Calculation the Excess Life Time Lung Cancer Risk

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Abstract

In this work, radon concentrations were measured in 8 health centers of Al- Hay city in Wasit, Iraq in Desember 2019 using LR-115 type II solid state nuclear track detectors (SSNTDs). Also, we calculated the annual effective dose rate and the excess lifetime cancer risk in all healthy center under study. After 45 days exposure of detectors to radon in the health centers, the track densities in the etched detectors due to the emitted alpha from radon were measured and then converted to radon concentration values.

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The radon concentration in these healthy centers ranges from (183.47±22.93 to 17.15±2.14)Bq/m3 with an average of (100.483Bq/m3), which within the acceptable radon levels recommended by the International Commission on Radiological Protection (ICRP). The mean the excess lifetime cancer risk were found to be ranges from 0.6±0.1 to 14.3±1.8 with an average value of 5.319 per 105 persons. These values are within in the safe limits recommended by the international organizations.

Introduction

Uranium is widespread in nature and can be found at low levels in most rock and soil.

238U is a radionuclide which undergoes spontaneous decay chain through 226Ra which then decays into Radon(222Rn). The half-life of 222Rn is 3,82 day long enough for much of the gas to work its way out into the atmosphere. Soil and rocks under houses are ordinarily the principal contributors to indoor radon, which is typically four or five times more concentrated than radon outdoors, where greater air dilution occurs. Additional contributions to indoor radon come from outside air, building materials, and the use of water and natural gas.

Radon in indoor environment contributes more than one half to the collective effective dose received by human population from all sources of exposure.

Precisely out of 98% of average radiation dose received by man from natural sources, about 52% is due to breathing of radon, thoron and progeny present in dwellings. If radon gas is inhaled, the high energy alpha particles emitted by the decay products of 218Po and 214Po which are highly effective in damaging tissues and can cause lung cancer in human beings.

Abid, A. A., Mraity Hussien, A. A., Husain, A. A., (2017) measured the radon using SSNTD technique and the estimation of the excess life time cancer risk from radon exposure in some buildings of Kufa technical institute. Radon concentrations ranged from 38.4 to 77.2 Bq/m3, with a mean value of 50 Bq/m3.

Abood H. N., (2018) studied indoor radon levels and the associated effective dose rate determination at Al-Elaf distinguish secondary school for girls in the Basrah governorate. The value of concentration of radon ranges from 28 to 128 Bq/m3with an average value of 57 Bq/m3.

Rejah B. K.,(2018) studied radon and thoron concentrations and resultingdose in air of southeast Baghdad regions using LR-115 type II. The average radon and thoron concentrations were found to be 45.47 and 43.15 Bq/m3 respectively.

(Hashim A. K. and Nayif S. S., 2019) measured radon concentrations in the air of nineteen schools in Karbala city using the passive accumulative technique, which includes solid-state nuclear track detectors LR-115 type II and CN-85. Radon concentrations ranged from 13.140±4.11 Bq/m3 to 38.439±6.79 Bq/m3 and ranged from 13.842±2.35 Bq/m3 to 36.867±4.28 Bq/m3 with an average value(25.408±4.54 and 25.317±3.15) Bq/m3 in closed dosimeters for LR-115 and CN-85 detectors respectively.

Ahmed F. H. et al., )2019) studied indoor radon concentrations measurements for selected dwellings in Some Baghdad districts using DURRIDGE RAD7 detector. the radon concentrations were changed from 89 Bq/m3 (Hay Ur district) to 191 Bq/m3 (Al-Mansour district) with an average value of 123.3±24.3 Bq/m3.

The aim of this study is to measure the concentrations of radon in the air of eight health centers of Al- Hay city in Wasit, calculate the annual effective dose of radon as well as excess lifetime cancer risk due to inhalation of radon in the air by using SSNTDs technique LR-115. This survey will help in assess the safety of these buildings and take action to reduce the indoor radon levels in the health centers (if necessary).

Study Areas

Al- Hay city is one of the districts of Wasit governorate, located to the southeast 220 km from Baghdad, the capital of Iraq and 40 km south from Al-Kut. It is located on the banks of Al- Graff River, with location of latitude (32.166667°N), and longitude ( 46.05°E). The area of Al- Hay city is (2000 km2).

Materials and Methods

Experimental method for radon detection and measurements are based on alpha particle counting of radon. The plastic track detector (LR-115 type-II) red colored based on cellulose nitrate with a thickness of about 12 μm was used to record alpha tracks manufactured by Kodak Pathe, France[11]. This plastic track detector film of size 1cm×1cm was fixed at the bottom by double-sided cello-tape inside of the container (Fig,3). These plastics films were hung in the ceiling at distance 168cm above the floor. After the exposure period of 45 days, the detectors were etched for 90 minutes in 2.5 N NaOH solution maintained at 70°C. The etched detectors were washed with distilled water and finally dried in air and count the number of tracks by the track counting technique, which was performed using an optical microscope at the magnification of 400 x.

The measured signal of the etched track detectors is the integrated track density as follows:

ρ(Track/〖cm〗^2 )=(No.Track)/(Area of View)

here ρ (track/cm2) recorded on the detector, Radon 222Rn (CRn) in (Bq/m3) concentration was determined using the following the equations (i.e. 2, 3 and 4) [13,14]:

C(Bq/m^3 )=ρ/(K×t)

where C : 222Rn concentration within the seals-cup air above the detector in (Bq/m3), ρ : Track density of the detectors exposed to the samples under study, t : Exposure time (days) and K is the average value of the calibration factor of 222Rn in (Bq/m3 .day per tracks. cm2).

The calibration factor was obtained by exposing reference dosimeters for a period ranged from (5-30) day to Radium 226Ra (Radon source) of activity 3.3 kBq which was measured to be (0.0217± 0.0013) [(track.cm-2) per (Bq.d. m-3)]. The latter value is approximately similar to that reported in many previous works.

The expected annual effective doses were calculated using UNSCEAR, WHO model (2000, 2009):

AED(mSv/y)=C×H×F×D×T

Where,

H: is the occupancy factor (0.8)

F: is the equilibrium factor (0.4)

T: is the time that people spend indoors (7008 hour) [11]

D: is the dose conversion factor (9×10-6 m Sv/h per Bq/ m3).

The excess lifetime cancer risk (ELCR) per million persons per year (MPY) was calculated using formula in Ref .

ELCR=AED×DL×RF

Where, DL is the Duration of Life (70 y) and RF is the Risk Factor (0.055 Sv-1) recommended by the ICRP.

Results and Discussions

The measured concentrations of radon in 8 healthy centers at Al- Hay city in Wasit are given in Table 1. The values of radon concentration vary from 17.15±2.14 Bq/ to m3183.47±22.93 Bq/m3. The values have been found to agree with the permissible limit (200-300 Bq/m3) as recommended by International Commission of Radon Protection(ICPR). The higher value of radon concentration in Al- Towaisat health center (Doctor's room) coded as (A1) may be attributed to the building material and unventilated. In the locations coded as (B2, C1, D1, G3, H1 and H3) are unventilated because the windows are kept mostly closed in winter to conserve heat, but the radon concentration is less than the location coded as (A1) because the building material and the coating material(cement) contain higher uranium and radium whereas the average of radon concentrations in Al- Towaisat health center (103.65±28.53 Bq/m3) is highere than the radon concentrations average of other health centers.

The lower value of radon concentration in Al- Wahda health center (care room) coded as (B2) because it has good ventilation and the room volume is larger than the other rooms in the same health center(75 m3).

In Fayrouz hospital, the average of radon concentration (62.3±17.21 Bq/m3) whereas the units of hospital are very larg and has direct cross ventilation although the hospital is old built, established in 1966. In advisory unit (ground floor) coded as (F1) is the concentration of radon(94.88±11.86 Bq/m3) higher than the concentration of radon in children advisory unit(20.58±2.57Bq/m3) because radon is seven times heavier than air.

The health center in Saeed is a caravan, and radon concentrations are assumed to be low because there are no building materials that contribute to increasing radon concentrations. However, we noticed that the radon concentration in the care room and then the doctor's room is higher than the radon concentration in other rooms. Perhaps this is due to the presence of cracks in the ground in addition to lack of good ventilation.

Table 1: Results of Radon Concentrations

No.	Name of Health Center	Location	Sample Code	Radon Concentrations (Bq/m³)
1	Doctor's Room	Al-Towaisat	A1	183.47±22.93
2	Care Room	Al-Towaisat	A2	93.96±11.75
3	Immunization	Al-Towaisat	A3	89.16±11.15
4	The Laboratory	Al-Towaisat	A4	48.01±6.00
	Average	Al-Towaisat		103.65±28.53
5	Doctor's Room	Saeed	B1	72.02±9.00
6	Care Room	Saeed	B2	118.31±14.79
7	Immunization	Saeed	B3	26.29±3.29
8	The Laboratory	Saeed	B4	29.15±3.64
	Average	Saeed		61.44±21.64
9	Doctor's Room	Al-Wahda	C1	135.12±16.89
10	Care Room	Al-Wahda	C2	7.54±0.94
11	Immunization	Al-Wahda	C3	29.15±3.64
12	The Laboratory	Al-Wahda	C4	62.87±7.86
	Average	Al-Wahda		58.67±27.91
13	Doctor's Room	Al-Bashaer	D1	161.18±20.15
14	Care Room	Al-Bashaer	D2	17.15±2.14
15	Immunization	Al-Bashaer	D3	30.86±3.86
16	The Laboratory	Al-Bashaer	D4	27.43±3.43
	Average	Al-Bashaer		59.15±34.13
17	Doctor's Room	Al-Salam	E1	34.29±4.29
18	Care Room	Al-Salam	E2	51.44±6.43
19	Immunization	Al-Salam	E3	78.88±9.86
20	The Laboratory	Al-Salam	E4	35.44±4.43
	Average	Al-Salam		50.013±10.39
21	Advisory Unit	Fayrouz Hospital	F1	94.88±11.86
22	Children Advisory Unit	Fayrouz Hospital	F2	20.58±2.57
23	Emergency	Fayrouz Hospital	F3	85.73±10.72
24	The Laboratory	Fayrouz Hospital	F4	48.01±6.00
	Average	Fayrouz Hospital		62.3±17.21
25	Doctor's Room	Military District	G1	41.15±5.14
26	Care Room	Military District	G2	51.44±6.43
27	Immunization	Military District	G3	170.32±21.29
28	The Laboratory	Military District	G4	33.15±4.14

Table 2. shows the values of annual effective dose (DRn) and the excess lifetime cancer risk per million persons per year(ELCR). The annual effective dose of the study area vary from 0.15 mSv/y to 3.7 mSv/y with an average of 1.382 mSv/y. This average was lower than the permissible limits recommended by International Commission of Radon Protection(ICPR) which it is equal (3-10) mSv/y. According to ours estimations, Table 2 shows the radon induced lung cancer risk for all health centers in Al-Hay city was found and ranges from 0.6±0.1 to 14.3±1.8with an average value of 5.319 per 105 persons. In general, these estimates indicated that the health centers under study are characterized by low radon exposure dose, so the workers in those health centers are subject to relatively low risk factor for radon induced lung cancer.

Table 2: Results of Annual Effective Dose and Excess Lifetime Cancer Risk

No.	Sample Code	Annual Effective Dose (mSv/y)	Excess Lifetime Cancer Risk ×10^-3
1	A1	3.70±0.46	14.3±1.8
2	A2	1.90±0.24	7.3±0.9
3	A3	1.80±0.22	6.9±0.9
4	A4	0.97±0.12	3.7±0.5
5	B1	1.45±0.18	5.6±0.7
6	B2	2.39±0.30	9.2±1.1
7	B3	0.53±0.07	2.0±0.3
8	B4	0.59±0.07	2.3±0.3
9	C1	2.73±0.34	10.5±1.3
10	C2	0.15±0.02	0.6±0.1
11	C3	0.59±0.07	2.3±0.3
12	C4	1.27±0.16	4.9±0.6
13	D1	3.25±0.41	12.5±1.6
14	D2	0.35±0.04	1.3±0.2
15	D3	0.62±0.08	2.4±0.3
16	D4	0.55±0.07	2.1±0.3
17	E1	0.69±0.09	2.7±0.3
18	E2	1.04±0.13	4.0±0.5
19	E3	1.59±0.20	6.1±0.8
20	E4	0.72±0.09	2.8±0.3
21	F1	1.91±0.24	7.4±0.9
22	F2	0.42±0.05	1.6±0.2
23	F3	1.73±0.22	6.7±0.8
24	F4	0.97±0.12	3.7±0.5
25	G1	0.83±0.10	3.2±0.4
26	G2	1.04±0.13	4.0±0.5
27	G3	3.44±0.43	13.2±1.7
28	G4	0.67±0.08	2.6±0.3

Conclusion

The results of the study show that the radon levels in health centers of Al-Hay city in Wasit are lower than the permissible limit (200-300 Bq/m3). The average equals to (100.483) Bq/m3. It was within the permissible limit recommended by ICRP and there is no health risks. The building material, for example, cement, unventilation is found as the main sources of higher radon concentrations in addition to the presence of cracks in the ground. Ventilated health centers have lower radon concentrations than unventilated ones.