Assessment of Radioactivity Levels and Radiological Hazards Indices in Sediments and Fish from Coastal Marine Areas of Tanzania

Abstract

Environmental radioactivity monitoring is essential for assessing potential exposure risks to humans and marine ecosystem, particularly in coastal marine areas where anthropogenic and natural radionuclides may accumulate. However, research studies on natural radioactivity in Tanzania's coastal marine areas remain scarce. This study was therefore conducted to assess the radioactivity levels of natural radionuclides ( 226 Ra, 232 Th, and 40 K) in marine sediments and fish samples from the Tanzanian coastal areas, and to estimate the associated radiological health hazards for both humans and marine ecosystem. A total of 49 samples comprising both sediment and fish were randomly collected from 12 coastal sites and composited for analysis. Radioactivity concentrations were measured using gamma spectrometry. For fish samples, the mean activity concentrations were 4.9 ± 1.9 Bq kg⁻ 1 dry weight (dw) for 226 Ra, 488.8 ± 34.1 Bq kg⁻ 1 dw for 40 K, while 232 Th was below the detection limit. In sediments, the corresponding mean values were 15.1 ± 2.2, 14.9 ± 2.0, and 320.8 ± 27.4 Bq kg⁻ 1 dw for 226 Ra, 232 Th, and 40 K, respectively. Based on these data, a comprehensive set of radiological hazard indices was computed, including radium equivalent activity (Raₑq), absorbed dose rate (D), annual effective dose equivalent (Eₑff), external and internal hazard indices (Hₑₓ and Hᵢₙ), representative gamma index (Iᵧ), annual gonadal dose equivalent (AGDE), excess lifetime cancer risk (ELCR), and annual effective dose (AED). The results showed that the computed total annual effective committed dose for fish consumption was below the 1 mSv y⁻ 1 as recommended by the ICRP, although the mean 40 K activity in fish exceeded the global average of 420 Bq kg⁻ 1 . All evaluated hazard indices (Ra eq , H ex , D, E eff , I γ , AGDE, and ELCR) for sediments, as well as Hᵢₙ and ELCR for fish, were within permissible levels values. In conclusion, the current radioactivity levels in the studied coastal area do not pose a significant radiological risk to human health or the marine ecosystem. Nevertheless, it is advisable to keep monitoring for purpose of detecting any future changes due to natural or anthropogenic influences.