Cesium-137 concentration of soils in Pest County, Hungary

Abstract

This paper presents the results of measurements of 137Cs in soils in Pest County, Hungary. We investigated forty five soil monoliths from monitoring locations of a countrywide Soil Information and Monitoring System (SIMS) at depths of 0–30, 30–60, 60–90, 90–120 and 120–150 cm. The 137Cs concentrations were determined by gamma spectroscopy. We found that only the upper layer of soil (0–30 cm) contained 137Cs above the detection limit (0.5 Bq kg−1). The 137Cs concentration values ranged from the detection limit to 61.1 Bq kg−1 ± 2.2 Bq kg−1 and were lognormally distributed. The concentrations had a geometric mean 6.4 Bq kg−1 and a geometric standard deviation 2.3 (an arithmetic mean 9.5 Bq kg−1, an arithmetic standard deviation 11.3 Bq kg−1). We constructed a 137Cs map for Pest County this is the first detailed 137Cs map in Hungary. Concentrations were systematically higher (10.0–61.1 Bq kg−1) than average in the Pilis and Buda Mountains and the Northern part of the Gödöllő Hills. In contrast, low concentrations (0.0–10.0 Bq kg−1) characterized the southern part of the Gödöllő Hills, the Pest Plane and the Börzsöny Mountains. Two highest values were 46.9 Bq kg−1 and 61.1 Bq kg−1: one of these localities, a loamy brown forest soil was chosen to study relationship between 137Cs migration and clay materials of the soil. According to differential thermal analysis (DTA) and x-ray diffraction (XRD) analyses, illite and kaolinite were dominant in the soil. The amount of clay was closely proportional to 137Cs concentration (R = 0.89). At the locality having the highest surface concentration, 78% of the total detected 137Cs concentration was measured in the top 3 cm layer of soil profile and there was no detectable concentration below 20 cm. This result indicates that penetration of 137Cs into the soil is a very slow process in this case. Analysis of this depth profile showed lower 137Cs migration parameter values (effective diffusion coefficient and migration velocity) than predicted in a previous study for brown forest soils in the same area of Hungary.