EFFECT OF THALLIUM FRACTIONS IN THE SOIL AND POLLUTION ORIGINS ON Tl UPTAKE BY HYPERACCUMULATOR PLANTS: A KEY FACTOR FOR THE ASSESSMENT OF PHYTOEXTRACTION

Abstract

Phytoremediation is often discussed as a means of extracting trace metals in excess in the soil, but to increase its efficiency a better understanding of the factors controlling plant uptake is required. The main objective of this study was to examine the effect of origin (anthropogenic vs. geogenic) and mobility of thallium (Tl) in the rhizosphere on Tl uptake. Two Tl-hyperaccumulating Brassicaceae species, kale (Brassica oleracea acephala L. cv. Winterbor F1) and candytuft (Iberis intermedia Guers.), were grown in a rhizobox system to investigate the dynamics of Tl in the rhizosphere soil. Four different soils were used. Two soils contained high Tl amounts due to anthropogenic sources (emissions from a cement plant and mining activities). High Tl content in the two other soils was due to a high rock content (geogenic origin). On completion of growth in the rhizoboxes, the depletion of Tl in seven different chemical fractions, determined by sequential extraction, was compared to the plant uptake. Most of the Tl taken up was derived from the so-called "easily accessible" fractions in both soils with geogenic Tl as well as in the soils polluted by mining activities. Due to the small amounts of easily accessible Tl in the geogenic soils, Tl uptake by Brassicaceae was low. On the other hand, for the air emission-polluted soil, a high depletion of Tl from "less accessible" fractions was observed in addition to depletion of the easily accessible fractions. Hence, the latter soil demonstrated the highest potential for effective soil decontamination by phytoextraction within an appropriate time frame.

Influence of Rapeseed Cake on Heavy Metal Uptake by a Subsequent Rice Crop After Phytoextraction UsingSedum plumbizincicola

“…Although the heavy metal concentrations in the soil decreased after phytoextraction, at the early growth stages (from pre-tillering to booting) of the rice crop the soil solution heavy metal concentrations increased (Figure 2). The water-soluble and exchangeable fractions of heavy metals are the main sources of the metals absorbed by plants, however a certain amount of heavy metal accumulation by hyperaccumulator plants is derived from potentially bioavailable heavy metals (Al-Najar et al 2003;McGrath et al 1997;Whiting et al 2001). Thus hyperaccumulators can activate unavailable heavy metals to resupply depleted metals from the non-mobile fractions (Long et al 2008;Liu et al 2011;.…”

Phytoremediation of Soil Trace Elements

“…Green cabbage accumulated much higher Tl levels than most other vegetable crops [239,240]. Fortunately, unusual hyperaccumulator species were discovered for Tl and they accumulate high plant Tl from soils with moderate to high Tl contamination [241,242]. The strong hyperaccumulator, Iberis intermedia, accumulated Tl in the leaf vascular system rather than in vacuoles or trichomes as seen for some other hyperaccumulated elements [243].…”

Role of Humic Substances in the Rhizosphere

“…It has been established that the depletion zone generally extends from < 1 mm for phosphate to some millimeters for K, and up to several centimeters for nitrate (Hinsinger, 1998 ;Jungk, 2002 ), although it is variable depending on root hair length. Depletion zones of poorly mobile trace pollutants can also develop in the rhizosphere, as shown recently for arsenic (Fitz et al, 2003 ), nickel (Puschenreiter et al, 2005 ), and thallium (Al -Najar et al, 2003 ) in metal hyperaccumulator plants.…”