Assessment of 222 Rn Activity in Bottled Water from Baghdad and Its Radiological Impact †

Presented


Introduction
Drinking water serves as an essential resource for sustaining life but also acts as a matrix that often contains substances detrimental to human health, including radionuclides.Natural radionuclides are frequently detected in drinking water owing to their release from rock formations via processes such as erosion and dissolution [1].Uranium-238 ( 238 U) is the most abundant element in rocks and serves as a parent element for several progeny radionuclides, notably radon-222 ( 222 Rn).Radon-222 is an odorless, tasteless, and colorless noble gas with a half-life of 3.8 days.The primary health risks associated with 222 Rn arise from internal exposure, primarily through inhalation.Once inhaled, 222 Rn and its decay products ( 218 Po, 214 Po) can reach bronchiolar cells, where emitted alpha particles may induce DNA damage, potentially leading to carcinogenesis [2][3][4][5][6].The World Health Organization (WHO) acknowledged radon gas as the second leading cause of lung cancer following tobacco smoking in 2009 [7].Similarly, the International Agency for Research on Cancer (IARC) classified radon as a Group 1 carcinogen in 1998 [8].
In addition to inhalation, ingestion serves as another route for internal exposure to 222 Rn.Although 222 Rn is the most frequently occurring radionuclide in water, its solubility in water is relatively low and inversely proportional to temperature [9,10].Water usage liberates radon into indoor air; consequently, nearly 90% of the 222 Rn dose from drinking water originates from inhalation rather than ingestion [11].Ingestion of radon-laden water also poses direct health risks, as 222 Rn can irradiate the sensitive cells of the intestinal tract before being rapidly expelled from the body [12][13][14][15].Despite the potential hazards, no studies have definitively established a link between ingested radon and gastrointestinal tumors [16].
The present study aims to quantify the activity concentration of 222 Rn in bottled drinking water in Baghdad city and to assess the potential health impacts through the evaluation of the annual effective dose due to radon ingestion.

Sample Collection and Analysis
Bottled drinking water samples, with capacities ranging from 0.25 to 20 L, were procured from local markets in the Baghdad governorate in January 2022.These samples were classified based on their trade names, and a total of 25 such samples were analyzed.Each sample was assigned a unique code and stored in a refrigerator until the time of analysis.

Measurement of Radon Concentration
For assessing cumulative radon concentration, time-integrated passive radon dosimeters equipped with CR-39 solid-state nuclear track detectors (SSNTDs) were utilized.The CR-39 detector employed in this study is composed of polyallyl diglycol carbonate and has a thickness of 1.5 mm and an effective area of 2.38 cm 2 .This detector fits into the groove of the dosimeter, which also features slits that permit the diffusion of radon gas while excluding other contaminants.Alpha particles emitted from the decay of 222 Rn and its daughter isotopes interact with the CR-39 film, inducing molecular bond damage.This damage manifests as sub-microscopic tracks on the surface of the film.Under specific chemical or electrochemical etching conditions, these latent tracks can be enlarged to become permanent, observable tracks.The number of these tracks is quantified using an optical amplification readout device, and the equilibrium radon concentration is subsequently calculated using an appropriate Equation (1) [17].
In this equation, C Rn represents the equilibrium radon concentration in Bq/m 3 ; N T is the total number of tracks registered in the CR-39 detector; N B signifies the background tracks in the detector; A is the effective area of the CR-39 detector in cm 2 ; k is the calibration factor of the CR-39 detector in Tr•cm −2 /kBq•m −3 •h; and T is the effective exposure time in hours (960 h, 40 days).

Measurement of Total Dissolved Solids
The concentrations of total dissolved solids (TDS) in the samples were determined using a TDS meter.

Estimation of 222 Rn Annual Effective Dose (AED)
The annual effective dose (AED) serves as the metric for assessing the radiological effects of radon exposure.The calculation of the AED requires consideration of the yearly water consumption rates.Based on reference [12], average water consumption rates were categorized into three age groups: infants, children, and adults.These were further distributed across six subgroups (G1-G6), as listed in Table 1.The AED is computed using the following Equation (2) [12,18]: In this equation, A represents the radon activity concentration in water (Bq/L); C denotes the average water consumption rate (L/year); and DCF is the dose coefficient factor, valued at 3.5 × 10 −9 Sv/Bq.

Results and Discussion
The study analyzed 222 Rn concentrations in 25 bottled water samples available in local markets in Baghdad, along with their total dissolved solids (TDS) values.As summarized in Table 2, the 222 Rn concentrations varied significantly among the samples.The highest concentration of 11.12 Bq/L was observed in a sample from the Royal brand, while the lowest of 1.5 Bq/L was found in an Aquafina-branded sample.
The mean 222 Rn concentration across all samples was 4.58 Bq/L.These variations are likely influenced by the distinct geological characteristics of the water sources, affecting the radioactive content in the soil and rocks.Notably, all measured 222 Rn concentrations were below the regulatory threshold of 100 Bq/L [12].Correlation was observed between samples showing high radioactivity and elevated TDS values, indicating a direct relationship between the concentration of dissolved solids and 222 Rn radioactivity levels.This observation was further substantiated by data from the Tigris River in Baghdad, which displayed a 222 Rn level of 42 Bq/L and a TDS value of 472 ppm.Hence, water purification methods that effectively remove solid materials could potentially reduce 222 Rn levels.To evaluate the potential health risks associated with long-term consumption of the analyzed bottled water, annual effective doses (AEDs) were calculated using Equation ( 2).The AED results, categorized by age and further divided into six groups (G1-G6), are presented in Table 3.The highest dose recorded was 1.17 × 10 −5 Sv/y for adults aged over 17 years, and the lowest was 3.21 × 10 −6 Sv/y for infants aged 0-1 years.All calculated doses were found to be well below the reference dose level of 0.1 × 10 −3 Sv/y [19], thereby indicating negligible health risks under standard conditions.Figure 1 further elucidates these dose assessments, revealing the highest and lowest dose rates to be 2.84 × 10 −5 Sv/y and 1.05 × 10 −6 Sv/y, attributed to the Royal and Aquafina brands, respectively.

Conclusions
The present study examined the radiological implications of 222 Rn concentrations in bottled drinking water sold in local markets in Baghdad.The 222 Rn concentrations in the analyzed samples ranged from 1.5 to 11.12 Bq/L, all of which were below the regulatory reference value of 100 Bq/L [12].Thus, the sampled bottled waters do not pose a significant radiological hazard to consumers.The annual effective dose (AED) due to 222 Rn ingestion was calculated to evaluate its impact on different age groups.For an average activity concentration of 4.58 Bq/L, the potential radiation doses ranged from 3.21 × 10 −6 Sv/y for infants (0-1 years) to 1.17 × 10 −5 Sv/y for adults (>17 years).These doses are well below the reference dose limit of 0.1 × 10 −3 Sv/y [19], indicating a negligible risk to public health.Furthermore, the study evaluated the correlation between 222 Rn activity concentrations and total dissolved solids (TDS) values in bottled water samples.
The findings suggest that samples with higher 222 Rn concentrations generally also exhibit higher TDS values, implicating the dissolved solids as a contributing factor to elevated 222 Rn levels.

Figure 1 .
Figure 1.Results of dose assessment for different populations groups and for different bottled water types.

Table 1 .
[12]average consumption rate of water for each age category, as reported in reference[12].

Table 2 .
222Rn and TDS concentrations in investigated bottled mineral water samples.

Table 3 .
Results of dose assessment for different population groups.