Activity concentration of ¹³⁷Cs in undisturbed attic dust collected from Salgótarján and Ózd (northern Hungary)

Due to the Chernobyl nuclear power plant accident, contaminated air masses, containing ¹³⁷Cs, were widely propagated across all of Europe. Cesium-137 is easily adsorbed on aerosol particles as it returns to the lithosphere/pedosphere/via wet and dry deposition in the form of a radioactive fallout component. Following the nuclear accident, primary attention was paid to agricultural areas and less to urban environments. Our ¹³⁷Cs activity study using undisturbed attic dust samples has been carried out from two residential areas (city of Salgótarján and Ózd) in northern Hungary, approx. 1000 km away from Chernobyl. A total of 61 attic dust samples were collected in 2016 and 2018 from houses (>30 years) functioning as family house, kindergarten, blockhouse and church. Activity concentration of ¹³⁷Cs was determined for 1-2 g homogenized (<125 μm) attic dust samples in a low background iron chamber with a well-type HPGe detector. The mean ¹³⁷Cs activity concentrations in attic dust samples are 88.5 ± 5.1 Bq kg^-1 and 87.8 ± 4.5 Bq kg^-1 in Salgótarján and Ózd, respectively. The dependence between ¹³⁷Cs activities and the age of the houses was found to be significant (p=0.02), which could be explained by Chernobyl nuclear accident-causing elevated activity concentrations in location built prior to the accident. Three outliers in Ózd (>223 Bq kg^-1), are probably related to the first rainfall event after the Chernobyl accident. Isotopic landscapes (isoscapes) of ¹³⁷Cs were derived for both cities by means of kriging interpolation. In Salgótarján the ¹³⁷Cs activity concentrations were higher than in Ózd which might have been due to redistribution loadings and local topographical features. We concluded that components of attic dust are highly useful indicators of home exposure to pollution events and remain detectable after several decades.