Phytoremediation experiments with Helianthus tuberosus under different pH and heavy metal soil concentrations

Abstract

Since the last twenty years, phytoremediation became an emerging remediation technology due to its low costs and high sustainability. In this study, experiments for the investigation of phytoextraction and growth behaviour of Helianthus tuberosus under different soil pH values and heavy metal concentrations were performed. Aim of the work was to study the growth and heavy metal accumulation of H. tuberosus under these conditions for a subsequent optimization of the growth conditions and for a later improvement of the growth and phytoremediation yields under field conditions. Experiments were performed for the preparation of the remediation of a contaminated mining site with low to medium heavy metal (HM) concentrations.Plant experiments were carried out in a pH range stepwise from 4.0–6.0 and with a combination of different HM (Cd, Cu, Fe, Mn, Ni, Zn, Pb) in three different concentration ranges (slight/medium/high); experimental conditions were typical for mining sites with Acid Mine Drainage (AMD) and slight to medium heavy metal impact. Yields of roots, tubers, leaves and shoots under the appropriate conditions were investigated, and the heavy metal accumulation of different plant parts was analyzed.As results, soil pH and heavy metal concentrations were identified as crucial factors for plant growth and success of phytoremediation. High accumulation of Fe (up to 1.48g/kg), Mn (up to 1.68g/kg) and Zn (up to 853mg/kg) was measured in the roots; shoots accumulated up to 2.6g/kg Ni, 11.4g/kg Mn and 6.06g/kg Zn. The accumulation factors for the main heavy metals in the roots were determined. The heavy metal transfer factors Tf from roots to shoots for Ni, Zn and Mn were in the range of 11 to 15; hence the upper plant parts accumulated these metals more than the tenfold compared to the root concentrations. In contrast, heavy metal concentrations in tubers were reduced to 50% of Ni, 30% of Zn and Cu, 20% of Mn, 12% of Cd and 10% of Pb compared to the root contents. Fe, Cu and Pb were much less accumulated in the shoots, they mostly had been retained in the root system. The results also demonstrate the effects of specific transport, sequestration and protection mechanisms for each metal species in the plants. As results of the experiments, H. tuberosus represents a suitable and robust phytoremediation plant species for the phytoextraction of Mn, Zn, Cd and Ni under the given conditions from the site.