Road dust–driven elemental distribution in megacity Dhaka, Bangladesh: environmental, ecological, and human health risks assessment

Road dust, which reflects ambient air quality, receives various pollutants including toxic metal(oid)s from several natural and/or anthropogenic sources. This manuscript reports a comprehensive evaluation of the levels of seventeen metal(oid)s in road dust of a megacity (Dhaka, Bangladesh). Different evaluation approaches were implemented including statistical analysis and GIS mapping, besides environmental, ecological, and human health risk indices. From 30 sampling sites, representative samples were collected, which were analyzed by neutron activation analysis. The average concentrations (± SD) of Na, Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Zn, As, Rb, Sb, Cs, Ba, and W were 11,738 ± 560 µg g−1, 12,410 ± 1249 µg g−1, 62,127 ± 5937 µg g−1, 8.89 ± 0.47 µg g−1, 5224 ± 1244 µg g−1, 66 ± 8 µg g−1, 66.7 ± 6.9 µg g−1, 547 ± 110 µg g−1, 25,150 ± 1723 µg g−1, 8.39 ± 0.65 µg g−1, 125 ± 17 µg g−1, 3.63 ± 0.56 µg g−1, 87 ± 9 µg g−1, 0.75 ± 0.28 µg g−1, 4.40 ± 0.48 µg g−1, 397 ± 87 µg g−1, and 3.82 ± 1.77 µg g−1, respectively. The distance-based redundancy analysis showed that the northern region was enriched with Na, Mn, Al, Fe, Zn, and Rb, while the southern region was enriched with Fe, Al, Ti, Cr, and Mg. The GIS mapping shows hot spots of Sc, Cr, Zn, and Cs were observed mostly in heavy traffic areas. Significant positive correlations of Fe-Sc, Al–Mg, V-Mg, V-Al, Cs-Rb, Cs-Sc, Rb-Sc, As-Na, and Cs-Rb invoked their inter-dependency and persistence in road dust. Depending on a set of environmental and ecological index–based calculation, the degree of metal(oid) pollution followed the descending order as W > Sb > Zn > Cr > As > Ti > Sc > V, while no pollution was recorded by Mn, Fe, Al, Rb, Cs, Co, and Ba. Importantly, the total hazard index values for adults and children were higher than unity, indicating potential non-carcinogenic health risks from exposure of road dust. Furthermore, the total carcinogenic risks from Cr and As through ingestion and dermal contact exceeded the standard guideline values. The implementation of different evaluation approaches strengthens the findings of metal(oid) source apportionment.