Soil, dust, and leaf-based novel multi-sample approach for urban heavy metal contamination appraisals in a megacity, Dhaka, Bangladesh

Abstract

The fast-growing megacities in the South Asian region have been facing environmental issues such as heavy metal load due to anthropogenic activities including Dhaka city. Thus, this study was executed to understand the heavy metal contamination in the urban environment using a novel multi-sample (soil, dust, and tree leaves) approach in Dhaka city, Bangladesh. 13 sites were selected for the analysis of nine heavy metals using AAS. The concentration (ppm) of Cd (4.95 0.06), Zn (254.8 0), Cu (56.25 0.06), and Mn (995.9±0.0) in the soil and Cr (135.500 0.00), Ni (68.35 1.30), Zn (275.73 0.00), Cu (68.35 1.30) and Mn (1076.84 0.00) in the dust exceeded the maximum permissible limit. In tree leaf samples except for Ni all the heavy metals exceeded the standard value. Environmental pollution indices revealed that the study area is mostly contaminated with Cu, Pb, Ni, Zn, Cd, Mn, and Cr. Vehicle emissions were recognized as the major source of Zn, Cu, Pb, Ni in soil; Cr, Pb, Mn, Zn in the dust; and Ni, Mn, Pb, Zn in tree leaves, according to the multivariate statisticalanalysis. Industrial emissions were identified as the primary source of Cd in soil, Cu, Cd, Ni in dust, and Cr, Cd in tree leaves. However, the analysis of metals in tree leaves among five species Ficus aurea, Ficus benghalensis, Ficus religiosa, Ficus rubiginosa, and Polyalthia longifolia revealed that Ficus aurea is a hyperaccumulator of Cd and good accumulator for other metals, making it a suitable candidate for urban greening. Polyalthia longifolia is a better barrier of toxic elements. Cr possesses the highest carcinogenic risk for the inhabitants and Cd was found to cause the highest potential ecological risk. Metals in each sample type in each sampling site reveal almost a nonpareil relationship that indicates the appraisal of the multi-sample approach. Therefore, it can be said that this scientific study provides an effective tool for assessing urban metal pollution.