A time-series phytoremediation experiment with sunflowers (Helianthus annuus) on a former uranium mining site

Abstract

On a test field situated at a former uranium mining site near Ronneburg (Thuringia, Germany) a small scale time-series field experiment with sunflowers (Helianthus annuus) was carried out. This area ghas elevated contents for the heavy metals Cd, Co, Cr, Cu, Ni, Zn including the radionuclides U and Th. Over a time period of 24 weeks the sunflowers were cultivated on homogenized soil substrate and regularly harvested. The aim was to find the ideal moment to harvest the sunflowers, being defined as having the best balance between the extraction of the contaminants and a high biomass produced. The contents of the elements were determined in soil, roots and above-ground plant parts. The contents in the above-ground plant showed no clear increasing or decreasing trend over time, so they were not the appropriate values to determine the best moment to harvest. Instead the total extracted masses (content in μg/g x biomass in g) of the contaminants in the above-ground plant parts were calculated. According to this the best moment to harvest the sunflower plants was reached after 24 weeks of vegetation, because the highest extracted masses for all contaminants were calculated to this time. Additionally the biomass, which could be used e.g. for bio-fuel production, was highest at this time.

Keywords

• Heavy metals
• time-series experiment
• sunflower
• phytoremediation