Distribution characteristics of radionuclides (137Cs, 239+240Pu, 237Np, and 241Am) in vertical vegetation zone in Changbai Mountain, China

Abstract

• First study on the relationship of radionuclide and vegetation distribution. • 137 Cs, 239,240 Pu, 237 Np and 241 Am distributions in northeast China were studied. • Radionuclide inventories vary widely in vertical vegetation zones. • A reference soil site for multidisciplinary studies in Northeast Asia . Changbai Mountain has vegetation distribution characteristics, which is an important location in northeast China to study the variation characteristics of radionuclides with vegetation distribution. Soils from three vegetation zones of mixed broadleaf and coniferous forest (MBCF), coniferous forest (CF), and alpine birch forest (ABF) in Changbai Mountain were collected to measure the artificial radionuclides of 239+240 Pu, 237 Np, and 241 Am by SF-ICP-MS, as well as 137 Cs by anti-Compton HPGe. The mean values of 240 Pu/ 239 Pu and 237 Np/ 239 Pu atomic ratios, 241 Am/ 239+240 Pu and 137 Cs/ 239+240 Pu activity ratios were 0.19 ± 0.02, 0.37 ± 0.23, 0.56 ± 0.31, 22 ± 17, respectively, indicating that the global fallout was the main source of 239+240 Pu, 237 Np, 137 Cs and 241 Am in these regions. 137 Cs, 239+240 Pu, 237 Np, and 241 Am activities in the samples are 1.1–218, 0.065–9.1, (0.018–2.9) × 10 -3 , and 0.039–2.0 Bq/kg, respectively. The activities of 137 Cs, 239+240 Pu, and 237 Np in the surface soil have a similar distribution characteristic, i.e. CF > MBCF > ABF, and 241 Am is CF > ABF > MBCF. The simulation results of the CDE model suggest that the migration of these radionuclides is dominant in Changbai Mountain forest soil. The inventories of 137 Cs, 239+240 Pu, 237 Np, and 241 Am in the soil cores are 1263–20843, 110–1425, 0.017–0.38, and 91–493 Bq/m 2 , respectively. The inventories distribution of these nuclides in the vegetation zone were as follows: 137 Cs and 239+240 Pu had similar distribution characteristics as ABF > CF > MBCF; 237 Np as CF > MBCF > ABF; 241 Am as ABF > MBCF > CF. These results showed that the content, accumulated inventory, and vertical distribution characteristics of these radionuclides were influenced by the vegetation zone distribution in the Changbai Mountain.