¹³⁷Cs accumulation by woody plants and edible mushrooms at the «Taiga» peaceful nuclear explosions site

In 1971 in the Perm region (the Russian Federation), three thermonuclear charges of the “Taiga” series were simultaneously detonated in order to test nuclear explosive technologies for creation of the Pechora-Kama canal. As a result of the underground explosions, long-lived technogenic radionuclides were released onto the surface of the earth along with soil and rock. Over time, a new forest ecosystem formed on the mound of the radioactively contaminated ground. The purpose of this study was to assess the 137Cs accumulation by woody plants and edible mushrooms at the “Taiga” underground nuclear explosions site at a remote stage (38 years) after radioactive contamination of the environment. Content of 137Cs was determined in organs of birch (Betula pubescens), spruce (Picea abies), aspen (Populus tremula), and pine (Pinus sylvestris), as well as in the fruiting bodies of mushrooms of the species Boletus edulis, Leccinum aurantiacum, Russula, and Suillus luteus. The activities of 137Cs in the samples were measured by gamma-ray spectrometry using a HPGe detector. The values of 137Cs activity concentration (on a dry weight basis) in the samples of wood, leaves/needles (1st year), and mushrooms were in the ranges of 0.5–6.8 Bq/kg, 54–112 Bq/kg, and 212-3260 Bq/kg, respectively. Aggregated transfer coefficients (kg/m2) for the radionuclide in the biota species were calculated using these results and previously reported data on the density of soil contamination by 137Cs at the “Taiga” site. It has been found that the transfer coefficients of 137Cs from soil to biota for all studied species at the “Taiga” site are abnormally low compared to those obtained by many authors for other places of radioactive contamination, in particular for the areas contaminated by 137Cs as a result of the Chernobyl accident. Possible reasons for the low accumulation of 137Cs in the biota at the “Taiga” site are discussed.