Lead phytoextraction: Species variation in lead uptake and translocation

Lead transport has been characterized in corn (Zea mays L. cv. Fiesta) and ragweed (Ambrosia artemisiifolia L.), and the Pb phytoextraction efficiency of these species has been compared with that of Triticum aestivum, Thlaspi rotundifolium, Thlaspi caerulescens and Brassica juncea, using both nutrient solutions and Pb-contaminated soils. Our results demonstrated that plant species differ significantly in Pb uptake and translocation. In short term (60 min) experiments, Pb uptake by ragweed roots was threefold higher than that by corn roots. After 2 wk of Pb (100 mu M) exposure in hydroponics, root-Pb concentration was 24000 mg kg(-1) for ragweed and 4900 mg kg(-1) for corn. In contrast to root-Pb concentration, shoot-Pb concentration was significantly higher in corn (560 mg kg(-1)) than in ragweed (30 mg kg(-1)). At an external Pb concentration of 20 mu M, corn concentrated Pb in shoots by 90-fold, and ragweed concentrated Pb in shoots by 20-fold over the solution Pb concentration. Of the 11 species/cultivars tested using both nutrient solutions and Pb-contaminated soils, corn accumulated the highest shoot-Pb concentration. Using this corn cultivar, we investigated the role of synthetic chelates in Pb phytoextraction. Addition of HEDTA (2.0 g kg(-1) soil) to a Pb-contaminated soil (total soil Pb 2500 mg kg(-1)) resulted in a surge of Pb accumulation in corn. The shoot Pb-concentration was increased from 40 mg kg(-1) for the control (-HEDTA) to 10600 mg kg(-1) for the HEDTA-treated soil. To our knowledge, this is the highest shoot Pb concentration reported in the literature for plants grown on Pb-contaminated soils. Our results suggest that in combination with soil amendment, some agronomic crops, such as corn, might be used for the clean-up of Pb-contaminated soil.