Cadmium tolerance and its phytoremediation by two oil yielding plants Ricinus communis (L.) and Brassica juncea (L.) from the contaminated soil

The effect of increasing level of cadmium in soil was investigated on biomass production, antioxidants, Cd bioaccumulation and translocation in Ricinus communis vis-à-vis a commonly studied oil crop Brassica juncea. The plants were exposed to 25, 50, 75, 100, and 150 mg Cd/Kg soil for up to 60 days. It was found that R. communis produced higher biomass at all the contamination levels than that of B. juncea. Proline and malondialdehyde in the leaves increased with increase in Cd level in both the species, whereas soluble protein decreased. The bioaccumulation of Cd was higher in B. juncea on the basis of the per unit biomass, total metal accumulation per plant was higher in R. communis. The translocation of Cdfrom roots to shoot was also higher in B. juncea at all Cd concentrations. R. communis appeared more tolerant and capable to clean Cd contaminated soil for longer period in one sowing than B. juncea and the former can grow in wasteland soil also in which later cannot be cultivated.     

Phytoremediation of Metal Contaminated Soil Using Willow: Exploiting Plant-Associated Bacteria to Improve Biomass Production and Metal Uptake

Short rotation coppice (SRC) of willow and poplar is proposed for economic valorization and concurrently as remediation strategy for metal contaminated land in northeast-Belgium. However, metal phytoextraction appears insufficient to effectuate rapid reduction of soil metal contents. To increase both biomass production and metal accumulation of SRC, two strategies are proposed: (i) in situ selection of the best performing clones and (ii) bioaugmentation of these clones with beneficial plant-associated bacteria. Based on field data, two experimental willow clones, a Salix viminalis and a Salix alba x alba clone, were selected. Compared to the best performing commercial clones, considerable increases in stem metal extraction were achieved (up to 74% for Cd and 91% for Zn). From the selected clones, plant-associated bacteria were isolated and identified. All strains were subsequently screened for their plant growth-promoting and metal uptake enhancing traits. Five strains were selected for a greenhouse inoculation experiment with the selected clones planted in Cd-Zn-Pb contaminated soil. Extraction potential tended to increase after inoculation of S. viminalis plants with a Rahnella sp. strain due to a significantly increased twig biomass. However, although bacterial strains showing beneficial traits in vitro were used for inoculation, increments in extraction potential were not always observed.     

A Study on Cadmium Phytoremediation Potential of Indian Mustard,Brassica juncea

The objective of this study was to investigate Cd phytoremediation ability of Indian mustard, Brassica juncea. The study was conducted with 25, 50, 100, 200 and 400 mg Kg^?1 CdCl₂ in laboratory for 21 days and Cd concentrations in the root, shoot and leaf tissues were estimated by atomic absorption spectroscopy. The plant showed high Cd tolerance of up to 400 mg Kg^?1 but there was a general trend of decline in the root and shoot length, tissue biomass, leaf chlorophyll and carotenoid contents. The tolerance index (TI) of plants were calculated taking both root and shoot lengths as variables. The maximum tolerance (TI _shoot = 87.4 % and TI _root = 89.6 %) to Cd toxicity was observed at 25 mg Kg^?1, which progressively decreased with increase in dose. The highest shoot (10791 μg g^?1 dry wt) and root (9602 μg g^?1 dry wt) Cd accumulation was achieved at 200 mg kg^?1 Cd treatment and the maximum leaf Cd accumulation was 10071.6 μg g^?1 dry wt achieved at 100 mg Kg^?1 Cd, after 21 days of treatment. The enrichment coefficient and root to shoot translocation factor were calculated, which, pointed towards the suitability of Indian mustard for removing Cd from soil.     

EDTA Supported Phytoextraction of Cd from Contaminated Soil by Four Different Ornamental Plant Species

In this study, some ornamental plant species such as Althaea rosea Cavan, Lonicera japonica Thunb, Salvia virgata Jacq. (Lamiaceae), and Dahlia hybrida growing in the natural vegetation of Black Sea Region (Turkey) were investigated for their phytoextraction potential of cadmium (Cd) from artificially contaminated soil of 10, 25, 50, and 100 mg/kg concentration under pot conditions. Effect of ethylenediaminetetracetic acid (EDTA) on this removal has also been studied. To evaluate the removal efficiency of the studied plants, the bioconcentration factor (BCF) and translocation factor (TF) values were also calculated. Higher BCF and TF values obtained from stems and leaves of A. rosea Cavan, L. japonica Thunb, and S. virgata Jacq. (Lamiaceae) show that those plants might be cultivated and used as hyperaccumulators in the removal of Cd from the contaminated soils. EDTA enhanced the Cd phytoextraction in plants; however, at the same time it resulted in a slight decrease in the dry matter.     

Phytoextraction of Heavy Metals from Highly Contaminated Soils Using Sauropus androgynus

It has been found that Sauropusandrogynus has a strong adaptive capacity in multiple heavy-metal-contaminated soils. Field trials in highly heavy-metal-contaminated soils were conducted to investigate the extraction efficiency of Cd, Cu, Pb, and Zn by S. androgynus. The yield of S. androgynus could reach 10.01 t ha^?1, and the amount of Cd, Cu, Pb, and Zn extracted by the plant was 57.36, 218.57, 2078.11, and 19.64 g ha^?1, respectively. S. androgynus removed 0.35%, 0.01%, 0.03%, and 1.37% of the total soil Cd, Cu, Pb, and Zn in one growing season, respectively. By comparing the extracting capability and yield with some hyperaccumulators reported in the literature, S. androgynus was considered to be a highly effective plant to extract heavy metals (Cd, Cu, Pb, and Zn). The plant should be useful for phytoextraction of soils contaminated by the heavy metals.     

Arbuscular Mycorrhizal Fungi Enhance Zinc and Nickel Uptake from Contaminated Soil by Soybean and Lentil

Generally, soils in Pakistan are deficient in P and N. Due to intensive cropping and irrigation, Pakistani soils have also become deficient in micronutrients such as Zn, Fe, Cu, and Mn. Arbuscular mycorrhizal fungi, which form symbiotic associations with roots of most land plants, are known to enhance uptake of P and trace elements such as Cu, Ni, Pb, and Zn. The present study was conducted to investigate the role of arbuscular mycorrhizae (AM) in uptake of nickel (Ni) and zinc (Zn) by crops viz. soybean (Glycine max (L.) Merrill) and lentil (Lens culinaris Medic). Zn and Ni were applied as ZnSO₄ 7H₂O and NiCl₂ respectively, in four concentrations (0.0, 1.0, 3.0, and 5.0 g kg^-1 soil). AM inoculum consisted of sand containing sporocarps, spores, and AMF infected root pieces from a pot culture of Glomus mosseae. Control plants received pot culture filtrate containing soil microflora minus AM fungal propagules. A significant difference (p < 0.05) was observed in the dry weights of roots and shoots of the mycorrhizal (M) and nonmycorrhizal (NM) cereal plants. The sievate-amended treatments did not stimulate plant growth to the same extent as the AM fungal amended treatments. Trace metals inhibited the extent of mycorrhizal colonization of the cereal roots. The concentrations of the trace metals in the plant tissues of 12-week old cereal plants were found significantly (p < 0.05) higher in M than NM plants. These results indicate that mycorrhize can be used as effective tools to supply sufficient Zn in generally Zn-deficient Pakistani soils and to ameliorate the toxicity of trace metals in polluted soils. The contents of Ni in mycorrhizal soybean plant tissues were higher than those in the mycorrhizal lentil plant tissues. The implications of these results in mycorrhizo remediation of agricultural soils are discussed.     

Phytoremediation of Heavy Metals in Contaminated Water and Soil Using Miscanthus sp. Goedae-Uksae 1

The aim of this study is to characterize the heavy metal phytoremediation potential of Miscanthus sp. Goedae-Uksae 1, a hybrid, perennial, bio-energy crop developed in South Korea. Six different metals (As, Cu, Pb, Ni, Cd, and Zn) were used for the study. The hybrid grass effectively absorbed all the metals from contaminated soil. The maximum removal was observed for As (97.7%), and minimum removal was observed for Zn (42.9%). Similarly, Goedae-Uksae 1 absorbed all the metals from contaminated water except As. Cd, Pb, and Zn were completely (100%) removed from contaminated water samples. Generally, the concentration of metals in roots was several folds higher than in shoots. Initial concentration of metals highly influenced the phytoremediation rate. The results of the bioconcentration factor, translocation factor, and enrichment coefficient tests indicate that Goedae-Uksae 1 could be used for phytoremediation in a marginally contaminated ecosystem.     

Chemically Assisted Phytoextraction: A Review of Potential Soil Amendments for Increasing Plant Uptake of Heavy Metals

The contamination of soils by trace metals has been an unfortunate sideeffect of industrialization. Some of these contaminants can interfere with vulnerable enduses of soil, such as agriculture or nature, already at relatively low levels of contamination. Reversely, conventional civil–technical soil-remediation techniques are too expensive to remediate extended areas of moderately contaminated soil. Phytoextraction has been proposed as a more economic complementary approach to deal with this specific niche of soil contamination. However, phytoextraction has been shown to be a slow-working process due to the low amounts of metals that can be annually removed from the soil under normal agronomic conditions. Therefore, extensive research has been conducted on process optimization by means of chemically improving plant availability and the uptake of heavy metals. A wide range of potential amendments has been proposed in the literature, with considerable attention being spent on aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA). However, these compounds have received increasing criticism due to their environmental persistence and associated risks for leaching. This review presents an overview of potential soil amendments that can be employed for enhancing metal uptake by phytoextraction crops, with a distinct focus on more degradable alternatives to persistent compounds such as EDTA.     

Effects of Bacterial Inoculation to Immobilize Nickel in Wheat Grown on Ni-Contaminated Soil

Abstract

Plant growth stimulating bacteria are very effective in immobilization of metals and reducing their translocation in plants through precipitation, and adsorption. A pot experiment was conducted to investigate the effectiveness of chitosan- and hematite-modified biochar and bacterial inoculations on the immobilization of nickel (Ni) in polluted soil under wheat cultivation. Application of modified biochars and inoculation with Pseudomonas putida significantly increased both wheat root and shoot dry matter yields but decreased Ni phytoextraction efficiency. The Ni concentration, translocation factor and uptake in wheat shoot and root significantly decreased the application of either modified or unmodified biochars. Bacterial inoculation significantly decreased mean translocation factor and also root and shoot concentration and the uptake Ni in the shoot. Chitosan-modified biochar was the most influential treatment in decreasing Ni uptake by wheat followed by P. putida inoculation treatment. The results demonstrated positive effects of chitosan modified biochar and inoculation with P. putida in increasing dry matter yield and decreasing Ni uptake in wheat grown on Ni-contaminated soil. According to the results of present study, modified biochars application and bacterial inoculation are influential treatments which prevent Ni toxicity probably.     

The Importance of Nickel Phytoavailable Chemical Species Characterization in Soil for Phytoremediation Applicability

In this work Ni speciation in natural and spiked soils (with similar total concentration) was studied. Spiked soils were prepared by addition of NiSO₄.6H₂O to obtain concentration similar to the one in natural soils. In soils mobile species were determined with a simplified sequential extraction as follows: H₂O for water-soluble metal, KNO₃ for exchangeable species, DTPA for complexed/adsorbed species. Results show that in spiked soils the exchangeable and adsorbed Ni concentrations are considerably higher than in natural soils. A study of plant uptake was carried out in order to evaluate the relation between mobile species and phyto-availability. Alfalfa (Medicago sativa L.), even though it is not a hyperaccumulator, was selected for its tolerance to high metal concentrations in soil. Preliminary results show a very high correlation between Ni mobile species and Ni uptake by alfalfa. Significant differences were found between spiked and natural soils. In the latter, high levels of total Ni did not correspond to relevant uptake as in the case of spiked soil. Results stress the importance of evaluating preliminarly heavy metal speciation in soil before planning phytoremediation procedures.     

Assessment of the Efficiency of a Metal Phytoextraction Process with Biological Indicators of Soil Health

The ultimate goal of any soil remediation process should be not only to remove the contaminant(s) from the polluted site but to restore soil health as well. In consequence, reliable indicators of soil health are needed if we are to properly evaluate the efficiency of a soil remediation process. The aim of the current work was to determine the effect of metal phytoextraction, through the utilization of the Zn hyperaccumulator T. caerulescens, on biological parameters of soil health, on the assumption that biological indicators of soil health might be valid monitoring tools to assess the efficiency of a metal phytoextraction process. To this end, a short-term microcosm phytoextraction study was carried out, with two heavy metal polluted soils collected from an abandoned mine, to determine the effect of metal phytoextraction on soil biological parameters. Higher values of biomass C, basal respiration, substrate induced respiration, and β-glucosidase activity were observed in the presence of T. caerulescens plants, as compared to unplanted pots. Our data confirm the great capacity of T. caerulescens to phytoextract Zn from polluted soils and, interestingly, suggest that metal phytoextraction has indeed a beneficial effect on soil biological activity. It was concluded that the revegetation of these metal polluted soils with T. caerulescens could help activate their biochemical and microbial functionality.     

Comparison of EDTA- and Citric Acid-Enhanced Phytoextraction of Heavy Metals in Artificially Metal Contaminated Soil by Typha Angustifolia

A pot experiment was conducted to study the performance of EDTA and citric acid (CA) addition in improving phytoextraction of Cd, Cu, Pb, and Cr from artificially contaminated soil by T. angustifolia. T. angustifolia showed the remarkable resistance to heavy metal toxicity with no visual toxic symptom including chlorosis and necrosis when exposed to metal stress. EDTA-addition significantly reduced plant height and biomass, compared with the control, and stunted plant growth, while 2.5 and 5 mM CA addition induced significant increases in root dry weight. EDTA, and 5 and 10 mM CA significantly increased shoot Cd, Pb, and Cr concentrations compared with the control, with EDTA being more effective. At final harvest, the highest shoot Cd, Cr, and Pb concentrations were recorded in the treatment of 5 mM EDTA addition, while maximal root Pb concentration was found at the 2.5 mM CA treatment. However, shoot Cd accumulation in the 10 mM CA treatment was 36.9% higher than that in 2.5 mM EDTA, and similar with that in 10 mM EDTA. Shoot Pb accumulation was lower in 10 mM CA than that in EDTA treatments. Further, root Cd, Cu, and Pb accumulation of CA treatments and shoot Cr accumulation in 5 or 10 mM CA treatments were markedly higher than that of control and EDTA treatments. The results also showed that EDTA dramatically increased the dissolution of Cu, Cr, Pb, and Cd in soil, while CA addition had less effect on water-soluble Cu, Cr, and Cd, and no effect on Pb levels. It is suggested that CA can be a good chelator candidate for T. angustifolia used for environmentally safe phytoextraction of Cd and Cr in soils.     

Phytoremediation of Landfill Leachate with Colocasia esculenta,Gynerum sagittatum and Heliconia psittacorum in Constructed Wetlands

This study assessed the accumulation of Cd (II), Hg (II), Cr (VI) and Pb (II) in Gynerium sagittatum (Gs), Colocasia esculenta (Ce) and Heliconia psittacorum (He) planted in constructed wetlands treating synthetic landfill leachate. Sixteen bioreactors were operated in two experimental blocks. Metal concentrations in the influent and effluent; root, stem, branch and leaves of plants were analysed, as well as COD, N-NH₄⁺, TKN, T, pH, ORP, DO, and EC. Average removal efficiencies of COD, TKN and NH₄⁺-N were 66, 67 and 72%, respectively and heavy metal removal ranged from 92 to 98% in all units. Cr (VI) was not detected in any effluent sample. The bioconcentration factors (BCF) were 10⁰ -10². The BCF of Cr (VI) was the lowest: 0.59 and 2.5 (L kg^?1) for Gs and He respectively; whilst Cd (II) had the highest (130–135 L kg^?1) for Gs. Roots showed a higher metal content than shoots. Translocation factors (TF) were lower, He was the plant exhibiting TFs >1 for Pb (II), Cr (T) and Hg (II) and 0.4–0.9 for Cd (II) and Cr (VI). The evaluated plants demonstrate their suitability for phytoremediation of landfill leachate and all of them can be categorized as metals accumulators.     

Phytoremediation of lead (Pb) and Arsenic (As) by Melastoma malabathricum L. from Contaminated Soil in Separate Exposure

This study was conducted to investigate the uptake of lead (Pb) and arsenic (As) from contaminated soil using Melastoma malabathricum L. species. The cultivated plants were exposed to As and Pb in separate soils for an observation period of 70 days. From the results of the analysis, M. malabathricum accumulated relatively high range of As concentration in its roots, up to a maximum of 2800 mg/kg. The highest accumulation of As in stems and leaves was 570 mg/kg of plant. For Pb treatment, the highest concentration (13,800 mg/kg) was accumulated in the roots of plants. The maximum accumulation in stems was 880 mg/kg while maximum accumulation in leaves was 2,200 mg/kg. Only small amounts of Pb were translocated from roots to above ground plant parts (TF < 1). However, a wider range of TF values (0.01–23) for As treated plants proved that the translocation of As from root to above ground parts was greater. However, the high capacity of roots to take up Pb and As (BF > 1) is indicative this plants is a good bioaccumulator for these metals. Therefore, phytostabilisation is the mechanism at work in M. malabathricum's uptake of Pb, while phytoextraction is the dominant mechanism with As.     

Environmental Assessment of the Caveira Abandoned Mine (Southern Portugal): Part 1: Characterization of Metal Contaminated Soil

Mine activity in Portugal had a huge impact on the growth of the regions where it took place, like in the Iberian Pyrite Belt. Nowadays, most of these mines are abandoned, as is the case for the Caveira mine. Soil geochemistry indicates that high contents of Cu, Pb, Zn, As, Cd, and Hg occur in the soils collected near the tailings. Multiple Correspondence Analysis identifies two areas with high concentrations of Pb, As, Hg, Sb, Mo, and Tl. However, the results suggest a different geochemistry for each of the areas. The non-site-specific methods (Hazard Index and GLC guidelines) classify all the areas as contaminated. Metal fractionation in the soil phases is different for the several elements studied. The articulation of the metal fractionation results with the GLC guidelines reduces the area of soil contaminated by Pb, but not by As.     

Ecofriendly Heavy Metal Stabilization: Microbial Induced Mineral Precipitation (MIMP) and Biomineralization for Heavy Metals within the Contaminated Soil by Indigenous Bacteria

Heavy metals (HMs) pollution is a serious problem, worldwide. The present study focuses on HMs removal (HMs mobility restricted within soil) by microbial induced mineral precipitation (MIMP) using indigenous isolates. Indigenous isolates were identified as Bacillus subtilis C(225)(MK334652), Oceanobacillus indicireducens 5(225)(MK334653), and Bacillus pumilus 7(225)(MK334654) by 16S-rRNA from HMs polluted industrial-soil (soil-225) that is used for bioremediation. The studied soil contained high level (mg/kg) of Cr(307.41?±?1.02), Cu(576.35?±?1.02), and Zn(708.81?±?1.50) as per Taiwan permissible limit (TPL) and/or Canadian Soil Quality Guidelines (CSQG). Minimum inhibitory concentration (MIC) of Bacillus species were higher compare to Oceanobacillus. Bioavailable-fraction (F₁) of HMs (Cr/Cu/Zn) in untreated 225-soil was noticed to be higher compared to F₂–F₅ fraction. Bacillus subtilis C(225) are more efficient for HMs-mineralization, compared to other isolates where Cr/Cu/Zn immobilized within soil, transforming from bioavailable-fraction (F₁) (high-mobility) (60–90% reduction) to residual-fraction F₅ (low-mobility) (50–80% increment). Organic-bound-fraction (F₄) (medium-mobility) of Cr increased (42.66?±?2.1%), compared to Cu/Zn, by Bacillus subtilis C(225). Urease (40.8%) and dehydrogenase (8.3%) activity increased in bio-remediated soil, compared to control. MIMP of HMs by ingenious bacteria reflects the transformation-pathway from F₁ to F₅ of HMs to fix strongly within soils with inadequate mobility. Thus, MIMP by indigenous microbe can be applicable for HMs stabilization/removal in contaminated soil for ecofriendly environmental cleanup.     

Recent Findings on the Phytoremediation of Soils Contaminated with Environmentally Toxic Heavy Metals and Metalloids Such as Zinc,Cadmium, Lead,and Arsenic

Due to their immutable nature, metals are a group of pollutants of much concern. As a result of human activities such as mining and smelting of metalliferous ores, electroplating, gas exhaust, energy and fuel production, fertilizer and pesticide application, etc., metal pollution has become one of the most serious environmental problems today. Phytoremediation, an emerging cost-effective, non-intrusive, and aesthetically pleasing technology, that uses the remarkable ability of plants to concentrate elements and compounds from the environment and to metabolize various molecules in their tissues, appears very promising for the removal of pollutants from the environment. Within this field of phytoremediation, the utilization of plants to transport and concentrate metals from the soil into the harvestable parts of roots and above-ground shoots, i.e., phytoextraction, may be, at present, approaching commercialization. Improvement of the capacity of plants to tolerate and accumulate metals by genetic engineering should open up new possibilities for phytoremediation. The lack of understanding pertaining to metal uptake and translocation mechanisms, enhancement amendments, and external effects of phytoremediation is hindering its full scale application. Due to its great potential as a viable alternative to traditional contaminated land remediation methods, phytoremediation is currently an exciting area of active research.     

Potential of Indigenous Plant Species for the Phytoremediation of Arsenic Contaminated Land in Kurdistan (Iran)

To evaluate the potential of the indigenous plant species for Arsenic (As) phytoremediation, a total of 138 plant samples and 138 soil samples from rooting zones were collected from two As-contaminated areas in Kurdistan, western Iran. The areas were the Sari Gunay Gold Mine (SG) and Ali Abad Village (AA). The soil of both areas naturally contains As, with mining activities at SG. Soil and plant samples were collected at five sites in the SG (SG1 to SG5) and at two sites in the AA (AA1 and AA2). Soil samples were analyzed for total and water-soluble As concentration, as well as for the main soil physical and chemical properties such as electrical conductivity (Ec), pH, organic carbon (C_org.), available phosphorus (P_ava.), and soil texture. Plant samples were analyzed for As concentration in their shoots and roots.

The average total and water–soluble As concentrations in soil were 751.6 and 6.2 ppm at SG and 920.8 and 8.0 ppm at AA, respectively. The highest root and shoot As concentration was found in Juncus inflexus (751.5 ppm) at AA2 and in Astragalus gossypinus (158.7 ppm) at AA1, respectively. With regard to phytoremediation strategies, Acantholimon brachystachyum, Astragalus gossypinus, Stipa barbata, and Ephedra major with a high translocation factor (TF) can be potentially used for As phytoextraction. However, Juncus inflexus, Phragmites australis, Bromus tomentellus, and Elymus sp., which show high bioconcentration factor (BCF) and low TF, are suggested as good candidates for As phytostabilization. In general, the TF values of terrestrial plants were higher than those of amphibious plants; meanwhile, BCF values showed the opposite behavior.     

Assessment of potential indigenous plant species for the phytoremediation of arsenic-contaminated areas of Bangladesh

Soil and water contaminated with arsenic (As) pose a major environmental and human health problem in Bangladesh. Phytoremediation, a plant-based technology, may provide an economically viable solution for remediating the As-polluted sites. The use of indigenous plants with a high tolerance and accumulation capacity for As may be a very convenient approach for phytoremediation. To assess the potential of native plant species for phytoremediation, plant and soil samples were collected from four As-contaminated (groundwater) districts in Bangladesh. The main criteria used for selecting plants for phytoremediation were high bioconcentration factors (BCFs) and translocation factors (TFs) of As. From the results of a screening of 49 plant species belonging to 29 families, only one species of fern (Dryopteris filix-mas), three herbs (Blumea lacera, Mikania cordata, and Ageratum conyzoides), and two shrubs (Clerodendrum trichotomum and Ricinus communis) were found to be suitable for phytoremediation. Arsenic bioconcentration and translocation factors > 1 suggest that these plants are As-tolerant accumulators with potential use in phytoextraction. Three floating plants (Eichhornia crassipes, Spirodela polyrhiza, and Azolla pinnata) and a common wetland weed (Monochoria vaginalis) also showed high BCF and TF values; therefore, these plants may be promising candidates for cleaningup As-contaminated surface water and wetland areas. The BCF of Oryza sativa, obtained from As-contaminated districts was > 1, which highlights possible food-chain transfer issues for As-contaminated areas in Bangladesh.     

Heavy Metal Uptake by Willow Clones from Sewage Sludge-Treated Soil: The Potential for Phytoremediation

Willow (Salix spp.) has shown potential for use in the phytoremediation of soil contaminated with heavy metals. In particular, it can be grown in short rotation coppice systems to produce biomass that can be used for energy production. Twenty different species or varieties of willow, grown over 2 years (1995 to 1997) on a soil that was highly contaminated with heavy metals due to long-term sewage sludge disposal, showed considerable variation in survival, biomass production and metal uptake. The willows could be divided into two groups after the first harvest. One group had relatively low Ni and Cu in the bark and high Cd and Zn in the wood, with a good survival rate and biomass production. This group partitioned Cu, Cd, and Zn into the wood tissue from the bark, whereas Ni was excluded. The second group had relatively high Ni and Cu in the bark and low Cd and Zn in the wood and performed poorly in terms of survival and biomass production. Of the 20 types of willow used, 11 showed potential for use in phytoremediation, combining good survival and biomass production with high metal uptake. Of the others, 2 failed to survive until the second harvest and the other 7 had very poor survival rates.