Natural radioactivity and heavy metal contamination in edible fish, shellfish and mollusks at the Bay of Bengal, Kuakata, Bangladesh

In this study, gamma activity concentrations, gross alpha and gross beta activity of natural radionuclides, and heavy metal concentrations were measured in eleven edible marine fish, four shellfish, two mollusks, and a common seaweed sample collected from a local sea fish market and sea beach area of the northern part of the Bay of Bengal, Kuakata, Bangladesh. Using HPGe gamma spectrometry, the activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K were measured and found to be 19.7 ± 1.5 Bq/kg, 12.2 ± 0.9 Bq/kg, and 188 ± 15 Bq/kg, respectively, with the ²³²Th concentration surpassing that of ²³⁸U. The ZnS scintillation detector was used to assess the gross alpha and gross beta activity. The average gross alpha activity and gross beta activity were found to be 9.4 ± 1.4 Bq/kg and 26 ± 4 Bq/kg, respectively, with the latter attributed to beta emitting radionuclides's abundance. The activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K in the analyzed samples varied in the order of Shellfish > Seaweed > Fish > Mollusks, Seaweed > Shellfish > Mollusks > Fish, and Seaweed > Shellfish > Fish > Mollusks. The annual effective dose due to consumption of analyzed seafood was found to be within the world limit of 2400 μSv/y recommended by UNSCEAR. The main contributor to the annual effective dose was ²³⁸U. The excess lifetime cancer risk (ELCR) results were below the permissible threshold of 10^-3 for radiological risks. Furthermore, average concentrations of Zn and Mn were higher than WHO/FAO recommended values, and carcinogenic Pb, Cd, Cr, and Hg concentrations were below detection limits, according to heavy metal analysis performed by AAS. The average concentration of heavy metals in all of the seafood samples under investigation was in the order of Zn > Fe > Mn. The calculated hazard index (HI), target hazard quotient (THQ), and estimated daily intake (EDI) were compared to the permissible safety limits.