Phytoremediation of Lead-Contaminated Soils:  Role of Synthetic Chelates in Lead Phytoextraction

Abstract

Lead phytoextraction, using plants to extract Pb from contaminated soils, is an emerging technology. Calculations of soil Pb mass balance suggest that this technology will be economically feasible only if systems can be developed to employ high biomass plants that can accumulate greater than 1% Pb in their shoots. In this study, we investigated the potential of adding chelates to Pb-contaminated soils to increase Pb accumulation in plants. The addition of chelates to a Pb-contaminated soil (total soil Pb 2500 mg kg-1) increased shoot Pb concentrations of corn (Zea mays L. cv. Fiesta) and pea (Pisum sativum L. cv. Sparkle) from less than 500 mg kg-1 to more than 10000 mg kg-1. The surge of Pb accumulation in these plants was associated with the surge of Pb level in the soil solution due to the addition of chelates to the soil. For the chelates tested, the order of the effectiveness in increasing Pb desorption from the soil was EDTA > HEDTA > DTPA > EGTA >EDDHA. We also found that EDTA significantly increased Pb translocation from roots to shoots. Within 24 h after applying EDTA solution [1.0 g of EDTA (kg soil)-1] to the contaminated soil, Pb concentration in the corn xylem sap increased 140-fold, and net Pb translocation from roots to shoots increased 120-fold as compared to the control (no EDTA). These results indicate that chelates enhanced Pb desorption from soil to soil solution, facilitated Pb transport into the xylem, and increased Pb translocation from roots to shoots. Results from this study suggest that with careful management, chelate-assisted Pb phytoextraction may provide a cost-effective soil decontamination strategy.

Enhanced phytoextraction of Cu, Pb, Zn and Cd with EDTA and EDDS

“…Chemically enhanced phytoextraction has been proposed as an effective approach for removing heavy metals from soils using plants (Huang et al, 1997;Blaylock et al, 1997;Liphadzi et al, 2003). Several chelating agents, such as citric acid, EDTA, CDTA, DTPA, EGTA, EDDHA, EDDS, HEDTA and NTA have been tested for their ability to mobilize and increase the accumulation of heavy metals, particularly Pb.…”

“…Most hyperaccumulators, such as Thlaspi, Urtica, Chenopodium, Polygonum sachalase and Alyssim are characterized by slow growth and low-biomass production, which make these plants impractical for use in phytoextraction in the field (Mulligan et al, 2001;Puschenreiter et al, 2001). For this reason, more recent research projects on phytoextraction have focused on high biomass crop species, such as maize (Zea mays), peas (Pisum sativum), oats (Avena sativa), barley (Hordeum vulgare) and Indian mustard (Brassica juncea), and on relevant plant husbandry and soil management practices to enhance the metal uptake of these high biomass species (Blaylock et al, 1997;Huang et al, 1997;Ebbs and Kochian, 1998;Shen et al, 2002;Chen et al, 2004a). Although several conditions must be met in order for phytoremediation to be effective, the bioavailability of metals to plant roots is considered to be a critical requirement for plant uptake to occur (Kayser et al, 2000).…”

“…Soil factors such as pH, cation exchange capacity, or organic matter content play an important role in successful soil remediation processes. To increase metal availability, a number of chelates such as EDTA (ethylenediaminetetraacetic acid), CDTA (trans -1, 2 -diaminocyclohexane -N, N, N', N'-tetraacetic acid), EGTA [ethyleneglycol -bis (ß -aminoethyl ether), N, N, N', N-tetraacetic acid], and EDDHA [etylenediamine-di (ohydroxyphenylacetic acid)]) have been used to desorb metals from the soil matrix into soil solution to facilitate the transport of metals into xylem, and increase the translocation of metals from the roots to shoots of some fast-growing, high-biomass-producing plants (Blaylock et al, 1997;Huang et al, 1997;Cooper et al, 1999;Wu et al, 1999;Shen et al, 2002).…”

Effects of EDTA and low molecular weight organic acids on soil solution properties of a heavy metal polluted soil

“…EDTA and LMWOA can chelate and mobilize the heavy metals in soil, and these two organic acids have been used in decontamination or phytoremediation enhancement of metal polluted soils (Heil et al, 1996;Blaylock et al, 1997;Huang et al, 1997;Wasay et al, 1998). Kedziorek et al (1998) found in the early days that Pb and Cd were readily solved and translocated by EDTA.…”

Nutrients Can Enhance Phytoremediation of Copper-Polluted Soil by Indian Mustard

“…One of the most promising and potentially cost-effective soil remediation techniques is phytoremediation (Ebbs & Kochian, 1997;Huang et al 1997;Blaylock 2000). The ideal plant species to remediate a heavy metal contaminated soil would be a high biomass crop that can both tolerate and accumulate the contaminants of interest.…”