Lichens as monitors of radiocesium and radiostrontium in Austria

Many areas of Austria were contaminated to various degrees with radionuclid es, following the reactor accident in Chernobyl. In Styria, a province of A ustria, the Cs-137 activity in lichens rose to over 50 kBq kg(-1) from an i nitial value of 0.4 kBq kg(-1) dry weight before Chernobyl. The Cs-137 cont amination of Pseudevernia furfuracea exceeded the natural radioactivity of K-40 up to 430 fold. The ecological half-life of Cs-137 in Pseudevernia fur furacea which grows on spruce was found to be approximately 3 years, wherea s 3.8 additional years were needed to reach a fourth of the initial Cs-137 activity. The half-life of Cs-134 was found to be 1.3 and that of Sr-90 was between 1.2 and 1.6 years. The corresponding values for the terricolous li chen Cetraria islandica were 2.5 year for Cs-137 and 1.2 for Sr-90. The Cs- 137 levels were found to vary even within short distances. Two reasons, oth er than the uneven distribution of the radioactive precipitation, are given here for this observation. Pseudevernia, which grew on dead trunks, was co ntaminated about three times as much at the top end of the trunk as in the lower sections of the tree. This was due to the fact that the rainfall was rather vertical shortly after the Chernobyl accident, so that the upper lic hens adsorbed the main part of the radionuclides. Secondly, on a mountain s lope, the Cs-137 level was shown to increase with altitude. This was becaus e it rained slightly more in the higher regions shortly after the Chernobyl accident and because of the shorter vegetation period. A good indication o f the high levels of contamination through various gamma-ray emitting radio nuclides following the reactor accident is also given here by the levels re ached by those radionuclides in a soil sample from Graz, capital of Styria. In this sample the activity of all gamma emitting radionuclides was 1654 k Bq m(-2). Cs-137 showed 2.8% of the overall radioactivity, the correspondin g value for Cs-134 was 1.1%. (C) 1999 Published by Elsevier Science Ltd. Al l rights reserved.