Upcoming ICRP documents: Occupational Intake of Radionuclides

The ICRP has brought series (in three parts) of draft reports “Occupational Intake of Radionuclides” for consultation. The documents are replacing the Publication 30 series and Publication 68 to provide revised dose coefficients for occupational intakes of radionuclides (OIR) by inhalation and ingestion. The revision was necessary in view of the fact that 2007 Recommendations of the ICRP (ICRP Publication 103) introduced changes to the  radiation weighting factors used in the calculation of equivalent dose to organs and tissues and also changes to the tissue weighting factors used in the calculation of effective dose. The revision adopts reference anatomical computational phantoms (that is, models of the human body based on medical imaging data), in place of the composite mathematical models that have been used for all previous calculations of organ doses.

The ICRP Publication 103 also clarified the need for separate calculation of equivalent dose to males and females and sex-averaging in the calculation of effective dose (ICRP, 2007). In the revision of dose coefficients, the opportunity has also been taken to improve calculations by updating radionuclide decay data (ICRP, 2008) and implementing more sophisticated treatments of radiation transport (ICRP, 2010) using the ICRP reference anatomical phantoms of the human body (ICRP, 2009).

The revised dose coefficients have been calculated using the Publication 100 Human Alimentary Tract Model (HATM) and a revision of the Publication 66 Human Respiratory Tract Model (HRTM) which takes account of more recent data. In addition, information has been provided on absorption to blood following inhalation and ingestion of different chemical forms of elements and their radioisotopes. Revisions have been made to many models for the systemic bio-kinetics of radionuclides absorbed to blood, making them more physiologically realistic representations of uptake and retention in organs and tissues, and of excretion.

The reports in this series provide data for the interpretation of bioassay measurements as well as giving dose coefficients, replacing Publications 54 and 78. This report provides some guidance on monitoring programmes and data interpretation (source: www.ICRP.org).

ICRP Publication 118: ICRP Statement on Tissue Reactions / Early and Late Effects of Radiation in Normal Tissues and Organs – Threshold Doses for Tissue Reactions in a Radiation Protection Context, Ann. ICRP 41(1/2), 2012

This report provides a review of early and late effects of radiation in normal tissues and organs with respect to radiation protection. It provides updated estimates of ‘practical’ threshold doses for tissue injury defined at the level of 1% incidence. Estimates are given for morbidity and mortality endpoints in all organ systems following acute, fractionated, or chronic exposure. The organ systems comprise the hematopoietic, immune, reproductive, circulatory, respiratory, musculoskeletal, endocrine, and nervous systems; the digestive and urinary tracts; the skin; and the eye. 

Particular attention is paid to circulatory disease and cataracts because of recent evidence of higher incidences of injury than expected after lower doses; hence, threshold doses appear to be lower than previously considered. This is largely because of the increasing incidences with increasing times after exposure. In the context of protection, it is the threshold doses for very long follow-up times that are the most relevant for workers and the public; for example, the atomic bomb survivors with 40–50 years of follow-up. Radiotherapy data generally apply for shorter follow-up times because of competing causes of death in cancer patients, and hence the risks of radiation-induced circulatory disease at those earlier times are lower. 

Most tissues show a sparing effect of dose fractionation, so that total doses for a given endpoint are higher if the dose is fractionated rather than when given as a single dose. However, for reactions manifesting very late after low total doses, particularly for cataracts and circulatory disease, it appears that the rate of dose delivery does not modify the low incidence. This implies that the injury in these cases and at these low dose levels is caused by single-hit irreparable-type events.  For these two tissues, a threshold dose of 0.5 Gy is proposed herein for practical purposes, irrespective of the rate of dose delivery, and future studies may elucidate this judgment further (source:www.ICRP.org).

Latest ICRP Publication: ICRP Publication - 115, Lung Cancer risk from radon exposures

Lung Cancer Risk from Radon and Progeny and Statement on Radon. ICRP Publication 115, Ann. ICRP 40(1), ICRP Publication 115, Ann. ICRP 40(1), 2010.

The document reviews recent epidemiological studies of the association between lung cancer and exposure to radon and its decay products. Particular emphasis is given to pooled case-control studies of residential exposures and to cohorts of underground miners exposed to relatively low levels of radon. The residential and miner epidemiological studies provide consistent estimates of lung cancer risk with statistically significant associations observed at average annual concentrations of about 200 Bq m-3 and cumulative occupational levels of about 50 WLM, respectively.

Based on recent results from combined analyses of epidemiological studies of miners, a lifetime excess absolute risk of 5 × 10-4 per WLM (14 × 10-5 per mJ h m-3) should now be used as the nominal probability coefficient for radon and radon progeny induced lung cancer, replacing the previous ICRP Publication 65 value of 2.8 × 10-4 per WLM (8 × 10-5 per mJ h m-3).

Unlike the recommendations of ICRP Publication 65, it is now concluded that radon and its progeny should be treated in the same way as other radionuclides within the ICRP system of protection; that is, doses from radon and radon progeny should be calculated using ICRP biokinetic and dosimetric models.

ICRP will provide dose coefficients per unit exposure to radon and radon progeny for different reference conditions of domestic and occupational exposure, with specified equilibrium factors and aerosol characteristics (source:www.ICRP.org).

Current regulations are too much stringent?

Like any other pollutant, radioactive materials and radiation are also present in our environment since the formation of earth.

The fear of radiation in everyone’s mind is due to the destruction caused by the effects of explosions of atomic bombs over Japan in 1945. The possible innumerable benefits of radiation in medicine and industry are simply not considered or exploited enough or publicized by the policy makers due to fear of negative reaction by the public. The ghost memories of the bombings and the Chernobyl disaster always remained fresh in the public mind! This is typical “Culture of fear” being promoted by various groups of people (so-called anti-nuclear lobby) with vested interests.

The organizations dealing with radiation protection also promote this culture by accepting the Linear Non-Threshold (LNT) approach for radiation protection and safety. Regulators have not much choice but to formulate regulations to address the acceptable dose limits which are based on the calculated risks assuming much debated LNT approach.

As such, the background radiation levels around us vary quite a bit from place to place and in some places it is of the order of the current dose limits. People are living in those places of high background radiation for ages. No abnormal health issues are observed.

At the Chernobyl accident site, the emergency workers (about 30 workers) who received doses above 4000 mSv have died within a few weeks due to Acute Radiation Syndrome (ARS). There were 140 workers who received less than 2000 mSv dose (which is 100 times more than the annual dose limit for radiation workers) and none died. In Fukushima (Japan), 30 workers received doses in the range of 100 and 250 mSv range in a few days and none is expected to die of the radiation exposure. In medical therapy, for the treatment of cancer, thousands of mSv doses are given to kill the cancer tissues.

There was no increased risk of cancer observed amongst the survivors of Hiroshima and Nagasaki whose exposures were below 100 mSv. Animal experiments could not prove the non-threshold theory to induction of cancer by radiation exposure assumed by the radiation protection fraternity.

Once we accept this fact, there is no need to have such stringent regulations for the applications of radiation and radioisotopes. One can save un-justified expenditure of resources, hardship and suffering to the population (based on the lecture given by Prof. Wade Allison, University of Oxford, August 2011).

Let us NOT say NO to the benefits of applications of radiation such as food irradiation, medical / industrial applications, pest control and electricity generation.

Radiation emission from towers

Since last three years, “I care for you” has been pursuing the issue of potential health hazard from exposure to radiation from mobile phones and towers through the blog: http://radsafe.blogspot.com. The potential hazards to the public from exposure to radiation from the towers are being highlighted. Periodically, articles are appearing in Mumbai Mirror, Times of India and DNA. But, there is no persistence in the reporting.

However, it is understood now that some actions are being taken in this direction by the Indian Government authorities to control this avoidable public health concern. DNA Navi Mumbai reported on September 4, 2011 that the radiation levels measured in certain areas of Navi Mumbai are 100 times higher than what is considered safe!

Is this not a matter of grave concern for every one of us?

NORM MANAGEMENT

The acronym NORM means all Naturally Occurring Radioactive Materials. Humans are continuously exposed to these materials such as potassium-40, uranium, thorium and their daughter products present in our environment. Some times, human activities such as uranium mining, phosphate mining, oil exploration, etc enhance the NORM concentration, which increases the potential of exposures of population groups to the radiation. Two important decay products of concern are Ra-226 and a radioactive gas - Radon-222. NORM received a global attention during last 4 decades.

Hence, it is important that the concentration of NORM is measured in suspected industrial activities and take appropriate measures to protect the workers and the environment. The industrial activities which generate NORM waste should be regulated to prevent environmental hazard from the disposal of the waste. Many countries have already aware of the issue and initiated remedial measures to control occupational exposures and to ensure environmental safety. NORM is discovered in the sludge being generated in deep oil well exploration /production activities. GM detectors or scintillation detectors are used for the NORM survey.

Radiation levels due to NORM are measured at the work sites. Personnel monitoring and personal protective equipments, if required are used to measure radiation exposures of the workers and its control. Thermoluminescence dosimeters (TLDs) are used to measure personal exposures and respirators (dust/gas), gloves, overalls, goggles are some of the personal protective equipments (PPEs) used. Above all, the workers should be made aware of the possible NORM exposures so that they follow proper and safe work procedures for the NORM management and environmental safety.

Revision of the Basic Safety Standards (BSS)

The IAEA International Basic Safety Standards for Protection Against Ionizing Radiation and for the Safety of Radiation Sources is in the final stage of revision.

A review of the Basic Safety Standards (the BSS) was carried out in 2006 in cooperation with the cosponsors (FAO, ILO, NEA, PAHO and WHO) and potential cosponsors UNEP and EC. The review concluded that, while there was no major issue requiring urgent revision, there was a case to be made for the revision of the BSS in order to take account of the many improvements that have been suggested. The International Atomic Energy Agency (IAEA), in cooperation with the co-sponsoring and potential co-sponsoring organizations, initiated the revision of the BSS in 2007.

The revised International Basic Safety Standards was endorsed by the Commission on Safety Standards (CSS) at its meeting from 25-27 May 2011. The CSS has asked that Member States be consulted about the change (Draft 5.0) to the dose limit for the lens of the eye. Member States are invited to on this change by 7 July 2011. This is a major milestone in the development process of the revision. The revised BSS will now be submitted to the Board of Governors for approval at its meeting to be held from 12-16 September 2011 (IAEA News).