Differential distribution of metals in tree tissues growing on reclaimed coal mine overburden dumps, Jharia coal...

Opencast bituminous coal mining invariably generates huge amount of metal-polluted waste rocks (stored as overburden (OB) dumps) and reclaimed by planting fast growing hardy tree species which accumulate metals in their tissues. In the present study, reclaimed OB dumps located in Jharia coal field (Jharkhand, India) were selected to assess the accumulation of selected metals (Pb, Zn, Mn, Cu and Co) in tissues (leaf, stem bark, stem wood, root bark and root wood) of two commonly planted tree species (Acacia auriculiformis A.Cunn. ex Benth. and Melia azedarach L.). In reclaimed mine soil (RMS), the concentrations of pseudo-total and available metals (DTPA-extractable) were found 182-498 and 196-1877% higher, respectively, than control soil (CS). The positive Spearman's correlation coefficients between pseudo-total concentration of Pb and Cu (r = 0.717; p < 0.05), Pb and Co (r = 0.650; p < 0.05), Zn and Mn (0.359), Cu and Co (r = 0.896; p < 0.01) suggested similar sources for Pb-Cu-Co and Mn-Zn. Among the five tree tissues considered, Pb selectively accumulated in root bark, stem bark and leaves; Zn and Mn in leaves; and Cu in root wood and stem wood. These results suggested metal accumulation to be "tissue-specific". The biological indices (BCF, TF_leaf, TF_{stem bark} and TF_{stem wood}) indicated variation in metal uptake potential of different tree tissues. The study indicated that A. auriculiformis could be employed for Mn phytoextraction (BCF, TF_leaf, TF_{stem bark} and TF_{stem wood} > 1). The applicability of both the trees in Cu phytostabilization (BCF > 1; TF_leaf, TF_{stem bark} and TF_{stem wood} < 1) was suggested. The study enhanced knowledge about the selection of tree species for the phytoremediation of coal mine OB dumps and specific tree tissues for monitoring metal pollution.