Assessment of indoor radon exposure in kermanshah’s educational facilities, and its determinants, health risks, and mitigation strategies

Abstract

Ensuring a healthy indoor environment for children is crucial, as they are particularly vulnerable to environmental hazards. Indoor radon exposure is a significant concern due to its carcinogenic effects. This study assessed radon concentrations in primary schools and kindergartens in Kermanshah, Iran, estimated the annual effective dose, and evaluated potential health risks. This cross-sectional study randomly selected 24 primary schools and kindergartens across Kermanshah. Radon concentrations were measured seasonally using a radon meter (SARAD, RTM1688). Air samples were collected at breathing height and at least 40 cm from walls. Building characteristics were recorded using a checklist, and meteorological parameters were measured during sampling. Statistical analysis was conducted using SPSS version 25. The average annual radon concentration was 37.1 ± 6.1 Bq/m² in kindergartens and 30.9 ± 6.5 Bq/m² in primary schools. The highest concentration was recorded in winter (39.4 ± 4.9 Bq/m²) and the lowest in summer (30.6 ± 6.1 Bq/m²). Radon concentrations correlated significantly with classroom size and relative humidity (p ≤ 0.01) but not with building age. Ground-floor rooms had higher concentrations, particularly in winter. Rooms with granite walls exhibited the highest radon concentrations (39.15 Bq/m²), while those with plaster and paint had the lowest (28.5 Bq/m²). The estimated annual effective lung dose was 0.28 mSv/y in kindergartens and 0.23 mSv/y in primary schools, both below the UNSCEAR recommended limit of 1.15 mSv/y. Indoor radon concentrations in Kermanshah’s primary schools and kindergartens were below WHO and ICRP safety thresholds. However, as radon’s effects build up over time, even low levels can contribute to a higher lifetime dose of radiation, increasing health risks over decades and the World Health Organization (WHO) recommend mitigation even at relatively low levels. Therefore, efforts should be made to increase public awareness, and policymakers must implement radon-resistant building codes while maintaining adequate ventilation systems. Further research is needed to identify influencing factors and develop mitigation strategies.

Introduction

Indoor air pollution is a critical public health issue, contributing to approximately 3.8 million deaths annually from pneumonia, stroke, heart disease, chronic obstructive pulmonary disease, and lung cancer^1–3. Among indoor pollutants, radon (Rn-222), a naturally occurring radioactive gas, poses a significant health risk due to its carcinogenic properties⁴. This colourless, odourless, and tasteless gas is produced from the decay of uranium (U-238) and radium (Ra-226) in soil and rock, accumulating in enclosed spaces such as homes, schools, and underground mines⁵. Radon decay products, particularly polonium isotopes (Po-214 and Po-218), emit alpha particles that can damage DNA and contribute to lung cancer development⁶.

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), radon is a major source of human radiation exposure⁷. The World Health Organization (WHO) and the U.S. Environmental Protection Agency (US-EPA) identify radon as the second leading cause of lung cancer after tobacco smoke^8,9. Studies indicate a strong correlation between residential radon exposure and lung cancer incidence, with estimated annual deaths in Germany reaching 2800 ¹⁰. Similar research in Iran and Turkey has reported indoor radon concentrations exceeding WHO’s recommended limit of 100 Bq/m² in certain regions^11,12.

Children are particularly vulnerable to radon exposure due to their higher breathing rates, developing lungs, and increased time spent indoors. Children inhale more air (and potentially more radon and its radioactive decay products) relative to their body weight. A child’s lungs are still growing and developing, making them more susceptible to damage from radon-induced radiation. This increases their lifetime risk of lung-related diseases. Since lung cancer caused by radon exposure takes years or even decades to develop, children have a longer remaining lifespan during which the effects of early exposure can manifest. Studies suggest that children’s rapidly dividing cells are more sensitive to DNA damage from ionizing radiation, including radon decay products^13,14. Schools, where children spend an average of 6.65 h daily, are a significant potential source of exposure¹⁵. A study in Portugal found Radon concentrations in some schools exceeding international safety standards¹⁶, while the US-EPA estimates that nearly 19.3% of U.S. schools have at least one classroom with radon concentrations above 148 Bq/m^{2 17}.

Iran has significant uranium deposits. Since radon is a decay product of uranium, areas with uranium-rich soil naturally emit more radon gas. Many parts of Iran have porous soil, which allows radon gas to move easily from underground sources into buildings through cracks, foundations, and water supplies. Some construction materials, such as granite, cement, and certain types of stone, can contain small amounts of uranium. In regions where, local stone or soil-based bricks are used, these materials can emit radon indoors, increasing exposure risks. Many homes and buildings in Iran, especially in colder regions, are designed to be airtight for energy efficiency, reducing ventilation and allowing radon to build up to dangerous levels indoors¹⁸. Studies have found elevated Radon concentrations in Iranian homes, particularly in areas with uranium-rich geology. Despite Iran’s geological susceptibility to elevated Radon concentrations, limited studies have assessed radon exposure in schools^19,20. Some research in cities of Iran like Tehran, Mashhad, and Ramsar has detected radon concentrations above the global average^21,22, however, no studies have specifically evaluated radon concentrations in primary schools and kindergartens in Kermanshah City.

While extensive research has been conducted on indoor radon levels globally, several critical gaps remain, particularly concerning educational facilities in specific geographic regions. The key research gaps that this study addresses include: limited data on indoor radon in Kermanshah City, seasonal and ventilation effects in educational buildings, the effect of geological and structural factors on indoor radon, and variability in radon accumulation based on building materials and room characteristics. This study fills a critical knowledge gap by providing the first comprehensive assessment of indoor radon exposure in schools and kindergartens in Kermanshah City. By analysing seasonal variations, geological influences, and structural factors, it provides practical mitigation strategies and establishes a foundation for future radon monitoring efforts in educational institutions worldwide. Given the importance of school air quality and children’s vulnerability, this study aims to assess indoor radon concentrations in Kermanshah’s primary schools and kindergartens, estimate the annual effective dose, and examine the relationship between radon concentration and building characteristics such as construction materials, ventilation systems, and classroom area.

Materials and methods

Study area and sampling sites

Kermanshah, the capital of Kermanshah Province, Iran, has a population of approximately 1.15 million and is located at 34°17′–34°26′ N latitude and 46°59′–47°14′ E longitude. Situated in the Kermanshah Syncline Plain at an altitude of 1300–1604 m above sea level, the city spans an area of 102 km². It has a semi-arid, hot steppe climate, with an annual mean temperature of 25.1 ± 35.6 °C, annual precipitation of 350–450 mm, relative humidity of 27.8 ± 5.7%, and prevailing westerly and south-easterly winds at 3.9–4.6 m/s (Table 1).

Table 1.

Annual average meteorological parameters of Kermanshah City and their seasonal variation.

Parameter	Spring	Summer	Autumn	Winter	Average
Temperature ºC	23.4 ± 5.2	33.4 ± 78.1	26.3 ± 54.7	17.2 ± 4.6	25.1 ± 35.6
Pressure (mbar)	856.3 ± 1.8	858.5 ± 5.3	859.4 ± 1.2	866.4 ± 4.9	860.2 ± 3.3
Relative humidity (%)	26.3 ± 4.5	21.3 ± 5.6	29.4 ± 6.2	34.3 ± 6.7	27.8 ± 5.7
Wind Speed (m/s)	5.0 ± 1.2	4.0 ± 8.6	5.0 ± 4.6	5.0 ± 2.8	4.7 ± 4.3
Wind Direction	W	SE	W	W	W, SE

Following coordination with the city’s Education Department and school administrators, 24 educational institutions (12 primary schools and 12 kindergartens) were randomly selected, ensuring geographic representation across the north, south, east, and west regions of Kermanshah. Figure 1 illustrates the locations of the selected sampling sites (Fig. 1).

Fig. 1.

Locations of schools and kindergartens subjected to radon testing in Kermanshah.

Sample size adequacy

The sample size was calculated using the following formula^23,24

1

where: n = required sample size; Z = Z-score (1.96 for 95% CI); σ = standard deviation (from pilot data: 6.5 Bq/m² for schools), and E = margin of error (desired precision: 2.5 Bq/m²).

n = (1.96² × 6.25²) / 2.5² = (3.84 × 39.06) / 6.25  = 24.

Thus, the sample size (24 locations) is statistically adequate to detect 10% differences in mean radon concentrations with 95% confidence, given the observed variability.

The sampling error calculation was carried out as follows:

2

where: x̄ = mean radon level (e.g., 34 Bq/m²) and n = actual sample size (24).

SE = (1.96 × 6.25 / √24) / 34 × 100 = (1.96 × 1.276) / 34 × 100 = = 7.35% error.

So, the true mean radon concentration in kindergartens lies within ± 14.7% of measured 34 Bq/m² (i.e., 34 ± 5 Bq/m²) with 95% confidence.

Radon measurement

Radon concentrations were measured in the basements, ground floors, first floors, and playgrounds of the selected schools and kindergartens. A portable radon meter (RTM1688-2, SARAD, Germany) was used, with each measurement session lasting 120 min. The RTM1688-2 is an alpha-spectroscopy-based monitor designed for high-sensitivity detection of radon and thoron (0–10 MBq/m²). In Fast Mode, it achieves a sensitivity of 3 counts/min at 1000 Bq/m², with a response time of 10 min to reach 90% of the final value. Statistical accuracy is maintained within a 10% error at 200 Bq/m² for 1-hour sampling intervals. The device also records relative humidity (0–100%), temperature (–20 to 40 °C), and barometric pressure (800–1200 mbar). An internal pump operates at 0.3 L/min (continuous or interval mode) to deliver air samples to the spectrometer. Before deployment, the instrument underwent pre-calibration by SARAD, followed by verification in a known radon concentration chamber to ensure measurement accuracy. Additionally, baseline validation was performed in a radon-free chamber to confirm instrument stability (manualslib.com).

The measurement was conducted in the middle month of each season, assuming that, the middle month of each season can be the best predictor of average meteorological condition for that season. Sampling was performed at breathing height, at least 20 cm from airflow obstructions and 40 cm from walls²⁵. Building characteristics, including construction materials, age, ventilation system, presence of cracks, and classroom size, were documented using a standardized checklist. Meteorological parameters such as temperature, humidity, and wind speed/direction were recorded concurrently with radon measurements.

Health risk assessment

The annual effective dose (AED) due to radon exposure was calculated using the UNSCEAR methodology^7,26:

3

where: C_Rn​ = Mean radon concentration (Bq/m²), H = Indoor occupancy factor (0.1, based on 880 annual school hours), D = Dose conversion factor (9 nSv/Bq·h·m²), F = Indoor radon equilibrium factor (0.4) and T = Total annual hours (8760 h).

The average equivalent dose (AEqD) was obtained by multiplying AED by the radiation weighting factor (W_R= 20, based on ICRP value for alpha particles)^7,27:

4

The annual effective dose to the lung (AED_L) was then estimated using the lung tissue weighting factor (W_T =0.12, as recommended by ICRP):

5

Excess lifetime cancer risk (ELCR) can be determined using AED, average lifespan (D_L​=70 years), and the fatal cancer risk coefficient (R_F=5.5 × 10^{− 2} per Sievert)^28,29:

6

However, as the calculated AED due to radon exposure was below the recommended threshold, the estimation of ELCR was not included in this study.

The lung cancer cases per million people per year (LCC) were estimated using a lung cancer induction risk factor of 18 × 10^− 6 mSv-1 ^12,30:

7

Statistical analysis

Descriptive statistics, including mean, standard deviation, median, and interquartile range, were used for quantitative variables, while frequency and percentages were used for categorical variables. Normality was assessed using the Kolmogorov-Smirnov test. Depending on normality, group comparisons were performed using independent t-tests or one-way ANOVA; otherwise, the Mann-Whitney U and Kruskal-Wallis tests were applied. Correlation analyses were conducted using Pearson or Spearman coefficients. Statistical analyses were performed using SPSS v.25, with significance set at p < 0.05.

Results and discussion

Radon concentration in classrooms and playgrounds

A comparison of average radon concentrations in playgrounds and classrooms across primary schools and kindergartens, as well as their seasonal variations and annual averages, is presented in Fig. 2. The highest indoor radon concentration was recorded in winter belonging to kindergartens (39.4 ± 4.9 Bq/m³), while the lowest was observed in summer belonging to primary schools (30.6 ± 6.1 Bq/m³). Across all seasons, radon concentrations in kindergartens were consistently higher than those in primary schools, with an annual average of 37.1 ± 6.1 Bq/m³ in kindergartens compared to 30.9 ± 6.5 Bq/m³ in primary schools. However, the difference in annual outdoor radon concentrations between kindergartens (28.2 ± 6.3 Bq/m³) and primary schools (27.4 ± 5.9 Bq/m³) was not statistically significant (p ≤ 0.01). Radon concentrations in all sampled buildings remained below the WHO-recommended threshold of 100 Bq/m³. According to the US-EPA classification, radon concentrations fall into three risk categories: safe (< 74 Bq/m³), low-risk (74–148 Bq/m³), and high-risk (> 148 Bq/m³). All measured values in this study were within the safe range suggested by the US EPA.

Fig. 2.

Mean radon concentration in indoor/outdoor kindergartens and primary schools of Kermanshah in different seasons, and its annual average.

Previous studies have reported varied radon concentrations in educational and residential settings in Iran. For instance, radon concentrations in university buildings in Isfahan ranged from 3 ± 0.3 to 322 ± 48.3 Bq/m³ in winter and were below detectable levels to 145 ± 11.6 Bq/m³ in summer³¹. Similarly, in Khorramabad, Iran, the mean indoor radon concentration was 43.4 ± 40.4 Bq/m³, with 10% of residents exposed to levels exceeding WHO guidelines³². In Yazd, Iran, indoor radon concentrations in primary schools averaged 47.8 ± 1.7 Bq/m^{3 33}. Seasonal variations have also been reported, with the highest radon concentrations occurring in winter, as observed in Tehran hospitals³⁴ and Gorgan dwellings³⁵. The seasonal increase in radon concentrations is attributed to reduced ventilation during colder months, leading to gas accumulation indoors. In winter, windows and doors are typically kept closed to retain heat and ventilation systems may be used less frequently. This traps radon inside and prevents it from dissipating, allowing it to accumulate at higher concentrations. Cold outdoor air and warm indoor air create a pressure difference, pulling radon gas from the soil into buildings through foundation cracks, basements, and gaps. This effect is stronger in winter, increasing radon infiltration. A layer of snow or frozen soil can act as a barrier, preventing radon from escaping into the atmosphere. Instead, it is forced to seep into buildings through available entry points³⁶.

Health risk of radon exposure in children

Table 2 presents the seasonal and annual values of indoor radon concentrations and their associated health risk parameters. The average annual effective dose (AED) was 0.117 mSv/y in kindergartens and 0.097 mSv/y in primary schools, both well below the permissible limit of 3 mSv/y. In comparison, previous research in university buildings estimated an AED of 0.26 mSv/y ³¹, while the AED for Tehran dwellings was reported at 1.09 mSv/y ³⁷. These discrepancies may be attributed to differences in occupancy factors used in AED calculations and ventilation practices. Since radon exposure primarily occurs indoors, people who spend more time inside will receive a higher AED compared to those who spend more time outdoors. Cultural and environmental factors influence occupancy. For instance, people in cold climates stay indoors longer, while those in warmer regions may spend more time outside, leading to different AED values. Schools typically have lower occupancy (6–8 h/day) compared to dwellings (24 h), reducing cumulative exposure. Educational facilities often implement scheduled ventilation (e.g., breaks between classes), whereas homes may have poorer airflow.

Table 2.

Values ​​of health risk assessment parameters for indoor radon exposure for each season and the annual values in the kindergartens and primary schools.

Place	Season	CRn (Bq/m3)	AED (mSv/y)	AEqD (mSv/y)	AEDL (mSv/y)	LCC -
Kindergartens	Spring	37.6	0.119	2.372	0.285	2.13
	Summer	34.5	0.109	2.176	0.261	1.96
	Autumn	36.9	0.116	2.327	0.279	2.09
	Winter	39.4	0.124	2.485	0.298	2.24
	Annual	37.1	0.117	2.340	0.281	2.11
Primary Schools	Spring	31.1	0.098	1.962	0.235	1.77
	Summer	30.6	0.097	1.930	0.232	1.74
	Autumn	30.8	0.097	1.943	0.233	1.75
	Winter	31.3	0.099	1.974	0.237	1.78
	Annual	30.9	0.097	1.949	0.234	1.75

The annual effective dose to lung tissue (AED_L) was estimated at 0.28 mSv/y in kindergartens and 0.23 mSv/y in primary schools, lower than the UNSCEAR-recommended threshold of 1.15 mSv/y ⁷. The annual equivalent dose (AEqD) was 2.34 mSv/y in kindergartens and 1.95 mSv/y in primary schools, with the highest seasonal value recorded in winter (2.48 mSv/y) and the lowest in summer (1.93 mSv/y).

The higher winter doses align with global trends of elevated indoor radon in colder months due to reduced ventilation (UNSCEAR, 2010). Notably, the AEqD winter peak (2.48 mSv/y) coincides with closed-window behaviours during heating seasons, as observed in European schools³⁸, and stack effect amplification in ground-floor rooms, where warmer indoor air draws radon from cooler subsurface soil³⁹.

The estimated number of lung cancer cases per million people per year (LCC) was 2.11 in kindergartens and 1.75 in primary schools, significantly below the ICRP benchmark range of 170–230 ⁴⁰. All assessed health risk parameters remained within safe limits, indicating minimal radon-induced health risks in these educational settings. However, most risk models are calibrated for adult exposures; children’s shorter exposure duration and developing lung physiology could alter actual risk⁴¹. Chronic low-dose exposure (as in schools) may have different biological impacts than acute high-dose scenarios underpinning regulatory thresholds⁴². While Kermanshah’s schools show lower risks than high-radon regions (e.g., UK schools with AEDL ranging between 0.58 and 3.07 mSv/y; ⁴³), they align with similarly arid, low-background areas (e.g., Saudi schools: 0.09–0.21 mSv/y; ⁴⁴. This reinforces the role of geological context, as Kermanshah’s bedrock likely has lower radium content than granite-rich high-risk zones.

Factors influencing indoor radon concentrations

The primary source of indoor radon is the infiltration from soil and rocks through foundation cracks, utility openings, and drainage systems. Additionally, building materials, water supply, and natural gas contribute to indoor radon presence. Materials rich in uranium and radium, such as granites and some clays, emit radon through natural decay processes. Other influencing factors include building design, floor level, room size, ventilation type, building age, and meteorological conditions.

In this study, radon concentrations were highest on ground floors and basements compared to upper floors, consistent with findings from Tabriz residential homes⁴⁵ and university buildings³¹. This is attributed to radon’s higher density compared to air (9.7 vs. 1.2 g/L), leading to accumulation near the ground. Additionally, basements tend to have higher radon levels due to several key factors related to their location and construction which include, proximity to the radon-emitting soil and rocks., less ventilation, cracks and gaps in foundations, uranium-rich concrete and building materials, and air pressure differences (stack effect). The stack effect in a building, creates a vacuum in the basement that draws radon from the soil. This effect is stronger when homes are tightly sealed for energy efficiency, especially in colder months.

Geological permeability plays a role in indoor radon concentration. High-permeability materials such as sand and fractured rock facilitate radon movement through soil, increasing indoor radon concentrations, while low-permeability layers like clay restrict its flow, though cracks or fractures can still allow entry. Geological fissures can dramatically enhance radon migration even in dense bedrock, making permeability a key factor in determining necessary mitigation measures, with high-permeability areas often requiring more robust radon control. A thorough understanding of local geology is therefore essential for accurately assessing radon risk and implementing effective mitigation strategies.

A significant inverse correlation was observed between classroom size and radon concentration (p ≤ 0.01), with smaller classrooms exhibiting higher radon concentrations due to limited air exchange. However, no significant association was found between building age and radon concentrations. Similar findings were reported by Haddadi et al., who observed higher radon concentrations in bedrooms than in living rooms due to reduced ventilation⁴⁵.

Radon concentrations were notably higher in buildings with mechanical ventilation (34.6 ± 6.9 Bq/m³) compared to those with natural ventilation (30.5 ± 46.8 Bq/m³). This aligns with findings from Kermanshah Hospitals²⁰., where natural ventilation was more effective in reducing radon accumulation. Mechanical ventilation can sometimes lead to higher radon concentrations compared to natural ventilation due to the way air pressure and airflow are controlled in a building. When mechanical systems, such as HVAC or heat recovery ventilators, create pressure imbalances, they can draw more radon gas from the soil into the building, particularly through basements. Unlike natural ventilation, which allows passive airflow to help disperse radon, mechanical systems may recirculate contaminated air without proper exhaust, increasing indoor radon levels. Additionally, mechanical ventilation can distribute radon more uniformly throughout the building, raising overall exposure, whereas natural ventilation may keep radon confined to lower levels like basements, reducing its spread into living spaces. The high standard deviation in natural ventilation data (30.5 ± 46.8 Bq/m³) refers to the significant variation or spread in the measured radon levels across different locations or over time. This can arise from several factors, including geological variability, building characteristics such as foundation type, floor level and materials used, different ventilation systems and practices, and seasonal changes.

Statistical analysis revealed a significant positive correlation between indoor radon concentration and indoor/outdoor relative humidity (p ≤ 0.01), whereas no significant relationship was observed with outdoor temperature or wind speed (p > 0.05). These results are consistent with studies in Tehran hospitals³⁴. and Aksu schools, Kazakhstan⁴⁶, which found humidity to be a key factor in radon accumulation, while temperature and wind speed had negligible effects. Humidity can impact radon accumulation in buildings in complex ways, as high moisture levels may reduce radon release from soil while simultaneously trapping it indoors if ventilation is insufficient. Excess humidity can also impair ventilation efficiency and lead to poor sealing or condensation, potentially increasing radon infiltration. Additionally, high humidity may interfere with radon measurement devices, and skewing readings, and can intensify the stack effect, drawing more radon from the ground into the building. To minimize radon risks, proper humidity control, effective ventilation, and structural sealing are essential, particularly in humid climates.

Table 3 presents radon concentrations relative to building reinforcement and finishing materials. Building construction materials’ data were collected using a standardized checklist before radon measurement. Then, the average radon concentration measured in the building with each type of material was obtained. The highest radon concentrations were detected in buildings reinforced with gypsum and clay (59.5 Bq/m³), followed by stone and cement (51.6 Bq/m³). In contrast, buildings constructed with concrete and cement or brick facades exhibited the lowest concentrations (~ 30.3 Bq/m³). Similarly, radon concentrations varied by flooring material, with asphalt (42.14 Bq/m³) and cement (41.8 Bq/m³) showing the highest concentrations, whereas mosaic floors exhibited the lowest (26.7 Bq/m³). Regarding wall finishes, granite walls had higher radon concentrations (39.15 Bq/m³) compared to plaster and paint (28.5 Bq/m³). Additionally, false ceilings were associated with higher radon concentrations than plaster and paint ceilings. These findings align with studies by Pirsaheb et al., which identified travertine as the least suitable and plastic materials as the most effective for minimizing radon exposure²⁰.

Table 3.

Average radon concentration in relation to type of Building reinforcement and finishing materials.

Type	Material	Mean (Bq/m3)	SD (Bq/m3)
Reinforcement	Brick with cement facade	36.3	6.5
	Gypsum and clay	59.5	11.4
	Concrete with cement facade	30.3	4.7
	Thin refractory brick	35.4	6.7
	Concrete with brick facade	30.3	4.6
	Stone and cement	51.6	10.2
Floor finishing	Asphalt	42.1	8.5
	Asphalt and Cement	36.5	7.1
	Stone	32.5	4.5
	Cement	41.8	6.9
	Mosaic	26.7	3.7
Wall finishing	Travertine stone	32.8	4.7
	Brick and cement	38.4	6.9
	Marble stone	33.1	4.4
	Plaster and paint	28.5	3.8
	Granite	39.2	7.2
Ceil finishing	False ceiling	33.7	4.9
	Plaster and paint	28.4	3.7

Building materials can significantly influence indoor radon concentrations. Concrete, due to its compact structure, limits radon infiltration, whereas plaster, which contains high levels of radium, tends to emit more radon unless properly sealed with paint or wallpaper⁴⁷. However, Yousefi et al. reported contradicting results regarding mosaic flooring³⁵. Mosaic flooring can produce conflicting radon concentration results across studies due to variations in materials, installation techniques, and environmental conditions. The uranium content in flooring materials like marble or granite can elevate radon levels, while ceramic or concrete tiles typically pose less risk, contributing to inconsistent findings. Differences in grout application, sealing methods, and local factors such as soil composition and ventilation further influence radon emissions, making direct comparisons difficult. As a result, mosaic flooring alone cannot reliably explain radon variations, emphasizing the need to assess all contributing factors when interpreting study discrepancies. Overall, materials derived from soil and rock naturally contain radon-emitting elements, underscoring the importance of material selection in construction practices.

The findings from this study have broad applications globally, especially in countries with similar geological, climatic, and construction conditions. Governments, researchers, and institutions can use these insights to strengthen public health policies, improve ventilation and construction practices, and implement regular radon testing in educational and occupational settings. Ultimately, these applications will contribute to reducing radon-related health risks worldwide.

Study limitations and future work

While the study provides an important initial step in understanding radon levels in schools and kindergartens in Kermanshah City, several limitations, including sample size, measurement methods, geological assumptions, and the lack of continuous monitoring, suggest that further research is needed to gain a more accurate and comprehensive understanding of radon exposure in these settings. Long-term studies with greater geographic coverage, more detailed building data, and continuous monitoring would strengthen the findings and allow for more precise risk assessments and mitigation strategies. Future research should expand long-term radon monitoring in schools, particularly in high-risk geological areas, to better understand exposure patterns. Studies need to examine how building design, materials, and ventilation systems affect radon concentration while developing practical mitigation solutions. Health research should assess children’s cumulative exposure and potential synergistic effects with other pollutants. Implementation studies should evaluate radon awareness programs and policy effectiveness.

Conclusion

This study presents the first measurement of indoor radon concentrations in schools and kindergartens in Kermanshah City. While average radon concentrations remained below the thresholds set by the WHO and USEPA, the potential health risks warrant ongoing attention. As the second leading cause of lung cancer, chronic exposure to radon, even at low concentrations, may pose health risks, particularly to children. Research suggests that there is no completely safe level of radon exposure. The US EPA and the WHO recommend mitigation even at relatively low levels. The primary source of indoor radon is infiltration from underlying soil and rock, and the relatively low levels observed in this study likely reflect both low radium content and reduced geological permeability, in which, low-permeability layers like clay and dense bedrock restrict radon gas flow inside building. Notably, radon concentrations were highest in the winter and lowest in the summer, a pattern attributed to decreased ventilation during colder months.

Kindergartens exhibited consistently higher radon concentrations than primary schools, likely due to smaller room sizes and restricted ventilation. In contrast, larger, naturally ventilated rooms on upper floors accumulated less radon than smaller, artificially ventilated spaces on the ground floor or in basements. Among meteorological factors, only relative humidity significantly influenced indoor radon concentrations. High humidity can reduce radon release from the soil due to moisture acting as a barrier, but it can also increase indoor radon concentrations if ventilation is inadequate. Regarding building materials, structures incorporating concrete with cement or brick facades, along with plaster and paint for wall and ceiling finishes, demonstrated greater resistance to radon infiltration.

Given the potential health risks of even low-level radon exposure in children, effective mitigation strategies are essential. To reduce radon emissions and improve indoor air quality in schools and kindergartens, regular radon testing should be conducted, followed by appropriate mitigation measures such as installing sub-slab depressurization systems. Improving ventilation, whether through mechanical systems or natural airflow, along with sealing cracks in foundations, walls, and floors can significantly minimize radon infiltration. Additionally, maintaining structural integrity, educating staff and parents about radon risks, and implementing radon-resistant designs in new constructions are essential preventive steps. By adopting these measures, educational institutions can effectively lower radon exposure, ensuring a healthier and safer environment for children and staff alike.

Since indoor radon concentrations vary spatially and temporally, further research is necessary to identify key determinants and establish continuous monitoring in educational facilities throughout the academic year. Long-term studies with greater geographic coverage, and more detailed building data would strengthen the findings and allow for more precise risk assessments of children and mitigation strategies.

Author contributions

Y.H. Conceptualization, Supervision, validation, writing review & editing, methodology, visualization, preparation. S.S. Formal analysis and investigation, methodology, validation, visualization, writing original draft, preparation. M.P. Conceptualization, Supervision, validation, methodology, visualization, writing original draft preparation. H.T. writing original draft, validation, visualization, writing review & editing. K.S. Validation , methodology and writing review and editingAll authors read and approved the final manuscript.

Funding

declaration.

This work was financially supported by Isfahan University of Medical Sciences (No: 399566).

Data availability

The datasets of the study are available from the corresponding author on reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Conflict of interest

The authors declare that there is no conflict of interest.