GEOCHEMICAL EVOLUTION OF RADON GAS IN URBAN ENVIRONMENT

The in-situ gamma radiation levels measured in the coastal sediments of Chennai ranged from 5.6 to 7.5 µR h⁻¹, which are considerably lower than the background radiation levels reported from several other coastal regions of Tamil Nadu. This observation suggests that the concentration of naturally occurring radioactive minerals in the Chennai coastal sediments is relatively low compared to other parts of the state's coastline. Airborne radon and thoron concentrations were evaluated to assess the emanation of radioactive gases from geological materials and indoor environments. Radon concentrations ranged from 0.36 to 8.94 Bq m⁻³, while thoron concentrations varied between 0.12 and 2.90 Bq m⁻³. Higher concentrations were observed in closed and air-conditioned rooms compared to naturally ventilated spaces, indicating the accumulation of these gases under restricted ventilation conditions. Nevertheless, all measured values remained within the limits recommended by the World Health Organization (WHO). Groundwater radon concentrations were found to be strongly influenced by the geological characteristics of the host rocks. Bore wells located in charnockite formations exhibited relatively higher radon concentrations, reflecting the presence of radioactive minerals within the bedrock. In contrast, coastal aquifers showed comparatively lower radon levels. Open wells generally recorded lower radon concentrations than bore wells, as dissolved radon can readily escape into the atmosphere from open water surfaces, whereas it tends to accumulate in confined groundwater systems. The measured radon concentration in groundwater along the Chennai coastal region ranged from 2.1 to 28.4 Bq L⁻¹. Inland groundwater sources generally exhibited higher radon concentrations than coastal aquifers, with values ranging from 2.1 to 13.86 Bq L⁻¹. These variations highlight the significant role of lithology, groundwater circulation, and well type in controlling radon distribution within the study area. Overall, the results indicate that the levels of gamma radiation, airborne radon, thoron, and groundwater radon in the Chennai coastal environment remain within acceptable safety limits and do not pose significant radiological risks to the local population.

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