Vertical distributions of 210Pb excess, 7Be and 137Cs in selected grass covered soils in Southeast Queensland, Australia

Net accumulated areal activity densities and profiles of 210Pbex, 7Be and 137Cs in the surface 10 cm of the soil are reported for eight sites in Southeast Queensland, Australia. Areal activity densities of 210Pbex and 7Be varied from 1080 to 4100 Bq m−2 and from 176 to 778 Bq m−2, respectively. A significant (p < 0.001) portion of the variance (R2 > 0.99) in their vertical distributions was explained by depth in the profile using an exponential function. Around 85% of accumulated 210Pbex was present in the surface 10 cm of the soil. Beryllium-7 was mainly confined to the grass and surface 2 cm of the soil. Average penetration half-depths of 3.6 ± 0.2 and 0.3 ± 0.1 cm were determined for 210Pbex and 7Be, respectively. Areal activity densities of global fallout 137Cs varied from 10 to 361 Bq m−2. Its signal was well mixed within the surface 10 cm. Comparison of the measured 137Cs values to the estimated input value for the region (∼490 Bq m−2) and profiling of a 1 m deep soil core suggests a vertical migration of 137Cs over the past decades.The paleo-radon activity flux determined from the 210Pbex areal activity density (5.1 ± 0.9 mBq m−2 s−1) was not statistically different to that measured using activated charcoal cups (5.5 ± 0.4 mBq m−2 s−1), tending to suggest that Southeast Queensland is neither a net source nor a net sink of 210Pb-bearing aerosols.