Abstract
A greenhouse study was conducted to evaluate the effects of ethylenediamine tetraacetic acid (EDTA) addition to soils on the lead (Pb) phytoextraction potential of jack beans (Canavalia ensiformis L.). In a pot experimentSoil samples (dystrophic Rhodic Hapludox) were treated with six Pb rates (0, 100, 200, 350, 1,200, and 2,400 mg kg-1 soil) applied as Pb(NO3)2 without and with EDTA application (0 and 0.5 g kg-1, respectively). Lead, Cl-, NO3-, NH4+, SO4(2-), H2PO4-, Zn2+, Cu2+, Fe3+, Al3+, Ca2+, Mg2+, K+ and DOC (dissolved organic carbon) concentrations obtained in a saturation soil extract (soil:water ratio of 1:0.3) were used for Pb speciation by means of the software Visual-Minteq 2.30. Soil Pb-availability was assessed with Diethylene triamine pentaacetic acid (DTPA) extraction. EDTA treated soils showed higher Pb (as PbEDTA2-), and Fe (as FeEDTA-) concentrations in soil solution leading to higher uptake of these elements by the jack bean. On the other hand, it decreased the concentration of stable complexes as Pb-DOC and Fe-DOC. EDTA also induced better nutrition to plants building up the concentration of non target metals (Ca, K, Mg, Zn, Cu, Fe and Mn) in shoots. Shoot dry matter yield remained constant even at the highest Pb rates after EDTA treatment. Jack bean can be considered as a potential Pb-phytoextractor. In addition, the DTPA solution was effective to assess Pb availability to the plants at all applied Pb rates.
Highlights
In the São Paulo State, Brazil, guiding values for soil Pb contamination were proposed by the Environmental and Sanitation Technology Company (CETESB, 2001) which define: i) guiding value for enhanced monitoring (100 mg kg–1 soil); ii) intervention values for agricultural areas (200 mg kg–1 soil ), for residential areas (350 mg kg–1 soil); and iii) for industrial areas (1,200 mg kg–1 soil)
These interactions will be discussed in some detail below: Jack Bean Phytoremediation Potential The dry matter yield of jack bean shoots was lower under the etilenodiamino tetraacético (EDTA) treatment as compared to the control (Figure 1)
The yield reduction could be due to a chelate-induced heavy metal availability or to toxic effects of the chelant itself, there were no obvious symptoms of chelate toxicity
Summary
In the São Paulo State, Brazil, guiding values for soil Pb contamination were proposed by the Environmental and Sanitation Technology Company (CETESB, 2001) which define: i) guiding value for enhanced monitoring (100 mg kg–1 soil); ii) intervention values (defined as concentration limits causing potential risks for human health) for agricultural areas (200 mg kg–1 soil ), for residential areas (350 mg kg–1 soil); and iii) for industrial areas (1,200 mg kg–1 soil). In this State, 197 heavy metal contaminated locations have been located including Pb contaminated sites according to CETESB (CETESB, 2006). A successful phytoextraction system depends on several factors such as concentration of metal in soil solution and the ability of plants to accumulate metals in top parts (Ernst, 1996; Schmidt, 2003)
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