Acute and long-term effects of irradiation on pine (Pinus silvestris) strands post-Chernobyl.

The effect of ionizing irradiation on the viability of pine stands after the fallout from the damaged nuclear energy plant at Chernobyl (ChNPP) was shown within the territory of the 10-km zone. During the period 1986-1991, irradiated and damaged forest stands, so-called 'red forest', located in this area were systematically classified by observation. Mortality rate, re-establishment, development of tree canopies, reproduction anomalies and stand viability were shown to be dependent on absorbed irradiation dose, on the age of the stand and on forest composition. For pine stands in the acutely affected zone, doses of more than 60 Gy resulted in a massive mortality and no regeneration of pine trees since 1987. The injured trees had burned or had dried-up. The drying process was accelerated by a massive production of pathogenic insects invading the dying trees. Specifically, irradiation doses of 10-60 Gy, 1-10 Gy and 0.1-1 Gy caused high, medium and low injury to the forest stands, respectively. Doses of less than 0.1 Gy did not cause any visible damage to the trees. In 1987, repair processes were displayed by the tree canopies and practically the entire viability of the forest stands had recovered except for trees in the acute and highly affected zones. The young forest was reestablished in the same place as the perished trees and new pine saplings were planted on the reclaimed areas.

[Mutagenesis of enzyme loci, induced in megaspores of Pinus sylvestris L. by ionizing radiation from the accident at the Chernobyl Atomic Power Plant]. / Mutagenez ferementnykh lokusov, indutsirovannyi v megasporakh Pinus sylvestris L. ioniziruiushchim izlucheniem pri avarii na Chernobyl'skoi AES.

Mutagenesis of alleles of 20-allozyme loci was studied using the electrophoresis methods in polyacrylamide gel in seeds of Pinus sylvestris within the 30 km zone of the Chernobyl NNP and the limits of contamination levels by Cs-137 from 5 up to 600 Cu/km (the absorbed doses being 0.5 to 10 Gy). The frequency of emergence of corresponding mutations which change the synthesis of enzymes in endosperms within the zone constituted on the average 2.7-10 per gene as compared with 0.6-10 in control version. Linear dependence was observed between low doses absorbed and the frequency of gene mutations, while in case of high doses this decreased. Genetic effectivity was 0.001 mutations/locus/Gy. Various radiosensitivity levels were shown among the loci studied. Spontaneous level of mutations frequency in P. sylvestris populations was found to be within the limits of 0.5 to 1.5 Gy under conditions of the 30 km zone. The high rate of mutagenesis was revealed in seeds of the first two post-accident reproductions.

137Cs mobility in soils and its long-term effect on the external radiation exposure.

To predict the external gamma-dose rate of Chernobyl-derived 131Cs for a period of about 100 years after its deposition, the vertical distribution of radiocesium in several meadow soils in the Chernobyl area and in Germany was determined, and the corresponding residence half-times of his radionuclide in the various soil layers were evaluated using a compartment model. The resulting residence half-times were subsequently used to calculate the vertical distribution of 137Cs in the soil as a function of time and finally to predict the external gamma-dose rates in air for these sites at various times. A regression analysis of the data obtained showed that the time dependence of the relative gamma-dose rate in air D(t) at the Chernobyl sites can be described by an exponential equation D(t) = a + b x exp (-t/c), where t is the time after deposition. For the ten German sites the best fit was obtained using the two-exponential equation D(t) = a x exp(-t/b) + c x exp(-t/d). The gamma-dose rate of 137Cs at the Chernobyl sites decreases significantly more slowly with time than at the German sites. This means that after e.g. 30 years the mean relative gamma-dose rate at the German sites will have decreased from 100% (corresponding to an infinite plane source on a smooth surface) to 9% (95% confidence interval 8%-10%), while at the sites in the Chernobyl area it will have decreased only to 21% (20%-23%). This difference is the result of the longer residence half-times of 137Cs in the soils at the Chernobyl sites. All results are compared with estimates from earlier studies.