Excess lifetime cancer risk due to natural background radiations of soil in North Kashmir

Correspondence Dr. Mudasir Ashraf, Ph.D Research Officer, Department of Radiological Physics and Bio-engineering, SKIMS, Srinagar Email: mudasirashraf8@gmail.com Background: Long term exposure to environmental radioactivity and the associated external exposure due to gamma emitting radionuclides have serious health effects particularly on cancer risk. Of course, the soil radioactivity depends on the underlying rocks and consequently, the soil type and the geographic conditions. Objectives: Evaluation of excess life time cancer risk due to natural radioactivity of the soil of surface layer of the Nichahoma lignite belt and the soil of villages surrounding the lignite belt. 226 232 40 Methods: In this particular study, stirring radionuclides of the Ra , Th , and K present in the soil samples of the lignite belt and soil of the villages surrounding the lignite belt were measured by using a low-background Pb-shielded gamma spectroscopic counting assembly utilizing NaI(Tl) detector for the measurement and to evaluation the radiation hazard indices and excess life time cancer risk. -3 -3 -3 -3 Results: The excess life time cancer ranged from 0.65×10 to 0.71× 10 (average ~0.68×10 ) for the soil of the lignite belt and from 1.15×10 to -3 -3 1.34×10 (average ~1.25×10 ) for the soil of the villages surrounding the belt. The correlation analyses, performed between the radium equivalent activity and excess life time cancer risk for the two types of the sample, showed very strong and linear dependence of excess life time cancer risk on radium equivalent activity and measured dose rate for the soil of the lignite belt compared to the soil of the villages surrounding the lignite belt. Conclusion: Compared to world average, the average value of computed excess life time cancer risk for both the categories of investigated samples in the study was found to be higher than 0.29. JMS 2018: 21 (2):101-108 Keyword: Excess life time cancer risk, measured dose rate, radium equivalent activity, correlation analysis, lignite belt. INTRODUCTION Ionizing radiations were discovered by Wilhelm Conrad Roentgen in 1895, and their diagnostic applications were quickly found. The first radiation induced skin cancer was identified in 1902 and the first radiation caused leukemia case found by1911.Various such cases of radiation-induced cancer were found and described over the ensuing decades, radon induced lung cancer in underground metal miners in Eastern Europe, and osteogenic sarcoma in radium dial painters. By1944, based on more formal epidemiological inquiry, an excess of leukemia was reported among [1] radiologists in the United States. By Second World War, there was sufficient understanding of the risks of radiation to motivate a program of protection for workers at the [2] Manhattan Project in the United States. The characteristic evidence of the carcinogenic nature of ionizing radiations comes from a variety of sources like prolonged and ongoing studies on exposed human populations (Atomic bomb survivors), medical use of ionizing radiation and occupational sources such as Uranium miners, Radium [3] painters. Life originated on the planet, Earth and moved through a regular procession in aradiation field that was more powerful than now. Natural radioactivity is prevalent in the earth's environment and they exist in a variety of physical, biological and environmental formations such as rocks, earth crust, plants, water and air. The concentrations and associated external radiation doses to the general public in different environmental matrices depend on the geology and geographical conditions of such environmental processes, due to weathering, rainfall of a place and other environmental processes, radionuclides in different environmental matrices such as soil and rocks may build up in the sediments and dissolve into drinking water, air we Journal of Medical Sciences 2018; 21(2):101-108 101 breathe, thus lead to human exposure which in turn produce biological damage of the human tissue. The pathways of human exposure include: uptake from tainted water through roots of the plants and trees, inhalation of soil dust, and direct exposure from primitive radionuclides in the indoor and outdoor environments, etc. Research on environmental natural radiations have received universal awareness and lead to widespread study in numerous countries like Spain, Turkey, Nigeria, Malaysia, Iran, and Botswana. The absorbed dose rate in air depends principally on the radionuclide content in the soil, as the largest part of the gamma radiation from the terrestrial and the extra-terrestrial [4, 5] radiations. Radiation induced cancer may appear only several years after the radiation exposure. This is time period between the radiation exposure and the manifestation of cancer is called as Latent period, which may lengthen from 10 to 30 years. The risk of causing a particular type of cancer is measured by comparing the number of cancers produced in the irradiated population sample in excess of those expected in the same size of the un-irradiated population sample. Leukemia has the highest risk factor among all cancers, since tissue cells are rapidly dividing. The excess lifetime cancer risk is the likelihood that an individual will develop [6] cancer over his/her lifetime of exposure. Our preceding [6, 7] monographs by Mudasir Ashraf et al. looked at the radiological health assessment due to gamma radiation levels of natural radioactivity of soil in the vicinity of Nichahoma lignite belt, Kashmir Valley and evaluation of excess life time cancer risk due to natural radioactivity of the Lignite samples of the Nichahoma, lignite belt, North Kashmir, India. This particular study was aimed to focus on the excess life time cancer risk due to natural radioactivity of the soil of surface layer of the Nichahoma lignite belt and the soil of villages surrounding the lignite belt.


INTRODUCTION
Ionizing radiations were discovered by Wilhelm Conrad Roentgen in 1895, and their diagnostic applications were quickly found.The first radiation induced skin cancer was identified in 1902 and the first radiation caused leukemia case found by1911.Various such cases of radiation-induced cancer were found and described over the ensuing decades, radon induced lung cancer in underground metal miners in Eastern Europe, and osteogenic sarcoma in radium dial painters.By1944, based on more formal epidemiological inquiry, an excess of leukemia was reported among [1] radiologists in the United States.By Second World War, there was sufficient understanding of the risks of radiation to motivate a program of protection for workers at the [2] Manhattan Project in the United States.The characteristic evidence of the carcinogenic nature of ionizing radiations comes from a variety of sources like prolonged and ongoing studies on exposed human populations (Atomic bomb survivors), medical use of ionizing radiation and occupational sources such as Uranium miners, Radium [3] painters.
Life originated on the planet, Earth and moved through a regular procession in aradiation field that was more powerful than now.Natural radioactivity is prevalent in the earth's environment and they exist in a variety of physical, biological and environmental formations such as rocks, earth crust, plants, water and air.The concentrations and associated external radiation doses to the general public in different environmental matrices depend on the geology and geographical conditions of such environmental processes, due to weathering, rainfall of a place and other environmental processes, radionuclides in different environmental matrices such as soil and rocks may build up in the sediments and dissolve into drinking water, air we breathe, thus lead to human exposure which in turn produce biological damage of the human tissue.The pathways of human exposure include: uptake from tainted water through roots of the plants and trees, inhalation of soil dust, and direct exposure from primitive radionuclides in the indoor and outdoor environments, etc. Research on environmental natural radiations have received universal awareness and lead to widespread study in numerous countries like Spain, Turkey, Nigeria, Malaysia, Iran, and Botswana.The absorbed dose rate in air depends principally on the radionuclide content in the soil, as the largest part of the gamma radiation from the terrestrial and the extra-terrestrial [4,5] radiations.
Radiation induced cancer may appear only several years after the radiation exposure.This is time period between the radiation exposure and the manifestation of cancer is called as Latent period, which may lengthen from 10 to 30 years.The risk of causing a particular type of cancer is measured by comparing the number of cancers produced in the irradiated population sample in excess of those expected in the same size of the un-irradiated population sample.Leukemia has the highest risk factor among all cancers, since tissue cells are rapidly dividing.The excess lifetime cancer risk is the likelihood that an individual will develop [6] cancer over his/her lifetime of exposure.Our preceding [6,7] monographs by Mudasir Ashraf et al.
looked at the radiological health assessment due to gamma radiation levels of natural radioactivity of soil in the vicinity of Nichahoma lignite belt, Kashmir Valley and evaluation of excess life time cancer risk due to natural radioactivity of the Lignite samples of the Nichahoma, lignite belt, North Kashmir, India.This particular study was aimed to focus on the excess life time cancer risk due to natural radioactivity of the soil of surface layer of the Nichahoma lignite belt and the soil of villages surrounding the lignite belt.

Study area
The study region has quartz veins carrying sulphides of copper and iron with some oxide, carbonates and arsenides.The presence of gold and silver in traces is indicated in the quartz veins carrying sulphides of copper and iron in association with some oxides, carbonates and arsenides in Lolab area of Jammu and Kashmir region.The upper Cambrian region of Kupwara in the northwest Kashmir contains several thick bands of hard and siliceous recrystallised limestone, which is currently being mined and marked as "Kupwara Marble".The estimated lignite reserves at Nichahoma are found to be 80 million tons.This lignite occurs in a track which is around 80 km long and 16 km wide that has lignite showing rapid variation in thickness and quality.The geological survey of India proved 4.5 million tons reserves of lignite up to a depth of 36.5 min Nichahoma area.The Indian Bureau of Mines indicated proven reserves of 7.26 million tons.The quarriable reserves in Nichahoma area were estimated to be 5.26 [8] million tons.The geographic map of the study area is presented in Figure1.

Sample Collection
A total of twenty different samples were collected, the ten different soil samples from the surface of the lignite belt and ten soil samples of from the villages adjacent the lignite belt.After collection, the samples were placed in labeled polyethane bags then transferred to the laboratory for preparation and analysis.The collected samples were processed in accordance with the standard protocols available in the literature.The fundamental aim of the sample processing is to compose the sample look like the standard that was used for efficiency calibration.The sample had been prepared in a manner that the physical properties like dimensions, density and particle size and its distribution of the samples under investigation were similar to that of calibration standards.
The samples were pulverized, heated and dried out in an 0 oven at a temperature of 125 C for 24 hours so as to make them moisture free and sieved through a 2mm mesh.1000 g of samples were filled and sealed in leak-proof, air tight PVC merinelli beakers, weighed and stored for a time of four weeks to allow the samples to attain a state of secular equilibrium, where the rate of progeny becomes equal to 226 232 [6,7,9] that of the parent (Ra and Th ).

Activity Concentration Measurement
The radiometric analysis for the radioactivity 226 232 40 concentrations of Ra , Th , and K in the lignite samples collected from the Nichahoma, lignite belt was performed by using the gamma-ray spectrometer consisting of a NaI(Tl) detector (crystal size 40.0 mm x 60.0 mm) connected to 1024 channel multichannel analyser (MCA).Before measurement, the samples were pulverized, heated 0 and dried out in an oven at a temperature of 125 C for 24 hours so as to make them moisture and sieved through a 2mm mesh.1000 g of samples was filled and sealed in leakproof, air tight PVC merinelli beakers, weighed and stored for a period of four weeks to enable the samples to attain a state of secular equilibrium, where the rate of progeny 226 232 [10] becomes equal to that of the parent (Ra and Th ) and 137 60 the system is calibrated using Cs and Co radioactive sources produce γ-ray energies of 662 KeV,1173 KeV and 1332 KeV, respectively.Ac , 583.1 (86%) and 2614 KeV from Tl .Each sample was examined for 18000 seconds.The Activity concentrations in the soil samples were calculated [12,13,14] according to the following relation: ( Where C is the count rate of gamma rays, ε is the detectors efficiency of the specific γ-rays, P is the absolute transition

Absorbed dose rate in air
In order to evaluate any radiological hazard, the exposure due to terrestrial radiations arising from radionuclides present soil can be estimated in terms of several parameters.A direct association between radioactivity concentrations of natural radionuclides and their exposure rate is known as the absorbed dose in the air at 1 meter above the ground surface.

238
The average activity concentrations of Ra (of U series), Commission.UNSCEAR and the European Commissions have provided the dose conversion coefficients for the typical room centers.

External hazard index
In order to bound the radiation exposure character of natural radionuclides present in the investigated samples to -1 permissible dose equivalent limit of 1mSv.y , the H index ex based on a criteria have been incorporated by making use of [16,17] a model Krieger which is given by: To maintain the radiation hazard of no consequence, the value of H must not exceed the limit of one (unity).The ex maximum value of H equal to one corresponds to the upper ex -1 [7] limit of Ra 370 Bq.kg measured dimensions and eq calculated densities.

Radium equivalent activity
The radium equivalent activity, Ra , was incorporated to from the activity concentrations of U , Th , and K radionuclides in the studied soil samples.The calculated values of Ra were obtained by the help of the following eq [18,10] equation: Th , and 4810 Bq.kg of K produce an equal gamma ray dose rate.Radium equivalent activity is straight forwardly related to the external and internal gamma dose due to radon [13] and its progenies.

Annual effective dose equivalent
The annual effective dose equivalent E (AEDE) received T by persons was estimated from the computed values of absorbed dose rate by applying the dose rate conversion -1 factor of 0.7Sv.Gy ) and the occupancy factors of 0.2× (5∕24) and 0.8×(19∕24) for outdoors and indoors, [19] respectively.
The annual effective outdoor doses, D ; out the annual effective indoor doses, D ; and total annual in effective doses, D , were calculated according to the tot [20] following equation.

Excess lifetime cancer risk
It is a well-established fact that exposure ionizing radiations cause cancer in many diverse species of animals and in nearly all parts of the body.It is one of the few precisely established carcinogens in human beings, although it appears to be a relatively weak carcinogen compared to various chemical agents.The numerous years may go by between the radiation exposure and the manifestation of cancer.
The type of cancer that can be caused by exposure to radiation can also arise naturally (without increased exposure to radiation), but some occur more frequently as a result of exposure to radiations.For example, a higher percentage of small cell lung cancers occur in uranium miners as a result of exposure to alpha particle irradiation.
Organs differ in their sensitivity to the effects of radiation.
The thyroid gland and bone marrow are most sensitive to radiation, while the kidney, bladder, and ovary seem to be least affected.The cancer of blood forming cells (leukemia), a type of cancer that arises in the bone marrow; appear to be [20] the most common radiation induced cancer.
Radiation carcinogenesis is a most important stochastic effect, in human beings exposed occupationally to small doses of radiation.Human beings are always exposed to background radiation that arises both from natural and manmade sources.Natural radionuclides are omnipresent and when an ionizing radiation passes through a living tissue, it deposits energy in the tissue randomly and rapidly via excitation and ionization, in turn produces moving electrons.These electrons interact with atoms and molecules leading to chemical and molecular changes thereby altering the structure of the cells.These cells may be damaged directly by the radiation or indirectly by the free radicals (OH and H) produced in the adjacent cells.Many forms of damage could occur from radiation but the most vital is that done to the deoxyribonucleic acid (DNA).A break to the DNA results in gene mutation, chromosomal aberration, breakages or cell death, oncogenic transformation and acute radiation sickness.More frequently, repairs can take place.This however depends on the condition that the damage is not a lethal damage.If mend is not faultless, it may result in a genetically modified cell.When human cells in an organ or tissue are killed or prevented from reproducing and functioning normally, there will be loss of organ function.A modified germ cell for instance in the gonads of an individual may transmit incorrect hereditary information, which may cause severe hereditary effects.Exposure to ionizing radiation over extended period is known to result in non-lethal mutation, [23] which could increase the risk of cancer.There is a linear, no-threshold (LNT) association between radiation dose and the incidence of cancer.This dose-response hypothesis suggests that any increase in radiation dose, no matter how small, could results in an increase in cancer risk.Diseases caused by natural radiation exposure include lung cancer, pancreas, hepatic, skin, kidney cancers, cataracts, sterility, [24] atrophy of the kidney and Leukemia.
A radiation -induced cancer can grow from a single damaged cell autonomously of other damage cells in the tissue of interest.The period between radiation exposure and the recognition of cancer is known as the latent period and could be numerous years.Therefore, excess lifetime cancer risk is the chance that an individual will develop cancer over his/her lifetime of exposure.
The excess lifetime cancer risk (ELCR) values are [6,12] calculated using the equation.
Where D is the length of life (approximately 70 years), and R is the risk factor (Sv ), which reflects the fatal cancer risk F per Sievert.For Stochastic effects, ICRP 60 uses values of [25,26] 0.05 for the public.

232 40
The radioactivity concentration of Ra , Th , and K in soil samples of the lignite belt and in the soil of the villages surrounding the lignite belt are presented in the Tables 1&2   226  232 respectively.The Ra was distinctly higher than Th and mean values of Ra and Th are higher than the world 40 average.While as the average values of K was well below [13] the world average.The Ra activity a relevant quantity eq for when considering radiation risk to humans were estimated using the Equation ( 4) for all the soil samples and other radiological hazard indices determined are summarized in the Tables1&2.The gamma absorbed rate in air at a height of 1m above the ground due to concentrations 226 232 40 of Ra , Th and K in the soil of the lignite belt and soil of the villages surrounding the lignite belt, estimated by the using Equation ( 2), is presented in the respective tables.The external hazard index is also presented in the tables for both the types of the samples.
As shown in Tables 1 & 2, the excess life time cancer risk, determined for soil of the lignite belt and the soil of the the lignite belt and 1.15×10 to 1.34×10 with an average of -3 1.25×10 for the soil of the villages surrounding the belt.

DISCUSSION
The radionuclide concentrations for the two different classes of soil samples under investigation indicate and envisage the disagreement of geological formation for the area under study.Soils are considered as weathered byproducts of rock types and circulation of radioactive elements is enormously affected by natural processes like weathering, rainfall of a place and erosion.Soil radioactivity depends mainly on the types of rocks from which the soil originates.
The mean value of absorbed dose rate due to soil of the lignite belt and due soil of the villages surrounding the belt -1 are 39.5 and73.1 nGy.h respectively.The absorbed rate estimated from soil for the Indian sub-continent is about -1 [12] -1 [10] 69.0 nGy.h and the world average is 51.0 nGy.h .In the present study the average absorbed dose rate due soil of the villages surrounding the lignite belt is higher than the global value.The annual effective dose rate ranges from value of 0.09 mSv.y for the soil of villages surrounding the lignite belt respectively.The mean value annual effective dose rates for the soil of the villages surrounding the lignite -1 belt are higher than the value 0.07 mSv.y given by [13] UNSCEAR as the world wide representative value.
Radiation induced cancer being a stochastic effect may appear only some years after the irradiation and the likelihood of occurrence increases with increasing absorbed dose and there is no threshold.Radium being a solid radioactive element is chemically similar to calcium, and is absorbed from soil by plants and conceded up the food chain to humans.Microscopic quantities of radium in the environment can lead to some accumulation of radium in bone tissue whereby it degrades bone marrow and can mutate bone cells.Ingestion or body exposure to radium causes serious health effects which included sores, anemia, 226 238 bone cancer and other disorders.Ra is a product of U decay series.Emitted energy from the decay of radium causes vexed on the skin and produces many other detrimental effects.Radium is a naturally occurring radioactive metal moreover it is present in soil, sand, rock, water, plants and animals.Higher values of radium in sand contribute significantly in the enhancement of indoor radon [17] in dwellings.
Radium is one million times more radioactive than the same mass of uranium.Its decay occurs in at least seven stages, the following main products were called radium emanation recognized as radon.Radon is a heavy gas and the later products are solids.These products are themselves radioactive in nature.Radon is the first leading cause of lungs cancer among non smokers and second leading cause in smokers.
In order to find the dependence of excess life time cancer  higher than the world average of 0.29.Radiation induced cancer is probabilistic in nature and there is no threshold for it.Hence all doses carry some form of risk.Hence radiation induced cancer cannot be prevented, only can be reduced by minimizing the radiation dose.

CONCLUSION
The measurement of activity concentrations for primordial radionuclides in the soil of the lignite belt and the soil ofthe villages surrounding the lignite belt have been carried out by using a Pb-shielded NaI(Tl) gamma ray spectrometer in order to evaluate the associated radiological health hazards with an intention that this study will serve as the baseline data for carrying out the extensive research in the area.The activity concentrations of the soil of the villages surrounding the lignite belt reported in the table 2 shows higher value compared to the activity concentration of the soil of the lignite belt table     surrounding the belt are 39.5 and 73.1 nGyh respectively.
The average value of excess life time risk of cancer determined for both the soil types in the present study is [24] higher than the world average of 0.29.Further the correlation analyses performed between the radium equivalent activity and excess life time cancer risk for the two types of the sample show very strong and linear dependence of excess life time cancer risk on radium equivalent activity and measured dose rate for the soil of the lignite belt compared to the soil of the villages surrounding the lignite belt.

Figure 1 :
Figure 1: Simplified geological map of the area under study.

γ
probability of the γ-decay, M is the mass of the sample in s Kgs and T is the counting time in seconds obtained for the -1 measured radionuclides and are expressed in Bq.Kg per dry weight.
K (Bq.kg ) in soil samples are used to compute the absorbed dose rate given using the following relation provided by United Nations Scientific Committee on [ eq recognize the consistency to radiation exposure.The calculated values of Ra were usually used to evaluate the eq specific activity of materials containing diverse amounts of 238 232 40 activity concentrations U , Th , and K .Besides, Ra data eq can be used to assess the health hazard effects produced 238 232 40

1
. The radionuclide concentrations for the two different classes of soil samples under investigation indicate and envisage the disagreement of geological formation for the area under study.The 226 232 observed mean values of Ra , Th are greater than the 40 world average while as the average values of K is well below the world average.The mean value of absorbed dose rate due to soil of the lignite belt and due soil of the villages

Figure 2 :
Figure 2: Correlation between excess life time cancer risk and (a) radium equivalent activity and (b) measured dose for the soil of the villages surrounding the lignite belt.

Figure 3 :
Figure 3: Correlation between excess life time cancer and (a) activity and (b) measured dose for the soil of the lignite belt.

Table 1 .
The activity concentrations of the soil of the villages surrounding the lignite belt reported in the Table2shows higher value compared to the activity concentration of the

Table 1 :
Activity concentration of R 226 , Th 232 , K 40 , Radium equivalent activity, radiological hazard indices and excess life time cancer risk for the soil of lignite belt.

Table 2 :
Activity concentration of R 226 , Th 232 , K 40 , Radium equivalent activity, radiological hazard indices and excess life time cancer risk for the soil of villages surrounding the lignite belt.

Table 3 :
The average value of concentrations of the natural radionuclides in soil samples Bq. -1 on the activity concentration and the dependence of excess life time cancer risk with other radiological hazard indices, correlation analysis was performed between the Ra and excess life time cancer risk and measured dose rate eq and excess life time cancer risk Figures 2&3 for both types of the soil.A very strong correlation was observed between the Ra and excess lifetime cancer risk (r=1) and between eq measured dose rate and excess life time risk of cancer (r=1) for the soil of the lignite belt compared to the correlation between the Ra and excess life time cancer risk (r=0.73)eq and between measured dose rate and excess life time cancer risk (r=0.74) for the soil of the villages surrounding the lignite belt.The average value of excess life time risk of cancer determined for both the soil types is present study is risk