Population exposure to airborne thorium at the high natural radiation areas in India

High natural radiation areas in the coastal and peninsular India were studied for airborne thorium and resultant population exposure due to inhalation. Four locations covering three states viz., Ayiramthengu and Neendakara in Kerala, Kudiraimozhi in Tamil Nadu and Bhimilipatnam in Andhra Pradesh were investigated. External gamma radiation fields 1 m above the monazite ore bodies ranged from 200 to 3000 nGy h(-1). Soil samples showed Th-232 specific activity varying from 0.1 to 1.5 Bq g(-1) with surface alpha activity in the range of 1.0-12.5 Bq cm(-2). Suspended particulates in the samples ranged from 60-140 mu g m(-3) with Th-232 showing a wider variation of < 0.03-0.3 mBq m(-3). There was poor correlation between suspended particulates and long-lived alpha airborne activity (r = -0.3). The resuspension factors for Th-232 were in the range of 1.5 x 10(-8)-7.9 x 10(-7) cm(-1). Higher resuspension was correlated with dry sand dunes, The upper limits for Committed Effective Dose (CED) due to inhalation of airborne Th-232 at the respective high natural radiation areas were estimated to range from 50 +/- 30 to 300 +/- 130 mu Sv (5-30 ml ent) per pear per adult member of public assuming an activity median aerodynamic diameter of 1 mu m for the air borne particulates. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.