Indoor and Outdoor Radon in the Dwellings of Al-Najaf Province, Iraq
Article information
Abstract
Background:
Radon, a radioactive gas, is ubiquitous and commonly inhaled by individuals. It was originating from the Earth's crust. Radon can also be released by building materials, water, basement air, soil, and other environmental components. When radon gas decays, it produces radioactive particles that can be inhaled. These particles damage lung tissue, increasing the risk of lung cancer over time.
Materials and Methods:
Indoor and outdoor radon concentrations were determined in 24 houses in two cities in Al-Najaf province, Al-Najaf city and Al-Kufa city, using Airthings Corentium Digital Radon Detector.
Results and Discussion:
The arithmetic mean of indoor radon concentration was 18.09±9.41 Bq/m3, while the arithmetic mean of outdoor radon concentration was 4.50±2.96 Bq/m3. The arithmetic mean of ‘the annual effective dose’ received by home occupants by indoor radon was 0.46±0.24 mSv/yr. The arithmetic mean of the ‘effective dose to the lung’ was 1.09±0.57 mSv/yr.
Conclusion:
The total annual effective dose due to indoor and outdoor radon concentration was lower than the reference level of International Commission on Radiological Protection. The results of the radiological survey due to indoor and outdoor radon levels in studied dwellings suggest that the radionuclides and their radiological hazard indexes in all studied dwellings do not impose a health hazard.
Introduction
The world we inhabit is consistently subjected to radiation, which results in a continual and inescapable exposure of all living organisms to differing levels of ionizing radiation. This is referred to as background radiation, which originates from both natural and human-made sources. Natural sources include cosmic rays and long-lived radionuclides from the Earth’s crust, which are ubiquitous in the environment—even within the human body [1–3]. Among these radionuclides, radon (radon-222) and its decay products [4]—commonly found within the Earth’s crust—represent the primary natural radioactive source to which humans are exposed [5]. The predominant natural radiation exposure is attributed to radon, constituting roughly 50% of this exposure [6, 7]. Radon is a gas that is colorless, odorless, and tasteless. Notably, it is the second largest contributor to lung cancer after smoking [8]. The radioactive gas radon emits alpha radiation. It is a daughter product of radium-226 that decays radioactively, having a half-life of 3.82 days [9, 10]. While a portion of the radon produced by soil and rocks disperses into the surrounding environment, where it is rapidly diluted and poses less risk, it tends to accumulate to potentially hazardous concentrations in confined indoor spaces [11]. Radon was categorized as a human carcinogen by the ‘International Agency for Research on Cancer’ in 1988 due to studies linking exposure to radon with a higher likelihood of developing cancer of the lungs [12]. Monitoring for airborne radon can be conducted in various settings, including indoor, outdoor, and underground mining environments. Indoor radon and its decay products originate from both internal and external sources. Construction materials, water, basement air, soil, and other components of the interior environment are examples of internal sources [7]. On the other hand, external sources are primarily associated with the radon in the outdoors [13]. The majority of exposure to radon and its progeny occurs indoors mainly because people tend to spend a considerable portion of their time inside, and indoor radon concentrations frequently exceed those found outdoors [14]. Indoor radon levels can be influenced by seasonal and daily fluctuations [11], the types of building materials employed, and the effectiveness of ventilation systems. The relationship between indoor radon levels and ventilation is significant because ventilation plays a crucial role in diluting and removing radon gas from indoor spaces [15]. The relationship between indoor radon and ventilation is well-established: proper ventilation reduces radon concentrations by diluting and expelling the gas, while inadequate or improper ventilation can exacerbate radon accumulation. Scientific guidelines and studies recommend a combination of natural ventilation, mechanical ventilation, and specialized radon mitigation systems to effectively control indoor radon levels and minimize health risks [16]. When radon becomes trapped indoors, concentrations can rise to unacceptable levels, particularly during temperature reversals or in homes with inadequate natural or artificial ventilation [17]. Inhaling radon gas can result in DNA damage within the lungs [7, 14]. This is because the highly ionized alpha particles emitted by radon’s daughters, like polonium-218 and polonium-214, have the potential to interact with lung tissues. This interaction can cause DNA damage that can lead to mutations in cells, ultimately increasing the risk of developing cancer [7]. Consequently, in the last three decades, there has been a strong emphasis on measuring indoor radon levels within buildings to gain a better understanding of this health risk and take steps to mitigate it effectively [18, 19]. Given that most individuals spend over 80% of their daytime hours in their homes and workplaces, and public exposure to radon is primarily concentrated in enclosed spaces, this environmental risk factor is a global concern [20]. As a result, multiple authors have recently carried out many studies to measure radon concentration within homes [21–26]. Radon and its decay products maintain a steady equilibrium in a closed system. However, because radioactive decay, surface deposits, and ventilation continuously remove decay products from the inside air, this equilibrium cannot be sustained in indoor environments. The equilibrium factor (EF) estimates the ratio of all short-lived radon daughters’ activity to the activity required to achieve equilibrium with the radon parent and quantifies the degree of imbalance between radon and its daughters. As a result, the EF has values ranging from 0 to 1 [13]. Iraq has long suffered environmental pollution because of urbanization, development in industry, growth in agriculture, and the past wars that took place in it, specifically Gulf Wars I and II in the years 1991 and 2003, respectively. Also, the building materials predominantly used in this region emit significant amounts of radon. This leads to the exposure of humans to these environmental pollutants and then causes harmful effects on humans. This study set out to assess radon levels and related health hazards in a variety of residences in the province of Al-Najaf. The study utilized an active technique to measure radon and calculated the annual effective radon dose for occupants residing in examined homes.
Materials and Methods
1. Area of Study
Al-Najaf Governorate is situated in southwestern Iraq, approximately 160 km southwest of Baghdad (coordinates: 31°59´N, 44°19´E; elevation: 70 m above sea level) (Fig. 1). The urban area of Al-Najaf province comprises four administrative sectors [27, 28].
Map of the research area. DW, code of dwelling.
This study focuses on two of these sectors: Al-Najaf city and Al-Kufa city, each containing multiple residential districts. For data collection, we employed a representative sampling strategy by selecting one residential building from each district in both Al-Najaf city and Al-Kufa city for indoor radon concentration measurements. All selected buildings were constructed using regionally typical building materials.
This study focuses on two sectors: Al-Najaf city and Al-Kufa city. Each of these sectors is comprised of numerous districts. To gather data, one house from each district in Al-Najaf city and Al-Kufa city was selected for measuring indoor radon concentration. This approach would yield reliable and representative data, helping to assess radon exposure risks and inform public health interventions. The study ultimately included 24 residential buildings, all constructed using locally prevalent building materials to ensure representative sampling of typical living environments in the region.
2. Measurement System
This study assessed radon concentrations in 24 residential units across Al-Najaf province, measuring both indoor and outdoor levels. For accurate radon monitoring, we employed the Airthings Corentium Digital Radon Detector (Model: Corentium Home), specifically designed to measure radon-222 concentrations in Bq/m³. The measurments of radon were conducted in occupied rooms (living room, bedroom, kitchen, and first-floor room) as well as outdoors (the outer courtyard) for each residence. The ‘Corentium Home’ radon monitor is designed for measuring radon-222 levels in Bq/m3. It suits various settings, including family homes, public buildings, and workplaces. This instrument is user-friendly, runs on batteries, and can be easily transported throughout a building to assess radon distribution within the living space comprehensively (Fig. 2).
Set-up of the Airthings Corentium Digital Radon Detector used in this study.
The radon monitor utilizes a passive diffusion chamber to sample indoor air and employs alpha spectrometry for accurate measurement of radon levels. This detection process involves silicon photodiodes that count and analyze the energy of alpha radiation generated through the radon decay series. This technology ensures accurate and reliable measurements of radon levels in various environments [29]. The radon survey meter operates on the basis of radon propagation into a detecting chamber. As radon atoms disintegrate, they emit alpha particles. A silicon photodiode detects these alpha particles and generates a modest signal current on hit. A lowpower amplifier step is then used to increase the signal current, turning it into a higher voltage signal. An analog-to-digital converter detects and samples the voltage signal’s peak amplitude. The energy of the alpha particle that strikes the photodiode determines the signal’s magnitude. A microcontroller serves as the monitor’s central processing unit, recording both the time and energy associated with each detected alpha particle. This data is subsequently utilized to compute the average radon concentration over daily, weekly, monthly, and yearly periods. The detector operates continuously, generating a data point every hour that adds to the calculation of an average value. This is why radon levels are typically measured as the mean values observed over specific intervals, such as 24 hours, 48 hours, 1 week, 1 month, and so forth. The gadget exhibits short-term averages, including a 1-day average, a 7-day average, and a long-term average, calculated based on the cumulative number of days during which measurements have been taken. The information about radon concentrations in Al-Nagaf governorate buildings is still scant data. As well as, Al-Najaf city was exposed to bombardment, their buildings were ancient, and they were exposed to environmental neglect. Therefore, in this study, the radon detector was placed within specific rooms that were selected for monitoring purposes, roughly 75 cm from the ground and 150 cm distant from each window and entrance. It was also positioned 25 cm away from the walls [30]. The detector remained in each selected room for 2 days (48 hours) before being relocated to another room or home. This radon detector provides accurate readings after 24 hours, with a stated accuracy of ±10% at 200 Bq/m³. Extending the measurement period to 48 hours improves the reliability of the results by allowing the device to stabilize and account for short-term fluctuations in radon levels [31]. Also, the U.S. Environmental Protection Agency recommends short-term radon testing for a minimum of 48 hours to obtain reliable results. This duration is considered sufficient to capture meaningful data while being practical for homeowners and researchers [6]. To ensure measurement accuracy during a 48-hour period, the windows and doors were kept closed, preventing any disturbance of indoor air and maintaining measurement consistency.
Every reading from this radon detector yields two values: the ‘long-term average’ and the ‘short-term average.’ The ‘long-term average’ reflects the average radon concentration observed over time, with a maximum value updated once daily. On the other hand, the ‘short-term average’ represents the radon concentration averaged over the last 24 hours (day 1), updated hourly, along with the average concentration during the previous weekday (day 7), also updated hourly. These values provide insights into both short-term fluctuations and long-term trends in radon levels. The longer update interval for short-term measurements on the Airthings Corentium Digital Radon Detector is a deliberate design choice to ensure accuracy and reliability. By averaging data over a longer period, the device minimizes the impact of short-term fluctuations and provides a more stable reading. In contrast, long-term measurements can afford shorter update intervals because the extended averaging period inherently smooths out variability. This approach aligns with international guidelines and ensures that users receive meaningful and actionable data.
3. Radon Radiological Parameters
The annual effective dose (AED) in the (mSv/yr) unit can be performed as Equation (1) [32, 33]:
where C represents the radon concentration, EF indicates the worldwide average of the EF for radon-222 and its progeny, which has a value of 0.4. H represents the occupancy factor, valued at 0.8, and T, which equals 8,760, denotes the number of hours per year, while D represents the dose conversion factor for adult age groups and is equal to 9×10–6 mSv/(Bq. hr/m3) [27].
The annual effective dose to the lung (AEDL) can be calculated as Equation (2):
WR denotes the ‘radiation weighting factor,’ specifically assigned a value of 20 for alpha radiation, WT represents the ‘tissue weighting factor’ that has a value of 0.12 for the lung according to International Commission on Radiological Protection (ICRP) [34].
Potential alpha energy concentration (PAEC) could be calculated with the Equation (3) [35]:
PAEC units are working level (WL) units.
The exposure to radon progeny (EP) in a unit (working level month [WLM]/yr) can be calculated as Equation (4) [36]:
The lung cancer cases per year per million person (CPPP) have been determined by applying the Equation (5) [37]:
Results and Discussion
Indoor and outdoor radon concentrations were measured in 24 dwellings in different occupied rooms (living room, bedroom, kitchen, and first-floor room) as well as outdoors in two cities in Al-Najaf province: Al-Najaf city and Al-Kufa city. Table 1 shows the results of indoor radon concentrations in all studied dwellings for the period from June to October 2023. The maximum average value of indoor radon concentration was 36.50 Bq/m3 in dwelling coded DW24 in the Maytham Altamaar district in Al-Kufa city. In contrast, the minimum value was 5.00 Bq/m3 in dwelling coded DW15 in the Tamoz district in Al-Kufa city. The arithmetic mean was 18.09±9.41 Bq/m3. All indoor radon results were below the recommended level of 100 Bq/m3, according to World Health Organization (WHO) [7]. Also, it can be observed from this table that the results of radon concentration in the living rooms ranged between 4 Bq/m3 to 67 Bq/m3 with an arithmetic mean of 24.75±15.88 Bq/m3. The radon concentration in the bedrooms varies between 1 Bq/m3 and 49 Bq/m3, with an arithmetic mean of 17.54±11.24 Bq/m3. The radon concentration in the kitchen varies between 1 Bq/m3 and 28 Bq/ m3 with an arithmetic mean of 15.79±7.58 Bq/m3. The results of radon concentration in first-floor rooms ranged between 1 Bq/m3 and 44 Bq/m3 with an arithmetic mean of 14.29±10.27 Bq/m3. The results of the average value of radon concentrations in the living room are greater than the other rooms in the order living room>bed room>kitchen>first floor, as shown in Fig. 3. This variation in radon levels among different rooms within the same dwelling can be attributed primarily to ventilation differences. While all rooms are typically constructed using similar base materials, the finishing materials vary. For instance, ceramics are commonly used in Iraqi kitchens, replacing traditional wall paints found in living rooms and bedrooms.
Indoor Radon Concentrations (Bq/m3) in Each Selected Room among the Residences under Study
Indoor radon levels among different rooms within dwellings of the 24 locations.
Higher radon levels in living rooms may also be due to the use of building materials known to contain naturally occurring radioactive elements, such as marble and granite, as well as limited ventilation in these spaces. Additionally, the study compared radon levels between the ground floor and the first upper floor. It was found that 87.5% of the dwellings had higher radon concentrations on the ground floor. The ground-floor/first-floor radon concentration ratio was 1.35, which aligns with values reported in the literature (typically ranging from 1.4 to 1.6) [38].
The indoor radon results, shown in Fig. 4A, display an approximately normal distribution of concentrations across the studied dwellings. This is supported by the Shapiro-Wilk test, which confirmed normality (p>0.05), as also shown in Fig. 4B.
(A) The histogram of the radon distribution inside studied dwellings. (B) The Q-Q plot of the indoor radon results.
An analysis of variance (ANOVA) test was conducted to assess whether there were statistically significant differences in mean indoor radon levels among the various rooms. The results revealed a significant difference in radon concentrations across different room types, with a p<0.05, indicating that room type has a statistically significant effect on indoor radon levels.
Table 2 summarizes the radon concentration results in Al-Najaf city and Al-Kufa city. It is evident that radon concentrations in Al-Kufa city are higher than those in Al-Najaf city, as illustrated in Fig. 5. The median radon concentration values were 12.25 Bq/m³ for Al-Najaf city and 25.00 Bq/m³ for Al-Kufa city.
Indoor Radon Concentrations (Bq/m3) in Al-Najaf City and Al-Kufa City
Indoor radon results for Al-Najaf city and Al-Kufa city (the black line represents the median and the circle with number 4 represents outlier that due to the code of dwelling 4).
Table 3 presents the descriptive statistics of several radiological parameters associated with indoor radon concentrations. The AED received by residents due to indoor radon exposure ranged from 0.13 mSv/yr to 0.92 mSv/yr, with an arithmetic mean of 0.46±0.24 mSv/yr. The maximum AED value was well below the ICRP (1993) recommended reference level, which ranges between 3 mSv/yr and 10 mSv/yr [39]. The AEDL varied between 0.30 mSv/yr and 2.21 mSv/yr, with an average value of 1.09±0.57 mSv/yr. The PAEC ranged from 0.54 mWL to 3.95 mWL, with an arithmetic mean of 1.96±1.02 mWL. These values are significantly lower than the United Nations Scientific Committee on the Effects of Atomic Radiation (1993) recommended level of 53.33 mWL [40]. The EP ranged between 22.28 mWLM/yr and 162.67 mWLM/yr, with an average of 80.64±54.59 mWLM/yr. All EP results were below the National Council on Radiation Protection and Measurements (1989) recommended limit, which is in the range of 1–2 WLM/yr [41]. The estimated CPPP ranged from 2.27 to 16.58×10–⁶, with an arithmetic mean of 8.22± 4.27×10–⁶. These values are considerably lower than the ICRP (1993) reference range of 170–230 cases per year per million people, as illustrated in Fig. 6 [39]. In addition to indoor measurements, this study also evaluated outdoor radon concentrations and their associated radiological parameters for each of the studied dwellings, as summarized in Table 4.
The Descriptive Statistics of AED, AEDL, PAEC, EP, and CPPP for Indoor Radon in Selected Dwellings
A comparison between the global limit and the radiological parameters under study. AED, annual effective dose; PAEC, potential alpha energy concentration; EP, exposure to radon progeny; CPPP, lung cancer cases per year per million person.
Radon Concentration, AED, PAEC, EP, and CPPP in the Outdoor for Selected Dwellings
The outdoor radon concentration ranged from 0 Bq/m³ to 13 Bq/m³, with an arithmetic mean of 4.50±2.96 Bq/m³. The AED received by residents due to outdoor radon exposure varied between 0 mSv/yr and 0.16 mSv/yr, with an average of 0.06±0.03 mSv/yr. The PAEC ranged from 0 mWL to 1.41 mWL, with an arithmetic mean of 0.49±0.32 mWL. The EP was found to range between 0 mWLM/yr and 28.97 mWLM/yr, with an average value of 10.03±6.60 mWLM/yr. The CPPP varied from 0 to 2.95×10–⁶, with an arithmetic mean of 1.02± 0.67×10–⁶.
The frequency distribution of outdoor radon concentrations across the studied dwellings is illustrated in Fig. 7A. The distribution appears to be approximately normal, as confirmed by the Shapiro-Wilk test, which showed no significant deviation from normality (p>0.05), also illustrated in Fig. 7B. A t-test was conducted to determine whether a statistically significant difference exists between indoor and outdoor radon concentrations. The results indicated a significant difference, with t=6.75 and p=0.000 (p<0.05). This confirms that indoor radon concentrations are significantly higher than outdoor levels, with indoor values being, on average, approximately four times greater. This elevated indoor radon concentration is primarily attributed to the accumulation of radon gas within enclosed spaces, especially when ventilation is inadequate. Indoors, radon can build up to much higher levels than outdoors, where it disperses more readily into the atmosphere. Additionally, a correlation analysis was performed to examine the relationship between indoor and outdoor radon concentrations. As shown in Table 5, no significant correlation was found. This suggests that variations in outdoor radon levels do not predict or influence indoor radon levels. Therefore, relying on outdoor radon data as a proxy for indoor exposure assessment may not be appropriate. Furthermore, all associated radiological parameters (such as AED, AEDL, PAEC, EP, and CPPP) calculated for indoor radon were consistently higher than those for outdoor radon, reinforcing the importance of direct indoor measurements in risk assessments.
(A) The histogram of the outdoor radon in studied dwellings. (B) The Q-Q plot of the outdoor radon results.
Comparative Analysis between the Indoor Radon Levels Obtained in the Current Study and Those from Prior Research Conducted in Various Dwellings
Fig. 8 illustrates the variation in radon concentration across different residential locations. The median radon concentration in living rooms was higher than in other locations, corresponding to the highest arithmetic mean among all measured areas. In contrast, outdoor radon concentrations were the lowest. The living room results also exhibited greater variability, as reflected by a larger boxplot and longer whiskers, followed by the first-floor readings. This indicates a wider range of radon levels in living rooms, likely influenced by factors such as limited ventilation or specific building materials. Additionally, outliers were observed in the bedroom and outdoor measurements, suggesting occasional deviations from typical values in those areas. These outliers may be due to environmental conditions, ventilation differences, or structural characteristics of the dwellings.
Radon concentrations in all studied houses (the black line represents the median and the circle with numbers represents outliers that due to dwellings).
According to the results, the AED attributed to indoor radon accounts for approximately 88% of the total AED, highlighting the dominant contribution of indoor exposure to overall radiation risk. Furthermore, when comparing the average indoor radon concentrations obtained in this study with those reported in previous studies conducted in residential dwellings across other countries (as presented in Table 5) [9, 42–47], it is observed that the average radon levels in the present study are lower than those documented in all referenced studies—with the exception of Guinea, where lower values were reported. Finally, this study emphasizes that the results are based on the most conservative scenario (ventilation rate=0) and still indicate safety.
Conclusion
Indoor and outdoor radon concentrations were measured in 24 dwellings across various occupied rooms (living room, bedroom, kitchen, and first-floor room), as well as outdoors, in two cities of Al-Najaf province: Al-Najaf city and Al-Kufa city. The average radon concentrations, both indoors and outdoors, were found to be below the recommended limits set by WHO. Indoor radon levels varied due to factors such as differences in ventilation, the type of building materials used during construction, and variations in the radioactive content of the underlying soil [48]. Notable variations in radon concentrations were also observed among different rooms within the same dwelling. Among the tested locations, the living rooms exhibited the highest average radon concentrations, followed by bedrooms, kitchens, first-floor rooms, and lastly, outdoor areas, following the trend: living room>bedroom>kitchen>first floor>outdoor. Statistical analyses supported these findings: the ANOVA test revealed significant differences in radon levels across various indoor locations, while the t-test indicated a statistically significant difference between indoor and outdoor radon concentrations (p<0.05). In terms of health implications, the studied area was considered safe. The total AED attributed to radon exposure in Al-Najaf province was well below the threshold recommended by ICRP. Consequently, residents were determined to be at a low risk of health effects due to radon exposure.
Notes
Funding
The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.
Conflict of Interest
This article does not contain any studies with human participants or animals performed by any of the authors.
Ethical Statement
This article does not contain any studies with human participants or animals performed by any of the authors.
Data Availability
Data generated or analyzed during this study are included in this published article.
Author Contribution
Conceptualization: Dosh RJ, Abojassim AA. Methodology: Dosh RJ. Data curation: Dosh RJ. Formal analysis: Dosh RJ. Supervision: all authors. Investigation: Dosh RJ. Validation: all authors. Writing - original draft: Abojassim AA. Writing - review & editing: Salman EF, Jassim AS. Approval of final manuscript: all authors.
Acknowledgements
The authors are grateful to the Faculty of Sciences at the University of Kufa, and specifically to the Physics Department.