Chemically enhanced phytoextraction of Pb by wheat in texturally different soils

Bioassessment of Cd and Pb at Multiple Growth Stages of Wheat Grown in Texturally Different Soils Using Diffusive Gradients in Thin Films and Traditional Extractants: A Comparative Study

The bioavailability of heavy metals in soil is a crucial factor in determining their potential uptake by plants and their subsequent entry into the food chain. Various methods, including traditional chemical extractants and the diffusive gradients in thin films (DGT) technique, are employed to assess this bioavailability. The bioavailability of heavy metals, particularly cadmium (Cd) and lead (Pb), is also influenced by soil texture and their concentrations in the soil solution. The primary objectives of this experiment were to compare and correlate the assessment of the Cd and Pb bioavailability using the DGT technique and traditional extractants across two soil textural classes: sandy clay loam (SCL) and clay loam (CL) at two contamination levels: aged contaminated (NC) and artificially contaminated (AC). The specific objectives included assessing the bioavailability of Cd and Pb at different growth stages of the wheat plant and correlating the DGT-based bioassessments of Cd and Pb with their concentrations in various plant parts at different growth stages. This study also compared the effectiveness of the DGT method and traditional extraction techniques in assessing the bioavailable fractions of Cd and Pb in soil. The regression analysis demonstrated strong positive correlations between the DGT method and various extraction methods. The results showed that the wheat plants grown in the AC soils exhibited lower root, shoot, and grain weights compared to those grown in the NC soils, indicating that metal contamination negatively impacts plant performance. The concentrations of Cd and Pb in the wheat tissues varied across different growth stages, with the highest levels observed during the grain filling (S3) and maturity (S4) stages. It is concluded that the in situ assessment of Cd and Pb though DGT was strongly and positively correlated with the Cd and Pb concentration in wheat plant parts at the maturity stage. A correlation and regression analysis of the DGT assessment and traditional extractants showed that the DGT method provides a reliable tool for assessing the bioavailability of Cd and Pb in soils and helped in developing sustainable soil management strategies to ensure the safety of agricultural products for human consumption.

Low-dose lanthanum activates endocytosis, aggravating accumulation of lanthanum or/and lead and disrupting homeostasis of essential elements in the leaf cells of four edible plants

Rare earth elements (REEs) are emerging as a serious threat to ecological safety due to their increasing accumulation in environments. The accumulation of REEs in environments has significantly increased its accumulation in the leaves of edible plants. However, the accumulation pathway of REEs in the leaves of edible plants are still unknown. In this study, lanthanum [La(III), a widely used and accumulated REE] and four edible plants (soybean, lettuce, pakchoi, and celery) with short growth cycles were selected as research objects. By using interdisciplinary research techniques, we found that low-dose La(III) activated endocytosis (mainly the clathrin-mediated endocytosis) in the leaf cells of four edible plants, which provided an accumulation pathway for low-dose La in the leaf cells of these edible plants. The accumulation of La in the leaf cells was positively correlated with the intensity of endocytosis, while the intensity of endocytosis was negatively correlated with the density of leaf trichomes. In addition to the accumulation of La, low-dose La(III) also brought other risks. For example, the harmful element (Pb) can also be accumulated in the leaf cells via La(III)-activated endocytosis; the homeostasis of the essential elements (K, Ca, Fe, Mg) was disrupted, although the chlorophyll synthesis and the growth of these leaf cells were accelerated; and the expression of stress response genes (GmNAC20, GmNAC11) in soybean leaves was increased. These results provided an insight to further analyze the toxicity and mechanism of REEs in plants, and sounded the alarm for the application of REEs in agriculture.

Phytoextraction of Heavy Metals by Various Vegetable Crops Cultivated on Different Textured Soils Irrigated with City Wastewater

A challenging task in urban or suburban agriculture is the sustainability of soil health when utilizing city wastewater, or its dilutes, for growing crops. A two-year field experiment was conducted to evaluate the comparative vegetable transfer factors (VTF) for four effluent-irrigated vegetable crops (brinjal, spinach, cauliflower, and lettuce) grown on six study sites (1 acre each), equally divided into two soil textures (sandy loam and clay loam). Comparisons of the VTF factors showed spinach was a significant and the best phytoextractant, having the highest heavy metal values (Zn = 20.2, Cu = 12.3, Fe = 17.1, Mn = 30.3, Cd = 6.1, Cr = 7.6, Ni = 9.2, and Pb = 6.9), followed by cauliflower and brinjal, while lettuce extracted the lowest heavy metal contents (VTF: lettuce: Zn = 8.9, Cu = 4.2, Fe = 9.6, Mn = 6.6, Cd = 4.7, Cr = 2.9, Ni = 5.5, and Pb = 2.5) in response to the main (site and vegetable) or interactive (site * vegetable) effects. We suggest that, while vegetables irrigated with sewage water may extract toxic heavy metals and remediate soil, seriously hazardous/toxic contents in the vegetables may be a significant source of soil and environmental pollution.

Lead phytoextraction by Pelargonium hortorum: Comparative assessment of EDTA and DIPA for Pb mobility and toxicity

Soil amendments like ethylene-diamine-tetraacetic-acid (EDTA) have extensively been used for enhancing lead (Pb) phytoextraction. But due to its toxic effects, environment friendly substitute is required. Therefore, the present study was conducted to investigate the effect of EDTA and Di-iso-propanol-amine (DIPA) to enhance Pb phytoavailability and uptake by Pelargonium hortorum along with comparative toxicities of both organic amendments. For this purpose, soil was spiked with Pb concentrations (0, 500, 750, 1000 and 1500 mg kg¹) and amended with EDTA and DIPA at dosage levels (0, 1.5, 3, 5, 7.5, 10 mmol kg^-1) for plantation of Pelargonium hortorum. Soil samples were extracted with MgCl₂, plant samples were acid digested and analyzed for metal content. Biomass and root/shoot length of Pelargonium hortorum was decreased with increase in concentration of Pb and chelating agents. Phytoavailability of Pb at 1500 mg kg^-1 with EDTA 10 mmol kg^-1 was 0.3-folds in comparison to DIPA at the same dosage. Pelargonium hortorum plants amended with EDTA and DIPA at 10 mmol kg^-1 with Pb 1000 mg kg^-1 were found to uptake Pb 5.3-fold and 2.5-folds, respectively in comparison to Pb 1000 mg kg^-1 alone. Pb uptake decreased at 1500 mg kg^-1 with both chelating agents. The EDTA alone and in combination with 1500 mg Pb kg^-1 showed maximum genotoxicity by reducing the mitotic index and increasing the micronuclei formation. EDTA+Pb showed maximum toxicity followed by Pb and DIPA. Overall, 10 mmol kg^-1 of EDTA and DIPA performed better among all dosages in enhancing phytoavailability and uptake of Pb. DIPA showed less toxicity than that caused by EDTA, with comparable ability to promote Pb phytoextraction.

Performance of new biodegradable chelants in enhancing phytoextraction of heavy metals from a contaminated calcareous soil

Chelant-assisted phytoextraction has widely been exploited as a feasible option for removing heavy metals from the contaminated soils. Some synthetic chelants have shown promising performances for this option, but they have also revealed several negative environmental consequences. This study has sought to investigate the feasibility of two biodegradable eco-friendly chelants, namely methylglycinediacetic acid (MGDA) and N,N-Bis(carboxymethyl)-L-glutamic acid (GLDA), as compared to the resistant ethylenediaminetetraacetic acid (EDTA), in enhancing phytoextraction of Zn and Pb from a contaminated calcareous soil. For this purpose, a greenhouse experiment was carried out comparing the growth and metal absorption of maize (Zea mays L.) grown on soils treated with EDTA, MGDA, and GLDA chelants at 2, 4 and 8 mmol kg^- 1 levels. Results showed that the heavy metal uptakes by the plant shoots generally increased with increasing the chelant application level. Pb uptake by maize shoots increased from 10.6 mg plant^- 1 in control to 416, 398, and 416 mg plant^- 1 in the soils treated with 8 mmol kg^- 1 MGDA, GLDA, and EDTA, respectively. The corresponding increases in Zn uptake were from 100.9 mg plant^- 1 to 798.9, 718.9, and 530.4 mg plant^- 1 in the MGDA-, GLDA-, and EDTA-amended soils, respectively. Moreover, the amounts of water-extractable, and thereby potentially leachable, Pb and Zn in the post-harvest soil were considerably greater in the soil treated with EDTA than those treated with MGDA and GLDA. Therefore, MGDA and GLDA would be potential alternatives to environmentally-persistent EDTA for enhanced metal phytoextraction from contaminated soils.

Lead toxicity in plants: Impacts and remediation

Lead (Pb) is the second most toxic heavy metal after arsenic (As), which has no role in biological systems. Pb toxicity causes a range of damages to plants from germination to yield formation; however, its toxicity is both time and concentration dependent. Its exposure at higher rates disturbs the plant water and nutritional relations and causes oxidative damages to plants. Reduced rate of seed germination and plant growth under stress is mainly due to Pb interference with enzymatic activities, membrane damage and stomatal closure because of induction of absicic acid and negative correlation of Pb with potassium in plants. Pb induced structural changes in photosynthetic apparatus and reduced biosynthesis of chlorophyll pigments cause retardation of carbon metabolism. In this review, the noxious effects of Pb on germination, stand establishment, growth, water relations, nutrient uptake and assimilation, ultra-structural and oxidative damages, carbon metabolism and enzymatic activities in plants are reported. The Pb dynamics in soil rhizosphere and role of remediation strategies i.e. physical, chemical and biological to decontaminate the Pb polluted soils has also been described. Among them, biological strategies, including phytoremediation, microbe-assisted remediation and remediation by organic amendments, are cost effective and environmentally sound remedies for cleaning Pb contaminated soils. Use of organic manures and some agricultural practices have the potential to harvest better crops yield of good quality form Pb contaminated soils.

Ethylenediamine disuccinic acid enhanced phytoextraction of nickel from contaminated soils using Coronopus didymus (L.) Sm

In a screenhouse, the applicability of biodegradable chelant ethylenediamine disuccinic acid (EDDS) to enhance Ni-phytoextraction by Coronopus didymus was tested for the first time. This study assayed the hypothesis based upon the role of EDDS on physiological and biochemical alterations and ameliorating phytoextraction capacity of C. didymus under nickel (Ni) stress. Pot experiments were conducted for 6 weeks and C. didymus plants were cultivated in soil artificially contaminated with 30, 50, and 70 mg kg^-1 Ni treatments. Soil was amended with EDDS (2 mmol kg^-1). Plants were harvested, 1 week after EDDS application. At 70 mg kg^-1 Ni level, EDDS application dramatically enhanced the root and shoot Ni concentration from 665 and 644 to 1339 and 1338 mg kg^-1, respectively. Combination of Ni + EDDS induced alterations in biochemical parameters of plants. EDDS addition posed pessimistic effects on growth, biomass, photosynthetic activity and protein content of the plants. Besides, application of EDDS stimulated the generation of superoxide anion, H₂O₂ content and MDA level. However, EDDS assisted mount in antioxidant activities (superoxide dismutase, catalase and glutathione peroxidase) considerably neutralised the toxicity induced by reactive oxygen species in plant tissues. The results revealed EDDS efficacy to ameliorate the performance of antioxidant enzymes and improved Ni translocation in plant tissues, thus strongly marked its affinity to be used together with C. didymus for Ni-phytoextraction.

Dispersion and solubility of In, Tl, Ta and Nb in the aquatic environment and intertidal sediments of the Scheldt estuary (Flanders, Belgium)

Certain specialty elements are indispensable in modern technologies for their particular properties. Yet, potential risks associated to the release of these elements at any stage, remains unknown. Therefore, the dispersion of indium (In), thallium (Tl), tantalum (Ta) and niobium (Nb) in the aquatic environment of the Scheldt estuary (Flanders, Belgium) was studied. Maximum concentrations in intertidal sediments of 101 ± 15 μg kg^-1 for In, 481 ± 37 μg kg^-1 for Tl, 88 ± 19 μg kg^-1 for Ta and 1162 ± 4 μg kg^-1 for Nb appeared on the sampling location closest to the river mouth, i.e. 57.5 km upstream. Their distribution in the intertidal sediments depends on the physicochemical sediment characteristics along the flow of the river Scheldt. The same was the case for most other metals and aluminum as their occurrence also correlated (p < 0.05) with the occurrence of In, Tl and Nb. While in general, studied elements correlate to the OM content and sulfur and phosphorus herein included, a relative enrichment of In, Tl and Nb was seen at Rupelmonde (92.0 km from the river mouth). Mainly the intertidal sediment silt fraction is capable of retaining the elements by exchanging with other ions in the mineral interlayer. Increasing salinity towards the river mouth can furthermore induce the formation of insoluble chloride species. Overall, the solubility of In, Tl, Ta and Nb appeared extremely low upon extraction of pore water from intertidal sediments saturated to 100% field capacity.

A review with recent advancements on bioremediation-based abolition of heavy metals

There has been a significant rise in the levels of heavy metals (Pb, As, Hg and Cd) due to their increased industrial usage causing a severe concern to public health. The accumulation of heavy metals generates oxidative stress in the body causing fatal effects to important biological processes leading to cell death. Therefore, there is an imperative need to explore efficient and effective methods for the eradication of these heavy metals as against the conventionally used uneconomical and time consuming strategies that have numerous environmental hazards. One such eco-friendly, low cost and efficient alternative to target heavy metals is bioremediation technology that utilizes various microorganisms, green plants or enzymes for the abolition of heavy metals from polluted sites. This review comprehensively discusses toxicological manifestations of heavy metals along with the detailed description of bioremediation technologies employed such as phytoremediation and biosorption for the potential removal of these metals. It also updates readers about recent advances in bioremediation technologies like the use of nanoparticles, non-living biomass and transgenic crops.

Optimization of chelators to enhance uranium uptake from tailings for phytoremediation

A greenhouse experiment was set up to investigate the ability of citric acid (CA), oxalic acid (OA), nitrilotriacetic acid (NTA) and EDTA for phytoremediation of uranium tailings by Indian mustard [Brassica juncea (L.) Czern. et Coss]. Uranium tailings were collected from Umra mining region and mixed with 75% of garden soil which yielded a 25:75 mixture. Prepared pots were divided into four sets and treated with following different concentrations - 0.1, 0.5, 2.5 and 12.5 mmol kg(-1) soil additions for each of the four chelators. Control pots which were not treated with chelators. Experiments were conducted in completely randomized block design with triplicates. The optimum concentrations of these chelators were found on the basis of biomass production, tolerance and accumulation potential. The data collected were expressed statistically. EDTA produced maximum growth depression whereas, minimum occurred in the case of NTA. Maximum U uptake (3.5-fold) in the roots occurred at 2.5 mmol of CA, while NTA proved to be the weakest for the same purpose. Severe toxicity in the form of reduced growth and plant death was recorded at 12.5 mmol of each chelator. Minimum growth inhibition produced by chelators occurred in NTA which was followed by OA, moderate in CA and maximum was traced in EDTA applications. Chelator strengthened U uptake in the present study follows the order: CA>EDTA>OA>NTA.

The use of a biodegradable chelator for enhanced phytoextraction of heavy metals by Festuca arundinacea from municipal solid waste compost and associated heavy metal leaching

In a column experiment with horizontal permeable barriers, the effects of a biodegradable chelator-nitrilotriacetic acid (NTA) on the uptake of heavy metals from municipal solid waste (MSW) compost by Festuca arundinacea and metal leaching were investigated. The use of NTA was effective in increasing Cu, Pb, and Zn uptakes in shoots of two crops of F. arundinacea. In columns with barriers and treated with 20 mmol NTA per kg MSW compost, metal uptakes by the first and second crop of F. arundinacea were, respectively, 3.8 and 4.0 times for Pb, and 1.8 and 1.7 times for Zn greater with the added NTA than without it. Though NTA application mobilized metals, it caused only slight leaching of metals from MSW compost. Permeable barriers positioned between compost and soil effectively reduced metal leaching. NTA-assisted phytoextraction by turfgrass with permeable barriers to cleanup heavy metal contaminated MSW compost should be environmentally safe.

Behavior and impact of zirconium in the soil-plant system: plant uptake and phytotoxicity

Zirconium (Zr) is a transition metal that has both stable and radioactive isotopes.This metal has gained significant attention as a major pollutant of concern, partly because it has been prominent in the debate concerning the growing anthropogenic pressure on the environment. Its numerous past and present uses have induced significant soil and water pollution. Zr is generally considered to have low mobility in soils. The behavior of Zr particularly depends on the characteristics of the media in which it exists, and even its presence in the biosphere as a contaminate may affect its behavior. In this chapter, we describe the relationship between the behavior of Zrand its speciation in soils, its uptake and accumulation by plants, its translocation and toxicity inside plants, and mechanisms by which plants detoxify it.Zr is abundant and occurs naturally in the earth's crust. Zr emissions to the atmosphere are increasing from anthropogenic activities such as its use in industry and nuclear reactors. Zr forms various complexes with soil components, which reduces its soil mobility and phytoavailabilty. The mobility and phytoavailabilty of Zr in soil depend on its speciation and the physicochemical properties of soil that include soil pH, texture, and organic contents. Despite having low soil mobility and phytoavailability,amounts of Zr are absorbed by plants, mainly through the root system and can thereby enter the food chain.After plant uptake, Zr mainly accumulates in root cells. Zr does not have any known essential function in plant or animal metabolism. Although little published data are available, we conclude that the phytotoxicity of Zr is generally low.Notwithstanding, Zr can significantly reduce plant growth and can affect plantenzyme activity. When exposed to Zr-induced toxicity, plants possess numerous defense mechanisms to cope with the toxicity. Such strategies include Zr sequestration in plant roots and activation of various antioxidants. Because Zr may have impact on the biosphere, we believe it deserves to be evaluated in supplementary studies that will enhance the understanding of its behavior in soil-plant systems.

Review of Pb availability and toxicity to plants in relation with metal speciation; role of synthetic and natural organic ligands

Biogeochemical behavior of lead (Pb), a persistent hazardous pollutant of environmental concern, strongly depends on its chemical speciation. Therefore, in this review, link between Pb speciation: presence of organic ligands and its environmental behavior has been developed. Both, biogeochemical and ecotoxicological data are discussed in environmental risk assessment context and phytoremediation studies. Three kinds of organic ligands selected for this review include: (1) ethylene diamine tetra-acetic acid (EDTA), (2) low molecular weight organic acids (LMWOAs) and (3) humic substances (HSs). The review highlights the effect of Pb speciation on: (i) Pb fate and behavior in soil; (ii) Pb plant uptake and accumulation in different plant parts; and (iii) Pb-induced phyto-toxicity. Effects of organic ligands on Pb speciation are compared: how they can change Pb speciation modifying accordingly its fate and biogeochemistry in soil-plant system? EDTA forms soluble, stable and phytoavailable Pb-chelates due to high binding Pb affinity. LMWOAs can solubilize Pb in soil by decreasing soil pH or increasing soil organic contents, but have little effect on its translocation. Due to heterogeneous structure, HSs role is complex. In consequence Pb speciation knowledge is needed to discuss phyto-toxicity data and improved soil phytoremediation techniques.

Phytoextraction of Cu, Zn, and Pb Enhanced by Chelators with Vetiver (Vetiveria zizanioides): Hydroponic and Pot Experiments

Phytoextraction is a green remediation technology for clean-up contaminated soils. The effect of chelator application including EDTA, EDDS, and citric acid on phytoextraction of Cu, Zn, and Pb into high biomass vetiver (Vetiveria zizaniodides) was investigated in the hydroponic experiment and the pot experiment. In the hydroponic test, EDTA induced the most significant toxic symptom on vetiver compared to EDDS and citric acid. Obvious biofilm was attached in the rhizosphere of vetiver with the citric acid addition due to its serving as growth substrate while EDTA posed microbial toxicity to present clear solution. Sequential extraction results demonstrated that EDTA was better than EDDS and citric acid to change the adsorbed metal to loosely bound fraction which is more mobile and bioavailable. In the pot experiment, the critical finding was that vetiver has been demonstrated as a hyperaccumulator for treatment of EDDS with Cu; EDDS, citric acid, and EDTA with Zn; EDTA with Pb. EDDS and EDTA possess the viable phytoextraction ability and can be employed as an remediation alternative, though the groundwater leaching needs to be taken into serious consideration.