K.S.Parthasarathy
Date:03/04/2008 URL: http://www.thehindu.com/thehindu/seta/2008/04/03/stories/
2008040350041700.htm
Atomic bomb survivors, cancers
In utero exposure - cancer link was unknown
Study confirms that ionising radiation is a weak carcinogen
The study of atomic bomb survivors in Hiroshima and Nagasaki continues to provide very useful information on the effects of radiation on man.
Recently, Dr Dale Preston and co-workers examined the incidence of solid cancers in 2,452 atomic bomb survivors who got exposed to different radiation doses while they were in their mothers’ wombs.
They also evaluated the incidence of cancer in 15,388 persons who were younger than 6 years at the time of bombing. Both groups belonged to the age range of 12-55 for the period of 1955-1999.
Dose-related increases
They reported dose-related increases in the incidence of solid cancers in both groups (The Journal of the National Cancer Institute, March 19, 2008). Scientists knew that radiation exposure to foetus increases risks of childhood cancers and exposure in childhood is associated with increased risks of adult cancers. But until now they knew little about whether in utero radiation exposure leads to increased risks of adult cancers.
Heat rays
When U.S. aircraft dropped the bombs, Hiroshima and Nagasaki had an estimated population of 310,000 and 250,000 respectively.
About 90,000-140,000 people in Hiroshima and 60,000-80,000 in Nagasaki died immediately or within two to four months after bombing, resulting from collapse of houses caused by the blast and from heat rays and fires and radiation exposure.
In the 1950 Japanese national census, nearly 280,000 persons stated that they “had been exposed in the two cities” (The Hindu, September, 6, 2001)
One of the myths about the atomic bombing is that radiation released by atom bombs has been killing tens of thousands of persons in the two cities.
The deaths in areas of about a kilometre diameter are attributable to the effects of explosion and heat. Till 1990, RERF recorded 7,827 cancer deaths among the 86,572 persons who, the RERF included in its Life Span Study cohort.
Radiation exposure might have caused 421 excess cancer deaths (334 solid cancers + 87 leukaemias) among them (Radiation Research, 1996).
In 2007, researchers released the second general report on the incidence of solid cancers among the members of the Life Span Study. They based the analyses on 17,448 first primary cancers diagnosed from 1958 through 1998 among 105,427 cohort members with individual dose estimates, who were alive and not known to have cancer prior to 1958 (Radiation Research, July 2007). For all solid cancers as a group, scientists estimated that about 850 cancers were due to atomic bomb radiation exposure.
RERF, a bi-national Japan-U.S. scientific organization dedicated to studying the health effects of atomic bomb radiation took over the task of accumulating scientific results of significant versatility, quality, and quantity, through its studies of radiation effects on human health, with generous cooperation and support from A-bomb survivors and their family members (RERF release, March 5, 2008).
According to RERF, the majority of atomic bomb survivors are approaching their so-called cancer-prone years. “Cancer mortality associated with radiation exposure is expected to reach its peak during the next 10 years.
With great advances in genomic and other research, various powerful analytical techniques have become available.
Without a doubt, many important findings can only be produced at RERF by collecting, storing, and analyzing valuable clinical samples, such as cancer tissues, from the world’s largest prospective cohort for whom accurate and widely distributed dose information is available,” RERF noted.
“…These studies have important implications for risk assessment of low-dose medical and occupational exposures, since such exposures are expected to increase”, RERF argued.
Study’s confirmation
Overall, the study confirms that ionizing radiation is a carcinogen; also that it is a weak carcinogen (Scientists estimate that about 850 out of 17,448 solid cancers recorded during 1958 through 1998 may be due to radiation exposure).
The excess cancers may not have been noticed in the normal course.
K.S. PARTHASARATHY
FORMER SECRETARY, AERB
(ksparth@yahoo.co.uk)
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