Radionuclides' Dispersion from Coal-Fired Brick Kilns: Geo-Environmental Processes, Potential Risks and Management.

Abstract

In order to investigate the distributions and possible dispersion mechanism(s) of naturally occurring radioactive materials (NORMs: ²²⁶Ra, ²³²Th, and ⁴⁰K) from coal-based brick kilns, a systematic set (n = 60) of coal, ash, surface-soil, and subsurface soil samples were analyzed. High-quality analytical data of U, Th and K obtained from HPGe detector and TRIGA Mark-II research reactor-based neutron activation analysis were converted to the corresponding radioactivities. Average (n = 10) radioactivities of ²²⁶Ra, ²³²Th, and ⁴⁰ K in coal samples were 15.6, 16.7, and 145.5 Bq.kg^-1, respectively, where only ⁴⁰ K surpassed the corresponding global mean value. Average (n = 10) radioactivities of ²²⁶Ra, ²³²Th, and ⁴⁰ K in ash samples were 62.7, 88.5, and 521 Bq.kg^-1, respectively, where only ²²⁶Ra was within the established limit. In soil samples, average (n = 40) activities of ²²⁶Ra, ²³²Th, and ⁴⁰ K were 62.7, 95.1, and 641 Bq.kg^-1, respectively, which have surpassed the corresponding worldwide mean values. The observed differences in activity levels between soil samples collected near and far from the kilns, as well as between topsoil and subsoil samples, suggest the presence of distinct transport mechanisms for NORMs within the pedosphere. Dispersions of NORMs from the brick kilns to the ambient pedosphere are largely governed by aerodynamic convection and hydrodynamic leaching. These mechanisms are also influenced by geochemical mobility and relative solubility of NORMs, as well as factors such as rainfall patterns and wind-flow direction. Radiological indices invoke long-term carcinogenic-risks, whereas aerodynamic convection of finer particles (coal fly ash) from chimneys can cause significant health hazards to the nearby dwellers. Scientific processes as well as public awareness are essential to mitigate the risks.