Background Radiation and Cancer Incidence in Kerala, India—karanagappally Cohort Study

Abstract

The coastal belt of Karunagappally, Kerala, India, is known for high background radiation (HBR) from thorium-containing monazite sand. In coastal panchayats, median outdoor radiation levels are more than 4 mGy y-1 and, in certain locations on the coast, it is as high as 70 mGy y-1. Although HBR has been repeatedly shown to increase the frequency of chromosome aberrations in the circulating lymphocytes of exposed persons, its carcinogenic effect is still unproven. A cohort of all 385,103 residents in Karunagappally was established in the 1990's to evaluate health effects of HBR. Based on radiation level measurements, a radiation subcohort consisting of 173,067 residents was chosen. Cancer incidence in this subcohort aged 30-84 y (N = 69,958) was analyzed. Cumulative radiation dose for each individual was estimated based on outdoor and indoor dosimetry of each household, taking into account sex- and age-specific house occupancy factors. Following 69,958 residents for 10.5 years on average, 736,586 person-years of observation were accumulated and 1,379 cancer cases including 30 cases of leukemia were identified by the end of 2005. Poisson regression analysis of cohort data, stratified by sex, attained age, follow-up interval, socio-demographic factors and bidi smoking, showed no excess cancer risk from exposure to terrestrial gamma radiation. The excess relative risk of cancer excluding leukemia was estimated to be -0.13 Gy-1 (95% CI: -0.58, 0.46). In site-specific analysis, no cancer site was significantly related to cumulative radiation dose. Leukemia was not significantly related to HBR, either. Although the statistical power of the study might not be adequate due to the low dose, our cancer incidence study, together with previously reported cancer mortality studies in the HBR area of Yangjiang, China, suggests it is unlikely that estimates of risk at low doses are substantially greater than currently believed.

Impacts of Terrestrial Ionizing Radiation on the Hematopoietic System

“…Currently, uranium mining, industrial processes, or phosphate fertilizer production has contributed to the redistribution of the radionuclides. The presence of natural radioactivity in soil and other building materials results in internal and external exposure to the inhabitants [19,20].…”

“…In Kerala (India) and some parts of France and Brazil, the dose can be up to 20 times the global average. In some countries (e.g., Finland) the average dose is several times higher, and in particular, residents of many countries have received effective doses of the order of hundreds of milisieverts per year [19,20]. Uranium is a natural radioactive and chemotoxic heavy metal found in traces in soils, rocks, and plants, as well as in water sources [23][24][25][26].…”

Study of stillbirth and major congenital anomaly among newborns in the high-level natural radiation areas of Kerala, India

“…Our studies on biological and health effects of high-level natural radiation on the inhabitants, conducted at the field laboratory established by Department of Atomic Energy, Government of India, did not find any evidence to implicate high-level natural radiation in any of the outcomes like chromosomal aberrations, karyotype anomalies, micronuclei, overall congenital anomalies, stillbirths, late onset diseases, or telomere length in human adults (Jaikrishan et al 1999;Cheriyan et al 1999;Thampi et al 2002Thampi et al , 2005Das and Karuppasamy 2009;Das et al 2009). Studies on cancer incidence among population of the HLNR area also failed to show any relationship with the high-level natural radiation (Nair et al 1999;Nair et al 2009). …”

Biological Effectiveness of Ionizing Radiation: Acute vs. Protracted Exposures

“…Conscious or subconscious dose-dependent behavioral changes have probably contributed to the dose-effect correlations found in epidemiological studies: one additional X-ray, endoscopy or blood count can lead to a cancer diagnosis thus influencing statistics. The same mechanism can cause in future an increase in the registered cancer incidence in the high natural background radiation areas (Guarapari, Brazil; Kerala, India; Ramsar, Iran; Yangjiang, China), where no cancer increase has been detected so far [2,[45][46][47][48]; although singular reports on enhanced cancer risk in such areas have already appeared [45,49].…”