Heavy-Metal Bioavailability and Chelate Mobilization Efficiency in an Assisted Phytoextraction Process by Sesbania sesban (L.) Merr

Chelate-induced phytoextraction is an innovative technique for cleaning metal- contaminated soil. The present study evaluates the degree of metal mobilization in soil and enhancement of phytoextraction of cadmium (Cd), lead (Pb), and zinc (Zn) by Sesbania sesban (L.) Merr. from artificially contaminated soil by application of ethylenediaminetetraacetic acid (EDTA). After 30 days of plant growth, the pots were divided into three sets (0.0, 2.5, and 5.0 mmol EDTA per kg soil). Experimental results indicated that levels of diethylenetriaminepentaacetic acid (DTPA)–extractable metals and metals in the leachate decreased as the EDTA dose increased. Plant growth parameters and total chlorophyll contents in the plants with EDTA applied were less than those of control. However, EDTA application significantly reduced metal accumulation in root and increased metal accumulation in the shoot of plants; similar results were obtained for the bioconcentration factor and translocation factor. The application of 5 mmol EDTA kg^?1 to metal-spiked soil may be an efficient alternative for the chemically enhanced phytoextraction by S. sesban.     

Application of plant growth-promoting endophytes (PGPE) isolated from Solanum nigrum L. for phytoextraction of Cd-polluted soils

Many plant growth-promoting endophytes (PGPE) can assist their host plants cope with contaminant-induced stress responses, which can improve plant growth. In this study, four heavy metals resistant endophytic bacteria, Serratia nematodiphila LRE07, Enterobacter aerogenes LRE17, Enterobacter sp. LSE04 and Acinetobacter sp. LSE06, were isolated from Cd-hyperaccumulator Solanum nigrum L. grown in metal-polluted soil. Their plant growth promoting properties such as production of 1-aminocyclopropane-1-carboxylic (ACC) deaminase, indole-3-acetic acid (IAA), siderophores and phosphate solubilizing activity were characterized in vitro. When added to the Cd-amended soils, all of these four bacteria significantly increased Cd extraction from the soils. Subsequently, a pot experiment was conducted to elucidate the effects of inoculating of these PGPE on the plant growth and Cd uptake by S. nigrum L. grown in three different levels of Cd-contaminated soils. Results showed that the inoculation with these PGPE not only stimulated the growth of host plant, but also influenced the accumulation of Cd in the root, stem and leaf tissue of S. nigrum L. All four strains could colonize the rhizosphere soil and even some can be found in plant interior tissues. The present observations demonstrated that PGPE were valuable microorganism resource which can be exploited to improve the efficiency of phytoextraction.     

Interaction of Cd-hyperaccumulator Solanum nigrum L. and functional endophyte Pseudomonas sp. Lk9 on soil heavy metals uptake

Bioaugmentation is a promising method for assisting phytoextraction of heavy metals from contaminated soil, and the development of bioaugmentation-assisted phytoextraction requires the understanding of the mechanism involved in the interaction between plants and inocula. In this study, a pot study was conducted to evaluate the effect of bacterial endophyte Pseudomonas sp. Lk9 which can produce biosurfactants, siderophores and organic acids on the growth and metal uptake of Cd-hyperaccumulator Solanum nigrum L. growing in multi-metal-contaminated soil. The results revealed that Lk9 inoculation could improve soil Fe and P mineral nutrition supplies, enhance soil heavy metal availability, and affect host-mediated low-molecular-weight organic acids secretion, thereby significantly increasing S. nigrum shoot dry biomass by 14% and the total of Cd by 46.6%, Zn by 16.4% and Cu by 16.0% accumulated in aerial parts, compared to those of non-inoculated control. The assessment of phytoextraction showed that Lk9 inoculation elevated the bioaccumulation factor of Cd (28.9%) and phytoextraction rates of all metals (17.4%, 48.6% and 104.6% for Cd, Zn and Cu, respectively), while the translocation factors had negligible difference between Lk9 inoculation (3.30, 0.50 and 0.40 for Cd, Zn and Cu, respectively) and non-inoculated control (2.95, 0.53 and 0.42 for Cd, Zn and Cu, respectively). It was also found that the symbiotic association between S. nigrum and Lk9 significantly increased the soil microbial biomass C by 39.2% and acid phosphatase activity by 28.6% compared to those in S. nigrum without Lk9. This study would provide a new insight into the bioaugmentation-assisted phytoextraction of heavy metal-contaminated soils.     

Plant availability and leaching of (heavy) metals from ammonium‐, calcium‐, carbohydrate‐, and citric acid‐treated uranium‐mine‐dump soil

Remediation of an uranium‐mine soil from Settendorf (East Germany) includes phytoextraction under conditions which make its heavy metals more plant‐available but less leachable. A second way is active inhibition of heavy metal uptake by the plant. In a pot trial with Chinese cabbage (Brassica chinensis L.), planted and unplanted soil samples were daily irrigated with deionized water or aqueous solutions with a total of (g (kg soil)^–1) CaCl₂ (0.26 Ca), NH₄Cl (1.39), casein, sucrose, citric acid (13), and an extract of rape (B. napus L.) shoots (13 DW) in a phytotron for 26 d. Water‐irrigated plants were also treated with a 50 mM citric acid solution (10.5 g (kg soil)^–1) 6 and 7 d prior to harvesting. Total elements in plant tissue and soluble elements in aqueous extracts from control and postharvest soils were determined by ICP‐AES. Supplements of NH , and the NH ‐generating casein and rape extract reduced soil pH during nitrification, and increased plant uptake of Cd, Cu, Ni, and Zn. Citric acid at 50 mM adjusted soil to pH 4.5–6.0 and enhanced uptake of all elements. Long‐term application of sucrose and citric acid increased pH and inhibited uptake of Cd, Cr, Cu, Ni, and Zn. Contemporarily, leaching of heavy metals and humic substances was lowest with Ca and NH and highest with sucrose and citric acid amendments. It is concluded that Chinese cabbage grown for chelate‐assisted phytoextraction should be supplied with Ca and NH to obtain a high plant biomass on soil with a low hazard of leaching. Metal uptake should be stimulated by application of chelator 7 d prior to harvesting. Undesired uptake of heavy metals by Chinese cabbage determined as food should be inhibited with carbohydrate amendments. Long‐term application of NH or chelator, which reduces the solubility of certain elements but increases their uptake moderately, is recommended as a tool for continuous phytoextraction technologies.     

Bioavailability and Accumulation of Cadmium and Zinc by Sedum plumbizincicola after Liming of an Agricultural Soil Subjected to Acid Mine Drainage

A glasshouse pot experiment was conducted to study the effects of liming on plant growth and zinc (Zn) and cadmium (Cd) accumulation by Sedum plumbizincicola in a heavy-metal-contaminated acidified paddy soil. Lime application significantly increased the soil pH, which reached a maximum of 5.53 after addition of 4.0 g kg^?1 lime to soil, about 1.4 units more than that of the control. Sedum plumbizincicola grew larger after lime application but aboveground biomass did not increase significantly with increasing soil pH. Liming significantly reduced shoot Zn and Cd concentrations and uptake except at the lowest lime application rate (0.5 g kg^?1 lime to soil). This indicates that S. plumbizincicola can grow well in acidic soil at a soil pH of 4.15, and application of lime did not increase plant heavy-metal extraction. Consequently, it is promising to use this plant for Cd and Zn phytoextraction from agricultural soils polluted with acid and metals.     

Heavy‐metal mobilization and uptake by mycorrhizal and nonmycorrhizal willows (Salix × dasyclados)

Ectomycorrhizal fungi have been shown to affect metal transfer from the soil to the host plant, but the use of these fungi for increased phytoextraction of heavy metals has been scarcely investigated. Therefore, a two‐factorial pot experiment was conducted with Salix × dasyclados and (1) two contaminated soils with different concentrations of NH₄NO₃‐extractable metals and (2) two strains of the ectomycorrhizal fungus Paxillus involutus (one strain originating from a noncontaminated site—Pax1, and another from a contaminated site—Pax2). The inoculation with Pax2 increased the phytoavailability of Cd in the soils. Inoculation with both fungal strains increased the stem and root biomass, but had no effect on metal concentrations in the stems. Decreased Cd and increased Cu concentrations were observed in the roots of inoculated willows. The inoculation with P. involutus increased Cd (up to 22%), Zn (up to 48%), and Cu content in the stems. Decreased Pb content (Cu and Pb content were always <1 mg per plant) occurred in the stems from plants at the soil with the higher concentration of NH₄NO₃‐extractable metals. Contrary to this, in the soil with lower concentrations of NH₄NO₃‐extractable metals, the inoculation had no significant effects on the total uptake of Zn and Cu and even caused decreased Cd (Pax2) and Pb (Pax1) contents in the stems. Strain Pax2 had higher colonization densities, but the plants had lower mycorrhizal dependencies in the contaminated soils than after inoculation with the strain Pax1. Generally, metal extractability in the soils substantially affected the mycorrhizal dependency and heavy‐metal uptake of the willows. We concluded, that the inoculation with P. involutus offers an opportunity to particularly increase the phytoextraction of Zn, but the metal extractability and fungal strain effects have to be tested.     

植物提取影响因素研究进展（英文）

Hyperaccumulators concentrate trace metals and heavy metals in their shoots when grown in metal-contaminated soils and these trace metal-loaded plants may be removed by harvesting the fields.Studies exploring the beneficial role of these hyperaccumulators to clean up the environment have led to the development of phytoextraction.The success of phytoextraction depends upon the high biomass of plant species and bioavailability of metals for plant uptake.The phytoavailability of metals is influenced by soilassociated factors,such as pH,redox potential,cation exchange capacity,soil type,and soil texture,and by plant-associated factors,such as root exudates and root rhizosphere processes(microorganisms).Efficiency of phytoextraction can be improved by advanced agronomic practices including soil and crop management by application of genetic engineering to enhance the metal tolerance,shoot translocation,accumulation,and sequestration and by application of chelate treatments to enhance metal bioavailability.Application of microorganisms including bacteria and mycorrhiza may facilitate the phytoextraction application at commercially large scale.     

植物提取影响因素研究进展

Hyperaccumulators concentrate trace metals and heavy metals in their shoots when grown in metal-contaminated soils and these trace metal-loaded plants may be removed by harvesting the fields. Studies exploring the beneficial role of these hyperaccumulators to clean up the environment have led to the development of phytoextraction. The success of phytoextraction depends upon the high biomass of plant species and bioavailability of metals for plant uptake. The phytoavailability of metals is influenced by soil-associated factors, such as pH, redox potential, cation exchange capacity, soil type, and soil texture, and by plant-associated factors, such as root exudates and root rhizosphere processes (microorganisms). Efficiency of phytoextraction can be improved by advanced agronomic practices including soil and crop management by application of genetic engineering to enhance the metal tolerance, shoot translocation, accumulation, and sequestration and by application of chelate treatments to enhance metal bioavailability. Application of microorganisms including bacteria and mycorrhiza may facilitate the phytoextraction application at commercially large scale.     

Phytoextraction and Assisted Phytoextraction of Metals from Agriculture Used Soil

The clone (Salix?×?smithiana, Willd.) was cultivated in lysimeter pots to monitor lead (Pb), cadmium (Cd), and zinc (Zn) leachate and to compare the effect of ectomycorrhizal inoculum (ECMI; Paxillus involutus, Bartsch. ex Fr.) on plant growth and metal uptake by willows during two consecutive vegetation periods. The willow clone was able to reduce metal leaching significantly because of its high phytoextraction potential. In addition, ECMI (i) significantly enhanced plant growth; (ii) decreased metal-induced plant stress, which was represented by greater N_total in biomass and by greater productions of free amino acids AA_free (from 128 ± 10 to 204 ± 16 μmol kg^?1 fresh weight); and (iii) showed no additional effect of metal uptake. Furthermore, treated willows were affected indirectly, probably because of unsuccessful inoculation by Paxillus involutus, Bartsch. ex Fr., caused by high level of volumetric water content (θ_v) during both vegetation periods (θ_v = 25%).     

The Effect of Sulfur and Urea on the Heavy Metal Extraction by African Wild Sunflower (Tithonia diversifolia) in an Artificially Contaminated Soil

The research evaluated the comparative effect of two media of soil acidification on lead (Pb), cadmium (Cd), and zinc (Zn) extractive ability of Tithonia diversifolia in alkaline soil. Application of both amendments increased the solubility of the metals. Sulfur (S) addition was more effective at reducing the soil pH compared with the addition of urea. Lead and cadmium uptake by the plant was significantly higher in the urea treatments compared with sulfur treated soils. Generally, the addition of urea resulted in a higher amount of lead and cadmium in the plant parts. The acidification effect due to S addition was too high for the plant to perform optimally. The addition of S increased the uptake of Zn by the plant compared with the effect of adding urea. The complimentary effect of N addition with the soil acidification enhanced metal uptake. Tithonia diversifolia was classified as a hyper accumulator of metals.     

Interactive and Single Effects of Ectomycorrhiza Formation and <Emphasis Type="Italic">Bacillus cereus</Emphasis> on Metallothionein <Emphasis Type="Italic">MT1</Emphasis> Expression and Phytoextraction of Cd and Zn by Willows

Single and joint ectomycorrhizal (+ Hebeloma mesophaeum) and bacterial (+ Bacillus cereus) inoculations of willows (Salix viminalis) were investigated for their potential and mode of action in the promotion of cadmium (Cd) and zinc (Zn) phytoextraction. Dual fungal and bacterial inoculations promoted the biomass production of willows in contaminated soil. Single inoculations either had no effect on the plant growth or inhibited it. All inoculated willows showed increased concentrations of nutritional elements (N, P, K and Zn) and decreased concentrations of Cd in the shoots. The lowest biomass production and concentration of Cd in the willows (+ B. cereus) were combined with the strongest expression of metallothioneins. It seems that biotic stress from bacterial invasion increased the synthesis of these stress proteins, which responded in decreased Cd concentrations. Contents of Cd and Zn in the stems of willows were combination-specific, but were always increased in dual inoculated plants. In conclusion, single inoculations with former mycorrhiza-associated B. cereus strains decreased the phytoextraction efficiency of willows by causing biotic stress. However, their joint inoculation with an ectomycorrhizal fungus is a very promising method for promoting the phytoextraction of Cd and Zn through combined physiological effects on the plant.     

EDDS对海州香薷修复重金属复合污染土壤的田间效应

两年田间小区试验研究了加入易降解络合剂EDDS后污染土壤及修复植物海州香薷地上部Cu、Zn、Pb含量及地下水水质变化。结果显示,添加EDDS能在一定程度上提高海州香薷对Cu、Zn、Pb的吸收量,但是对地下水水质影响不大,符合国家III类地下水水质标准。EDDS强化海州香薷修复复合污染土壤有一定的应用前景,且对于地下水的潜在淋滤风险较小,但是在应用期间应注意对环境因素特别是降水及地下水的影响。     

Hot NTA Application Enhanced Metal Phytoextraction from Contaminated Soil

To increase the phytoextraction efficiency of heavy metals and to reduce the potential negative effects of mobilized metals on the surrounding environment are the two major objectives in a chemically enhanced phytoextraction process. In the present study, a biodegradable chelating agent, NTA, was added in a hot solution at 90°C to soil in which beans (Phaseolus vulgaris L., white bean) were growing. The concentrations of Cu, Zn and Cd, and the total phytoextraction of metals by the shoots of the plant from a 1 mmol kg^?1 hot NTA application exceeded those in the shoots of plants treated with 5 mmol kg^?1 normal NTA and EDTA solutions (without heating treatment). A significant correlation was found between the concentrations of metals in the shoots of beans and the relative electrolyte leakage rate of root cells, indicating that the root damage resulting from the application of a hot solution might play an important role in the process of chelate-enhanced metal uptake in plants. The application of hot NTA solutions did not significantly increase metal solubilization in soil in comparison with a normal application of solution of the same dosage. Therefore, the application of a hot NTA solution may provide a more efficient alternative in chemical-enhanced phytoextraction, although further studies of techniques of application in fields are sill required.     

Effects of plant growth-promoting bacteria on the phytoremediation of cadmium-contaminated soil by sunflower

This paper describes the effect of plant growth-promoting bacteria on sunflower growth and its phytoremediation efficiency under Cd-contaminated soils. Four levels of bacteria inoculation (non-inoculation, inoculation by Bacillus safensis, Kocuria rosea and co-inoculation by Bacillus safensis+Kocuria rosea) and four Cd concentrations (0, 50, 100 and 150 mg Cd per kg soil) were arranged as factorial experiment based on a completely randomized design (CRD). Results showed that Cd significantly decreased growth by decreasing the shoot and root length and biomass (p < 0.01). In addition, Cd dramatically decreases photosynthetic pigments, Fe transport to shoot and Zn uptake (p < 0.01). Bacterial inoculation increased Fe and Zn uptake by plants, Cd concentration in the aboveground part of plants and Cd uptake by the enhancement of Cd concentration in plant tissue and biomass production. Results showed that the highest shoot Cd uptake was ?observed in ?inoculated plants by Bacillus safensis at Cd100 (20.35 mg pot^?1). However, in average of Cd treatments, the performance of co-inoculation in Cd uptake (13.04 mg pot^?1) was better than singular inoculation (10.68 and 12.58 mg pot^?1 for Bacillus safensis and Kocuria rosea, respectively). Results revealed that bacterial inoculation increased the Cd uptake performance in shoot and total biomass by 30% and 25%, respectively.     

Application of plant growth-promoting bacteria associated with composts and macrofauna for growth promotion of Pearl millet (Pennisetum glaucum L.)

Plant growth-promoting bacteria (PGPB) were reported to influence the growth, yield, and nutrient uptake by an array of mechanisms. We selected seven different plant growth-promoting traits and antagonistic ability to screen 207 bacteria isolated from composts. Fifty-four percent of PGPB were from farm waste compost (FWC), 56% from rice straw compost (RSC), 64% from Gliricidia vermicompost (GVC), and 41% from macrofauna associated with FWC. Twelve isolates based on different plant growth-promoting traits and seed vigor index were evaluated at glasshouse for plant growth-promoting activity on pearl millet. Seven isolates significantly increased shoot length and ten isolates showed significant increase in leaf area, root length density, and plant weight. Maximum increase in plant weight was by Serratia marcescens EB 67 (56%), Pseudomonas sp. CDB 35 (52%), and Bacillus circulans EB 35 (42%). Plant growth-promoting activity of composts and bacteria (EB 35, EB 67, and CDB 35) was studied together. All the three composts showed significant increase in growth of pearl millet, which was 77% by RSC, 55% by GVC, and 30% by FWC. Application of composts with bacteria improved plant growth up to 88% by RSC with EB 67, 83% with GVC and EB 67. These results show the synergistic effect of selected bacteria applied with composts on growth of pearl millet.     

Metal removal from and microbial property improvement of a multiple heavy metals contaminated soil by phytoextraction with a cadmium hyperaccumulator Sedum alfredii H.

Purpose

Effects of phytoextraction by Sedum alfredii H., a native cadmium hyperaccumulator, on metal removal from and microbial property improvement of a multiple heavy metals contaminated soil were studied under greenhouse conditions.

Materials and methods

A rhizobox experiment with an ancient silver-mining ecotype of S. alfredii natively growing in Zhejiang Province, China, was conducted for remediation of a multiple heavy metals contaminated soil. The rhizobox was designed combining the root-shaking method for the separation of rhizospheric vs near-rhizospheric soils and prestratifying method for separation of sublayers rhizospheric soils (0–10 mm from the root) and bulk soil (>10 mm from the root). Soil and plant samplings were carried out after 3 and 6 months of plant growth.

Results and discussion

Cadmium (Cd), zinc (Zn), and lead (Pb) concentrations in shoots were 440.6, 11,893, and 91.2 mg kg^?1 after 6 months growth, and Cd, Zn, and Pb removed in the shoots were 0.862, 25.20, and 0.117 mg/plant. Microbial biomass C, basal respiration, urease, acid phosphatase, and invertase activities of the rhizospheric soils were significantly higher than that of unplanted soils after 6 months growth. Microbial biomass carbon (MBC) of 0–2 mm and basal respiration (BR) rate of 0–8 mm sublayer rhizospheric soils were significantly higher than that of bulk soil after 6 months growth. So were the three enzyme activities of 0–4 mm sublayer rhizospheric soils. BR rate and urease were significantly negatively correlated with soluble Cd, so were MBC, acid phosphatase, and intervase activities with soluble Zn, MBC, BR rate, and three enzyme activities with soluble Pb.

Conclusions

Harvesting shoots of S. alfredii could remove remarkable amounts of Cd, Zn, Pb, and lower water-soluble Cd, Zn, and Pb concentrations in the rhizospheric soils. MBC, BR rate, and enzyme activities of the metal polluted soil, especially the rhizospheric soils increased with phytoextraction process, which is attributed to the stimulation of soil microbes by planting as well as the decrease in soil-soluble metal concentration.     

Phosphatic fertilizers as a source of heavy metals in protected cultivation

Abstract

In order to quantify the uptake by lettuce plants (Lactuca sativa L.) of heavy metals contained in the phosphate fertilizers and to evaluate their residual bioavailability in the growth substrate a greenhouse experiment was carried out. The superphosphate added to the soil contained varying amounts of heavy metals, particularly Cd, Cr and Zn which accumulated in the soil and increased the amounts available for plant uptake. The accumulation of metals observed in the plant tissues did not have physiological effects on lettuce and did not affect negatively the growth of the plants. The heavy metal speciation in soil indicated that metals extractable by EDTA increased by increasing the phosphorus added. These amounts of metals, adsorbed or complexed in the soil after harvest, represent in protected environments a potentially bioavailable species for the following cultivations.     

Is rhamnolipid biosurfactant useful in cadmium phytoextraction?

Purpose  

Successful chelant-assisted phytoextraction requires application of an eco-friendly metal-complexing agent which enhances metal uptake but does not pose a significant risk of off-site movement of metals. Rhamnolipid biosurfactant has been used to enhance cadmium (Cd) removal from contaminated soil by washing. It has a strong affinity for Cd compared to some other hazardous metals, suggesting that rhamnolipid could be useful in Cd phytoextraction. This study investigated the potential use of rhamnolipid to enhance Cd phytoextraction.     

Phytoextraction of heavy metal contaminated soils with Thlaspi goesingense and Amaranthus hybridus: Rhizosphere manipulation using EDTA and ammonium sulfate

Selection of appropriate plant species and rhizosphere manipulation to enhance metal uptake are considered key factors in the development of phytoextraction technologies. A pot trial was conducted with two contaminated soils to investigate the effect of EDTA and ammonium sulfate on the accumulation of heavy metals into shoots of the low‐biomass hyperaccumlator Thlaspi goesingense Hálácsy (Brassicaceae) and the high‐biomass non‐hyperaccumulating plant Amaranthus hybridus (Amaranthaceae). Upon application of 1 g EDTA (kg soil)^—1 metal extractability with 1 M NH₄NO₃ increased substantially, whereas the application of (NH₄)₂SO₄ was less effective. The EDTA treatment increased the heavy metal concentrations in both plant species, however, the difference to the control was larger for A. hybridus. EDTA enhanced shoot concentrations in A. hybridus grown on soil Arnoldstein from 32.7 mg kg^—1 to 1140 mg kg^—1 for Pb and from 3.80 mg kg^—1 to 10.3 mg kg^—1 for Cd. Cd concentrations in shoots of T. goesingense were also increased by EDTA application, however, a slight decrease was observed for Pb. T. goesingense accumulated 2840 mg Pb kg^—1 without any treatment. This is the first report of Pb hyperacumulation by T. goesingense. A decrease of shoot Pb concentration was observed in T. goesingense upon treatment with ammonium sulfate. Although metal concentrations in the shoots were rather large and significantly increased upon application of EDTA, plant growth and heavy metal removal were still too small to obtain reasonable extraction rates in soils heavily polluted by metals. It should be also noted that metal lability largely increased in EDTA‐treated soils and this lability persisted for several weeks after the application of the chelating agent, which is likely to be associated with the risk of groundwater contamination.     

Predicting the Phytoextraction Duration to Remediate Heavy Metal Contaminated Soils

The applicability of phytoextraction to remediate soils contaminated with heavy metals (HMs) depends on, amongst others, the duration before remediation is completed. The impact of changes in the HM content in soil occurring during remediation on plant uptake has to be considered in order to obtain a reliable estimate of the phytoextraction duration. To simulate the decrease in the HM content in soil and to assess the resulting decrease in the uptake of HMs by plants, contaminated soil was mixed with uncontaminated, but otherwise similar soil. Uptake of Cd, Pb, and Zn by the indicator plant Lupinus hartwegii and the Zn hyperaccumulator Thlaspi caerulescens (La Calamine ecotype) was a log-linear function of the in-situ measured HM soil solution concentrations. Over a wide range in dissolved Cd and Zn concentrations, uptake of these HMs by T. caerulescens was (much) greater than by L. hartwegii. Experimentally derived regression models describing the relationships between soil, soil solution, and plant were implemented in a HM mass balance model used to obtain estimates of the phytoextraction duration. For our target soils, estimates of the Cd phytoextraction duration using L. hartwegii or T. caerulescens increased significantly by more than 100 or 50 years when experimental soil—soil solution—plant relationships were used instead of the assumption of constant plant uptake of Cd. The two approaches gave similar results for phytoextraction of Zn by T. caerulescens.