In Situ Ground Radiometric Survey and Risk Assessments of Allanite-Bearing Beach Sands in Erawan, Palawan - Philippines - 2021

Uranium (Nuclear Minerals) / Exploration, Mining, Marketing, & Acquisitions

Diwa and 5 co-authors reported in mid-2021 that:

• Elevated radioactivity and high risk indices attributed to Th in allanite,
• High K and U contents potentially from phosphate fertilizer use in farms,
• High human health risk associated with the radionuclides, and
• Radiological risk indices evaluate the safety of beach sands as building materials.

Past exploration for U deposit in the Philippines discovered the mineralization of radioactive allanite in Palawan. The allanite occurs as sand component in the heavily populated beach of Erawan, San Vicente, Palawan. This work assessed the risks associated with the radionuclides in Erawan beach by in situ ground radiometric survey of K, U, and Th in 694 sampling points.

Principal component analysis (PCA) and Pearson correlation coefficient were used to determine the similarity between the radionuclides and to identify other probable anthropogenic sources of radionuclides. Their results showed that the mean activity concentrations of K (597.8 Bq kg^-1) and Th (93.15 Bq kg^-1) are equivalent to 1.5 and 3.1 times of the world average natural radioactivity levels in soil, respectively, while the mean U (34.7 Bq kg^-1) is similar to the world average.

The mean radiological risk assessments like radium equivalent, gamma specific activity index, external hazard index, internal hazard index, absorbed gamma dose rate, annual effective dose equivalent, annual gonadal equivalent dose, and excess lifetime cancer risk are 213.96 Bq kg^-1, 0.78, 0.58,
0.67, 97.24 nGy h^-1, 119.25 μSv y^-1, 684.39 μSv y^-1, and 0.42 (10^-3), respectively.

Th consistently correlated most to the risks. They attributed the occurrence of Th to the presence of allanite, K to fertilizer use for farming, and U to both the allanite and farming. The results of their study can provide important baseline data for future detailed studies or monitoring of the long-term effects of elevated radiation levels to the local population of Erawan.

The authors utimately concluded that in situ ground radiometric survey showed that the mean activity concentrations of K and Th in the beach in Erawan, Palawan are several times higher than the world mean concentrations in soils while U is similar to the world average.  As stated, the Th is attributed to the occurrence of allanite in the beach sands, K is to fertilizer use for farming, and U to both the allanite and fertilizer use. The mouth of the river traversing the study site consistently have the highest risks associated with the radionuclides. This is because of the prevalence of the allanite being carried by the river towards the shore. The mean of risk assessments like the mean Raeq, Iγ, Hex, and Hin are in accordance with the international safe reference values.

Although the other risk indices associated to human health such as the Dair, AEDE, AGED, and ELCR exceed the safe limits or the world average values which suggests human health hazard in the long term. It is significant to note that the risks become more extreme to areas proximal to the river mouth.

Of the three radionuclides analyzed, Th from the allanite consistently have the highest correlation to the risks. The elevated radioactivity in Erawan beach is a result of combined natural and anthropogenic sources. There is no serious hazard on using the sands as construction materials except for the sands from the river mouth. Long-term human exposure to the sands can theoretically cause serious health problems. Since this study is limited to background radiation levels, the authors recommended conducting a detailed study on the health effects to the local populace. This includes review of mortality and morbidity statistics and conduct of more challenging epidemiological studies.