Radon, Radium, and Uranium Concentrations in the Blood of Cigarette-Smoking Women and Lung Cancer Risk

Radon and its daughters are of the natural radioactive decay of the uranium series. Exposure to radon gas leads to lung cancer, so the risks are significantly higher for smokers than for non-smokers. Therefore, the risk of radon increases for both active and passive smokers. The radioactivity of alpha particles emitted by radium 226, the main source of radon 222, has become harmful because its prevalence and inhalation increase with increased smoking. In this study, a CR-39 detector was used to measure radon, radium, and uranium concentrations and then calculate risk parameters in seven cigarette-smoking females in vitro study of human blood samples, and three normal females with no actual and passive cigarette smoking. The radon concentrations in blood samples varied from 147.36±0.08 Bq/kg to 659.92±0.04 Bq/kg with an average of 316.83±150.42 Bq/kg, the radium concentration varied from 13.55±0.27 Bq/kg to 60.70±0.13 Bq/kg with an average value 29.05±13.84 Bq/kg, and uranium concentration varies from 11.89±0.29 ppm to 53.23±0.14 ppm with an average value 25.47±12.13 ppm. The annual effective dose ranged from 4.42±0.48 to 12.57±0.28 mSv/y with average value of 8.35±3.10 mSv/y. The annual risk cases of lung cancer varied from 79.50±.0.11 to 226.26±0.07 with an average value of 150.22±55.78 per million people. The results deal with the radioactive effect of female cigarette smokers as a risk factor for lung cancer. Most of the results exceed the permissible international limits. Hence, human health and their life are at risk of radioactivity resulting from cigarette smoking that is concentrated in the blood of female smokers examined in this work.


Introduction
Radon-222 is a serious problem when inhaled. When cigarette smoke is present in the lung, the radon daughters are attached to the lung cells with radioactive particles causing lung function damage because of the increased alpha radiation [1]. The decay of naturally existing radium is regarded as a source from which radon is exhaled from the ground. Other radioactive elements in the earth, such as uranium, thorium, and potassium, emit alpha, beta, and gamma radiation [2]. Radon decays into several solid decay products, which achieve equilibrium within four days [3]. Most studies relate a significant association between radon exposure and lung cancer risk for its risk assessment. To investigate whether cigarette tobacco is a potential source of radon concentration in blood, the levels of radon, radium, and uranium from radioactive decay were measured in blood samples of ten cigarette-smoking women using CR-39 nuclear track detectors. When radon gas is inhaled into the lung, it travels to the rest of the body, where the blood is responsible for transporting it from the lung to the body's organs [4][5][6]. The high concentration of radon inhalation poses a great danger to human health and increases the incidence of lung cancer [7].
The aims of this study are to investigate the radon, radium, and uranium concentration levels, using CR-39 solid state nuclear track technique, in the blood of cigarette-smoking women. Also, to calculate the risk indices such as potential alpha energy concentration (PAEC), exposure to radon progeny (EP), annual effective dose (AED), and lung cancer cases per year per million person (CPPP) to reach conclusions regarding the hazardous effects of radioactivity on females due to cigarette smoking.

Materials and Methods
This study was conducted on seven selected cigarette-smoking females, whose age are 30-61 years old, as the donor group, and three non-smoking females as the control group of the age range 23-84 years. Ten millilitres of venous blood samples were drawn from donor and control subjects using a disposable syringe. The blood was transported into disposable test tubes containing an anticoagulant kind of sodium citrate (Partial-Thromboplastin-Time (PTT)). The tubes were labelled with a defined code. Subsequently, the blood samples were kept in an ice box (4°C) and then transferred to a laboratory for refrigeration until the start date of the analysis. The blood samples were transferred to a petri dish while keeping each code. Then they were placed in an electric oven (made in Germany, with serial number 412.2744 manufactured 2010) at a temperature of 70°C for 3 hours to dry, after which they were crushed in a melting pot (quartz crucible) and stored in sterilized plastic cans with dimensions of 7 cm height and 3.7 cm diameter. Each empty can was weighed before and after placing the powdered blood sample in it to know the weight of the sample. CR-39 detector with an area of 1 × 1 2 was pasted on the inside of the can cover. Then the can was tightly sealed with adhesive tape (type Para-film). The cans were left for two months. Alpha particles are received by the CR-39 detector after the decay of radon and its daughters. After the two months, the detectors were taken out and placed in NaOH solution with normality 6.25N and placed in a water bath at 60 °C for 5 hours to complete the etching process. The detectors were then taken out, rinsed with distilled water, and dried to be prepared for track reading under an optical microscope. The optical microscope (Pro.Way made in China) was equipped with a 5-megapixel camera developed with LED light instead of tungsten light, which has proven to be of high efficiency in terms of clarity of vision and track number [8,9]. It is able to give magnification by an objective (4X, 10X, 40X, and 100X) and two eyepieces (40X) to count the number of tracks. Ten images were taken for each detector to increase the accuracy of the readings; the number of tracks in each image was counted, averaged and divided by the reading vision area to obtain the track density.
The track density is the average number of total tracks per area of the field view of the ten images, is the exposure time 60 days, is the slope of the experimentally obtained calibration curve of CR-39 detector which was performed using 88 226 standard source with a half-life of 1600y and activity 1.3μCi (48100 Bq), which decay to radon 86 222 . This activity was corrected up to the measurement time. The CR-39 detector and the standard source of 88 226 were placed in a glass container. Thus, the radon activity within the container can be estimated after different exposure times of the detectors. Thus, the relationship between the track density of the standard source ρs (tracks/cm 2 ) and the radon exposure of the standard source Es (Bq.day/m 3 ) gives the calibration curve from which the slope (k) can be obtained, as shown in Figure 1.

Radon Concentration in Sample
The concentration of radon 86 222 in the studied female blood samples can be calculated according to the proposal given by Somogyi et al. [11], in terms of radon concentration in the air above the sample, which can be expressed as in the equation: is the decay constant for 86 222 (0.1814 −1 ), ℎ is the height above the blood surface up to the detector in cm., is the exposure time 60 days, is the thickness of the blood powder inside the can in cm.

Activity Concentration of Radon in Sample
The activity concentration of 86 222 , ( ), in the blood samples was estimated using Equation (3) [12]: (3) Where: is surface area of the sample (cm 2 ) and is the mass of the sample ( ).

Radium Concentration in Sample
The radium 88 226 concentration in the blood samples can be estimated in terms of radon concentration in the air inside the can as in Equation (4) [12]:

Radon Progeny Concentration
The estimation of the concentration of radon progeny 84 214 and 84 218 emitting alpha particles which were deposited on the walls of the can and on the face of the detector can be calculated using the following equations [13,14]: Where: is the radius of the can, is the critical angle (35°) of the CR-39 detector, and is the average range of alpha particles in the air (4.15 cm).

Uranium Concentration in Sample
Radon activity in the blood samples can be calculated in terms of radon concentration ( 3 ⁄ ) in the sample, as in Equation (7) [12]: Where: is the sample volume ( Where: is uranium decay constant (4.9 × 10 −18 / ). Therefore, uranium weight (g) in the sample is given by Equation (9) [16]: Where: is the mass number of 92 238 , is Avogadro's number. Therefore, the uranium concentration can be calculated from Equation (10):

Potential Alpha Energy Concentration
The daughters, 3700 is the working level conversion factor. However, most countries have professional guidelines for the effects of radon exposure from prolonged exposure to radon [17,18]. It can be calculated by Equation (11) [19,20]: Where: is the equilibrium factor = 0.4, as recommended by UNSCEAR [21].

Exposures to Radon Progeny
The exposures to radon progeny in terms of radon concentration is indicated in Equation (12)

Lung Cancer Cases
The number of lung cancer cases per year per million people , can be calculated using the following expression [21]:

Results and Discussion
In this work, CR-39 detector was used because it has good sensibility to register low energy alpha particles. Also, it possesses good stability to resist environmental variables sensitive to alpha particles [23]. The aim of this work is to find out if the concentration levels of radioactive elements present in the blood samples of cigarette-smoking women are in excess of the permissible levels in order to quit smoking or at least reduce it. (1.49±0.56 ⁄ ) is weakly related with recommended limit. The Uranium concentrations in the blood of cigarette-smoking females ranged from 11.89±0. 29 in 7FC sample to 53.23±0.14 in 4FC sample with an average value of 25.47±12. 13 . While the control group average value was 1.31±0.49 , which is higher than the recommended value 0.115 reported by ICRP [25]. The high concentration of uranium in the samples depends strongly on the concentration of radon in the samples and on the mass of the material, so this was observed in the increase in the concentration of uranium.  Figure 2 shows a comparison between the different concentrations of cigarette-smoking females with the control group concentrations. It can be seen that the variation of radon concentration in the blood samples depends mainly on the uranium concentration in the blood samples, which it decays to different radioactive elements including radon. Among individuals who never smoked, the statistically significant P value was <0.05 in the activity concentration of radon, in the selected female group.
The ICRP [25] recommended the permissible limit the of radon concentration to be 200-300 3 ⁄ , and that for uranium concentration 0.115 . While the US EPA [19] estimated that 26% of lung cancer deaths were radon-related. Because of the lognormal distribution of radon, the majority of radon-induced lung cancers for many countries occur below the radon action or reference levels adopted by that country [27]. Hence, this committee estimated that two-thirds of the radon-related deaths in the United States occur below the EPA's action level of 148 3 ⁄ .

Figure 2:
Comparisons of radon, radium, radon activity, and uranium concentrations for women smokers with normal group concentrations Table 2: displays the calculated values of potential alpha energy concentration (PAEC), exposure to radon progeny ( ), annual effective dose ( ), and lung cancer cases per year per million persons ( ). The maximum value of potential alpha energy concentration was 53.87±0.14 in the 5FC sample and the minimum value was 18.93±0.22 in the 7FC sample with an average value 35. 76 . The results were lower than the recommended value of 53.33 reported by the UNSCEAR committee [28], even that for the control group except for those in the 5FC sample which is slightly higher. The exposure values for radon progeny varied between 0.78±1.13 ⁄ in the 7FC sample and 2.22±0.67 ⁄ in the 5FC sample with an average value 1.47 ⁄ . All results were less than the recommended 1-2 ⁄ value reported by NCRP [29] except for the 4FC and 5FC samples which were 2.00±0.71 ⁄ and 2.22±0.67 , ⁄ respectively. When compared with the results obtained for the control group with that of cigarette-smoking females blood samples, the average exposure value for radon progeny was 0.10±0.03 ⁄ which is less than the recommended limit.  Figure 3 shows the relationship between percentages of dose absorbed and periods of cigarette smoking for female blood samples. It can be seen from the present results that the absorbed dose clearly depends on the smoking period. Hence, the absorbed dose ranged from 5% for the 7FC woman blood sample whose smoking period was four years, to 28% for the 5FC woman blood sample whose smoking period was 24 years. The annual effective dose depends on the smoking period, therefore when the period of smoking increases the annual effective dose also increases. Figure 4 confirms and clarifies a positive strong correlation coefficient between absorbed dose rate and the period of smoking to be 92.57%. While the correlation coefficient with the number of cigarettes smoking per day is less strong 65.99%, it showed a weak correlation with the age of cigarette-smoker women of 0.82%.
The lung cancer cases per year per million people in the blood for cigarette-smoking females varied between 79.50±.0.11 per million people in 7FC sample to 226.26±0.07 per million people in 5FC sample, with average value 150.22±55.78 per million people. The results in 1FC, 4FC, and 5FC samples exceed the permissible limit of 170 recommended by ICRP [30]. While the average control group value was 9.81±3.21 per million people. Not all control values exceeded this limit. Figure 5 shows that there is a strong correlation between lung cancer cases per million people with radon concentration.

Conclusions
Concentrations of radon, radium, and uranium in female blood are noteworthy because they give a significant indicator of smoking and lung cancer risk. This research found that the maximum concentration of radon in female blood samples was higher than the 200 3 ⁄ limit allowed by ICRP. The minimum concentration of radon was higher than the recommended limit of 148 3 ⁄ given by the Environmental Protection Agency and higher than the reported limit of 100 3 ⁄ given by WHO. From the results, it can be observed that the lung cancer cases varied with radon concentration; a significantly strong positive correlation was found. Hence, there is a close relationship between radon and cigarette smokers and its impact on increasing lung cancer rates. The distribution of radium and uranium concentrations also gave a similar strong correlation. The increase of the percentage of annual effective dose was noticeable with the increase of the period of smoking years poses clear with correlation 93%. While the correlation of the absorbed dose rate with the number of cigarette smoked per day was 0.66%. The results of this study will help women smokers whose rate of concentration of radioactive elements in their blood exceeded the permissible scientific limits to take one of two decisions either to quit or reduce smoking, to prevent the transportation of these harmful radiation elements into the human organs.