Increased Pb Uptake Research Articles

Arbuscular mycorrhizal fungi improve growth and tolerance of Platycladus orientalis under lead stress

Platycladus orientalis is a significant woody plant for phytoremediation in heavy metals contaminated soils. The growth and tolerance of host plants under the lead (Pb) stress were enhanced by arbuscular mycorrhizal fungi (AMF). To evaluate the adjustment by AMF on growth and activity of antioxidant system of P. orientalis under Pb stress. The two-factor pot experiment was conducted with three AM fungal treatments (noninoculated, Rhizophagus irregularis, and Funneliformis mosseae) and four Pb levels (0, 500, 1000, and 2000 mg kg−1). AMF increased dry weight, phosphorus uptake, root vitality, and total chlorophyll content of P. orientalis in spite of Pb stress. Compared with nonmycorrhizal treatments, mycorrhizal P. orientalis had lower H2O2 and malondialdehyde (MDA) contents under Pb stress. AMF increased Pb uptake in roots and decreased the Pb translating to the shoots yet under Pb stress. Total glutathione and ascorbate in roots of P. orientalis were decreased by AMF inoculation. Mycorrhizal P. orientalis had higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S-transferase (GST) activities in shoots and roots than nonmycorrhizal counterparts. Mycorrhizal P. orientalis under Pb stress showed higher expression of PoGST1 and PoGST2 in roots than that in CK treatments. Future studies will explore the function of induced tolerance genes by AMF of P. orientalis under Pb stress.

OsNRAMP5 Is a Major Transporter for Lead Uptake in Rice.

Lead (Pb) is one of the most toxic metals affecting human health globally. Food is an important source of chronic Pb exposure in humans. How Pb is taken up by rice, a staple food for over half of the global population, remains unknown. In the present study, we investigated the role of OsNRAMP5, a member of the NRAMP (Natural Resistance-Associated Macrophage Protein) transporter family, in Pb uptake by rice roots. Heterologous expression of OsNRAMP5 in yeast increased Pb uptake and sensitivity toward Pb. Knockout of OsNRAMP5 in rice by CRISPR/Cas9 gene editing resulted in significant decreases in root uptake of Pb and accumulation in rice shoots. The maximum influx velocity (Vmax) for Pb uptake of the knockout mutants was 70% lower than that of wild-type plants. When grown in Pb-contaminated paddy soil, OsNRAMP5 knockout mutants accumulated approximately 50 and 70% lower Pb concentrations in the grain and straw, respectively, than the wild type. OsNRAMP5 expression in rice roots was not affected by Pb exposure. These results indicate that OsNRAMP5 is a major transporter for Pb uptake in rice, in addition to its role in the uptake of manganese and cadmium. This study provides a mechanistic understanding of Pb uptake in rice plants and a potential strategy to limit Pb accumulation in rice grains.

Lead poisoning of backyard chickens: Implications for urban gardening and food production

Increased interest in backyard food production has drawn attention to the risks associated with urban trace element contamination, in particular lead (Pb) that was used in abundance in Pb-based paints and gasoline. Here we examine the sources, pathways and risks associated with environmental Pb in urban gardens, domestic chickens and their eggs. A suite of other trace element concentrations (including As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn) are reported from the sampled matrices. Sixty-nine domestic chickens from 55 Sydney urban gardens were sampled along with potential sources (feed, soil, water), blood Pb concentrations and corresponding concentrations in eggs. Age of the sampled chickens and house age was also collected. Commercial eggs (n = 9) from free range farms were analysed for comparative purposes. Study outcomes were modelled using the large Australian VegeSafe garden soil database (>20,000 samples) to predict which areas of inner-city Sydney, Melbourne and Brisbane are likely to have soil Pb concentrations unsuitable for keeping backyard chickens. Soil Pb concentrations was a strong predictor of chicken blood and egg Pb (p=<0.00001). Almost 1 in 2 (n = 31/69) chickens had blood Pb levels >20 μg/dL, the level at which adverse effects may be observed. Older homes were correlated with higher chicken blood Pb (p = 0.00002) and egg Pb (p = 0.005), and younger chickens (<12 months old) had greater Pb concentrations, likely due to increased Pb uptake during early life development. Two key findings arose from the study data: (i) in order to retain chicken blood Pb below 20 μg/dL, soil Pb needs to be < 166 mg/kg; (ii) to retain egg Pb < 100 μg/kg (i.e. a food safety benchmark value), soil Pb needs to be < 117 mg/kg. These concentrations are significantly lower than the soil Pb guideline of 300 mg/kg for residential gardens. This research supports the conclusion that a large number of inner-city homes may not be suitable for keeping chickens and that further work regarding production and consumption of domestic food is warranted.

Relationship between lead absorption and iron status and its association with oxidative stress markers in lead-exposed workers

BackgroundThe emission of lead (Pb) occurring during the extraction, processing and industrial applications of this element remains a significant environmental risk factor. The absorbability of lead in humans is strongly associated with the general health status of exposed individuals. Existing mineral deficiencies are considered being a predisposition to an increased Pb uptake. Both, iron deficiency and lead poisoning are the major causative factors responsible for the prevalence of anemia within the vulnerable population, especially in children. Although some of the intervention programs of counteracting lead poisoning by iron supplementation proved to be effective in the Pb-exposed population, the exact mechanisms of this interaction still require further studies. The objective of the presented study was to examine the association of iron level on oxidative stress measures and its effects on the severity of lead toxicity in the exposed population. MethodsThe analyzed population consisted of 270 male workers from the lead-zinc smelter. The studied population was divided into two sub-groups based on the serum iron concentration: low iron level group (L-Fe; Fe < median value) and high iron level group (H-Fe; Fe > median value). Measured traits comprised of blood lead (PbB), serum Fe and zinc protoporphyrin (ZPP) levels as well as a blood count and oxidative stress markers. ResultsNo significant correlation between serum iron concentration and PbB in the tested cohort was found. On the contrary, the analysis of ZPP levels (long-term marker related to a hematologic toxic effect of Pb) within the subgroups differing in serum Fe level shown that ZPP was 12.3 % lower (p = 0.043) in subjects classified within the H-Fe group. A positive correlation of serum Fe and total antioxidant capacity (TAC) was found (R = 0.1999). The conducted 3-D PCA analysis showed that individuals classified within the H-Fe group were characterized by the co-occurrence of higher Fe levels, lower ZPP, and higher TAC value. ConclusionThese results support the existing evidence providing that maintaining the optimal status of Fe may play a significant role in preventing the lead poisoning and alleviating harmful effects of Pb on the oxidative balance in humans.

Arbuscular Mycorrhizal Fungi Increase Pb Uptake of Colonized and Non-Colonized Medicago truncatula Root and Deliver Extra Pb to Colonized Root Segment.

Arbuscular mycorrhizal (AM) fungi establish symbiosis and improve the lead (Pb) tolerance of host plants. The AM plants accumulate more Pb in roots than their non-mycorrhizal counterparts. However, the direct and long-term impact of AM fungi on plant Pb uptake has been rarely reported. In this study, AM fungus (Rhizophagus irregularis) colonized and non-colonized roots of Medicago truncatula were separated by a split-root system, and their differences in responding to Pb application were compared. The shoot biomass accumulation and transpiration were increased after R. irregularis inoculation, whereas the biomass of both colonized and non-colonized roots was decreased. Lead application in the non-colonized root compartment increased the R. irregularis colonization rate and up-regulated the relative expressions of MtPT4 and MtBCP1 in the colonized root compartments. Rhizophagus irregularis inoculation increased Pb uptake in both colonized and non-colonized roots, and R. irregularis transferred Pb to the colonized root segment. The Pb transferred through the colonized root segment had low mobility and might be sequestrated and compartmented in the root by R. irregularis. The Pb uptake of roots might follow water flow, which is facilitated by MtPIP2. The quantification of Pb transfer via the mycorrhizal pathway and the involvement of MtPIP2 deserve further study.

Effects of zinc on tissue uptake and toxicity of lead in Sprague Dawley rat

Lead (Pb) exposure occurs together with other metals including zinc (Zn). This study investigated the impact of Zn on Pb tissue accumulation and Pb-induced toxicities. Animals (n=6 rats per group) were exposed to lead acetate (PbAc) or a combination of PbAc and zinc acetate (ZnAc) under the following groups: control (deionized water), low PbAc [12 mg/kg PbAc (3 mg PbAc/rat/day)], low PbAc–ZnAc [12 mg/kg PbAc (3 mg PbAc/rat/day) + 0.2 mg ZnAc/rat/48 hr], high PbAc [120 mg/kg (30 mg PbAc/rat/day)], and high PbAc–ZnAc [120 mg/kg (30 mg PbAc/rat/day) + 1 mg ZnAc/rat/48 hr] for 8 weeks. A significant reduction in body weight gain was observed in the high PbAc group relative to the control group. Muscles and testes both had reduced and increased Pb uptake in low PbAc–ZnAc and high PbAc–ZnAc groups compared to PbAc only groups, respectively. Bone Pb levels in the high PbAc–ZnAc group were lower than the high PbAc group. Zinc co-administration attenuated Pb-induced inhibition of delta aminolaevulinic acid dehydratase enzyme and enhanced catalase enzyme activity at a high level of exposure. Moreover, ZnAc seems to have minimized the effects of Pb-induced mRNA dysregulation in antioxidant and antiapoptotic enzymes encoding genes. Heme oxygenase-1 was downregulated in the kidney and brain in the low PbAc group. Liver glutathione peroxidase and thioredoxin reductase-1 were downregulated in the high PbAc group. These findings suggest that zinc co-administration with lead may partially mitigate against Pb-induced toxicities.

Phytoremedial Potential of Tagetes Erecta Under Mycorrhizal Inoculation in Heavy Metal Polluted Soil

Investigation of the growth of Tagetes erecta under different levels of contamination of Copper (Cu) and Lead (Pb) in the soil and effects of mycorrhizal species (Glomus mosseae) on Cu and Pb to identify hyperaccumulator plants in tropical environment that could be used in remediation of heavy metal from contaminated soils. It was a greenhouse experiment consisted of factorial combination of two heavy metal (Cu and Pb) treatments which were replicated three times in Complete Ramdomized Design (CRD) with two mycorrhizal (Glomus mosseae and non-mycorrhizal) treatments. Metal solutions of Cu and Pb at the concentrations of Cu are 0, 125, 250, 500, 1000 mg kg-1 and concentrations of Pb are 0, 25, 50, 75, 100 mg kg-1 were prepared using CuCl2 and PbCl2 soluble compounds respectively. Soil mycorrhizal inocula of Glomus mosseae was applied at the rate of 20 g per pot. Five seeds of Tagetes erecta were planted per pot and were thinned to two stands per pot at two weeks after planting. Pre- and post- soil tests were carried out to determine soil physical and chemical properties, using standard methods. At 12 Weeks After Planting (WAP), Tagetes erecta was harvested and analyzed for Copper and Lead uptake using Atomic Absorption Spectrophotometer. The data collected were analyzed using descriptive and inferential statistics. The results showed that Arbuscular Mycorrhizal Fungi enhanced the number of leaves, height and stem girth of Tagetes erecta in high concentration (1000 mg kg-1) of Cu contaminated soil. Glomus mosseae inoculation did not enhance the growth parameters of Tagetes erecta irrespective of the levels of Pb contamination Glomus mosseae inoculation significantly (p≤0.05) increased Cu uptake of Tagetes erecta at 500 mg kg-1 of Cu concentration of a polluted soil. In contaminated soil, containing 50 mg kg-1 Pb Glomus mosseae significantly (p≤0.05) increased Pb uptake in Tagetes erecta.

Potential of efficient and resistant plant growth-promoting rhizobacteria in lead uptake and plant defence stimulation in Lathyrus sativus under lead stress.

The ability of plant growth-promoting rhizobacteria (PGPR) to enhance Lathyrus sativus tolerance to lead (Pb) stress was investigated. Ten consortia formed by mixing four efficient and Pb-resistant PGPR strains were assessed for their beneficial effect in improving Pb (0.5mM) uptake and in inducing the host defence system of L.sativus under hydroponic conditions based on various physiological and biochemical parameters. Lead stress significantly decreased shoot (SDW) and root (RDW) dry weight, but PGPR inoculation improved both dry weights, withhighest increases in SDW and RDW of plants inoculated with I5 (R.leguminosarum (M5) + P.fluorescens (K23) + Luteibacter sp. + Variovorax sp.) and I9 (R.leguminosarum (M5)+Variovorax sp.+Luteibacter sp.+S.meliloti) by 151% and 94%, respectively. Additionally, inoculation significantly enhanced both chlorophyll and soluble sugar content, mainly in I5 inoculated leaves by 238% and 71%, respectively, despite the fact that Pb decreased these parameters. We also found that PGPR inoculation helps to reduce oxidative damage and enhances antioxidant enzyme activity, phenolic compound biosynthesis, carotenoids and proline content. PGPR inoculation increased Pb uptake in L. sativus, with highest increase in shoots of plants inoculated with I5 and I7, and in roots and nodules of plants inoculated with I1. Moreover, PGPR inoculation enhanced mineral homeostasis for Ca, Cu and Zn under Pb stress, mainly in plants inoculated with I1, I5, I7 and I9. Results of our study suggest the potential of efficient and Pb-resistant PGPR in alleviating harmful effects of metal stress via activation of various defence mechanisms and enhancing Pb uptake that promotes tolerance of L.sativus to Pb stress.

Phytoremediation of Pb contaminated paddy field using combination of Agrobacterium sp. I3, compost and ramie (Boehmeria nivea)

Industry sector exerts a negative effect on the environment. Industrial waste is often disposed to the rivers. The industry contributes to the accumulation of heavy metals in the environment. In farming sector, the accumulation of heavy metals can result in water pollution and be washed into the ground. Therefore, the farming product can be contaminated with heavy metals and they can be harmful to human health. The objective of this research was to reduce the Pb heavy metal content in paddy soil. This research was taken place in the Pb contaminated paddy soil using a randomized complete block design with three factors and three replicates. This research employed combination of inorganic fertilizer, ramie and Agrobacterium sp . I 3 or compost as a chelator to improve Pb uptake. The results showed that combination of the three treatments increased Pb uptake. The combination of chemical fertilizers, ramie with compost increased the Pb uptake of 11.93 μg/g or 45.9%. The combination of chemical fertilizers, ramie with Agrobacterium sp. I 3 resulted in the highest Pb uptake of 12.85 μg/g or 49.8%. The combination also decreased the soil Pb level by 7.8 μg/g or 23.5% of the control.

Heavy metal (Pb) accumulation in metallophytes as influenced by the variations in rhizospheric and non-rhizospheric soils physico-chemical characteristics

ABSTRACTActivities at root-soil interface determine the solubility and uptake of metals by plants. Metal accumulation in plant species (Imperata cylindrical, Cynodon dactylon, Eleucine indica, Gomphrena celosoides, Sporobolus pyramidalis, Chromolaena odorata and Rhynchospora corymbosa) growing on Pb contaminated site as influenced by variations in physico-chemical characteristics, dissolved organic matter (DOM), Pb fractionation and different functional groups (using Fourier Transmittance Infra-red) of rhizospheric and non-rhizospheric soils was assessed. The electrical conductivity (2660–5520 µs) and Pb concentrations (51390.0–64080.0 mg/kg) were more in non-rhizospheric than rhizospheric soils having 276 µs to 3160 µs EC and 3289.0 to 44850.0 mg/kg Pb. More nutrients, DOM and carbohydrates functional groups (C-O; 1100 -1000 and O-H; 3700–3600) were found in rhizospheric compared to non-rhizospheric soils. The pH was slightly acidic (5.0–5.54) and E. indica with the lowest pH (5.0) accumulated highest Pb concentrations in shoot (8030 mg/kg) and root (16380 mg/kg) while C. odorata with highest values of pH, P, Ca and Mg in rhizospheric soil accumulated the least (root; 331.6 and shoot: 209.0 mg/kg). Pb was more in organic and residual fractions of rhizospheric and non-rhizospheric soils respectively. Reduction in pH, EC coupled with nutrients and DOM availability increased Pb uptake by plants.

The effect of two humic substances on the growth and lead Uptake of corn in calcareous soil

ABSTRACT- In the past few decades, accumulation of heavy metals, such as lead (Pb), in soils has increased as a result of human activities.The environmental hazard associated with soil enrichment in heavy metals is related to their mobility and plant availability. Application of various materials such as humic may influence the amount of Pb taken up by plant. Four levels of each of liquid and solid commercial humic substances were applied in this study which were performed as two completely randomized factorial design experiments in a calcareous soil polluted with three levels of Pb. Results of a greenhouse study with corn (Zea mays L., cv Hido) showed that the two commercial humic substances with different chemical composition, affected dry mater yield differently. Influences of humic substances on dry mater yield were most likely dependent on their chemical composition. Maximum dry mater yield was observed at manufacturer's recommended levels of humic substances. But, the solid humic treatments had no significant effect on dry mater yield. Application of both liquid and solid commercial substances significantly increased uptake of Pb in corn shoots. Addition of humic substances significantly increased the enrichment factor in both experiments but affected the micronutrient uptake only slightly.

Effect of fulvic acids on lead-induced oxidative stress to metal sensitive Vicia faba L. plant

Lead (Pb) is a ubiquitous environmental pollutant capable to induce various morphological, physiological, and biochemical functions in plants. Only few publications focus on the influence of Pb speciation both on its phytoavailability and phytotoxicity. Therefore, Pb toxicity (in terms of lipid peroxidation, hydrogen peroxide induction, and photosynthetic pigments contents) was studied in Vicia faba plants in relation with Pb uptake and speciation. V. faba seedlings were exposed to Pb supplied as Pb(NO3)2 or complexed by two fulvic acids (FAs), i.e. Suwannee River fulvic acid (SRFA) and Elliott Soil fulvic acid (ESFA), for 1, 12, and 24 h under controlled hydroponic conditions. For both FAs, Pb uptake and translocation by Vicia faba increased at low level (5 mg l−1), whereas decreased at high level of application (25 mg l−1). Despite the increased Pb uptake with FAs at low concentrations, there was no influence on the Pb toxicity to the plants. However, at high concentrations, FAs reduced Pb toxicity by reducing its uptake. These results highlighted the role of the dilution factor for FAs reactivity in relation with structure; SRFA was more effective than ESFA in reducing Pb uptake and alleviating Pb toxicity to V. faba due to comparatively strong binding affinity for the heavy metal.

Suitability of urban wastes for crop production in Zaria, northern Nigeria: bioavailability and geochemical fractions of potentially toxic elements

A savannah soil amended with two urban wastes and planted with sorghum (Sorghum bicolor) in a pot experiment was evaluated for chemical forms and phytoavailability of Cr, Ni and Pb. The metals were partitioned into seven operationally defined chemical fractions: mobile (F1), easily mobilisable (F2), occluded in Mn oxides (F3), organically bound (F4), occluded in amorphous Fe oxides (FeOxam, F5), occluded in crystalline Fe oxides (FeOxc, F6), and residual (F7). Although the application of the urban wastes increased the total concentrations of the metals in the soil, there were no corresponding increases in Cr and Ni uptake by sorghum except for Pb uptake. Waste application increased mobile Ni (F1) but decreased the residual form (F7). The organically bound Pb (F4) was increased at the expense of residual Pb (F7). With respect to Cr, waste application increased Cr form occluded in non-crystalline Fe oxides (F5) in the soil. Bioassay of the test crop indicated that the uptake of Pb by sorghum (Y-Pb) correlated significantly with Pb occluded in non-crystalline and crystalline Fe oxides (F5 and F6). Since a single application of urban wastes to this savannah soil significantly increased Pb uptake by sorghum, the consequences of long-term applications under urban and peri-urban agriculture (UPA) should be of great concern; particularly with respect to children’s exposure to Pb through consumption of food and vegetables.

Effects of Pinus densiflora on soil chemical and microbial properties in Pb-contaminated forest soil

We investigated the effect of Pb uptake by Pinus densiflora and the Pb fraction in forest soil. We also investigated the change in soil physicochemical characteristics, microbial activity, and root exudates of Pinus densiflora in Pb-contaminated soils. Three-year-old pine seedlings were exposed to 500 mg/kg Pb for 12 months. The metal fractions were measured using sequential extraction procedures. Additionally, factors that affect solubility (three soil enzyme activities and amino acids of root exudate compounds) were also determined. The results showed that Pb contamination significantly decreased enzyme activities due to soil characteristics. In addition, organic matter, nitrate content, and Pb concentration were time dependent. The results indicate that changes in the Pb fraction affected Pb uptake by pine trees due to an increase in the exchangeable Pb fraction. The concentrations of organic acids were higher in Pb-spiked soil than those in control soil. Higher rhizosphere concentrations of oxalic acid resulted in increased Pb uptake from the soil. These results suggest that pine trees can change soil properties using root exudates due to differences in the metal fraction.

Fractionation of lead in paddy soils and its bioavailability to rice plants

The impact of heavy metal pollution on growth and water quality has become a public concern. Fractionation of soil lead (Pb) is an important approach of chemical characterization and can provide useful information on its bioavailability. A greenhouse study was undertaken to estimate the availability of Pb fractions to rice in two paddy soils of Inceptisol (Fluventic Umbrepts) and Ultisol (Plinthudic Aquults). Lead fractionation was performed by using a sequential extraction procedure (SEP) and single extraction with 1 mol NH 4Ac L − 1 . The increased Pb loading (0–1200 mg kg − 1 ) in two paddy soils had variable effects on plant dry biomass, and Pb concentration in rice plants. Plant dry biomass was higher in Ultisol than Inceptisol, and grain yield in both soils decreased with increasing Pb loadings. The concentrations of Pb in root, leaf, stalk, and grain of rice increased significantly with increasing levels of Pb in both soils, and this increase was more pronounced in Ultisol than Inceptisol. Lead accumulated mainly in the roots and the increase in Pb concentrations due to external Pb input for different plant parts was in the order of root > stalk > leaf > grain. Soil NH 4OAc extractable Pb was higher in Ultisol than Inceptisol and was better correlated with root Pb than grain or straw Pb, indicating slow translocation of Pb from root to shoot, especially to grain. The dominant fractions of Pb in Ultisol were residual and exchangeable fractions, whereas in Inceptisol Pb was mainly bound to residual and Fe/Mn oxides fractions. Lead was more mobile in the Ultisol than in the Inceptisol soil. External Pb loading decreased soil pH and increased Pb bioavailability in soil, thus resulting in increased Pb uptake and accumulation in the edible parts of rice. These results indicate that plant availability of externally loaded Pb is related to Pb transformation and fractionation in soils, which are affected by basic soil properties such as clay and oxide content and composition, pH, and organic matter. External Pb loading increases Pb uptake by rice plant, but most of the absorbed Pb is accumulated in the root with a minimal increase in grain Pb. This information merits attention in the management of Pb-polluted soils.

Effect of indole-3-acetic acid on lead accumulation in maize ( Zea mays L.) seedlings and the relevant antioxidant response

The effect of indole-3-acetic acid (IAA) on lead (Pb) accumulation in maize ( Zea mays L. cv. TY2) seedlings, and the responses of maize to Pb, IAA or Pb + IAA stress were investigated under hydroponic conditions. Exogenous IAA significantly increased Pb accumulation in roots, but significantly decreased Pb accumulation in shoots over the culture period of 5 days. Increased Pb uptake in maize roots partly took place through calcium and potassium channels, and also depended upon membrane potential. Lipid peroxidation in terms of malondialdehyde (MDA) content was enhanced, indicating that Pb and/or IAA caused oxidative stress in maize seedlings. Under stress conditions the antioxidant defense mechanism was activated. Some antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were up-regulated compared to the control. Pb, IAA or Pb + IAA treatments resulted in a general reduction of macro- and micronutrient contents, especially of K, Ca and Mn. Compared to a single Pb or IAA treatment, treatment with a combination of Pb + IAA induced more severe oxidative stress on maize roots and shoots as inferred from the higher observed MDA and lower nutrient contents. A Fourier transform infrared (FTIR) spectroscopic study indicated that Pb reacted with the carboxylic acid group of the IAA pyrrole cycle.

Effects of exogenous chelators on phytoavailability and toxicity of Pb in Zinnia elegans Jacq.

Chelate-enhanced phytoremediation is considered as an effective method for the extraction of lead (Pb) by plants. However, more detailed studies are needed to evaluate the effect of exogenous chelators on phytoavailability and toxicity of Pb in plants, then to find out the proper applied concentration of chelators to minimize the combined toxicity to the plants and maximize phytoavailable Pb. To clarify these questions, the seed germination test of Zinnia elegans Jacq. exposed to solutions containing Pb and four types of chelators including sodium ethylenediamine tetra-acetic acid (Na 2EDTA), oxalic acid, tartaric acid and citric acid was observed. The results showed that the roots and shoots treated with equimolar chelators and Pb were longer than those treated with half and two folds of the molar concentrations of Pb. The growth of seedlings was inhibited by surplus addition of chelators, and the toxicity of complexes was less than that of Pb and chelators. In particular, 2.4 mM EDTA and 1.2 mM oxalic acid significantly ( P < 0.05) increased Pb uptake when the seeds were treated with 2.4 mM Pb. In the 4.8 mM Pb solution, Pb accumulation in the seedlings was markedly ( P < 0.05) increased by 4.8 mM EDTA, 2.4 mM tartaric acid, 4.8 mM tartaric acid and 2.4 mM citric acid, and amounted to 6752.4, 6453.8, 6541.4 and 6598.3 μg g −1, respectively. With the superfluous addition of chelators, Pb accumulation in the seedlings decreased in a concentration-dependent manner. When Pb was used at 2.4 mM, an equimolar concentration of EDTA not only increased Pb uptake but also stimulated the seedling growth. Thus, chelating agents in their appropriately concentrations could counteract Pb toxicity, but superfluous chelators resulted in less Pb uptake and growth inhibition of the seedlings.

Limitation of Pb and Cd Uptake by Pine

Model experiments were carried out using 1-year-old pine plants grown in water cultures with the aim of investigating whether and to what extent the accumulation of Pb and Cd in plants can be decreased through decreasing the nutrient solution concentration, supplementing with forest soil, supplementing with calcium carbonate, and addition of brown coal. It was found that with increased doses of Pb and Cd in water cultures pine plants take up more of those elements. Whereas Pb accumulates mainly in the roots, about half of the Cd is transported to the above-ground part of the plants. Addition of Pb, Cd, and forest soil to the nutrition medium increased Pb uptake by pine plants compared to the control treatment. The effect of soil addition was not that evident in the case of Cd uptake. Furthermore, it was observed that addition of brown coal resulted in a slight increase of Pb accumulation in the shoots and in a considerable decrease of its accumulation in roots. A higher increase of Cd accumulation in the shoots was observed after brown coal was added to the nutrient solution. The amounts of Cd and Pb accumulated in plants, mainly in the shoots, decreased following the addition of CaCO3. When CaCO3 and brown coal were added jointly, this effect was markedly more pronounced. The decrease of nutrient supply (down to one-quarter of the original concentration) increased the content of Pb, especially in the roots; for Cd, changes in its content in pine were not univocal.

The effect of EDDS chelate and inoculation with the arbuscular mycorrhizal fungus Glomus intraradices on the efficacy of lead phytoextraction by two tobacco clones

Two pot experiments were conducted to investigate the effect of inoculation with the arbuscular mycorrhizal (AM) fungus Glomus intraradices on Pb uptake by two clones of Nicotiana tabacum plants. Non-transgenic tobacco plants, variety Wisconsin 38, were compared in terms of Pb uptake with transgenic plants of the same variety with inserted gene coding for polyhistidine anchor in fusion with yeast metallothionein. Bioavailability of Pb in experimentally contaminated soil was enhanced by the application of a biodegradable chelate ethylenediaminedissuccinate (EDDS). EDDS addition (2.5 and 5.0 mmol kg −1 substrate) increased Pb uptake from the substrate and enhanced Pb translocation from the roots to the shoots, with shoot Pb concentrations reaching up to 800 mg kg −1 at the higher chelate dose. Application of a single dose of 5 mmol kg −1 proved to be more efficient at increasing shoot Pb concentrations than two successive doses of 2.5 mmol kg −1, in spite of a marked negative effect on plant growth and phytotoxicity symptoms. Pb amendment (1.4 g kg −1 substrate) connected with either dose of EDDS decreased significantly plant biomass as well as reduced the development of AM fungi. AM inoculation promoted the growth of tobacco plants and partly alleviated the negative effect of Pb contamination, mainly in the case of root biomass. No consistent difference in Pb uptake was found between transgenic and non-transgenic tobacco plants. The effect of AM inoculation on Pb concentrations in plant biomass varied between experiments, with no effect observed in the first experiment and significantly higher root Pb concentrations and increased root–shoot ratio of Pb concentrations in the biomass of inoculated plants in the second experiment. Due to probable retention of Pb in fungal mycelium, the potential of AM for phytoremediation resides rather in Pb stabilisation than in phytoextraction.

Bioavailability and mobility of Pb after soil treatment with different remediation methods

The risk of Pb contaminated soil after treatment with different remediation techniques was assessed. Soil vitrification (microwaves) reduced Pb orally available from the stomach and intestinal phase measured by a&amp;nbsp;physiologically based extraction test. Solidification of Pb (Slovakite) did not reduce the concentration of orally available Pb and increased the Pb uptake by Thlaspi goesingens for 2-times compared to plants grown on the original soil. Soil extraction with 40 mmol/kg EDTA removed 57.6% of Pb. However, the concentration of orally available Pb and Pb uptake by T. goesingens increased. The concentration of mobile soil Pb also increased for 14-times measured by a toxicity characteristic leaching procedure. Soil leaching with 10 mmol/kg biodegradable chelator [S,S] ethylenediamine disuccinate and using a horizontal permeable reactive barrier for Pb accumulation from the washing solution removed 17.8% of Pb, but increased Pb uptake by T. goesingens by 3-times and slightly increased the concentration of Pb in the intestinal phase. Leaching did not significantly effects Pb availability from the stomach phase or Pb mobility.