Now it is official. There is a general perception that birth defects among the population in the high level natural radiation areas of Kerala are more than those in areas of normal background radiation. Scientists from the Departent of Paediatrics, Victoria Hospital, Kollam, Directorate of Health Services, Government of Kerala and the Bhabha Atomic Research Centre, Mumbai have demonstrated that there is no scientific basis for this perception.
In an extensive study published in Journal of Community Genetics, the authors showed that there are no excess stillbirths or birth defects among the newborns in the high level natural radiation areas (HLNRA) of Kerala.
The study area
The HLNRA in Kerala is a stretch of coastal land about 55 km long and 0.5 to 1.5 km wide in Kollam and Alappuzha districts. The background radiation doses in the region measured by scientists range from normal levels to over 45 times the normal levels due to the natural deposit of monazite sand which contains highlevels of thorium (8 to 10%), uranium (0.3%) and their decay products.
HLNRA has a high density of stable, non-migratory population living 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.
Scientists divided the area into grids of 100 square metres and measured radiation levels at one metre above ground at each of the grid locations.
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)
Hospital records
Researchers 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.
The study is unique; it was carried out by scientists, paediatricians, trained nurses and paramedical staff collecting data such as stillbirths and overall as well as specific major congenital anomalies (MCA) such as clubfoot, heart disease, Down syndrome, cleft lip/ palate, neural tube defects, and hypospadias (a urogenital anomaly in the male in which the external urethral opening is at other than the normal location) and socioeconomic factors.
In the final analysis, 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
Results
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. This defect at a prevalence of 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.
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.
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
ksparth@yahoo.co.uk
[The writer is former Secretary , Atomic Energy Regulatory Board]
