Heavy metals in road dust of megacity Kolkata: contamination, source apportionment, and health risks

Vismay, K. (2019) Heavy metals in road dust of megacity Kolkata: contamination, source apportionment, and health risks. Masters thesis, Indian Institute of Science Education and research Kolkata.

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Abstract

Urban road dust is a major indicator of heavy metal contamination in the environment, and it receives depositions of anthropogenic metals from various stationary and mobile sources. To study the contamination levels, potential sources and health risks associated with heavy metals in Kolkata, 57 road dust samples were collected from 7 different land use categories; residential, roadside, traffic, railway, port and industrial areas in the city, during summer 2018 (June 2018). Heavy metal content in different size fractions; <75 μm, 75-125 μm and 125-300 μm were determined using a wavelength dispersive X-ray fluorescence (WD-XRF) system. The overall mean concentrations of anthropogenic trace metals like Mn (743 ± 129 μg g⁻¹) >Zn (289 ± 95 μg g⁻¹) > Cr (164 ± 114 μg g⁻¹) > Pb (128 ± 127 μg g⁻¹) > V (106 ± 20 μg g⁻¹) > Cu (92 ± 47 μg g⁻¹) > Ni (36 ± 31 μg g⁻¹) > Co (14 ± 2.7 μg g⁻¹) > Sc (14 ± 3.1 μg g⁻¹) > Cd (0.9 ± 0.8 μg g⁻¹) were high the smallest size fraction (<75 μm) by factors in the range 1.2 – 3.1 compared to other two size fractions. The contamination indices show that there are comparable levels of pollution in residential areas similar to traffic and industrial areas. Pb in industrial areas and Cr in port areas shows highest enrichment factors of 11.9 and 11.6. Based on PMF analysis, 5 major sources of heavy metals were selected. Traffic emissions and crustal origin were the main sources of heavy metals with percentage contribution of 39% each. The next largest contribution (12%) was from construction activities followed by industrial emissions and vehicular metal abrasion with percentage contributions of 7% and 4%. Health risk assessment for non-carcinogenic metals indicates risk for children with Hazard indices (HI) > 1. Also, the Incremental lifetime cancer risks (ILCR) due to carcinogenic elements shows high risks of cancer for both children and adults with ILCR values of 7 × 10⁻⁴ and 4 × 10⁻⁴.

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