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 Table of Contents  
Year : 2016  |  Volume : 4  |  Issue : 3  |  Page : 88-92

Biological risk assessment resulting from terrestrial radionuclides in Iran

1 Department of Radiation Medicine Engineering, Shahid Beheshti University, Tehran, Iran
2 Department of Crisis Management, Research Institute of Shakhes Pajouh, Isfahan, Iran
3 Department of Physical Geography, Shahid Beheshti University, Tehran, Iran

Date of Web Publication26-Sep-2016

Correspondence Address:
Alireza Kamali Asl
Department of Radiation Medicine Engineering, Shahid Beheshti University, Tehran
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2347-9019.191107

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Background: A large part of total dose resulted from the natural sources is due to the environmental radionuclides such as 238Th and 238U decay chain and 137Cs and 40K radioisotopes. Given the importance of identifying environmental pollutants and protection against them. Materials and Methods: In this study, the activity of the terrestrial radionuclides was analyzed in different parts of Iran, and their biological risk was reviewed using parameters presented by international organizations such as United Nation Scientific Committee on the Effects of Atomic Radiation. Effective dose equivalent map resulting from Iranian terrestrial radionuclides was prepared by using of ArcGIS software and Inverse Distance Weight method. Findings: West of Mazandaran Province, especially the Ramsar region and Villadareh village in the Ardabil Province are reported critical based on standards, and there is need to additional studies to or not to carry out environmental measurements in these areas.

Keywords: 137Cs, environmental radiation pollution, natural exposures, terrestrial radionuclides

How to cite this article:
Kahani MM, Asl AK, Hashemi S, Kahani MM, Amini M. Biological risk assessment resulting from terrestrial radionuclides in Iran. Int J Health Syst Disaster Manage 2016;4:88-92

How to cite this URL:
Kahani MM, Asl AK, Hashemi S, Kahani MM, Amini M. Biological risk assessment resulting from terrestrial radionuclides in Iran. Int J Health Syst Disaster Manage [serial online] 2016 [cited 2021 Mar 1];4:88-92. Available from: https://www.ijhsdm.org/text.asp?2016/4/3/88/191107

  Introduction Top

Background radiation is one of the main sources of human exposures. An important part of background radiation is resulting from environmental radionuclides, and another important part is due to cosmic radiation. Natural radioisotopes of the environment have been produced by Earth's appearance or cosmic rays. The main source of natural radioactivity in Earth's crust that leads to large exposure by organisms is due to radionuclides of 238 U and 238 Th decay series and 40 K radioactive radionuclides, and they were present at Earth's crust according to their high half-life since the Earth's formation.[1]

Environmental pollution of radioactive isotopes can be hazardous to humans in two methods. In the first method (external contamination), received dose by a human is due to radiations emitted from radioactive isotopes outside the body and in the environment. The gamma ray is the most effective factor in this type of pollution due to their emission from radioisotopes (the presence in the environment) and their range, and then they are considered in assessing the risk of radioisotopes in the environment. In the second method (internal contamination), received dose by a human is due to radioisotopes enter and sediment in the human body which can enter into the body by inhalation, ingestion, or contact. In this type of pollution, charged particle radiations such as alpha and beta are more dangerous due to their high linear energy transfer in the body that increase the biological degradation of the body, therefore they are more considered.

Dose estimation in the environment depends on the concentration of radionuclides in the environment. The natural radioisotopes in the environment such as 232 Th,238 U, and 40 K and their decay products at different levels can provide important information on dose amount and the environment changes resulting from nuclear sources and human activities.[2] It is noteworthy that a new way used to estimate radionuclide concentration is biomonitoring.[3]

Potassium is a vital component in the human body, and its 40 K isotope is radioactive. Its mean concentration in the human body is about 60 Bq/kg.[4] In addition to natural radioisotopes,137 Cs radioisotope is present in the environment that is a human-made radioisotope and is the most important fission products. Possible production sources include using or testing nuclear weapons, nuclear power plants output, and nuclear accidents.[4]

This study aims to analyze and study the concentration of terrestrial radionuclides in some areas of Iran and their risk assessment through computing some parameters presented by the international organizations and responsible organization measures to protect areas that are determined as risky in Iran.

  Materials and Methods Top

In this study, information of 22 important areas in Iran was analyzed. The common and reliable method for measuring the concentration of radioisotopes in soil is terrestrial sampling in random or nonrandom ways, with specific intervals; spectroscopy is done after conducting a series of laboratory procedures and concentration of various radioisotopes is obtained.[1],[5]

Equivalent radium activity is used to compare the specific activity of areas including the specific activity of 226 Ra,232 Th, and 40 K radioisotopes which is defined as follows:[6]

Where ARa, ATh, and AK are specific activities of 226 Ra,232 Th, and 40 K isotope, respectively. Gamma dose rates resulted from terrestrial radionuclides can be estimated using the concentration of radioisotopes in soil. Gamma absorbed dose rate in air due to 137 Cs,226 Ra,232 Th, and 40 K radioisotopes in one meter above ground is calculated using Equation (2) and annual effective dose equivalent of Equation (3).[2],[6],[7]

Where ADRA, DCF, and OF, respectively, are absorbed dose rate in air (nGy/h), effective dose equivalent conversion factor (0.7Sv/Gy), and outdoor factor which is equal to 0.2, and T is time conversion factor (8760 h/year).[2],[6] The double risk of cancer as an attractive parameter during mean length of life due to terrestrial isotopes (excess lifetime cancer risk) is estimated by the following equation in terms of percentage.

Where DL is the mean duration of human life that is considered 70 years and RF is the risk factor of fatal cancer per Sv that recommends 0.057 as random effects for public ICRP 103.[2],[6] Since, human gonads are the most sensitive tissues relative to radiations, especially in men, the annual effective dose equivalent of gonads resulted from gamma rays of terrestrial natural radioisotopes is calculated using the following equation.[2]

External risk parameter (Hex) which reflects the external exposure and is widely used is defined as follows.[2],[6],[8] In addition to external risk, radon and its short-lived daughter nuclei are harmful to respiratory organs. Internal exposure from radon and its daughters are quantified by internal risk parameter (Hin) and is calculated using Equation (7).[2],[6],[8]

Since in 238 U decay chain to 226 Ra radionuclide, there is no high-energy gamma ray and no probability of high emission,238 U activity can be used in calculations in cases where the specific activity of 226 Ra is not available in terrestrial samples.[9],[10] It must be noted that reported concentration for each area is the mean values obtained for that area. In some areas, the amount of 137 Cs radioisotopes is not reported, or its amount is not measurable because of its low value. Using ArcGIS software version 10.1 (http://www.esri.com/software/arcgis) and based on the specific activity of terrestrial radionuclides were measured, the results were calculated from Equation (3), effective dose equivalent map of Iranian terrestrial radionuclides was drawn. Effective dose equivalent of areas, where the measurements were not performed, was interpolated and mapped using Inverse Distance Weight method in ArcGIS software [Figure 1].
Figure 1: Map of annual effective dose equivalent resulting from Iranian terrestrial radionuclides

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  Results Top

The specific activity values of different regions in Iran and using Equation (1) results are given in [Table 1]. The calculation results of other risk parameters can be found in [Table 2].
Table 1: Important terrestrial radionuclides concentration in different regions of Iran

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Table 2: The physical and biological parameters of terrestrial radioisotopes calculated from studied areas

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  Discussion Top

Environmental radiations from terrestrial radionuclides depend on geological composition, soil type, and region geographic conditions, while the amount of cosmic rays in the atmosphere is related to altitude and latitude of the area. Studies show that for synthetic radioisotopes such as 137 Cs, concentration in the atmosphere is inversely related to their distance from the incident area or nuclear activity, while this is not true for natural radionuclides.[25] As noted in [Table 2], Ramsar in West of Mazandaran Province has the largest amount of radium equivalent activity (10125.6 Bq/Kg) and the area around Saghand mine in Yazd Province has the lowest amount of radium equivalent activity (14.82 Bq/Kg).

Using the results of [Table 2], it can be seen that the highest absorbed dose of terrestrial radioisotopes in air, at one meter above ground, was registered at Ramsar (4682.73 nGy/h) and Vila Darre (122.32 nGy/h), and then Süngün Mine in East of Azerbaijan (96.97 nGy/h). The most effective dose equivalent (5746.8 μSv/year), the most effective dose equivalent received by gonad (31,339 μSv/year), and the highest risk of cancer during mean human life (2.29%) was belonged to Ramsar city, and the most annual effective dose equivalent (150.12 μSv/year) was belonged to Vila Darre. The 2.29% double risk of cancer means that exposure resulted from terrestrial radionuclides increase cancer risk as much as 2.29% during human life. In a comprehensive study by Sohrabi et al., it was found that the mean annual effective dose of each individual member of the public from terrestrial radionuclides and cosmic radiation, indoors and outdoors, is 0.86 + 0.16 mSv/year by measurements and 0.8 + 0.2 mSv/year by calculations.[26] However, in this study, the total dose is obtained from all of the natural sources and not only from terrestrial radionuclides.

In one recent study by Zare et al.,[3] they used United Nation Scientific Committee on the Effects of Atomic Radiation biological risk assessment parameter to estimate hazards from sediment and soil radionuclides, like this work in Anzali port of Iran. Their results showed Anzali port in Iran is not a critical area because of its sediment and soil radionuclide radiations hazard. Noncritical condition of each region based on radioisotope contamination in soil is less than the unit of Hin and Hex parameters.[2],[7] According to the calculated values for Hex and Hin, West of Mazandaran, especially Ramsar, as well as Vila Darre village in Ardabil is called the critical region considering terrestrial radioisotope contamination. This means that radiation risk cannot be ignored. A good way must be considered to reduce the exposure of people in this area. These cumulative radionuclides are based on nuclear accidents such as atomic bomb explosion in Japan and Chernobyl nuclear power plant accidents. [27,28] In this regard, more environmental investigations and comparison of biological parameters with environmental standards are proposed to make decisions for preventive measures.

One of the important and green ways to control and decontaminate terrestrial radioactive substances and reduce the radiation exposure of terrestrial radioisotopes that can be proposed for these areas is phytoremediation. This method is based on planting vegetation in the infected area; the roots of these plants absorb terrestrial radionuclides highly so that the concentration of radioactive materials is decreased in soil. A notable point of this approach is that these plants must not be placed in the food chain.[3] Another proposed method is people migration through informing them and facilitating the issue by the government. Selecting a control method must be performed based on social and climate studies.

  Conclusion Top

Since acquiring the power of nuclear fission, human nuclear activities and some of the geological conditions have been disturbed the balance of radioactive isotopes in some regions of the world. Study and identifying of these regions is one of the tasks of nuclear scientists to improve people lives. In this regard, 22 important areas of Iran were evaluated in this study. Based on results, Ramsar in the West of Mazandaran and Vila Darre village in Ardabil have a critical situation, so more environmental investigations proposed and a good control method must be performed in these areas.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1]

  [Table 1], [Table 2]

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