Spatial variation of Cs-137 activity concentration in urban environment using attic dust samples from city of Salgotarjan in northern part of Hungary

*davaakhuu@caesar.elte.hu

The ¹³⁷Cs is a principal radioisotope introduced into the environment through the atmospheric bomb tests (from 50s to 60s) and the major nuclear accidents (Chernobyl, 1986 and Fukushima, 2011).  From atmosphere, ¹³⁷Cs adsorbs to precipitation and returns to lithosphere by wet and dry deposition as radioactive fallout component.  Due to the Chernobyl nuclear accident, the released contaminated air mass contained particles with attached Cs, largely propagated, deposited and distributed across northern and eastern European countries in the ambient environment (Balonov et al., 1996) in case of Fukushima disaster also contributes to the increase, but only by minor amount.  These particles could have reached the houses (e.g. through open windows, doors, fractures, and vents) in urban environment and deposited inside resulting in the exposition of the habitants to ¹³⁷Cs.  In areas that are not accessible for regular cleaning (e.g., attics) physical state and chemical composition of attic dusts remain constant i.e. unchanged in time.

Accordingly, undisturbed attic dust samples from Salgótarján (Hungary), a former heavy industrial city, were collected and studied as past records of anthropogenic pollution, with intention of elucidating the pathways of radioactive contamination in urban environment.

The specific activity of Cs-137 was measured in 36 attic dust samples.  Construction ages of the selected houses range from 1880 to1989, a selection criterion superimposed on the 1x1 km grid design. The Homogenized samples (amount: 1-1.5 g, grain size: <0.125 mm) were analyzed by a well-type HPGe detector placed in a low-background iron chamber at the laboratory of the Hungarian Center for Energy Research.  The obtained ¹³⁷Cs activity ranges from 4.34 ± 0.27 Bq/kg ^-1 to 140.74 ± 1.66 Bq/kg ^-1 (Detection limit: 0.75 Bq/kg ^-1).  Arithmetic mean of the values is 73.32 ± 1.58 Bq/kg ^-1, whereas geometric mean and standard deviation is 59 ± 1.36 Bq/kg ^-1 and 39.83 ± 0.76 Bq/kg ^-1, respectively (all decay corrected into year of sampling, 2016). Specific activity of radionuclide is higher than result published in other regions of Hungary and neighboring countries.  This confirms that attic dust is very effective material for monitoring past fallouts of production from early nuclear weapon testing and nuclear catastrophe(s).

Our results performed that a higher activity concentration of ¹³⁷Cs is found in the oldest houses (1890-1970) were present in the high elevated areas. Thus, it indicates that deposition of ¹³⁷Cs was strongly influenced by local physical conditions (geomorphology and meteorology).  Due to the geostatistical analysis, interpolation was done with ordinary point kriging using the obtained variogram model.  Adjusted model shows a best fit (r²=0.606) with spherical model.  The results of ¹³⁷Cs activity concentration suggest a good spatial dependency verifying our sampling strategy.  Therefore, it can be considered that attic dust remained undisturbed for decades and preserve past records of components of atmospheric pollution.

Keywords: attic dust, ¹³⁷Cs activity concentration, geostatistical analysis, urban environment, high altitude, Hungary

Reference:

Balonov, M., Jacob, P. és Minenko, V. (1996) Pathways, Levels and Trends of Population Exposure after the Chernobyl Accident, Radiological Consequences of the Chernobyl Accident.