An experiment was carried out in greenhouse to evaluate total content and distribution of heavy metals in seedlings of twenty different tree species growing in a soil contaminated by Zn, Cd, Cu and Pb. Plantable size seedlings were transfered to 3.3 kg pots containing a contaminated soil mixture and to a control soil without contamination where they were allowed to grow for ninety days. Metal foliar concentrations for plants grown in the contaminated soil were high, ranged from (mg kg-1): Zn= 154 to 1177; Cd = 0.6 to 54.6 and Cu= 2.8 to 134. In most cases, these concentrations were superior to what has been considered as critical toxic levels, whereas foliar Pb concentrations ranged from 0.1 to 4.3 mg kg-1, below the critical toxic level. In some species that were highly affected by contamination such as Machaerium nictidans, Myroxylon peruiferum, Piptadenia gonoacantha, Senna macranthera and Trema micrantha it was found high translocation index for Zn and/or Cd. However, Dendropanax cuneatum that was only slightly affected by contamination, exhibited high translocation of Zn and Cd to shoots. In contrast to others species, Dendropanax cuneatum retained these elements in the stems. Other group of plants that were only slightly affected by soil contamination such as Acacia mangium, Copaifera langsdorffi and Cedrella fissilis accumulated more Zn and Cd in the roots than in the shoots, therefore indicating that reduced translocation is involved in their tolerance to the excess of heavy metal in soil. The proportional distribution pattern of Zn and Cd in the roots and shoots of the studied plant species is related to their behavior to the excess of heavy metals in soil.
Heavy metal toxicity; critical levels; soil pollution; tropical tree seedlings
