No abstract

No abstract

Monitoring newborns for adverse outcomes like stillbirth and major congenital anomalies (MCA) is being carried out in government hospitals since 1995 in and around high-level natural radiation areas, a narrow strip of land on the southwest coast of Kerala, India. Natural deposits of monazite sand containing thorium and its daughter products account for elevated levels of natural radiation. Among 141,540 newborns [140,558 deliveries: 139,589 singleton, 957 twins (6.81 ‰), 11 triplets (0.078 ‰), and one quadruplet] screened, 615 (4.35 ‰) were stillbirth and MCA were seen in 1,370 (9.68 ‰) newborns. Clubfoot (404, 2.85 ‰) was the most frequent MCA followed by hypospadias (152, 2.10 ‰ among male newborns), congenital heart disease (168, 1.19 ‰), cleft lip/palate (149, 1.05 ‰), Down syndrome (104, 0.73 ‰), and neural tube defects (72, 0.51 ‰). Newborns with MCA among stillbirths were about 20-fold higher at 190.24 ‰ (117/615) compared to 8.89 ‰ (1,253/140,925) among live births (P<.001). Logistic regression was carried out to compare stillbirth, overall, and specific MCA among newborns from areas with dose levels of ≤1.5, 1.51-3.0, 3.01-6.0 and >6 mGy/year after controlling for maternal age at birth, gravida, consanguinity, ethnicity, and gender of the baby. Clubfoot showed higher prevalence of 3.26 ‰ at dose level of 1.51-3.0 mGy/year compared to 2.33 ‰ at ≤1.5 mGy/ year (OR01.39; 95 % CI, 1.12-1.72), without indication of any clear dose-response. Prevalences of stillbirth, overall MCA, and other specific MCA were similar across different dose levels and were relatively lower than that reported elsewhere in India, probably due to better literacy, health awareness, and practices in the study population.

The International Commission on Radiological Protection dose limits for radiation protection have been based on linearly extrapolating the high-dose risk coefficients obtained from the Japanese A bomb survivor data to low doses. The validity of these extrapolations has been questioned from time to time. To overcome this, epidemiological studies have been undertaken across the world on populations chronically exposed to low-radiation levels. In the past decade, the results of these studies have yielded widely differing, and sometimes, contradictory, conclusions. While recent residential radon studies have shown statistically significant radon risks at low doses, high-level natural radiation (HLNR) studies in China and India have not shown any low-dose risks. Similar is the case of a congenital malformation study conducted among the HLNR area populations in Kerala, India. It is thus necessary to make efforts at overcoming the uncertainties in epidemiological studies. In the context of HLNR studies, assigning radon and thoron doses has largely been an area of considerable uncertainty. Conventionally, dosimetry is carried out using radon concentration measurements, and doses have been assigned using assumed equilibrium factors for the progeny species. Gas-based dose assignment is somewhat inadequate due to variations in equilibrium factors and possibly due to significant thoron. In this context, passive, deposition-based progeny dosimetry appears to be a promising alternative method to assess inhalation doses directly. It has been deployed in various parts of India, including HBRAs and countries in Europe. This presentation discusses the method, the results obtained and their relevance to dose assignment in Indian epidemiological studies.

No abstract