Risk Assessment of Radioactivity Levels in Naturally Occurring Radioactive Materials (NORM) Along the Nzima Coastline of Ghana

Abstract

Evaluation of naturally occurring radioactive material concentrations was conducted to establish the radioactivity levels of 238U, 232Th, 228Th, 226Ra, 228Ra and 40K in sea water, sand, and sediment along the coastal area of Western Ghana. The corresponding health hazards and risk associated with exposure to these radionuclides were also assessed. The findings from this study contributes to the environmental impact assessment and provide baseline information to assist in the selection of a site for the building of the planned nuclear power plant in Ghana. The radioactivity concentrations were determined by gamma and alpha spectrometry analyses using a high-purity germanium (HPGe) detector and an alpha analyst, respectively. The total samples collected were 80 beach sand samples, 80 sea sediment samples and 80 sea water samples. The results of activity concentration in the beach sand samples using the high- resolution gamma-ray spectrometry was 21.97±3.6 Bqkg-1 for 238U; 22.41±4.5 Bqkg-1 for 232Th; 344.98±90.7 Bqkg-1 for 40K and 21.31±1.8 Bqkg-1 for 226Ra; 20.65±6.4 Bqkg-1 for 228Ra and 20.42±2.4 Bqkg-1 for 228Th. The results of the sediment samples were 21.24±3.8 Bqkg-1 for 238U; 21.77±3.7 Bqkg-1 for 232Th; 305.54±68.4 Bqkg 1 for 40K and 19.00±1.4 Bqkg-1 for 226Ra; 16.54±4.6 Bqkg-1 for 228Ra and 26.86±2.9 Bqkg-1 for 228Th. The sea water samples also provided values of 1.55±0.6 BqL-1 for 238U; 2.05±0.5 BqL-1 for 232Th; 11.83±1.6 BqL-1 for 40K and 0.86±0.1 BqL-1 for 226Ra and 2.65±0.4 BqL-1 for 228Th. The calculated average activity concentration of beach sand samples using alpha spectrometry analysis for 232Th, 238U, 234U and 230Th were 1.10 ±0.3 Bq.kg-1, 2.02±0.6 Bq.kg-1, 1.34±0.7 Bq.kg-1, and 1.66±0.8 Bq.kg-1, respectively. That of the sea sediment were estimated to be 2.69±0.4 Bq.kg-1, 3.11±0.8 Bq.kg-1, 1.53±0.6 Bq.kg-1, and 2.23±0.8 Bq.kg-1 for 232Th, 238U, 234U and 230Th, respectively. The estimated average absorbed dose rate (D), radium equivalent activity (Raeq) and the annual gonadal dose (AGD), for beach sand samples were 36.62 nGyy-1, 77.12 Bqkg-1, and 259.85 μSvy 1 , respectively. The estimated average annual effective dose (AED) from soil samples was 0.11 mSv y-1, which is below the recommended value of 1 mSv y-1 for the public. The external hazard index (H𝑒𝑥𝑡) and the internal hazard index for beach sand were 0.21 and 0.27, respectively. The activity utilization index and the representative level index also gave average values of 0.47 and 0.11, respectively. The estimated mean cancer risk for beach sand was 0.17×10-3. The estimated absorbed dose rate (D) for sea sediment was 35.41 nGyy-1, while the mean value obtained for radium equivalent activity (Raeq) was 75.29 Bqkg-1. The average estimated annual effective dose (AED) from soil samples was 0.11 mSv y-1. The average estimated annual gonadal dose (AGD) was 250.55 μSvy-1. The external hazard index (H𝑒𝑥𝑡) and the internal hazard index recorded mean values of 0.20 and 0.26, respectively. On the other hand, the activity utilization index and the representative level index recorded average values of 0.48 and 0.12, respectively. All the hazard indices show that the samples from the western coast area do not pose any significant hazard. The Excess Lifetime Cancer Risk (ELCR) of sea sediment was 0.15×10-3 which is within the globally accepted reference level of 0.29×10-3 as recommended by UNSCEAR. These values suggest that the risk of cancer due to exposure to these radionuclides is minimal for the coastal population. An empirical model was developed using statistical techniques in R programming to assess the risk of exposure to Naturally Occurring Radioactive Materials (NORM) along the coastal areas of Western Ghana. The analysis focused on determining the relationships between key radionuclides, using a multiple linear regression approach. The 228Ra radionuclide was set as the dependent variable, while 232Th, 228Th, and 40K were the independent variables. R code scripts were employed for data manipulation, regression analysis, and diagnostic checks. The output of the model provided the intercept and coefficients for the predictor variables, highlighting that 232Th had the strongest positive influence on 228Ra levels, while 40K had an insignificant impact. Statistical diagnostics such as p-values, R-squared, and adjusted R-squared values were calculated to evaluate the model's fit, revealing that the model explained 99.36% of the variability in 228Ra concentrations which suggests its close relationship to the predictor variables. Residual diagnostics, correlation tests, and multicollinearity assessments were also performed to ensure the model's validity and to interpret the relationships among radionuclides accurately. The overall codebase supported effective data analysis, provided a robust predictive model for radiation risk assessment, and stressed on the need for targeted monitoring of key radionuclides, particularly 232Th, to ensure effective management of NORM-related risks in the western coast of Ghana.