Estimating future radiocaesium contamination of fungi on the basis of behaviour patterns derived from past instances of contamination

Since 1987, 134Cs and 137Cs measurements have been carried out on about 350 samples of different fungal species which have grown in a coniferous Bavarian forest. It was established, through these measurements, that different fungal species have their mycelia in different soil horizons. Since the radiocaesium activity in these soil horizons changes with time, the activities of radiocaesium in different fungal species are also expected to behave differently over time. The time-dependent behaviour of the radiocaesium activity in mushrooms was therefore compared with the time-dependent behaviour of radiocaesium activity in certain soil horizons where mycelia of these species are located, for 14 species gathered in at least four different years. By means of least-squares regressions, non-time-dependent transfer factors with standard error levels of less than 20% were derived. Fungal species were identified in which radiocaesium contamination was decreasing, constant, or increasing. In the future, the mean radiocaesium activity will decrease giving ecological half-lives of between 3 and 8 years for all species. These results are useful for describing radiocaesium contamination of mushrooms in terms of generic models currently being developed for forest ecosystems.