Environmental radiological monitoring and risk assessment in shale gas areas

Naturally occurring radioactive materials (NORM) are present in waste generated during shale gas drilling activities and pose potential risks to the environment, drawing increasing public and scientific attention. In this study, soil, wastewater and effluent samples were collected across multiple operational stages of shale gas development in Southwest China. A combination of in-situ gamma absorbed dose rate in air, soil radon concentration, radionuclide activity concentrations, and conventional hazard indices was used to evaluate environmental radioactivity and potential occupational exposure. The results showed that both the gamma absorbed dose rates and soil radioactivity were comparable to those observed in other oil and gas fields, that were strongly correlated with uranium-series nuclides. A strong linear relationship between ²³⁸U and ²²⁶Ra, indicating the two radionuclides were in near radioactive equilibrium within the soil. The ²¹⁰Pb/²²⁶Ra ratio was consistently greater than 1 and increased with platform operation time, suggesting an accumulation of radon progeny. Discrepancies between measured and calculated dose rates highlighted the need to prioritize direct measurements in dose assessments. Worker dose assessments revealed annual effective doses below 1 mSvy^-1. Furthermore, elevated concentrations of ²²⁶Ra, ²²⁸Ra, and ⁴⁰K were detected in untreated-water, which could be effectively reduced by existing treatment technologies. These findings provide a baseline for radiological risk evaluation in shale gas fields and highlight the necessity for continuous monitoring and wastewater management.