Annual effective dose and associated health risk estimation using gross alpha and Beta activity concentrations in bottled mineral water in Morocco

Abstract

 

Water usually contains small quantities of radioactivity. The presence of significant levels of radioactivity in drinking water sources poses potential health risks to the public. Consequently, determining the concentrations of gross alpha and gross beta activity in water is essential for ensuring water safety. Thirteen commercially bottled mineral water samples were collected from Moroccan markets and analyzed using the Liquid Scintillation Counting technique, based on the ISO 11704:2018 method. The results show that the activity concentrations range from a minimum below the lower limit of detection to a maximum of 0.21 ± 0.02 and 0.15 ± 0.01 Bq·L⁻¹ for gross alpha and gross beta, respectively. The concentrations of anions and cations are within recommended limits for drinking water. For each sample, the annual effective dose was calculated and lifetime cancer risks were estimated. The levels of the annual effective dose and lifetime cancer risk were all below the World Health Organization’s recommended values for drinking water quality.

Highlights

• Natural radioactivity in Moroccan bottled mineral water is below acceptable limits for gross alpha and beta activity.

• Ionic Composition in the samples is within recommended drinking water limits.

• The annual effective dose from radiation exposure is within safety limits and aligns with low cancer risk thresholds.

• The mineral water samples are radiologically safe and pose no significant health risks to the public.

Introduction

Drinking water quality is one of the most important parameters in environmental studies, and it is vital to have regulations regarding natural radioactivity in this water, particularly in mineral waters, through the estimation of the annual effective dose and lifetime cancer risk. Mineral waters are naturally radioactive due to the long-lived uranium, thorium, and radium isotopes found in rocks and soils [1]. These isotopes decay to release gamma, beta, and alpha radiation. Environmental radioactivity can be detected in the Earth’s crust and is caused by radionuclides belonging to the ²³²Th, ²³⁸U, and ²³⁵U series. It is acceptable to assume that some natural radionuclides will be present in trace concentrations in drinking water, such as bottled mineral water [2].

The temperature, the solubility of the elements encountered, the contact time (water age), the geological composition of the terrain they cross and other factors all have an impact on the natural radioactivity of the water. Because mineral waters naturally contain many radionuclides, some of them have significant levels of radioactivity that need to be monitored. Stricter regulations regarding exposure to alpha and beta emitters from drinking water intake in general and mineral water in particular, have been put in place by national and international organizations [3].

In addition to naturally occurring radionuclides, human activities such as uranium mining, phosphate mining, and nuclear facility operations can significantly increase the levels of radioactive substances in water. These activities often result in the release of radionuclides like uranium, radium, and thorium, which can be transported into groundwater or surface water sources [4].

The measurement of gross alpha and gross beta activity is one of the simplest radioanalytical procedures widely applied as screening techniques in the fields of radioecology, environmental monitoring, and industrial applications. This measurement enables the calculation of the ingestion annual effective dose received by individuals consuming the water. Based on these results, this approach allows for the assessment of potential health risks and ensures adherence to established safety standards [5].

One of the purposes of this work is to calculate the ingestion effective dose in mineral water by analyzing gross alpha and gross beta activity concentrations, using liquid scintillation counting to clarify the importance of these measurements in estimating possible radiation exposure and health risks from drinking bottled mineral water in the Moroccan market. The selection of bottled water brands for this study focused exclusively on natural mineral waters, which are characterized by their stable mineral composition and natural purity. It is important to note that this study did not include “table water”, which typically consists of treated municipal water or mixed water sources that do not share the unique characteristics of natural mineral waters.

This work utilizes the method for determining gross alpha and gross beta activity in drinking water, which is based on the Moroccan standard approved by the decision of the Director of the Moroccan Institute of Standardization (IMANOR) No. 3711–14, dated 17th October 2014, published in B.O. No. 6310 on 20th November 2014, and performed at the National Centre for Nuclear Energy and Technology.

Liquid scintillation counting (LSC) is one of the most important laboratory methods for determining the radioactivity of low-energy radionuclides, primarily beta-emitting and alpha-emitting nuclides. [6] Below 80 °C, most of the radionuclides of concern are nonvolatile. Drinking water, natural mineral water, precipitation, surface water, groundwater, and all other forms of water samples with a total dissolved solids (`) content of <5 g/L are among the common methods used to monitor gross alpha and gross beta activities [7].

Sampling preparation and analysis techniques

Water samples used for this study were collected from 13 brands of bottled mineral water from Moroccan markets. The majority of them are locally produced, while some are international. The samples were taken to the laboratory for successive analysis.

Physicochemical analysis

Physical and chemical characterization is used to make a classification of the different mineral waters, basing on the analysis of main parameters, like pH, temperature, and hardness (TDS) [8].

Conductivity measures the ability of water to conduct an electric current between two electrodes [9]. It is influenced by the presence of electrically charged ions in the water. To measure conductivity, a water quality multimeter (WTW, Multi 340i) is used by immersing the device’s electrode in a beaker filled with water.

The pH (hydrogen potential) measures the concentration of H⁺ ions in the water and indicates the balance between acid and base on a scale of 0 to 14. The pH depends on several factors, including the origin of the water [10]. To measure pH, a water quality multimeter (WTW, Multi 340i) is used. Its probe, consisting of a glass electrode and a reference electrode, is immersed in the beaker filled with water and the measurement value is then recorded.

The nature of the ions present in mineral waters, as well as their concentrations, is indicated on the labels affixed to the mineral water bottles. Similarly, the dry residue (TDS) for the majority of the samples is indicated on the labels attached to the mineral water bottles; however, we assessed the dry residue for samples 4, 5, and 7. In fact, the TDS was determined by evaporation to dryness and weighing the residue.

Gross alpha and gross Beta counting

Measurement of gross alpha activity is one of the most simple radioanalytical methods and frequently utilized as screening techniques in the fields of radioecology, environmental monitoring and industrial applications [5]. The validation of the method was carried out through our participation to a proficiency test organized by the International Atomic Energy Agency (IAEA) “World-Wide Open Proficiency Test IAEA-TEL-2018-03 Part II”.

Sample preparation

Every sample must have its pH adjusted before using this approach. An acid like HCl is used to change the pH. To each 400 ml aliquot of the samples, a few drops of nitric acid (HNO₃) were added during stirring. The pH probe was simultaneously inserted into the aliquot to ensure that the pH consistently drops to 1.7 ± 0.2 [7].

A thermal pre-concentration was employed to increase the sensitivity of the process. A 200 ml volumetric flask was used to weigh an aliquot of each water sample, which was ~200 g (the mass prior to the initial evaporation). The beaker was previously weighed empty using a stirrer magnet (mass m₀). We used nitric acid to acidify the aliquot while stirring it to a pH of 2.7 ± 0.2. The sample was placed on a heated plate and gradually evaporated while stirring to a final mass of roughly 20 g. A 200 ml volumetric flask was used to add a second weighed aliquot of the water sample. While being agitated, the sample evaporated a second time, producing a final mass of ~20 g [7]. The sample cooled down to room temperature after the second evaporation. The scintillation plastic vials were filled with a weighed aliquot of each sample, ~10 ml in volume. To ensure sample homogeneity, 10 ml of scintillation cocktail was added and vigorously mixed.

LSC analysis

LSC is a technique for measuring not just beta-emitting radionuclides, but also radionuclides that decay via electron capture and alpha emission [11]. Although it is a conventional radiometric technique, it remains a competitive method for quantifying several radionuclides. It is an analytical technique based on the detection of light generated by radioactive decay. Radioactive decay occurs with the emission of particles or electromagnetic radiation from an atom due to a change within its nucleus [12].

Liquid scintillation counters are primarily used for measuring the activity of aqueous samples in environmental monitoring. The sensitive LSC detection method requires specific cocktails to absorb energy and convert it into detectable light pulses. The basic principle involves mixing an aliquot of the solution to be measured with a scintillating liquid. The sample is manually inserted into the counting chamber, which is equipped with two photomultipliers (PMs). The radiation emitted by the decay of a radioactive substance excites the scintillator, which then emits light. The PMT is an electron tube that detects the blue light flashes from the scintillation, converts them into a flow of electrons, and subsequently measures them as an electric pulse [13]. The two PMs, placed opposite each other and operating in double coincidence, detect the light pulses and allow for the determination of the activity present in the aliquot of the aqueous sample, defined as the number of radioactive decays per unit of time.

Thus, the wide popularity of LSC is due to various advantages, such as high detection efficiencies, the capability for simultaneous detection of different nuclides, and improvements in sample preparation techniques and automation, including computer data processing [14].

For gross alpha and gross beta activity counting, mineral water samples were counted for five cycles of 3600 seconds (60 minutes) per cycle. The results were displayed as count rates in counts per minute. Data were acquired for both alpha and beta modes. The specific activities for alpha and beta emitters in the samples were also calculated.

Standards preparation

To carry out the calibration of the Liquid Scintillation Counter (QUANTULUS 1220), four standards of known activity must be prepared. Each sample is ready for use in a 20 ml polypropylene vial. For water counting, a predetermined quantity of commercial scintillation cocktails is used [7]. However, only a limited percentage of commercial scintillation cocktails have adequate specifications for low-level counting and even fewer contain substantial amounts of water. Only the eco-friendly cocktails were selected from all of these [15]. In light of these factors, the scintillation cocktail utilized in this study is OptiPhase HiSafe 3.

Standard radioactive sources, polonium-209 (²⁰⁹Po), and strontium-90 (⁹⁰Sr/⁹⁰Y), produced by the CERCA LEA radioactive standard laboratory, were used to calibrate the system for alpha and beta energies, respectively. The activity of ²⁰⁹Po is A(²⁰⁹Po) = 10.49 Bq/g with a combined uncertainty of 0.8%, reference date 01/06/2011, and the activity of ⁹⁰Sr/⁹⁰Y is A(⁹⁰Sr/⁹⁰Y) = 108.5 Bq/g with a combined uncertainty of 3%, reference date 01/04/2013.

Specific masses of radioactive sources, polonium-209 (²⁰⁹Po), and strontium-90 (⁹⁰Sr/⁹⁰Y), were added to the standard vials. The ²⁰⁹Po radionuclide was used as a pure alpha source, while the 90Sr/90Y radionuclide was used as a pure beta emitter [7].

Decision thresholds and detection limits

In this study the detection limits (DL_α and DL_β) represent the minimum detectable activity (MDA). The DL_α and DL_β are calculated using the following equations, which considers the sample preparation, background radiation, efficiency, and counting time. The decision thresholds, |${A}_{\alpha}^{\ast }$| and|${A}_{\beta}^{\ast }$|⁠, are calculated from the following expressions (1 and 2) [16]:

V: sample volume (L), ε_α et ε_β are alpha and beta counting efficiencies respectively which are close to 1 (100%), |${r}_{0\alpha }$|and |${r}_{0\beta }$| are the blank count rates per second in the alpha window and in the beta window, respectively, and T is the counting time (s). The detection limits, |${DL}_{\alpha }$| and |${DL}_{\beta }$|⁠,were calculated from the following expressions (3 and 4) [16]:

With |$ {w}_{\alpha }=\frac{1}{V{\varepsilon}_{\alpha }} $| and |$ {w}_{\beta }=\frac{1}{V{\varepsilon}_{\beta }},\ {u}_{rel}^2\left({w}_{\alpha}\right) $| and |$ {u}_{rel}^2\left({w}_{\beta}\right) $| are the relative standard uncertainties of |$ {w}_{\alpha } $| and |$ {w}_{\beta } $| respectively.

Data processing

Ionic balance

According to the principle of electroneutrality, all water bodies are electrically neutral, meaning that the sum of the concentrations of cations must equal the sum of the concentrations of anions when expressed on a charge-equivalents basis [10]. This principle is crucial for evaluating the quality of chemical analyses; therefore, the analytical error for each water sample was assessed using the ionic balance equation (5) [17], which checks whether the measured concentrations of cations and anions are in equilibrium:

r represent the ionic concentration (meq/L):

Generally, the results of cation and anion contents are considered as follows [18]:

• Excellent when e < 5%;

• Acceptable when 5% < e < 10%;

• Doubtful when e ≥ 10%.

Ingestion annual effective dose and lifetime risk assessment

The main source of gross alpha activity concentrations in water is alpha emitter radionuclides, like ²³⁸U, ²³⁴U, ²³⁰Th, ²³²Th, ²¹⁰Po, and ²²⁶Ra. The gross beta activities were due to beta emitter radionuclides: ²¹⁰Pb, ²²⁸Ra, and ⁴⁰K [19]. As a result, we used the following annual dose conversion factors shown in Table 1 [20]:

The calculation of the annual effective dose due to the ingestion of mineral water (DEA) is based on taking into account the most pessimistic prediction, in which the overall alpha and beta activities are assumed to come from the radionuclides ²¹⁰Po and ²²⁸Ra. These radionuclides are more soluble and can leach into groundwater and surface water, and have high effective dose coefficients. Thus, the calculation formula to evaluate the annual effective dose (DEA) [21, 22]. is as follows:

A_α: the overall alpha activity (Bq/L),

A_β: the overall beta activity (Bq/L),

CF: the dose conversion factor for ingestion of ²¹⁰Po and ²²⁸Ra respectively,

R: the rate of annual consumption rate 730 L/year as a daily water intake recommended for adults is estimated at 2 L per day according to [3].

If the guideline value is based on weight, a child should consume 1 L/day (365 L/year) and infant 0.5 L/day (183 L/year). This consumption can vary depending on the season and climate.

The selection of ²¹⁰Po as the representative radionuclide for gross alpha activity in this study is based on its prevalence and radiological significance in natural water sources. ²¹⁰Po, a decay product of the ²³⁸U series, is commonly found in groundwater and mineral waters due to uranium rocks and soils. Its relatively high dose conversion factor (1.2 × 10⁻³ mSv/Bq) makes it a significant contributor to the ingestion effective dose. Or, ²³²Th, while possessing a higher dose conversion factor (2.1 × 10⁻³ mSv/Bq), is generally less soluble and less frequently detected in significant concentrations in bottled mineral waters (the concentration of soluble thorium will be very low) [23].

On the other hand, ²²⁸Ra contributes significantly to gross beta activity because of its high beta decay energy and its relatively short half-life (5.75 years). ²²⁸Ra has a relatively high dose conversion factor for ingestion (6.9 × 10⁻⁴ mSv/Bq) compared to other beta emitters like ⁴⁰K. This makes it a critical radionuclide for estimating health risks from water consumption [3].

To estimate the lifetime risk (L_R), we can use the annual effective dose (DEA), D_L duration of life (estimated at 70 years for adults) and risk factor recommended as 5.5 × 10⁻² Sv⁻¹ [20] as fellow:

Results and discussion

Physico-chemical parameters

The physicochemical analysis of bottled water includes several measurements, such as conductivity, pH, the composition of cations and anions and dry residue rate (TDS). For each sample, these parameters were evaluated. Tables 2 and 3 display TDS, pH, and conductivity as well as the mineral composition of 13 brand of bottled mineral water respectively.

The pH values of bottled mineral water samples varied from 6.92 to 8.26, with a mean of 7.64. These values respect the maximum admissible range, which is 6.5 < pH < 8.5, according to the Moroccan standard: NM 03.7.001 (Quality of human drinking water) [24].

Conductivity measurements reveal variations depending on the water analyzed. The maximum values are observed for mineral waters 7 and 9, with values of 2020 and 1096 μS/cm, respectively. These results can be explained by the high concentrations of dissolved matter (TDS) in mineral waters, which are 2078 and 1084 μS/cm, respectively. In addition, it is important to note that the recorded values are lower than the limit of 2700 μS/cm set by the national standard (NM 03.7.001) for the quality of water intended for human consumption [24].

The measurements taken allowed us to assess the quantity of salts dissolved in the water that meet the requirement of the standard method (TDS < 5 g/L) [7]; this is clearly seen in Fig. 1, which shows a strong positive correlation between the measured conductivity and the TDS values.

Although the presence of TDS in water has no effect on health, the taste of drinking water is affected depending on the level of these dissolved solids. We consider drinking water to taste excellent when the TDS level is below 300 mg/L; good between 300 and 600 mg/L; fair between 600 and 900 mg/L; poor between 900 and 1200 mg/L and unacceptable if it is >1200 mg/L [15]. Therefore, we can classify the 13 bottled mineral water samples according to Table 3.

While TDS itself does not pose health risks, it significantly affects the taste of drinking water, with lower levels generally being preferred for a better drinking experience. Low TDS water is often described as more refreshing, while higher TDS levels can indicate an excess of minerals, which may negatively impact flavor.

Concerning ionic composition, before processing and interpreting the results of water collected at the different samples, the ionic balance calculated for all samples (Table 4), show that the quality of chemical analyzes is acceptable for all samples.

The imbalance of anions and cations can be attributed to either unmeasured charged species, such as carboxylate groups found in natural organic matter, or the analysis may not have included all major inorganic ions (meaning the concentration of one or more significant inorganic ions is not reported). This argument is unlikely because the majority of inorganic ions in natural waters typically consist of the eight ions listed in Table 4 [10].

The ionic composition bottled mineral water samples (Fig. 2) is dominated by HCO³⁻, which presents 45.96% of the total ionic composition, followed by SO₄²⁻ with an abundance of 27.33% and Ca²⁺ of 15.89%, while other ionic compositions are less abundant with percentages not exceeding 4%.

This ionic composition may occur naturally depending on the geological composition of the water source or may be artificially added in varying quantities depending on the brand, due to its nutritional value, taste, or importance for health.

The high values recorded for SO₄²⁻, Ca²⁺, and Mg²⁺ in samples 7 and 9 may be related to the elevated levels of TDS and conductivity observed for these two samples. In fact, the high values of TDS and conductivity recorded for samples 7 and 9 may indicate a high concentration of dissolved solids, including SO₄²⁻, Ca²⁺ and Mg²⁺, possibly due to the presence of soluble salts containing these ions in the water. Other factors such as the geology of the region and human activities may also contribute to these elevated values. Additionally, the presence of Ca²⁺ and Mg²⁺ can suggest the existence of hard water [10].

The dominance of HCO₃⁻, SO₄²⁻, and Ca²⁺ in this mineral water suggests it comes from a source influenced by carbonate and sulfate minerals. This composition provides a balanced taste and enhances the water’s appeal due to its beneficial mineral content, qualifying it for bottled mineral water standards. The usual acceptable ranges of main ions in mineral water can vary greatly depending on the brand’s source. Although these values are typically acceptable for daily consumption, water with a balanced ion composition is generally recommended [26].

Gross alpha and gross beta activity concentrations

Table 5 shows the results of activity concentrations of gross alpha (A_αTot) and gross beta (A_βTot) as well as their detection limits (DL) obtained for 13 bottled mineral water samples.

The results presented in Table 5 show that the presence of alpha and beta activities in mineral water does not pose any health problems. Furthermore, the concentrations of alpha and beta activities are generally below detection limits, and the activity concentrations recorded in these waters are in line with WHO standards for drinking water, specifically 0.5 Bq/L for gross alpha activity and 1 Bq/L for gross beta activity [7].

Principal component analysis (PCA)

In order to reduce the dimensionality of the data and determine the correlations between the 13 variables (Na⁺, Ca²⁺, Mg²⁺, K⁺, SO₄²⁻, HCO₃⁻, NO₃⁻, Cl⁻, TDS, pH, Conductivity, alpha and Beta) in the 13 samples of bottled mineral water, Principal Component Analysis (PCA) was applied. When values are below the detection limit (DL), they are replaced by the average of the available values that are above the detection limit. This is a common practice in statistical analysis, chosen by default to ensure that the dataset remains complete for principal component analysis (PCA).

The quality of representation of the variables (extraction, Table 6) varies between 72% and 98%, which means that all the variables are taken into account by the PCA. According to Table 6, the application of PCA allowed us to obtain four principal components after varimax rotation with Kaiser Normalization, explaining 87.66% of the total cumulative variance. More information on PCA was presented in our previous work [27–29].

- The first component, which explains 51% of the total variance, is associated with the majority of variables: Ca²⁺, Mg²⁺, SO₄⁻, TDS, conductivity, A_αTot, and A_βTot, with a strong correlation. We have already observed in fig. 1, that conductivity and TDS (Total Dissolved Solids) show a strong positive correlation. These two factors measure the total quantity of solids dissolved in water, which can include ions such as Ca²⁺, Mg²⁺, and SO₄⁻. Their presence can influence the gross alpha and gross beta activities.

- The second component, explaining 17.44% of the total variance, shows a significant correlation between Na⁺ and K⁺, possibly due to the classification of brands of bottled mineral water based on Na⁺ and K⁺.

- The third component, explaining 10.73% of the total variance, is associated with a positive correlation with NO₃⁻ and a negative correlation with Cl⁻. This correlation can be explained by the fact that these two variables have opposite influences on the composition of bottled mineral water. According to Table 3, when the concentration of NO₃⁻ increases, the concentration of Cl⁻ decreases and vice versa.

- Finally, the last component, which explains only 8.50% of the total variance, shows a strong negative correlation with pH. Therefore, we can say that pH and this component have an inverse relationship.

The annual effective dose due to the ingestion and lifetime cancer risk

The annual effective dose equivalents due to the ingestion (DEA) derived from gross alpha and gross beta activity concentrations of mineral water samples are shown in Table 7. In the DEA calculation, if the activity of A_α or A_β was below the detection limit, the value of A_α or A_β was substituted with zero (Equation 7). Annual effective dose values were between minimum <LLD and maximum 0.12 mSv/year. These results were lower than the WHO limit value, which is 0.1 mSv/year [20].

The lifetime cancer risk calculated using annual effective dose of mineral water samples are presented in Table 8. It is important to consider the health risks associated with the presence of naturally occurring radionuclides in drinking water [30]. However, under normal circumstances, drinking water has a small impact on cumulative radioactive exposure. The average lifetime risk is around the appropriate 10⁻⁴ limit [3]. The results show that there is no risk for consumption of bottled mineral water can be consumed safely.

Conclusion

This research is a comprehensive study on the concentration of radioactivity in bottled mineral water and the associated health hazards, based on the annual effective dose. Gross beta and gross alpha radioactivity measurements were used as the initial step to determine the water’s radioactivity. Gross alpha and gross beta activity analyses were performed for 13 commercially bottled mineral water samples collected from the Moroccan markets. The results indicate that the natural radioactivity levels in these bottled mineral water samples are lower than the acceptable limits concerning gross alpha and gross beta activity concentrations. The analysis of the ionic composition has been affected. The concentrations of anions (Cl⁻, HCO₃⁻, NO₃⁻, and SO₄²) and cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) in the bottled mineral water samples are generally within the recommended limits for drinking water. Water with balanced ion concentrations (e ≤ 5%) is typically preferred for general health. Some specialty mineral waters may contain higher concentrations of specific ions for therapeutic purposes. To evaluate the potential health risks for adults in society, we calculated the annual effective dose from radiation exposure through the consumption of these water samples. The sources used in this study provide guidance on acceptable radiation levels in drinking water, aligning with low cancer risk thresholds to protect public health over a lifetime of exposure. The annual effective dose due to the ingestion of radionuclides in mineral water has been calculated and found to be within the recommended safety limits. In our study, we found that the mineral water samples contained approximately low-level radioactive isotopes, making them acceptable as good quality drinking water in terms of radioactivity. According to these findings, samples of bottled mineral water taken from the Moroccan market are radiologically safe and do not pose a serious risk to public health in Morocco.

Acknowledgements

This work has been carried out as part of the internal project“Radioanalytical Methods Development” of the National Centre for Nuclear Energy, Sciences and Technology.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

Not applicable in this section.

Data availability

All data generated or analyzed during this study are included in this published article.

Ethics approval and consent to participate

Not applicable in this section.

Consent for publication

Not applicable in this section.

Author statement

All authors certify that they have participated sufficiently in the work to take public responsibility for the content, furthermore; each author certifies that this material or similar material has not been and will not be submitted to or published in any other country.

References