OCCURRENCE OF LUNG CANCER : A POSSIBILITY OF RADIATION HORMESIS

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1 OCCURRENCE OF LUNG CANCER : A POSSIBILITY OF RADIATION HORMESIS DR. K.KANT 1, DR. R.P.CHAUHAN 2 AND DR. S.K.CHAKARVARTI 3 1. Department of Physics, K.L.M.D.N.College, Faridabad (Haryana) , India. 2. Department of Physics, I.G.N.College, Ladwa (Kurukshetra) Haryana , India. 3. Dept.of Applied Physics, National Institute of Technology, Kurukshetra , India. ABSTRACT Through various epidemiological studies, researches and investigations, it is established that exposure to 222 Rn in mines has caused excess lung cancer in several group of miners. Substantial controversy, however, exists regarding the health effects of exposure to low level alpha radiation emitted from radon in dwellings and general environment. The exposure response to miners is generally linear (Lubin et ai. 1997). Not withstanding this, there are several epidemiological and experimental evidences where average radon levels are high, and in all of these cases lung cancer rates are well below average i.e., there is a negative correlation between radon level and lung cancer (Cohen 1995 and 1997). In this paper, a comprehensive study and critical analysis of the available literature, data and reports has been carried out so as to reach some definite conclusion. As a support to the finding that a negative correlation between radon level and lung cancer exists, the results of a limited study of radon levels and lung cancer incidences in Haryana are also presented. KEYWORDS: Radon, Lung cancer, Hormesis, Health INTRODUCTION The potential effect of ionizing radiation on human population has been a concern to the scientific community and the public at large, for a long time. The study of health effects of exposure to low-level-exposure to alpha radiation emitted from radon in dwellings and general environment has received continuing attention as the radon has been found to be a ubiquitous indoor radioactive air pollutant to which all persons are exposed (Cole 1993; Proctor 1995). In the published literature, data and reports regarding the health effects of low-level-exposure to alpha radiation emitted from radon there are two schools of thought. First one favours the linear no-threshold (LNT) hypothesis and states that exposure to alpha radiation emitted from radon is potentially harmful, no matter how small be its level. The exposure to alpha radiation emitted from radon poses grave health hazards not only to uranium miners but also to people living in normal houses, buildings and work place like coalfields, thermal. power plants etc. (Schaeffner et al. 2001; Lubin et al. 1997). The second school of thought (Hormesis Hypothesis) believes that such a low-levelexposure to alpha radiation emitted from radon may not be harmful after all or may even have beneficial effects i.e., low-level-exposure to alpha radiation emitted from radon can stimulate repair mechanisms which mitigate the ef fect of subsequent high exposures leading to a decrease in the lung cancer incidences. Both schools quote 3 8

2 epidemiological studied on human beings as well as the laboratory research using experimental animals. This paper is focusing on various epidemiological studies carried out at international level that relates, to low-level-exposure to alpha radiation emitted from radon and its progeny. RADIATION HORMESIS Hormesis may be defined to be natural response, probably homeostatic, evoked in an organism by low levels of insult that would be lethal or seriously incapacitating at high level exposures. Radiation Hormesis is the stimulatory or beneficial effect of low doses of ionizing radiation. The term refers to a process whereby low doses of ionizing radiation may result in beneficial or stimulatory effects. The underlying property is a physiological effect that cannot be anticipated by linear downward extrapolation from the toxic levels of exposure (KoppenoI1989; Sagan 1987). NEGATIVE CORRELAT ION BET WEEN RADON AND LUNG CANCER: Epidemiological Evidence - [Hofman 1986] has reported two adjacent, equally populated, well matched areas of Guangdong Province, People s Republic of China, which have average radon levels of 70.3 Bq/m3 and 29.6 Bq/m3 but the lung cancer rate in the high Rn area is only 85 (f: 26)% of that in the low Rn area. - In a study of Cumberland County, PA, average indoor Rn level of 340 Bq/m3 was reported, whereas the white female lung cancer rate in was below average, 5.4 (:to.65)xl0-5/y vs. the national average of 6.2xl0-5/y [Cohen 1987]. - In a national survey of 101 universities in U.S.A., the RRs for lung cancer for 10 universities with highest average radon levels, plotted as a function of average radon concentration are shown in fig. 1. This shows that the RR for two universities having highest radon levels (226 Bq/m3 and 170 Bq/m3) is 0.55 and 0.51, respectively i.e., the observed lung cancer rates are much lower than the expected lung cancer rates. It indicates the protective effect of radon in the range ( ) Bq/m3. As the average radon concentration for the counties of other universities decreases, the RR value fluctuates about 1 with an exception at radon level of 111 Bq/m3 where the value ofrr is The average RR for all the 10 counties is If there were a significant correlation between radon level and lung cancer, all the ratios would have been greater than 1. - In a study in the U.S., it has been reported that the three states (Colorado, North Dakota, and Iowa) with the highest mean radon levels showed a lung cancer death rate of 41 per 105, as compared to a rate of 66 per 105 in the three lowest radon level states (Delaware, Louisiana, and California) (Yalow 1990). - The epidemiological study in the United States, Sweden, Finland, India and China with increased radon concentrations upto 12 pci/i as well as those areas below the average radon concentration of 1 pci/i, have all demonstrated a negative correlation of lung cancer with radon concentration (Fremlin 1989). - In 1992, an extensive National Survey of radon in homes by University of Pittsburgh based upon 2,72,000 measurements in the homes of 1217 counties was completed. In this study [Cohen 1994] found that lung cancer rates decreased with an increase in radon levels. Various confounding factors were corrected for in this study. In an earlier study based upon data for 965 counties, - Negative correlation between radon level and age adj usted overall cancer death rate; and lung and bronchus cancer deaths in Rockey Mountain States (RM.S.) and Gulf Coast States (G.C.S.) has 3 9

3 been reported [Jagger 1998]. An analysis of the data from (ACS 1998) reveals that i) The natural background radiation in RM.S. is 3.2 times that in G.C.S., but the overall cancer death rate in G.C.S. is 1.26 times more than that for the RM.S. ii) The average radon level in the RM.S. is 5.2 times that in the G.C.S., but the lung and bronchus cancer death rate in G.C.S. is 1.45 times more than in RM.S. iii) It shows a negative correlation (a potentially protective effect) of cancer mortality with natural radiation levels. All these reports and studies mentioned above advocate in favour of the non-linearity of the dose- response curve, Besides, these observations also speak in favour of protective effect of radon i,e, a negative correlation between radon and lung cancer for the concentration range Bq/m3 (typical range values changing with the place, environment and other factors), PRESENT STUDY In order to ascertain as to the validity and the support of what has been reported as above, we carried out a study in the Haryana State of India. The indoor radon levels in various district headquarters were measured using track etch technique (LR-115, Type-II Solid State Nuclear Track Detectors) and the lung cancer data was collected from the regional cancer hospital, Rohtak. The average radon levels, average annual population and lung cancer prevalence per million population per year in each district were calculated. A correlation study between radon levels and lung cancer prevalence rate reveals that there is a negative correlation. The results also support the above observations. EXPERIMENTAL 100 days in bare mode (Fig. 2). The exposed detectors were etched in 2.5 NaOH solution at 60 0 C for one and half- hour. The tracks were counted using an optical Olympus microscope using CCTV camera and a monitor at magnification 600 X. The tracks formed on LR-115 plastic track detector are shown in fig. 3. Calibration factor used was, 0.02 track/cm2 /day = 1 Bqm-3 (Kant et al. 2001). RESULT AND DISCUSSION The average radon levels, average annual population and lung cancer prevalence per million population per year in each district are shown in the table 1. The variation in the lung cancer incidence/106 population vs radon level in various districts of Haryana (five year follow up, ) is as shown in fig. 4A. In order to establish a systematic correlation between radon level and lung cancer incidence, we found that the best fitting curve equation was a polynomial equation (linear quadratic equation) of two degrees i.e., y = x X (1) By comparing it with the linear quadratic mathematical model with general equation (Bailer and Oris 1997) y =a o + a l X + a 2 x (2), where y is the lung cancer incidence, and x is the radon level, ao, al and a2 are the fitting parameters, we find here in the present case a o = , a l = and a 2 = The theoretical curve (B), obtained after fitting the various parameters for different values of radon levels, is shown in fig. 4. The epidemiological study in the Haryana State with higher radon concentrations has demonstrated a negative correlation of lung cancer with radon concentration. LR-115 type-ii detectors were exposed for 4 0

4 Table 1: Average radon concentration, annual population and annual lung cancer prevalence rate per million population in various districts of Haryana, India. (Five year follow up) Districtin Average Radon Average Average Annual Haryana Level(r) Population* Lung Cancer Prevalence Bq/m3 Rate/10 6 Kurukshetra Ambala # 0 Jhajjar Panchkula # 0 Sirsa Fatehabad Jind Kaithal Bhiwani Population Rohtak Karnal Hisar Sonipat Mahender Garh Gurgaon Rewari Yamuna Nagar Panipat Faridabad *Source: Census ofindia-2001, Provisional Population Totals, Series-7, Directorate of Census Operations, Haryana. # No lung cancer cases were reported and registered (five years follow up). From the linear quadratic equation (1) so obtained, the following information is obtained: i) Below radon level 80 Bq/m3, the value of y - the lung cancer incidence/106 population is -ve. It clearly supports the thesis of hormesis, i.e. the low levels of radiation are not harmful, may be even stimulatory or beneficial. ii) The value of y increases with the increase in radon level above 80 Bq/m3 and becomes maximum at radon level of 191 Bq/m3. iii) As the radon level further increases, the prevalence of lung cancer decreases and again becomes zero at radon level of303 Bq/m3. CONCLUSION Analysis of a number of statistically significant epidemiological studies of population exposed to alpha radiation emitted from radon demonstrates a negative correlation between radon levels and lung cancer incidences. In our study also, there appears to be so for radon levels in the range Bq/m3. From the findings of epidemiological studies, the most reasonable conclusion is that the levels of environmental radon in United States are either too low to be a significant cause of lung cancer mortality, or that, at these low doses, there is a non-linearity of the dose- response curve, or even hormesis (beneficial or stimulatory effects of low doses of ionizing radiation). ACKNOWLEDGEMENTS The authors thank all those who have helped in making this study a success particularly Dr. G.S. 4 1

5 Sharma, Reader, Dept. of Physics, B.S.A.College, Mathura (U.P.) and Dr. Hooda, Dept. of Radiotherapy, Regional Cancer Hospital, Rohtak. REFERENCES American Cancer Society. In: Landis, S.H. et al. (eds.) Cancer Statistics, CA Cancer J. Clin., 1998, 48, 6. Bailer, A.J. and Oris, J.T. Estimating inhibition concentrations for different responses scales using generalized linear models, Environ. Toxicol. Chem., 1997, 16, Cohen, B.L. and Colditz, G.A. Test of the linear no-threshold theory for lung cancer induced by exposure to radon, Environmental Res., 1994, 64, Cohen, B.L. A national survey of radon in homes and correlation factor, Health Phys., 1986, 51,2-10. Cohen, B.L. and Nason, R. Indoor radon levels in Cumberland County, PA, Env. Int., 1987, 57, Cohen, B.L. Test of the linear no-threshold theory of radiation carcinogenesis for inhaled radon decay products, Health Phys., 1995, 68, Cohen, B.L. Lung cancer rate vs mean radon level in US counties of various characteristics, Health Phys., 1997, 72, Cole, L.A. Elements of risk: The politics of radon, Washington, D.C.: AAAS Press, Fremlin, J.H. Power Production-What are the Risk? 2nd Ed., Adam Hilger, Bristol, UK, Hofmann, W, Katz, Rand Chunxiang, Z. Lung cancer risk at low dose of alpha particles, Health Phys., 1986, 51, Jagger, J. Natural background radiation and cancer death in Rocky Mountains States and Gulf Coast States, Health Phys., 1998, 75, Koppenol, W.H. and Bounds P.L. Hormesis, Science, 1989, 245, 311. Kant, K., Chauhan, R.P., Sharma, G.S. and Chakarvarti, S.K. Radon induced radiological impact of coal, fly ash and cement samples, Ind. J. Pure and Appl. Phys., 2001, 39, Lubin, J.H. and Boice, J.D. Lung cancer risk from residential radon: meta- analysis of eight epidemiological studies, J. Natl. Cancer Inst., 1997, 89, Proctor, R.N. Cancer wars. How politics shapes what we know and don t know about cancer, New York.. Basic Books, Sagan, L.A. What is horrnesis and why haven t we heard about it before?, Health Phys., 1987, 52, Schaeffner, B.S., Miller, D.P., Wain, J.C. and Christiani, D.C. Use of asbestos exposure score and the presence of pleural and parenchymal abnormalities in a lung cancer case series, Int. J.Occup.Environ. Health, 2001, 7(1), Yalow, R.S. Concerns with low level ionizing radiation: Rational or phobia?, J. Nuc Med, 1990, 31, 17A-18A, 26A. 4 2