A STUDY OF RADON CONCENTRATIONS AND THE RADIATION DOSE LEVELS IN SALT SAMPLES EXTRACTED FROM SAMAWA SALTERN-IRAQ

* Abdulameer Kazem Farhood, Laith Mohamed Rasheed and Thill Akeel Kadhum. Department of Physics, College of Science, Al-Muthanna University, Samawa, Iraq. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

349 as radon exposure is concerned, Rn 222 is the most significant isotopes due to its longer half-life (3.82d) which is long enough for it to enter into indoor and cause an increase in the indoor concentration, but it is relatively too long to enter into the respiratory tracts and to irradiate the cells. The decay series which indicates the origins of Rn 222 is illustrated in Figure 1.
Because the salt is an important constituent of the foodstuff, and a large quantity of it is prepared for human consumption, whereas a lot of quantities go to different industries, it is therefore necessary to measure the radon concentrations in the environment of saltern area due to its health hazards and environmental pollution and is of concern with the control and minimization of such radiation exposure, as well as , such information can be used as the associated parameter values for radiological assessment [5].
However, a through literature search reveal that no studies on the radon concentration measurements in salt samples extracted in Iraq . Such lake was the main motive to conduct the current study in addition to meet the annual inhalation dose received by the salt extraction workers in the environment of surrounding saltern area.
Thus, the purpose of the present work is to measure the radon concentrations in salt samples extracted from Samawa saltern -south of Iraq using the active (RAD-7) technique which were not reported previously, and hence knowing about the intake exposure of salt extraction workers to alpha particles from radon and its decay product, and radioactive inhalation dose levels, with a view to establishing their radiological risk.

Samawa Saltern area:-
The Samawa saltern was located in Al-Muthanna Province 280 km south of Baghdad the capital of Iraq. it is situated at 20km to the southwest of Samawa city (The modern capital of the Al-Muthanna Governorate ). It is the oldest in Iraq which is discovered in 1986 and the salt production started in 1989. The latitude and longitude of the steady area is 31 0 19 -N and 45 0 17 -E , respectively, and at an altitude of (9m) above the sea level. The location map of Samawa saltern in the Al-Muthanna province is shown in Figure 2, and in the map of Iraq is shown in Figure 3. The Samawa saltern have been estimated to contain a total of 43 million tons of salt deposits and are the Iraq's first largest reservers of rock salt. The current annual production from the saltern is 200.000 tons. The Samawa saltern have 4 stories below the ground level. The total length of the middle canal is more than 6000m and the width of about 10m and depth of 5 to 7m in the center of the canal, covering an area of about 60,000m 2 .The salt of Samawa saltern is transparent, white, and rock salt is 98.74% pure NaCl.

Sample Collection and Processing:-
A total of thirty seven salt samples were collected from different locations of the Samawa saltern to represent the overall salt body. The samples were first drying in an electric oven (memmert type UNB200, Germany ) at 110 o C for 12 hours to ensure complete removed of moisture and cooled to room temperature. After that they were grounded into affine powder, and sieved by using 100 micron mesh to obtain homogenized particle size (uniform emanation of radon). About (70gm) from each sample were enclosed in a 250ml glass cylindrical can which was used as the radon accumulation chamber, and sealed for a period of 30days in order to get secular equilibrium between radium and radon.
A radon gas detector (RAD-7) was used to measure radon emanation from the salt samples. In this system, the above accumulation chamber is connected to the RAD-7 detector by vinyl tubing (Figure 3), with a gas drying unit filled with a desiccant CaSO 4 with 3% COCl 2 as an indicator between them, to maintain the relative humidity at less than 10% within the measurement system. The system is a closed loop in which the gas circulates continuously. The experiment was performed at a relative humidity of 10%, 18-25 o C, and normal room atmospheric pressure.

Radiological hazard:-
The radiological hazard in the Samawa saltern environment can be estimated as due to the exposure to radon daughters and the annual inhalation dose. The exposure to radon daughters in the Samawa saltern was calculated on the basis of the measured radon concentration using the following equation [6,7]: Where E R , is exposure to radon daughters in WLMy -1 , R c is the radon concentration in Bq/m 3 , (2.7 x 10 -4 ) is the factor for the conversion of radon concentration to the WL per Bq/m 3 , F is the indoor equilibrium factor ( = 0.4), n is the occupancy factor ( = 0.42). The annual inhalation dose from radon was calculated according to ICRP publication (1993) [8]: Where D is the annual inhalation dose (mSvy -1 ), R c is the radon concentration , K is the ICRP dose conversion factor (5mSv/WLM for occupational workers), and H, is the annual occupancy at the location (2160 hr for workers). The excess lifetime cancer risk (ELCR)due to radon exposure in the Samawa saltern was determined using the following equation [6]: Where E R , is the exposure to radon in WLMy -1 , T is the average lifetime expectancy, which is (70.4) years in Iraq as per WHO [9], and F R is the risk coefficient factor for exposure to radon in equilibrium with its daughters. Based on the recommendations of ICRP [10], the F R is taken as 5x10 -4 per WLM.

Results and Discussions:-
The concentrations of R n 222 measured with the RAD-7 varied from (7.2 Bq/m 3 ) to (52.3 Bq/m 3 ), with an average value of (24.99 Bq/m 3 ), which indicates low emission of radon by the salt samples. However, this average value of radon concentration is quite lower than that values measured in most of the buildings (houses, schools, hospitals, offices, universities…..etc) in Iraq [11,12,13]. Also, this indicates that there is no or very little radon or radon sources in the area of Samawa saltern. From the result (Table 1 ), it is noted that only one region (sample 16) located at the middle of main tunnel have high radon concentration (52.3 Bq/m 3 ) as shown in Figure 2. Figure 4 shows the histogram that represents the observed values. The high radon region it may be is composed of rocks contain uranium minerals in traces which yield radon or, this radon seems to have been brought in by the incoming water to the center of the middle tunnel as it the lowest region in it.
The low radon concentration region (samples 27, 29, 32, 33, 34, and 35) located at different positions in the saltern as indicated in table 1. The main reason for this low concentration is the non-existence of naturally occurring radioactive decay series in the salt samples. In general, the present measurement of radon indicate that radon level in the Samawa saltern were below the action level of (500-1500 Bq/m3 ) recommended by the International Commission on Radiological Protection (ICRP 1993) [14], and in the range of a reference level (100 Bq/m 3 ) proposed by the World Health Organization (WHO) [15] to minimize health hazards due to indoor radon exposure.
The exposure to radon daughters (E R ) was calculated by applying Eqn. (1). It is calculated from radon concentrations in different salt samples extracted from different region in Samawa saltern, and the results are given in Table (1). The (E R ) varied from (0.017) to (0.122) WLMy -1 with an average value of (0.058) WLMy -1 . The average value of exposure rate to radon daughters (0.058 WLMy-1 ) is much lower than the values reported from other salt mines in the world [7], and according to USA law, an mine workers should not be exposed to a radiation exceeding (4WLMy -1 ) [7].
The annual inhalation dose due to Rn 222 in salt samples was calculated using Eqn. (2) and it was found to varies from (0.124 mSvy -1 ) to (0.898 mSvy -1 ) with an average value of (0.429 mSvy -1 ). The results are presented in Table  (1) and Figures 5. The average of annual inhalation dose observed in this study was less than the average of the world wide inhalation dose. According to UNSCEAR report (2000), the permissible worldwide average of annual inhalation exposure of radon in salt mines is ( 1.15 mSvy -1 ). Also, it is lower than the typical range of annual inhalation exposure of radon in the world salt mines of (0.20 -10.00 mSvy -1 ) [7], and the world range in other mines ( excluding uranium ) of ( 0.5 -7.00 mSvy -1 ) [7].
The excess lifetime cancer risk (ELCR) was calculated using Eqn. (3), and the results are given in Table (1). The (ELCR) due to Rn 222 progeny in the Samawa saltern varies from (0.06) to (0.43%) with an average of (0.21% ) which is less than the estimated lifetime cancer risk of (1.3%) due to a radon exposure of 148 Bq/m 3 , as recommended by EPA for the entire population [6].

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However, in the scope of the above results, the average of exposure to radon daughters and annual inhalation dose due to radon daughter is much lower than the values reported for other salt mines in the world as given in Table (2). The estimated average annual inhalation dose due to radon daughters for the present study, however, is well below the effective does of (20 mSvy -1 ) recommended by ICRP [16] due to radon in work place. As per the above results, the Samawa slattern and the salt extracted from it are very safe for the salt extraction workers and general public from radiological hazard point of view, and does not pose any kind of internal hazard to the consumers.

Conclusions:-
Using active method (radon alpha detector RAD-7), radon concentration levels have been measured in the salt samples extracted from Samawa salternsouth of Iraq. On the basis of the measured radon concentration, the exposure to radon daughters, annual inhalation dose and excessive lifetime cancer risk were estimated. The results of this study showed that the radon concentrations are low enough and below the permissible level as per recommendation of ICRP and UNSCEAR.
The average of the annual inhalation dose received by members of the salt extraction workers was found to be (0.429 mSvy -1 ) which gives an ELCR of (0.21%). Consequently, the estimated risk has no significant health hazard, and the studied salt samples are radiologically safe, as per international standards, and that harmful effects are not expected.
Howeve, The present study is the first at the national level (in Iraq ) to investigate radon (Rn 222 ) concentrations in salt samples extracted from Samawa saltern.