RADIONUCLIDES IN DRINKING

Transkript

1 RADIONUCLIDES IN DRINKING WATER A SURVEY REGARDING MITIGATION MEASURES Caroline Karlsson Maj 2010 TRITA-LWR Degree Project ISSN X LWR-EX-10-07

2 Caroline Karlsson TRITA-LWR Degree Project c Caroline Karlsson 2010 Master Thesis Environmental Geochemistry and Ecotechnology Department of Land and Water Resources Engineering Royal Institute of Technology (KTH) SE STOCKHOLM, Sweden Reference should be written as: Karlsson, C (2010) Radionuclides in drinking water a survey regarding mitigation measures TRITA-LWR Degree Project 10-07, (91 p.)

3 Radionuclides in drinking water a survey regarding mitigation measures ACKNOWLEDGEMENTS First and foremost I would like to thank my supervisor Professor Jon Petter Gustafsson at KTH, for much valuable advice concerning this thesis. I would also like to thank my co-supervisor Kirlna Skeppström at the Swedish Radiation Safety Authority for all the support, feedback and help throughout this project. A heartfelt thanks to the Swedish Radiation Safety Authority (SSM) for funding this project. A sincere gratitude goes out to Britt Chow, Lars-Eric Svahn, Misse Wester and the KTH Postal office for all the help and advises I received during the survey part of the thesis, and not to forget all the people that took time to answer the questions in the survey. I would also like to acknowledge the teachers at the Department of Land and Water Resources Engineering, especially Associate Professor Joanne Robison Fernlund, for being such inspiring people through their love for their work. Finally, I would like to thank my family, relatives and friends for their support, laughs and advise I received throughout my educational years and the time in between. Caroline Karlsson Stockholm, May 2010 iii

4 Caroline Karlsson TRITA-LWR Degree Project iv

5 Radionuclides in drinking water a survey regarding mitigation measures ABBREVIATIONS, ACRONYMS AND GLOSSARY Activity Anemia Bq GAC Half-life Hemotopoiesis Hydroxyapatite KTH Leukopenia National Board of Health and Welfare Necrosis National Food Administration Nucleotide Radionuclide RO SGU SSI SSM Teratogenic TID Number of disintegrations per unit of time. Measured in becquerel (Bq). When the number of red blood cells or normal quantity of hemoglobin in the blood is less than normal. Becquerel. Unit for radioactive disintegration rate. 1 Bq = 1 disintegration/sec Granular Activated Carbon. Period of time it takes for a substance to decrease by 50% through, for example, radioactive decay. Development of blood cells. A calcium phosphate mineral with the formula Ca 5 (PO 4 ) 3 OH(s). Royal Institute of Technology. A condition when the number of white blood cells is lower than normal. Socialstyrelsen (SoS). Death of living cells or tissues. Livsmedelsverket (SLV). A subunit of DNA or RNA. Thousands of nucleotides in a long chain forms a DNA or RNA molecule. An atom that may undergo radioactive decay, giving rise to ionizing radiation. Reverse Osmosis. Geological Survey of Sweden. Swedish Radiation Protection Authority (Formerly). Swedish Radiation Safety Authority (Present). A chemical substance that can disturb the development of embryo and fetus. It can also cause birth defects. Total indicative dose. A radiation dose of atleast 0.1 msv/year is referred to as the Total Indicative Dose and is the threshold value for the amount of radiation dose received from all radioactive elements in water, both artificial and natural, except potassium-40, tritium, radon and its disintegration products. v

6 Caroline Karlsson TRITA-LWR Degree Project vi

7 Caroline Karlsson TRITA-LWR Degree Project SAMMANFATTNING Vattenförsörjningen till det svenska folket sker på två sätt, antingen via privata brunnar eller kommunala vattenledningar. Det vatten som distribueras kommunalt kontrolleras strikt med avseende på olika parametrar för att säkerställa ett säkert livsmedel. För de ca 2,5 miljoner svenskar som får sitt vatten från enskilda brunnar är kvalitetskontrollen deras eget ansvar. Enligt Socialstyrelsen är det rekommenderat att ta prov och analyzera sitt vatten vart tredje år och i vissa fall kan tätare provtagning förespråkas till exempel om brunnen lätt kan påverkas av yttre förhållanden. Många hushåll som tar prover på sitt brunnsvatten tar prover med avseende på mikrobiologiska parametrar eller kemiska- och fysikaliska parametrar. Vanligt är att man tar prover för en kontroll av de grundämnen som man vet kan finnas i höga halter eller är vanligt förekommande, till exempel järn, mangan, kalcium, bor, nickel, aluminium och bly. Radionuklider kan finnas i vatten och kan finnas i så höga halter att de kan orsaka kroniska skador hos den person som dricker det. Radon är den radionuklid, ur uran-238s sönderfallskedja, som är mest känt och vars negativa effekt på biologiska organismer såsom människan är väldokumenterade. Radon kan diffundera från vatten till luft och sedan ner i våra lungor när vi andas där en del av radonet sönderfaller till sina mer långlivade radondöttrar bly- 210 och polonium-210. Dessa radondöttrar emitterar alfa- eller betastrålning som kan skada eller döda celler i närheten av dessa ämnen. Detta kan tillslut orsaka så pass stora skador på cellerna att de antingen dör eller att dess del som har hand om celldelningen blir störd. Just fallet med störd celldelning brukar förknippas med cancer och det är det som anses som största problemet med radon i bostäder. Förutom radon kan man även konstatera att vatten kan innehålla uran, radium, bly-210 och polonium-210. Konsumtion av uran har påvisats orsaka förändrad njurfunktion. Radium är ett cancerogent ämne som vid intag absorberas till största delen i skelett och mjukdelar. Samma sak gäller för bly, nämligen att intag av detta ämne slutligen kommer att assimileras till största delen i kroppens skelett. Känsligheten för bly skiljer sig mellan könen. Kvinnor har visats vara mer känsliga för bly än män. Polonium som upptas i kroppen påvisas främst i lever, njurar och mjälte. För de människor vars vatten innehåller förhöjda halter av radionuklider finns det flera avskiljningsmetoder tillgängliga på marknaden. I vissa fall kan det vara lämpligt med en kombinering av avskiljningsmetod för att säkerställa optimal avskiljning av en radionuklid. Val av metod och konstruktionstyp ska alltid föregås av vattenanalys. Radon avskiljs lämpligast med luftning eller aktivt kol. Luftning fungerar genom att öka ytarean mellan vatten och luft. Genom en utökning av ytarean ökas diffusionshastigheten. Vid luftning är det viktigt att avleda radongasen som frigjorts ut ur bostaden. Aktivt kol fungerar genom att adsorbera radon ur vattnet och inte släppa tillbaka det. I detta fall kan ett annat problem uppstå, nämligen strålning från filtret då det radon som upptagits sönderfaller. Om det vatten som ska behandlas innehåller höga halter av partiklar som skulle kunna täppa till avskiljningsutrustningen och reducera avskiljningen kan det vara lämpligt med ett förbehandlingssteg, till exempel sedimentering eller filter, för att minimera mängden partiklar. Uran avskiljs lämpligast med jonbytare eller omvänd osmos. Jonbytare fungerar genom att den jon med störst affinitet byter plats med en annan jon som ursprungligen suttit fast på jonbytarmassans fixerade "jonbytarplatser". På detta sätt upptas den oönskade jonen ur vattnet och jonen som byts ut urlakas till vattnet. Genom att spola jonbytaren med en hög koncentration av ursprungliga jonen kan man regenerera jonbytaren, det vill säga förnya den. Radium avskiljs lämpligast med jonbytesteknik eller omvänd osmos. Bly-210 och polonium-210 avskiljs lämpligast med membranteknik som omvänd osmos eller nanofiltering. Omvänd osmos är en teknik som använder semipermeabla membran för filtrering. vii Detta

8 Radionuclides in drinking water a survey regarding mitigation measures membran tillåter bara molekyler av en viss storlek att passera igenom. Genom att applicera ett tryck på den sida av membranet som har hög koncentration, den sida som innehåller det oönskade ämnet, kan man få vattnet att passera genom filtret till den sidan med lägre koncentration och på så sätt erhålla ett mycket rent vatten. Detta kan dock innebära att vattnet blir så rent att det inte är hälsosamt att dricka varför en viss tillsats av salter kan behövas. Kemisk utfällning som reningsmetod är inte att förespråka för hushåll. Vid kemisk fällning krävs noga kontroll så att vattnet har optimalt ph-värde och att doseringen av kemikalier är rätt. Genom en enkätundersökning, som gick ut till de hushåll som tidigare deltagit i en undersökning utförd av Sveriges Geologiska Undersökning (SGU) och dåvarande Statens Strålskyddsinstitut (SSI), kunde man erhålla en övergripande syn på hur personer i Sverige med brunn, förhåller sig till provtagning i allmänhet, vilka radionuklider de känner till och om de använder någon form av reningsutrustning för att rena deras vatten. Radon var den radionuklid som flest personer kände till. Ca 53 % av alla hushåll provtar sitt vatten med avseende på radon. 49 % av hushållen kände till att uran och bly kunde finnas i vatten. Av alla hushåll sa ca 52 % att de visste att radium kan finnas i vatten. För polonium var resultatet 20 %. Enbart 17 % hävdade att de analyserade sitt vatten med avseende på polonium. När husållen tillfrågades vem som var provtagningsansvarig angav majoriteten dem själva. Provtagningsfrekvensen låg mellan varje år till vart tionde år. Många personer hävdade att de aldrig provtar sitt vatten. Ett antagande var att provtagningsfrekvensen inte skulle öka om den enskilde personen var ansvarig för provtagningen men en sådan korrelation kunde inte påvisas. Av de personer som svarade på frågan om de använde någon reningsutrustning, svarade ca 66,5 % nej och ca 31,2 % ja. Av de som svarade ja, renade majoriteten sitt vatten med avseende på järn och/eller mangan. Denna metod följdes sedan av radonavskiljare och jonbytesteknik med backspolning. Det var även vanligt förekommande att kombinera järn- och/eller manganavskiljning med antingen radonavskiljning eller jonbytesteknik med backspolning. viii

9 Radionuclides in drinking water a survey regarding mitigation measures ABSTRACT Water in Sweden is supplied to the public by municipal systems or private wells. The water supplied by the municipal systems is under strict control and must be sampled and analyzed regularly. For approximately 2.5 million Swedes relying on private wells the water quality control is solely their responsibility. The Swedish National Board of Health and Welfare recommends a water sampling and analysis for chemical, physical and microbiological parameters every third year and if necessary mitigation should be undertaken. Many rural households mitigate their well water due to high concentration of different elements exceeding the threshold values recommended by the Swedish National Board of Health and Welfare. For the households with high concentration of radionuclides in their well water there are efficient mitigation methods available such as ion exchange, reverse osmosis, aeration and activated carbon. A previous study was conducted in order to map the occurrence of radionuclides in wells across Sweden. That study was done by the former Swedish Radiation Protection Authority (SSI) and the Geological Survey of Sweden. The main purpose of this thesis was to follow up on that previous study and investigate the general knowledge about radionuclides in the rural households that had participated in the earlier study. Through a survey the households were asked to answer different questions regarding radionuclides and mitigation measures. Of approximately 780 initial households 173 households decided to participate. 81 % of the households did know that radon could be present in water and about 53 % stated that radon was a parameter they analyze their water for. Approximately 49 % of the households knew that uranium and lead can be present in water. About 52 % of the households stated that they knew that radium could be present in water. For polonium the results were 20 %. Approximately 31 % of the households mitigated their water and the most common mitigation measure was iron and/or manganese filters. The second most common method was radon removal ( 20 %). Iron was the parameter that the majority of the households analyzed their water for. 17 % of the households stated that they analyze their water for polonium. Only 2 % of the households sampled and analyzed their well water every third year as recommended. Some households stated that they never sample and analyze their water. A few of the households combined one mitigation measure with another where the most common combination was iron and manganese filter with either radon removal or ion exchange with backwashing. Water with high concentration of radionuclides generally comes from drilled wells and the numbers of households with drilled wells will most likely increase. This is because more people have started to move to rural areas due to infrastructural expansion and the more entrepreneurs have started to offer a drilled well service. Many households stated that they never sampled and analyzed their water or only sampled when they thought that there was something wrong with their water. But since the carcinogenic radionuclides are invisible, odourless and tasteless they cannot be determined and mitigated without sampling and analysis. Many households relying on visual parameters in order to determine when to sample might be exposed to high concentrations of radionuclides without knowing it. This indicates that there is a household need for easy and accessible information regarding radionuclides, mitigation methods and sampling recommendation. It is also important to inform the households of injunctions regarding filtermass disposal to avoid illegal dumping. Key words: Radionuclides; Drinking water; Household water; Survey; Private well; Mitigation measures. ix

10 Caroline Karlsson TRITA-LWR Degree Project x

11 Table of Contents ACKNOWLEDGEMENTS ABBREVIATIONS, ACRONYMS AND GLOSSARY SAMMANFATTNING ABSTRACT iii v vii ix 1. INTRODUCTION Problem statement Previous study and survey sampling approach RADIATION Different types of radiation Alpha radiation Beta radiation Gamma radiation RADIONUCLIDES IN WATER Radon Radon and geology Radon in water Health aspects of radon Uranium Uranium and geology Uranium in water Health aspects of uranium in drinking water Radium Radium in water Health aspects of radium in drinking water Lead Lead in water Health aspects of lead Polonium Polonium in water Health aspects of polonium in drinking water REMOVAL METHODS FOR RADIONUCLIDES IN WATER Radon removal Aeration Activated carbon Uranium removal Membrane filtration Chemical precipitation xi

12 4.2.3 Ion exchange Radium removal Lead removal Polonium removal METHODOLOGY Literature review Survey SURVEY RESULTS ANALYSIS AND DISCUSSION Sampling frequency Sampling responsibility What parameters are analyzed Radionuclides in water Mitigation of well water and what method is common Radionuclides in wells CONCLUSIONS FUTURE WORK LIMITATIONS 43 REFERENCES 45 OTHER REFERENCES 46 APPENDIX I - COVER LETTER 50 APPENDIX II - SURVEY QUESTIONS 52 APPENDIX III - SURVEY RESULTS 60 APPENDIX IV- LIST OF PARAMETERS 77 xii

13 Radionuclides in drinking water a survey regarding mitigation measures 1. INTRODUCTION Water is an important component in our daily life. We use it to shower, wash our clothes and to prepare and cook our food. We even use it in our industry in different processes. Because water is such an important aspect in our daily life we need to have clean and healthy water. In many households water is supplied through municipal systems. For those who live in rural areas the water is often taken from wells. Some water treatment plants barely need to treat the water in order reach the specification set for potable water. However municipally distributed water must be thoroughly controlled before it is released to the public. For those households that use wells as their water source there are water quality control regulations that need to be adhered to. The Swedish National Board of Health and Welfare recommends a water sampling and analysis to be carried out every third year. The problem with this is that many people might not know what to sample their water for. How many people ponder over the elements present in the water in their drinking glass? It may be assumed that the number of people who do is likely to be small. Some elements, such as iron, can change the color of the water. By using the senses of sight and taste many problems related to water quality can be prevented. However, some elements cannot be seen, tasted or smelled; a fact that can pose a health problem especially if some are carcinogenic for humans. Radon-222 or uranium-238 are example of radionuclides that may be hazardous if present in high concentrations. Radionuclides are considered carcinogenic for humans and that is why it is of considerable importance to analyze the water for constituents that may pose a potential health hazard. If it turns out that the water contains too high concentrations of radionuclides, proper mitigation measures should be undertaken. 1.1 Problem statement The main purpose of this thesis was to investigate the general knowledge about the occurence of radionuclides in rural household well water and whether any mitigation measures have been undertaken to reduce the concentration of radionuclides in drinking water, when found in high concentration. The following specific research questions were addressed: What types of mitigation measures are available on the market for the removal of radionuclides such as radon, uranium, lead- 210, radium and polonium-210? To what extent are mitigation measures used to remove radionuclides from drinking water, and what are the common techniques. What sampling frequency is used for the analysis of radionuclides in drinking water? 1

14 Caroline Karlsson TRITA-LWR Degree Project To what extent are households knowledgeable about radionuclides in drinking water and the health risk the latter may constitute? 1.2 Previous study and survey sampling approach The previous study was conducted by SSI and SGU during the year The purpose was to investigate and map the occurrence of radioactive elements and metals found in the water from private wells. The sampling was done in a random fashion throughout Sweden targeting mainly drilled wells. However dug wells in soil aquifers were also included in the study. The sampling density was increased when the bedrock and soils were known to have enhanced concentrations of radioactive elements. More details about selection of sampling points can be found in Ek et al, The sampling resulted in more than 1100 samples from 722 bedrock drilled wells, 46 dug wells and 10 springs. The study also showed that the radon-222 concentration in 8 % of the selected wells exceeded 1000 Bq/l. This is the current threshold value for radon stated by the National Board of Health and Welfare. The uranium concentration exceeded the recommended value of 15 µg/l in approximately 17 % of the wells. A uranium concentration in the water which exceeded 100 µg/l was determined in 2 % of the wells. One well in the county of Dalarna gave drinking water with a radiation dose of greater than 5 msv/year. A person who relies on drinking water with a uranium concentration that exceeds 100 µg/l will be subjected to a radiation dose of at least 0.1 msv/year. This value is referred to as the TID (Total Indicative Dose) (Ek et al, 2008). The selection of the households that received the survey was done by using the 780 households already investigated during the previous study. 2. RADIATION Many elements with large mass numbers are instable. The instability comes from the tension created in the nucleus, due to the large difference in the number of protons and neutrons. This tension gives rise to excess energy that is released in form of radiation. Different radioactive substances release their excess energy in different ways, either as a particle, an electromagnetic pulse or both. The process is called radioactive disintegration (Jönsson G, 1992; Wahlström B, 1996). There are four disintegration series where 238 U, 235 U, 232 Th are found naturally. The fourth disintegration serie Neptunium-237 is no longer found naturally (Kaye & Laby online, 2009; Wikipedia, 2009). A disintegration series depicts an elements journey from unstable to stable isotope. It describes the transformation from one element to another, the radiation emitted during transformation and how long it takes before half of the mass is transformed into the next element, the so called half-life. See Fig.1 that depicts the disintegration from uranium-238 ( 238 U) to stable lead-206 ( 206 P b). 2

15 Radionuclides in drinking water a survey regarding mitigation measures Fig. 1: The decay chain for U-238, only the primary disintegrations are shown. Modied from SSI, As 238 U disintegrates it releases alpha radiation but because of the long half-life the activity is low. Radium-226 ( 226 Ra) is one of the disintegration products and its half-life is short (1620 years) compared to 238 U. As 226 Ra disintegrates it emits alpha radiation and creates a gaseous daughter, radon-222 ( 222 Rn). When 222 Rn disintegrates it creates both short-lived and long-lived radon daughters. The longlived radon daughters lead-210 ( 210 Pb) and polonium-210 ( 210 Po) has the ability to be stored in the human body. 238 U, 226 Ra, 222 Rn, 210 Pb and 210 Po are radionuclides that can be present in water and can, if the concentration is high, cause damage to the human body when consumed. 2.1 Different types of radiation Depending on how much energy that needs to be released and what element that releases it, the excess energy can be emitted as alpha, beta or gamma radiation, or a combination of them Alpha radiation Alpha radiation occurs when an element releases its excess energy in the form of an alpha particle, consisting of a nucleus of helium, 4 2 He. Alpha radiation can easily be stopped with a sheet of paper, skin or clothes. However if ingested it can cause problems (Wahlström B, 1996; A.I.C, 2007) Beta radiation Beta radiation is a process in which an electron is sent out from the radioactive isotope. The radiation can be stopped with a piece of wood (Jönsson G, 1992; A.I.C, 2007). 3

16 Caroline Karlsson TRITA-LWR Degree Project Gamma radiation Gamma radiation is a release of excess energy in form of an electromagnetic pulse. This is often due to the insufficient reduction in energy after an alpha or beta emission. The frequency is dependent on the amount of energy that needs to be released. To stop gamma radiation e.g. water, concrete or lead can be used. The thicknesses of these that are required are dependent on the energy of the gamma radiation (Jönsson G, 1992; A.I.C, 2007). 3. RADIONUCLIDES IN WATER 3.1 Radon This chapter will cover the radionuclides 238 U, 226 Ra, 222 Rn, 210 Pb and 210 Po. Radon is a disintegration product of radium, and the only disintegration product of both the uranium and thorium decay chain that is in gaseous form (CA.gov, 2009; Radonguiden, 2009). Radon-222 or simply radon is an isotope that can occur both in the ground and indoors. Radon-220 or thoron can be found in the ground where the element thorium is present. Because of the short half-life (55.6 seconds) of thoron it is not found in the indoor air at appreciable amounts since it cannot be transported long distances before it is disintegrated (Jönsson G, 1992). This is also the case for the radon isotope radon-219 or actinon which has a half-life of 3.92 seconds (TFD, 2009). There exist 18 isotopes of radon. Radon is monoatomic meaning that the gaseous molecule only consists of one atom. The characteristics of an inert gas imply that the radon atom is electrically neutral outwards. Although some observations have shown that the electric neutrality or the monoatomic characteristics are incomplete (Jönsson G, 1992). When radon disintegrates it creates the so called radon daughters, or specifically radioactive metal atoms (Radonguiden, 2009). These daughters emit either alpha, beta or both beta and gamma radiation (SSI, 2008). Since the radon progeny are not in the form of gas as their mother they will in general stay at the place where they were created. Radon daughter can be attached to aerosols found in the air or be unattached. Unattached means that the daughters are found in the air as independent atoms or ions that readily bonds to other molecules in the air. In the indoor air different particles can be found. These particles can be either dust, water and soot particles or simply air molecules and the term used for particles or droplets in the air is aerosol (Jönsson G, 1992; CDC, 2009a). The aerosols can stay a short or a long time in the indoor air, and the occurrence of the radon daughters is mainly determined by the quality of the indoor air (Jönsson G, 1992) Radon and geology Radon can be found ubiquitously in the ground, air and water. The ground is the primary source that contributes the most to the elevated 4

17 Radionuclides in drinking water a survey regarding mitigation measures radon levels indoors ( Jönsson G, 1992). Because of the short half-life of radon (3.823 days) its diffusion in large volumes is inhibited by time. The radon gas can only by the process of diffusion reach the ground surface from depths less than 5 meters. However with the help of flow radon can reach the ground surface from fractures in the bedrock or along different layers of soil types that is several meters underneath. Radon can also be transported sideways with the help of ground water as the water flows from one point to another. Transportation of radon from large depths must occur rapidly in order to reach the ground surface before disintegration. It is thought that the radon atoms attach themselves to other atoms or travel with other gases such as CO 2 and He up to the ground surface (Jönsson G, 1992). The process from which radon is exudated from a material is called exhalation and the material must contain 226 Ra. This process is not dependent upon where the material is located. The porosity and the granularity of the material will determine the efficiency of the exhalation. The radon gas leaves the material by using the pores and cracks in the material in order to reach the surface of the material. Water within a material will affect how well the radon gas can leave the material (Jönsson G, 1992). Areas with elevated uranium content within the rock types such as granite, pegmatite and alum shale will cause elevated levels of radon in that area. As the grain size of the uranium rich minerals becomes smaller the radon content increases. This is because the surface area of the grains will increase and result in a larger exhalation. Radon can reach the ground surface through weak zones e.g. zones with crushed material within the bedrock, see Fig.2. Eskers are a highly wanted geological formation due to the permeability which allows large quantities of water to be withdrawn. Many people get their household water from eskers, and when water is extracted from wells the radon can enter the dwelling from either the esker itself or from the water Radon in water Water withdrawn from soil layers and bedrock will contain radon. Surface waters such as lakes and inland waters rarely contain radon due to aeration and mixing. Water distributed municipally rarely contains high amounts of radon but there are exceptions (SSM, 2009). The highest radon concentration is found in wells where the water is drawn from bedrock and can be above 1000 Bq/l. Dug wells that take water from surrounding soil layers usually have low concentration of radon, normally between Bq/l in the water but these wells are however susceptible to other problems. When water is used, e.g. shower or drawn, the radon in the water shifts phases from the liquid phase to the gaseous phase, i.e. it intermixes with the indoor air. A rule of thumb is that a concentration of 1000 Bq/l in the water will contribute to the radon concentration in the indoor air with about 100 Bq/m 3. Water with a radon concentration greater than 100 Bq/l radon is classified as suitable 5

18 Caroline Karlsson TRITA-LWR Degree Project Fig. 2: The three main radon sources. Blue arrow is the water source, green arrow the ground source and grey arrow the construction material source. but with remarks and a concentration above 1000 Bq/l is classified as unsuitable for household use (Radonguiden, 2009; SSM, 2009) Health aspects of radon Drinking water that contains radon is considered a low risk at least when the levels are under 1000 Bq/l (Jönsson G, 1992). When inhaled the radon and radon daughters will reach the lungs and the air ways. Most of the radon gas inhaled will leave the lungs within an hour (Radonguiden, 2009). Some of the radon atoms will however disintegrate when inside the lungs and air ways. Since the range for a particle released through alpha radiation is in the magnitude of millimeters the particles must be very close to live cells in order to be harmful (Jönsson G, 1992). As mentioned earlier, the radon daughters can bond to other particles in the air, aerosols. Some of these aerosols, with the radon daughters attached, are very small and can reach the lower parts of the air ways when inhaled. They can also get stuck onto the walls of the air ways and the pulmonary alveolus. The four short-lived daughters have half-lives less than 30 minutes and because of this the body s defense mechanisms have not enough time to eliminate the problem. Mucus in the lungs and air ways can give some protection to the surrounding cells during disintegration. Some off the radon daughters are also coughed up. The short-lived radon daughters are followed by the more long-lived radon daughters. Some uptake of the long-lived radon daughters occur in the body. The effects of these are thought to be small compared to the effects of the short-lived daughters. Ionizing radiation affects the cells in the body in different ways. Some cells can die and others can have their part that is in charge of the programming into new cells changed, resulting in abnormal cell-divisions 6

19 Radionuclides in drinking water a survey regarding mitigation measures 3.2 Uranium and possibly cancer. Lung cancer is the main concern regarding radon and radon daughters. It takes time however to develop lung cancer, between years for adults subjected to radon and with a shorter time span for children (Jönsson G, 1992). The risk is greater the longer a person is subjected to radon and the higher the radon concentration is. The Swedish Radiation Safety Authority has estimated that approximately lung cancer cases in Sweden are caused by radon in our dwellings. Some tenths of these is thought to be caused by radon leaving the household water (Radonguiden, 2009; SSM, 2009). In nature uranium is found in 5 different valence states, +2, +3, +4, +5 or +6, and the tetravalent U(IV) and the hexavalent U(VI) form are the most common. The hexavalent form of uranium is usually associated with oxygen as a uranyl ion UO 2+ 2 (Health Canada, 2001; Ek et al, 2008). There are three naturally occurring uranium isotopes; 238 U, 234 U and 235 U (Ek B-M, 2005). Of those isotopes the predominant one is 238 U. The fractions in which these are present are as following 99.3 % ( 238 U), % ( 234 U) and 0.72 % ( 235 U) respectively. Although the fraction of 238 U is predominant it is the fraction of 234 U which is of importance. It is because the half-life of 234 U is the shortest (2.47 x 10 5 years); hence it is the activity that is of importance (Ek B-M, 2005). Because of its short half-life compared to the other isotopes 234 U will disintegrate faster and emit more alpha radiation compared to the others (UNEP, 1991) Uranium and geology Uranium can be found in the earth s crust and in many different chemical compositions, e.g. oxides and silicates. Minerals with high concentration of uranium are minerals such as uraninite, the oxidized or partly oxidized massive form of uraninite, pitchblende, coffinite, autunite and uranophane. Despite the high concentration of uranium these minerals are rare and mainly found in zones in the bedrock where uranium mineralization has occurred. Uranium can then be transported from one point to another due o hydrothermal alteration, weathering and erosion (Smedley el al, 2006). Sweden is considered to have less than 1 % of the global uranium assets (Schröder et al, 2009; SGU, 2010). Uranium is generally found in four main areas in Sweden. The first area is Arjeplog-Arvidsjaur-Sorsele with one uranium deposit and a group of more than 20 occurrences. The second uranium area is located in northern Sweden close to Åsele. The third uranium area is located north of Östersund. The last area is located in southern and central Sweden in the upper Cambrian and lower Ordovician sediments and along the border of the Caledonian mountain range (OECD et al, 2005). The rock types that primarily contain uranium are granite, pegmatite and syenite which are rich in silicic acids. Uranium can also be found in other rock and soil types. Sedimentary rock types usually have 7

20 Caroline Karlsson TRITA-LWR Degree Project low concentration of radioactive substances. However, alum shale can contain high amounts of uranium (Ek et al, 2008). The Billingen plateau mountain in southern Sweden has the highest uranium content found in the alum shale, tones or approximately 300 g/t. The total uranium content in Swedish bedrock is about half of the one found in the alum shale in Billingen (SGU, 2010). Although varying from location to location. An average is 2.3 g U/t soil. Soil types such as glacial till and coarse-grained glaciofluvial sediments usually have a uranium concentration that reflects the underlying bedrock (Ek B-M, 2005). Because of the poor water quality in general wells are not usually constructed in soils that contain alum shale (Ek et al, 2008). Natural deposits, emission from the nuclear industry, combustion of carbon and other fuels etc. can all increase the uranium content in our water supplies. Fertilizers that contain phosphate can also contain uranium. When fertilizers are spread on the field s uranium can leach out and enter the groundwater. If water with high concentration of uranium is ingested the chemical toxicity of the uranium becomes a concern. 1 µg of natural uranium has an activity of Bq (Health Canada, 2001; OECD et al, 2005) Uranium in water For the speciation of the uranium in water many factors are important. The hydrogeochemical conditions such as the ph value, redox potential, ion strength, mineralogy, complex forming capacity, available ligands and the total surface of the solid substance, will all determine the speciation of uranium (Öhlund F, 2007; Dässman E, 2008). The difference between the speciation in different conditions means that uranium can be dissolved at one location under oxidized conditions by erosion and enter the groundwater, or be deposited on fractures surfaces and mineral grains at another location as the conditions change to reducing conditions (Dässman E, 2008; Ek et al, 2008). Uranyl minerals are least soluble when the ph value is in the interval of 5 and 8.5. In order to control uranium mobility it is important to consider sorption rather than mineral preciptitation (Vaaramaa K, 2003). Other factors are water supply, CO 2 and O 2 in water, uranium content in bedrock, rate in which bedrock weathers or is dissolved, available ligands and adsorbing materials (Dässman E, 2008). The hexavalent form of uranium U(VI), is soluble and predominant in oxidized conditions. At low ph values the U(VI) form of uranium is found as a uranyl ion, the cation UO This cation can also be formed under aerobic conditions, when U(IV) is oxidized to U(VI) (Gustafsson et al, 2007; Dässman E, 2008). The uranyl ion UO 2+ 2 preferentially binds to oxygen ligands in aqueous solutions. These ligands can be inorganic anions such as CO 2 3, SO2 4, SiO(OH) 3, HPO 4 and NO 3, or organic molecules with an oxygen-containing functional group (Prat el al, 2009). It can also form complexes with fluoride; however the uranyl-fluoride-complexes are only important when the ph value is low. 8