Is Brassica juncea a suitable plant for phytoremediation of cadmium in soils with moderately low cadmium contamination?: Possibility of using other plant species for Cd-phytoextractio

We evaluated the ability of Brassica juncea (L.), which has already been recognized as a plant suitable for metal phytoremediation, and of several other plant species (maize, rice and sugar beet) to extract cadmium (Cd) from soils with moderately low levels of Cd contamination. Two of the 56 cultivars of B. juncea were preliminarily screened as high-Cd accumulators using a hydroponic culture solution containing a high level of external Cd (1 mg L-1). Thereafter, 7 cultivars within 4 plant species (maize, B. juncea [2 cultivars], rice [3 cultivars with different subspecies] and sugar beet) were grown in a hydroponic culture solution containing a low Cd level (0.05 rng Cd L-1) or in pots filled with 2 types of contaminated soils containing moderately low Cd levels under upland conditions. The 2 soils consisted of a Fluvisol and an Andosol and contained 1.82 and 4.01 mg Cd kg(-1) on a dry soil weight basis, respectively, determined using 0.1 mol L-1 HCl-extraction. The results indicated that B. juncea was less able to accumulate Cd in shoots compared with hydroponically cultured rice and sugar beet, and was even less effective when grown in soil culture. Rice and sugar beet displayed a higher accumulation not only of Cd but also of other heavy metals (Cu, Fe, Mn and Zn) in their shoots than B. juncea when they were grown in the two Cd-contaminated soils. Maize displayed the lowest metal accumulation among the plant species tested. Growing the rice cultivars in both soil types led to the most significant decrease in soil Cd concentration determined using extraction with 0.1 mol L-1 HCl. In contrast, we did not observe any significant decrease in soil Cd concentration in B. juncea. Sequential Cd extraction of soil revealed that rice was more effective than B. juncea in phytoextracting Cd from less-soluble fractions in soils. Based on the plant and soil analyses, it was suggested that B. juncea does not offer much promise for phytoextraction of Cd from soils with relatively low contamination, and that rice may be an eligible plant for metal phytoremediation of such soils.