Chapter 22 - Heavy Metal Accumulation in Serpentine Flora of Mersin-Findikpinari (Turkey) – Role of Ethylenediamine Tetraacetic Acid in Facilitating Extraction of Nickel

Abstract

Field and laboratory studies were performed to: (1) determine heavy metal concentration of serpentine soils in Mersin-Findikpinari, Turkey, (2) find possible metal hyperaccumulator plant species (ecotypes and cultivars) growing on the serpentine soils in the region, and (3) determine the effects of EDTA (ethylenediaminetetraaacetic acid) on the phytoextraction potential of selected plant/plants as metal hyperaccumulators. A total of 11 soil samples and 123 plant species (members of 23 genera and 15 families) from different sampling locations were collected during sampling periods covering a period of 24 months. Total and available Cr, Ni, Cu, Zn, Cd, Pb and Co concentrations in the collected soil and plant samples were analyzed by ICP-MS (inductively coupled plasma mass spectrometer). The results indicated that each soil contained a high concentration of one or more metals. The maximum concentrations of total metals in soils (as dry matter) were 909mgCrkg−1, 3615mgNikg−1, 246mgCukg−1, 467mgZnkg−1, 8.2mgCdkg−1, 111mgPbkg−1 and 214mgCokg−1. Among all plant species, Thlaspi elegans Boiss. (15,693mgNikg−1 dry matter), Alyssum murale Waldst. & Kit. (13591mgNikg−1 dry matter) showed the highest Ni concentration. A pot experiment was therefore conducted to examine the effect of adding EDTA to improve the phytoextraction of Ni from artificially contaminated soil by T. elegans which is an endemic Ni hyperaccumulator in the Mersin-Findikpinari (Turkey) serpentine soils. This is the first report on the effect of Ni hyperaccumulation in T. elegans exposed to different Ni and EDTA concentrations in pot experiments. T. elegans seeds were planted in pots with Ni concentrations ranging from 0 to 2000mgkg−1 (0, 500, 1000, 1500 and 2000mgNikg−1) in the absence or presence of 10mgkg−1 EDTA. The plants showed a remarkable resistance to Ni toxicity, with no visual toxic symptoms including chlorosis and necrosis when exposed to high Ni concentrations throughout 60 days of growth. After 60 days of growth, the dry matter, Ni concentration and Ni content of plants were analyzed. In order to indicate the ability of plants to tolerate and accumulate Ni, we calculated the biological accumulation coefficient (BAC). The addition of 10mgkg−1 EDTA significantly increased both plant growth as well as Ni uptake, compared to the control. Although the Ni uptake by T. elegans increased with increasing initial Ni concentrations, at higher concentrations a significant decrease was observed in the plant growth. The plant accumulated 13216mgkg−1 Ni in the absence of EDTA, an addition of 10mgkg−1 EDTA increased Ni uptake and accumulation to 16632mgkg−1 Ni at Ni application dose of 2000mgkg−1. The maximum Ni content accumulated by the plant was 44831μg per plant in the absence of EDTA, the addition of 10mgkg−1 EDTA increased Ni uptake to 53740μg per plant at an initial Ni application dose of 500mgkg−1. The results showed that T. elegans can be used for phytoextraction of Ni-contaminated soils and that EDTA induces phytoextraction in soils. Similar results were obtained for the BAC. The values were greater than 1, providing further evidence for the transport of Ni from Ni-contaminated soils to plant shoots. The results also showed that EDTA increased the solubility of Ni in soil due to the formation of less toxic and highly soluble Ni–EDTA complexes and can be a good chelator candidate for T. elegans used for the environmentally safe phytoextraction of Ni in soils.