Potential of Ornamental Trees to Remediate Trace Metal Contaminated Soils for Environmental Safety and Urban Green Space Development

Abstract

Heavy metals are notoriously toxic pollutants which can potentially harm living beings and are serious health hazards. The aim of the present study was to assess the levels of cadmium (Cd) and nickel (Ni) throughout the year in the urban areas of the densely populated industrial city of Faisalabad in eight commonly raised ornamental tree species with phytoremediation potential. High levels of Cd and Ni were recorded in all study areas, with spatio-temporal heterogeneity. Heavy metal uptake varied among plant species with Cd and Ni in soil ranging between 6.78–8.57 mgkg−1 and 46.31–55.85 mg kg−1 respectively. Plant species accumulated 6.73–8.98 mg kg−1 Cd and 26.42–52.50 mg kg−1 Ni with Conocarpus erectus, Dalbergia sissoo and Bismarckia nobilis showing higher accumulation potential than others. Dalbergia sissoo accumulated the highest levels of Ni and was shown to a good bio-indicator for this metal. The highest accumulation of Cd was recorded in Conocarpus erectus (9 mg kg−1), followed by Dalbergia sissoo (8.2 mg kg−1) and Bismarckia nobilis (8.1 mg kg−1) while the leaves of Azadirachta indica retained the lowest (6.3 mg kg−1) Cd levels. The highest levels of metals were accumulated by all species during the summer season while the second highest were observed in the autumn season. The study revealed that ornamental species can help in minimizing heavy metal pollution as well as providing green space in urban settings for maintaining a clean and healthy environment.