METAL UPTAKE AND DISTRIBUTION IN RUSH (JUNCUS-CONGLOMERATUS L) PLANTS GROWING IN PYRITES MINE TAILINGS AT LOUSAL, PORTUGAL

Juncus conglomeratus L. is the main plant species growing in the pyrites mine tailings at Lousal, in southern Portugal, where it forms extensive monospecific communities occupying permanently water-saturated hillsides and, less frequently, waterlogged depressions at the foot of spoil heaps. Concentrations of Fe, Mn, Zn, Cu and Pb were measured in the root and shoot systems of J. conglomeratus plants, as well as in the supporting substrate. With the exception of Mn, the levels of all other metals in the mine tailing-derived soils were extremely high, with Fe amounting to up to 30% of the total soil weight. Metal levels, excluding Mn, of the rush plants growing in the mine tailings were several times higher, particularly in the root system, than in the controls collected upstream of the mine area. Plants grown under waterlogged conditions had larger amounts of Fe associated with their roots, probably due to the formation of a ferric hydroxide plaque. In spite of the relatively high contents of Cu and Pb found in the roots, the rush plants succeeded in keeping the levels of these metals below toxicity limits in their shoots. Possible mechanisms explaining the adaptation of J. conglomeratus to this metal-contaminated environment are discussed.