Zinc accumulation in plant species indigenous to a portuguese polluted site: relation with soil contamination

The levels of zinc accumulated by roots, stems, and leaves of two plant species, Rubus ulmifolius and Phragmites australis, indigenous to the banks of a stream in a Portuguese contaminated site were investigated in field conditions. R. ulmifolius, a plant for which studies on phytoremediation potential are scarce, dominated on the right side of the stream, while P. australis proliferated on the other bank. Heterogeneous Zn concentrations were found along the banks of the stream. Zn accumulation in both species occurred mainly in the roots, with poor translocation to the aboveground sections. R. ulmifolius presented Zn levels in the roots ranging from 142 to 563 mg kg^-1, in the stems from 35 to 110 mg kg^-1, and in the leaves from 45 to 91 mg kg^-1, vs. average soil total Zn concentrations varying from 526 to 957 mg kg^-1. P. australis showed Zn concentrations in the roots from 39 to 130 mg kg^-1, in the stems from 31 to 63 mg kg^-1, and in the leaves from 37 to 83 mg kg^-1, for the lower average soil total Zn levels of 138 to 452 mg kg^-1 found on the banks where they proliferated. Positive correlations were found between the soil total, available and extractable Zn fractions, and metal accumulation in the roots and leaves of R. ulmifolius and in the roots and stems of P. australis. The use of R. ulmifolius and P. australis for phytoextraction purposes does not appear as an effective method of metal removing, but these native metal tolerant plant species may be used to reduce the effects of soil contamination, avoiding further Zn transfer to other environmental compartments.