A phytogeochemical study of the Tra´s-os-Montes region (NE Portugal): Possible species for plant-based soil remediation technologies

Phytoremediation techniques are now considered to be promising alternatives to conventional techniques for the remediation of diffused or moderately contaminated soils. Despite their growing acceptance relatively few plant species have been studied for phytoremediation purposes. Further geobotanical surveys and plant screenings are necessary since these could lead to the identification of additional species with potential value for such applications. Serpentine areas could prove valuable sources of such plants. In this study heavy metal accumulation was determined in the flora associated with ultramafic and non-ultramafic soils of the Tra´s-os-Montes region of NE Portugal. Study sites were selected to represent a wide range of soil-forming rocks (serpentinized (S), ultrabasic (UB), basic (B) and acid (migmatite, M and schists, SC) rocks) and plant metal accumulation was related to soil metal bioavailability. Nine plant species (representing 7 families) were sampled including the Ni hyperaccumulator Alyssum serpyllifolium subsp. lusitanicum. The greatest metal accumulation, transport (leaf[metal]:root[metal]) and bioaccumulation (leaf[metal]/soil[metal]) was found in four of the non metal-hyperaccumulating species: Cistus ladanifer, Lavandula stoechas, Plantago subulata subsp. radicata and Thymus mastichina. Metal accumulation depended on both the plant species and the edaphic conditions at its provenance. While P. subulata is of less interest due to its low biomass the remaining three species could be of use in phytoremediation technologies such as phytoextraction, and particularly in soils contaminated with Cr, Mn and Zn. These three species are also of economic interest due to their oil and fragrance producing biomass.