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Responses to Public Comments on the Proposed Revision to the Radon Guideline
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Health Canada has proposed that the current guideline for exposure to radon gas be reduced from 800 to 200 becquerels per cubic metre (Bq/m3). The Federal Provincial Territorial Radiation Protection Committee (FPTRPC) appointed a Radon Working Group to review this recommendation and report back on its findings. This review was completed in the fall of 2005 and supported Health Canada's proposal.
The FPTRPC requested that a draft revision to the Canadian radon guideline and the associated Working Group report be made available for public consultation. The purpose of the consultation was to solicit comments on the proposed guideline and the approach used for its development. This public consultation ran from April 24, 2006 to June 22, 2006 inclusive.
Comments received by Health Canada and the FPTRPC have been carefully studied and responses have been provided to each individual or organization as appropriate. In general, Health Canada and the FPTRPC agreed with many of the comments submitted. Based on these comments, the radon guideline and the Working Group report have been revised as appropriate. A summary of the comments and the responses is provided below. The comments are divided into the following categories: general comments or questions, suggestions for a lower guideline than proposed, comments recommending changes to the text of the proposed guideline or the report, recommendations for implementing the guideline, and non-support for revising the guideline or suggestions for a higher guideline than proposed.
Although most of the comments received have been summarised, a few were of a very technical or detailed nature. In these cases the comments may be partially or entirely reproduced below to ensure all points are properly conveyed. In all cases the anonymity of the individual or organization has been maintained.
General Comments or Questions
Overall, we are all very happy with the proposed revision to the guideline and think that the report was well prepared.
Accepting this guideline will speak well to the world health community about Canada's concern for its residents.
A revision to the radon guideline is long overdue and welcomed.
Response:
No response is necessary.
How do I test my home for radon?
Response:
Commercial services are available to homeowners who wish to measure radon levels in their homes. Consult your local Yellow Pages for home inspection services or radon testing services, or contact Health Canada for a list of service providers.
Where can the original report on the 1978-1980 cross-Canada radon survey be located? Did Health Canada correlate the results from this survey with other parameters such as rock type?
Has Health Canada reviewed the impacts or benefits of radon remediation actions performed as initiatives in specific communities?
Response:
Data from the radon survey performed by Health and Welfare Canada in the summers of 1977, 1978 and 1980 is available in a publication entitled "Design and Interpretation of Large Surveys for Indoor Exposure to Radon Daughters", in Radiation Protection Dosimetry, Vol. 7, No. 1-4, pp 303-308. Health Canada did not perform a comparison of local rock type or other parameters with the radon data collected from this study.
Health Canada does not have any information on the impact or benefit of actions to remediate dwellings in specific communities.
Does Health Canada have standard methods or additional information for:
- radon testing in air and in other media,
- for radon testing equipment,
- certification programs for providers of testing and mitigation services?
Response:
Health Canada is working with federal/provincial/territorial partners on an implementation plan for the new guideline, which includes development of standard protocols for radon testing and mitigation and the development of a certification program for providers of radon testing and mitigation services. All conventional radon detection equipment will be considered and evaluated as part of these efforts. Health Canada's protocols will only address radon testing in air; not soils, water or phosphogypsum.
Suggestions for a Lower Guideline
The radon action level for Canada should be the same as the action level near Canadian nuclear facilities - 4.0 pCi/L.
Response:
Canada's nuclear regulatory organization, the Canadian Nuclear Safety Commission (CNSC), regulates radiation exposure to members of the public from nuclear facilities. The CNSC has set a limit of 1 mSv/a for exposure to the public from all sources at such facilities. This is above exposure due to natural sources of radiation, such as radon found in homes. Therefore, the action level that is referred, 4 pCi/L for radon from nuclear facilities, is not correct for Canada. The CNSC (formerly known as the Atomic Energy Control Board) set a maximum permissible limit of 4 pCi/L for radon concentrations in new homes built in Port Hope, Ontario. However, this limit was very specific to the cleanup of the Port Hope area and does not apply to the entire country.
Why is the recommended guideline for Canada above the U.S. action level of 150 Bq/m3?
Response:
The U.S. EPA has recommended a non-mandatory action level of 4 pCi/L. Unlike Canada and most of the rest of the world, the United States does not use the SI system of measurement. The unit used by Canada for radon concentration is Bq/m3. Part of the difference stems from the conversion between the two units. The recommended guideline for Canada is based on the risk to health, available mitigation technology and cost to mitigate. Canada's proposed guideline is consistent with most other countries that have set guidelines or action limits.
Why does Canada propose a guideline for such a significant public health issue, instead of a standard?
Response:
Health effects from background or natural radioactivity, such as radon, is a provincial/territorial jurisdiction. Health Canada with the FPTRPC can recommend a guideline; however, it is up to the individual provinces and territories to set a standard in this case.
Unfortunately, the governments' rationale for setting a new guideline of 200 Bq/m³ is weak and fails to adequately protect Canadians. To begin with, the first point of the rationale refers to "recent scientific evidence of a health-based risk associated with radon exposure at 200 Bq/m³." This statement is incorrect, and is contradicted in the following paragraph of the rationale, which states that the recent North American and European studies "indicate a measurable risk of lung cancer at radon levels as low as 100 Bq/m³." The North American and European studies provide compelling scientific support for setting the new Canadian radon guideline at 100 Bq/m³.
Response:
In the past there had been arguments that extrapolation of the data from the uranium miner studies was an inappropriate means by which to predict lung cancer risk at lower radon concentrations found in most homes. Therefore, there was resistance to reduce the radon guideline from 800 Bq/m3. The guideline statement was meant to show that with the data from the North American and European studies, evidence of measurable risk had been shown at lower radon levels, including 200 Bq/m3. Therefore, maintaining the radon guideline at 800 Bq/m3 would be unjustified. The author has correctly pointed out that there is an inconsistency between the opening statement of the first point of the guideline rationale and that in a subsequent paragraph. This inconsistency will be corrected in subsequent versions of the report and guideline.
It has also been brought to our attention by others that while the North American and European studies show an elevated risk of lung cancer at 200 Bq/m3, they do not indicate a measurable risk of lung cancer at radon levels as low as 100 Bq/m3. This correction in the wording will also be added in revisions to the guideline.
It is vital to understand that Health Canada formulated the proposed guideline in 2004, prior to the publication of either the North American or the European studies that concluded there is a significant risk to health at radon concentrations of 100 Bq/m³. Further support for establishing an action level for radon concentrations of 100 Bq/m³ is provided by British experts who estimate that 90 per cent of the lung cancer deaths in the United Kingdom are caused by exposure to radon at concentrations below 200 Bq/m³. Thus, the Canadian guideline should be updated to acknowledge the advance in scientific understanding and risk assessment.
Response:
The European study by Darby et al. was published in December 2004 and the North American study by Krewski et al. in March 2005. However, Health Canada was aware of the data and the conclusions from both studies long before the information appeared in print. It is important to note that Dr. Jan Zielinski, a co-author on the North American study, is an epidemiologist with Health Canada, and Dr. Daniel Krewski is a former Health Canada employee and continues to have close ties with scientists in this Department. Thus in March 2004, when Health Canada made the original proposal to change the guideline, it was with knowledge and understanding of the preliminary data and the conclusions of the two studies.
Darby et al. have predicted that 90% of lung cancer deaths in the United Kingdom are caused by exposure to radon at concentrations below 200 Bq/m3. However, their estimates also show that more than 75% of lung cancer deaths are caused by exposures below 100 Bq/m3. Thus most deaths are caused by exposure to radon concentrations that approach background (outdoor levels) and at levels where the availability and success rate of radon technology for remediation becomes questionable. The value of 200 Bq/m3 was chosen to reflect a measurable risk, and for which testing and remediation technologies exist and are successful.
The second flaw of the rationale for the proposed Canadian guideline is a reference to the need for international harmonization. This is important since Canada's current radon guideline has been embarrassingly out of line internationally. Inexplicably, the rationale fails to mention that the U.S., Canada's neighbour and largest trading partner, has a stronger guideline than Canada is proposing. The American guideline for radon is 150 Bq/m³. The harmonization portion of the rationale also fails to refer to the World Health Organization's recommendation of 100 Bq/m³ as the appropriate action level for radon.
Response:
The author seems to have interpreted international harmonization only with the United States. The Working Group report has taken a wider view of international harmonization. Of the 16 countries identified in Table 2 of the Working Group report, only the United States has recommended a lower radon action level than the value of 200 Bq/m3 recommended by Health Canada and the Federal Provincial Territorial Radiation Protection Committee. The author's own research has shown that the European Union has recommended a radon guideline of 200 Bq/m3. The World Health Organization has not recommended a radon guideline. The "level" that is referred is for radon progeny; not for radon gas: "In general, simple remedial measures should be considered for buildings with radon progeny concentrations of more than 100 Bq/m3 equilibrium equivalent radon as an annual average, with a view to reducing such concentrations wherever possible." Estimation of the radon concentration associated with a specific radon progeny concentration requires knowledge of the relevant equilibrium factor. In most homes it is highly unlikely that radon would achieve 100% (secular) equilibrium with its progeny. Generally the ratio of progeny to radon is about 0.4 to 0.5. Both UNSCEAR and the International Commission on Radiological Protection have adopted a typical worldwide equilibrium factor of 0.4. Therefore, in a home where the concentration of radon progeny is 100 Bq/m3, the corresponding radon concentration would typically be 250 Bq/m3, slightly higher than the proposed new Canadian radon guideline of 200 Bq/m3.
The international comparison of radon guidelines demonstrates that Health Canada's proposal would merely change the Canadian guideline to a level that has been in effect in other nations for decades--at a time when new scientific evidence clearly suggests that the existing guidelines elsewhere must be strengthened.
Response:
The radon guidelines set by other countries were in part based on the assumption that lung cancer risk at residential radon concentrations could be derived from extrapolation of the data from the uranium miner studies. The "new scientific" evidence supports this assumption. This does not mean that guidelines in all other countries are in need of change, but instead reinforces the initial decision made in setting them at this low level.
It is also important to understand that what Health Canada is proposing is a voluntary guideline, not a legally enforceable regulation. At a minimum, Canadians deserve a guideline that fully informs them of the magnitude of the risk they are facing, rather than a guideline that cultivates a false sense of security in residents whose radon concentrations may be below 200 Bq/m³ but still pose a significantly increased risk of lung cancer. It would be preferable to set the guideline at 100 Bq/m³, not only to accurately reflect the risk, but also to enable citizens to make informed choices about the risk trade-offs they are facing.
Response:
We agree that Canadians must be properly informed of the risk in order to allow them to make an appropriate choice regarding remediation efforts. The documents that support the guideline present a thorough risk analysis. The guideline emphasizes action and remediation to address the risk. The same remediation technology is used at all radon levels. Based on the experiences of the U.S. EPA, remediation is predicted to reduce the radon concentration to less than 200 Bq/m3 in more than 90% of homes and to less than 100 Bq/m3 in more than 75% of homes remediated using approved methods. Therefore, even if the guideline is set at 200 Bq/m3, in 75% of the cases, the radon concentration will be reduced to less than 100 Bq/m3 as a result of remediation efforts. Note also the response to Comment 1 on page 10. Epidemiological studies do not indicate a statistically measurable risk at radon levels as low as 100 Bq/m3.
Suggested Changes to the Guideline and Report Text
The "radon hot spots" around Canada as identified in the advisory report creates a misinformation and confusion among the administrators and the general public that areas outside these "hot spots" could be complacent about radon.
It is better to state explicitly that the "hot spots" identified in the report are with reference to the geological occurrence of uranium-radium in the environment, and that this identification is not adequate to address the issues related to indoor radon concentrations of concern to the health of the general public.
It should be made explicit that high radon concentrations can arise anywhere in Canada because: 1. in general, radon is a soil gas encountered everywhere in Canada; 2. radon concentration in soil is much higher than radon concentration encountered in air in most parts of Canada; 3. the indoor radon concentration is affected by the condition of the foundation and type of foundation of a dwelling and the ventilation of the dwelling.
Response:
The Working Group report does not refer to radon "hot spots". In fact the report only refers to Health Canada's efforts to establish a radon potential map of Canada. The report states: "Even though the radon concentration varies from house to house even in the same area, the average radon concentration in a group of houses is a reasonable predictor of the probability that a house in the area may have elevated radon concentrations." The map would be generated using a combination of aerial radiation survey data, geological information and radon test data from homes and other buildings. The purpose of the map is simply to help determine where priorities should initially be focused for testing. Section 5 of the Working Group report deals with radon migration and factors that can affect indoor radon concentration.
The points of clarification accompanying the guideline should be modified to indicate that:
- the National Building Code must be extended to include radon monitoring and testing,
- the normal occupancy area includes any area where a person or pet spends several hours a day.
Response:
This section of the guideline provides points of clarification to the guideline only. The guideline does not deal with implementation specifically. Health Canada is working with federal/provincial/territorial partners on an implementation plan for the new guideline, which will include the need to address building codes.
While it is recognized that many people value their pets as family members, the guideline as written is felt to adequately cover the issue with respect to pets. Pet owners generally keep their pets in the "normal occupancy area" for humans.
Cost estimates used in the report underestimate the current state for radon testing and mitigation.
The costs don't adequately reflect the case when a homeowner asks for a service provider to come to the home to personally perform the radon test.
Response:
Health Canada used data based on U.S. EPA cost estimates. If more up-to-date information is available and could be provided, Health Canada would be pleased to receive it in order to update its cost estimates.
Home owners may encounter higher costs if they engage a contractor to come to their home to provide radon testing. An estimate of $50 was based on testing provided by a service provider that mails a detector to the home owner and assumes the home owner follows instructions to set it up, remove it and mail it back to the service provider. Costs for analyzing the detector and reporting the results to the home owner are included in the service provider's price. This is the most common means by which to obtain radon testing in Canada at this time. Clarification on this issue will be added to the report.
The phrase "in the normal occupancy area" in the guideline should be replaced with "indoors" to reflect the use of basements as living spaces and the existence of crawlspaces.
Response:
It is agreed that radon is expected to be higher in basements and that measurements should be performed in the lower occupied areas. However, it is doubtful that changing the phrase "normal occupancy area" to "indoors" would ensure that measurements are always performed in these areas. The purpose of the points of clarification that accompany the guideline was to ensure that Canadians understand the need to test in basements or the lowest lived-in area of a dwelling.
A comment should be made in the report that other factors affecting indoor environmental quality (IEQ) and indoor air quality (IAQ) should be considered when planning radon mitigation measures and such measures should only be undertaken by a professional knowledgeable in IEQ/IAQ and based on building science principles and not on a radon air test alone.
Response:
Health Canada is working with federal/provincial/territorial partners on an implementation plan for the new guideline, which includes development of standard protocols for radon testing and mitigation and the development of a certification program for providers of radon testing and mitigation services. These comments will be considered in the development of these standards and certifications.
Under the points of clarification for the guideline the normal occupancy area is defined in terms of a location where a person spends "several hours per day." How many hours does "several" represent?
Response:
In this context, "several" is meant to represent more than 4 hours spent in any location in a home or building.
The guideline maintains a link to the old guideline by mentioning a timeframe for action at 800 Bq/m3. This can cause confusion.
Response:
During the development of the recommended radon guideline, there was considerable concern by members of the Working Group that members of the public who found their homes tested above the guideline would want guidance on how fast they should act to remediate. This guidance was considered particularly important for medical officers of health and other officials who might receive calls from concerned citizens. There is considerable difficulty in developing such guidance in order to ensure the person acts in a reasonable time period without causing widespread panic. The general consensus was that the current guideline of 800 Bq/m3 was unacceptable and homeowners with concentrations above this should act quickly, and that one year was a reasonable length of time in which to complete any remediation activities. Response times for other concentrations were then scaled from this starting point at 800 Bq/m3. In order to avoid the confusion associated with the old guideline value of 800 Bq/m3, the final version of the new guideline will be amended to exclude this value.
The rationale for the guideline states: "As the radon concentration is lowered from 800 to 200 Bq/m3, the number of lives saved steadily increases and the cost-per-life-saved decreases". How can the cost-per-life-saved decrease as mitigation is undertaken at decreasing radon concentrations?
Response:
The wording is misleading. What is actually meant is that when comparing at different radon guideline or action levels (and assuming that all Canadians tested and remediated as appropriate), the number of lives saved increases with lower guideline values. Since most of the cost for implementing a guideline results from initial screening, which is independent of action level, and the total number of lives saved is greater at lower action levels, the cost-per-life-saved actually decreases when comparing costs at a guideline of 800 Bq/m3 to those at 200 Bq/m3. Clarification will be added to the report and to the guideline rationale.
Suggestions for Guideline Implementation
The federal, provincial and territorial governments should:
- Continue to monitor research results related to radon health effects on children
- Ensure that radon testing, and if necessary the implementation of radon protection measures, is undertaken in all schools, hospitals, long-term care facilities, and other public buildings
- Clarify the timeframes within which remedial work should be done for radon levels above 200 Bq/m3 and work with homeowners to decrease these timeframes.
- Develop and implement a public education program, including the development of educational and informational materials for the public related to radon, its health effects and testing and mitigating techniques for homes
- Expand the public education/awareness campaign if public participation in testing and remediation is not sufficiently increased by the planned efforts
- Develop a strategy to decrease the cost of testing for high levels of radon and to create a system of grants and subsidies to aid homeowners with testing and mitigation costs
- Consider following the example of the United States National Safety Council in providing radon tests to its citizens at a lower or reduced price
- Support the development of industry standards for radon protective measures when new homes are built and ensure that radon protection measures are incorporated into all building codes in Canada.
- Develop standard protocols for use in testing and mitigating existing homes for radon
- Ensure the availability of approved radon detectors or test kits
- Ensure the professional skill of individuals or companies performing radon testing and mitigation by establishing an accreditation or certification program
- Establish a national radon proficiency testing program in order to provide assurance that any radon monitor or detector used for radon testing meets minimum technical standards
- Develop guidance for physicians who may be required to respond to patients with concerns they may have been exposed to radon in their homes
- Develop information for the medical community on the medical rationale associated with the new guideline
- Develop a national radon map to provide predictions of whether buildings in specific areas may have elevated radon concentrations
- Ensure that the national radon map is developed on the basis of new testing data rather that existing data on file with Health Canada as it is insufficient for the purpose and unreliable
- Establish a National Radon Registry for radon testing results which can be used as a database for analysis and research purposes
- In cooperation with real estate and financial institutions establish requirements for disclosure of radon results to home buyers during real estate transactions
Response:
The purpose of the report prepared by the Working Group was to solicit comments on the proposed guideline and the approach used for its development. Health Canada is now working with federal/provincial/territorial partners on an implementation plan for the new guideline, which includes development of standard protocols for radon testing, remediation and new construction, certification of radon testing and remediation service providers, development of a comprehensive national public awareness and communication plan, and a map of radon prone areas in Canada, which would include a health database of radon test results. As part of this plan, Health Canada would carry out research on radon health effects, which would include vulnerable populations such as children. In developing this implementation plan, Health Canada and its federal/provincial/territorial partners will consider all suggestions and recommendations made during this consultation.
If radon testing is to become a mandatory requirement for real estate transactions the following should be considered:
- Radon concentrations in a home vary over the year and tend to be higher during winter
- There should be a means by which to prevent tampering with the testing device to reduce the radon concentration measured
- Should consultants or professionals be used or should the onus be placed on the seller, builder or new owner?
- In the case of new housing, who would be responsible for mitigation work?
- What would be the legal implications for a new dwelling sold that was not previously tested and for which the warranty period has just expired?
Response:
The guideline being proposed by Health Canada and the Working Group will not be a regulation. Although there could be a requirement to have testing performed as part of a real estate transaction, there are no plans at this time to make this mandatory. There are ways in which to prevent or detect radon testing interference during real estate transactions. These include using a test device that frequently records radon levels to detect unusual swings, employing a motion detector or a proximity detector, recording the barometric pressure and temperature, and applying tamper-proof seals to windows. Should there be a decision to require mandatory radon testing as part of real estate transactions, a standard protocol would be developed to deal with such testing and the issues of preventing testing interference.
It is recommended that the radon action level be expressed in milliWorking levels (mWL) for the measurement of radon progeny in homes and buildings.
It is recommended that the unit of measurement commonly used in the United States be referenced in the radon guideline document.
Response:
The guideline is for radon, not its progeny. The use of non-SI units in the guideline (pCi and mWL) would cause confusion as pCi/L is most often associated with the U.S. radon action level of 4 pCi/L.
It is recommended that the phrase radon "guideline value" be replaced with radon "action level".
Response:
Other countries may refer to this as an "action level", "reference level" or "advisory level", however, historically, in Canada the accepted phrase has been "radon guideline", and has been referred to as such in publications. It would cause confusion to change the phraseology at this point.
It is recommended that all workplaces in Canada be covered under the new radon guideline, except those workplaces already governed by Canadian Nuclear Safety Commission (CNSC) regulations.
Response:
In developing the recommended radon guideline, the consensus of the Working Group was that workplaces are adequately covered by the existing guidelines for Naturally Occurring Radioactive Materials (NORM). Therefore, there was reluctance to extend the radon guideline to workplaces in order to avoid confusion between the two guidelines.
It is recommended that the guideline clearly state the aim of remedial action should be to reduce the radon in a home or building to a level below the 200 Bq/m3 guideline value.
Response:
The guideline stipulates "as low as practicable". Experience has shown that it is feasible to achieve a level below 200 in virtually all cases.
All references to costs for radon testing and mitigation measures should be removed from the radon report. Pricing for private sector homes and buildings should be established by the competitive market.
Response:
Based on past requests for information on radon, Health Canada and the Working Group felt that an estimate of the cost to perform testing and mitigation of all homes, schools, hospitals and other public buildings would be of interest to many federal departments as well as provincial, territorial and municipal governments and the Canadian public. Therefore, Section 6 was added to the report. It would be impossible to provide this estimate without making and stating assumptions regarding the costs for testing and mitigating such buildings. Therefore, this information cannot be removed from the report. In addition, Canadian citizens interested in more information routinely call Health Canada for assistance. Requests for typical costs are common. Therefore, it was felt that this was relevant information to provide in a public report. Providers of radon testing and mitigation services will presumably set their prices in accordance with the market demand.
Non-Support for a Revised Guideline or Recommendation for a Higher Value
The alarming mortality figures, and the proposed guideline, are based on assumed linearity without threshold between exposure and risk. This is not what Nature teaches us. In the many experiments in which animals were exposed to alpha radiation, there are many instances of apparent thresholds and no unambiguous indication of linearity between exposure (dose) and cancer risk at the lowest dose levels. In fact, the only statistically strong evidence is for threshold responses, all the others are extrapolated linearly down to dose zero. Unambiguous thresholds are observed in human populations exposed to alpha radiation (radium painters, for example). The German Schneeberg study, not mentioned in the Krewski and Darby papers shows a clear threshold in lung cancer risk, up to about 1000 Bq/m3. At low dose levels, confidence intervals are large enough to accommodate any shape of dose-response, including a risk, no risk, or a beneficial effect, which is actually observed in a number of experiments. Another difficulty in estimating the risk of lung cancer due to radon exposure is that the risk is much dependent on socio-economic status. According to a Canadian study, the risk of lung cancer in a low socio-economic group is about double that in a high socio-economic group, a difference much larger than the difference in theoretical risk between a low and a medium radon exposure. It is difficult to correct mortality studies for socio-economic status because global indexes such as education level or individual income are generally relatively poor indicators of the true socio-economic status of a given person. Several studies, among radiation workers, show socio-economic status is a bigger factor of risk than dose. The Report of the Radon Working Group on a New Radon Guideline would have benefited from using the conditional tense when citing the number of lung cancer deaths theoretically attributable to the exposure to indoor radon.
The Guideline, if applied, may result in considerable expenditures at scale of the whole country. Such expenditures may be better used to address risks for which the benefits are real and measurable, as opposed to the hypothetical nature of indoor radon risk.
Response:
The studies which implied a clear threshold (e.g., radium dial painters, animal experiments) involved, for the most part, the ingestion of long-lived alpha emitters and the induction of bone cancer. This is a very different scenario from the exposure of the bronchial epithelium to inhaled radon progeny. The results of both Krewski and Darby indicate linear dependence down to 100 Bq/m3 with no apparent threshold. Darby et al. attempted to fit a threshold model to their data but found that it did not give a significantly better fit than the linear model. Their results indicated an upper 95% confidence limit of 150 Bq/m3 for a threshold, which is less than the proposed guideline value of 200 Bq/m3. Dosimetric considerations imply that, if a threshold exists, it is likely to be much lower than this. If one uses the ICRP lung model to estimate annual lung doses from exposure at various radon concentrations, one obtains the following:
| Radon concentration (Bq/m3) | Approx. lung dose (mSv/year) |
|---|---|
| 100 | 50 |
| 200 | 100 |
| 400 | 200 |
| 800 | 400 |
Exposure at 200 Bq/m3 over a period of 30 years would give a lung dose of 3 Sieverts - well above any proposed threshold. If the ICRP alternate method of dose estimation is used (based on epidemiology rather than dosimetry), the above doses would be reduced by a factor of 3 or 4 but would still be very high.
It is true that lower socio-economic status could be associated with higher smoking prevalence and a lower standard of health care, hence a greater risk of lung cancer. However, for this to be a confounding factor in studies of radon-induced lung cancer, one would have to find a plausible mechanism by which high radon concentrations are associated with low socio-economic status. If anything, one would expect the contrary. Lower socio-economic status tends to occur in urban settings with multi-storey dwellings, precisely where one would expect radon concentrations to be lower.
It is not clear whether the writers had in mind an objective to ensure that any individual is prompted to take remedial action where appropriate or whether the issue is seen as one of public health; i.e., ensuring that the number of cases of lung cancer avoided in the population warrants the expenditure of public funds.
Response:
The intention is actually both to prompt individuals to take remedial action and to guide public health officials in lowering the lung cancer burden.
Page iv Rationale for the Guideline
Although it is fair to say that the two cited studies (Krewski et al. and Darby et al.) do indicate an elevated risk of lung cancer at some radon levels found in homes it is exaggerating to state (as in the first rationale) that they indicate a measurable risk of lung cancer at radon levels as low as 100 Bq/m3. The confidence intervals for all the odds ratios in the Krewski paper include unity and on only one measured concentration band in the Darby paper is the relative risk (RR) above unity at the 95% confidence level; the RR in the band above that one includes unity and it is not until one gets into the uppermost band that the relative risk is firmly elevated. That there is an elevated risk at 100 Bq/m3 depends on the fitted assumed model; i.e., the best fit straight line forced through the origin. (This point also applies to the first paragraph in Section 1 of the Report.)
Response:
It is true that in both pooled studies the lower confidence interval drops to 1.00 or even slightly below 1.00 . Thus, it becomes a statistician's judgment call as to whether the effect is "significant" or not. In either case, it would be imprudent to ignore the implied health risk at 100 Bq/m3. Moreover, it is notable that two separate pooled studies with different investigators, data sets, methodologies and assumptions came to very similar conclusions. An upcoming study, to be published next year, will combine the North American and European results.
The second rationale seems to be the driver of the three posited rationales; i.e., others have chosen a lower guideline therefore so should Canada. This is a poor reason for doing anything. A sound rationale would be science-based, taking into account Canadian mores, particularly as they are believed to influence actions that individuals might take.
Response:
We agree that the rationale should be scientifically-based. We also agree that the rationale should take Canadian mores into consideration. An important guiding principle is that Canadians should receive a degree of protection from ionizing radiation that is at least equal to that in other developed countries. From our consultations we have learned that many Canadians are aware of the 150 Bq/m3 in the U.S. and wonder why the existing Canadian limit is more than 5 times higher. They are also aware of the 200 Bq/m3 in the U.K., Ireland, Australia, Norway, Sweden and Spain. It is hard to explain to Canadians why it is acceptable to be exposed to radon levels two times, three times, or four times the world levels, especially when the science seems to be pointing toward significant risks at lower levels.
The discussion of the ICRP position could also include the advice, suggested in ICRP Publication 65 and reiterated in the most recent (2006 June 6) draft general recommendations, that the action level selected should be within the range 200 Bq/m3 to 600 Bq/m3 and that the lower value could be considered as an exemption level. The latter point is made in the draft ICRP report on the scope of radiological protection regulations, (Spring 2006 version). The concentrations intended here are long-term average values; an important point that bears on the comparison of measurements with the value of a guideline concentration as discussed below in these comments.
Response:
The June 2006 draft ICRP sets a dose constraint of 600 Bq/m3 for domestic dwellings (paragraph 301), but qualifies this in the next paragraph by stating that "It is the responsibility of the appropriate national authority, as with other sources, to establish their own constraints, and then to apply the process of optimization of protection in their country." The earlier ICRP Publication 65 suggested a range of radon concentrations between 200 and 600 Bq/m3 without implying that the lower value was to be regarded as an exemption level. The June 2006 recommendations (paragraph 294) suggest an exclusion level for radon at 40 Bq/m3.
The third rationale is inaccurate. The intention in the first sentence seems to be to state that the risk (not the relative risk) is doubled for a lifetime exposure to 200 Bq/m3 based on the discussion in a later Section (3.3).
Response:
If you double the relative risk, you also double the absolute risk, provided the cancer baseline remains the same.
Such a doubling would appear to be associated with a much higher concentration if the risks as estimated in the cited studies are correct (see discussion below on that Section).
There are several things wrong with the point about lowering the radon concentration from 800 Bq/m3 to 200 Bq/m3. First, "lives saved" is a poor measure. Much better would be lung cancer cases avoided. Second, "steadily increases" hardly represents the variation in cases avoided with reducing action level since it ignores the distribution of numbers of houses at various concentrations and the subsequent distribution of lung cancer cases that are predicted on the basis of the linear model that has been applied. The distribution is skewed for example, as noted in Section 6.2, only 2.67% (surely this precision is unwarranted) of the houses have concentrations above 200 Bq/m3 so that if one looks at the collective radon exposure, 80% of the collective radon exposure is below this concentration. This estimate is based on rough averaging but the essential point is that a large fraction of the predicted lung cancer case linked to radon will be in houses below 200 Bq/m3. This is a consequence of using the linear non-threshold model for fitting. I am not advocating that one should or should not use such a model; merely following the consequences of the assumption made in the report. So from a public health point of view a guideline of 200 Bq/m3 is not very effective, as is the case with the current guideline of 800 Bq/m3.
Response:
The figures are based on lung cancer mortality, not incidence, so it is more appropriate to speak of lives saved rather than lung cancers avoided. Actually, the difference between lung cancer incidence and mortality is not great, since lung cancer has a five-year survival of only about 16%.
"Steadily increases" may not be the best phrase, but the point is that the number of lives saved becomes progressively greater as the radon action level is reduced.
We agree that a large fraction of collective radon exposure is due to concentrations below 200 Bq/m3, and it will not be possible to prevent every radon-induced lung cancer. For practical reasons, it is not feasible to set an action level much lower than 200. However, by setting the level at 200, it will be possible to significantly reduce the risk to the most highly-exposed individuals and also to have a substantial impact on the number of lung cancer cases.
Note that there may be a threshold for radon-induced lung cancer, but it is almost certainly less than 200 Bq/m3, based on the work of Krewski and Darby and also from dosimetric considerations. Darby's results indicate an upper 95% confidence limit of 150 Bq/m3 for a threshold if one exists. If there is a real threshold greater than zero but less than 150 Bq/m3, then our estimate of total radon-induced lung cancers will be too high, but the number of lung cancers to be avoided by lowering the guideline from 800 to 200 should remain the same.
The logic of the last sentence in #3 rationale seems faulty. With the assumed linear relationship between radon concentration and probability of lung cancer, the overall radiation background is irrelevant.
Response:
The annual dose from exposure to radon at 60 Bq/m3 is 1 mSv, based on the ICRP method of conversion. This is comparable to the natural background radiation from other sources: cosmic, terrestrial gamma, ingested natural radionuclides. Even if one accepts the LNT hypothesis, there comes a point where it makes very little sense to try to achieve further radon reduction.
Page 4, Section 3.1
Here and elsewhere (e.g., Section 3.2, paragraph 4) the odds ratio (OR) is equated with the relative risk (RR). They are not the same quantities and generally they do not have the same value. There are good statistical reasons for expressing results in ORs, as Krewski et al. do, but the reader needs to be aware that ORs are always greater than RRs and it is only when there is virtually no effect do the values converge.
Page 4, Section 3.2
Darby et al. actually espressed their estimates as RRs, not ORs.
Response:
The point is well taken and a correction will be made in the report.
Page 5, Section 3.3
The sources of the values listed in this section are not given. The relative lifetime risks for smokers and non-smokers are not what others have deduced from the papers cited earlier. For example, Darby et al. state: . . . then at the usual radon levels of 0, 100, 400, and 800 Bq/m3, respectively, cumulative absolute risks of lung cancer by age 75 years would be 0.41%, 0.47%, 0.67%, and 0.93% in lifelong non-smokers and 10.1%, 11.6%, 16.0%, and 21.6% in cigarette smokers. . .
The ICRP in its latest draft general recommendations concur with this estimate, sensibly reducing the quoted precision:
Recent pooled analyses of European and North American and Chinese residential case-control studies (Darby et al 2005, 2006; Krewski et al. 2005, 2006; Lubin et al. 2004) indicate a significant association between the risk of lung cancer and exposure to residential radon. On the basis of currently available information, the Commission believes that the measurement adjusted risk coefficients reported from the European pooling study (Darby et al 2005, 2006) currently provides a basis for estimating lifetime risks to people at home, i.e. an ERR per 100 Bq m3 of 0.16 (95% CI: 0.05 - 0.31) after adjustment for smoking status. In the absence of other causes of death, absolute lung cancer risks by age 75 at usual radon concentrations of 0, 100, and 400 Bq/m3 would be about 0.4%, 0.5% and 0.7% respectively for lifelong non-smokers, and about 25 times greater (10%, 12% and 16%) for cigarette smokers.
Note the big discrepancy between the values for non-smokers estimated by Darby et al., (and agreed to by the ICRP) and those in Section 3.3.
The correct values for Section 3.3 for the lifetime risks to non-smokers exposed to radon are:
Radon at 800 Bq/m3 0.93%
Radon at 200 Bq/m3 0.54%
No exposure to radon in home 0.41%
On this basis the lifetime risk to a non-smoker living in a house at 200 Bq/m3 would appear to be about 30% above that for a non-smoker in a house with no home radon exposure. The lifetime risk for such a person would be doubled at a concentration of radon of 680 Bq/m3. (Compare the statement in the #3 rationale.)
Response:
The estimated risks of radon-induced lung cancers in Section 3.3 of the Working Group report were based on a U.S. EPA adaptation of the BEIR-VI report. BEIR-VI applied two approaches: an exposure-age-concentration model and an exposure-age-duration model, both based on relative risk. The model parameters were derived from the uranium miner studies. A sub-multiplicative interaction between smoking and radon exposure was found to give a better fit to the miner data. The U.S. EPA approach combines the two models but gives results closer to the lower estimates of the exposure-age-duration model. The Working Group report applied this model using Canadian statistics for overall mortality, baseline lung cancer rates, and smoking prevalence, to obtain risk estimates from lifetime exposure to various household radon concentrations (equilibrium ratio = 0.4; occupancy = 70%). The details of this calculation will be spelled out more clearly in subsequent reports.
From their residential study, Darby et al. derive an excess relative risk of 16% for each 100 Bq/m3 exposure to household radon. From this, one can readily estimate the radon concentration that doubles the relative risk: 100% /16% x 100 Bq/m3 = 625 Bq/m3. Darby et al. then assume that the same relative risk applies equally to both smokers and non-smokers. This is the origin of the difference in lifetime risk estimates to non-smokers derived in the Working Group report. A sub-multiplicative interaction between smoking and radon exposure, as recommended by BEIR-VI, implies a higher relative risk to non-smokers as compared to smokers. (Of course the absolute risk of radon-induced lung cancer to smokers is much higher because of the higher baseline lung cancer rate.)
The reason for the higher relative risk to non-smokers can be understood from the following simplified argument. Let (1+ α) represent the increased relative risk from smoking one pack of cigarettes per day for a lifetime. Let (1+β) represent the increased relative risk for lifetime exposure to radon at 100 Bq/m3. In a purely multiplicative model, the combined risk from smoking and radon exposure = (1+ α) (1+β). In a sub-multiplicative model, the combined risk is <(1+ α) (1+β). Since smoking is the dominant cause of lung cancer, we can assume that the factor (1+ α) is affected very little by the interaction. This means that the (1+β) must be smaller for the smoker than for the non-smoker, due to the sub-multiplicative nature of the interaction.
We believe it is more prudent to follow the BEIR-VI recommendation for a sub-multiplicative model. This gives a doubling of the relative risk to a non-smoker at a lifetime exposure to 200 Bq/m3 radon.
In the light of the recent drive to eliminate exposure to second-hand smoke in public places, based on studies that have been interpreted to indicate a risk from such exposures, some thought needs to be given to the possibility that the estimated radon-linked risk to non-smokers may have been influenced by exposure of the non-smokers to second-hand smoke. Such an influence, if present, increases the conservatism of recommendations here as they relate to non-smokers. Note that this comment should not be seen as endorsing the results from any such studies; it is merely pointing to the implications of their interpretation.
Response:
Exposure to second-hand smoke may well be a factor in the baseline rate of lung cancer in non-smokers. However, there is no apparent reason why exposure to second hand smoke should increase with a higher radon exposure. In fact, one would expect the opposite; exposure to second hand smoke would be higher in public places and multi-storey dwellings in urban areas, just where radon levels are expected to be lower. Thus, it is unlikely that the correlation between lung cancer risk and radon in non-smokers can be explained by exposure to second-hand smoke.
Page 6, Section 3.4
In this Section, the public health aspects of the issue are stressed but, as noted in these comments earlier, the proposed strategy is not actually addressing public health. The occurrence of most lung cancers (on the basis of the model applied) will be in the houses with concentrations below 200 Bq/m3.
Response:
This point was addressed above.
The details of the derivation for the estimated lung cancers attributed to radon are not given but an approximate reality check can be made. Taking the absolute incremental lifetime risk for lung cancer in non-smokers as 0.06% per 100 Bq/m3 and that for smokers as 1.4% per 100 Bq/m3, the fraction of smokers in the population as 30%, a lifetime as 75 years and the population of Canada as 30 million, we can estimate that 10% of the lung cancers linked to radon are in non-smokers (from the weighted absolute risk) and the number of annual lung cancer cases is 900. This latter number is the same order of magnitude as given in Table 3.4. Hence, if we take the estimated lung cancers attributable to radon as 1500 (as a rounded number) annually then 150 will be in non-smokers and 1350 in smokers. (Were we dealing with a non-smoking population the annual number of 1500 would be reduced to about 25%; i.e, about 400.)
Were all homes above 200 Bq/m3 to be remediated down to essentially zero concentrations, then, as noted above, only 20% of the estimated radon-linked lung cancer cases would be eliminated because of the skewed distribution of radon concentrations and the linear risk model assumed. Hence the annual number of cases avoided would be 30 in non-smokers and 270 in smokers.
It needs to be kept in mind that the error bars on the risk estimates are wide and simply propagating those error bars from the epidemiological studies would give the corresponding ranges (95% confidence values) in annual numbers of cases to be 10 to 60 for non-smokers and 90 to 540 for smokers.
These numbers provide a perspective for the financial implications for the National Energy Plan noted in Section 7.6.
The conclusion I draw from this analysis is that any rationale has to be on the basis of individual risk rather than attempts to make large reductions in the overall numbers of cancers linked to radon. This is, of course, contingent on the linear model being valid.
Response:
The point is well taken that if smoking prevalence could be reduced to zero, then conformity with a 200 Bq/m3 guideline would save only an additional 10 to 60 lung cancer deaths per year. Given the addictive nature of tobacco smoking, conformity with the radon guideline may be achieved more quickly and cost-effectively than the elimination of all smoking. A comprehensive health policy should strive to tackle the causes of cancers on all fronts, including smoking and radon exposure.
Page 7, Section 4.1
There is an interesting issue that arises were decisions to be made based on short-term measurements in homes, which does not appear to have been addressed in the report.
Darby et al. make the point that the concentrations as measured over short periods are high compared with usual radon concentrations; i.e, the long-term averages over years. They adjust the values of radon concentration applied in the estimation of relative risk accordingly. Hence, their reported risk values are based on long-term average radon concentrations.
If the value for an action guideline is set on the basis of the purported lifetime risk (as seems to be the case) then the measurement should be appropriate to that guideline and should reflect long-term average radon concentrations. But some of the monitoring to be carried out may well be short term (i.e., less than a year). There needs to be some warning about the likely bias, possibly with a protocol to apply some correction (reduction) to measured concentrations, depending on their magnitude. An alternative is that the guideline is adjusted upwards to partially reflect at least a relative risk based on Darby et al.'s unadjusted radon concentrations. There is roughly a factor of two here (see Table 2 and Figure 1 in Darby et al.) This is the more straightforward resolution - some slight conservatism built into the guideline.
Response:
Health Canada is now working with federal/provincial/territorial partners on an implementation plan for the new guideline. This point will be addressed in the plan being developed.
(2) Conclusions and Recommendations
Conclusions
(a) If the criterion mentioned in rationale #3 is maintained, then doubling the lifetime risk for lung cancer in a non-smoker would appear, on the basis of the cited studies, to be at a concentration of about 700 Bq/m3.
Response:
The commenter seems to agree that doubling the risk to a non-smoker is a valid criterion for setting a guideline. Our analysis, as described above, is based on BEIR-VI recommendations and implies that the risk to a non-smoker is doubled at a lifetime exposure to 200 Bq/m3.
(b) The risk value (from Darby et al.) is based on the average long-term concentration of radon and is twice the value that would have been obtained if actual measured values were used in the estimation. Those authors note the bias often found in measurements. Measured values appear to be as much as a factor of two high compared with actual long-term year-to-year values at 800 Bq/m3 and above. Hence, as in (a), if the criterion of rationale #3 is maintained, it could be argued that the value for the guideline to which actual measurements will be compared could be up to twice the concentration noted in (a); i.e, 1400 Bq/m3.
Response:
There is a tendency for short-term radon measurements to be biased high; however, we would be reluctant to take credit for this effect when testing a dwelling for compliance with a radon guideline.
(c) Given the uncertainty cited for the risk value (a range from about 0.3X to 2X), conservatively applying the upper value for risk brings us back to 700 Bq/m3.
(d) The estimates above follow from the rationale given in the report. I am not suggesting that either of these values should be selected as the guideline. The point is that a guideline of 200 Bq/m3 is inconsistent with the rationale in the report.
(e) There has been no consideration of the influence that secondhand smoke may have had on the incidence of lung cancer in those designated as non-smokers in the various studies.
Response:
The data show a positive association between lung cancer and radon concentration. We cannot find a plausible mechanism to explain how exposure to second-hand smoke could be a confounding factor in this association.
(f) The current and anticipated international recommendations are that an action guideline should be set in the range 200 Bq/m3 to 600 Bq/m3. Further, there is a suggestion that a value of concentration up to 200 Bq/m3 could be selected as an exemption level.
Response:
Our understanding is that the draft ICRP document sets a maximum constraint of 600 Bq/m3 and then recommends that national authorities set their own constraint equal to or less than this maximum value.
(g) Points (a) through (f) lead to the conclusion that the current guideline value of 800 Bq/m3 is a fair compromise as a value that should trigger remediation. However, recognizing there is a desire to show some solidarity with the international community, I believe that a reduction to 600 Bq/m3 for the fundamental guideline would make sense.
(h) A problem would appear to be persuading members of the public to take any action, at any level, so it seems likely that there are houses still with concentrations substantially greater than the current guideline. The introduction of a high value (along with the slightly revised value for the actual guideline) that should trigger urgent action, backed up by real incentives and pressure that have been absent from the current guideline seems a useful idea.
Response:
Public inaction will be an obstacle to action at any guideline value. We believe that a higher value of the guideline would only encourage a greater degree of complacency.
Recommendations
The first two points in the radon guideline as given in the report should be revised to:
Remedial measures should be undertaken in a dwelling whenever the average annual radon concentration exceeds 600 Bq/m3 in the normal occupancy area.
The higher the radon concentration, the sooner remedial measures should be undertaken. At concentrations of 1200 Bq/m3 or above, these measures should be completed within one year after measuring and confirming the concentration.
Response:
For the reasons discussed in the report, a guideline value of 600 Bq/m3 gives an individual risk that is unacceptably high. It also does not allow a significant reduction in lung cancer rates, since only a small fraction of Canadian homes exceed this level. Many homes have radon levels between 200 and 600 Bq/m3, and compliance with a 200 Bq/m3 guideline could prevent several hundred cases of lung cancer per year.
The latest version of the recommendations state that, at concentrations above 600 Bq/m3, remediation should be completed within one year. To allow more than one year for concentrations just below 1200 Bq/m3 would again imply an unacceptably high risk.
