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

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 (Po-210, Pb-210 or Pb-210(ex) (excess Pb-210 is defined as the activity of Pb-210 minus the activity of Ra-226), Be-7, K-40, Ra-226, U-238, and Th-232) and anthropogenic radionuclides (Cs-137) 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 (Po-210, Pb-210 (Pb-210(ex)), Be-7, and Cs-137) and a terrestrial group (K-40, U-238, Ra-226, and Th-232). The activity concentrations of Po-210 and Pb-210(ex) in moss body profiles were mainly concentrated in the stems-rhizoid parts, in which we measured some of the highest Po-210 and Pb-210(ex) levels compared to the results in the literature. Be-7 mainly accumulated in the leaves-stem parts. Different positive correlations were observed between Po-210 and Pb-210 and between Be-7 and Pb-210, which indicated that the uptake mechanisms of Po-210, Pb-210, and Be-7 by moss plants were different, to some extent. Cs-137 was detected only in some moss samples, and the fraction of Cs-137 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 K-40, the terrestrial radionuclide (U-238, Ra-226, and Th-232) 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.