Elevated concentration of radioactive potassium in edible algae cultivated in Malaysian seas and estimation of ingestion dose to humans

Although the various benefits of seaweeds are well recognised, potential health hazards are much less well researched, as an instance the possible presence of concentrated levels of natural radionuclides. In present work the concentrations of natural radionuclides in seaweed cultivated in Malaysian seas are assessed using conventional HPGe gamma-ray spectrometry. An edible species of seaweed has been collected from several seaweed farms located along coasts of the Andaman and South China Sea. Activity concentrations of Ra-226, Ra-228 and K-40 in samples collected from Langkawi are observed to be greater than those from Sabah, while K-40 radioactivity levels (2.2E3 +/- 100 - 3.8E3 +/- 180 Bq kg(-1)) in all samples are noted to be well above the world average value of between 400 and 580 Bq kg(-1). The estimated amount of total potassium is in the range 68 - 120 g (kg of seaweed) (-1) and 53-106 g kg(-1) obtained via ICP-OES, which are in line with data for New Zealand seaweed of between 43.7 and 123 g kg(-1). The estimated total effective dose of 84 mu Sv.y(-1) is lower compared to a global internal dose of 290 mu Sv.y(-1) as reported by UNSCEAR. Accordingly, the mean cancer risk from such consumption was also estimated to be slightly lower (1.92 x 10(-3)) compared to the ICRP cancer risk factor of 2.5 x 10(-3) based on the additional annual dose limit of 1 mSv for a member of the general public, which gives an annual mortality probability of 10(-5) (1 in 100,000; ICRP, 1991). Although posing a low risk health hazard, periodic monitoring of natural radioactivity in foodstuff remains important in seeking to ensure the radiological safety of the public.