In Kerala, there is a stretch of coastal land about 55 km long and 0.5 to 1.5 km wide in Kollam and Alappuzha districts, where the natural background radiation levels in some areas are up to 45 times higher compared to normal values. This is due to the natural deposit of monazite sand which contains high levels of thorium (8 to 10%),uranium (0.3%) and their decay products.
There is a popular belief that birth defects and cancer among the population in the high level natural radiation areas (HLNRA) are more than those in areas of normal background radiation. In two separate studies, scientists have demonstrated that there is no scientific basis for this perception.
HLNRA has a high density of stable, non-migratory population (over 100,000) living in the area for generations and exposed to a wide range of doses providing an invaluable opportunity to investigate health effects of low-level chronic radiation exposure directly on human population. Radiation exposures to people in these areas are of the same order as occupational radiation doses. This is an ideal situation to verify whether there are any adverse health effects due to low level radiation.
Scientists from the Department of Paediatrics, Victoria Hospital, Kollam, Directorate of Health Services, Government of Kerala and the Bhabha Atomic Research Centre, Mumbai have carried out the study on birth defects (.Journal of Community Genetics, 2012)
The average radiation dose in control areas of Kollam district is 1.2 mGy/year with a range of <1.0 to 1.5 mGy/year. Hence, areas with a radiation exposure above 1.5 mGy/year were considered as HLNRA and those below 1.5 mGy/year, as normal level natural radiation area(NLNRA).
(Gray-Gy- is a unit of radiation dose ; it is the dose when the radiation energy absorbed per kg of material is one joule. Since Gy is a large unit researchers normally use one thousandth of a Gy or milligray in practice)
Scientists, paediatricians, trained nurses and paramedical staff monitored newborns from August 1995 to June 2011 and collected information on 141,540 newborns from 140,558 deliveries. The study covered women admitted for delivery with a gestational age of more than 28 weeks at three hospitals and a community health centre in the area.
Scientists controlled the confounding or competing factors such as maternal age at birth, ethnicity, marriage between blood relations, and gender of the newborn, which may influence the frequency of the anomalies.
The researchers did not find statistically significant differences in the prevalence of stillbirths, heart disease, or birth defects, at different dose levels at parental residence. The frequency of clubfoot was found to be higher in areas of dose level 1,5 mGy per year to 3 mGy per year. It did not show any indication that it depends on radiation dose. The prevalence of this defect at 2.85/1,000 was generally comparable to that reported from elsewhere in the country.
The frequency of about four stillbirths among 1,000 newborns in this coastal community is comparable to that in developed countries. Overall prevalence of major congenital anomalies (MCA) in this population at 1 per cent, was lower than 2.11 to 4.42 per cent reported from other parts of India. Frequency of Down syndrome in this study was 1 in 1,361 births; its prevalence is low because of lower maternal age at birth.
There is no scientific evidence to show that population groups exposed to low level radiation may suffer any harmful effect. The congenital anomalies in newborns found in HLNRA is not different from or their frequency higher than those found in any other part of the country. Some of the anomalies are lower in HLNRA probably because of higher literacy, health awareness, and practices in the study population.
An earlier study published in Health Physics in 2009 by scientists from the Regional Cancer Centre and the Bhabha Atomic Research Centre showed no excess cancer risk from radiation exposure at the same high level natural radiation areas. In the coastal panchayats, the median outdoor gamma radiation levels are more than 4 mGy in a year. This is comparable to the average annual radiation doses to radiation workers in many industrial and medical practices. In certain locations, the annual levels are as high as 70mGy.
During 1990-97, survey teams collected data on 359,619 subjects in 71,674 households using a standardized questionnaire which covered socio demographic factors, lifestyle, dietary habits and tobacco and alcohol use.
Based on radiation level measurements, by a method perfected by scientists of the Bhabha Atomic Research Centre, the researchers chose a radiation sub cohort consisting of 173,067 residents and analyzed the cancer incidence in the sub cohort, aged 30 to 84y ( Totally 69958 persons followed up for 10.5 years).
They estimated the cumulative radiation dose to each individual in the age group based on the radiation doses received indoors and outdoors and taking into account how long and where they stayed during the period. Unlike similar studies done on nuclear workers elsewhere, the present study included smoking habits,
an important contributing factor.
By the end of 2005, they identified 1379 cases of cancer including 30 cases of leukaemia. Statistical analysis of the data showed no excess cancer risk from exposure to terrestrial gamma radiation. In site-specific analysis, they did not find any cancer site or leukaemia to be significantly related to cumulative
radiation dose.
“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,” the researchers concluded.
The results of the studies are reassuring; it indicated that radiation workers who may receive low does are also unlikely to suffer any harmful effect due to radiation exposure.
– PTI Feature
