239+240Pu, 90Sr and 137Cs inventories in surface soils of Vietnam

Fallout 239+240Pu, 238Pu, 90Sr and 137Cs inventories in surface soils were measured for 20 locations in northern Vietnam yielding the mean values (± standard error) of 26.5±3.8 Bq m−2 for 239+240Pu, 1048±143 Bq m−2 for 137Cs and 212±28 Bq m−2 for 90Sr. The concentrations of 137Cs and plutonium isotopes strongly correlate with each other resulting in a stable 239+240Pu/137Cs inventory ratio of 0.025±0.002. Among soil parameters, organic matter and fulvic acids strongly correlate with caesium and plutonium isotopes, especially in the 0–10 cm layer. 137Cs and 239+240Pu are distributed rather similarly over the 0–10 cm and 10–20 cm layers. At locations with high contents of sand (82–93%) along the South China Sea coast, the downward percolation by rainwater results in a higher accumulation of 239+240Pu and 137Cs in the 10–20 cm layer. The mean 137Cs/ 90Sr inventory ratio is 9.3±2.2, and the correlation is weak between these isotopes.