Bioaccumulation of Heavy Metals by Herbaceous Species Grown in Urban and Rural Sites

The ability of seven herbaceous species (Hypericum perforatum L., Dactylis glomerata L., Plantago lanceolata L., Verbascum thapsus L., Picris hieracioides L., Cichorium intybus L., Daucus carota L.) to accumulate heavy metals such as Cd, Cr, Cu, Ni, Pb, and Zn has been studied. The concentration of heavy metals was determined in roots, basal and cauline leaves, flowers, and stalks for each collected species. The species were selected according to their cosmopolitan characteristics, morphology, life cycle, and phenology. Soils and plants were collected from two sites: close to a high traffic road in the inner city of Rome and in a natural park north of Rome (Canale Monterano). The concentration of elements in soil in descending order were Zn>Pb>Cu>Ni>Cr>Cd, while the EDTA extractable element concentrations in the roots followed the sequence Zn>Cu≈Pb>Cd>Cr>Ni. The bioaccumulation factors (BF) and the transport factors (TF) were calculated for each plant species. Results showed a significant relationship between heavy metals content in soil and plant species. H. perforatum showed a high Pb accumulation capacity in the stalk (70.30 mg kg⁻¹) and roots (73.41 mg kg⁻¹); moreover, BF>1 for this species at urban site has been obtained. Plantago lanceolata and Dactlys glomerata have shown higher Cd absorption (BF=1.33 and 0.55 in rural and urban sites, respectively). Plantago lanceolata in general shows high heavy metal uptake. The distribution of metals within the plant strongly depends on the species; the main accumulation of Ni, Cd, and Cu was observed in the leaves, while the highest Cr concentration was observed in the flowers. Plant species can be effectively considered as valid bioindicators of heavy metals derived from human activities and can be used to monitor pollution changes in the environment.