Effect of Root-Induced Chemical Changes on Dynamics and Plant Uptake of Heavy Metals in Rhizosphere Soils

doi:10.1016/S1002-0160(10)60039-2

Pedosphere

Volume 20, Issue 4, August 2010, Pages 494-504

https://doi.org/10.1016/S1002-0160(10)60039-2 Get rights and content

Abstract

It is increasingly recognized that metal bioavailability is a better indicator of the potential for phytoremediation than the total metal concentration in soils; therefore, an understanding of the influence of phytoremediation plants on metal dynamics at the soil-root interface is increasingly vital for the successful implementation of this remediation technique. In this study, we investigated the heavy metal and soil solution chemical changes at field moisture, after growth of either Indian mustard (Brassica juncea) or sunflower (Helianthus annuus L.), in long-term contaminated soils and the subsequent metal uptake by the selected plants. In addition, the fractions of free metal ions in soil solution were determined using the Donnan membrane technique. After plant growth soil solution pH increased by 0.2–1.4 units and dissolved organic carbon (DOC) increased by 1–99 mg L⁻¹ in all soils examined. Soluble Cd and Zn decreased after Indian mustard growth in all soils examined, and this was attributed to increases in soil solution pH (by 0.9 units) after plant growth. Concentrations of soluble Cu and Pb decreased in acidic soils but increased in alkaline soils. This discrepancy was likely due to a competitive effect between plant-induced pH and DOC changes on the magnitude of metal solubility. The fractions of free Cd and Zn ranged from 7.2% to 32% and 6.4% to 73%, respectively, and they generally decreased as pH and DOC increased after plant growth. Metal uptake by plants was dependant on the soil solution metal concentration, which was governed by changes in pH and DOC induced by plant exudates, rather than on the total metal concentrations. Although plant uptake also varied with metal and soil types, overall soluble metal concentrations in the rhizosphere were mainly influenced by root-induced changes in pH and DOC which subsequently affected the metal uptake by plants.

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Our study contributes to gain a more complete picture of the Zn pathway in the rhizosphere-plant system of J. acutus. We demonstrated that this vegetal species is not only capable of developing site-specific tolerance mechanisms, but it is also capable to differently modulate Zn transformation when Zn is additionally supplied by watering. These findings are necessary for predicting the fate of Zn during phytoremediation of sites characterized by specific mineralogical properties and subject to water chemical variations.
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Citation Excerpt :
With respect to the corresponding vegetables, the total concentrations of PTEs showed obvious element-specific discrepancies (Table 1). In the translocation of PTEs from soil to vegetables, the bioaccumulation coefficient of vegetables exhibited a descending order of Cd > Zn > As > Ni > Cu > Cr > Pb, which might be related to the concentrations of PTEs in soils and the discrepant capacities on the uptake and accumulation of different metals by plants (Antoniadis et al., 2017; Kim et al., 2010). According to the Chinese standards for food safety (MOH, 2017), the average values of total PTEs in vegetables were within the maximum permissible levels, but the maximum values of Cd (0.35 mg kg−1) and Pb (0.67 mg kg−1) concentrations exceeded the limits (Table 1).
The study of potentially toxic element (PTE) hazards around e-waste recycling areas has attracted increasing attention but does not consider elemental bioaccessibility. Here, the respiratory and oral bioaccessibilities were incorporated into probabilistic health risk evaluation and source contribution apportionment. The results showed that soil Cd yielded the highest respiratory and oral bioaccessibility, whereas Cr in soils and vegetables attained the lowest oral bioaccessibility. When incorporating metal bioaccessibility into health risk assessment, a 48.3%–55.7% overestimation of non-cancer and cancer risks can be avoided relative to the risk assessment based on the total concentrations of PTEs. More importantly, priority control metals were misidentified without consideration of bioaccessibility. Cadmium, As, and Cr were screened as the priority metal(loid)s for targeted risk control based on the total PTEs, whereas Cd, Zn, and Cu were the priority metal(loid)s based on the bioaccessible PTEs. Furthermore, source apportionment revealed that >50% of oral bioaccessible Cd, Cu, Ni, Pb, and Zn in farmland were contributed by e-waste dismantling activities, whereas bioaccessible As and Cr mainly originated from agrochemical applications and natural sources, respectively. This study emphasizes the refinement of risk estimation and source apportionment through metal bioaccessibility adjustment, which facilitates the realistic assessment of adverse health effects in humans and the precise identification of high-risk sources.
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With the rapid development of society, the soil and water environments in many countries are suffering from severe pollution. Pollutants in different phases will eventually gather into the soil and water environments, and a series of migrations and transformations will take place at ecohydrological interfaces with water flow. However, it is still not clear how ecohydrological interfaces affect the migration and the transformation of pollutants. Therefore, this paper summarizes the physical, ecological, and biogeochemical characteristics of ecohydrological interfaces on the basis of introducing the development history of ecohydrology and the concept of ecohydrological interfaces. The effects of ecohydrological interfaces on the migration and transformation of heavy metals, organic pollutants, and carbon‑nitrogen‑phosphorus (C-N-P) pollutants are emphasized. Lastly, the prospects of applying ecohydrological interfaces for the removal of pollutants from the soil and water environment are put forward, including strengthening the ability to monitor and simulate ecohydrological systems at micro and macro scales, enhancing interdisciplinary research, and identifying main influencing factors that can provide theoretical basis and technical support.
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The long term vertical and horizontal mobility of mercury (Hg) in soils of agricultural areas of a historically contaminated Italian National Relevance Site (SIN Brescia-Caffaro) was investigated. The contamination resulted from the continuous discharge of Hg in irrigation waters by an industrial plant (Caffaro S.p.A), equipped with a mercury-cell chlor-alkali process. The contamination levels with depth ranged from about 20 mg/kg dry weight (d.w.) of soil in the top (plow) layer to less than 0.1 mg/kg d.w. at 1 m depth. The concentrations varied also spatially, up to one order of magnitude within the same field and showing a decreasing trend from the Hg source (i.e., irrigation ditches). The concentration profiles and gradients measured were explained considering Hg loading, soil properties, such as the texture, organic carbon content, pH and cation exchange capacity. A Selective Sequential Extraction (SSE) was also applied on soil samples from an ad hoc greenhouse experiment to investigate the role of different plant species in influencing Hg speciation in soils. Although most of the extracted Hg was included in scarcely mobile or immobile forms, some plant species (i.e., alfalfa) showed to importantly increase the soluble and exchangeable fractions with respect to the unplanted control soils, thus affecting mobility and potential bioavailability of Hg.
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Wetlands can act as “metal sinks” and play a vital role in the remediation of metal-contaminated environments. In an integrated steel plant, metal-laden toxic effluents are produced during the production of coke from bituminous coal. Untreated/partially treated coke-plant effluents contaminate the aquatic ecosystems by the release of organic and inorganic pollutants including heavy metals. Heavy metals are persistent in nature and toxic to human beings. Treatment methodologies incorporating natural wetlands and the development of artificial wetlands could be a holistic approach with multiple benefits to treat contaminated coke-plant effluent. Naturally growing emergent macrophytes (Typha latifolia, Colocasia esculenta, Scirpus grossus) can be used for the design of constructed wetlands for the treatment of coke-oven effluent. By studying the metal-specific accumulation in root and shoot, the bioconcentration factor and translocation factor can be calculated and remediation potential for each plant can be evaluated for the design of wetlands. This chapter highlights the feasibility and utility of wetlands (natural and constructed) to remediate metal-contaminated coke-plant effluents.
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The effect of plant roots in modifying Pb solubility and bioavailability in an historically contaminated orchard (Hudson) and a Pb phosphate-spiked (Arkport) soil was determined by measuring soluble Pb in the soil solutions as well as content of Pb in radish shoots grown in these soils. Soluble Pb and dissolved organic carbon (DOC) contents were greater in the rhizospheres of both Pb-contaminated soils than in the unplanted high-Pb soils. The rhizosphere effect increased soluble Pb 15-fold in the field-contaminated orchard soil, whereas the effect was much smaller in the Pb phosphate-spiked soil. The rhizosphere effect persisted in the Pb-phosphate spiked soil after adjustment of the soil pH from 7.8 to 6.7. The results indicate that Pb phosphate added to a non-acid soil has lower solubility than Pb in an orchard soil contaminated by historical Pb arsenate applications; nevertheless, some uptake of Pb into plant shoots resulted from both sources of soil Pb contamination. The rhizosphere effect was observed for trace metals in addition to Pb, with the solubility of Al, Fe, Cu and Ni all increasing in the rhizosphere soil. In contrast, the solubility of alkali and alkaline earth metals (K, Ca, Mg, Sr, Ba) all decreased in the rhizosphere soil. The results indicate that the rhizosphere effect associated with plant roots can raise the solubility of Pb in soils contaminated by legacy Pb and by insoluble Pb phosphate.

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: Supported by the University of South Australia, Australia.

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Pedosphere

Abstract

References (30)

Bioavailability of heavy metals and decontamination of soils by plants

Appl. Geochem.

Changes in composition of soil aqueous phase influence chemistry of indigenous heavy metals in alkaline sodic and acidic soils

Geoderma.

Root-induced changes of lead availability in the rhizosphere of Oryza sativa L

Agr. Ecosyst. Environ.

Soil solution Zn and pH dynamics in non-rhizosphere soil and in the rhizosphere of Thlaspi caerulescens grown in a Zn/Cd-contaminated soil

Chemosphere.

Phytoextraction of metals from a multiply contaminated soil by Indian mustard

Chemosphere.

Excess cation uptake, and extrusion of protons and organic acid anions by Lupinus albus under phosphorus deficiency

Plant Sci.

Linking plant tissue concentrations and soil copper pools in urban contaminated soils

Environ. Pollut.

Determination of the chemical speciation of trace metals in aqueous systems by the Wageningen Donnan Membrane Technique

Anal. Chim. Acta.

Relationship between the extractable metals from soils and metals taken up by maize roots and shoots

Chemosphere.

Comparison between fractionation and bioavailability of trace elements in rhizosphere and bulk soils

Chemosphere.

Effect of root exudates on mobilization in the rhizosphere and uptake of iron by wheat plants

Plant Soil.

Phytofiltration of metals

Changes in trace metal species and other components of the rhizosphere during growth of radish

Plant Cell Environ.

Bioavailability of trace elements as related to root-induced chemical changes in the rhizosphere

Heavy metal distribution, bioaccessibility and phytoavailability in long-term contaminated soils from Lake Macquarie, Australia

Aust. J. Soil Res.

Cited by (51)

Plant-minerals-water interactions: An investigation on Juncus acutus exposed to different Zn sources

Novel insights into probabilistic health risk and source apportionment based on bioaccessible potentially toxic elements around an abandoned e-waste dismantling site

Effects of ecohydrological interfaces on migrations and transformations of pollutants: A critical review

Mercury vertical and horizontal concentrations in agricultural soils of a historically contaminated site: Role of soil properties, chemical loading, and cultivated plant species in driving its mobility

Removal of heavy metals from coke-plant effluents by using wetlands

Rhizosphere effect on Pb solubility and phytoavailability in Pb-Contaminated soils