Geology-Driven Variability of Urban Terrestrial Gamma Radiation and Soil Contamination Index UCSI: Evidence from Carborne Surveys in Peninsular Malaysia

Abstract

Aims: This study aims to evaluate geology-driven variability in terrestrial gamma radiation (TGR) and urban soil radioactivity in major cities of Peninsular Malaysia, and to determine whether underlying lithology continues to influence radiation levels despite extensive urban modification. A secondary aim is to quantify the Urban Soil Contamination Index (USCI) to assess anthropogenic contributions to radiological variability. Study Design: A cross-sectional environmental radiation survey integrating carborne gamma measurements, soil radioactivity analyses, and geological mapping. Place and Duration of Study: Surveys were conducted across 13 major urban areas in Peninsular Malaysia between December 2023 and October 2024. Methodology: A systematic carborne survey was performed with a spatial resolution of ~1.5 km² per measurement, yielding 9,754 TGR dose-rate records. Calibration followed IEC and IAEA protocols using a Ludlum Model 19 Micro R Meter, supported by HPGe spectrometry. A total of 120 surface soil samples were analysed for activity concentrations of the 238U and 232Th decay series and 40K. USCI values were calculated from radionuclide ratios (U/K, Th/K, Th/U) to characterise anthropogenic alteration in superficial urban soils. Results: Urban TGR ranged from 47–371 nGy h⁻¹, with the lowest means in Kangar and Kuala Terengganu and the highest in Ipoh, Seremban and Melaka. Soil radionuclide concentrations varied widely: 238U (27–347 Bq kg⁻¹), 232Th (27–590 Bq kg⁻¹), and 40K (61–1857 Bq kg⁻¹), reflecting mixed geological and anthropogenic sources. USCI values (0.05–4.50) indicate substantial contamination from construction materials, industrial particulates and urban fill. Overall, integrating geological mapping with the spatial distribution of urban TGR measurements reinforces the conclusion that underlying lithology remains the dominant factor controlling terrestrial gamma radiation fields in Peninsular Malaysia. Urbanisation amplifies existing geological signatures but does not override them. While granite-dominated provinces consistently show high TGR values, anomalies in cities such as Klang Valley, Kuantan and Kota Bharu highlight the growing role of urban development in modifying local radiological environments. Conclusion: Geology exerts primary control over urban TGR, while anthropogenic processes strongly influence soil radioactivity and contamination intensity. These integrated results provide updated baseline data essential for urban radiological protection, geoscientific assessment and environmental planning across rapidly developing Malaysian cities.