Retrospective determination of 137Cs specific activity distribution in spruce bark and bark aggregated transfer factor in forests on the scale of the Czech Republic ten years after the Chernobyl accident

The 137Cs specific activities (mean 32 Bq kg−1) were determined in spruce bark samples that had been collected at 192 sampling plots throughout the Czech Republic in 1995, and were related to the sampling year. The 137Cs specific activities in spruce bark correlated significantly with the 137Cs depositions in areas affected by different precipitation sums operating at the time of the Chernobyl fallout in 1986. The ratio of the 137Cs specific activities in bark and of the 137Cs deposition levels yielded bark aggregated transfer factor Tag about 10.5 × 10−3 m−2 kg−1. Taking into account the residual specific activities of 137Cs in bark 20 Bq kg−1 and the available pre-Chernobyl data on the 137Cs deposition loads on the soil surface in the Czech Republic, the real aggregated transfer factor after and before the Chernobyl fallout proved to be T*ag = 3.3 × 10−3 m−2 kg−1 and T**ag = 4.0 × 10−3 m−2 kg−1, respectively. The aggregated transfer factors T*ag for 137Cs and spruce bark did not differ significantly in areas unequally affected by the 137Cs fallout in the Czech Republic in 1986, and the figures for these aggregated transfer factors were very similar to the mean bark Tag values published from the extensively affected areas near Chernobyl. The magnitude of the 137Cs aggregated transfer factors for spruce bark for the pre-Chernobyl and post-Chernobyl period in the Czech Republic was also very similar. The variability in spruce bark acidity caused by the operation of local anthropogenic air pollution sources did not significantly influence the accumulation and retention of 137Cs in spruce bark. Increasing elevation of the bark sampling plots had a significant effect on raising the remaining 137Cs specific activities in bark in areas affected by precipitation at the time when the plumes crossed, because the sums of this precipitation increased with elevation (covariable).

Research Highlights► Current 137Cs activities in bark indicate Chernobyl radioactive fallout loads. ► 137Cs transfer from soil to bark is not affected by soil activities of 137Cs. ► Elevation as a factor affecting wet 137Cs deposition and stand pollution. ► An estimate of pre-Chernobyl soil-bark transfer factor for 137Cs.