Unexpected News about Monazite Sands at Amritapuri

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Date:01/01/2009 URL:

http://www.thehindu.com/thehindu/seta/2009/01/01/stories/2009010150131

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Monazite sand does not cause excess cancer incidence

 

 

 

 

 

 

 

— Photo: C. Suresh Kumar

 

Cancer risk: The study found that there is no excess cancer risk to

people living in the area of high natural background radiation in

Kerala.

 

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.

 

Follow up study

 

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.

 

It appears that the researchers were in a hurry to publish the paper.

They did not use the complete data but selected four coastal

panchayats (Chavara, Neendakara, Panmana and Alappad) which had HBR

and two control areas (Oachira and Thevalakkara) which have

relatively low natural radiation levels.

 

They estimated the excess risk as -0.13 Gy{+-}{+1} (95 per cent

confidence limit:-0.58, 0.46). The authors pointed out that the upper

limit of 95 per cent confidence limit was lower than 0.97, which

other researchers got for pooled analysis for nuclear workers from 15

countries (BMJ, 2005) and slightly lower than 0.47 Gy{+-}{+1}

reported in the study of atomic bomb survivors in Hiroshima and

Nagasaki (Radiation Research, 2007)

 

Authors highlighted some unique features of their data. 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.

 

Regrettably, the researchers did not estimate the substantial

contribution of airborne radon and thoron daughters to the individual

radiation dose. This may not affect the main conclusion that there is

no excess cancer in areas of high natural background radiation.

 

The limitations

 

Though the analysis limited to six panchayats cannot be faulted

scientifically, they should use complete data including internal dose

from all panchayats for a reanalysis to do justice to the project and

to examine whether precise radiation risk estimate can be arrived at

from this 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.

 

 

 

K.S. PARTHASARATHY

FORMER SECRETARY, AERB

 

 

ksparth

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