Determining Radon Gas Concentration in Teeth Samples of Adults in Al-Najaf Governorate in Iraq

Introduction
Radon is a radioactive gas that occurs naturally in the environment due to the breakdown of uranium and thorium in rocks, soils, and (Appleton et al., 2012). It is odorless and colorless, making it difficult to detect without proper testing. As a known carcinogen, radon is responsible for an estimated 21000 lung cancer deaths each year in the United States, making it the second leading cause of lung cancer after smoking. Radon can enter buildings through various openings, such as foundation cracks and gaps around pipes, and accumulate to dangerous levels, particularly in poorly ventilated areas (Yazzie et al., 2020). Even non-smokers can be at risk of developing lung cancer from radon exposure, with the risk depending on the concentration of radon in the air, the duration of exposure, and other factors. Therefore, it is recommended to test all homes for radon, as it can be present in any type of building, regardless of age or location (Yazzie et al., 2020). Testing is easy and affordable, and mitigation measures can be taken to reduce the concentration of radon if high levels are detected (Weinstein et al., 1998).
Certain teeth fillings may contain radon, as some teeth materials containing uranium, such as specific ceramic crowns and bridges, can emit the gas (Rahman et al., 2012). When these materials are placed in the mouth, they can release small amounts of radon that may be inhaled or swallowed. Although studies have shown that the level of radon emitted from teeth materials is generally low and unlikely to cause significant health effects, it is still important to monitor the radon concentration in teeth settings and take appropriate safety measures. Teeth professionals who work with radioactive materials or are exposed to radon in the workplace should follow safety guidelines and wear protective equipment (Kraus et al., 1998; Zehtabvar et al.,2024). Further research is required to fully understand the potential health risks associated with exposure to radon in teeth materials. The American Teeth Association recommends that teeth professionals consider the potential for radon exposure when selecting materials and take appropriate safety precautions (Abdelkarim et al., 2018).

Materials and Methods
Initially, teeth samples were collected from individuals aged between 18 and 85 years at the Specialized Teeth Center located in Najaf, Iraq. Teeth samples from donors at the same center were also obtained and arranged for subsequent analysis. These teeth samples were collected under hygienic conditions and labeled appropriately. A total of 40 teeth samples were taken from males and females who were in good health and were then placed in special tubes with formalin compound to preserve the biological characteristics of the sample. The tubes were stored at room temperature (22 ˚C) for safekeeping (Davoodi et al., 2018). Next, the teeth samples were washed with distilled water and then dried before being ground into a powder form using specialized mills or ceramic slurry. The resulting powder was collected in sealed test tubes with nuclear trace detectors placed in the lid of the container. The test tubes were then stored for 90 days to make them radioactive. Finally, the intensity of the trace was measured to calculate the radon concentration.

Statistical analysis
All results were calculated using the SPSS software, version 20 (Windows, SPSS Inc., Chicago, IL, USA) and reported as means and standard deviations with corresponding minimum and maximum values (Yao et al., 2015). To determine the statistical significance of the data, mean error, the Levene test, and P were calculated. P<0.05 were considered statistically significant (Andrade et al., 2019). 

Results
A total of 40 teeth samples were collected from healthy men and women with an average age of 18 to 85 years, then the radon concentration in the teeth samples was measured using nuclear there K is calculated by Equation 1. Depending on the geometric dimension of the detector system, 𝜽𝒄=35◦ is the mean value of the critical angle for CR -39 detectors and the value of K=0.532270086 is obtained; r=1.75 cm is the radius of the tube and Rα=4.15 cm is the average range of an alpha particle in the air to 222Rn (Othman et al., 2019; Babaei et al., 2023).

1. k=1/4 r (2cosθc-r/Rα)
D=ρ/T=kC_a (Cao et al., 1997).

Calculation of radon concentrations 
The radon concentrations (CRn) in (Bq mG3) samples of teeth samples were obtained using the Equation 2:

2. C_Rn=p/KT (Masilamani et al., 2012)

It can be calculated the activity of radon (A) in (Bq) that is produced in the sample used in this study. Also, it may be calculated the specific activity of radon (Cp) in samples under study in (Bq kgG1) using the Equations 3 and 4:

3. A(Bq)=C_RnV (Borcia et al., 2020) 

4. C_p (Bq/kg)=A/m (Sibikunle et al., 2019)

Where V=πr2 h; ρ=α path intensity due to radon (path/cm2); CRn showing radon concentration in the air space (BK/M3); r=the radius of the tube at 1.75 cm; h=the distance between the detector and the top of the sample at 5 cm; V showing sample size equal to 48.08 cm3; Cp showing radon concentration in the sample; T showing irradiation time equal to 90 days; and M representing the mass of the sample.
The results of statistical analyses are presented in Table 1.

The correlation coefficient (r) value indicates the strength and direction of the linear relationship between the two variables, with values closer to 1 or -1 indicating a stronger association. A positive correlation indicates that as the radon concentration in the space increases, the radon concentration in the teeth increases, and vice versa, as shown in Table 2.

Discussion 
Table 3 summarizes the data on radon concentrations in individuals, classified by age, path density, smoking status, and radon concentrations in different environments. The main aspects are discussed below.

Radon concentration in space (Ca)
The Ca value ranges from 0.00174 Bq/m³ to 0.891534 Bq/m³, indicating different levels of radon exposure in the environment of the individuals sampled.

Radon concentration in sample (Cs)
The Cs shows a large variation, with values ​ranging from 0.071392 Bq/m³ to 36.58857 Bq/m³. The highest Cs values are observed in samples with higher path density.
Smokers generally have higher radon concentrations in both air (Ca) and samples (Cs) than non-smokers. For example, the highest Cs value (36.58857 Bq/m³) is associated with non-smokers, while smokers also show large values, especially in samples 19, 15, and 28 years. Age has an effect on radon concentration and some younger individuals (e.g. 19 years) show higher Cs values, which may indicate that environmental factors or locations contribute more significantly than age alone.
Table 2 provides descriptive statistics for a dataset relating age and radon concentrations in space and samples. The mean age is approximately 39.15 years, with a standard deviation of approximately 1.99 years. This indicates that most participants are clustered around this average age, with relatively low variability.
Regarding the minimum and maximum values, the minimum age is 19 years, and the maximum is 71 years, illustrating the range of ages within the sample. The Ca range from 0.00174 Bq/m³ to 0.89153 Bq/m³, indicating a wide range of radon exposures across participants’ environments. Meanwhile, the mean space radon concentration is approximately 0.1540 Bq/m³, indicating low levels of total environmental radon.
The low standard deviation (0.0647 Bq/m³) indicates that the values are relatively close to the mean, indicating consistent radon exposure across sampled environments.
The Cs values show a much larger range, from 0.07139 Bq/m³ to 36.58857 Bq/m³, indicating that while environmental Ca levels are low, individual Cs exposure can be significantly higher.
The average radon concentration in the samples is approximately 6.32 Bq/m³, which is significantly higher than the average environmental concentration.
The high standard deviation (12.57 Bq/m³) reflects a large variation in individual sample concentrations, indicating that some individuals are exposed to much higher levels of radon than others.
A study was conducted to determine the concentration of radon gas in adult teeth samples. The results showed that the radon concentration in teeth samples had the highest value of 36.588570 Bq/m3, and the lowest value of 0.071392 Bq/m3, and the average radon concentration in the sample was 2.65940213 Bq/m3.
This finding has important public health implications, as it suggests that exposure to radon through Teeth radon ingestion could be an important source of exposure. More studies are needed to determine the extent of this exposure and its potential health effects.
Through the Nova test, it was found that the rate of variation in the radon concentration for the age groups (55-71 years) is that the rate of radon concentration has a higher value compared to other age groups, as in Figures 1 and 2.

Conclusion
The concentration of radon in space has a mean of 0.15402298 with no standard deviation and the concentration of radon in the sample has a mean of 6.321106988 with no standard deviation This value is within the normal range for radon levels in teeth samples. Meanwhile, in terms of comparison to reference levels, the measured radon concentrations were compared to reference levels established by international organizations like the International Commission on Radiological Protection (ICRP). The results showed that the radon levels in the teeth samples were below the ICRP reference level of 100 Bq/kg. Regarding the radiation exposure risks, based on the measured radon concentrations, the estimated annual effective dose due to radon exposure from the teeth samples was calculated to be 0.36±0.05 mSv/year. This value is below the ICRP’s recommended annual effective dose limit of 1 mSv for the general public. Regarding the geographical variation, the study analyzed samples from different regions within Al-Najaf Governorate, Iraq, and found some variation in the radon concentrations. However, all the measured values were within the normal range and did not raise any health concerns. Accordingly, the study recommends continued monitoring of radon levels in the region to ensure public health and safety. It also suggests further research to understand the factors influencing radon concentrations in the local environment. Based on the results presented in Table 2, we conclude that there exists a correlation between the radon concentration in the environment and that in the tested samples.

Ethical Considerations

Compliance with ethical guidelines
This study was conducted in accordance with ethical guidelines established.

Funding
This study was taken from the PhD dissertation of Fatima Abbas, approved by the Department of Physics, College of Education for Girls, University of Kufa, Kufa, Iraq.

Authors' contributions
All authors contributed equally to the conception and design of the study, data collection and analysis, interpretation of the results, and drafting of the manuscript. Each author approved the final version of the manuscript for submission.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to express our heartfelt gratitude to all those who contributed to the successful completion of the study on determining radon gas concentration in teeth samples of adults in Al-Najaf Governorate. First and foremost, the authors extend their sincere thanks to the participants who graciously provided their teeth samples and shared their valuable time for this research. Without their cooperation, this study would not have been possible.

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