.g., pH, total N, available N, available P, and exchangeable K, Ca, and Mg). Additionally, MC-washed soil had the least influence on the soil enzymes activities, and had the highest germination and growth of Chinese cabbage. Accordingly, MC is a moderate washing solution in the removal of heavy metals from multi-metal contaminated soils, and had minimal negative effects on soil qualities.

Effect of soil washing with only chelators or combining with ferric chloride on soil heavy metal removal and phytoavailability: Field experiments.

In a field experiment on multi-metal contaminated soil, we investigated the efficiency of Cd, Pb, Zn, and Cu removal by only mixture of chelators (MC) or combining with FeCl3. After washing treatment, a co-cropping system was performed for heavy metals to be extracted by Sedum alfredii and to produce safe food from Zea mays. We analyzed the concentration of heavy metals in groundwater to evaluate the leashing risk of soil washing with FeCl3 and MC. Results showed that addition of FeCl3 was favorable to the removal of heavy metals in the topsoil. Metal leaching occurred mainly in rain season during the first co-cropping. The removal rates of Cd, Zn, Pb, and Cu in topsoil were 28%, 53%, 41%, and 21% with washing by FeCl3+MC after first harvest. The application of FeCl3 reduced the yield of S. alfredii and increased the metals concentration of Z. mays in first harvest. However, after amending soil, the metals concentration of Z. mays in FeCl3+MC treatment were similar to that only washing by MC. The grains and shoots of Z. mays were safe for use in feed production. Soil washing did not worsen groundwater contamination during the study period. But the concentration of Cd in groundwater was higher than the limit value of Standard concentrations for Groundwater IV. This study suggests that soil washing using FeCl3 and MC for the remediation of multi-metal contaminated soil is potential feasibility. However, the subsequent measure to improve the washed soil environment for planting crop is considered.

[Enhanced Phytoextraction of Heavy Metals from Contaminated Soils Using Sedum alfredii Hance with Biodegradable Chelate GLDA].

Chemically enhanced phytoextraction by hyperaccumulator has been proposed as an effective approach to remove heavy metals from contaminated soil. Pot experiment was conducted to investigate the effect of application of the biodegradable chelate GLDA (L glutamic acid N,N-diacetic acid) at different doses or the combination of GLDA with EDTA (ethylenediamine tetraacetic acid) or CIT (citric acid) on the uptake of Cd, Zn and Pb by Sedum alfredii Hance (a Zn and Cd hyperaccumulator). Experimental results showed that GLDA addition to soil significantly increased the concentrations of Cd and Zn in Sedum alfredii Hance and its Cd and Zn phytoextraction compared to the control. Additionally, GLDA at 2.5 mmol · kg(-1) resulted in the highest phytoextraction, being 2.5 and 2.6 folds of the control for Cd and Zn, respectively. However, the combined application of GLDA + EDTA (1:1) and GLDA + CIT (1 :1 and 1:3) at a total dose of 5 mmol · kg(-1) did not increase the phytoextraction of Zn and Cd, compared to the GLDA only treatment. Therefore, the biodegradable chelate GLDA could be regarded as a good chelate candidate for the phytoextraction of heavy metals of heavy metals from contaminated soils, particularly for Cd and Zn contaminated soils.

Phytoremediation of sewage sludge and use of its leachate for crop production.

The land application of sewage sludge has the potential risk of transferring heavy metals to soil or groundwater. The agricultural reuse of sludge leachate could be a cost-effective way to decrease metal contamination. Sludge leachate collected during the phytoremediation of sludge by co-cropping with Sedum alfredii and Zea mays was used for irrigating vegetables in a field experiment. Results indicate that the concentrations of Cu, Zn, Pb, and Cd in sludge leachates complied with the National Standards for agricultural irrigation water in China. For the vegetable crop Ipomoea aquatica, nutrients obtained only from the sludge leachate were not sufficient to support growth. For the second crop, Brassica parachinensis, no differences in biomass were observed between the treatment with leachate plus a half dose of inorganic fertilizer and the treatment with a full dose of inorganic fertilizers. The concentrations of heavy metals in I. aquatica and B. parachinensis were not significantly affected by the application of sludge leachates. Compared with initial values, there were no significant differences in Zn, Cd, Cu, and Pb concentrations in soil following treatment with sludge leachate. This study indicates that on range lands, sludge phytoremediation can be conducted at the upper level, and the generated sludge leachate can be safely and easily used in crop production at the lower level.

[Continuous remediation of heavy metal contaminated soil by co-cropping system enhanced with chelator].

In order to elucidate the continuous effectiveness of co-cropping system coupling with chelator enhancement in remediating heavy metal contaminated soils and its environmental risk towards underground water, soil lysimeter (0.9 m x 0.9 m x 0.9 m) experiments were conducted using a paddy soil affected by Pb and Zn mining in Lechang district of Guangdong Province, 7 successive crops were conducted for about 2.5 years. The treatments included mono-crop of Sedum alfredii Hance (Zn and Cd hyperaccumulator), mono-crop of corn (Zea mays, cv. Yunshi-5, a low-accumulating cultivar), co-crop of S. alfredii and corn, and co-crop + MC (Mixture of Chelators, comprised of citric acid, monosodium glutamate waste liquid, EDTA and KCI with molar ratio of 10: 1:2:3 at the concentration of 5 mmol x kg(-1) soil). The changes of heavy metal concentrations in plants, soil and underground water were monitored. Results showed that the co-cropping system was suitable only in spring-summer seasons and significantly increased Zn and Cd phytoextraction. In autumn-winter seasons, the growth of S. alfredii and its phytoextraction of Zn and Cd were reduced by co-cropping and MC application. In total, the mono-crops of S. alfredii recorded a highest phytoextraction of Zn and Cd. However, the greatest reduction of soil Zn, Cd and Pb was observed with the co-crop + MC treatment, the reduction rates were 28%, 50%, and 22%, respectively, relative to the initial soil metal content. The reduction of this treatment was mainly attributed to the downwards leaching of metals to the subsoil caused by MC application. The continuous monitoring of leachates during 2. 5 year's experiment also revealed that the addition of MC increased heavy metal concentrations in the leaching water, but they did not significantly exceed the III grade limits of the underground water standard of China.

Fate of heavy metals and major nutrients in a sludge-soil-plant-leachate system during the sludge phyto-treatment process.

Land application of sewage sludge usually leads to increased levels of heavy metals in soil, plants and groundwater. Pre-treatment using plants has been proposed to reduce the contents of heavy metals and water in sludge prior to land application. This study quantified the transfer of Zn, Cd, Pb and major nutrients in a sludge-soil-plant-leachate system during the treatment of sewage sludge. To accomplish this, a two year pot experiment was carried out to collect leachate, mono- and co-cropping of Sedum alfredii and feed crops was conducted in sludge with an under-layer soil support. Sludge phyto-treatment increased Zn and Cd concentrations in the under-layer soil, but not Pb. Specifically, 70%, 70% and 80% of the original Zn, Cd and Pb, respectively, remained in the sludge, while about 40%, 70% and 60% of the original N, P and K remained. Only 3% to 5% of Cd and Zn and < 1% of Pb were transferred into the under-layer soils or leachates, while more than 12% of the N and P were transferred. Co-planting S. alfredii and feed crops led to a significant reduction of heavy metals in leachates when compared with sludge without planting. Overall, sludge leachate is more appropriate than whole sludge for recycling in agriculture since it reduces the chance of heavy metal contamination in the agro-ecosystem; therefore, co-cropping phytotreatment of sludge can be coupled with sludge leachate recycling for crop production and re-collection of the sludge residue for landfilling.

Dissolution of different zinc salts and zn uptake by Sedum alfredii and maize in mono- and co-cropping under hydroponic culture.

Previous soil pot and field experiments demonstrated that co-cropping the hyperaccumulator Sedum alfredii with maize increased Zn phytoextraction by S. alfredii and decreased Zn uptake by maize shoots. This hydroponic experiment was conducted to investigate whether the facilitation of Zn phytoextraction by S. alfredii resulted from improved dissolution in this co-cropping system and its relation to root exudates. S. alfredii and maize were mono- and co-cropped (without a root barrier) in nutrient solution spiked with four Zn compounds, ZnS, ZnO, Zn3(PO4)2 and 5ZnO x 2CO3-4H2O (represented as ZnCO3) at 1000 mg/L Zn for 15 days without renewal of nutrient solution after pre-culture. The root exudates were collected under incomplete sterilization and analyzed. The results indicated that the difference in Zn salts had a greater influence on the Zn concentration in maize than for S. alfredii, varying from 210-2603 mg/kg for maize shoots and 6445-12476 mg/kg for S. alfredii in the same order: ZnCO3 > ZnO > Zn3(PO4)2 > ZnS. For the four kinds of Zn sources in this experiment, co-cropping with maize did not improve Zn phytoextraction by S. alfredii. In most cases, compared to co-cropped and mono-cropped maize, mono-cropped S. alfredii resulted in the highest Zn2+ concentration in the remaining nutrient solution, and also had a higher total concentration of low molecular weight organic acids (LMWOA) and lower pH of root exudation. Root exudates did partly influence Zn hyperaccumulation in S. alfredii.

[Effects of mixed chelators on the leaching of cadmium in contaminated soils under intercropping system].

In order to elucidate the influence of chelators on Cd leaching in contaminated soil, outdoor soil column (100 cm) leaching experiments were conducted using two paddy soils irrigated with Pb-Zn mining wastewater. Soil samples which under intercropping systems were collected from Qingyuan City (acid soil with pH 4.63) and Lechang city (neutral soil with pH 6.51), Guangdong Province of China. The mixture of chelators (MC) comprised of citric acid, monosodium glutamate waste liquid, EDTA and KCl with molar ratio of 10 : 1 : 2 : 3 at the concentration of 5 mmol x kg(-1) soil. The intercropping system used in this study was a Zn- and Cd-hyperaccumulator (Sedum alfredii) and a low-accumulating crop (Zea mays). Results showed that at day 2 after the application of MC, the Cd concentrations in leachates from every layer of neutral and acid soils increased significantly in the treatment with intercropping and MC. At day 8 the concentrations of Cd in leachate from layers below 20 cm in the neutral soil and below 60 cm in the acid soil were still significantly higher than those of control. However, the mobility of Cd was decreased greatly compared with that at day 2. At day 2 and day 8 the Cd concentrations in leachates from every layer of neutral and acid soils in the Co-crop + MC treatments exceed the value of the Groundwater Quality Standards (GB/T 14848-93). Cd in all soil columns showed the trend to migrate downwards, especially in the acid soil. The total Cd in the soil layers of 20 cm and 40 cm was decreased by 40% -58% and 39%-49% respectively at the end of the experiments compared to the initial value. After leaching of 100 days,the total Cd in 0-40 cm soil layer of acid soil reached the limit of National Soil Environmental Quality Standards (GB 15618-1995). The results also implied that in Cd-contaminated soil MC addition might enhance the potential risks of Cd contamination in groundwater.

[Reducing nutrients loss by plastic film covering chemical fertilizers].

With the low utilization rate of fertilizers by crop and the growing amount of fertilizer usage,the agricultural non-point source pollution in China is becoming more and more serious. The field experiments planting corns were conducted, in which the applied chemical fertilizers were recovered with plastic film to realize the separation of fertilizers from rain water. In the experiments, the influences of different fertilizing treatments on the growing and production of sweet corn were observed. The fertilizer utilization rate and the nutrient contents in surface run-off water with and without the film covering were also determined. Results showed that, with only 70% of the normal amount of fertilizers,the sweet corn could already get high yield under the experimental soil conditions. Soil analysis after corn crops showed that the amounts of available N, P and K in the soil increased obviously with the film-covering, and the decreasing order was: 100% fertilizers with film-covering > 70% fertilizers with film-covering > 100% fertilizers, 70% fertilizers > no fertilizer. The average utilization coefficients of fertilizers by the crop were 42%-87%, 0%-3%, 5%-15% respectively for N, P and K. It was higher with film-covering than that without covering, especially for the high fertilization treatment. Analysis of water samples collected for eight run-off events showed that, without film-covering, N, P and K average concentrations in the runoff waters with fertilizations were 27.72, 2.70 and 7.07 mg x L(-1), respectively. And they were reduced respectively by 39.54%, 28.05%, 43.74% with the film-covering. This can give significant benefits to the decrease of agricultural non-point source pollution and water eutrophication.

[Metal removal from contaminated soil by co-planting phytoextraction and soil washing].

Combining the different soil remediation technologies can overcome the shortcoming of a single technique, for example, the combination of phyto-extraction with chemical washing can enhance the phytoextraction and build up an effective technology. In a pot experiment, the co-crop of Sedum alfredii and Zea mays was conducted, chemical washing was also applied with different mixtures of chelators (MC). Metals amounts washed by leaching, the uptake of metals by plants and the metals contents remained in soils were determined. Results showed that the co-crop combining with 10 mmol x L(-1) MC washing removed the highest amount of Zn and Cd,and after 2 crops, the removal rates reached 6.0% and 40.46% of the soil total metal respectively for Zn and Cd, which were higher than those for the only co-planting. Soil analysis showed that the two successive co-crops with MC washings decreased soil Cd,Zn and Pb by 27.8% - 44.6%,12.6% -16.5% and 3.6% - 5.7%, respectively. Chemical washing with 50 mmol x L(-1) MC affected the growth of S. alfredii and resulted in higher metal contents in thereafter leachate water than the other less concentrated washing agents. EDDS ([S, S]-ethylenediaminedisuccinic acid) enhanced the phytoextraction of Cd and Zn but did not effectively wash Pb. Zn and Cd removal mainly depended on phytoextraction while Pb removal relied on MC-washing in this combined technology, by which the multi-metals contamination problem could be resolved.