Residence related exposure in Lithuania from national survey to remedial measures

Transcription

1 Residence related exposure in Lithuania from national survey to remedial measures G.Morkunas 1, L.Pilkyte 1, G.Akerblom 2, 1 Radiation Protection Centre, Kalvariju 153, Vilnius, Lithuanian genmo@takas.lt, l.pilkyte@rsc.lt 2 Swedish Radiation Protection Authority, S Stockholm, Sweden g.akerblom@ssi.se Abstract. Radioactivity in the living environment is one of the most important sources of public exposure. Indoor radon and radionuclides in construction materials account for more than a half of annual effective dose both from natural and artificial sources in Lithuania. Annual average dose to inhabitants of detached houses according to the national survey is more than 1 msv, however the strong dependency on location of houses, i.e., conditions of radon transport into houses is observed. Measurements of concentrations of natural radionuclides in construction materials show that these concentrations in some cases can not be neglected from the point of view of radiation protection and the potential use of construction materials should be taken into account when deciding on possibility of their use. The results of surveys are used not only for determination of the national situation but also for drafting of national legislation on protection from natural exposure. It helps to keep the optimized approach based on existing situation and national resources. However, the problems are encountered both in selection of the appropriate remedial and prevention measures and in their implementation. Though designers of buildings and constructing companies, media and population are informed by different means about the existing situation and needs for optimization of protection from natural exposure not so much attention is paid to the problem. The problem is complicated by psychological priorities given to nuclear energy and radioactive waste management, though the increasing attention paid to the issues related with NORM might help to attract public attention to natural radiation in general. Information on exposure levels, approaches used in creation of legislation and public information and natural exposure related problems with particular emphasis of optimization issues and international co-operation are discussed in presentation. 1. Introduction Radiation protection of members of public among other factors depends on sources and pathways of exposure and amenability of these sources and pathways to control. Many artificial sources of public exposure might be relatively easily controlled. For example, when new practices are planned in Lithuania the dose constraints of 0,2-0,3 msv of annual effective dose depending on the type of practice are used on the stage of designing of radiation protection measures. Doses due to past events such as Chernobyl accident or atmospheric nuclear tests are relatively low. The most difficult problems arise when radiation protection measures are to be taken against natural exposure, particularly in residential dwellings. The problems arise not only in assessment of this exposure and identification of the most affected areas but also in informing public and media about problems related with this exposure, selecting practical and effective approach to limitation of this exposure. This paper describes problems in this field in Lithuania and experience gained within 9 years of cooperation of Swedish and Lithuanian radiation protection authorities in finding the optimized solutions for protecting members of public from residential natural exposure. 2. Sources of public exposure The first national indoor radon survey in Lithuania was performed in Measurements of indoor radon concentrations were carried out in randomly selected detached houses. Density of such houses in different regions was taken into account when selecting houses to be investigated. E-PERM T techniques and equipment was used during measurements [1]. They were carried out during cold season, duration of one measurement was not shorter than 3 weeks. The results showed that the average indoor radon concentration in detached houses was (55±5) Bq/m 3. Regions with indoor radon concentrations exceeding this average by more than twice have been identified. It has been found that the main source of indoor radon in such houses is soil air and karstic bedrock and that concentrations of indoor radon depend on soil properties and some characteristics of houses. 1

2 More detailed investigations of indoor radon situation were started in Regions with higher indoor radon concentrations identified during the survey of were included. One of such regions is the karst one in the northern part of Lithuania. The average indoor radon concentration in the whole region was (88±7) Bq/m 3, in the area with the most intensive karst phenomena (109±9) Bq/m 3. The difference of these averages is statistically significant. It indicates that karst phenomena have an impact on transportation of soil gas containing radon into houses. More detailed investigations in selected regions confirmed that some of these regions might be characterized by more intensive radon intake into buildings and higher indoor radon concentrations. Before these results were received the construction materials were considered to be the main source of radon indoors. Lithuanian soil was considered as relatively free of radium. The presumption that Lithuanian houses can not contain higher indoor radon concentrations was prevailing. The results of the above mentioned measurements were not readily accepted by some part of scientific community. More and more data collected as investigation of the problem proceeded could not change the general opinion that Chernobyl contamination and radionuclides from nuclear industry are the most important for public exposure. The characteristic illustration of it might be the reports on danger posed by plutonium radionuclides from Chernobyl accident in the sediments of lakes The fact that doses due to plutonium are by a few orders lower than ones due to indoor radon was not taken into account by investigators of plutonium problem. Indoor radon risk studies was the next step in collecting more objective information on public exposure. Pilot investigations in the development area of one of the largest Lithuanian cities were carried out. Measurements of radon concentrations in soil air were coupled with analysis of permeability of soil under consideration [2]. The results of study indicated that sites with increased radon risk were available and prevention measures against radon were recommended. Construction materials are also an important source of exposure in dwellings. Survey of concentrations of natural radionuclides in construction materials both produced and used in Lithuania is performed. For this the standard techniques of measurements of concentrations of 226 Ra, 232 Th and 40 K are employed. Though these concentrations most often do not exceed the maximum permissible levels the higher concentrations in some construction materials are recorded. Then these concentrations can not be neglected from the point of view of radiation protection and the potential doses due to the use of these construction materials should be taken into account when deciding on possibility of their use. 3. Development of legal instruments in limitation of public exposure due to natural sources Radiation protection in Lithuania has its own legal basis. All the legal documents take into account the appropriate recommendations of ICRP, documents of the IAEA and European Commission. The first standard on radiation protection from natural sources was approved in Regulations on such items as indoor radon, radioactivity in construction materials, external radiation indoors were included in the standard. This standard was a good starting point for development of more specific and realistic regulations. Results of investigation of residence related exposure were used in drafting of amendments to the existing standard. Particularly data on indoor radon situation helped to make the further standard more user friendly and to avoid excessively strict requirements which in fact are impossible to implement. In the beginning of 2004 the last version of the standard Natural exposure. Radiation protection requirements was adopted. The last developments in limitation of exposure due to radioactivity in construction materials were taken into account when drafting this standard. In general, this standard and the more general Basic radiation protection standards are the result of attempts of optimization of radiation protection the social and economic conditions taken into account. Though indoor radon concentrations are limited no mandatory remedial measures are required by the standard in residential buildings. Inhabitants are to be informed about the potential harm to their health due to indoor radon and advice on possible remedial measures is to be given. The requirements for protection in workplaces are stricter and the employer is obliged to take the appropriate remedial measures. 2

3 On the other hand, if radioactivity levels in construction material exceed some screening levels and calculations show that use of this material might cause the annual effective dose higher than 0.6 msv, the construction material can not be sold or used. Such a system takes into account the facts that no national resources exist for supporting of remedial measures, that the employer has to take measures for protection of health of its workers in any case and that increased exposure due to construction materials can be easily avoided by replacing materials with higher concentrations of natural radionuclides with the ones with lower radioactivity. The experience of application of the above mentioned standards shows that no serious complications or undue limitations are caused by them though the standards can not resolve all the potential problems arising in connection with their application. Residential exposure is also to be optimized and sometimes case specific solutions are to be taken. Particularly, it might happen when doses due to use of specific construction materials are to be assessed. Though different models for such assessment exist it is very important to have these models sufficiently user friendly, simple and precise. 4. Public information Public information on residence related exposure is one of the most important concerns. It is developed in a few directions. First of all the information on indoor radon problems is given to all the inhabitants of dwellings where measurements of indoor radon concentrations are performed. There are a few ways of doing so. Before measurements are started in the particular region the municipality is informed about it, contacts with persons dealing with ecology and public health established, the information on upcoming campaign posted in local newspapers. During measurements the leaflets informing people in simple language about indoor radon, tasks of measurements, behavior of inhabitants during measurements are given. The fact that inhabitants of dwellings under investigations often have some fears is taken into account. For this reason attempts to avoid such words as radiation or radioactivity in the leaflets are made though the attention to reliability and objectivity of this information is also paid. Information on results after measurements are finished is given to the appropriate officials in these regions. It is in the form of reports, however such forms as meetings and seminars are also used. A brochure on indoor radon related problems was also published. It contains the information on radon sources and characteristics, its transport into buildings and impact on human health, situation in Lithuania and other countries, short description of remedial measures [3]. The remedial measures described take into account the local peculiarities in construction of buildings. Papers and articles are also published, messages on radio and TV given. Measurements of indoor radon concentrations are also performed in schools, children informed about the problem and techniques of measurements. They also are given a possibility to participate in these measurements. It yields the results. In the end of 90 s the general public new very little about sources of exposure in the dwellings. Though no survey of awareness of public is done it is clear that more and more people are concerned about natural exposure. A good indicator of it is the increasing number of people which are coming to professionals dealing with these problems. However, many problems still remain. The information given to public has to be more user friendly. It should contain comparisons of importance of natural exposure with importance of artificial one rather than data on magnitude of doses. More practical advice should be given how to deal with exposure in dwellings. It is also important that public information only on residential exposure is to be given in connection with information on general issues of radiation, radiation protection, etc. People have to see this specific problem in the context of other problems other risks than radiological ones, other radiological risks, limitations in controlling different dangers. Such issues as readiness of public to accept the specific and hardly acceptable problems as protection from natural exposure in dwellings should be also taken into account. Sometimes the feedback in 3

4 dealing with public is lost, no psychological priorities given by public to nuclear energy or radioactive waste management are considered. The increasing attention paid to the issues related with NORM might help to attract public attention to natural radiation in general. 5. Remedial measures Remedial measures are closely connected with awareness of public and its readiness to accept the problem as the one which can make an influence on human health. As it was mentioned above no resources are available for support of remedial measures in dwellings in Lithuania. Also, no companies exist which could give a practical advice on remedial measures and implement them in practice. The measurements might be performed and advice given by radiation protection authority which is involved in the problem. For this reason the book on indoor radon and remedial measures was published [4]. This books contains practical advice on different remedial measures elaborated in Sweden, Canada, USA and other countries. The remedial measures cover not only indoor radon but also construction materials. It is a practical guide which nevertheless can be used by professional construction companies. A few seminars on natural radiation in dwellings and remedial measures took place in different locations of Lithuania. The target audience was designers of buildings, construction engineers, public health and ecology authorities. These seminars proved to be an effective tool for dissemination of information on the problem. The scope of the seminars was not limited only by fundamental problems or outlining the situation. Practical advice on remedial measures was also given though due to restrictions in duration of the seminars it did not allow to give a very detailed guidance. The main task of such seminars is to show the problems and give an understanding that even with such a complicated problem as residential exposure might be dealt with. However, many steps are still to be taken in creation of effective and self sustaining system of prevention and remediation of high exposure indoors due to natural exposure. The necessary condition for it is the knowledge in situation which can be only obtained by large scale well planned and designed measurements. On the basis of results of these measurements the extent of the problem and scope of necessary measures might be planned. After it training of professionals capable to perform assessment of ways of radon intake indoors and impact of construction materials on exposure and to design and implement the optimized remedial measures should take place. 6. Cooperation in resolving the problem Solution of the above mentioned problems requires many efforts, large resources and extensive knowledge and experience. Swedish and Lithuanian co-operation in the field of natural exposure started in Equipment for measurements on indoor radon concentrations and concentrations of natural radionuclides in construction materials was given, measuring techniques implemented. Close contacts are maintained during all the surveys, results discussed, common publications prepared. With the help of Swedish experts and with support of Swedish authorities the seminars are organized, the above mentioned publications prepared and published, Lithuanian professionals trained, participation in intercomparisons supported, equipment calibrated, standards on protection from natural sources drafted [5]. This co-operation each year acquires many new aspects. For example, recently one of the most important issues is creation of quality assurance systems in measurements techniques. Standard protocols developed by the Swedish Radiation Protection Authority are adopted in Lithuania. The experience gained during measurements in Lithuania is taken into account when these protocols are developed for their use in Lithuania. It indicates what the co-operation is permanently developing. Such close connection of this cooperation with existing situation helps in creation of self sustaining system of protection from natural exposure in Lithuania. 4

5 7. Conclusions Creation of system of protection of public from natural radiation is a long and complicated process. It starts with planning of strategy, design of practical means of evaluation of situation. Experience shows that the initial presumptions of public and radiation protection professionals often underestimate this kind of exposure. But even the results received during more or less extensive national survey of problem do not change these presumptions on their own. Many efforts are to be made in order to raise public awareness in residential exposure. The problem is complicated also by the fact that very often no resources are available for support of preventive and remedial measures in dwellings. On the other hand, this problem can not be left without any attention. The role of optimization of approach is very important, and the optimized solution again can be found using data on national situation. Public awareness should be raised by any appropriate means. Public health authorities, municipalities, construction companies should be among target audience of information campaigns. Information on residential exposure can not be isolated from information about other risks and dangers. Even more, public information has always to contain the fundamentals of radiation and radiation protection even if efforts to inform about such specific problems as indoor radon or radioactivity in construction materials are made. The role of international co-operation in resolving this problem is also very important. Joint efforts of a few countries in the region encountering the same problems might increase the efficacy, particularly if the authorities and professionals with wide experience in protection from natural exposure are in such consortiums. Radiation protection of members of public from natural radiation sources has to take into account not only the results of exposure monitoring, radiation protection principles and availability of national resources for solution of this problem, as it is in case of, e.g., occupational exposure. Very important issue is also readiness of public to accept the problem which depends on many other factors such as level of concern of public to its living standards, cultural traditions, openness of society to the new and not so easily seen and understood problems. Unfortunately, these factors are very difficult to control, at least by radiation protection community. Nevertheless, they are also to be taken into consideration. REFERENCES 1. Kotrappa P., Dempsey J.C., Ramsey R.W., Stieff L.R. A practical E-PERM TM (Electret Passive Environmental Radon Monitor) system for indoor 222 Rn measurement. Health Physics. 58.4: , (1990) 2. Abromaityte R., Pilkytė L., Morkunas G. Radon risk investigation in Panevezys city development area. Health Sciences. 3: 32-35, (2003) (in Lithuanian) 3. Morkunas G., Pilkyte L., Plyciuraitiene-Plyciene J., Akerblom G., Clavensjo B. Indoor radon. Remedial measures. Vilnius, (2002) (in Lithuanian) 4. Clavensjo B., Akerblom G., Morkunas G. The radon book. Measures against radon. Vilnius, (1999) (in Lithuanian) 5. Morkunas G., Akerblom G., Pilkytė L. Results of the Swedish and Lithuanian co-operation in protection from natural exposure. Health Sciences. 2: 80-84, (2002) 5