90Sr IN SOME VEGETABLES COLLECTED IN

J. Kovac, G. Marovic, L. Petroci, J. Sencar

Institute for Medical Research & Occupational Health Radiation Protection Unit, Ksaverska cesta 2, P.O.Box 291, HR-10000 , Croatia

INTRODUCTION As part of the national survey of radioactivity level in the environment the Radiation Protection Unit of the Institute for Medical Research and Occupational Health in Zagreb has been regularly monitoring the presence of radioactivity in environmental samples. The focus of attention was mainly the content of radionuclides in human and animal food samples. Strontium (90Sr) is an artificial radionuclide, which has been released into environment by atmospheric nuclear bomb tests mainly in the late 50’s and early 60’s as well as (to a much lesser extent on a global basis) following the Chernobyl accident. It is a bone seeker, and its short-lived daughter, yttrium (90Y), which soon reaches equilibrium emits hard beta particles with a maximum energy of 2.3 MeV. Therefore, there is considerable interest in levels of 90Sr in food. Unfortunately, the determination of radiostrontium involves complicated chemical separations. Therefore, the number of determinations of 90Sr in various foodstuffs is small compared to the number of determinations of 137Cs. In order to assess retrospectively the levels of environmental contamination and thus to estimate the contamination of foodstuff, a ranges of methods have been developed[1-4]. Such methods have been created on the basis of a classical method. Among them are also the methods, which uses strong base anion exchangers and alcoholic solutions of nitric acid [5-6]. For the purpose of these investigations we used method recommended by IAEA[7].

EXPERIMENTAL To estimate the impact of radiostrontium on the radioactive contamination of the Croatian environment, as well as internal radiation doses to the Croatian population, investigations in this paper were focused on human foodstuff samples collected in different parts of Republic of Croatia.

The sites where the foodstuffs have been collected are:  Zagreb (4551' N, 1559' E), the capital of Croatia, with about 800 000 inhabitants,  (4406' N, 1515' E), the city located on the Adriatic seashore, and  Osijek (4533' N, 1842' E), the city situated at the eastern part of Croatia.

The collected samples involved potato for root vegetables, cabbage and lettuce as examples for green leafy vegetables and bean (kidney bean) for legumes. According to Statistical Yearbook of Republic of Croatia[8] consumed quantities of food in households (annual average per household member) for chosen vegetables are: - potato 42.80 kgy-1 - cabbage (with kalle) 9.66 kgy-1 - lettuce 13.91 kgy-1 - kidney bean (dry) 5.28 kgy-1

Food sampling was undertaken at the producers and subsequently at the retail market. The samples were cleaned and edible portions retained for analyses. Samples were dried in ovens at a temperature of 105°C for several days. After burned with a bunsen burner at an open fire, they were ashed at 600°C in electric muffle furnaces for about 24 hours. About 10-20 g of ashed sample was taken for analysis.

The ashed material is digested in concentrated nitric acid. Yttrium carrier solution (10 mg of yttrium per mL, as nitrate, standardized) is added to the purified strontium solution and, radiostrontium was isolated by extraction in TBP (tributylphosphate) and precipitated as yttrium oxalate. Yttrium was counted on in low background level anti-coincidence shielded GM counter. Counting time depended on 90Sr activity concentration in samples, but was never less than 80,000 seconds. The efficiency calibration was carried out using sources provided by the IAEA and WHO. The details of the chemical analysis are described elswere [9].

RESULTS AND DISCUSSION Contaminated plants are important link in the movement of radionuclides through the food chain leading to man. Soluble radionuclides in fallout can enter plants through the aboveground parts, i.e., leaves, steams, fruit, and bark, and also through the root, which is the principal nutrient absorbing organ.

The samples of potato, cabbage, lettuce and kidney beans were repeatedly collected by Institute’s staff during the harvesting period, for more than three decades. In this work are presented data for the last five years (from 1997 through 2001).

The concentrations of 90Sr determined in selected samples for that period on locations Zagreb, Zadar and Osijek are summarized in Figs. 1-3. Figure 1. Activity concentration of 90Sr in foodstuff collected in Zagreb

Figure 2. Activity concentration of 90Sr in foodstuff collected in Zadar Figure 3. Activity concentration of 90Sr in foodstuff collected in Osijek

The highest activity concentrations of 90Sr, regardless of the site of collection, over the investigated period, were measured in dry kidney beans samples. The highest value of all was determined in 1998 collected in Osijek (2.030±0.007 Bqkg-1). The lowest value was obtained in potatos samples (minimum was 15.6±9.9 mBqkg-1 in Osijek, 2001 and maximum was 101±17 mBqkg-1 in Zadar, 1999). Results for the lettuce and cabbage samples were some order of magnitude, ranging from 35±10 mBqkg-1 in lettuce to 521±65 mBqkg-1 in cabbage, both collected in Zadar, 2001.

On the basis of obtained data the assessment of the annual effective doses from 90Sr intake by ingestion of vegetables has been performed for an adult member of Croatian population according to IAEA Basic safety standards[10] and the public consumption habits in Croatia[8]. The dose conversion factor used for dose assessment was 2.810-8 SvBq-1. Figs. 4-6 shows annually effective doses from 90Sr intake for an adult member of Croatian population. Figure 4. Annual effective doses from 90Sr intake for an adult in Zagreb.

Figure 5. Annual effective doses from 90Sr intake for an adult in Zadar. Figure 6. Annual effective doses from 90Sr intake for an adult in Osijek.

CONCLUSION REMARKS The public consumption habits in the Republic of Croatia differ within the geographical regions, but vegetable consumptions are similar in spite of location (according to Statistical Yearbook). The assessment of the annual effective doses from 90Sr intake by ingestion of potato, cabbage, lettuce and bean shows that contribution of potato is same order of magnitude as that of bean. Although, the activity concentration of 90Sr in bean is an order of magnitude higher than that of potato, due to differences in intake of amount of vegetables (consumption of potato is about eight times higher than that of bean), the assessment of the effective doses from 90Sr intake by ingestion of these two vegetables, show that their contribution to annual effective dose is of same order of magnitude.

Concerning exposure from intake of radionuclides, the limit to members of the public is 1mSv a year[10]. In our study all the estimated doses are far below this value – yearly effective dose levels and, therefore, current risk for the population of Croatia associated with 90Sr ingestion of vegetables can be considered negligible.

However, the number of analysis is rather small and there are necessary further investigations as well as more detailed data on total diet, to make more reliable conclusions. REFERENCES

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