97/00643 Metabolism and excretion of polycyclic aromatic hydrocarbons in rat and in human

Abstract

The radiocesium activity in soils and plants of undisturbed environments often shows an exceptionally high variability in soils and in the above-ground vegetation. To examine the underlying reasons, we selected a l ha alpine pasture area on a slope with 100 randomly selected sampling plots and assessed the 137Cs and 40K activity concentrations in soil and plants. The variability of the radiocesium values was high (coefficient of variance 43% for soil and 82% for plants) and the minimum number of samples taken was 57 for soil and 82 for plants, if an error in the median of 20% at the 95% confidence level is tolerable. Geostastistical evaluation of the data revealed that the activity concentrations of radiocesium in soils is randomly distributed, at least for a distance between 5 and 90 m, but the natural occurring 40K radionuclide showed a spatial dependence with a range of 75 m. In contrast, the radiocesium and also the potassium concentrations in mixed vegetation had a clear spatial dependency with a range of about 20 m (137Cs) or 25 m (K) and are not statistically significant associated with the 137Cs or K content in soil. Therefore changing plant communities are more responsible for the radiocesium concentration in vegetation than the soil concentration itself. On a mesoscale (100 m) level, no significant accumulation of radiocesium in relation to different slope conditions was found. Small scale (m) hollows, however, contained a higher amount of Chernobyl-derived 137Cs than small scale collines, but there was no statistically significant differences found for radiocesium from global fallout. It is concluded that the inhomogenous distribution of radiocesium is caused by a run-off phenomenon during the deposition of Chernobyl-derived 137Cs in May 1986 rather than by sediment redistribution in the last 35 years. The consequences of these results for soil-to-plant radiocesium transfer models based on soil/plant radiocesium concentrations or transfer factors are discussed.