Total Metal Uptake Research Articles

Effect of hydrogel based soil amendments on heavy metal uptake by spinach grown with wastewater irrigation

Food crops irrigated with wastewater can uptake heavy metals, causing serious health ailments in humans. Use of a polyacrylamide superabsorbent polymer hydrogel and the same hydrogel mixed with pyrolyzed plantain peel biochar as soil amendments are proposed to reduce heavy metal uptake by wastewater-irrigated spinach (Spinacia oleracea L.) plants. A sorption test was carried out to establish the ability of these treatments to bind the heavy metals. In a lysimeter field experiment, the amendments were mixed in the top 0.10 m of soil (1% w/w) and spinach plants were grown using synthetic wastewater irrigation. After each irrigation, soil samples were obtained at different depths (0, 0.10, 0.30, and 0.60 m from the surface) for heavy metal analysis. Spinach leaves, root, and stem samples were obtained at the harvest for metal analysis. Sorption test results showed that the hydrogel-biochar amended soil adsorbed 0.80, 0.46, and 0.44 mg g−1 of cadmium, copper, and zinc, respectively, from a 0.5 mM multi-metal solution; the hydrogel treatment adsorbed 0.59, 0.41, and 0.24 mg g−1 of the metals, respectively. These amounts were at least 90% more than those adsorbed by the non-amended soil. In terms of the total metal uptake by spinach leaves, the hydrogel-biochar mix treatment performed better than the hydrogel treatment; it reduced the total uptake by 48%, whereas the hydrogel treatment was only able to reduce it by 15% when compared to the control that exhibited a total metal load of 1028 mg kg−1. Both treatments were able to significantly (p < 0.05) reduce copper uptake in plant stems, and exhibited the potential to reduce chromium, copper, and iron uptake by spinach leaves.

Endophyte Pseudomonas putida enhanced Trifolium repens L. growth and heavy metal uptake: A promising in-situ non-soil cover phytoremediation method of nonferrous metallic tailing

Non-soil cover phytoremediation is the most promising method for high heavy metal contaminated, pH imbalanced and oligotrophic tailing remediation. In this study, a promising method of tailing non-soil cover phytoremediation by endophyte assisting Trifolium repens L. was established. Endophytic Pseudomonas putida strain RE02, with great heavy metal detoxification ability, could colonize in both rhizosphere and endosphere of roots. With RE02 inoculation, the germination percentage of Trifolium repens L. seeds was improved form 40.33%, 45.33% and 56.67%–60.00%, 57.00% and 73.33% in 20 mg/kg Cd, 20 mg/kg Cr and 100 mg/kg Pb contained tailing. The LC50 (concentrations causing 50% mortality of seedlings) and IC50 (concentrations inhibiting the dry biomass by 50%) of Cd, Cr and Pb increased by 6.62, 4.87, 6.27, 4.28, 22.18 and 22.63 mg/kg respectively. Moreover, RE02 inoculation improved soil fertility that the available P and available K was dramatically enhanced in endophyte inoculated groups. Thus, plant NPK concentration was significantly enhanced by 16.72%, 30.55% and 3.81% respectively, and the total heavy metal uptake by 30.03–574.58%. Taken together, Trifolium repens L. successfully grew and developed in heavy metal contaminated, oligotrophic and pH imbalanced tailing, realizing non-soil cover phytoremediation by RE02 inoculation. Overall, this study provided a feasible and promising method for in-situ non-soil cover phytoremediation of tailing, laying a foundation for ecological restoration of tailing.

Differences in phytoextraction by the cadmium and zinc hyperaccumulator Sedum plumbizincicola in greenhouse, polytunnel and field conditions

Differences in growth conditions in the glasshouse and in the field may affect the consistency of phytoextraction results. Two crops of the hyperaccumulator Sedum plumbizincicola were grown in six contrasting soils in pot experiments under three different sets of growth conditions (glasshouse, polytunnel and field) to compare the phytoextraction of cadmium (Cd) and zinc (Zn). The total shoot biomass of two crops in the glasshouse was significantly smaller than in the polytunnel or field. However, in general there were no significant differences in total shoot metal uptake of two crops per pot among three sets of growth conditions. And greater decreases in soil metal than plant uptake in the polytunnel and field in an acid soil indicate high leaching losses of soil metals in the polytunnel and field, and this was confirmed by analysis of metal concentrations in soil profiles. This brings into question on the validity of estimating the practical applicability of phytoextraction based only on plant metal uptake in glasshouse conditions. It is advisable to examine leaching losses in acid soils in the field when estimating the duration of phytoextraction.

Zinc Presence during Mineral Formation Affects the Sorptive Reactivity of Manganese Oxide

The sorptive reactivity of layered manganese (Mn) oxides is controlled by their layer and interlayer structure, which can be affected by processes such as metal coprecipitation. This study investigated the effects of Zn coprecipitation on the sorptive reactivity of δ-MnO2, a common layered Mn oxide mineral. Selected cation (i.e., Cd) and anion (i.e., phosphate and arsenate) species were used to probe the changes in δ-MnO2 sorptive reactivity. Cd uptake by δ-MnO2 was suppressed by Zn coprecipitation but total metal uptake (Cd and Zn) was enhanced, indicating more available vacancy sites (e.g., smaller particle size and higher vacancy site density) in Zn-coprecipitated δ-MnO2. Phosphate and arsenate sorption on δ-MnO2 was significantly enhanced by Zn-coprecipitation, and the enhancement was more effective compared to Zn sorption on pure δ-MnO2. X-ray diffraction and X-ray adsorption spectroscopy analysis did not detect the formation of surface precipitations and/or ternary complexes. The enhanced anion sorption on Zn-coprecipitated δ-MnO2 was likely due to the compensation of negative surface charge by sorbed Zn, as well as the structural modifications introduced by Zn coprecipitation. Results from this study can provide a better understanding on the interactions between metal-coprecipitated Mn oxides and other species in natural environments.

Phytoextraction of Cd and Zn with Noccaea caerulescens for urban soil remediation: influence of nitrogen fertilization and planting density

Phytoextraction field trials with Noccaea caerulescens were conducted in Brussels (Belgium) to investigate the benefits of nitrogen fertilization and planting density on phytoextraction efficiency. Both metallicolous (Ganges) and non-metallicolous (NMET, Luxembourg) populations were grown for 6 months in an urban wasteland and in a vegetable garden contaminated with trace metals at two planting densities (50 and 100 plants·m−2, D50 and D100), with and without mineral nitrogen fertilizers. Trials showed that N. caerulescens responded positively to nitrogen fertilization through increased biomass production. However due to lower concentrations in Cd and Zn in fertilized plants, the total metal uptake was differently impacted by fertilization: on one site metal uptake was enhanced while on the other it was reduced. Moreover fertilization had collateral effects as enhancing fungal pathogen development. The effect of planting density of N. caerulescens assessed in this work for the first time highlighted a clear competition between individuals at higher density – proved by lower individual biomass – but the highest metal uptake was nevertheless achieved at the highest density of 100 plants·m−2 because of higher total biomass. Six months after harvest soil exchangeable concentrations were reduced by about 25% for Cd with Ganges population and by 9% for Zn with the NMET population on the best treatment (N fertilized and D100). The feasibility of using N. caerulescens for bioavailable contaminant stripping of moderately contaminated soils was confirmed for Cd and to a lesser extent for Zn.

Interaction of Vermiculite with Pb(II), Cd(II), Cu(II) and Ni(II) Ions in Single and Quaternary Mixtures

In this study, single and competitive sorption of Pb(II), Cd(II), Cu(II), and Ni(II) ions onto vermiculite were studied. Preliminary examination revealed that vermiculite possesses low bulk density (279 kg/m3), a high cation exchange capacity (41.3 meq/100 g), water holding capacity (62.5%), and air‐filled porosity (5.8%). The pH edge experiments indicated that the uptake capacity of vermiculite improved with enhancement in pH and highest value was detected at pH 5. Fourier transform IR spectroscopy along with scanning electron microscopy and energy dispersive X‐ray spectroscopy confirmed changes in the sorbent functionality after metal sorption, and the results were in agreement with metal removal studies. It was observed by isotherm experiments that vermiculite was capable of sorbing 0.238, 0.099, 0.199 and 0.115 mmol/g of Pb(II), Cd(II), Cu(II) and Ni(II), respectively, according to the Langmuir model. The reaction was rapid and the kinetic experimental data were successfully modelled using the pseudo‐first order model. Quaternary biosorption experimental results revealed that severe competition exists between metal ions during the sorption onto vermiculite surface and it was inferred that the total metal uptake was distributed among four elements.

Dry Matter Yield of Sunflower as Affected by EDTA and EDDS Application in Soil Remediation from Ibadan, Metropolis, Nigeria

Phytoremediation has been found to be cost effective in removing heavy metals (HM) from polluted soils. Enhanced phytoextraction with the use of chelating agents for solubility of metal in soils and their uptake in the aerial parts of plants had also been employed. Phytoextraction efficiency of plants will depend on the metal accumulated in the dry matter yield of plant. An attempt was made to study the influence of Ethylene diamine tetra acetic acid (EDTA) and ethylene diamine disuccinic acid (EDDS) on the growth and dry matter yield content of sunflower planted in heavy metal polluted soils in a greenhouse pot experiment. Total heavy metal contents of five metals (Cu, Cd, Cr, Pb and Zn) were determined by acid digestion with aqua regia solution. A greenhouse experiment was conducted to assess the phytoextraction potential of sunflower with EDDS and EDTA applied at seven weeks after planting. Treatments were laid out in a completely randomized design with four replicates. Data were collected on metal accumulation in root and shoot, Total metal uptake, shoot and root dry matter yield and analyzed using descriptive statistics and ANOVA at α0.05. Original Research Article Thomas and Omueti; IJPSS, 7(1): 67-79, 2015; Article no.IJPSS.2015.132 68 The result shows a significant increase in the overall accumulation of metals in the root and shoot of sunflower and dry matter yield with EDDS except for Zn. However, Zinc only recorded significant increase in shoot uptake at 3 mmol/kg EDDS. The application of EDDS at 3 and 9 mmol/kg did better in total uptake of Cu, Pb and Cd. Ethylene diamine disuccinic acid (EDDS) was more efficient than EDTA in mobilizing metal uptake in sunflower root and shoot and also in increasing total dry matter yield. Translocation factor of Cd, Pb and Cu were enhanced by the addition of EDDS than EDTA application.

Chemometrics applied to the analysis of induced phytochelatins in Hordeum vulgare plants stressed with various toxic non-essential metals and metalloids

Hordeum vulgare plants were stressed with Hg, Cd and As and their phytotoxicity was evaluated in terms of growth inhibition and total metal uptake by the plant. The synthesised phytochelatins ((γ-Glu-Cys)n-Gly, n=2-5; PCs) were determined by HPLC with amperometric detection at a glassy carbon electrode. The results indicate that H. vulgare is a good phytostabilisation plant due to its capacity to accumulate heavy metals in roots. Cd and Hg are the most uptake toxic elements, being Cd the most potent inducer of PCs. The data obtained on the different PCs and related peptides induced by each heavy metal were used to perform a Principal Component Analysis (PCA) of the results as a function of the contaminating toxic element or its concentration level. The nature of the stressor element could be predicted from the pattern of PCs and related peptides identified by PCA. PCs were the most strongly induced peptides under Cd and Hg stress, whereas As only tended to synthesise small thiols such as glutathione and γ-glutamylcysteine, both precursors of PCs synthesis. This finding indicates that PCs are induced at different rates depending on the metal stressor used.

Adsorption of Cu(II) and Zn(II) ions from aqueous solutions onto fine powder of Typha latifolia L. root: kinetics and isotherm studies

Fine powder of Typha latifolia L. root was used for adsorption of copper and zinc ions from buffered and nonbuffered aqueous solutions. The adsorption reached equilibrium in 60 min. During this time, more than 90 % of the adsorption process was completed. The effect of initial pH, initial concentration of metal ion, and contact time was investigated in a batch system at room temperature. The optimum adsorption performance was observed at pH 5.00 and 4.25 for nonbuffered solutions of Cu(II) and Zn(II), respectively, while for buffered solutions it occurred at pH 6.00. The total metal uptake decreased on application of ammonium acetate buffer, from 37.35 to 17.00 mg g−1 and 28.80 to 9.90 mg g−1 for Cu(II) and Zn(II) solutions, respectively, with 100 mg L−1 initial concentration. The pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models were used to describe the adsorption kinetics. The experimental data followed the pseudo-second-order kinetic model. The biosorption equilibrium was well described by Langmuir and Freundlich isotherm models.

Chelator-induced bioextraction of heavy metals from artificially contaminated soil by mushroom (Coprinus comatus)

This study investigated the potential use of chelator-induced bioextraction of heavy metals from soil by Coprinus comatus in a pot experiment. Two production waves of the mushroom were obtained to determine biomass and metal concentration. The application of ethylenediaminetetraacetic acid (EDTA) or nitrilotriacetate (NTA) slightly inhibited the growth of C. comatus, but significantly enhanced the accumulation of heavy metals in fruiting bodies compared with the control. The highest concentrations of Pb, Cu and Cd reached 900.60, 783.61 and 23.64 mg·kg−1 in a single pot, respectively. However, application of citric acid (CA) had no effect on metal uptake. Moreover, chelators applied to soil after fructification increased the dry biomass and metal concentration in fruiting bodies compared with those applied before sowing mycelia. EDTA was more efficient for inducing metal uptake by C. comatus than NTA or CA, and split applications of EDTA after fructification resulted in the highest total metal uptake by mushroom, i.e. 19.08±2.84, 17.57±0.69 and 0.55±0.06 mg for Pb, Cu and Cd, respectively, which were 130, 12 and 5 times values obtained with the control. Interestingly, many mushrooms turned blue after soil had been treated with chelator, indicating that these mushrooms are rich in Cu.

Endophyte-assisted promotion of biomass production and metal-uptake of energy crop sweet sorghum by plant-growth-promoting endophyte Bacillus sp. SLS18

The effects of Bacillus sp. SLS18, a plant-growth-promoting endophyte, on the biomass production and Mn/Cd uptake of sweet sorghum (Sorghum bicolor L.), Phytolacca acinosa Roxb., and Solanum nigrum L. were investigated. SLS18 displayed multiple heavy metals and antibiotics resistances. The strain also exhibited the capacity of producing indole-3-acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylic acid deaminase. In pot experiments, SLS18 could not only infect plants effectively but also significantly increase the biomass of the three tested plants in the presence of Mn/Cd. The promoting effect order of SLS18 on the biomass of the tested plants was sweet sorghum > P. acinosa > S. nigrum L. In the presence of Mn (2,000 mg kg(-1)) and Cd (50 mg kg(-1)) in vermiculite, the total Mn/Cd uptakes in the aerial parts of sweet sorghum, P. acinosa, and S. nigrum L. were increased by 65.2%/40.0%, 55.2%/31.1%, and 18.6%/25.6%, respectively, compared to the uninoculated controls. This demonstrates that the symbiont of SLS18 and sweet sorghum has the potential of improving sweet sorghum biomass production and its total metal uptake on heavy metal-polluted marginal land. It offers the potential that heavy metal-polluted marginal land could be utilized in planting sweet sorghum as biofuel feedstock for ethanol production, which not only gives a promising phytoremediation strategy but also eases the competition for limited fertile farmland between energy crops and food crops.

PHYTOEXTRACTION OF HEAVY METALS FROM MINE SOILS USING HYPERACCUMULATOR PLANTS

Phytoextraction is an environmental-friendly and cost-effective technology that uses metal hyperaccumulator plants to remove heavy metals from soils. The metals are absorbed by the roots, transported and accumulated in the aerial parts of the plants, which can be harvested and eliminated. The aim of this work was to study some hyperaccumulator species that could be useful to decontaminate mine soils and also to investigate the bioavailability and uptake of these metals by plants with the addition of organic amendments. Pot experiments were performed with soil samples collected from two mining areas in the north of Madrid, where there was an intense mining activity more than 50 years ago. Three species (Thlaspi arvense, Brassica juncea and Atriplex halimus) were grown under controlled conditions in pots filled with contaminated soils mixed with 0 Mg, 30 Mg and 60 Mg per hectare of two different organic amendments: a commercial compost made of pine bark, peat and wood fiber and other made of horse and sheep manure and wood fiber. Plants were harvested at the end of their crop cycle and were digested in order to measure metal concentration (Zn, Cu and Cd) in roots and shoots. Highest plant metal concentration was observed in pots treated with pine bark amendment and with pure soil due to an increase in metal bioavailability with decreasing pH. Also in those treatments the total plant biomass was lower, even some plants could not germinate. On the contrary, there was a lower metal concentration in plant tissues of pots with manure because its higher pH whereas plant growth was significantly larger so there was an incresing amount of metals removed from soil by plants. Comparing the three species results indicate a higher total metal uptake in A. halimus than B. juncea and T. arvense. In conclusion, results show that pH affects metal bioavailability and uptake by hyperaccumulator plants. Addition of organic amendments could be a successful technique for stabilization of metals in contaminated soils.

Simultaneous Hyperaccumulation of Multiple Heavy Metals by Helianthus Annuus Grown in a Contaminated Sandy-Loam Soil

Phytoremediation is a promising means for the treatment of contamination arising from heavy metal spills. Although several species have been identified as hyperaccumulators, most of the studies were performed with only one heavy metal. Experiments were conducted with two cultivars of H. annuus exposed to different combinations of metal contamination (30 mg/kg Cd, Cr, Ni, As, and/or Fe). Cultivar efficiency was based on total metal uptake, as well as translocation and selectivity of each metal. The results for each cultivar were also compared after 0.1 g/kg or 0.3 g/kg EDTA was added to enhance metal bioavailability. The key finding was that H. annuus achieved hyperaccumulator status for multiple metals simultaneously: Cd, Cr, and As.

Equilibrium Isotherm Studies for the Multicomponent Adsorption of Lead, Zinc, and Cadmium onto Indonesian Peat

This study evaluates the potential of Indonesian peat to sequester Pb, Cd, and Zn in single-, double-, and triple-solute systems. The adsorption isotherms of Pb, Cd, and Zn onto peat in single-solute and multisolute systems were simulated using the Langmuir two-site model satisfactorily. The model and experimental data of binary and ternary systems demonstrated that the presence of the secondary metal ions in the system resulted in a decrease in the sorption capacity of the primary metal, mainly because of the competitive effects of metals for adsorption sites. The metal adsorption follows the order of sequence Pb > Cd > Zn for both single-solute and multisolute systems. A three-dimensional representation of the total metal uptake in binary systems showed a good agreement with the corresponding experimental data. In addition to ion exchange, a surface adsorption−complexation mechanism must be involved in the sorption mechanism of metal ions. Fourier transform IR results confirm that the carboxyl functiona...

Metal uptake by corn grown on media treated with particle-size fractionated biosolids

Particle-size of biosolids may affect plant uptake of heavy metals when the biosolids are land applied. In this study, corn ( Zea mays L.) was grown on sand media treated with biosolids to study how particle-size of biosolids affected the plant uptake of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). Two biosolids, the Nu-Earth biosolids and the Los Angeles biosolids, of dissimilar surface morphology were utilized. The former exhibited a porous and spongy structure and had considerably greater specific surface area than that of the latter, which was granular and blocky. The specific surface area of the Los Angeles biosolids was inversely proportional to its particle-size, while that of Nu-Earth biosolids did not change significantly with particle-size. For each biosolid, the metal concentrations were not affected by particle sizes. The biomass yields of plants grown on the treated media increased as the biosolid particle-size decreased, indicating that plant uptake of nutrients from biosolids was dependent on interactions at the root–biosolids interface. The effect of particle-size on a metal's availability to plants was element-specific. The uptake rate of Cd, Zn, Cu, and Ni was correlated with the surface area of the particles, i.e., smaller particles having higher specific area provided greater root–biosolids contact and resulted in enhanced uptake of Cd and Zn and slightly less increased uptake of Cu and Ni. The particle morphology of biosolids had limited influence on the plant tissue concentrations of Cr and Pb. For both types of biosolids, total metal uptake increased as biosolid particle-size decreased. Our research indicates that biosolid particle-size distribution plays a deciding role in plant uptake of heavy metals when they are land applied.

Hydroponic phytoremediation of Cd, Cr, Ni, As, and Fe: Can Helianthus annuus hyperaccumulate multiple heavy metals?

Sundance sunflowers were subjected to contaminated solutions containing 3, 4, or 5 heavy metals, with and without EDTA. The sunflowers exhibited a metal uptake preference of Cd = Cr > Ni, Cr > Cd > Ni > As and Fe >> As > Cd > Ni > Cr without EDTA and Cr > Cd > Ni, Fe >> As > Cd > Cr > Ni with EDTA. As uptake was not affected by other metals, but it decreased Cd and Ni concentration in the stems. The presence of Fe improved the translocation of the other metals regardless of whether EDTA was present. In general, EDTA served as a hindrance to metal uptake. For the experiment with all five heavy metals, EDTA decreased Cd in the roots and stems from 2.11 to 1.36 and from 2.83 to 2.32 mg g −1 biomass, respectively. For the same conditions, Ni in the stems decreased from 1.98 to 0.94 mg g −1 total metal uptake decreased from 14.95 mg to 13.89 mg, and total biomass decreased from 2.38 g to 1.99 g. These results showed an overall negative effect in addition of EDTA. However it is unknown whether the negative effect was due to toxicity posed by EDTA or the breaking of phytochelatin-metal bonds. The most important finding was the ability of Sundance sunflowers to achieve hyperaccumulator status for both As and Cd under all conditions studied. Ni hyperaccumulator status was only achieved in the presence of three metals without EDTA.

Metal biosorption capability of Cupriavidus taiwanensis and its effects on heavy metal removal by nodulated Mimosa pudica

A novel metal biosorption system consisting of the symbiotic combination of an indigenous metal-resistant rhizobial strain, Cupriavidus taiwanensis TJ208, and its host plant Mimosa pudica has been developed for the removal of heavy-metal pollutants. Free-living C. taiwanensis TJ208 cells were able to adsorb 50.1, 19.0, and 19.6 mg/g of Pb, Cu, and Cd, respectively. After nodulation via inoculation with strain TJ208, the metal uptake ability of M. pudica markedly increased, as the nodulated M. pudica displayed a high metal uptake capacity ( q max) of 485, 25, and 43 mg/g, respectively, which is 86, 12, and 70% higher than that of nodule-free plants. Moreover, with TJ208 nodules, the M. pudica plant also displayed a 71, 81, and 33% enhancement in metal adsorption efficiency ( η) for Pb, Cu, and Cd, respectively. The nodulation appeared to give the greatest enhancing effect on the uptake of Pb, which is consistent with the preference of metal adsorption ability of TJ208. This seems to indicate the crucial role that the rhizobial strain may play in stimulating metal uptake of the nodulated plant. Furthermore, the results show that metal accumulation in the nodulated plant mainly occurred in the roots, accounting for 65–95% of total metal uptake. In contrast, the nodules and the shoots only contributed to 3–12 and 2–23% of total metal uptake, respectively. Nevertheless, the specific adsorption capacity of nodules is comparable to that of the roots. Hence, this work demonstrates the feasibility and effectiveness of using the nodulated plants to promote phyto-removal of heavy metals from the polluted environment as well as to restrict the metal contaminants in the unharmful region of the plant.

The effect of EDTA on Helianthus annuus uptake, selectivity, and translocation of heavy metals when grown in Ohio, New Mexico and Colombia soils

The use of two EDTA concentrations for enhancing the bioavailability of cadmium, chromium, and nickel in three natural soils (Ohio, New Mexico and Colombia) was investigated. The resulting uptake, translocation and selectivity with Helianthus annuus after mobilization were also examined. In general, plants grown in the sandy-loam Ohio soil had a higher uptake that resulted in a selectivity and total metal content of Cd > Cr ≫ Ni and 0.73 mg and Cr > Cd ≫ Ni and 0.32 mg for 0.1 and 0.3 g kg −1 EDTA, respectively. With the silty-loam New Mexico soil, although the total metal uptake was not statistically different the EDTA level did alter the selectivity; Cd > Cr ≫ Ni (0.1 g kg −1 EDTA) and Cd ≫ Cr > Ni (0.3 g kg −1 EDTA). Conversely, with the Colombian (sandy clay loam) soil increasing the EDTA level resulted in a higher total metal uptake (0.62 mg) than the 0.1 g kg −1 (0.59 mg) treatment. For all three soils, the translocation of Cd was limited. Evaluating the mobile metal fraction with and without EDTA determined that the chelator was capable of overcoming mass transfer limitations associated with the expandable clay fraction in the soils. Root wash results and root biomass concentrations indicated that Cd sorption was occurring. Therefore limited Cd translocation was attributed to insufficient phytochelatin levels.

Effect of cadmium, zinc and substrate heterogeneity on yield, shoot metal concentration and metal uptake by Brassica juncea: implications for human health risk assessment and phytoremediation

• Heavy metal contaminants are usually heterogeneously distributed in soils. However, their effects on plants are usually studied under homogeneous conditions. Here we examined the effects of Cd, Zn, and their spatial distribution on shoot yield, shoot metal concentrations, and total metal uptake by Brassica juncea. • One Cd concentration and three Zn concentrations were used. Metals were applied to the substrate either singly or in combination. • Heterogeneous metal distribution enabled growth reduction to be avoided, even at concentrations that were highly phytotoxic when distribution was homogeneous. Moderate Zn contamination reduced Cd uptake by 40%. With high Zn contamination, metal concentrations were two to four times lower when metals were heterogeneously, rather than homogeneously, distributed; shoot yields were up to 24-times greater and total shoot Cd and Zn uptakes were on average six-times higher. • It is suggested that human health risk from consuming plant parts grown on Cd-contaminated substrates is lower when Zn is also present and metal distribution is heterogeneous, and that phytoremediation potential is greater when contaminant distribution is heterogeneous.

The effect of EDTA and citric acid on phytoremediation of Cd, Cr, and Ni from soil using Helianthus annuus

The possibility to clean heavy metal contaminated soils with hyperaccumulator plants has shown great potential. One of the most recently studied species used in phytoremediation applications are sunflowers. In this study, two cultivars of Helianthus annuus were used in conjunction with ethylene diamine tetracetic acid (EDTA) and citric acid (CA) as chelators. Two different concentrations of the chelators were studied for enhancing the uptake and translocation of Cd, Cr, and Ni from a silty-clay loam soil. When 1.0 g/kg CA was used, the highest total metal uptake was only 0.65 mg. Increasing the CA concentration posed a severe phytotoxicity to both cultivars as evidenced by stunted growth and diminished uptake rates. Decreasing the CA concentration to 0.1 and 0.3 g/kg yielded results that were not statistically different from the control. EDTA at a concentration of 0.1 g/kg yielded the best results for both cultivars achieving a total metal uptake of ∼0.73 mg compared to ∼0.40 mg when EDTA was present at 0.3 g/kg.