The effect of application time of mobilising agents on growth and phytoextraction of lead by Brassica napus from a calcareous mine soil

Phytoremediation of heavy metal contaminated sites is often limited by the low-bioavailability of the contaminants. Complexing agents can help to improve this technique by enhancing heavy metal solubility. Pot experiments were conducted to determine the best time for the application of ethylene diamine tetraacetic acid (EDTA) and sheep manure extract (SME) for phytoremediation of a contaminated soil by Brassica napus. The plant was grown on a mine calcareous soil treated with increasing concentrations of EDTA or SME 30 and 10?days before sowing (T1 and T2) and 10 and 30?days after sowing (T3 and T4). Soil available Pb and lead concentrations in plant organs of Brassica napus increased with EDTA concentration. The EDTA application before seed germination significantly reduced rapeseed seedling emergence and dry weight. However, the actual amount of phytoextracted Pb by rapeseed did not decrease significantly, due to severe growth depression, at high EDTA concentrations when it had applied at a suitable time (T4). SME application after sowing increased plant dry weight and Pb concentration in the soil solution and enhanced the accumulated metal concentrations in shoots and roots. Comparing the effect of EDTA and SME on Pb phytoextraction, the study showed that SME is not more effective than EDTA. The efficiency of EDTA on Pb phytoextraction by Brassica napus depends on the time of application. The most efficient treatment for Pb phytoextraction by rapeseed was application of 2?g EDTA/kg soil at T4.