High Level Natural Radiation Areas In Kerala: No Evidence Of Adverse Health Effects – Analysis

This article is a summary of several articles I wrote on the adverse health effects, if any, in areas of high levels of natural radiation in Kerala. I based  them on scientific papers in peer reviewed journals. 

Parts of Kerala and Tamil Nadu are high level natural  radiation areas (HLNRA) because of the presence of large quantities of monazite in the soil. Thorium content in monazite ranges from 8-10.5 per cent. Researchers found that the radiation levels in 12 Panchayats in Karunagappally varied between 0.32 to 76 milligrays per year; the levels in 90 per cent of over 71,000 houses were more than one milligray per year.

(Gray-Gy- is a unit for absorbed dose; when ionizing radiation energy imparted to a kg of material is one joule, it is called a Gray. Since Gray is very large one thousandth of a Gray-milligray –mGy- and one millionth of a gray-microgray-µGy- are commonly used).  

The average value of population dose in HLNRA is 3.8 milligray per year. One milligray is the average value for areas of normal background radiation. The units milligray and millisievert are the same in these instances. Study at the HLNRA during 1990-99 by the researchers from the Regional Cancer Centre and Bhabha Atomic Research Centre did not show any health effect attributable to radiation.

Ionising radiation can cause mutations in all parts of the cell including the DNA. Dr Lucy Forster from the University of Cambridge and her team analysed mitochondrial DNA from 248 families (mostly over three generations) that have been exposed to natural radiation throughout their lives.

Widely published

They found 22 mutations in individuals from the high radiation areas and one in persons from areas of low radiation (Proceedings of the National Academy of Sciences, 2002). The media widely published the results as the authors, during interviews, suggested that people exposed to even low levels of radiation may be at risk of cancer. BBC’s headline was `cancer risk for radiation workers.’ Responding to my queries, Ray Dunne, Health Reporter, BBC news online agreed that BBC did not suggest that that was the conclusion of the original research. BBC focused on it as it was of more relevance to more people. It was purely speculative. A mutation to manifestation of cancer involves several steps.

Low doses

Responding to my e-mail query, Prof K.Sankaranarayanan, Professor Emeritus, Leiden University Medical Centre, The Netherlands, stated that at the current state of knowledge, we cannot attach any importance to these mutations from the standpoint of adverse health effects at low doses of radiation. He must know as he wrote all the reports on genetic effects of radiation for the United Nations Scientific Committee on the Effects of Atomic Radiation!

“It might be worth considering whether to lower the allowed limits for radiation workers of reproductive age,” Dr Peter Forster, one of the authors, warned.

Exposed populations

“It is premature to try to draw any conclusion concerning cancer risk from the study, let alone to call for a reduction in dose limits etc… ” After all, our risk estimates (which form a part of the basis for dose limitation) are computed from epidemiological data on populations exposed to radiation. In other words, although we may have been unaware of this particular mechanism, its contribution to the total risk due to the combinations of mutations is already taken into account, automatically,” Dr Jack Valentin, a geneticist and Scientific Secretary of the International Commission on Radiological Protection — the agency which recommends dose limits, clarified in an e-mail response.

Survey result

In a thorough health survey of about 400,000 people (100,000 from HLNRA), researchers from the Regional Cancer Centre and Bhabha Atomic Research Centre did not see that cancer occurrence is consistently higher because of external gamma radiation exposure in the monazite-rich areas (Radiation Research, 1999).Scientists did not observe significant differences in any of the reproductive parameters between the two population groups based on monitoring of 26,151 newborns from HLNRA and 10,654 from areas of normal background radiation in the Kerala coast. The stratification of newborns with malformations, still births or twinning showed no correlation with the natural radiation levels in different areas. (Radiation Research, 1999) 

Critical review

In a critical review, of the health studies at HLNRA carried out by different authors till 1981, Dr K.S.B. Rose, UK Atomic Energy Research Establishment, Harwell concluded that none of them produced any reliable evidence that the high level natural radioactivity in the area has a detectable adverse effect on the inhabitants (Nuclear Energy, 1982). More recent studies published in peer reviewed journals led to the same conclusion.

Now it is official. In the January 2009 issue of the Health Physics Journal, researchers from the Regional Cancer Centre (RCC), Thiruvananthapuram, and their collaborators have shown that there is no excess cancer risk to people living in the area of high natural background radiation in Kerala from exposure to terrestrial gamma radiation. 

The Journal highlighted the importance of the paper by carrying a photo of the beaches in its cover page. 

Gamma radiation

The coastal belt of Karunagappally, Kerala, is known for high background radiation (HBR) from thorium-containing monazite sand. 

In the coastal panchayats, the median outdoor gamma radiation levels are more than 4 mGy y{+-}{+1} and in certain locations, the levels are as high as 70mGy y {+-}{+1}.(Gy is a unit of radiation dose; mGy is one thousandth of a Gy; the annual gamma radiation level in normal locations is on an average one mGy).

During 1990-97, survey teams collected data on 359,619 subjects in 71,674 households using a standardised 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, they chose a radiation sub cohort consisting of 173,067 residents and analysed the cancer incidence in the sub cohort, aged 30 to 84y (N=69958 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. 

By the end of 2005, they identified 1379 cases of cancer including 30 cases of leukaemia. 

The results

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.

 Unlike the nuclear workers study, RCC study included smoking habits, an important contributing factor. The estimate of atomic bomb survivors is a sex-averaged estimate for solid cancer unlike the RCC study. The currently accepted radiation risk estimate is mostly based on atomic bomb survivor study. 

Highlighting the negative radiation risk coefficient of -0.13 Gy{+-}{+1}, proponents of those who believe in the beneficial effects of radiation (hormesis theory) may argue that low level radiation is helping to lower cancer risks! 

They may not agree that lack of statistical power may be the reason for the negative result.

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.

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).

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