Radiation Protection Dosimetry Advance Access published August 25, 2014 Radiation Protection Dosimetry (2014), pp. 1–5
doi:10.1093/rpd/ncu239
THE PLANNED BRAZILIAN INDOOR RADON SURVEY—CONCEPTS AND PARTICULAR CHALLENGES N. C. Da Silva1 and P. Bossew2,* 1 Laboratory of Poc¸os de Caldas (LAPOC), Brazilian Commission for Nuclear Energy (CNEN), Rodovia Poc¸os de Caldas—Andradas km 13, Poc¸os de Caldas, Minas Gerais 37701-970, Brasil 2 German Federal Office for Radiation Protection, Ko¨penicker Allee 120-130, Berlin 10318, Germany *Corresponding author: [email protected]
INTRODUCTION Radon is increasingly acknowledged as a significant hazard to health. Estimates based on large-scale epidemiological studies(1) suggest that exposure to indoor radon (Rn) is the second most important cause of lung cancer after smoking. Extensive Rn surveys in Europe and North America performed over 30 y evidenced regionally high indoor Rn levels resulting in exposure and finally radiation doses sometimes deemed unacceptably high. As a consequence, steps towards regulation aimed to limit this hazard have been taken. The new European Basic Safety Standards of radiation protection(2), which must be implemented as laws and regulations in EU member states, define a maximum reference level for dwellings and workplace of 300 Bq m23 (long-term average) and require the development and implementation of radon action plans aimed at reducing Rn exposure, in line with the recommendations of the WHO handbook(1). Traditionally, Brazil has been considered a country with no major indoor Rn problem because of the overall benign climate that allows high ventilation rates and because of common building styles and living habits. However, regional small screening surveys have revealed that this is not necessarily the case; some results are shown in Figure 1. These results, together with an increasing interest in Rn studies, in line with the international trend, led to the idea that a countrywide Rn survey might be embarked. First attempts of coordinating Rn studies and surveys carried out by different groups across the country and initial discussions how to proceed on a larger scale were made at the First Rn Seminary, September 2012, Natal (www.1srnbr.larana.geologia .ufrn.br/index.php). So far only first concepts exist. Such survey would be a challenge given the size of the
country (about equal to whole Europe) and its diversity in many respects. DEVELOPING A STRATEGY A radon strategy consists of several conceptual steps: † Identification of targets, i.e. which quantity (or quantities) shall be assessed; † Next a monitoring survey must be designed, which is capable of achieving the targets; † A large-scale survey includes logistic efforts that require special attention; this includes building a team of experts from different disciplines, coordination of activities, technical facilities for evaluation and quality assurance (QA); † Results must be evaluated and interpreted; † Response to the results must be prepared in time, in terms of advice to the public and to authorities. Usually, the target of an Rn survey is estimating mean Rn concentrations in dwellings and/or workplace as proxies to exposure. One will also want to know the geographical distribution of local or regional means in the form of Rn maps. Additionally, one is often interested in risk, defined as probability that a reference level is exceeded. Also this quantity will usually be mapped. Another quantity of interest is potential risk, which is the component of the Rn problem generated by natural causes, essentially geology. Quantified by a variable often called Rn potential (RP), this indicates where a higher probability of elevated exposure can be expected. IDENTIFICATION OF PRIORITIES The size of the country and the big logistical problems that can be expected suggest setting priorities. As
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at University of Windsor on October 29, 2014
Similar to the tendency in Europe and North America, awareness towards environmental hazards to health has been rising strongly in Brazil for some years. Among these, indoor radon (Rn) is increasingly being acknowledged as an indoor pollutant that contributes to lung cancer and which one therefore attempts to limit by regulations. Scattered regional surveys performed in Brazil have shown that Rn problem may exist in certain regions, but not much is known about its possible overall extent. Therefore, the idea of a national survey has been brought forward. It is still in the conceptual phase; in this contribution, the authors present the state of knowledge and addressing of particular challenges that can be expected to be encountered.
N. C. DA SILVA AND P. BOSSEW
indoor Rn is, putting qualitatively, the product of a geogenic factor, related to geology, and an anthropogenic factor, related to building style and living habits (in turn partly dependent on climatic factors), one will try to identify situations that may result in elevated probability for higher indoor Rn levels. Geogenic factors Geological structures that have higher RP are those with higher source term, i.e. Ra concentration, in particular, acid plutonites (granite) and sedimentites (possibly metamorphic) whose origin are sediments bearing organic matter, such as typically black shale. The second factor is permeability. High permeability can lead to high RP even without high Ra concentration. The most important examples are karst (in limestone which is itself usually of low RP) or recent (in geological terms) rather loose alluvial/colluvial sediments and rubble, in Europe typically post-glacial structures. However, it has been shown in Brazil that also other structures can lead to high RP, such as the alkaline extrusive rocks of the Poc¸os de Caldas unit in which one would perhaps not expect high RP. Therefore, screening of geological units for their RP may be a priority to identify the ‘geogenic radon-
prone areas’, which for geological reasons should be investigated first. A strongly simplified geological map is shown in Figure 2 [obtained by rough digitisation of the geological map shown in (14)]. Anthropogenic factors In analogy with radon-prone geology, one can speak about Rn prone buildings. These are ones that (a) allow infiltration and (b) accumulation. Infiltration is easier if living areas are connected to the ground without efficient barrier against gas exchange. Such barriers are insulating layers in the foundations or basements without connection to living rooms in higher levels. Accumulation depends on ventilation rate. One can expect ventilation to depend on climate whose zones range from temperate ones in the South that can have harsh winters, thus affording heating and house insulation, to tropical in the North, from humid along coasts and in part of the tropical zones to arid in the NorthEast. Air conditioning is increasingly common in hot summers in the South and in tropical regions, and for security reasons, people tend to sleep with closed windows although the climate would allow otherwise. Building styles also depend on socio-economic factors more in Europe, ranging from typical middle-
Page 2 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Windsor on October 29, 2014
Figure 1. Regional indoor Rn surveys (values in Bq m23)(3 – 13).
PLANNED BRAZILIAN INDOOR RADON SURVEY
class high-rise apartments in cities to suburbia-type family houses and over rural farm and village houses to poor neighbourhoods where direct contact of living rooms with the ground can be expected. Also building materials can be Rn sources. A particular problem may occur if raw clay is used, as is common particularly in poorer rural regions of the North-East. Clay can contain relatively high concentrations of thorium, which together with high porosity can lead to high 220Rn (thoron, Tn) exhalation. This possible problem is being investigated more systematically only recently in clay buildings in China, India and Europe. Cases with important or even dominant contribution of Tn have been found. As a consequence, one may attempt to identify ‘radon-prone building styles’, for which one may consider screening a priority. An indoor Rn survey requires an appropriate design, which includes the possibility to select dwellings as representatively as achievable, given the demographic reality. Although good databases exist in Brazil, actual selection is difficult, as is the subsequent step, contacting the inhabitants. Also the size of the country and the resulting large number of samples poses particular
logistic problems, from detector deployment and collection to lab capacities for evaluation. REPRESENTATIVE AND ACCURATE SAMPLING The quantity that is being assessed must be sampled in a way that the wanted statistics is an unbiased and accurate—up to an allowable tolerance—estimate of the true one. For example, if the target value is the mean Rn concentration per municipality, to which citizens are exposed, samples from dwellings in the municipality must be taken representatively, i.e. such that the spatially varying population density as well as types of dwellings and houses are included according to the proportion in which they occur. Such approach is called design based, because it relies on appropriate sampling design. In contrast, a model-based approach takes existing, possibly unrepresentative or not optimal data and applies models that allow recovering the required statistics. Although the first approach is simpler in concept, an ideal design is rarely achievable. One may therefore think in some cases to include modelling steps to tentatively remove
Page 3 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Windsor on October 29, 2014
Figure 2. Strongly simplified geological map of Brazil.
N. C. DA SILVA AND P. BOSSEW
Sociological aspects Representative sampling can be the most challenging part of a survey. Designing a sampling scheme requires constructing a representative sample, which implies knowing demographic data and above all, a way to address inhabitants and perform the measurements. This can be difficult to very different degree depending on socio-economic factors. Designing and implementing a representative sampling scheme therefore requires inclusion of experts in demography and sociology. Also importantly, the public must be informed on rationale and objectives and, in essence, about the procedure, which implies inclusion of multiplicators such as trustworthy media, teachers and health workers. Again this requires specialised experts. Workplace Increasingly in civilisation, people spend time working indoors. Therefore, working environments may contribute significantly to the Rn burden. Because building characteristics of indoor workplace may be completely different from the ones of dwelling environments, it cannot be assumed automatically that exposure in homes and schools is comparable even on top of the same geogenic RP. In particular, it may be necessary—for the sake of focussing on priorities—to identify ‘radon-prone workplaces’ (also addressed in the EU BSS(2)). Quality assurance Surveys that allow drawing conclusions with possibly far-reaching consequences require reliable measuring.
This includes establishing measurement protocols and also facilities for calibration of devices (themselves quality assured with respect to primary standards) and intercomparison exercises to assure comparability of results. Also logistics itself, from coordination over budgeting to communication, must comply with modern QA standards.
AUXILIARY INVESTIGATIONS Some of the issues addressed in the previous sections will have to be investigated in separate projects that may run in parallel with the actual surveys. Among these studies are the following: † †
†
†
Characterisation of geologies with respect to their RP; Physical properties of certain types of buildings regarding Rn infiltration and accumulation; role of air-conditioning systems; possible function of elevators (ubiquitous in high-rise apartment buildings) and installation tubes as ‘Rn ducts’; clay walls as Tn sources; Usability of geochemical quantities or dose rate [which exist already to larger extent and are easier to collect than Rn(18)] as proxies for geogenic or indoor Rn; Establishing regional calibration and intercomparison facilities, developing sampling protocols.
CONSEQUENCES OF FINDINGS Once results of surveys are available and public, authorities will have to respond. Citizens as well as local authorities will rightly want to know which action is required if elevated Rn levels were found. This implies that action plans and strategies to communicate with the public will have to be prepared in time. Experience from Europe has shown that this can be a tedious and time-consuming subject whose difficulty and importance should definitely not be underestimated. Even though more difficult, one must be aware that recommending remediation has possibly heavy economic implications both for house owners and authorities, as public buildings, from schools and hospitals to offices, are concerned. Also, once geogenic radonprone areas have been identified, one may think about implementing building codes, because constructing in a way that decreases Rn infiltration is far more economic than remediation afterwards. REFERENCES 1. WHO. WHO handbook on indoor radon—a public health perspective. Available on www.who.int/ionizing_radiation/ env/radon/en/index1.html (3 September 2013, date last accessed) (2009).
Page 4 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Windsor on October 29, 2014
biases. If one has to rely on imperfect samples only, because for example they come from a survey that had different objectives, modelling is the only way. The uncertainty of the mean has its physical origin in the true variability of the sampled quantity, also inevitable measurement uncertainty contributes. Given a true (in general unknown) variability, the uncertainty of the mean depends on the number of samples. The higher the variability, the more samples are necessary to achieve a required accuracy. Methods to estimate the necessary number of samples to achieve a wanted accuracy have been proposed; however, their discussion would exceed the possibilities of this article. IAEA documents statistical aspects of Rn surveys, including the matter of representativeness(15). A standard book on environmental sampling and monitoring covers many statistical aspects(16). Zielinski et al.(17) proposed a sampling rate of 0.5 % of dwellings in cities with .100 000 inhabitants, resulting in 110 000 samples. Smaller cities and rural regions would come in addition.
PLANNED BRAZILIAN INDOOR RADON SURVEY 11. Santos, T. O., Rocha, Z., Barreto, A. A., de Souza, L. A. C., Miguel, R. A. and de Oliveira, A. H. Indoor radon distribution in metropolitan region of Belo Horizonte, Brasil. In: 2009 International Nuclear Atlantic Conference—INAC 2009, Rio de Janeiro, Brazil, 27 September–2 October 2009. Available on http:// library.sinap.ac.cn/db/hedianwencui201104/%E5%85% A8%E6%96%87/41109064.pdf (20 February 2013, date last accessed) (2009). 12. Santos, T. O., Rocha, Z., Barreto, A. A., de Souza, L. A. C., Miguel, R. A. and de Oliveira, A. H. Indoor radon distribution in the metropolitan region of Belo Horizonte, Brazil. Revista Brasileira de Cieˆncias Ambientais. 13, 10–17 (2009b). Available on www. rbciamb.com.br/images/online/RBCIAMB-N13-Ago2009-Materia02_artigos212.pdf (20 February 2013, last accessed date). 13. Veiga, L. H. S., Koifman, S., Melo, V. P., Sachet, I. and Amaral, E. C. S. Preliminary indoor radon risk assessment at the Poc¸os de Caldas plateau, MG –Brazil. J. Environ. Radioactiv. 70(3), 161– 176 (2003). 14. Schenk, C. J. et al. Maps showing geology, oil and gas fields and geological provinces of the South America region. US Geological Service Report 97470D. Available on http://pubs.usgs.gov/of/1997/ofr97-470/OF97-470D/ (12 June 2014, date last accessed) (n.y.). 15. IAEA. National and regional surveys of radon concentration in dwellings; review of methodology and measurement techniques. IAEA Analytical Quality in Nuclear Application Series No. 33, Report IAEA/AQ/33. Available on www-pub.iaea.org/MTCD/Publications/ PDF/IAEA-AQ-33_web.pdf (28 February 2014, date last accessed) (2013). 16. Gilbert, R. O. Statistical Methods for Environmental Pollution Monitoring. J. Wiley (1987), ISBN: 9780471288787. 17. Zielinski, J. M., Canoba, A. C., Shilnikova, N. S. and Veiga, L. H. S. Working towards Residential Radon Survey in South America. IRPA 12 Buenos Aires, 19– 24.10.2008. Available on www.foroiberam.org/web/guest/ fondo-documental?documentoId=523207 (28 February 2014, date last accessed) (2008). 18. Projeto Planalto. Projeto Planalto Poc¸os de Caldas– Pesquisa Caˆncer e Radiac¸a˜o Natural. Ed. Secretaria de Estado de Sau´de de Minas Gerais. Available on www.cnen. gov.br/lapoc/Projeto_pocos_de_caldas.pdf (28 February 2014, date last accessed) (2009).
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2. BSS. European Council: Council Directive 2013/59/ Euratom laying down basic safety standards for protection, etc. Available on http://eur-lex.europa.eu/JOHtml. do?uri=OJ:L:2014:013:SOM:EN:HTML (24 February 2014, date last accessed ) (2014). 3. Campos, T., Petta, R. and Pastura, V. Residential radon and the risk of malignity: the case of Lages Pintadas city, North-eastern Brazil. GeoMed2011, Italy. Only abstract available. Available on www.cprm.gov.br/pgagem/bari_ italia/176.pdf (20 February 2013, date last accessed) (2011). 4. Canoba, A. et al. Indoor radon measurements in six Latin American countries. Geofisica Int. 41(4), 453–457 (2002). 5. Correˆa, J. N. Avaliac¸a˜o dos niveis de concentrac¸a˜o de radoˆnio em ambientes e a´guas de poc¸os no estado do Parana´. Thesis, Universidade Tecnolo´gica Federal do Parana´, Curitiba, 2011. Available on http://files.dirppg. ct.utfpr.edu.br/cpgei/Ano_2011/teses/CPGEI_Tese_068_ 2011.pdf; More information in Correˆa J. N. Avaliac¸a˜o da concentrac¸a˜o de radoˆnio em ambientes de convı´vio humano na regia˜o metropolitana de Curitiba. Master thesis, Universidade Tecnolo´gica Federal do Parana´, Curitiba, 2006. Available on www.ppgem.ct.utfpr.edu. br/dissertacoes/CORREA,%20Janine%20Nicolosi.pdf (both last accessed 18 February 2013). 6. Lima Marques, A., Geraldo, L. P. and dos Santos, W. Nı´veis de radioatividade natural decorrente do radoˆnio no complexo rochoso da Serra de Sa˜o Vicente, SP. Radiologia Brasileira. 39(3), 215– 218. Available on www.rb.org.br/detalhe_artigo.asp?id=1287 (22 February 2013, date last accessed) (2006). 7. Magalha˜es, M. H., Amaral, E. C. S., Sachett, I. and Rochedo, E. R. R. Radon-222 in Brazil: an outline of indoor and outdoor measurements. J. Environ. Radioactiv. 67(2), 131–143 (2003). 8. Malanca, A. and Gaidolfi, L. Environmental radon in some Brazilian towns and mines. Radiat. Protect. Dosim. 69(3), 211–216 (1997). 9. Malanca, A., de Azevedo, L. L., Repetti, M. and Gaidolfi, L. Background airborne radioactivity in an equatorial Brazilian town. J. Radioanalyt. Nucl. Chem. 221(1– 2), 189– 191 (1997). 10. Santos, T. O., Rocha, Z., Barreto, A. A., Ferreira, A. V. and de Oliveira, A. H. Indoor radon measurements in dwellings and other buildings in the metropolitan region of Belo Horizonte, Brazil. IRPA 12, Buenos Aires. Available on http://irpa12.org.ar/fullpapers/FP3224. pdf (20 February 2013, date last accessed) (2008).
doi:10.1093/rpd/ncu239
THE PLANNED BRAZILIAN INDOOR RADON SURVEY—CONCEPTS AND PARTICULAR CHALLENGES N. C. Da Silva1 and P. Bossew2,* 1 Laboratory of Poc¸os de Caldas (LAPOC), Brazilian Commission for Nuclear Energy (CNEN), Rodovia Poc¸os de Caldas—Andradas km 13, Poc¸os de Caldas, Minas Gerais 37701-970, Brasil 2 German Federal Office for Radiation Protection, Ko¨penicker Allee 120-130, Berlin 10318, Germany *Corresponding author: [email protected]
INTRODUCTION Radon is increasingly acknowledged as a significant hazard to health. Estimates based on large-scale epidemiological studies(1) suggest that exposure to indoor radon (Rn) is the second most important cause of lung cancer after smoking. Extensive Rn surveys in Europe and North America performed over 30 y evidenced regionally high indoor Rn levels resulting in exposure and finally radiation doses sometimes deemed unacceptably high. As a consequence, steps towards regulation aimed to limit this hazard have been taken. The new European Basic Safety Standards of radiation protection(2), which must be implemented as laws and regulations in EU member states, define a maximum reference level for dwellings and workplace of 300 Bq m23 (long-term average) and require the development and implementation of radon action plans aimed at reducing Rn exposure, in line with the recommendations of the WHO handbook(1). Traditionally, Brazil has been considered a country with no major indoor Rn problem because of the overall benign climate that allows high ventilation rates and because of common building styles and living habits. However, regional small screening surveys have revealed that this is not necessarily the case; some results are shown in Figure 1. These results, together with an increasing interest in Rn studies, in line with the international trend, led to the idea that a countrywide Rn survey might be embarked. First attempts of coordinating Rn studies and surveys carried out by different groups across the country and initial discussions how to proceed on a larger scale were made at the First Rn Seminary, September 2012, Natal (www.1srnbr.larana.geologia .ufrn.br/index.php). So far only first concepts exist. Such survey would be a challenge given the size of the
country (about equal to whole Europe) and its diversity in many respects. DEVELOPING A STRATEGY A radon strategy consists of several conceptual steps: † Identification of targets, i.e. which quantity (or quantities) shall be assessed; † Next a monitoring survey must be designed, which is capable of achieving the targets; † A large-scale survey includes logistic efforts that require special attention; this includes building a team of experts from different disciplines, coordination of activities, technical facilities for evaluation and quality assurance (QA); † Results must be evaluated and interpreted; † Response to the results must be prepared in time, in terms of advice to the public and to authorities. Usually, the target of an Rn survey is estimating mean Rn concentrations in dwellings and/or workplace as proxies to exposure. One will also want to know the geographical distribution of local or regional means in the form of Rn maps. Additionally, one is often interested in risk, defined as probability that a reference level is exceeded. Also this quantity will usually be mapped. Another quantity of interest is potential risk, which is the component of the Rn problem generated by natural causes, essentially geology. Quantified by a variable often called Rn potential (RP), this indicates where a higher probability of elevated exposure can be expected. IDENTIFICATION OF PRIORITIES The size of the country and the big logistical problems that can be expected suggest setting priorities. As
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at University of Windsor on October 29, 2014
Similar to the tendency in Europe and North America, awareness towards environmental hazards to health has been rising strongly in Brazil for some years. Among these, indoor radon (Rn) is increasingly being acknowledged as an indoor pollutant that contributes to lung cancer and which one therefore attempts to limit by regulations. Scattered regional surveys performed in Brazil have shown that Rn problem may exist in certain regions, but not much is known about its possible overall extent. Therefore, the idea of a national survey has been brought forward. It is still in the conceptual phase; in this contribution, the authors present the state of knowledge and addressing of particular challenges that can be expected to be encountered.
N. C. DA SILVA AND P. BOSSEW
indoor Rn is, putting qualitatively, the product of a geogenic factor, related to geology, and an anthropogenic factor, related to building style and living habits (in turn partly dependent on climatic factors), one will try to identify situations that may result in elevated probability for higher indoor Rn levels. Geogenic factors Geological structures that have higher RP are those with higher source term, i.e. Ra concentration, in particular, acid plutonites (granite) and sedimentites (possibly metamorphic) whose origin are sediments bearing organic matter, such as typically black shale. The second factor is permeability. High permeability can lead to high RP even without high Ra concentration. The most important examples are karst (in limestone which is itself usually of low RP) or recent (in geological terms) rather loose alluvial/colluvial sediments and rubble, in Europe typically post-glacial structures. However, it has been shown in Brazil that also other structures can lead to high RP, such as the alkaline extrusive rocks of the Poc¸os de Caldas unit in which one would perhaps not expect high RP. Therefore, screening of geological units for their RP may be a priority to identify the ‘geogenic radon-
prone areas’, which for geological reasons should be investigated first. A strongly simplified geological map is shown in Figure 2 [obtained by rough digitisation of the geological map shown in (14)]. Anthropogenic factors In analogy with radon-prone geology, one can speak about Rn prone buildings. These are ones that (a) allow infiltration and (b) accumulation. Infiltration is easier if living areas are connected to the ground without efficient barrier against gas exchange. Such barriers are insulating layers in the foundations or basements without connection to living rooms in higher levels. Accumulation depends on ventilation rate. One can expect ventilation to depend on climate whose zones range from temperate ones in the South that can have harsh winters, thus affording heating and house insulation, to tropical in the North, from humid along coasts and in part of the tropical zones to arid in the NorthEast. Air conditioning is increasingly common in hot summers in the South and in tropical regions, and for security reasons, people tend to sleep with closed windows although the climate would allow otherwise. Building styles also depend on socio-economic factors more in Europe, ranging from typical middle-
Page 2 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Windsor on October 29, 2014
Figure 1. Regional indoor Rn surveys (values in Bq m23)(3 – 13).
PLANNED BRAZILIAN INDOOR RADON SURVEY
class high-rise apartments in cities to suburbia-type family houses and over rural farm and village houses to poor neighbourhoods where direct contact of living rooms with the ground can be expected. Also building materials can be Rn sources. A particular problem may occur if raw clay is used, as is common particularly in poorer rural regions of the North-East. Clay can contain relatively high concentrations of thorium, which together with high porosity can lead to high 220Rn (thoron, Tn) exhalation. This possible problem is being investigated more systematically only recently in clay buildings in China, India and Europe. Cases with important or even dominant contribution of Tn have been found. As a consequence, one may attempt to identify ‘radon-prone building styles’, for which one may consider screening a priority. An indoor Rn survey requires an appropriate design, which includes the possibility to select dwellings as representatively as achievable, given the demographic reality. Although good databases exist in Brazil, actual selection is difficult, as is the subsequent step, contacting the inhabitants. Also the size of the country and the resulting large number of samples poses particular
logistic problems, from detector deployment and collection to lab capacities for evaluation. REPRESENTATIVE AND ACCURATE SAMPLING The quantity that is being assessed must be sampled in a way that the wanted statistics is an unbiased and accurate—up to an allowable tolerance—estimate of the true one. For example, if the target value is the mean Rn concentration per municipality, to which citizens are exposed, samples from dwellings in the municipality must be taken representatively, i.e. such that the spatially varying population density as well as types of dwellings and houses are included according to the proportion in which they occur. Such approach is called design based, because it relies on appropriate sampling design. In contrast, a model-based approach takes existing, possibly unrepresentative or not optimal data and applies models that allow recovering the required statistics. Although the first approach is simpler in concept, an ideal design is rarely achievable. One may therefore think in some cases to include modelling steps to tentatively remove
Page 3 of 5
Downloaded from http://rpd.oxfordjournals.org/ at University of Windsor on October 29, 2014
Figure 2. Strongly simplified geological map of Brazil.
N. C. DA SILVA AND P. BOSSEW
Sociological aspects Representative sampling can be the most challenging part of a survey. Designing a sampling scheme requires constructing a representative sample, which implies knowing demographic data and above all, a way to address inhabitants and perform the measurements. This can be difficult to very different degree depending on socio-economic factors. Designing and implementing a representative sampling scheme therefore requires inclusion of experts in demography and sociology. Also importantly, the public must be informed on rationale and objectives and, in essence, about the procedure, which implies inclusion of multiplicators such as trustworthy media, teachers and health workers. Again this requires specialised experts. Workplace Increasingly in civilisation, people spend time working indoors. Therefore, working environments may contribute significantly to the Rn burden. Because building characteristics of indoor workplace may be completely different from the ones of dwelling environments, it cannot be assumed automatically that exposure in homes and schools is comparable even on top of the same geogenic RP. In particular, it may be necessary—for the sake of focussing on priorities—to identify ‘radon-prone workplaces’ (also addressed in the EU BSS(2)). Quality assurance Surveys that allow drawing conclusions with possibly far-reaching consequences require reliable measuring.
This includes establishing measurement protocols and also facilities for calibration of devices (themselves quality assured with respect to primary standards) and intercomparison exercises to assure comparability of results. Also logistics itself, from coordination over budgeting to communication, must comply with modern QA standards.
AUXILIARY INVESTIGATIONS Some of the issues addressed in the previous sections will have to be investigated in separate projects that may run in parallel with the actual surveys. Among these studies are the following: † †
†
†
Characterisation of geologies with respect to their RP; Physical properties of certain types of buildings regarding Rn infiltration and accumulation; role of air-conditioning systems; possible function of elevators (ubiquitous in high-rise apartment buildings) and installation tubes as ‘Rn ducts’; clay walls as Tn sources; Usability of geochemical quantities or dose rate [which exist already to larger extent and are easier to collect than Rn(18)] as proxies for geogenic or indoor Rn; Establishing regional calibration and intercomparison facilities, developing sampling protocols.
CONSEQUENCES OF FINDINGS Once results of surveys are available and public, authorities will have to respond. Citizens as well as local authorities will rightly want to know which action is required if elevated Rn levels were found. This implies that action plans and strategies to communicate with the public will have to be prepared in time. Experience from Europe has shown that this can be a tedious and time-consuming subject whose difficulty and importance should definitely not be underestimated. Even though more difficult, one must be aware that recommending remediation has possibly heavy economic implications both for house owners and authorities, as public buildings, from schools and hospitals to offices, are concerned. Also, once geogenic radonprone areas have been identified, one may think about implementing building codes, because constructing in a way that decreases Rn infiltration is far more economic than remediation afterwards. REFERENCES 1. WHO. WHO handbook on indoor radon—a public health perspective. Available on www.who.int/ionizing_radiation/ env/radon/en/index1.html (3 September 2013, date last accessed) (2009).
Page 4 of 5
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biases. If one has to rely on imperfect samples only, because for example they come from a survey that had different objectives, modelling is the only way. The uncertainty of the mean has its physical origin in the true variability of the sampled quantity, also inevitable measurement uncertainty contributes. Given a true (in general unknown) variability, the uncertainty of the mean depends on the number of samples. The higher the variability, the more samples are necessary to achieve a required accuracy. Methods to estimate the necessary number of samples to achieve a wanted accuracy have been proposed; however, their discussion would exceed the possibilities of this article. IAEA documents statistical aspects of Rn surveys, including the matter of representativeness(15). A standard book on environmental sampling and monitoring covers many statistical aspects(16). Zielinski et al.(17) proposed a sampling rate of 0.5 % of dwellings in cities with .100 000 inhabitants, resulting in 110 000 samples. Smaller cities and rural regions would come in addition.
PLANNED BRAZILIAN INDOOR RADON SURVEY 11. Santos, T. O., Rocha, Z., Barreto, A. A., de Souza, L. A. C., Miguel, R. A. and de Oliveira, A. H. Indoor radon distribution in metropolitan region of Belo Horizonte, Brasil. In: 2009 International Nuclear Atlantic Conference—INAC 2009, Rio de Janeiro, Brazil, 27 September–2 October 2009. Available on http:// library.sinap.ac.cn/db/hedianwencui201104/%E5%85% A8%E6%96%87/41109064.pdf (20 February 2013, date last accessed) (2009). 12. Santos, T. O., Rocha, Z., Barreto, A. A., de Souza, L. A. C., Miguel, R. A. and de Oliveira, A. H. Indoor radon distribution in the metropolitan region of Belo Horizonte, Brazil. Revista Brasileira de Cieˆncias Ambientais. 13, 10–17 (2009b). Available on www. rbciamb.com.br/images/online/RBCIAMB-N13-Ago2009-Materia02_artigos212.pdf (20 February 2013, last accessed date). 13. Veiga, L. H. S., Koifman, S., Melo, V. P., Sachet, I. and Amaral, E. C. S. Preliminary indoor radon risk assessment at the Poc¸os de Caldas plateau, MG –Brazil. J. Environ. Radioactiv. 70(3), 161– 176 (2003). 14. Schenk, C. J. et al. Maps showing geology, oil and gas fields and geological provinces of the South America region. US Geological Service Report 97470D. Available on http://pubs.usgs.gov/of/1997/ofr97-470/OF97-470D/ (12 June 2014, date last accessed) (n.y.). 15. IAEA. National and regional surveys of radon concentration in dwellings; review of methodology and measurement techniques. IAEA Analytical Quality in Nuclear Application Series No. 33, Report IAEA/AQ/33. Available on www-pub.iaea.org/MTCD/Publications/ PDF/IAEA-AQ-33_web.pdf (28 February 2014, date last accessed) (2013). 16. Gilbert, R. O. Statistical Methods for Environmental Pollution Monitoring. J. Wiley (1987), ISBN: 9780471288787. 17. Zielinski, J. M., Canoba, A. C., Shilnikova, N. S. and Veiga, L. H. S. Working towards Residential Radon Survey in South America. IRPA 12 Buenos Aires, 19– 24.10.2008. Available on www.foroiberam.org/web/guest/ fondo-documental?documentoId=523207 (28 February 2014, date last accessed) (2008). 18. Projeto Planalto. Projeto Planalto Poc¸os de Caldas– Pesquisa Caˆncer e Radiac¸a˜o Natural. Ed. Secretaria de Estado de Sau´de de Minas Gerais. Available on www.cnen. gov.br/lapoc/Projeto_pocos_de_caldas.pdf (28 February 2014, date last accessed) (2009).
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2. BSS. European Council: Council Directive 2013/59/ Euratom laying down basic safety standards for protection, etc. Available on http://eur-lex.europa.eu/JOHtml. do?uri=OJ:L:2014:013:SOM:EN:HTML (24 February 2014, date last accessed ) (2014). 3. Campos, T., Petta, R. and Pastura, V. Residential radon and the risk of malignity: the case of Lages Pintadas city, North-eastern Brazil. GeoMed2011, Italy. Only abstract available. Available on www.cprm.gov.br/pgagem/bari_ italia/176.pdf (20 February 2013, date last accessed) (2011). 4. Canoba, A. et al. Indoor radon measurements in six Latin American countries. Geofisica Int. 41(4), 453–457 (2002). 5. Correˆa, J. N. Avaliac¸a˜o dos niveis de concentrac¸a˜o de radoˆnio em ambientes e a´guas de poc¸os no estado do Parana´. Thesis, Universidade Tecnolo´gica Federal do Parana´, Curitiba, 2011. Available on http://files.dirppg. ct.utfpr.edu.br/cpgei/Ano_2011/teses/CPGEI_Tese_068_ 2011.pdf; More information in Correˆa J. N. Avaliac¸a˜o da concentrac¸a˜o de radoˆnio em ambientes de convı´vio humano na regia˜o metropolitana de Curitiba. Master thesis, Universidade Tecnolo´gica Federal do Parana´, Curitiba, 2006. Available on www.ppgem.ct.utfpr.edu. br/dissertacoes/CORREA,%20Janine%20Nicolosi.pdf (both last accessed 18 February 2013). 6. Lima Marques, A., Geraldo, L. P. and dos Santos, W. Nı´veis de radioatividade natural decorrente do radoˆnio no complexo rochoso da Serra de Sa˜o Vicente, SP. Radiologia Brasileira. 39(3), 215– 218. Available on www.rb.org.br/detalhe_artigo.asp?id=1287 (22 February 2013, date last accessed) (2006). 7. Magalha˜es, M. H., Amaral, E. C. S., Sachett, I. and Rochedo, E. R. R. Radon-222 in Brazil: an outline of indoor and outdoor measurements. J. Environ. Radioactiv. 67(2), 131–143 (2003). 8. Malanca, A. and Gaidolfi, L. Environmental radon in some Brazilian towns and mines. Radiat. Protect. Dosim. 69(3), 211–216 (1997). 9. Malanca, A., de Azevedo, L. L., Repetti, M. and Gaidolfi, L. Background airborne radioactivity in an equatorial Brazilian town. J. Radioanalyt. Nucl. Chem. 221(1– 2), 189– 191 (1997). 10. Santos, T. O., Rocha, Z., Barreto, A. A., Ferreira, A. V. and de Oliveira, A. H. Indoor radon measurements in dwellings and other buildings in the metropolitan region of Belo Horizonte, Brazil. IRPA 12, Buenos Aires. Available on http://irpa12.org.ar/fullpapers/FP3224. pdf (20 February 2013, date last accessed) (2008).
