This study investigates the specific activities of natural radionuclides in sediments dredged from Lagos State and assesses the associated radiological risks when these sediments are used as building materials. Using a Sodium Iodide (NaI (Tl)) detector, the specific activities of 226Ra, 232Th and 40 K were measured ranging from below detectable limit (BLD)—75.45 Bq/kg, 25.30 −106.63 Bq/kg and 49.30–374.83 Bq/kg with a mean of 26.20 \(\pm\) 0.56 Bq/kg, 60.80 \(\pm\) 0.09 Bq/kg and 156.10 \(\pm\) 0.17 Bq/kg respectively. While the mean specific activities of 226Ra and 40 K are lower than the world average values (35, 400 Bq/kg),232Th is over 2 times its world average value (30 Bq/kg) in sediments. The mean of radium equivalent (Req) external hazard index (Hex), internal hazard (Hin) and representative level index (Iγr) are 125.52 Bq/Kg, 0.34, 0.41 and 0.89 each within permissible safe limits (370 Bq/kg, 1.00,1.00, and 1.00 respectively). However, the indoor absorbed dose rate (Din) ranged from 87.74 to 172.93 \(\text{nGy}/\text{h}\) with an average of 126.00 \(\text{nGy}/\text{h}\) , indoor annual effective dose (Ein) ranged from 0.43–0.85 with an average of 0.62 \(\text{mSv}/\text{y}\) , excess life cancer risk (ELCR) ranged from 1.51 to 2.97 × 10–3 with a mean of 2.16 × 10–3. The mean values of Din, Ein and ELCR are approximately 50.00%, 53.00% and six times higher than their world average values. The high levels of 232Th, Din, Ein and ELCR suggest that using these sediments as building materials may pose significant radiological health risks to the public.
