Cadmium accumulation in the shoots and roots of 93 weed species

Abstract

The present study was conducted to find useful weed species for cadmium (Cd) phytoremediation. Ninety-three weed species and eight crop species were grown for 2 months in pots containing sandy loam soil with 3 mg Cd kg−1 dry weight (DW). The Cd concentrations in the shoots and roots of all species were determined by inductively coupled plasma optical emission spectroscopy and atomic absorption spectrometry. Shoot Cd concentrations (mg kg−1 DW) of Cichorium intybus (77.0) and Matricaria chamomilla (64.4) were higher than that of Polygonum thunbergii (56.2), which is a recognized hyperaccumulator. Root Cd concentrations (mg kg−1 DW) were relatively high (≥ 100) in 11 species, for example, Oenothera biennis (171.9), Calystegia sepium var. americana (122.6) and Cassia obtusifolia (122.2). Shoot–root ratios (ratio of shoot and root Cd concentrations) were higher in Compositae species, for example, Cichorium intybus (3.56) and Bidens frondosa (3.30), than in Gramineae species, for example, Oenothera biennis (0.01), Oryza sativa cv. Milyang 42 (0.02) and Coix lacryma-jobi (0.03). Twelve species, for example, Cyperus brevifolius var. leiolepis (50.0), Polygonum thunbergii (49.7) and Bidens frondosa (40.5), had relatively high plant contents of Cd (≥ 20.0 µg plant−1). These results suggest that: (1) Cichorium intybus and Matricaria chamomilla accumulate high shoot Cd concentrations, (2) Oenothera biennis, Calystegia sepium and Cassia obtusifolia accumulate high root Cd concentrations, (3) Compositae species are better able than Gramineae species to translocate Cd from roots to shoots. As both plant biomass and Cd concentration are related to Cd content, it was concluded that Bidens frondosa, Bidens pilosa and Amaranthus viridis, which not only have a high Cd accumulation ability but also a large biomass, are useful species for Cd phytoremediation.