complex assessment OF environmental radioactivity IN Yerevan

A. Nalbandyan

Center for Ecological-Noosphere Studies of the NationalAcademy of Sciences of Armenia, Yerevan, Republic of Armenia

Today, the issue of radioactive pollution of biosphere is acquiring a special topicality worldwide due to specificity of ionizing radiation. Rapid development of nuclear technologies and energy, nuclear weapon testing, accidents in nuclear power plants have brought to the occurrence of short- and long-living man-made radionuclides - environmental pollutants. Such pollutants are especially harmful for any living organisms, their habitats and biosphere as a whole as they may easily join the natural process of element turnover. All this dictates a necessity of complex radioecological environmental monitoring i.e. understanding of past and present observations, studying radionuclides transfer in the environment and assessing their impact upon the ecosystem [1].

This paper highlights the results of first ever complex radioecological research in system atmospheric precipitation-soil-plant performed in Yerevan - the capital of Armenia - a densely populated city located some 30 km far from the Armenian NPP.

Material and Methods

The study material – atmospheric precipitation, soil, plant and moss samples were collected in Yerevan. To comprehensively assess radioecological situation in the city, the author processed and analyzed data obtained in period 1969-1997 [2] alongside with sampling, field and lab sample treatment and analyses performed by her own in period 1998-2003. Collating all the data obtained for the entire study period, compiling relevant database, producing -radioactivity distribution maps are important constituents of this independent research aimed to getting an exhaustive picture of Yerevan environment radioactive pollution. Atmospheric precipitation samples were collected through the sedimentation method [2], soil, plant and moss samples - by the method developed at the V.V. Dokuchaev Soil Institute [3]. All the samples were processed and prepared for further analysis. 40K, 226Ra, 232Th, 210Pb, 137Cs concentration was determined through -spectrometric analysis on NaI(Tl) semi-conductor and HpGe detectors (Canberra, USA) using Genie-2000 computer software, 90Sr concentration – by -spectrometric analysis on NaI(Tl) detector (Progress, Russia). Gross -radioactivity measured on -radiometer RKB4-1eM (Russia). KCl was used as a calibration standard. Totally, processed, collated and interpreted were data on 408 atmospheric precipitation, 847 soil, and 22 plant and moss sample analyses. Based on the results, the Yerevan soil -radioactivity distribution maps (1:10000) were produced by the author using GIS Arc View 3.2 and Surfer 6.04 Programs.

Results and Discussion

The basic outcomes of this radioecological research in atmospheric precipitation-soil-plant system in period 1969-2003 in Yerevan are as follows:

1. Atmospheric precipitation: A)Radionuclide composition is mainly represented by 40K, 226Ra, 232Th, 137Cs, 90Sr. B) Gross -radioactivity level variations are timed to nuclear weapon testing in different regions of the world and global pollution. In period 1969-1977 (1st stage) -radioactivity level significantly varied: max value in 1971 (1857,4 Bq/m2/y), min. - in 1973 (111,0 Bq/m2/y), high indices were observed in 1974 (1073,8 Bq/m2/y) and 1977 (743,8 Bq/m2/y). In 1989-2001 (2nd stage) an inclination to -radioactivity level decrease and stabilization was established, mean value making 304 Bq/m2/y vs. 672 Bq/m2/y in 1969-1983 (Fig. 1).

The same is true for global radionuclides 90Sr and 137Cs which contents decreased by 36,6 and 45,5% at the 2nd stage, respectively.

2. Soils. A) As of 2000, Yerevan soils radionuclide composition is mainly represented by 40K, 226Ra, 232Th, 137Cs, 90Sr. In 2000 137Cs concentration decreased by some 20% vs. 1990. Wholly, the research results on soil radioactivity correlate to those on atmospheric precipitation.

B) In1990, Yerevan soils gross -radioactivity was distributed unevenly throughout the city: max. value 919 Bq/kg, min.– 538 Bq/kg (Fig.2). The analysis of soil gross -radioactivity in 2002 vs. 1990 testified to decrease of Yerevan radioactive pollution level and increase in areas characterized by natural background (500-600 Bq/kg). The produced Yerevan soil gross -radioactivity distribution map is included into General Urban Development Plan.

3. Plants. A) In period 1989-2001, 137Cs/90Sr ratios in plants averaged 5,2 vs. 1,9 in atmospheric precipitation, i.e. plants accumulate 137Cs which concentration is 5-9 times higher than that of 90Sr. B)As found out, relatively high gross -radioactivity level in plants depends on local man-made pollution, as well. In 2003, gross -radioactivity level insignificantly decreased vs. 2000: 1455 and 1556 Bq/kg respectively. -spectrometric measurements of moss samples (2000-2003) show that mosses accumulate larger amounts of radionuclides and particularly 137Cs vs. plants and thus may serve radioactive pollution indicators.

Conclusion

1. The first long-term radioecological monitoring shows that large urban centers like Yerevan are exposed to both global and local radioactive pollution. 2. The obtained data and compiled databases may underpin further relevant investigations. 3. The gained experience and developed research methods may be applied in long-term complex radioecological monitoring of urban sites.

References

  1. SHAW, G., 2002. Future needs in Radioecology. Intern. conf. on radioactivity in the environment, Monaco, ISBN 82-90362-14-5: 23-27.
  2. ANANYAN, V.L., L.A. ARARATYAN, 1990. Atmospheric precipitation, their chemical composition and radioactivity in Armenian SSR. Yerevan: 56-77.
  3. Methodological guidelines for geochemical assessment of pollution sources, 1987, Moscow: Publishing House of IMCGRE: 86 (in Russian).