Cadmium accumulation in six common plant species associated with soils containing high geogenic cadmium concentrations at Le Gurnigel, Swiss Jura Mountains

The uptake of cadmium (Cd) was analyzed for six different perennial plant species growing in a wooded pasture of the Swiss Jura Mountains, where the soils are geogenically enriched in Cd (4.58 mg.kg(-1) on average (n = 36); maximal value: 16.3 mg.kg(-1)). The six selected plants - Hypericum maculatum (Hypericaceae), Alchemilla xanthochlora (Rosaceae), Cynosurus cristatus (Poaceae), Ranunculus acris (Ranunculaceae), Dactylis glomerata (Poaceae) and Acer pseudoplatanus (Sapindaceae) - show variable Cd contents among the species and among individuals from the same family (Poaceae). Average Cd concentrations in the selected plants are in the 2-6 mg.kg(-1) range and exceed the maximal Cd concentration tolerated in vegetal feed for animals, which is established at 1 mg.kg(-1). High Cd concentrations in the soil result in a reduction of Cd accumulation in the shoots and a corresponding increase in the roots. This implies that Cd transfer coefficients from the soil/rhizosphere to the plant are inversely proportional to the total Cd concentrations in soils and do not depend on plant species but instead on soil type. Sequential chemical extractions reveal that variations in Cd distribution between the bulk soil and the corresponding rhizospheric soil occur mainly in the Cd-bearing phases, which are exchangeable, bound to carbonates, and associated with organic matter. This is principally due to the incorporation of root exudates, which modify pH and redox conditions of the rhizosphere. Elevated Cd concentrations in the shoots of A. xanthochlora (up to 8 mg.kg(-1)), C. cristatus (9 mg.kg(-1)) and H. maculatum (3 mg.kg(-1)) may represent a long-term hazard for livestock and human health since these plants are used either by grazing cattle or for medicinal purposes. On the contrary, R. acris, A. pseudoplatanus, and especially D. glomerata show lower Cd concentrations and are of minor concern with regards to their environmental impact. (C) 2014 Elsevier B.V. All rights reserved.