Fractionation of environmental radioactivity in road dust from a megacity: external and internal health risks.

Naturally occurring radioactive materials (NORMs: Th, Ra, K) can reach our respiratory system by breathing of road dust which can cause severe health risks. Targeting the pioneering consideration of health risks from the NORMs in road dust, this work reveals the radioactivity abundances of NORMs in road dust from a megacity (Dhaka) of a developing country (Bangladesh). Bulk chemical compositions of U, Th, and K obtained from neutron activation analysis were converted to the equivalent radioactivities. Radioactivity concentrations of Ra, Th, and K in road dust ranged from 60-106, 110-159, and 488-709 Bq kg with an average of 84.4 ± 13.1, 126 ± 11, and 549 ± 48 Bq kg, respectively. Estimated Ra, Th, and K radioactivities were, respectively, 1.7-3.0-, 3.7-5.3-, and 1.2-1.8-folds greater than the affiliated world average values. Mechanistic pathway of NORMs' enrichment and fractionation relative to the major origin (pedosphere) were evaluated concerning the water logging, relative solubility-controlled leaching and translocation, climatic conditions, and aerodynamic fractionations (dry and wet atmospheric depositions). Computation of customary radiological risk indices invokes health risks. Noticing the ingress of NOMR-holding dust into the human respiratory system along with the associated ionizing radiations, the computed radiological indices represent only the least probable health hazards. Nevertheless, in real situations, α-particles from the radioactive decay products of Th and U can create acute radiation damages of respiratory system. Policymakers should emphasize on limiting the dust particle evolution, and public awareness is required to alleviate the health risks.