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World high background natural radiation areas: Need to protect public from radiation exposure
Radiation Measurements 50 (2013) 166e171
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World high background natural radiation areas: Need to protect public from radiation exposure Mehdi Sohrabi* Faculty of Physics, Amirkabir University of Technology, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 November 2011 Accepted 15 March 2012
Highlights of findings on radiological measurements, radiobiological and epidemiological studies in some main world high background natural radiation (HBNR) areas such as in Brazil, China, India and Iran are presented and discussed with special regard to remediation of radiation exposure of inhabitants in such areas. The current radiation protection philosophy and recommendations applied to workers and public from operation of radiation and nuclear applications are based on the linear non-threshold (LNT) model. The inhabitants of HBNR and radon prone areas receive relatively high radiation doses. Therefore, according to the LNT concept, the inhabitants in HBNR areas and in particular those in Ramsar are considered at risk and their exposure should be regulated. The HBNR areas in the world have different conditions in terms of dose and population. In particular, the inhabitants in HBNR areas of Ramsar receive very high internal and external exposures. This author believes that the public in such areas should be protected and proposes a plan to remedy high exposure of the inhabitants of the HBNR areas of Ramsar, while maintaining these areas as they stand to establish a national environmental radioactivity park which can be provisionally called “Ramsar Research Natural Radioactivity Park” (RRNRP). The major HBNR areas, the public exposure and the need to remedy exposures of inhabitants are reviewed and discussed. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Background Natural Radiation Areas Inhabitants Exposure Remediation Ramsar
1. Introduction Many areas in the world have high background natural radiation (HBNR) areas with potential public annual effective nonfractionated doses (HE) from external and internal exposures which are even higher than 20 mSv y1 dose limit for radiation workers. Some studies in the HBNR areas of Brazil, China, India and Iran have received more attention in recent years. The rationale for such studies has been the health and regulatory concern of the public, governments and international radiation protection community to resolve the dilemma of radiation health effects and risks at low doses and dose rates of radiation. Some physical and biological dosimetry and epidemiologic studies have been reported in the proceedings of the chain international conference on this topic and in other publications as well as in some comprehensive reviews (Eisenbud and Gesell, 1997; Sohrabi, 1998; Cardis, 2005; Hendry et al., 2009; Boice et al., 2010). The information available in the literature indicates that little attention or concern has been paid to the health of the public themselves being at risk due to living in * Tel.: þ98 21 64545256; fax: þ98 21 66495519 E-mail address: [email protected]. 1350-4487/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2012.03.011
such areas. Also, there is little information available on any remedial action undertaken in such areas. The cause and origin of such HBNR areas, population at risk, the doses received by public, etc. are different. Comprehensive physical and radiobiological dosimetry studies have been carried out in these areas but comprehensive epidemiological studies are limited to HBNR areas of China in Yangjian and India’s HBNR areas in the coastal belt of Karunagappally, Kerala (Wei, 1997; Nair et al., 2009; Akiba, 2010; Tao et al., 2012). Considering health risk e dose effect responses and the available risk data, ICRP’s (2007) main conclusion on biology is that the doseeresponse for cancer and hereditary effects has a simple proportionate relationship between dose and risk at low doses. Accordingly, the public living in HBNR areas in particular in Ramsar with the prospect of 50 years HE of over 10 Sv (over 10 times higher than that of 1.00 Sv for 50 years ICRP dose limit of radiation workers) have a high risk for developing cancer and hereditary effects. Having said the above, Akiba (2010) proposes a precautionary principle to avoid environmental risk and get rid of the sources of radiation exposure. The purpose of this paper is to highlight some important conclusions and findings of studies in such areas, propose protection of the inhabitants of such areas and the need to remedial actions to protect inhabitants in
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particular in HBNR areas of Ramsar, and make recommendations based on lessons learned from such studies to enhance the use of studies in such areas. 2. Classification of HBNR areas UNSCEAR (2010, Annex B) by referring to the world’s areas of high natural radiation discusses that there is no specific value of dose rate or of activity concentration in the environment that defines what constitutes an ‘enhanced natural radiation area’. In response, what has been developed in the past is reviewed here to bring more attention to the existence of such criteria in the literature (Sohrabi, 1997a, 1998). Accordingly, a general term HBNR area is defined as “an area or a complex of dwellings where the sum of exposures from cosmic radiation and natural radioactivity in soil, indoor and outdoor air, water, food, etc. lead to chronic exposure situations from external and internal exposures that result in an annual effective dose to the public above a defined level (Sohrabi, 1997a, 1998). Based on the annual effective doses of the inhabitants, HBNR areas have been classified accordingly into four levels: low, meaning HE below 5 mSv y1 (or about twice the global average of 2.4 mSv y1 reported by UNSCEAR, 2000); medium (5e20 mSv y1), high (20e50 mSv y1); and very high (>50 mSv y1) (Sohrabi, 1997a, b, 1998). This classification has taken into consideration the dose limits of ICRP (1991, 2007), UNSCEAR global average (2000), the International Basic Safety Standards (IBSS, 1996, 2011). The definition given above covers all potential affected areas or complexes either contaminated with naturally occurring radionuclides or technologically enhanced radioactivity areas or radon prone areas. Classifications such as given above are extremely important to prevent calling any area having 2 or 3 times higher that UNSCEAR’s global average a high background radiation area. It is recommended that the international radiation protection communities and radiation protection authorities further consider the above definition and classifications as a standardized approach when dealing with issues on HBNR areas or similar situations. In fact this can be considered as a base line for regulatory responsibilities for remediation of HBNR or radon prone areas. The areas have also been classified based on the “stability of natural radioactivity” in the area causing contaminated areas and in turn “stability of effective dose”; two conditions exist such as Static Areas where natural radioactivity or dose stay constant with time and Dynamic Areas where natural radioactivity or dose changes with time (Sohrabi, 1997a, 1998, 2000). 3. The International Committee on High Levels of Natural Radiation and Radon Areas The International Committee on High Levels of Natural Radiation and Radon Areas (ICHLNRRA) has been instrumental in harmonization of the above efforts. Its idea was originated at the 3rd IC-HLNRA held in Ramsar, Iran in 1990 and was materialized at the 4th IC-HLNRA in Beijing (1996). This led to continued extensive collaborative and results-based studies reported in a chain of international conferences on ICHLNRRA held in Germany (2000), Japan (2004), India (2010) and the next two will be in the Czech Republic (2014) and in IR Iran (2018). 4. Most studied world HBNR areas 4.1. Brazil The HBNR areas of Brazil perhaps are among those studied some decades ago where the first of chain of conferences in this field was initiated in 1975 (Cullen and Penna Franca, 1977). The main areas
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studied are the Poços de Caldas, Araxa and Tapira, comprising the zone of volcanic alkaline intrusive in the Minas Gerais State as well as Guarapari, located in the Espirito Santo State on the Atlantic Coast (Cullen and Penna Franca, 1977). The state of earlier studies in these areas has been reviewed (Sohrabi, 1998; Hendry et al., 2009). The level of exposure received of such areas in Brazil since the years of the earliest publications has changed significantly due to urbanization. The annual effective doses from external and internal exposures are now less than about 12 mSv. Some recent assessments however have been performed at Poços de Caldas (Veiga et al., 2000, 2004) and Guarapari (Sachett, 2002). There it was found that the radiation level in Guarapari can be considered as normal except at hot spots on the beaches and in the fishing village of Meaipe (Sachett, 2002). Also at Poços de Caldas, it is reported that only rural areas could be considered as HNBR areas and the radiation level in urban areas can be considered as normal (Veiga and Koifman, 2005). A very early chromosomal aberration studies, reported by Barcinski et al. (1975) where lymphocytes from 202 persons in Guarapari and 9001 lymphocytes from 147 persons in control areas were analyzed. However, the culture period of lymphocytes in this study was too long (72 h) for analyzing chromosome aberrations specific to radiation (Hendry et al., 2009). Epidemiological studies over the period 1991e2000 were carried out in two HBNR areas of Poços de Caldas and Araxa, with those in Minas Gerais State. A significantly elevated standardized mortality ratio was seen for cancers in Poços de Caldas and for noncancer mortality in both study areas (Veiga and Koifman, 2005). However, the reported study population was substantially larger than that which is thought to be living in HNBR areas and included cities, making these findings difficult to interpret (Hendry et al., 2009). 4.2. China The studies in HBNR areas in China have been reviewed by Sohrabi (1998) and Hendry et al. (2009) as well as in recent articles by collaborative studies between China and Japan (Zhou et al., 2005; Tao et al., 2000, 2012). The Yangjiang County in Guangdong province in the south of China consists of two regions (Dong-anling and Tongyou) separated by a short distance. The two regions cover a total area of about 540 km2. More than 125,000 people, primarily farmers, live in the two regions. The residents whose families have lived in those areas for six or more generations comprise 90% of the population. In this region, fine particles of monazite are washed down from the mountains by rain to the surrounding basin regions, giving rise to the HNBR areas (Sohrabi, 1998; Hendry et al., 2009). The level of natural radiation is relatively high due to radionuclides such as 232Th and 238U in the surface soil and in the building materials of houses. The average annual effective dose is reported to be 6.4 mSv with external dose of 1e3 mSv (average 2.1 mSv) and internal dose of 4.3 mSv; about three times higher than that of control areas. Chromosomal aberrations in peripheral blood lymphocytes (PBL) of people living in the HNBR region of Yangjiang analyzed for unstable-type aberrations (dicentrics and rings) compared to a control group showed a significant difference in the frequencies of dicentrics in adults, but not for those in children (Jiang et al., 2000). The stable-type aberrations analyzed by chromosome painting showed much higher frequencies of translocations than those of dicentrics but showed no statistically significant difference between translocations of the HNBR and NNBR areas (Hayata et al., 2004). The contribution of HNRB on the induction rate of translocations did not have a significant effect compared to the contribution of other mutagenic factors such as chemicals and/or
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metabolic factors (Zhang et al., 2004). The exposure received in people of HNBR played a less significant part than smoking in increasing the induction rate of translocations. Comprehensive epidemiological studies have been carried out in different periods as reported by Tao et al. (2000, 2012). In the estimation of cancer risk associated with an average annual effective dose of 6.4 mSv (including internal exposure) in the HBRA in Yangjiang, China carried out from 1987 to 1995, no increase in cancer mortality in HBRA were observed (Tao et al., 2000). Another comprehensive study was made during the period 1979e1998, on the mortality data of 31,604 men and women who attained the age of 30e74 by considering only external doses received by colon from external radiation with a mean of 2.1 mSv y1. The average annual doses of external radiation from the natural sources, including thorium, in the HBR area and in the control area were estimated to be 2.10 and 0.77 mSv y1, respectively. The mortality of cancer or all non-cancer diseases among residents in the HBR areas in Yangjiang was not increased when compared to the control area (Tao et al., 2012). 4.3. India The HBNR areas in India, located in the coastal belt of Karunagappally in Kerala, are due to thorium containing monazite sand in the surface of the soil. Some comprehensive studies have been carried in the HBNR areas of India on radiological, biological dosimetry, and epidemiology (Sunta, 1993; Cheriyan et al., 1999; Thampi et al., 2002; Jaikrishan et al., 1999; Jayalekshmi et al., 2005; Binu et al., 2005; Nair et al., 1999, 2009) which have also been comprehensively reviewed in the literature. The HNBR areas have a population of 385,000 inhabitants under study which generally have low migration rates. They receive on an average, external whole-body doses of about 4.5 mGy y1 from gamma-rays with about 2.4 mSv effective dose from internal exposures. In certain locations on the coast, the radiation levels may be as high as 70 mGy y1. There are relatively low concentrations of radon 215 Bq m3 and thoron 92 Bq m3 indoors (Eappen et al., 2000). Nair et al. (2009) reported the results of a comprehensive individual and ambient dosimetry and epidemiological study of cancer in a sub-cohort of a 173,067 members of the population by considering house occupancy factor and migration of the inhabitants. Cumulative radiation dose for each individual was estimated based on outdoor and indoor dosimetry of each household, taking into account sex- and age-specific house occupancy factors. Cancer incidence in this subcohort aged 30e84 years was analyzed. The indoor and outdoor gamma exposures were measured by using NaI and plastic scintillators while individual dose assessment was made by TLDs. Although HBNR areas have been repeatedly shown to increase the frequency of chromosome aberrations in the circulating lymphocytes of exposed persons, its carcinogenic effect is still unproven. Nair et al. (2009) also concluded that although the statistical power of the study might not be adequate due to the low dose, their cancer incidence study, together with previously reported cancer mortality studies in the HBNR areas of Yangjiang, China suggest it is unlikely that estimates of risk at low doses are substantially greater than currently believed. 4.4. Iran Ramsar, a northern city of Iran, has HBNR areas in an impressive natural landscape located at the foot of the Elburz mountains and overlooking the Caspian sea. The Hotel Ramsar is located in the middle of this landscape which is connected through a boulevard to the coasts of the Caspian Sea. The area has over 50 active and dynamic hot springs which continuously pump warm water
containing 226Ra into the surrounding areas. Some 9 springs are used as spa by believers of curing power of the water. Rather old dwellings and a school with high 226Ra content walls, high 222Rn levels indoors and high indoor and outdoor gamma exposures exist in these HBNR areas (Sohrabi, 1993). The external exposures (indoor and outdoor) measured in 1000 locations using pressurized ionization chamber and scintillation counters include 0.6e1.5 mSv y1 (mean: 0.70 mSv y1) in normal areas and 0.6e131 mSv y1 (mean: 6.00 mSv y1) in HBNR areas. About 45% of inhabitants receive doses <1 mSv y1; 30% from 1 to 5 mSv y1; 20% from 5 to 20 mSv y1, and 5% from 20 to 135 mSv y1 (Sohrabi and Esmaeli, 2002). The ratio of indoor to outdoor exposures is 1.55. The Cosmic rays dose over the Caspian Sea is 32 nGy h1. The 222Rn level indoors in over 500 houses by radon cups lead to radon levels up to 31 kBq m3 (Sohrabi and Babapouran, 2005). The HE based on 3 months seasonal radon measurements is 0.48e118 mSv (autumn) and 0.54e202 mSv (winter) with a mean HE ranging from 2.4 to 71 mSv y1. The total external and internal exposure HE lead to a range from 3.0 to 202 mSv y1. Accordingly the public’s 50 years HE by living in such areas is 10.10 Sv which is about 10 times higher than the sum of 50 year dose limit of 1.00 Sv for radiation workers. These are the highest level of doses reported for such areas in the world and protection of the public according to the present understanding of radiation risks is crucial. As regards to radiobiological dosimetry, the chromosome aberrations (CAs) in peripheral blood lymphocytes (PBLs) of inhabitants in HBNRs of Ramsar compared to a control group according to earlier studies showed an increase in unstable aberrations using the conventional method and also G-banding (Fazeli et al., 1993; Ghiassi-Nejad et al., 2004). Two other studies have shown no statistically significant differences in the background frequencies of CAs even in individuals of HBNRs concluded evidence for an adaptive response (Ghiassi-Nejad et al., 2002; Mortazavi et al., 2005). The above controversies were further verified in another study using an improved cytogenetic investigation in age-matched women (50e63 years old); 15 in the HBNR areas and 10 in the control area in a collaborative studies with Japan, clearly showed that individuals residing in the HBNR areas of Ramsar have increased frequency of detectable abnormalities in unstable aberrations from due to ionizing radiation (Zakeri et al., 2011). Epidemiological studies have been limited in HBNR areas of Ramsar and inconclusive requiring further studies (Mosavi-Jarrahi et al., 2005). Considering the high human exposures to public in these areas, an effective remedial action program to protect public should be of immediate concern. 5. Need to protect inhabitants of the HBNR areas The ICRP (2007) and IBSS (2011) have considered also the natural background radiation and most of the exposure situations to radon as the existing exposure situations; i.e. the exposure situations that already exist when a decision on control or remediation has to be taken. For radiological protection purposes, the ICRP statement (2009) recommends a detriment-adjusted nominal risk coefficient for a population of all ages of 8 1010 per Bq h m3 for exposure to radon-222 gas in equilibrium with its progeny. The Commission’s protection policy continues to set a level of annual dose of around 10 mSv from radon. However, considering the new risk findings, the reference level (RL) of 600 (ICRP, 2007) was reduced to 300 Bq m3 (ICRP, 2009). The national authorities should then consider setting lower reference levels according to local circumstances. In particular, where significant radon levels are identified, the government shall ensure that an action plan to reduce such levels in both existing and future buildings is
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established. These actions by a government include; (a) making all reasonable efforts to reduce radon concentrations and exposures to a level where protection can be considered optimized; (b) ensuring that, to the extent possible, the exposure does not remain above the applicable reference level, the value of which takes into account the prevailing social and economic circumstances, but for dwellings does not exceed a yearly average concentration of 222Rn in air of 300 Bq m3 (IBSS, 2011). As regards to responsibilities, the IBSS (2011) sets requirements on the responsibilities of the government and the regulatory body or other relevant authority on justification of remedial actions and protection actions and optimization of protection, identification of those persons or organizations responsible for remediation and post remediation controls, and among other things, provision of information on levels of radon indoors and the associated health risks and, if appropriate, shall establish and implement an action plan for controlling public exposure due to radon indoors. The ICRP (2009) considers the annual internal exposure reference level of 10 mSv only while the sum of the external and internal exposures will add to doses which are even far beyond 10 mSv y1. For example as discussed above, high mean total HE of up to 202 mSv y1 have been detected in HBNR areas of Ramsar. In fact, although the epidemiological studies in the HBNR areas have not yet proved the existence of radiation effects versus radiation exposure, the chromosome aberration studies indicate the effect exists. The inhabitant’s exposures are high enough that they should be protected the same way as regulated for example for radiation workers. As regards to remediation of the exposure, the information on actions undertaken in such areas is not available although some urbanization has reduced the exposure. Considering many factors involved in the remediation of such areas, the national regulatory authorities should consider necessary remediation methodologies to reduce the inhabitant’s exposure. This is in particular of high concern for inhabitants of the HBNR areas of Ramsar and priority should be provided to the protection of the inhabitants. 6. Remedial action alternatives in HBNR areas in particular in Ramsar In order to remedy the exposure of the inhabitants in the HBNR areas, two remedial action approaches may be considered: I) conventional methodologies, and II) a collective approach methodology.
c.
d.
e. f.
g.
h.
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and office buildings, roads, etc. and possibly subsidization of some cost of individual dwellings, This is a dynamic area due to 226Ra containing water which continuously being pumped into the area. This requires continuous monitoring of the environment and protection of the inhabitants before and after remediation, Loss of the uniqueness of the natural radiological features of the radioactive dwellings, open areas, spas, water streams, environment, etc. which will be destroyed and is irreversible, Need to implement regulatory requirements at present and in the future in such low-income areas, Above all, no matter how effective the remedial actions will be achieved, it is extremely difficult and highly expensive to reduce the present exposure levels to a normal background area and maintain it in the future, The continuous need to treatment and conditioning of the collected tailings and residues as waste which itself is a costly operation, Etc., etc.
6.2. Approach II This approach is a collective one and its purpose is twofold: a. To relocate the inhabitants of the HBNR areas to a normal radiation area with government provision compensation of equal, land/housings possibly by partial or full governmental subsidy. By this approach, the inhabitants’ exposure is simply reduced to a normal background level and the dwellings, public areas, roads, etc. will be maintained as they stand in its natural state, and b. Convert the HBNR areas into a national environmental radioactivity park to be provisionally called “Ramsar Research Natural Radioactivity Park” (RRNRP) by maintaining the areas as stand in their natural state. The RRNRP may be owned and established by the Government after adequately relocating the inhabitants. This approach does not have the obstacles given in the approach I, it is overall cost effective, the cost born by the inhabitants and the government, the future costs to protect the public by continuous monitoring and control, the loss of unique characteristics of the area, high cost of waste operation, etc. with a number of advantages of national and possibly of international interest. This approach will make ever-lasting reduction of exposure of inhabitants and their future generations of the HBNR areas from consequences of receiving such high internal and external exposures.
6.1. Approach I 7. Ramsar Research Natural Radioactivity Park (RRNRP) This approach considers the application of conventional methodologies to reduce the ambient exposure in each individual dwelling, public premises, etc. This requires that each single dwelling and public premises are technically well investigated and planned to implement a relevant methodology for remediation. This also requires renovation of each single dwelling, public premises, paving the radioactive roads, removal of stones and soils with high 226 Ra contents, rerouting the water from the springs, removing high 226 Ra content walls, etc. In particular, the remaining tailings/residues should be treated as waste. The only advantage of this approach is that the inhabitants will live in their present houses. However, there are a large number of disadvantages such as: a. Need to reduce radiation/radioactivity in all areas to normal levels including single dwelling, roads, etc., b. High cost of renovation being imposed on the inhabitants (usually under financial constraints) and for the government in particular for remediation of public premises such as schools
The HBNR areas of Ramsar have a dazzling natural beauty with aroma of tropical flowers all year round in particular from orange blossoms in spring. It is usually adored by visitors and participants of many international conferences in particular those attended the 3rd international conference on the same topic in November 1990. The city also benefits from rich coasts of the Caspian Sea with unique fish varieties where a unique resort is also for many Iranians and visitors. Then establishing the “Ramsar Research Natural Radioactivity Park” (RRNRP) fits well to the potentials existing in Ramsar and surrounding areas. This author believes that the RPNRP will become a valuable resource centre for the present and future generations in Ramsar as well as for the country. In additions the RPNRP will: a. preserve the natural radiation environment of the HBNR areas and their unique characteristics, b. have a natural radioactive environment park as national environmental laboratory with a number of single dwellings with
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various radon levels indoors and outdoors, natural warm spa, etc., for national and international research and education on geological, radiological, radiobiological, epidemiological, and other purposes, c. be a natural radioactivity museum for visitors in particular students at different levels, d. have a Sanitary Spa Centre for local, national and international use, and among other things, e. be a park under regulatory supervision for control of visitors exposure, etc.
8. Conclusions and recommendations The present and future generations continue to be increasingly exposed to the use of ionizing radiation in medicine, industry, energy production, etc. in addition to exposures to natural radiation in particular by the inhabitants of the HBNR areas around the world. Yet we are still in need of a health risk dose-eresponse curves with proved validity at low doses. Studies on the health risks in dependence of radiation doses on population in the HBNR areas with improved methodologies may provide the needed information. Through comprehensive review articles and proceeding papers of chain of conferences on this topic are available; the information has limitations on methodologies on how to protect the affected inhabitants of such areas. Some further recommendations follow here: 1. While the inhabitants of HBNR areas are the main elements of epidemiological studies, their protection should also be given a high priority. 2. Accurate retrospective individual dosimetry to be performed to obtain dose rates and lifetime doses from both external and internal exposures. 3. The international organizations and commissions such as IAEA, WHO, UNSCEAR, ICRP, etc. may wish to continue supporting such studies and provide advice to further improve methodologies so that the data obtained would be more respected by them. 4. Coordination of such studies at national and at international levels should be more considered to prevent duplications, scattered research, and invalid justifications and recommendations. 5. Collaborative studies such as what initiated by Japan with India and China should continue and expanded with agreed methodologies to enhance cohort size and dose ranges which may allow direct comparison of results and combined analyses e maximize the information from the studies. 6. By a simple cost benefit analysis, a government may be convinced and may subsidize fully or partially the required remedial actions in the affected dwellings for example for the very high level radiation areas such as in Ramsar. 7. The author highly recommends the protection of inhabitants of the HBNR areas in particular in Ramsar and establishment of the RRNRP.
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World high background natural radiation areas: Need to protect public from radiation exposure Mehdi Sohrabi* Faculty of Physics, Amirkabir University of Technology, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 November 2011 Accepted 15 March 2012
Highlights of findings on radiological measurements, radiobiological and epidemiological studies in some main world high background natural radiation (HBNR) areas such as in Brazil, China, India and Iran are presented and discussed with special regard to remediation of radiation exposure of inhabitants in such areas. The current radiation protection philosophy and recommendations applied to workers and public from operation of radiation and nuclear applications are based on the linear non-threshold (LNT) model. The inhabitants of HBNR and radon prone areas receive relatively high radiation doses. Therefore, according to the LNT concept, the inhabitants in HBNR areas and in particular those in Ramsar are considered at risk and their exposure should be regulated. The HBNR areas in the world have different conditions in terms of dose and population. In particular, the inhabitants in HBNR areas of Ramsar receive very high internal and external exposures. This author believes that the public in such areas should be protected and proposes a plan to remedy high exposure of the inhabitants of the HBNR areas of Ramsar, while maintaining these areas as they stand to establish a national environmental radioactivity park which can be provisionally called “Ramsar Research Natural Radioactivity Park” (RRNRP). The major HBNR areas, the public exposure and the need to remedy exposures of inhabitants are reviewed and discussed. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Background Natural Radiation Areas Inhabitants Exposure Remediation Ramsar
1. Introduction Many areas in the world have high background natural radiation (HBNR) areas with potential public annual effective nonfractionated doses (HE) from external and internal exposures which are even higher than 20 mSv y1 dose limit for radiation workers. Some studies in the HBNR areas of Brazil, China, India and Iran have received more attention in recent years. The rationale for such studies has been the health and regulatory concern of the public, governments and international radiation protection community to resolve the dilemma of radiation health effects and risks at low doses and dose rates of radiation. Some physical and biological dosimetry and epidemiologic studies have been reported in the proceedings of the chain international conference on this topic and in other publications as well as in some comprehensive reviews (Eisenbud and Gesell, 1997; Sohrabi, 1998; Cardis, 2005; Hendry et al., 2009; Boice et al., 2010). The information available in the literature indicates that little attention or concern has been paid to the health of the public themselves being at risk due to living in * Tel.: þ98 21 64545256; fax: þ98 21 66495519 E-mail address: [email protected]. 1350-4487/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2012.03.011
such areas. Also, there is little information available on any remedial action undertaken in such areas. The cause and origin of such HBNR areas, population at risk, the doses received by public, etc. are different. Comprehensive physical and radiobiological dosimetry studies have been carried out in these areas but comprehensive epidemiological studies are limited to HBNR areas of China in Yangjian and India’s HBNR areas in the coastal belt of Karunagappally, Kerala (Wei, 1997; Nair et al., 2009; Akiba, 2010; Tao et al., 2012). Considering health risk e dose effect responses and the available risk data, ICRP’s (2007) main conclusion on biology is that the doseeresponse for cancer and hereditary effects has a simple proportionate relationship between dose and risk at low doses. Accordingly, the public living in HBNR areas in particular in Ramsar with the prospect of 50 years HE of over 10 Sv (over 10 times higher than that of 1.00 Sv for 50 years ICRP dose limit of radiation workers) have a high risk for developing cancer and hereditary effects. Having said the above, Akiba (2010) proposes a precautionary principle to avoid environmental risk and get rid of the sources of radiation exposure. The purpose of this paper is to highlight some important conclusions and findings of studies in such areas, propose protection of the inhabitants of such areas and the need to remedial actions to protect inhabitants in
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particular in HBNR areas of Ramsar, and make recommendations based on lessons learned from such studies to enhance the use of studies in such areas. 2. Classification of HBNR areas UNSCEAR (2010, Annex B) by referring to the world’s areas of high natural radiation discusses that there is no specific value of dose rate or of activity concentration in the environment that defines what constitutes an ‘enhanced natural radiation area’. In response, what has been developed in the past is reviewed here to bring more attention to the existence of such criteria in the literature (Sohrabi, 1997a, 1998). Accordingly, a general term HBNR area is defined as “an area or a complex of dwellings where the sum of exposures from cosmic radiation and natural radioactivity in soil, indoor and outdoor air, water, food, etc. lead to chronic exposure situations from external and internal exposures that result in an annual effective dose to the public above a defined level (Sohrabi, 1997a, 1998). Based on the annual effective doses of the inhabitants, HBNR areas have been classified accordingly into four levels: low, meaning HE below 5 mSv y1 (or about twice the global average of 2.4 mSv y1 reported by UNSCEAR, 2000); medium (5e20 mSv y1), high (20e50 mSv y1); and very high (>50 mSv y1) (Sohrabi, 1997a, b, 1998). This classification has taken into consideration the dose limits of ICRP (1991, 2007), UNSCEAR global average (2000), the International Basic Safety Standards (IBSS, 1996, 2011). The definition given above covers all potential affected areas or complexes either contaminated with naturally occurring radionuclides or technologically enhanced radioactivity areas or radon prone areas. Classifications such as given above are extremely important to prevent calling any area having 2 or 3 times higher that UNSCEAR’s global average a high background radiation area. It is recommended that the international radiation protection communities and radiation protection authorities further consider the above definition and classifications as a standardized approach when dealing with issues on HBNR areas or similar situations. In fact this can be considered as a base line for regulatory responsibilities for remediation of HBNR or radon prone areas. The areas have also been classified based on the “stability of natural radioactivity” in the area causing contaminated areas and in turn “stability of effective dose”; two conditions exist such as Static Areas where natural radioactivity or dose stay constant with time and Dynamic Areas where natural radioactivity or dose changes with time (Sohrabi, 1997a, 1998, 2000). 3. The International Committee on High Levels of Natural Radiation and Radon Areas The International Committee on High Levels of Natural Radiation and Radon Areas (ICHLNRRA) has been instrumental in harmonization of the above efforts. Its idea was originated at the 3rd IC-HLNRA held in Ramsar, Iran in 1990 and was materialized at the 4th IC-HLNRA in Beijing (1996). This led to continued extensive collaborative and results-based studies reported in a chain of international conferences on ICHLNRRA held in Germany (2000), Japan (2004), India (2010) and the next two will be in the Czech Republic (2014) and in IR Iran (2018). 4. Most studied world HBNR areas 4.1. Brazil The HBNR areas of Brazil perhaps are among those studied some decades ago where the first of chain of conferences in this field was initiated in 1975 (Cullen and Penna Franca, 1977). The main areas
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studied are the Poços de Caldas, Araxa and Tapira, comprising the zone of volcanic alkaline intrusive in the Minas Gerais State as well as Guarapari, located in the Espirito Santo State on the Atlantic Coast (Cullen and Penna Franca, 1977). The state of earlier studies in these areas has been reviewed (Sohrabi, 1998; Hendry et al., 2009). The level of exposure received of such areas in Brazil since the years of the earliest publications has changed significantly due to urbanization. The annual effective doses from external and internal exposures are now less than about 12 mSv. Some recent assessments however have been performed at Poços de Caldas (Veiga et al., 2000, 2004) and Guarapari (Sachett, 2002). There it was found that the radiation level in Guarapari can be considered as normal except at hot spots on the beaches and in the fishing village of Meaipe (Sachett, 2002). Also at Poços de Caldas, it is reported that only rural areas could be considered as HNBR areas and the radiation level in urban areas can be considered as normal (Veiga and Koifman, 2005). A very early chromosomal aberration studies, reported by Barcinski et al. (1975) where lymphocytes from 202 persons in Guarapari and 9001 lymphocytes from 147 persons in control areas were analyzed. However, the culture period of lymphocytes in this study was too long (72 h) for analyzing chromosome aberrations specific to radiation (Hendry et al., 2009). Epidemiological studies over the period 1991e2000 were carried out in two HBNR areas of Poços de Caldas and Araxa, with those in Minas Gerais State. A significantly elevated standardized mortality ratio was seen for cancers in Poços de Caldas and for noncancer mortality in both study areas (Veiga and Koifman, 2005). However, the reported study population was substantially larger than that which is thought to be living in HNBR areas and included cities, making these findings difficult to interpret (Hendry et al., 2009). 4.2. China The studies in HBNR areas in China have been reviewed by Sohrabi (1998) and Hendry et al. (2009) as well as in recent articles by collaborative studies between China and Japan (Zhou et al., 2005; Tao et al., 2000, 2012). The Yangjiang County in Guangdong province in the south of China consists of two regions (Dong-anling and Tongyou) separated by a short distance. The two regions cover a total area of about 540 km2. More than 125,000 people, primarily farmers, live in the two regions. The residents whose families have lived in those areas for six or more generations comprise 90% of the population. In this region, fine particles of monazite are washed down from the mountains by rain to the surrounding basin regions, giving rise to the HNBR areas (Sohrabi, 1998; Hendry et al., 2009). The level of natural radiation is relatively high due to radionuclides such as 232Th and 238U in the surface soil and in the building materials of houses. The average annual effective dose is reported to be 6.4 mSv with external dose of 1e3 mSv (average 2.1 mSv) and internal dose of 4.3 mSv; about three times higher than that of control areas. Chromosomal aberrations in peripheral blood lymphocytes (PBL) of people living in the HNBR region of Yangjiang analyzed for unstable-type aberrations (dicentrics and rings) compared to a control group showed a significant difference in the frequencies of dicentrics in adults, but not for those in children (Jiang et al., 2000). The stable-type aberrations analyzed by chromosome painting showed much higher frequencies of translocations than those of dicentrics but showed no statistically significant difference between translocations of the HNBR and NNBR areas (Hayata et al., 2004). The contribution of HNRB on the induction rate of translocations did not have a significant effect compared to the contribution of other mutagenic factors such as chemicals and/or
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metabolic factors (Zhang et al., 2004). The exposure received in people of HNBR played a less significant part than smoking in increasing the induction rate of translocations. Comprehensive epidemiological studies have been carried out in different periods as reported by Tao et al. (2000, 2012). In the estimation of cancer risk associated with an average annual effective dose of 6.4 mSv (including internal exposure) in the HBRA in Yangjiang, China carried out from 1987 to 1995, no increase in cancer mortality in HBRA were observed (Tao et al., 2000). Another comprehensive study was made during the period 1979e1998, on the mortality data of 31,604 men and women who attained the age of 30e74 by considering only external doses received by colon from external radiation with a mean of 2.1 mSv y1. The average annual doses of external radiation from the natural sources, including thorium, in the HBR area and in the control area were estimated to be 2.10 and 0.77 mSv y1, respectively. The mortality of cancer or all non-cancer diseases among residents in the HBR areas in Yangjiang was not increased when compared to the control area (Tao et al., 2012). 4.3. India The HBNR areas in India, located in the coastal belt of Karunagappally in Kerala, are due to thorium containing monazite sand in the surface of the soil. Some comprehensive studies have been carried in the HBNR areas of India on radiological, biological dosimetry, and epidemiology (Sunta, 1993; Cheriyan et al., 1999; Thampi et al., 2002; Jaikrishan et al., 1999; Jayalekshmi et al., 2005; Binu et al., 2005; Nair et al., 1999, 2009) which have also been comprehensively reviewed in the literature. The HNBR areas have a population of 385,000 inhabitants under study which generally have low migration rates. They receive on an average, external whole-body doses of about 4.5 mGy y1 from gamma-rays with about 2.4 mSv effective dose from internal exposures. In certain locations on the coast, the radiation levels may be as high as 70 mGy y1. There are relatively low concentrations of radon 215 Bq m3 and thoron 92 Bq m3 indoors (Eappen et al., 2000). Nair et al. (2009) reported the results of a comprehensive individual and ambient dosimetry and epidemiological study of cancer in a sub-cohort of a 173,067 members of the population by considering house occupancy factor and migration of the inhabitants. Cumulative radiation dose for each individual was estimated based on outdoor and indoor dosimetry of each household, taking into account sex- and age-specific house occupancy factors. Cancer incidence in this subcohort aged 30e84 years was analyzed. The indoor and outdoor gamma exposures were measured by using NaI and plastic scintillators while individual dose assessment was made by TLDs. Although HBNR areas have been repeatedly shown to increase the frequency of chromosome aberrations in the circulating lymphocytes of exposed persons, its carcinogenic effect is still unproven. Nair et al. (2009) also concluded that although the statistical power of the study might not be adequate due to the low dose, their cancer incidence study, together with previously reported cancer mortality studies in the HBNR areas of Yangjiang, China suggest it is unlikely that estimates of risk at low doses are substantially greater than currently believed. 4.4. Iran Ramsar, a northern city of Iran, has HBNR areas in an impressive natural landscape located at the foot of the Elburz mountains and overlooking the Caspian sea. The Hotel Ramsar is located in the middle of this landscape which is connected through a boulevard to the coasts of the Caspian Sea. The area has over 50 active and dynamic hot springs which continuously pump warm water
containing 226Ra into the surrounding areas. Some 9 springs are used as spa by believers of curing power of the water. Rather old dwellings and a school with high 226Ra content walls, high 222Rn levels indoors and high indoor and outdoor gamma exposures exist in these HBNR areas (Sohrabi, 1993). The external exposures (indoor and outdoor) measured in 1000 locations using pressurized ionization chamber and scintillation counters include 0.6e1.5 mSv y1 (mean: 0.70 mSv y1) in normal areas and 0.6e131 mSv y1 (mean: 6.00 mSv y1) in HBNR areas. About 45% of inhabitants receive doses <1 mSv y1; 30% from 1 to 5 mSv y1; 20% from 5 to 20 mSv y1, and 5% from 20 to 135 mSv y1 (Sohrabi and Esmaeli, 2002). The ratio of indoor to outdoor exposures is 1.55. The Cosmic rays dose over the Caspian Sea is 32 nGy h1. The 222Rn level indoors in over 500 houses by radon cups lead to radon levels up to 31 kBq m3 (Sohrabi and Babapouran, 2005). The HE based on 3 months seasonal radon measurements is 0.48e118 mSv (autumn) and 0.54e202 mSv (winter) with a mean HE ranging from 2.4 to 71 mSv y1. The total external and internal exposure HE lead to a range from 3.0 to 202 mSv y1. Accordingly the public’s 50 years HE by living in such areas is 10.10 Sv which is about 10 times higher than the sum of 50 year dose limit of 1.00 Sv for radiation workers. These are the highest level of doses reported for such areas in the world and protection of the public according to the present understanding of radiation risks is crucial. As regards to radiobiological dosimetry, the chromosome aberrations (CAs) in peripheral blood lymphocytes (PBLs) of inhabitants in HBNRs of Ramsar compared to a control group according to earlier studies showed an increase in unstable aberrations using the conventional method and also G-banding (Fazeli et al., 1993; Ghiassi-Nejad et al., 2004). Two other studies have shown no statistically significant differences in the background frequencies of CAs even in individuals of HBNRs concluded evidence for an adaptive response (Ghiassi-Nejad et al., 2002; Mortazavi et al., 2005). The above controversies were further verified in another study using an improved cytogenetic investigation in age-matched women (50e63 years old); 15 in the HBNR areas and 10 in the control area in a collaborative studies with Japan, clearly showed that individuals residing in the HBNR areas of Ramsar have increased frequency of detectable abnormalities in unstable aberrations from due to ionizing radiation (Zakeri et al., 2011). Epidemiological studies have been limited in HBNR areas of Ramsar and inconclusive requiring further studies (Mosavi-Jarrahi et al., 2005). Considering the high human exposures to public in these areas, an effective remedial action program to protect public should be of immediate concern. 5. Need to protect inhabitants of the HBNR areas The ICRP (2007) and IBSS (2011) have considered also the natural background radiation and most of the exposure situations to radon as the existing exposure situations; i.e. the exposure situations that already exist when a decision on control or remediation has to be taken. For radiological protection purposes, the ICRP statement (2009) recommends a detriment-adjusted nominal risk coefficient for a population of all ages of 8 1010 per Bq h m3 for exposure to radon-222 gas in equilibrium with its progeny. The Commission’s protection policy continues to set a level of annual dose of around 10 mSv from radon. However, considering the new risk findings, the reference level (RL) of 600 (ICRP, 2007) was reduced to 300 Bq m3 (ICRP, 2009). The national authorities should then consider setting lower reference levels according to local circumstances. In particular, where significant radon levels are identified, the government shall ensure that an action plan to reduce such levels in both existing and future buildings is
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established. These actions by a government include; (a) making all reasonable efforts to reduce radon concentrations and exposures to a level where protection can be considered optimized; (b) ensuring that, to the extent possible, the exposure does not remain above the applicable reference level, the value of which takes into account the prevailing social and economic circumstances, but for dwellings does not exceed a yearly average concentration of 222Rn in air of 300 Bq m3 (IBSS, 2011). As regards to responsibilities, the IBSS (2011) sets requirements on the responsibilities of the government and the regulatory body or other relevant authority on justification of remedial actions and protection actions and optimization of protection, identification of those persons or organizations responsible for remediation and post remediation controls, and among other things, provision of information on levels of radon indoors and the associated health risks and, if appropriate, shall establish and implement an action plan for controlling public exposure due to radon indoors. The ICRP (2009) considers the annual internal exposure reference level of 10 mSv only while the sum of the external and internal exposures will add to doses which are even far beyond 10 mSv y1. For example as discussed above, high mean total HE of up to 202 mSv y1 have been detected in HBNR areas of Ramsar. In fact, although the epidemiological studies in the HBNR areas have not yet proved the existence of radiation effects versus radiation exposure, the chromosome aberration studies indicate the effect exists. The inhabitant’s exposures are high enough that they should be protected the same way as regulated for example for radiation workers. As regards to remediation of the exposure, the information on actions undertaken in such areas is not available although some urbanization has reduced the exposure. Considering many factors involved in the remediation of such areas, the national regulatory authorities should consider necessary remediation methodologies to reduce the inhabitant’s exposure. This is in particular of high concern for inhabitants of the HBNR areas of Ramsar and priority should be provided to the protection of the inhabitants. 6. Remedial action alternatives in HBNR areas in particular in Ramsar In order to remedy the exposure of the inhabitants in the HBNR areas, two remedial action approaches may be considered: I) conventional methodologies, and II) a collective approach methodology.
c.
d.
e. f.
g.
h.
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and office buildings, roads, etc. and possibly subsidization of some cost of individual dwellings, This is a dynamic area due to 226Ra containing water which continuously being pumped into the area. This requires continuous monitoring of the environment and protection of the inhabitants before and after remediation, Loss of the uniqueness of the natural radiological features of the radioactive dwellings, open areas, spas, water streams, environment, etc. which will be destroyed and is irreversible, Need to implement regulatory requirements at present and in the future in such low-income areas, Above all, no matter how effective the remedial actions will be achieved, it is extremely difficult and highly expensive to reduce the present exposure levels to a normal background area and maintain it in the future, The continuous need to treatment and conditioning of the collected tailings and residues as waste which itself is a costly operation, Etc., etc.
6.2. Approach II This approach is a collective one and its purpose is twofold: a. To relocate the inhabitants of the HBNR areas to a normal radiation area with government provision compensation of equal, land/housings possibly by partial or full governmental subsidy. By this approach, the inhabitants’ exposure is simply reduced to a normal background level and the dwellings, public areas, roads, etc. will be maintained as they stand in its natural state, and b. Convert the HBNR areas into a national environmental radioactivity park to be provisionally called “Ramsar Research Natural Radioactivity Park” (RRNRP) by maintaining the areas as stand in their natural state. The RRNRP may be owned and established by the Government after adequately relocating the inhabitants. This approach does not have the obstacles given in the approach I, it is overall cost effective, the cost born by the inhabitants and the government, the future costs to protect the public by continuous monitoring and control, the loss of unique characteristics of the area, high cost of waste operation, etc. with a number of advantages of national and possibly of international interest. This approach will make ever-lasting reduction of exposure of inhabitants and their future generations of the HBNR areas from consequences of receiving such high internal and external exposures.
6.1. Approach I 7. Ramsar Research Natural Radioactivity Park (RRNRP) This approach considers the application of conventional methodologies to reduce the ambient exposure in each individual dwelling, public premises, etc. This requires that each single dwelling and public premises are technically well investigated and planned to implement a relevant methodology for remediation. This also requires renovation of each single dwelling, public premises, paving the radioactive roads, removal of stones and soils with high 226 Ra contents, rerouting the water from the springs, removing high 226 Ra content walls, etc. In particular, the remaining tailings/residues should be treated as waste. The only advantage of this approach is that the inhabitants will live in their present houses. However, there are a large number of disadvantages such as: a. Need to reduce radiation/radioactivity in all areas to normal levels including single dwelling, roads, etc., b. High cost of renovation being imposed on the inhabitants (usually under financial constraints) and for the government in particular for remediation of public premises such as schools
The HBNR areas of Ramsar have a dazzling natural beauty with aroma of tropical flowers all year round in particular from orange blossoms in spring. It is usually adored by visitors and participants of many international conferences in particular those attended the 3rd international conference on the same topic in November 1990. The city also benefits from rich coasts of the Caspian Sea with unique fish varieties where a unique resort is also for many Iranians and visitors. Then establishing the “Ramsar Research Natural Radioactivity Park” (RRNRP) fits well to the potentials existing in Ramsar and surrounding areas. This author believes that the RPNRP will become a valuable resource centre for the present and future generations in Ramsar as well as for the country. In additions the RPNRP will: a. preserve the natural radiation environment of the HBNR areas and their unique characteristics, b. have a natural radioactive environment park as national environmental laboratory with a number of single dwellings with
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various radon levels indoors and outdoors, natural warm spa, etc., for national and international research and education on geological, radiological, radiobiological, epidemiological, and other purposes, c. be a natural radioactivity museum for visitors in particular students at different levels, d. have a Sanitary Spa Centre for local, national and international use, and among other things, e. be a park under regulatory supervision for control of visitors exposure, etc.
8. Conclusions and recommendations The present and future generations continue to be increasingly exposed to the use of ionizing radiation in medicine, industry, energy production, etc. in addition to exposures to natural radiation in particular by the inhabitants of the HBNR areas around the world. Yet we are still in need of a health risk dose-eresponse curves with proved validity at low doses. Studies on the health risks in dependence of radiation doses on population in the HBNR areas with improved methodologies may provide the needed information. Through comprehensive review articles and proceeding papers of chain of conferences on this topic are available; the information has limitations on methodologies on how to protect the affected inhabitants of such areas. Some further recommendations follow here: 1. While the inhabitants of HBNR areas are the main elements of epidemiological studies, their protection should also be given a high priority. 2. Accurate retrospective individual dosimetry to be performed to obtain dose rates and lifetime doses from both external and internal exposures. 3. The international organizations and commissions such as IAEA, WHO, UNSCEAR, ICRP, etc. may wish to continue supporting such studies and provide advice to further improve methodologies so that the data obtained would be more respected by them. 4. Coordination of such studies at national and at international levels should be more considered to prevent duplications, scattered research, and invalid justifications and recommendations. 5. Collaborative studies such as what initiated by Japan with India and China should continue and expanded with agreed methodologies to enhance cohort size and dose ranges which may allow direct comparison of results and combined analyses e maximize the information from the studies. 6. By a simple cost benefit analysis, a government may be convinced and may subsidize fully or partially the required remedial actions in the affected dwellings for example for the very high level radiation areas such as in Ramsar. 7. The author highly recommends the protection of inhabitants of the HBNR areas in particular in Ramsar and establishment of the RRNRP.
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