Radon Levels and Its Hazard on Human Due to Ingestion of Tap Water in Egypt

Radon levels and its hazard on human due to ingestion of tap water in Egypt

S. Harb (a), K. Salah El Din (a), A. Abbady (a), and Khaled Ali (a)

(a) Physics department, Faculty of Science, South Valley University,83523 Qena, Egypt

Tel: +2-01229457353, fax: +2-0965213383

Abstract

Radon levels in drinking tap water, Egypt, have been determined in 97 sample using ionization chamber Alpha GUARD PQ2000PRO. Data analyzes was performed, and the values of 222Rn activity concentrations were found in the range between 0.006±0.00051 and 0.117±0.002 Bq/l. the correlations between radon activity concentrations and the water geochemical parameters (Total dissolved salts and conductivity) were studied. The effect of the desalination processes inside the water stations on radon levels was examined. According to ICRP and WHO standards, the hazard on human due to ingestion of tap water in the study zone was estimated by calculating the annual effective doses for different age groups, which the values were found in the safe area for all.

Key Words: Radon, Tap water, Alpha GUARD, Effective doses

1Introduction

Natural water contains dissolved radon from the uranium series present in soil and rocks [1]. The occurrence of radon in ground and surface water can be reasonably related to the uranium contents of the bedrocks and it can easily enter into the interacting water by the effect of litho static pressure [2]. 222Rn in water can get released to indoor air when used in showers, humidifiers, clothes washers, dish washers, cooking and so on. Exposure to water borne 222Rn may occur by ingestion (drinking water containing 222Rn) and by inhalation (breathing radon gas, which has been released from household water). Both mechanisms pose potential health hazards [3], [4], [5]. Ingestion of water containing dissolved radon results in a radiation dose to the body from the radon gas and the radon daughters in the water. The main part of ingested radon is eliminated from the body very rapidly through the lungs [6]. Exposure to indoor radon and its progeny is believed to be associated with a potential health risk of lung cancer [7]. Estimation of potential health risk of lung cancer shows that the average life time probability of cancer induction from exposure to 222Rn in drinking water greatly exceeds that imposed by any other natural or anthropogenic environmental contaminant. Tap waters are considered the main sources of potable water in Egypt, so radon levels measurements and its hazard on human are very important. 222Rn activity concentrations in 97 tap water sample from Qena zone, were measured to (1) estimate the occurrence of radon gas in this samples, (2) study the correlations between radon concentrations and the geochemical parameters (TDS and Conductivity) in tap water, (3) evaluate the radiation hazard on human due to ingestion of tap water in the study zone, and (4) study the effects of the chemical treatments processes on the radon levels in the river Nile water.

2Materials and methods

Ionization chamber Alpha GUARD PQ2000PRO along with the additional special equipment “Aqua KIT” was used for determining radon activity concentrations in the studied samples, figure 1. It is based on exhaling 222Rn to avoid volume by continuous bubbling of air through the sample. The exhaled radon is then transferred in a closed circuit to a moderated radon gas pulse ionization chamber, for alpha spectrometric measurements, through filters removing radon daughters. The set-up consists of two vessels “security and degassing”, progeny filter, Alpha GUARD, and Alpha Pump. Before any measuring process, the system is flushed with normal air until 222Rn values are reached to the range of room air radon level. At each samples site, the tap was opened, and the water was allowed to run for at least 20 minutes, in order to ensure that the water not delayed in the pipes, the sample taken directly and slowly to the degassing vessel with volume 500 ml in the Aqua KIT measuring system to avoid diffusion of radon from the water into the air. The Alpha Pump was switched on with the flow rate0.3 liter/minute for 10 minutes, so 222Rn activity concentration in Bq/m3will be recorded every 10 minute. All drops would deposit in the security vessel if they had got into the gas cycle during the degassing process. Through this way, the stress of the water vapor was minimized for the radon monitor. After 10 minutes the pump was switched off and the Alpha GUARD remained switched on for another 20 min, so the radon measurement was continued. This cycle was repeated three times in order to obtain a better precision [8]. 222Rn activity concentrations were estimated using Expert-VEW software, for analyzes the alpha spectra. Determination of radon levels in the water samples is based on the concentration indicated on the radon monitor. E.g. this measuring value is not yet the 222Rn activity concentration in the measured sample because the radon driven out has been diluted by the air within the measurement set-up and a small part of the radon remains diluted in the watery phase. For quantifying the dilution effect the exact interior volume in the measurement set-up (Vsystem) is required. The quantity of radon remaining in the sample can be determined by the introduction of the distributing coefficient K, which describes the temperature dependent quantity of the sample which remains chemically dissolved. Thus the general approach as presented in the followed equation for the determination of the 222Rn concentration in the measured water sample is valid:

Where Cwater = 222Rn (Bq/l) in water sample, Cair = the indicated 222Rn (Bq/m³) by Alpha GUARD, C0 = 222Rn (Bq/m³) in the measuring set-up before sampling (zero level), Vsystem = interior volume (ml) of the measurement set-up, Vsample = volume (ml) of the water sample, K = Radon distribution coefficient [9].

K = 0.105 + 0.405 e -0.0502T [10]

Figure 1 measuring system

3Results and discussion

3.1Radon Concentration

The obtained results of radon levels in the investigated water samples in duration of few months are listed in table 1.The values of 222Rn activity concentrations in drinking tap water, Egypt were ranged between 0.006±0.00051 and 0.117±0.002 Bq/l, with an average value of 0.049±0.003 Bq/l. the concentrations in 57% of investigated samples were fluctuated between 0.045 and 0.065 Bq/l, whereas 19% of the samples were found in values less than 0.045 Bq/l, and 24% of the samples were found in values more than 0.065 Bq/l, as shown in figure 2.

Table 1 222Rn activity concentrations (Bq/l) in tap water samples

Figure 2 222Rn activity concentration ranges in the samples

The low levels of radon concentrations in the obtained results are attribute to the fact that, the river Nile is considered the main source of tap water in Egypt, after passing many analyzing processes, this give a chance to escape 222Rn from water, in addition, the open water sources contains very little dissolved radium, so we rarely find radon in significant concentrations in surface waters, due to its rapid dispersal into the atmosphere. Table 2 summarized the values of 222Rn activity concentrations in the present survey with the other published data in different countries.

Table 2 222Rn activity concentration of tap water in the present investigation with other published data in different countries

3.2222Rn concentrations with the geochemical parameters

Total dissolved salts (TDS) and conductivity values were measured for some samples using portable Jenway Model 4520 Laboratory TDS and conductivity meter. In order to study the correlation between TDS and conductivity values with 222Rn activity concentrations in tap water samples, it is noted that, there is no obviously correlations were observed in matching with the other published result in the same point [17].

3.3The effect of the chemicals treatment processes on radon levels for river Nile water

A set of samples have been compiled from the company of drinking water and sanitation facilities at El-Himadat in the city of Qena (20 sample), directly from the river Nile before entering to the chemicals treatment process inside the station, and also the same samples were collected in the same time after graduating from the treatment process in during more than month. The obtained values of 222Rn activity concentrations in this set of samples are shown in table 3, and presented in figure 3. It is noted that, in all measured samples the values of 222Rn activity concentrations for the samples before the chemical treatment are higher than those values ​​obtained from the samples after the treatment process.

table 3 222Rn activity concentrations (Bq/l) in drinking tap water samples before and after the chemical treatment process

Figure 3 222Rn activity concentrations (Bq/l) in drinking tap water samples before and after the chemical treatment process

3.4Assessment of the annual effective doses

Based on measured radionuclide activity concentrations in water and habitual consumption rate, the human health risk from irradiation due to direct ingestion can be assessed. A method to assess the annual radiological dose for a person drinking water that contains a certain level of radioactivity was applied according the equation [18]:

Eff = K×C×G

Where Eff is the annual effective dose (Sv/y), C is the radionuclide activity concentration in water (Bq/l), G is the volume of water ingested annually per liter "consumption rates", and K is the effective dose equivalent conversion factor (Sv/Bq). The annual effective doses were estimated by considering a consumption rate and the conversion factors reported by ICRP, as shown in table 4.

table 4 Consumption rates and the conversion factors [19]

The annual effective dose for different age groups, infants, children, and adults due to intake of 222Rn in tap water were calculated and listed in the table 5.

table 5 Annual effective doses for different age groups due to ingestion of 222Rn in drinking tap water, Egypt

The obtained values of the annual effective dose of tap water due to ingestion of 222Rn were ranged between 0.031 to 0.588, 0.043 to 0.823 and 0.064 to 1.235, with averages values of 0.246, 0.345 and 0.517 µSv/y, for adults, children and infants, respectively. The annual effective doses for the different age groups "adults, children, and infants" are presented in figure 4. It is noted that, the received doses due to the ingestion of 222Rn in drinking tap water by infants are higher than that received by children and adults. According to the recommended reference level of 0.26, 0.2 and 0.1 mSv/y for effective dose for infants, children and adults respectively, published by IAEA [20], from one year consumption of drinking water, it is noted that the obtained doses due to ingestion of 222Rn in drinking tap water are less than the recommended reference level, consequently, Egypt drinking tap waters are acceptable for life-long human consumption.

Figure 4 The annual effective doses for different age groups due to ingession of 222Rn in drinking tap water for some samples

4Conclusion

The obtainedresults of radon activity concentrations for Egypt tap water were found in low levels. Table 6 shows the statistical parameters of 222Rn activity concentrations in the investigated tap water samples.A set of drinking water samples have been compiled before and after the chemicals treatment process, it is noted that, the desalination presses for drinking water have appositive effect in radon levels. On the other hand no reasonable correlations between 222Rn activity concentrations in drinking tap water with the water geochemical parameters (conductivity and TDS) were observed. Considering 222Rn activity concentrations in drinking tap water and habitual consumption, the human health risk from irradiation due to direct ingestion of tap water was assessed. It’s observed that doses received by infants are higher than that received by children and adults. According to the recommended reference level for the annual effective dose, published by IAEA [20] and WHO [21] from one year consumption of drinking water. The obtained doses are lower than this recommended reference level, and consequently, we recommended that, the tap waterin Egypt is acceptable as drinking water for life-long human consumption.

Table 6 The statistical parameters of 222Rn activity concentrations in tap water

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