Hereditary effects of low and chronic radiation exposure: a case-control study of mental retardation and cleft lip/palate in the monazite bearing coastal areas of Southern Kerala

The high level natural radiation (HLNR) areas of Kerala in the south west coast of Kerala is suitable for direct human studies to assess the genetic and teratogenic effect of low and chronic radiation exposures. The radiation level in the region (about 55 km long and 0.5 km wide belt) range from ≤1.0 mGy to 45.0 mGy per year and is due to natural deposit of monazite sand containing Thorium (8-10%), Uranium (0.3%) and corresponding decay products. A population based case-control study was carried out in the area to assess the role, if any, of HLNR as a causative factor in the etiology of two relatively frequent and easily identifiable congenital malformations, viz., mental retardation (MR) and cleft lip/palate (CLP). Findings from the study are discussed in this paper