Possible use of airborne radionuclide content in soil and biomonitors

Transcription

1 Possible use of airborne radionuclide content in soil and biomonitors M. Krmar, D. Radnović 2, J. Hansman, N. Todorović, M. Velojić 3 Department of Physics, Faculty of Science, University Novi Sad, Novi Sad, Serbia 2 Department of Biology, Faculty of Science, University Novi Sad, Novi Sad, Serbia 3 PC Vojvodinašume, Petrovaradin, Serbia

2 Several radionuclides can be a useful tool for the investigation of transport processes in the atmosphere General idea to use terrestrial mosses to check possible temporal and spatial variations in atmospheric deposition over some relatively large area

3 Concentrations of radionuclides in air are measured by taking air samples and collecting aerosol particles on filter paper. After sampling, the raw filter paper or it s ash is measured by gammaray spectrometric detection systems The final result is the concentration of particular radionuclide in surface air (in Bq/m 3 ) Precipitation is usually collected by different fallout vessels and after some chemical procedure or evaporation, the gamma spectra of sample is measured The final result of this method is activity of fallout (in Bq/m 2 ) for the sampling time interval

4 N p 4 Be N n Be Li Once produced, Be atoms are almost immediately adsorbed onto aerosol particles He Aerosol particles are the most important reservoir of air pollutants, Be can be used in tracking their atmospheric paths and fallout. 6 O p Be B O p Be Li 8 6 O n Be Cosmogenic Be is a natural tracer not altered by anthropogenic activities 0 4 Be O n Be He He 4 2 He

5 Be is mainly formed in the stratosphere (about 6%) and higher layer of the troposphere (remaining 33%). Variations in Be production are associated with changes of the cosmic ray flux Cannizzaro, F., Greco, G., Raneli, M., Spitale, M.C., Tomarchio, E., Concentration measurements of Be at ground level air at Palermo, Italy comparison with solar activity over period of 2 years. Journal of Environmental Radioactivity 2, 259-2

6 Seasonal variations are determined by interaction between upper troposphere and lower stratosphere, precipitations, winds, etc. Daish, S.R., Dale, A.A., Dale, C.J., May, R., Rowe, J.E., The temporal variations of Be, 20Pb and 20Po in air in England. Journal of Environmental Radioactivity 84, 45-46

7 20 Pb is only one long-living daughter of 222 Rn which emanates from the soil. It is also released from industrial processes (ores sintering, coal fired power stations, agricultural fertilizers)

8 20 Pb variations depends on atmospheric conditions and status of soil (wet, snow, dry) Aldahan, A., Possnert, G., Vintersved, I., 200. Atmospheric interactions at northern high latitudes from weekly Be-isotopes in surface air. Applied Radiation and Isotopes 54,

9 Deposition of 3 Cs emitted in atmosphere + soil 3 Cs resuspension Ionidiu A., and Papastefanou C., (2006) Precipitation scaveniging of Be and 3Cs radionuclides in air, Journal of Environmental Radioactivity, 85, 2-36

10 Air sampling and precipitation can provide good evidence on radionuclide concentration or variations during a long time period at one fixed place. The spatial resolution of radionuclide distribution over large area is limited by the number of air or precipitation sampling centers. Mosses could be a good sampling medium for detection of radionuclides accumulated through some period. Moss sampling is a relative simple and inexpensive procedure, and a very dense network of sampling sites can be established to provide excellent spatial resolution. Preparation of the collected material is very simple, there is no need for chemical extractions and gamma spectra can be taken from the bulk samples.

11 Same place 4 months (time variation) Moss samples were taken every week, beginning from to Sampling location - horizontal roof over the entrance of the Biology Department building in Novi Sad, Serbia. Measurements low background Extended Range HPGe detector shielded by lead. New results

12

13 Gamma spectroscopy measurements of moss samples were carried out using high resolution HPGe detector (2.0 kev at 332 kev) with a relative efficiency of 22.5%, shielded by 25 cm thickness of pre-wwii iron was used in measurements. The integral background count rate, from 30 to 3000 kev was about.2 counts per second. Time of measurements up to 66 ks. Mass of dry samples from 9 to 40 grams. Standard cylindrical geometry d = 6 mm, h = 32 mm

14

15 Pb Monthly averaged values 20 Pb [Bq/kg] months 20 Cs 3 Cs [Bq/kg] months

16 25 Bi Bi [Bq/kg] months Be Be [Bq/kg] months

17 Average Be concentration and cumulative monthly precipitation (times 0) [mm] Be- prec. X 0 Be-

18 Average Be concentration and cumulative monthly duration of precipitation (divided by 0) [min] Be- dur. / 0 2 Be-

19 Same time different sampling sites (spatial distribution) Hypnum cupressiforme were collected in two days (26-th and 2-th October 2005) from 9 sampling sites distributed along the one direction. The sampling sites followed about a 400 km long route of the International Freeway E5. The sampling sites were located from 42º26 9 N to 45º23 2 N and from 9º35 9 E to 22º8 20 E. M. Krmar, D. Radnovic, S. Rakic, M. Matavuly: Possible use of terrestrial mosses in detection of atmospheric deposition of Be over large areas, Journal of Environmental Radioactivity, 95, (200) 53-6

20 Terrestrial mosses contain a measurable activity of Be. The lowest measured value of Be activity per unit mass of dry plant material was 95(24) Bq/kg and the highest one was 560(40) Bq/kg.

21 SUGESTION Use moss samples to map areal distribution of airborne radionuclides at some large area. It can provide information about pattern of atmospheric aerosol deposition. Be is uniformly produced, however deposition should not be uniform. Maybe some local conditions have significant influence on deposition. Other aerosol pollutants probably will follow the very same areal pattern.

22 Soil erosion is one of the most significant problems, especially in countries having limited resources and high growing population. It is estimated that in 0 years about % of cultivated soil is destroyed by erosion. Another consequence of erosion is degradation of the quality of water resources (after deposition of eroded soil and applied agricultural chemistry) Quantitative description of the erosion effects by the use of radionuclides is one of the must reliable

23 3 Cs is most frequently used radionuclide in qualitative and quantitative estimation of soil erosion. Global distribution of 3 Cs occurred during fifties and sixties years of last century after a number of atmospheric tests of nuclear weapon, mostly at northern hemisphere. Wet and dry deposition moved 3 Cs from atmosphere to the ground. Due to high adsorption affinity of Cesium, all 3 Cs is fixed in surface layers of the soil.

24 3 5 [Bq/kg] uncultivated 3 Cs tot =83 Bq/m 2 3 Cs depth distribution at referent locations 9 [cm] [Bq/kg] Cs [cm] cultivated 3 Cs tot =52 Bq/m 2

25 [cm] [Bq/kg] Cs Referent location 83 Bq/m2 [cm] 2960 Bq/m [Bq/kg] [cm] Bq/m 2 Uncultivated soil [Bq/kg] Bq/m 2

26 [cm] Cs [Bq/kg] [cm] Referent location 83 Bq/m Bq/m 2 [Bq/kg] [cm] Bq/m 2 Cultivated soil [Bq/kg] Bq/m 2

27 Proportional model B d X Y 0 00 T P Y = mean annual soil loss (t ha- yr-); d = depth of the plough or cultivation layer (m); B = bulk density of soil (kg m-3); X = percentage reduction in total 3Cs inventory (defined as (Aref-A)/Aref 00); T = time elapsed since the initiation of 3Cs accumulation or the commencement of cultivation, whichever is later (yr); Aref = local 3Cs reference inventory (Bq m-2); A = measured total 3Cs inventory at the sampling point (Bq m-2); P = particle size correction factor for erosion. Mass balance model Y 0 d B P X 00 /( t 963 )

28 Profile distribution model ( for uncultivated soil) ` x h0 A ( x ) A ref ( e ) A(x) = amount of 3 Cs above the depth x (Bq m -2 ); A ref = 3 Cs reference inventory (Bq m -2 ); x = depth from soil surface (kg m -2 ); h 0 = coefficient describing profile shape (kg m -2 ) y 0 ( t 963) P ln( X ) 00 Y = annual soil loss (t ha - yr - ); t = year of sample collection (yr); X = percentage 3 Cs loss in total inventory in respect to the local 3 Cs reference value (defined as (A ref -A u )/A ref 00); A u = measured total 3 Cs inventory at the sampling point (Bq m -2 ). h 0

29 Cs [Bq/kg] In last several years 20 Pb (unsupported, excess) was used for examination of soil erosion. [cm] [Bq/kg] Referent location [cm] 9 20 Pb Uncultivated soil 3 5 9

30 [cm] [Bq/kg] Pb uncultivated [cm] Pb tot =356 Bq/m 2 [Bq/kg] Depth distribution 20 Pb cultivated 20 Pb tot =4042 Bq/m 2

31 SUGESTION 2 Soil & Tillage Research 69 (2003) 3 3 The use of environmental radionuclides as tracers in soil erosion and sedimentation investigations: recent advances and future developments Felipe Zapata Soil and Water Management & Crop Nutrition Section, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, International Atomic Energy Agency, P.O. Box 00, Wagramer Strasse 5, A-400 Vienna, Austria Limitations Need for a multidisciplinary team for the successful application of the technique. This is a particular limitation in most developing countries with limited scientific staff. Specialized laboratories with sample preparation and costly gamma counting equipment are required. Requirements for quality assurance/control of low level gamma spectrometry measurements. There are uncertainties associated with the selection of the conversion models used to estimate erosion and deposition rates from the 3 Cs measurements. The technique needs further standardization of the protocols for its worldwide application.

32 INTERNATIONAL COOPERATIVE PROGRAMME ON EFFECTS OF AIR POLLUTION ON NATURAL VEGETATION AND CROPS publications.htm metals_report_pdf.htm

33 Cu -2006

34 2006

35 SUGESTION 3 For more serious quantitative treatment of data obtained in moss survey, it is necessary to have information regarding efficiency of heavy metal collection by mosses. How to calibrate mosses??????? Both soil and mosses have some kind of memory. They collect and trap airborne radionuclides ( 20 Pb). Comparison of effect of soil and moss accumulation of 20 Pb was not studied before.

36 A soil = measured total soil 20 Pb inventory at the sampling point (Bq m -2 ). B = flux of 20 Pb deposition (Bq m -2 year - ) B A soil

37 A moss = total 20 Pb inventory in moss collected at the sampling point (Bq m -2 ) R moss = areal density of collected moss (kg m -2 ) A moss k B R moss k A soil R moss To check possible relation between 20 Pb moss inventory and 20 Pb deposition flux, estimated by measurement of 20 Pb soil inventory, more reliable measurements should be done. A moss [Bq/m 2 ] B R moss [Bq/m 2 y][kg/m 2 ]