Radioactivity of Vegetables and Mushrooms in Finland After the Chernobyl Accident in 1986
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%>- STUK-A59 June 1987 RADIOACTIVITY OF VEGETABLES AND MUSHROOMS IN FINLAND AFTER THE CHERNOBYL ACCIDENT IN 1986 Supplement 4 to Annual Report STUK A55 Aino Rjntiiv.'Mrc) $ät*llyturvakÄ*ku« gfiF vJ" *CG*y ^ s^*y ? ^P^T* WMmj $r/$s -H^nki, Finland If «^ STUK-A59 June 1987 RADIOACTIVITY OF VEGETABLES AND MUSHROOMS IN FINLAND AFTER THE CHERNOBYL ACCIDENT IN 1986 Supplement 4 to Annual Report STUK-A55 Aino Rantavaara Finnish Centre for Radiation and Nuclear Safety P.O.Box 268, SF-00101 HELSINKI FINLAND ISBN 961-47-0490-8 ISSN 0781-1706 Helsinki 1987. Valtion painatuskeskus ABSTRACT The Finnish Centre for Radiation and Nuclear Safety determined gamma-emitting radionuclides in vegetables, fruit and mushrooms in the growing season of 1986. About 780 samples of the most common species were collected during six months in locations which represent different fallout areas of radioactivity. The samples were analysed for the gamma-emitting substances by semiconductor-spectrometry. 89Sr and 90Sr were determined radiochemically in a limited number of vegetable and berry samples. Early in May 1986, 131I and other short-lived radionuclides were dominating. Later in the sampling season, the most important substances detected were 13 *Cs and x3 7 Cs. The lowest con centrations of 137Cs were measured in leafy and fruit vegetables, root crops and potatoes, 0.3 - 8 Bq kg-1 on an average, depending on the species. In garden berries the nationwide mean 137Cs concentrations were 10 - 30 Bq kg*1 and in wild berries 80 - 120 Bq kg'1 . The average concentrations of i37Cs in different types of mushrooms varied from 220 to 1100 Bq kg'1 . The contents of 90Sr In vegetables and berries were about the same or slightly higher than in the previous years. The dally intake of 137Cs via the products studied was estimated using nationwide production-weighted mean contents of :37 Cs in 4 different species and data on the average consumption of foodstuffs. Fruit and vegetables of the season 1986 contributed 3.4 Bq d" to the dietary intake and mushrooms about 1 Bq d'1 . The effects of processing on vegetables and fruits were not taken into account in the intake calculations. The dietary intake of radionuclides other than 134 Cs and 137 Cs via the produce of season 1986 was very small. 5 CONTENTS ABSTRACT 3 CONTENTS 5 1 INTRODUCTION 1.1 Objective of the surveillance 7 1.2 Effects of the fallout on vege tables, fruit and mushrooms 8 2 MATERIAL AND METHODS 2.1 Sampling 9 2.2 Sample analysis 2.2.1 Gammaspectrometric deter minations 11 2.2.2 Determination of " Sr and »°Sr 12 2.3 Experiments on the effects of household practices 12 2.4 Data treatment 2.4.1 Background Information on the areal distribution of radioactive fallout 13 2.4.2 Background information on the areal distribution of yields 13 2.4.3 Nationwide means for radiocesium contents in different produce 14 2.4.4 Calculation of intake 16 RESULTS 3.1 Radioactive substances found 18 3.2 Concentrations 18 6 3.3 Effect of common types of household treatment on the amounts of radio active substances 19 3.4 Estimates of intake 20 4 DISCUSSION 4.1 Radioactive substances found 21 4.2 Radiocesium concentrations 21 4.3 Intake of radionuclides via vegetables, fruit and mushrooms 23 4.4 Recommendations to the public 24 5 ACKNOWLEDGEMENTS 20 REFERENCES 27 FIGURES 29 TABLES 39 7 1 INTRODUCTION 1.1 Objective of the surveillance As the national authority responsible for the research and monitoring of the environmental radioactivity, the Finnish Centre for Radiation and Nuclear Safety (STUK) regularly follows the radioactivity of fruit and vegetables, among other things. The objective of the surveillance is to estimate the radiation dose received by the Finns through foodstuffs. Vegetables have been monitored regularly since 1975 x . After the accident at the Chernobyl nuclear power plant, Finland consequently received a radioactive fallout which affected the country rather unevenly. Based on the first analyses of the fallout radioactivity in the spring 1986 it was evident that the edibility of the domestic vegetables and fruit would not be threatened by the fallout. However, the fallout situation as such and the regional variation in the fallout, especially, necessitated a wider study on vegetables, fruit and mushrooms than had been made In previous years. In May 1986, STUK in co-operation with the National Board of Trade and Consume Interests initiated an extensive country-wide survey of the concentrations of radioactive substances in vege tables, fruit and mushrooms harvested in 1986. The National Board of Trade and Consume Interests collected about two-thirds of the samples. STUK collected one third and analysed all the samples and prepared both the Interim report 3 and this final report. The different sampling and analysing programs already undertaken by STUK contribute to give a comprehensive picture of the fallout situation. Therefore, a substantially smaller number of samples in this study could be accepted than in Independent studies generally. 8 1.2 Effects of the fallout on vegetables, fruit and •ushrooas At the time of the fallout in the spring of 1986, the ground was still partly frozen and the outdoor growing season had not yet begun in Finland. The fields had not been ploughed yet. Only cereals and vegetables sowed or planted in the autumn were exposed directly to radioactive fallout. The earliest wild vegetables, the mushrooms Gyromitra esculenta and the leeks that had wintered in gardens or fields were in places exposed to the direct surface fallout. Perennial plants, for example berry bushes, also absorbed soluble radioactive substances from the spring fallout directly through their epithelium. The radioactive substances deposited on the soil were later mixed with the ploughing layer. Most cultivated vegetables took up radionuclides primarily with nutrients from the soil and, to some extent, externally from dust rising from the ground. Therefore, substantially lower amounts of radioactive substances accumulated in vegetables than if the fallout had occurred later, during the growing season. When the fallout radionuclides occured in the surface air in spring 1986, the early greenhouse vegetables were at the harvesting stage. A detectable contamination of vegetables with radioactive substances could mainly occur through ventilation air and, in some cases, watering with surface water. Besides the time of the year other factors affecting the concentrations of radioactive substances of the fallout in vegetables, fruit and mushrooms are the cultivation method, the type of soil and the nutrient contents of the soil, the length of the growing season, the time the sample is taken in the growing season, the type of the edible part of the plant and the typical element composition of the species of plant concerned. 9 MATERIAL AND METHODS 2.1 Sampling The samples were taken primarily in connection with the sampling for a survey of pesticide remnants carried out by the National Board of Trade and Consume Interests. STUK organized one third of the sampling. The major part of the berry and mushroom samples from the Province of Lapland was collected by the Northern Finland Research Station of STUK. Most samples were collected in the provinces that received the actual fallout, that is, south of the Province of Oulu and west of North Karelia (Figs. 1-2). The sampling in the fallout area was so directed that the regional distribution of production was also taken into account. The purpose was not to examine thoroughly all possible species, nor to study the variation in the radioactivity of vegetables and mushrooms within individual municipalities. Samples were taken from the most Important cultivated vegetables, berries and apples, and also from wild berries, mushrooms, wild salad vegetables and herbs. Different groups of products were represented in the following way: Sample group Number of Number of species analysed samples Leafy vegetables, cabbages and herbs 8 84 Fruit vegetables 5 45 Root vegetables, onions and leek 7 41 Potato 1 40 Pea and bean 2 11 Wild salad vegetables and herbs 4 8 10 Sample group Number of Number of species analysed samples Rhubarb Garden berries Strawberries 1 73 Dush berries 6 83 Apples 1 17 Wild berries 7 150 Mushrooms 32 known 205 species The number of samples per species varied from one to a few dozen. In all, 580 vegetable and 205 mushroom samples were analysed. Up to the midsummer, all the samples of leafy vegetables were collected from greenhouses and thereafter they were also taken from fields and gardens. Tomato and cucumber are grown in greenhouses throughout the season. The samples of cultivated vegetables were, in general, fetched from the farmers or gardeners who produce them and the samples of wild products were either delivered by local pickers or collected directly from the habitats. The sampling took place at different times of the season (Table 1). The study on vegetables and mushrooms undertaken jointly with the National Board of Trade and Consume Interests started after the middle of May and continued until the end of October. Early in May, STUK had studied the radioactivity of early outdoor vegetables and the mushroom Gyromitra esculenta 3. The preliminary estimates of the concentrations of radioactive substances in vegetables, fruit and mushrooms were based on samples collected before the harvest-time of the main crop. In 1986 the growing season was from one to three weeks ahead of the normal summer. This made it necessary to take additional samples at the beginning of the season, especially in the case 11 of berries. The normal timing of sampling would not have given the information to satisfy the great public demand. The sampling of mushrooms was initiated with common edible mushrooms picked in a few provinces.