1 Introduction

Radon (222Rn) is a noble radioactive gas present varying levels in soil, water, and rocks. Radon gas, possessing a half-life of 3.82 days, is colorless, odorless, and tasteless (Ebrahimi et al., 2023). It is a decay product of radium (226Ra) in the natural uranium (238U) decay series (Erdogan et al., 2015, Frederic Rey 2022). Radon is soluble and has greater solubility at low temperatures (UNSCEAR (United Nations Scientific Committe on the Effects of Atomic Radiation), 1993). Roughly half of the total radiation dose exposed to people is caused by radon (Mukherjee et al., 2023). Based on USEPA assessments, radon is the predominant factor for lung cancer in individuals who do not smoke, although it ranks as the second most prevalent cause among smokers (USEPA 2012). Inhaling air containing radon can lead it to the human lungs, thus potentially causing lung cancer. Drinking water with high radon concentrations may increase the risk of stomach and gastrointestinal cancer (Khan, 2021; Mukherjee et al., 2023).

Numerous research studies have been carried out in Turkey and various other countries to determine the concentration levels of radon and its harmful effects (Naskar et al., 2022; Selçuk et al., 2013; Bal 2021, Erdogan et al., 2015, Kayakökü and Kuluöztürk, 2023, Corrêa et al., 2014, Ting Li 2015, Mukharje 2022; Baykara et al., 2011; Lopes et al., 2017). When the conducted studies are examined, radon measurements in Turkey have generally been carried out in indoor air, water, soil, and coastal sand (Turhan et al., 2023; Aal-Shabeeb et al., 2023; Aydin and Söǧüt, 2019; Küçükönder et al., 2022; Celen et al., 2023). The employed counting systems vary depending on the specific requirements and objectives of each study. Passive counting systems, such as solid-state nuclear track detectors (SSNTDs), are widely used as they do not require electrical power or pumping machines (Takahashi et al., 2022). Active radon monitoring systems, such as the AlphaGUARD system, instantly and continuously assessment of the radon levels in air, water, and soil.

The objective of this research is to measure the radon concentration and the annual effective dose rates (Deff) in the water samples emitted from Arin Lake in Bitlis province. This study aims to determine whether radon poses a health risk to the residents of the villages surrounding the lake and migratory birds that use the lake as a migration stop.

Determining the radon activity concentration of a particular region and creating radon maps are important research topics worldwide, including in Turkey. Thus, this study holds immense significance for Bitlis and Turkey by contributing to the existing literature and serving as a foundation for future studies in this region.

2 Material and Methods

2.1 Study Area

Arin Lake is a soda lake situated in the Bitlis province in Turkey, covering an area of approximately 13.5 km2. It is located in the southeastern part of Mount Süphan and is surrounded by three villages (Nergiz and Durmus, 2017). The lake serves as a breeding ground for the endangered white-headed duck and is also an essential stopover for migratory birds, including flamingos and songbirds, during the autumn migration season. This further highlights the significance of Arin Lake It is worth noting that during the Ottoman Empire period, soda production took place at Arin Lake, along with Lake Van, due to the high soda content present in the lake (Yücel, 2020).

In this research, samples were collected from 27 distinct locations within the lake and filled in 500-mL polyethylene bottles and its cap was closed immediately to prevent radon escape. Subsequently, the collected samples were subjected to analysis at the laboratory of Bitlis Eren University. Sampling locations are shown in Fig. 1.

Fig. 1
figure 1

Sample location from Aygır Lake

Full size image

The radon concentration measurement in water was performed with a radon monitor system that comprised the ionization chamber AlphaGUARD PQ 2000 Pro, AquaKIT, and Alpha PUMP. It is powered with a 750 V D.C. and has a measurement range of 2–2 \(\times\) 106 Bq/m3. Despite its excellent calibration, the system had a 3% error rate (Instruments, 1998).

The radon concentrations in the water samples were determined utilizing the formula as follows:

$${C}_{{\text{water}}}=\frac{{C}_{{\text{air}}}\left(\frac{{V}_{{\text{system}}-}{V}_{{\text{sample}}}}{{C}_{{\text{sample}}}}-k\right)-{C}_{0}}{1000}$$

where \({C}_{{\text{water}}}\) is the concentration of radon in the water sample (Bq/L), \({C}_{{\text{air}}}\) is the value measured by the monitoring system, \({C}_{0}\) is the background concentration, Vsystem is the inner volume in the device (mL), Vsample is the sample volume (mL), and k is the radon diffusion coefficient.

Deff for ingestion of water samples were determined using the following formula;

$${D}_{{\text{eff}}-{\text{ing}}}\left(\frac{\mathrm{\mu Sv}}{{\text{year}}}\right)= {C}_{{\text{water}}}\times {10}^{-3 }\times {C}_{{\text{CW}}} \times {\text{EDC}}$$

where EDC is the effective dose coefficient (adults; 3.5 nSv/Bq), and CCW is the prediction of annual water consumption (730 L/year for adults) (Ahmad et al., 2015; Şahin et al., 2021).

Deff for inhalation (Deff-inh) was calculated for the water samples as follows:

$${D}_{{\text{eff}}-{\text{inh}}}\left(\mathrm{\mu Sv}/{\text{year}}\right)= {C}_{{\text{water}}} \times {R}_{a/w}\times I \times F \times \mathrm{ DCF}$$

where F is the equilibrium factor (0.4), Ra/w is radon in air/radon in water (10−4), DCF is the dose transformation factor (9 nSv(Bqhm−3)−1), and I is the mean occupation time (7000 h/year) (Şahin Bal et al., 2021).

3 Results and Discussion

Radon concentration levels were investigated in water samples collected from Arin Lake in Bitlis province. Subsequently, Deff values were computed for both ingestion and inhalation exposure routes in the water samples. The results of the radon concentration are reported in Table 1, while the frequency distributions of Cwater, Deff-ing, and Deff-inh values are presented in Fig. 2, Fig. 3, and Fig. 4, respectively.

Table 1 Cwater, Deff, Deff-ing, and Deff-inh values of samples in Arin Lake
Full size table
Fig. 2
figure 2

The frequency distribution of Cwater in the water of Arin Lake

Full size image
Fig. 3
figure 3

The frequency distribution of Deff-ing in the water of Arin Lake

Full size image
Fig. 4
figure 4

The frequency distribution of Deff-inh in the water of Arin Lake

Full size image

As indicated in Table 1 and Fig. 2, the radon concentration values in the water samples, denoted as Cwater, range from 0.06 to 0.39 Bq/L. The average value of Cwater is 0.17 Bq/L. In terms of Deff, the values for ingestion and inhalation range from 0.14 to 0.99 Bq/L. Additionally, the mean of Deff for ingestion and inhalation are calculated as 0.43 µSv/year and 0.44 µSv/year, respectively.

As observed from Fig. 2, the obtained results are relatively similar to each other, except for sample 26, which exhibits a higher radon concentration. This elevated value could potentially be attributed to its proximity to the living area. Additionally, it is believed that the reason for the close similarity between the Ding and Dinh values in Fig. 3 and Fig. 4 is the absence of any external contribution that could increase the radon level.

The United States Environmental Protection Agency (USEPA (U.S. Environmental Protection Agency), 2011) has suggested a maximum radon concentration level of 11.1 Bq/L in water, while the World Health Organization (WHO) has set a maximum level of 100 Bq/L in the drinking water (WHO (World Health Organization), 2011). Considering the results obtained from this study, it can be concluded that the levels of radon concentration in all 27 water samples collected from Arin Lake are significantly lower than the level suggested by the USEPA. When considering the effective dose value, it was determined that the total annual effective dose value obtained in this study was below the value of 0.1 mSv/year recommended by WHO (WHO (World Health Organization), 2011). Therefore, it can be inferred that the presence of radon gas does not pose any potential health risks to either the local human population or the migratory bird species inhabiting the lake and its surrounding areas.

The radon concentration levels obtained from studies conducted in various countries are presented in Table 2. As observed from Table 2, the radon concentration levels are in proximity to each other and are also below the limit recommended by USEPA.

Table 2 Some studies of radon concentration in different lakes of the world
Full size table

4 Conclusion

In this research, the radon concentrations in water samples collected from Arin Lake in Bitlis province were investigated to determine the radon levels. The measurement of radon concentration was made using the AlphaGUARD radon monitoring system in the Department of Physics, Bitlis Eren University. Subsequently, the annual effective dose values (Deff) were computed. Upon examination of the results obtained, it is observed that the radon concentration values and Deff in the water samples do not exceed the recommended limit of 11.1 Bq/L by the USEPA and suggested limit of 0.1 mSv/year by WHO (USEPA (U.S. Environmental Protection Agency), 2011, WHO (World Health Organization), 2011). This finding is of significant importance as Arin Lake and its vicinity serve as the migration paths for various migratory birds, such as flamingos and songbirds. The study results indicate that Arin Lake does not pose any risk to the natural habitat and health of these birds concerning the radon levels. Additionally, the study findings provide essential baseline information for evaluating radiation exposure in the natural environment and assessing environmental pollution.