Air radioactivity Monitoring by Higher Plants

Abstract

Plants represent an important link in transport and distribution of radionu clides, heavy metals, and other pollu tants in the environment and are often used as biomonitors of atmospheric pol lution. In this paper, two deciduous tree genera, linden (Tilia tomentosa L. and Tilia cordata Mill.) and chestnut {Aesculus hippocastanum L), were analysed as biomonitors of radionuclides in air. The study was conducted in an urban area (the city of Belgrade, Serbia), from 2002 to 2009. The activities of radionuclides in soils, tree leaves and aerosols were determined on an HPGe detector (Can berra, relative efficiency 18 %) by stan dard gamma spectrometry. The mean activities of 137Cs, 40K,and 210Pb in soils were 34 Bq/kg d.w., 384 Bq/kg dw (dry weight), and 51 Bq/kg dw, respectively, while their mean acti vities in linden and chestnut leaves were 1.8 Bq/kg dw, 498 Bq/kg dw, and 46 Bq/kg dw, respectively. The mean ^Be activity in leaves was 125 Bq/kg dw. The activities in aerosols were of order 10-6 Bq/m3 for 137Cs, 10-4 Bq/m3 for 210Pb, and 10-3 Bq/m3 for 7Be. The calculated ”soil-to-leaves" transfer factors for 40K and 210Pb were 1.3 and

0.9, respectively. The transfer factor for i 137Cs was close to zero suggesting at- mospheric deposition as the primary mode of 137Cs accumulation in leaves. The 40K activity in leaves decreased towards the end of the growing season, reaching around 70 % of the spring maximum. The concentrations of 210Pb I and 7Be measured in leaves were both higher in autumn than in spring. However, the 210Pb activities increased throughout the growing season, while the 7Be activities reached the maximum in il summer. There were no significant differences in 5 the radionuclides' activities between J the different sampling sites and between the tree genera. A strong positive S correlation for 210Pb activities in linden leaves and in air during preceding months was obtained, suggesting that mature linden leaves could be used as | biomonitors of recent exposure to 210Pb. i, The seasonal pattern of the 7Be activity in leaves partly followed the seasonal pattern in aerosols, but no large positive a correlation was found.