1 Introduction

In current years, natural radioactivity has acquired a great deal of interest and has been investigated due to public subject springing up from radiation-related risks and the possibility of injury to human health [1]. Elevated tiers of these natural radioactive elements in the surroundings can pose a danger to our health. One of the naturally happening radioactive gases is Radon (222Rn). 222Rn is a tasteless, colorless, and odorless gas. 222Rn was discovered with the aid of Friedrich Dorn in 1900 whilst elucidating radium’s decay series [2]. 222Rn considered the second-highest cause of lung cancers after smoking and may also pose a widespread longterm hazard to human health. Radon-222 (222Rn), or acquainted “radon”, is part of the 238U decay collection (Fig. 1). We are typically able to measure 222Rn air (in indoor or outdoor), water, and soil. 222Rn is an inert gas, therefore, it can get away from any chemical compound and diffuse into the air. Alpha particles from 222Rn emission are adsorbed to air dust and other suspended particles. The primary reason of 222Rn gas in the Earth’s environment is the radioactive nature of the Earth, which enters radioactive materials in all organisms, which includes the human body, through inhalation or ingestion. Moreover, some of the plant incorporates the remnants of average radioactive factors which transfer interior our bodies such as carbon-14 and potassium-40 [3, 4]. To center of attention on these inert gases, the radium 226 decay series, shown below, are these parts of the 238U decay series that consist of these 222Rn gas and their short-lived progeny [5].

Fig. 1
figure 1

Radium-226 decay chain

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Radon is without difficulty soluble in water underneath pressure. Hence, groundwater passing through uranium-rich soils has a excessive attention of 222Rn. 222Rn concentrations in groundwater sources are two to three times greater than different radioactive substances. Therefore, high concentrations of 222Rn (11 Bq/l) may also be of challenge involving its outcomes on human health. By inhalation or ingestion of consuming water containing 222Rn, this gas and its decay products (218Po [T1/2 = three minutes], 214Pb [T1/2 = 27 min], 214Po [T1/2 = 164 microseconds], and 214Bi [T1/2 = 20 min], are viewed the second-highest motive of lung cancer [6], as it enters the lungs and begins to decay, with the resultant alpha particles have the conceivable to harm DNA and its products protein, causing injury to the lung epithelium cells and in the end resulting in most cancers. 222Rn may additionally make bigger the hazard to stomach inducing cancers for some populations using groundwater as their essential sources of ingesting water [7]. In 1988, International Agency for Research on Cancer (IARC), and the cancer research institute of WHO, declared 222Rn to be carcinogenic to humans and classified it as a verified human carcinogen [8]. In Saudi Arabia, lung cancers are on the rise claiming an increasing number of lives [9]. Many international locations have currently attempted to measure 222Rn and radionuclide concentrations in water samples via several techniques [10,11,12,13,14]. The risk is increased significantly when floor water is used as the foremost water furnish for buildings that have closed structures and pump water directly to consumers, such that there is inadequate time for 222Rn to break out or decay [15]. The highest world recorded groundwater 222Rn concentration is 77,500 Bq/l in the Scandinavian region [16], where the world average is 183 Bq/l [17]. Groundwater 222Rn concentrations in Saudi Arabia, as derived generally from different locations, have been 0.01 to 67.4 Bq/l [18].

2 Materials and methods

2.1 The study area

This study was carried out in the city of Makkah, located in the western region of Saudi Arabia, and is the one of the most vital cities with an area of 1200 km2. Makkah is located at a latitude of 21° 25′  21.0360′′ N & a longitude of 39° 49′ 34.2048′′ E. Makkah is recognized as a holy region for all Muslims. It is one of the principal and greatest cities of the province of Hejazi. It is the location of the annual pilgrimage of the tens of millions of Muslims who, in accordance to the Qur'an, have to visit the Kaaba, the most sacred Mosque and vicinity at least once in their lives. Artesian wells are natural points of interest of province and are positioned in extraordinary sectors of Makkah. This study was carried out on ten artesian wells around Makkah, with the concentrations of 222Rn measured in each of them. Artesian wells have been chosen in accordance to its geographic distribution round Makkah metropolis accessibility to them. Figure 2 indicates the areas of the ten selected artesian wells.

Fig. 2
figure 2

Map showing water sample locations in Makkah

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2.2 Sampling

This study was performed between the 23 and 30 July 2022. In every sampling location, the neighborhood of artesian wells, water samples were accrued in plastic bottles with 250 ml capacities, then closed tightly to avoid any losses of 222Rn gas and labelled in accordance with their sampling time and location. All these samples were taken from the corresponding areas after turning them on and permitting runoff for about ten min. This used to purge any trapped air and to permit the water temperature to stabilize. Also, the stream of the flow was once decreased to about one-eighth of an inch in diameter, bringing the air bubbling to be minimized.

2.3 Measurement technique

The study was carried out using a RAD7 222Rn detector, as shown in Fig. 3a. RAD7 is used in conjunction with semiconductor detector running at excessive voltage to discover the positively charged 222Rn daughters, (218Po (T1/2 = 3.10 min) and 214Po (T1/2 = 164 s)), which are then used to calculate the 222Rn activity in the air. RAD7 can distinguish between 218Po or 214Po relying on emitted alpha energy (218Po emit the alpha energy at 6 MeV and 214Po at 7.7 MeV). Since RAD7 can distinguish between old and new 222Rn gas (new 222Rn incorporate giant quantity of 218Po but the ancient include giant amount of 214Po). The RAD7 can detect 222Rn concentration in the vary of 0.1 pCi/L—20,000 pCi/L with the relative uncertainty of ± 0.5 cpm [19].

Fig. 3
figure 3

RAD7 professional electronic radon detector

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RAD H2O is a RAD7 add-on that reliably detects 222Rn in water with diversity of concentrations and can provide a reading for the 222Rn content of water within half an hour (measurement duration) of taking the sample. Figure 3b shows how to measure a water sample the usage of RAD7 and its RAD H2O add-on [20]. The RAD H2O employs the RAD7’s normal, preset protocols to give a unique size of the 222Rn content material of the water sample. The formal 222Rn content in a water sample can be calculated by using doubling of the 222Rn concentration in the air loop due to a steady conversion coefficient. The quantity of the air circulation, the quantity of the sample, and the equilibrium 222Rn distribution coefficient at room temperature are used to calculate a conversion coefficient of four for a 250 ml groundwater sample vial. A closed loop aeration device is used in this system. A mechanism whereby the air and water volumes are maintained at the identical level and are unchanged with the aid of the charge of flow. The Wet-250 protocol water test takes about thirty minutes to complete. At the begin of a test, the RAD7’s built-in pump routinely starts off evolved working for 5 min, aerating the pattern and transporting the degassed 222Rn to the RAD7 detecting chamber. Throughout the 5 min airing out cycle, greater than 94 percentage of the 222Rn existing is eliminated from the water. The pump shuts down routinely after 5 min, after which the computer pauses for a further 5 min. Following that, the computing device starts counting. Every 5 min, the laptop generates a short file for a 5 min cycle. Five minutes later, the equal issue occurs, and again twice again for 5 min. Following every measurement, the machine needs to be purged for 30 min to minimize humidity ranges to less than six percent. RAD7 generates a rundown that carries the average 222Rn attention in each of the 4 of 5-min intervals, a bar map of the four counting, and a cumulative spectrum. In addition, these measurements additional environmental parameters such as relative humidity and temperature add above the 222Rn concentrations table.

2.4 Determination of annual effective dose of 222Rn gas

The collection, sealing, of samples till to counting took a some of days. This led to the reduction of the 222Rn content in the samples due to radioactive decay. To account for this radioactivity reduction, the measured concentrations have been corrected the usage of the decay correction factor (DCF), from the time of sample collection to the time of counting. DCF, a simple exponential characteristic of a time constant, is given with the aid of:

$$\begin{aligned} {\text{Time constant}} & = 3.825\;{\text{days}}(T_{1/2} \;of\;^{222} {\text{Rn}}) \\ & \quad \times 24({\text{h/day}})/\ln 2 = 132.4{\text{h}} \\ {\text{DCF}} & = e^{(t/132.4)},\end{aligned}$$

where t = decay time in hours [19].

222Rn concentrations were corrected (Corr. RC) for decay time between sample collection and measurement, and the measured volume of 250 ml transformed to a liter via multiplying the DCF through a factor of four using Eq. (1).

$${\text{Corr.RC}} = {\text{Measured}}\;^{222} {\text{Rn}}\;{\text{concentration}} \times {\text{DCF}} \times 4.$$
(1)

To evaluate the 222Rn outcomes and risks, we want to calculate the whole annual effective dose (AED).

1-Annual effective dose due to the ingestion of 222Rn from under groundwater, (Eing) was calculated using Eq. (2).

$$E_{{{\text{ing}}}} = {\text{CR}}_{n} ({\text{Bq}}/1) \times D_{{{\text{ing}}}} \times D_{w} \times T \times F,$$
(2)

where CRn is the mean 222Rn activity concentration in water, Dw is the daily water ingestion (2 l/ day), Ding is the ingesting dose conversion component of 222Rn (10− 8 Sv Bq− 1), T is equal to 365 day/year, and F is the indoor equilibrium factor between 222Rn and its progeny (0.4) [21].

2-The annual dose from inhalation, Einh, of 222Rn from water is received from Eq. (3), [21].

$$E_{{{\text{inh}}}} = {\text{CR}}_{n} ({\text{Bq}}/1) \times R \times D \times T \times F,$$
(3)

where CRn is the mean 222Rn activity concentration in water, R is the ratio of 222Rn in air to 222Rn in water (10−4), D is the dose conversion factor of 222Rn (9 nSv (hBqm3)−1, T is indoor time (7000 hy−1), and F is the indoor equilibrium factor between 222Rn and its progeny (0.4), [22, 23].

3 Results and discussion

Groundwater 222Rn measurements have been carried out in 10 exceptional places in Makkah as pronounced in Table 1, the place the mean, the minimum and maximum cost of 222Rn concentration were said as 2.851 Bq/l, 0.426 Bq/l, 18.628 Bq/l, respectively. The absolute best values had been in sample eight (18.628 Bq/l), which is located in Higher Nabe. The variability in the radon content ought to be attributed to the geological structure of the investigated region. Figure 4 indicates the histogram of groundwater 222Rn concentrations. As can be seen, all the measured values are beneath a hundred Bq/l endorsed by WHO. The annual tremendous dose of 222Rn in water from ingestion by using the stomach (Eing) and inhalation through the lungs (Einh) have been calculated the use of equations two and 3, are also in Table 1. The annual wonderful dose of ingestion used to be calculated. The highest Annual Effective Dose (AED) for the stomach was in sample eight (3.912 µSv/y), while the lowest at Umm algadb (0.089 µSv/y) had a suggest cost of 0.599 µSv/y. It may be noted that the highest possible Einh (annual dose from inhalation) used to be located in pattern 8, of 46.944 µSv/y, whilst the lowest value used to be found in pattern 1, which used to be equal to 1.073 µSv/y, and had a mean value of 7.184 µSv/y. It may additionally also be cited that the very best AED for the lungs used to be higher than the belly due to the gaseous nature of 222Rn. The minimum, maximum, and mean for complete annual nice doses in samples are 1.163 µSv/y, 50.855 µSv/y, and 7.783 µSv/y, respectively. As we observed that none of these samples had an annual tremendous dose greater than the most permissible limit of 0.2 mSv/y [23].

Table 1 Details of measured groundwater radon concentrations and calculated annual effective dose
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Fig. 4
figure 4

Radon concentration in Bq/l

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4 Conclusion

Today, a massive number of national and international agencies have established their own safe 222Rn ranges worldwide. For instance, the United States Environmental Protection Agency in its record of 1998 set the 222Rn concentration level in water at 11.1 Bq/l [24]. UNSCEAR has defined a value of 40 Bq/l in its posted report of 2016 [21], whilst the World Health Organization has described the 100 Bq/l as an action limit in 2012 [25]. In the current study, the results obtained from the more than a few samples had been observed not to exceed the endorsed levels of 222Rn in groundwater in accordance to USEPA 1999 [26]. In this regard, the spatial variability in the 222Rn concentration ought to be attributed to the geological structure of the investigated region, depth of the water source, differences in climate, and geo-hydrological strategies that occur in the area. Around 95 percent of the samples have been far less, by means of comparison, than the 222Rn ranges reported in the literature [27,28,29,30]. Furthermore, the estimated 222Rn concentrations in the existing learn about had been comparable to those discovered in the huge majority of regions of Saudi Arabia [31,32,33,34].