Assessment Of Radon-222 In Some Selected Water Sources
Radon is one of the sources of nuclear contamination in water and the largest contributor of the total radiation received by the general public from natural radioactive sources. Human exposure to high doses of radon through inhalation as gas or ingestion in water can lead to cancer. In this present work, the activity concentrations of Radon-222 (222 Rn) were investigated from fifteen (15) water samples collected at different locations within Dutsin-Ma town, Dutsin-Ma Local Government Area, Katsina State using Liquid Scintillation Counter. The concentrations of Radon were found to range from (11.67-152.81⁄), (0.61-172.25⁄) and (21.98-47.17⁄) with mean values of 64.66⁄, 41.15⁄and 34.57⁄for Borehole, open well and Earth-Dam respectively.
The results were compared with the world average maximum contaminant level (MCL) of 10⁄set by World Health Organization and it was noted that 86.67% of the samples exceeded the value with 20% of the samples above the World recommended reference level of 100/. Also, the Annual Effective Doses due to ingestion of Radon in water for the three (3) categories of people were estimated from the measured radon concentrations and their mean values were found to be (0.472, 0.944, 3.304)/ in borehole water, (0.308, 0.616, 2.156)/ in well water and (0.252, 0.504, 1.764)/in surface water (Earth-Dam) for adults, children and infants respectively.
All the mean values of the annual effective doses were above the recommended level of 0.1/set by World Health Organization as such it is recommended that the inhabitant of Dutsin-Ma town should always boil their water irrespective of it source before drinking so as to keep the concentration of Radon as low as reasonably achievable. Beside, further studies on the activity concentration of radon in water sources from Dutsin-Ma environs and other parts of Katsina State be carried out so as to determine the fitness of the water for consumption or otherwise.
Table Of Contents
- Table of Content
- 1.1 Background of the Study
- 1.2 Aim and objectives
- 1.3 Justification
- 1.4 Scope and Limitation
- 1.5 Definition of terms
- 2.1 Radioactivity
- 2.1.1 Radioactive decay law
- 2.1.2 Activity
- 2.1.3 Specific Activity
- 2.1.4 Half-life
- 2.2 Radiation
- 2.2.1 Sources of Natural Radiation
- 2.2.2 Terrestrial Sources
- 2.2.3 Cosmic Sources
- 2.3 Radon-222
- 2.3.1 Sources of Radon
- 2.3.2 Water
- 2.3.3 Soil
- 2.3.4 Health Effects of Radon
- 2.3.5 Radon guidelines for drinking water
- 2.4 Review of previous work
Materials And Method
- 3.1 Study area
- 3.1.1 Geology of the Study area
- 3.2 Materials and Reagents
- 3.3 Liquid Scintillation Counter
- 3.4 Method
- 3.4.1 Sample Collection
- 3.4.2 Sample Preparation
- 3.4.3 Sample Analysis
Results And Discussion
- 4.1 Results
- 4.2 Discussion
- 4.2.1 Borehole water
- 4.2.2 Well water
- 4.2.3 Surface water
- 4.2.4 Mean Radon concentrations
- 4.2.5 Distribution of Radon-222 Concentrations
- 4.2.6 Annaul Effective Doses
- 4.2.6 Mean Annual Effective Doses
Summary, Conclusion And Recommendations
- 5.1 Summary
- 5.2 Conclusion
- 5.3 Recommendations
List Of Tables
- Table1: Half-life of the natural Isotopes of radon
- Table 2: International Radon guidance and parametric values in drinking water
- Table 3: Results of Radon concentration ( / ) and their corresponding annual effective doses (AED) in ( / ) for Water Samples in Dutsin-Ma town
List Of Figures
- Sources and Average Distribution of Natural Background Radiation for the World Population
A chart of Uranium-238 decay series
- Block diagram of Uranium-238 decay series
- Map of Katsina showing Dutsin-Ma Local Government Area
- Geological map of the northern Katsina State showing Dutsin-Ma LGA
- Schematic Diagram illustrating the principle of Liquid Scintillation Counter
- Map showing some selected settlements in Dutsin-Ma town and Sample Collection Points
Map showing Sample Collection Points and Water type collected
- Bar Graph of Radon-222 concentrations for Borehole water samples
- Bar Graph of Radon-222 concentrations for well water samples
- Bar Graph of mean Radon-222 concentrations for the three water types
- Mapping of the distribution of Radon-222 Concentrations in selected settlement of Dutsin-Ma town, Dutsin-Ma Local Government Area, Katsina State
Bar Graph of the corresponding Annual Effective Doses for Adult
- Bar Graph of Adult Mean Annual Effective Doses for the three water types
List of Plates
- Liquid Scintillation Analyzer (Tri-Carb LSA 1000) CERT, ABU, Zaria
- Printer attach to the Liquid Scintillation Analyzer
- Vial in Counting Rack
- Counted Samples in Secondary Containment
List of Acronyms and Units
- AED: Annual Effective Dose
- BEIR: National Academy of Biological Effect of Ionizing Radiation
- ⁄ : Becquerel per Litre
- CERT: Centre for Energy Research and Training
- CNSC: Canadian National Safety Commission
- E-DWD: European Drinking Water Directives
- IAEA: International Atomic Energy Agency
- ICRP: International Commission on Radiation Protection
- LSA: Liquid Scintillation Analyzer
- LGA: Local Government Area
- MCL: Maximum Contamination Level
- ml: millilitre
- mSv: milliSievert
- NORM: Natural Occurring Radioactive Material
- PMT: Photomultiplier Tube
- UNSCEAR: United Nations Scientific Committee on the Effect of Atomic Radiation
- USEPA: United States Environmental Protection Agency
1.1 Background of the study
Water is the major constituent of the Earth’s streams, lakes and oceans and the fluid of most living organisms. It covers about 71% of the Earth surface. It is vital for all known forms of life especially man. Man uses water for various reasons such as transportation, power generation, Agriculture and other domestic activities hence its availability and quality as regard radiological, microbiological, chemical and any other form of contamination are delicate and vital issues (Garba et al., 2008). Unfortunately, access to potable drinking water in most developing countries such as Nigeria is a major challenge hence most people rely heavily on untreated surface and ground water sources for consumption.
For instance, Dutsin-Ma local Government Area of Katsina State where its inhabitant rely solely on untreated groundwater sources (well and borehole) as well as surface water source. This is because there are only few available pipe born water sources and in most places where such sources are available they are not operational. The Zobe dam located in Dutsin-Ma which is intended to remediate this problem is yet to be completed by the government (Isah, 2009). It is therefore important to investigate the radiological content of ground and surface water sources in Dutsin-Ma town so as to determine it fitness for consumption.
Radon is a naturally occurring radioactive inert gas with a half-life of 3.82 days which is a member of the Uranium decay series (Somlai, 2007). It contributes the largest proportion of the total radiation from natural sources. Studies have shown that Radon-222 (222Rn) and its progeny contribute about 50% of the total effective dose equivalent from natural sources. Radon-222 is soluble in water. The concentration of radon in water is due to the decay of Radium-226 associated with the rock and soil. The Radon-222 gas penetrates through soil and rocks and dissolves in water (Xinwei, 2006). Normally, drinking water from ground water sources has higher concentration of radon than surface water.
The exposure of a population to high concentration of radon and its daughters for a long period has significant health effects ranging from respiratory functional changes to cancer of the lungs (BEIR, 1999). Also a very high level of radon in drinking water can lead to stomach and gastrointestinal tract cancer (Kendel and Smith, 2002).
In Nigeria, most areas lack established data on the activity concentration of Radon-222. Dutsin-Ma town, Dutsin-Ma Local Government Area, Katsina State is one of such areas from the survey of literature and Author’s knowledge, despite the fact that most of its inhabitant rely heavily on untreated surface and groundwater sources for drinking, agriculture and their domestic activities. Since its geology revealed that it is enriched in granite, it is possible that the concentrations of radon in both surface and groundwater sources in Dutsin-Ma town are higher than normal. This research seeks to address the problem of lack of baseline data/information on the activity concentration of Radon-222 in Dutsin-Ma town, Dutsin-Ma Local Government Area, Katsina State, Nigeria.
Our investigation reveals that access to potable source of water has remained one of the major challenges for most people as well as animals in Dutsin-Ma Local Government Area, Katsina State as such majority rely on untreated surface and ground water sources for consumption. This is quite dangerous since the geology of Dutsin-Ma Local Government Area, Katsina State (figure 7), revealed that it is highly enriched in granites and gneisses as studies have shown that high activity concentration of Radon-222 is associated with areas rich in granite (David et al., 1989; Gilbert, 1988). As such, the level of Radon-222 in drinking water which, in high concentration, can lead to a significant risk of stomach and gastrointestinal tract cancer (Zhuo et al., 2001), among others, need to be investigated. This is more so because our knowledge of its level of availability could be of great help in resource planning.
1.2 Aim and Objectives:
The aim of this research is to investigate the activity concentration of Radon-222 in both surface and groundwater sources in Dutsin-Ma town using Liquid Scintillation Counter which will serve as a baseline study. The objectives of this research include:
- To measure the activity concentrations of Radon-222 in water samples collected from Dutsin-Ma town, Dutsin-Ma Local Government Area, Katsina State.
- To estimate the annual effective doses due to intake of Radon-222 from the measured samples for Adults, Children and Infants.
- To compare the result with WHO among others so as to have an idea of the risk level with respect to Radon-222.
The problem of 222Rn is still an issue of concern in the current scientific world. It is well known that Radon-222 and its progenies contribute 50% of the total effective dose from natural sources. In fact, it has been reported that diseases of major concern associated with radon are Stomach cancer from ingestion and lung cancer from inhalation (Mills, 1990). According USEPA (2012), Radon-222 is the second most frequent cause of lung cancer and number one among non-smokers. Research has shown that these diseases could be as a result of both chronic and acute dose exposure. USEPA has also estimated that 15000-25000 people died of Radon-222 induced cancer per annum in USA. Virk and Singh (1993) recorded that certain rocks including granites, light colored volcanic rocks, sedimentary rocks containing phosphate and metamorphic rocks have higher average Uranium contents. Therefore this study seeks to investigate the activity concentrations of Radon-222 in water within Dutsin-Ma town, Dutsin-Ma Local Government Area, Katsina State which will serve as a baseline study.
1.4 Scope and Limitation
This work focuses only on the analysis of activity concentrations of Radon-222 in water sources from Dutsin-Ma town using Liquid Scintillation technique as well as the estimation of the corresponding annual effective doses due to ingestion of Radon-222 in water for adults, children and infants. The sources of water involved were ground (open wells and Boreholes) and surface water (Earth Dam) collected from the following places within the town: Kadangaru, Hayin Gada, Yandakka, B/yarima, Kandahar, Lowcost, Isa Kaita College, Sokoto Rima and Dutsin-Ma Earth-Dam. The result is expected to provide the activity concentrations of Radon-222 which would be used to estimate the annual effective doses from water consumption.
1.5 Definition of Terms
The transformation of a radioactive nuclide into a different nuclide (or nuclides) by the spontaneous emission of radiation such as alpha, Beta or Gamma rays.
A positively charged particle consisting of two protons and two neutrons that is emitted by the nuclei of some radioactive elements as the decay.
Penetrating electromagnetic radiation emitted by an atomic nucleus during radioactive decay examples include: high-energy, short wavelength form of ionizing radiation.
The SI unit of activity of a radioactive substance. (1Bq = 27pCi).
The number of nuclear disintegrations in a radioactive material per unit time (it is used as a measured of the amount of radionuclide present in the material).
A general term used to refer to the amount of energy absorbed by tissue from ionizing radiation
A measure of the dose to a tissue or organ designed to reflect the amount of harm caused to the tissue or organ.
The unit of effective dose. It is equal to 1 joule/kilogram (symbol Sv).
A chemical element with symbol Rn and atomic number 86. Radon is a colorless, odorless, tasteless, naturally occurring, radioactive noble gas that is form from the decay Radium.
Summary, Conclusion And Recommendations
A total of fifteen (15) water samples which include eight (8) borehole water samples, five (5) well water samples and two (2) surface (Earth-dam) water samples from Dutsin-Ma town were analyzed for radon concentration using liquid scintillation counter at the Centre for Energy Research and Training (CERT) Ahmadu Bello University Zaria, Nigeria. Radon concentrations obtained from this analysis range within 0.61 / to 172.25 / . The highest and the lowest radon activity concentration were recorded from well water samples at Kadangaru and Bayan Yarima respectively. Borehole water samples recorded the highest mean radon concentration of 64.66 / followed by well water samples of 41.15 / while surface water sample (Earth-dam) recorded the lowest mean radon concentration of 34.57 / as shown in table 3.0.
It has been noticed that 86.67% of the recorded values of radon concentration in this study as well as the mean values obtained for the three (3) water types were found to be above the world average Maximum Contamination Level (MCL) of 10 / set by World Health Organization and the MCL of 11.1 / set by United States Environmental Protection Agency (USEPA, 1991). Also, 20% of the recorded values of radon concentration which include well and borehole water samples from Kadangaru, and borehole water sample from Hayin gada are above recommended action level of 100 / set by the World Health Organization (WHO, 2008). These higher values of Radon-222 concentrations in water which could be linked to the geology of the area (rocks and soil type), pose a threat to the health of the inhabitant of the study area particularly those living in Kadangaru and Hayin Gada indicating that such water is not fit for consumption from radiation point of view. However, the inhabitants of such areas are advised to boil the water if they must use it for consumption so as to degas radon thereby keeping the concentration of Radon-222 in the water as low as reasonably achievable. The corresponding mean annual effective doses estimated for the three (3) categories of people from the three (3) water types were found to be 0.472, 0.944 and 3.304 / in borehole water for adults, children and infant respectively. While due ingestion of Radon-222 in both well and surface water samples were found to be 0.308, 0.616, and 2.156 / and 0.252, 0.504 and 1.764 / for adults, children and infants respectively. All the mean annual effective doses were found to be above World Health Organization the recommended reference level of 0.1 / for intake of radionuclide in water set by World Health Organization (WHO, 2004).
Results obtained from the measurement of the activity concentrations of Radon-222 in water samples collected at different locations of Dutsin-Ma town, Dutsin-Ma Local Government Area, Katsina State revealed that 86.67% of the recorded values of radon concentrations in the present study as well as the mean values obtained for the three (3) water types were above the world average Maximum Contamination Level (MCL) of 10 / set by World Health Organization and the MCL of 11.1 / set by United States Environmental Protection Agency (USEPA, 1991). 20% of the recorded values of radon concentration which include well and borehole water samples from Kadangaru, and borehole water sample from Hayin gada also exceeded the recommended action level of 100 / set by the World Health Organization (WHO, 2008). These significantly high values of radon concentration can be ascribed to the nature of the basement rock and soil type in the study area for groundwater sources while that in the surface water (Earth-Dam) could be linked to the nature of the granitic rocks used in the construction of the dam bank, the soil type, as well as waste materials flooded into the surface water during raining season. Therefore these water sources pose a threat to the health of the inhabitant of Dutsin-Ma town, Dutsin-Ma Local Government Katsina State if continually ingested without proper treatment. The likelihood of this threat to health (which could be stomach or lung cancer) is more on infants and children than adults as evident from the estimated Annual Effective doses of the corresponding radon concentrations in water in which most of the estimated annual effective doses were found to be above the reference level of 0.1 / set by World Health Organization (WHO, 2004) for intake of radionuclide in water.
- Further studies on the activity concentrations of Radon-222 in water sources including tap water should be carried out in Dutsin-Ma environs and other parts of Katsina state since this is a pioneer work.
- The inhabitants of Dutsin-Ma town, particularly in locations where concentrations of Radon-222 were found to be higher than normal should boil their water before consumption so as to keep their exposure due to ingestion of Radon-222 as low as reasonably achievable.
- Epidemiological studies of the general population to determine lung and stomach cancer incidence should be carried out.
- A detailed geological map of the study area should be made available for research and academic purposes.
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