Excessive radon-based radiation in indoor air caused by soil building materials in traditional homes on Đồng Văn karst plateau, northern Vietnam.

Radon-based radiation from natural soil building materials is an important factor likely influencing residents' health as a contributing source of natural radiation. This survey aims to quantify the nuclide-specific α-radiation of isotopes Rn and Rn in common types of houses in a region of northern Vietnam, Đồng Văn karst plateau, to preliminarily (i) evaluate the total annual effective dose rates and (ii) assess the relative risk of cancer induction from indoor α-radiation for inhabitants. The average Rn concentrations in all house types were lower than 100 Bq m, but Rn abundances were far higher than Rn, even up to >1000 Bq m in air close to a wall of unfired-soil bricks. The estimated total annual effective dose rates from indoor Rn and Rn and their progenies to residents with daily exposure of 13 h in the various types of houses range from 3.1 to 4.3 mSv a for houses constructed with modified materials, but up to higher than 6 mSv a in houses with raw building materials. The average risk of developing lung cancer as a consequence of a lifetime exposure to indoor α-radiation in affected homes ranges from 3.9% to 14.6%. Rn and its metallic progenies contribute more than 80% of the total average lung cancer risk from total radon, being responsible for a range of 2.7-14.6% of the risk of developing lung cancer.