Friday, December 18, 2009
Radiation: cancer risk estimates remain same
The complete report (UNSCEAR 2006) with all Annexes from the United Nations Scientific Committee on the Effects of Atomic Radiation has now been published the first set of Annexes in 2008 and the next set in 2009. Because of resource crunch, UNSCEAR could not publish the report which was ready in 2006. That the Committee did not have funds to publish its report promptly is regrettable. UNSCEAR reports underpin international standards for radiation protection.
Dr K.S.Parthasarathy
Date:17/12/2009 URL: http://www.thehindu.com/thehindu/seta/2009/12/17/stories/2009121750111300.htm
________________________________________
Back Sci Tech
Radiation: cancer risk estimates remain same
Radiation protection specialists can breathe easy due to the overall view of the U.N. Committee on current risk estimates
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in its latest report has reiterated that the current risk estimates for cancer and hereditary effects in humans from irradiation need not be changed, in spite of new findings about non-targeted and delayed cellular effects.
Latest annexures
The October 2009 issue of the Health Physics Journal has summarised the latest annexures which covered “Non targeted and delayed effects of exposure to ionizing radiation,” “Effects of ionizing radiation on the immune system”, and “Source to effects assessment for radon in homes and work places”. UNSCEAR published two other earlier annexures in August 2008.
“Non-targeted and delayed effects occur in cells that were themselves not irradiated. They include genomic changes in the daughters of irradiated cells, changes in non-irradiated cells as a result of signals from irradiated cells (so-called bystander effects), and potential health effects in offspring due to irradiation of the parents,” the Committee clarified in a press release.
Scientists have observed “genomic instability” (effect appearing later in cells formed after several multiplications) and “bystander effects” (effects that manifest in cells not directly affected).
These could not be explained by conventional hypotheses. The International Commission on Radiological Protection (ICRP) did not consider them while estimating radiation risk estimates.
In 2000, I sought the views of Dr Jack Valentin, the Scientific Secretary, ICRP, on the impact of genomic instability on ICRP recommendations.
The argument
The then National Radiological Protection Board (NRPB), U.K., has argued that the estimates of radiation induced cancer risk in humans have been derived directly from epidemiological observations, and are, therefore, independent of the potential contribution from any novel cellular mechanism (Interview in AERB Newsletter 13: 1, 2000)
“At present, I find that unlikely, but it would seem wise to avoid being categorical,” he cautioned. “We must investigate it thoroughly,” he asserted.
UNSCEAR 2006 seems to have settled the issue.
Norman Gentner, Chairman of UNSCEAR conceded that these non-targeted effects may potentially amplify the biological effectiveness of a given radiation dose by increasing the number of cells that experience effects over those directly exposed to the radiation (UNSCEAR Release, 2009)
UNSCEAR noted that any clear relationship between non-targeted effects and observed health effects attributable to radiation remains contentious.
“Risk estimates are based on population health studies, which implicitly incorporate all elements including direct targeted effects of irradiation as well as non-targeted and delayed effects,” the latest UNSCEAR statement, is almost similar to NRPB’s, made nine years ago.
Radiation protection specialists and regulators can breathe easy; the overall view of the Committee is that the currently available risk estimates do not require changes.
UNSCEAR 2006 noted that some recent studies have shown that low levels of radiation can stimulate the immune system, at least for short periods.
Experimental studies
These findings emerge from experimental studies and large scale epidemiological assessments of A-bomb survivors, residents of areas in Russia and the U.S. contaminated by weapons production, Chernobyl emergency workers and residents and patients undergoing radiotherapy. Data from these groups showed common patterns (UNSCEAR release, 2009).
The impact of ionizing radiation may be stronger during foetal development and in some diseases such as HIV AIDS; autoimmune diseases and genetic disorders also compromise the immune system making it more sensitive to irradiation.
The disclosure
UNSCEAR disclosed that there is direct evidence to confirm a small but detectable risk of lung cancer from living with radon in home.
The Committee evaluated recent direct studies of the public in Europe, North America and China exposed to relatively low levels of radon in their dwellings.
Thus far, researchers estimated the risk from radon from health studies of underground miners who were exposed to high levels of radon and its decay products.
United Nations set up UNSCEAR in 1955; its mandate is to report on levels and effects of radiation to the UN General Assembly. Resource crunch delayed the publication of UNSCEAR 2006. It has hopefully been corrected. The work of the Committee is crucial as it underpins international standards for radiation protection.
Raja Ramanna Fellow, Department of Atomic Energy
( ksparth@yahoo.co.uk )
K.S. PARTHASARATHY
© Copyright 2000 - 2009 The Hindu
Dr K.S.Parthasarathy
Date:17/12/2009 URL: http://www.thehindu.com/thehindu/seta/2009/12/17/stories/2009121750111300.htm
________________________________________
Back Sci Tech
Radiation: cancer risk estimates remain same
Radiation protection specialists can breathe easy due to the overall view of the U.N. Committee on current risk estimates
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in its latest report has reiterated that the current risk estimates for cancer and hereditary effects in humans from irradiation need not be changed, in spite of new findings about non-targeted and delayed cellular effects.
Latest annexures
The October 2009 issue of the Health Physics Journal has summarised the latest annexures which covered “Non targeted and delayed effects of exposure to ionizing radiation,” “Effects of ionizing radiation on the immune system”, and “Source to effects assessment for radon in homes and work places”. UNSCEAR published two other earlier annexures in August 2008.
“Non-targeted and delayed effects occur in cells that were themselves not irradiated. They include genomic changes in the daughters of irradiated cells, changes in non-irradiated cells as a result of signals from irradiated cells (so-called bystander effects), and potential health effects in offspring due to irradiation of the parents,” the Committee clarified in a press release.
Scientists have observed “genomic instability” (effect appearing later in cells formed after several multiplications) and “bystander effects” (effects that manifest in cells not directly affected).
These could not be explained by conventional hypotheses. The International Commission on Radiological Protection (ICRP) did not consider them while estimating radiation risk estimates.
In 2000, I sought the views of Dr Jack Valentin, the Scientific Secretary, ICRP, on the impact of genomic instability on ICRP recommendations.
The argument
The then National Radiological Protection Board (NRPB), U.K., has argued that the estimates of radiation induced cancer risk in humans have been derived directly from epidemiological observations, and are, therefore, independent of the potential contribution from any novel cellular mechanism (Interview in AERB Newsletter 13: 1, 2000)
“At present, I find that unlikely, but it would seem wise to avoid being categorical,” he cautioned. “We must investigate it thoroughly,” he asserted.
UNSCEAR 2006 seems to have settled the issue.
Norman Gentner, Chairman of UNSCEAR conceded that these non-targeted effects may potentially amplify the biological effectiveness of a given radiation dose by increasing the number of cells that experience effects over those directly exposed to the radiation (UNSCEAR Release, 2009)
UNSCEAR noted that any clear relationship between non-targeted effects and observed health effects attributable to radiation remains contentious.
“Risk estimates are based on population health studies, which implicitly incorporate all elements including direct targeted effects of irradiation as well as non-targeted and delayed effects,” the latest UNSCEAR statement, is almost similar to NRPB’s, made nine years ago.
Radiation protection specialists and regulators can breathe easy; the overall view of the Committee is that the currently available risk estimates do not require changes.
UNSCEAR 2006 noted that some recent studies have shown that low levels of radiation can stimulate the immune system, at least for short periods.
Experimental studies
These findings emerge from experimental studies and large scale epidemiological assessments of A-bomb survivors, residents of areas in Russia and the U.S. contaminated by weapons production, Chernobyl emergency workers and residents and patients undergoing radiotherapy. Data from these groups showed common patterns (UNSCEAR release, 2009).
The impact of ionizing radiation may be stronger during foetal development and in some diseases such as HIV AIDS; autoimmune diseases and genetic disorders also compromise the immune system making it more sensitive to irradiation.
The disclosure
UNSCEAR disclosed that there is direct evidence to confirm a small but detectable risk of lung cancer from living with radon in home.
The Committee evaluated recent direct studies of the public in Europe, North America and China exposed to relatively low levels of radon in their dwellings.
Thus far, researchers estimated the risk from radon from health studies of underground miners who were exposed to high levels of radon and its decay products.
United Nations set up UNSCEAR in 1955; its mandate is to report on levels and effects of radiation to the UN General Assembly. Resource crunch delayed the publication of UNSCEAR 2006. It has hopefully been corrected. The work of the Committee is crucial as it underpins international standards for radiation protection.
Raja Ramanna Fellow, Department of Atomic Energy
( ksparth@yahoo.co.uk )
K.S. PARTHASARATHY
© Copyright 2000 - 2009 The Hindu
Friday, December 04, 2009
Kaiga incident serves as a wake-up call
Date:03/12/2009 URL: http://www.thehindu.com/thehindu/seta/2009/12/03/stories/2009120350081300.htm
________________________________________
Kaiga incident serves as a wake-up call
Tritium is the least toxic of all radioactive materials, not posing any external hazard but internal hazard if ingested
Treating ingestion: Tritium can be removed faster by drinking more fluids and water. Administering diuretics to the workers is another effective method.
Recently, a bizarre incident at the Kaiga Generating Station received wide media attention. Someone deliberately added some tritiated heavy water into a water cooler at the Kaiga Generating Station causing radiation exposure to 55 workers who drank water from it.
Authorities have characterised it as “sabotage,” “act of mischief,” “malevolent act” etc. Specialists in the appropriate discipline will identify the right term to be used!
Very serious incident
It is a very serious incident. It adds a new dimension to the already existing security and access control procedures. Some procedures need tightening. It is a wake up call.
Media reports reflected heightened perception, concerns and some misunderstanding about the way the Station handled the incident.
Extracts of the reports and the related facts are listed thus:
“Tritium is very difficult to remove from the body.” It is not true. Tritium is another form of hydrogen; like ordinary hydrogen it reacts with oxygen and forms tritiated water. Ninety seven per cent of tritium entering the body remains in soft tissue, will reach equilibrium in 2 hours and will get removed with a typical half period of 6 days, through urine and perspiration.
Three per cent remains for a longer period (about 40 days). The two components are considered in calculating the radiation dose. Tritium’s physical half life of 12.3 years is not relevant.
We can remove tritium faster by drinking more fluids and water. Administering diuretics to the workers is another effective method (diuretics are drugs that help to remove water from body). This has to be done under medical supervision.
Effective dose control
That is why the workers whose intakes exceeded certain limits were sent to the hospital (Such interventions are done for effective dose control over the monitoring period). They were not admitted. They did not fall sick as reported by some newspapers.
Is tritium, a highly radioactive substance? Tritium emits beta particles of very low energy. It does not pose any external radiation hazard; it poses internal hazard if ingested. Tritium is the least toxic of all radioactive materials. But we must control all tritium intakes.
“How is it likely to impact the employees who drank the water?” “Doctors say that even the smallest exposure to radiation will have a long term health impact.”
The impact depends on the dose received by the workers. In the present case, only two workers marginally exceeded the radiation dose limit of 30 mSv prescribed by the Atomic Energy Regulatory Board.
No worker had received contamination from any radionuclide other than tritium.
Even the currently estimated doses will be reduced further as these workers take diurectics under medical guidance. When radiation doses are within, close to or below the limit, the health impact is insignificant. However, the doses to workers must be as low as reasonably achievable. Getting doses close to the limit repeatedly is not acceptable. In such instances the work practices must be evaluated to reduce the dose further.
What happens to people living along the Kali River? Especially downstream, who spend a substantial amount of time standing in water to catch fish and eat it?
The contamination was confined to a single water cooler. Specialists located and isolated it from use. The contamination incident has no environmental impact.
The Annual report of AERB (available at www.aerb.gov.in) gives the data on radioactive releases from all power stations.
The resultant radiation doses are small fractions of the AERB limit and are within the variations in the natural background radiation present everywhere. The Kaiga Generating Station is no exception.
Are there legal provisions against such malevolent acts? Rule 23 of the Atomic Energy (Radiation Protection) Rules, 2004, issued under Section 17 of the Atomic Energy Act 1962 states that “Every worker shall observe the safety requirements and follow safety procedures and instructions and shall refrain from any wilful act that could be detrimental to self, co-workers, the radiation installation and public.”
The penalties
Violation of rules made under Section 17 of the Act shall be punishable with imprisonment for a term which may extend to five years, or with fine, or with both.
Depending on the circumstances, if proved guilty, the accused may be convicted for violating the provisions under Section 10 of The Weapons of Mass Destruction and their Delivery Systems (Prohibition of Unlawful Activities) Act, 2005.
K.S. PARTHASARATHY
Former Secretary, AERB
( ksparth@yahoo.co.uk )
Subscribe to:
Posts (Atom)