Accumulation of natural and anthropogenic radionuclides in body profiles of Bryidae, a subgroup of mosses.

ABSTRACT

Mosses can be used as biomonitors to monitor radionuclide deposition and heavy metal pollution in cities, forests, and grasslands. The aims of this work were to determine the activity concentrations of natural (210Po, 210Pb or 210Pbex (excess 210Pb is defined as the activity of 210Pb minus the activity of 226Ra), 7Be, 40K, 226Ra, 238U, and 232Th) and anthropogenic radionuclides (137Cs) in moss body profiles and in situ underlying soils of moss samples and to assess/determine the distribution features and accumulation of these radionuclides. Activity concentrations of radionuclides in the samples were measured using a low-background gamma spectrometer and a low-background alpha spectrometer. Consistent with their source, the studied radionuclides in the moss samples and underlying soils were divided according to the principal component analysis (PCA) results into an airborne group (210Po, 210Pb (210Pbex), 7Be, and 137Cs) and a terrestrial group (40K, 238U, 226Ra, and 232Th). The activity concentrations of 210Po and 210Pbex in moss body profiles were mainly concentrated in the stems-rhizoid parts, in which we measured some of the highest 210Po and 210Pbex levels compared to the results in the literature. 7Be mainly accumulated in the leaves-stem parts. Different positive correlations were observed between 210Po and 210Pb and between 7Be and 210Pb, which indicated that the uptake mechanisms of 210Po, 210Pb, and 7Be by moss plants were different, to some extent. 137Cs was detected only in some moss samples, and the fraction of 137Cs in the underlying soils was much lower than that in the moss, suggesting that mosses were protecting the underlying soils from further pollution. Except for 40K, the terrestrial radionuclide (238U, 226Ra, and 232Th) content in mosses was predominantly at low levels, which indicated not only the inability of mosses to use those elements for metabolic purposes but also the rather poor capability of mosses to directly mobilize, absorb, and transport elements (U, Ra, or Th) not dissolved in water.