A survey of natural terrestrial and airborne radionuclides in moss samples from the peninsular Thailand

The aim of this study was to determine the activity concentrations of natural terrestrial radionuclides (238U, 226Ra, 232Th and 40K) and airborne radionuclides (210Pb, 210Pbex and 7Be) in natural terrestrial mosses. The collected moss samples (46) representing 17 species were collected from 17 sampling localities in the National Parks and Wildlife Sanctuaries of Thailand, situated in the mountainous areas between the northern and the southern ends of peninsular Thailand (∼7-12 °N, 99-102 °E). Activity concentrations of radionuclides in the samples were measured using a low background gamma spectrometer. The results revealed non-uniform spatial distributions of all the radionuclides in the study area. Principal component analysis and cluster analysis revealed two distinct origins for the studied radionuclides, and furthermore, the Pearson correlations were strong within 226Ra, 232Th, 238U and 40K as well as within 210Pb and 210Pbex, but there was no significant correlation between these two groups. Also 7Be was uncorrelated to the others, as expected due to different origins of the airborne and terrestrial radionuclides. The radionuclide activities of moss samples varied by moss species, topography, geology, and meteorology of each sampling area. The observed abnormally high concentrations of some radionuclides probably indicate that the concentrations of airborne and terrestrial radionuclides in moss samples were directly related to local geological features of the sampling site, or that high levels of 7Be were most probably linked with topography and regional NE monsoonal winds from mainland China.