Reuse of Paper Industry Wastes as Additives in Phytoremediation of Heavy Metals Polluted Substrates from the Spoil Banks of the Kremikovtsi Region, Bulgaria☆

Heavy metal contamination of large areas due to mining and metallurgical operations poses a serious long-term environmental problem for some industrial regions of Bulgaria. The investigated Kremikovtsi region located near the capital city of Sofia, Bulgaria, is one of the most highly polluted ones by heavy metals, regarding both the soil and the spoil banks formed by long-term deposition of steel production residues and foundry. This research aimed at studying the possibility for reusing paper industry wastes as additives in phytoremediation of heavy metals polluted substrates of the spoil banks in the Kremikovtsi region. Greenhouse remediation experiments of heavy metals polluted substrates, collected from the spoil banks located in the vicinity of the metallurgical plant “Kremikovtsi”, have been performed. Phytoremediation was performed by planting 2- years-old seedling of the red oak (Quercus rubra L.) and Austrian pine (Pinus nigra Arn.) trees. In independent experiments with a polluted substrate and with a mixture of substrate and paper wastes and inorganic fertilizers - nitrogen (N), phosphate (P2O5), and potash (K2O), respectively were added in N-P-K ratio of 6-1-3 or 2-1-2. Plant biometric measurements, heavy metal content analyses, both in plants and substrates were performed at the end of the vegetative season. It was found that phytoremediation was enhanced by adding wastes from paper industry and mineral fertilizers. The results obtained showed that the simultaneous application of wastes from paper industry and fertilizers (N-P-K ratio equal to 2-1-2) improved both the sapling growth and the heavy metal accumulation. However, the bioaccumulation and translocation of heavy metals to the aerial part of the plants depended strongly on the tree peculiarities.