Relationship between the chemical form of nickel applied to the soil and its uptake and toxicity to barley plants ( Hordeum vulgare L.)

Abstract

Synthetic chelating agents, such as organic acids and amino acids, are used in remediation of soil contaminated with heavy metals, including Ni. It has not been clearly shown that the complexation of Ni by organics may increase the effectiveness of phytoremediation; the Ni complexation may increase the removable metal concentration, but may decrease its uptake by plants. The objective of this research was to investigate the Ni toxicity and the dynamics of its uptake by the barley plants ( Hordeum vulgare L.) from medium and heavy clay soils contaminated with inorganic Ni (as NiSO 4·7H 2O) and organic Ni(II) complexes, i.e. Ni(II)-citrate, Ni(II)-Glu and Ni(II)-EDTA (molar ratio Me/L was 1:1). In the pot experiment, Ni in these chemical forms was applied to the soils in the concentration of 75 mg Ni·kg −1. With respect to both absorption and phytotoxicity, the examined chemical forms of nickel can be put in the following order: NiSO 4·7H 2O>Ni(II)-citrate>Ni(II)-Glu>Ni(II)-EDTA. The molar ratio of Me/L (i..e. Ni/Ligands) in the plants differed from that in the soil; in the plants, the Ni concentration was higher than ligand concentrations. Thus, molar ratio Me/L was higher than 1:1. The highest concentration of nickel in the dry matter of plants, supplied from all examined forms of this element, was found in the initial growth stages (i.e. in emergence stage), and it declined with the progressing growth. No matter what the chemical form of Ni was supplied, the barley plants absorbed more Ni from the medium soil than from the heavy soil. Despite the fact that the degree of phytotoxicity of the chemical forms of nickel used in the experiment differed, the types of morphological and anatomical damages of plants were similar. Phytotoxicity of the examined chemical forms of Ni corresponded to the concentration of Ni absorbed from these forms by the barley plants.