Natural radioactivity and radiological hazards in sediments from the Lindi coast, Indian ocean, Tanzania

Abstract

The Lindi coast of the Indian Ocean, located in southeastern Tanzania, supports rich biodiversity and has recently experienced rapid growth in socio-economic activities such as fishing, mining, and oil and gas exploration. These activities may enhance levels of natural radioactivity in coastal sediments, potentially increasing radiation exposure to local populations. Therefore, monitoring radioactivity levels and estimating associated radiation doses in this region is important. In this study, thirty-six sediment samples were collected from twelve locations along the Lindi coast and analysed for naturally occurring radionuclides using high-purity germanium (HPGe) gamma-ray spectrometry. The activity concentrations of 226Ra, 232Th, and 40K ranged from 7.53 ± 1.59 to 21.72 ± 2.58 Bq kg⁻¹, 7.19 ± 2.02 to 36.76 ± 2.69 Bq kg⁻¹, and 27.19 ± 6.05 to 614.28 ± 58.64 Bq kg⁻¹, respectively. The mean activity concentrations of 226Ra and 232Th were below the recommended global averages, while elevated 40K levels were observed at several sites. Radiological hazard indices, including external and internal hazard indices, gamma radiation index, absorbed dose rate, annual effective dose equivalent, and excess lifetime cancer risk, were all below internationally recommended limits. However, the annual gonadal dose equivalent exceeded the global average at a few locations. Overall, the results indicate that sediments from the Lindi coast pose minimal radiological risk. However, continued monitoring is recommended, particularly in areas influenced by increasing anthropogenic activities