Dr.K.S.Parthasarathy
Date:05/02/2009 URL: http://www.thehindu.com/thehindu/seta/2009/02/05/stories/2009020550011300.htm Back Sci Tech
Cancer risk not high for radiation workers
Radiation doses to workers in various professions studied
Cancer incidence among 1,74,541 workers studied
A study published in the latest issue of the British Journal of Cancer (BJC, Vol.100, 2009) by the researchers at the UK Health Protection Agency (HPA) concluded that the risk of developing cancer among radiation workers increases with the dose of ionizing radiation they are exposed to.
This study and the latest research on cancer risks to populations residing in high background radiation areas in Kerala reported in the January 2009 issue of the Health Physics Journal (The Hindu, Jan 1, 2009) are reassuring.
The results of these studies will have no impact on radiological practices, as the observed cancer risks are consistent with the international scientific consensus on radiation protection.
The dose limits to workers are based on such consensus.
The UK study is the third analysis of deaths and cancer incidence among 1,74,541 radiation workers whose occupational histories are maintained in the National Registry for Radiation Workers from 1976. The present study relative to earlier analyses had longer follow-up (to 2001) and cancer registration data and gives more precise information on the risks of occupational radiation exposure. The registry covers virtually all radiation workers from all the main organizations involved in nuclear and related research and industrial sectors in the UK
“This is a continuation of a study started in 1976 and it provides reliable information on the health of people working with ionizing radiation.
The results confirm the cancer risk estimates observed in other studies even though, overall, radiation workers have lower cancer risks than the general population” an HPA release quoted Dr Colin Muirhead from the Health Protection Agency and the lead author of the paper.
This indicates the so called “healthy worker effect”. Usually, workers exhibit overall death rates lower than those of the general population due to the fact that the severely ill and disabled are ordinarily excluded from employment (biology-online.org October 2005).
Scientists who believe in the beneficial effects of radiation may argue that this is an indication of hormesis, a view which will be stoutly rejected by mainstream specialists.
Within the cohort, death from and incidence of both leukaemia excluding chronic myeloid leukaemia and the groupings of all cancers excluding leukaemia (CLL) increased to a statistically significant extent with increasing radiation dose (BJC, January 2009).
It is known that radiation does not induce CLL. The trend in risk was similar to those for the Japanese A-bomb survivors.
The researchers noted that some evidence of an increasing trend with dose in mortality from all circulatory diseases may, at least partly, be due to smoking, a known confounding factor.
So far, specialists have studied the health effects of ionizing radiation on over fifty groups of about two million persons; but the estimates of the long-term health risks from radiation are based largely on studies of the survivors of the atomic bombings at Hiroshima and Nagasaki and of groups exposed for medical reasons.
The dose rates in these instances were high and other exposure conditions were also not similar to those faced by radiation workers.
Radiation workers get exposed to low doses of radiation at relatively low rates.
The UK study is ideal as it represented the typical radiation doses to workers in various professions.
Data collected from employers consist of individual identifiers, factors such as date of birth, gender and industrial classification, and radiation dose histories (BJC, January 2009).
“Continued follow-up of these workers will be valuable in determining whether radiation-associated risks vary over time or by age, and enables the study of specific cancers and causes of death in more detail” HPA argued in a release (HPA release January 7).
In a separate paper in the same issue of the BJC, researchers at the Childhood Cancer Research Group at the University of Oxford and the Health Protection Agency have shown that their study does not support an earlier finding of a raised risk of cancer in children of female radiation workers.
In a subgroup of women who worked with radiation during pregnancy, a weak statistical association was found between maternal radiation work and childhood cancer, but the evidence is limited by the small numbers involved and the result may be due to chance (BJC release January 7, 2009)
Let us hope that HPA does not suffer any resource crunch which may adversely impact on such research.
K. S.PARTHASARATHY
FORMER SECRETARY, AERB
ksparth@yahoo.co.uk
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