Abstract
Heavy‐metal soil pollution is a common environmental problem all over the world. In the induced phytoextraction process plants can transport and translocate to their above‐ground tissues significant concentration of contaminants. Since some heavy metals are mostly presented in non‐soluble state, the application of chelating agents is needed. In this study we introduced into the rhizosphere of maize (var. Kneja 530) and sunflower (var. Favorit) plants 1 and 5 mmol l−1 of EDDS and NTA, and 5 g kg−1 of nutrients to enhance the accumulated concentrations of cadmium, lead and zinc. The fraction of CaCl2‐extractable metals increased incrementing the concentration of chelates. This was clearly pronounced for all the metals in the treatments with NTA and for Pb in those with EDDS. Generally, under all the experimental conditions the accumulated heavy‐metal concentrations were found to be significantly higher than in the control. Thus, in the case of higher concentration of NTA and EDDS, the accumulated Cd in the leaves of sunflower was found to be threefold higher. The highest accumulation of Pb in the leaves of maize was observed when nutrients were added (62 mg kg−1). On the other hand, negative effects of the used chelating agents on soil bacteria and fungi at plant harvest were not observed. Moreover, when nutrients were added, the number of studied microorganisms significantly increased.
Highlights
Heavy-metal contamination of the soil is the main environmental problem in many countries
The aim of this study was to evaluate the possibilities for induced phytoextraction of cadmium, lead and zinc from contaminated soils using maize and sunflower plants and rhizosphere inoculation of -biodegradable chelating agents and nutrients
The total soil metal content before the experiment was found to be higher than the maximum permissible limits established according to the Bulgarian law (Cd, 2.5 mg kg–1; Pb 80 mg kg–1; Zn, 340 mg kg–1), while at harvest these values varied in certain ranges, depending on the treatment (Table 2)
Summary
Heavy-metal contamination of the soil is the main environmental problem in many countries. Heavy metals are basically characterized by their toxicity, persistence and difficulty to be removed. An important toxicity mechanism of heavy metals is their capability to bind strongly the oxygen, nitrogen and sulfur atoms in plant cells, inactivate key enzymes binding the cisteine [2]. In other cases the enzyme inactivation occurs through substitution of one metal ion with another one in the molecule. Cations with the second valence could substitute the Mg2+ in the structure of some enzymes leading to the loss of activity [3]. The substitution of Ca2+ with Cd2+ results in inhibition of phosphoesterase cell activity [4]
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