In high natural radiation background areas of the world, as, for example, Brazil, India, China, and Iran, the radiation levels experienced by the local inhabitants are similar to or above the levels to which nuclear industry workers are exposed, as well as doses received by some residents of Three Mile Island.
Studying these populations directly may eschew the need to extrapolate or estimate risks from high doses to those receiving lower doses. If in fact there is a linear relationship between radiation dose and cancer induction, and, as some would have us believe, there is no safe dose, then in areas of high background levels, we should see high or increasing cancer rates, and in low background areas, low cancer rates.
Many areas of the world have natural backgrounds far in excess of those in Denver, the Mile High City, with 50 mrem (0.5 mSv), or in Leadville, Colorado, further up the Rocky Mountains, with 125 mrem (1.25 mSv). In most regions of the world natural backgrounds vary from 0.3 to 1.0 mSv, a variation by a factor of 3, but can exceed that by 10-100 times.
So, for example, the 33-mile-l ong coastal area of Kerala State, where the Indian subcontinent meets the Indian Ocean and the Arabian Sea, has natural deposits of monazite sands containing radioactive thorium. Kerala has been inhabited for over a thousand years, and its inhabitants have been inhaling and ingesting the alpha and beta particles and gamma rays emitted by the high levels of thorium all their lives—from infancy to adulthood to their dying days. Levels of total radiation have been measured at 70mGy per year, and on average they are more than 7 times the level monitored in interior areas.
Recently the Regional Cancer Center at Trivandrum studied the population for cancer prevalence, looking for the community's burden of cancer, but "found no evidence that cancer occurrence is consistently higher because of levels of external gamma radiation" . It is of interest to note that the investigators, using portable scintillometers, measured radiation levels in 66,306 houses. Following that, another team from the Cell Biology Division, Bhabha Atomic Research Center at Trombay, screened 36,805 newborn infants for congenital malformations and other pregnancy- and reproduction—related events. We are informed that "The stratification of newborns with malformations, still births, or twinning showed no correlation with the natural radiation levels in the different area. Thus no significant differences were observed in any of the reproductive parameters between the population groups based on the monitoring of 26,151 newborns from high-level natural radiation and 10,654 from the normal-level natural radiation areas of the Kerala coast" .
Another team from the Bhabha Atomic Research Center scrutinized lymphocytes of infants for chromosomal aberrations. In fact, this surveillance has been in place since 1986. During this time 10,230 infants have been screened for an array of abnormalities. Comparing 8493 infants from the coastal areas with 1737 infants from normal background areas, they found that "within the limitations of sample size, the frequencies of total autosomal and sex aneu-ploides as well as structural anomalies were comparable between the highlevel and natural radiation areas" .
Researchers of the Dental Wing, Medical College at Trivandrum, on the Malabar coast, concerned about the number of cases of oral submucus fibrosis (OSMF), a precancerous condition that they were seeing, studied the area. OSMF results in stiffening and thickening of the oral mucosa and deeper tissues, preventing the mouth from fully opening and causing protrusion of the tongue. This disorder is not uncommon in Southeast Asia, appearing to have a predisposition for the Indian ethnic group, and Kerala has a relatively high percentage of cases. The results of the investigation determined that there was "no significant difference between the observed prevalence of OSMF in the study and control populations." They noted, too, that "It appears highly improbable that the cases of OSMF encountered in the study area were induced by high background radiation alone. Our findings suggest that the observed prevalence of OSMF in the area sampled was on a par with that in other endemic areas; the high natural background radiation cannot be said to have a causal relationship with the disorder" .
Of additional interest is the fact that Trivandrum (also known as Thiruvanathapurum), on the ancient Malabar coast and port, as well as the entire coastal area of Kerala to the north, along with Tamil Nadu on the southeastern tip of the continent, sharing a common border with Kerala, have tourism as one of their main industries. Their light sandy beaches and aqua, crystal-clear balmy waters lapping at their shores, attracts thousands of tourists a year from around the world who also inhale and ingest thorium' s gamma rays with little, if any, apparent harm. As these studies multiply, a reevaluation of the effects of low-dose radiation exposure warrants consideration.
Researchers from the U.S. National Cancer Institute and the People's Republic of China conducted a study in the industrial city of Shenyang in the northeast of China that is reported to have the world's highest rates of lung cancer in women. Alpha-track radon detectors were placed in homes of 308 women with newly diagnosed lung cancer, while another 356 detectors were placed in homes of randomly selected female "controls." The median house hold level of radon was 2.3 picocuries per liter of air (pCi/L). Twenty percent of homes had levels greater than 4 pCi/L. After a year of monitoring for radon, levels were no higher in homes of those women who had developed lung cancer than in homes of those who did not. They also found that lung cancer did not rise with increasing radon levels. These results, they indicate, suggest that dose-response exposure relationships may not be as steep as risk models have suggested . Here again, direct observation of exposed populations provides outcomes different from those predicted by extrapolation from high to low doses. Surely worthy of further consideration.
Yet another US/Chinese team investigated thyroid nodularity and chromosomal aberrations among 1001 women aged 50-65 in a high -natural-background area of southern China, where radiation levels are 3 times higher than normal backgrounds. Women in the high background areas were compared to 1005 women of the same age in normal areas. Here again, the results were the same. "Continuous exposure to low-level radiation throughout life is unlikely to appreciably increase the risk of thyroid cancer" .
With Mexico City, at 6700 feet above sea level and with some 20 million people; Quito, Equador, at 8500 feet and one million people; and La Paz, Bolivia at well over 11,000 feet and another million people; and with natural radiation backgrounds 3, 4.2, and 7.5 times higher than populations at sea level, there are no indications that such exposures to cosmic radiation have caused radiation-induced cancers beyond normal expectations. What conclusions can be drawn from the panoply of studies of the world's diverse populations? One thing is certain—we live in a world of radiation. It is all around us, and from the many populations studied, it is reasonable to conclude that low-dose radiation, below a certain level, perhaps 60mSv and possibly higher, is safe. It is also reasonable to venture that many studies of low-dose radiation directly affecting diverse populations are at odds with the assumptions of a linear, no-threshold theory, that extrapolates from verifiable high-level radiation effects back linearly to low levels. In this no- t hreshold model, adverse effects are anticipated down to zero. The many direct studies show this to be an inappropriate use of the model. Nevertheless, governmental agencies prefer it. How this can be sustained in the face of data to the contrary remains a conundrum.
Of course, high doses of radiation can be harmful but are, as we have seen, exceptionally rare events. Our world, our environment, is a low-dose world, with no need to fear it. Why not determine your level? Figure 6.5 provides an opportunity to calculate the level of natural radiation in which you live. Why not fill it in.
It is also reasonable to wonder, then, whether additional studies are needed to convince a suspicious, fearful, and unaccepting public that support for radiation in the form of nuclear power as a means of generating much- needed electricity is entirely appropriate. However, given the level and type of information gathered over the past three decades that unequivocally shows low-l evel radiation to be safe, additional studies would be only more of the
Radon gas in our dwellings (average):
Cosmic radiation that reaches the earth:
Because cosmic radiation is modified by the atmosphere, add 1 for every 100 feet above sea level:
Pittsburgh is 1200 ft., so add 12 Denver is 5300 ft., so add 53 Atlanta is 1050 ft., so add 10 Chicago is 600 ft., so add 6 Coastal cities are at sea level so add 0
If your house is brick, concrete or stone add 7:
Ground radiation (US average):
Water, food, air radiation (US average):
Nuclear weapons testing fallout:
if you've had a chest x-ray this year add 9 for each one:
If you've had an intestinal x-ray add 210:
For each 1500 miles you've flown in a jet airplane during the year add 1:
If you live within 5 miles of a nuclear or coal-fired power plant add 0.3:
If you sleep with your spouse add 0.1: Your yearly total
Figure 6.5. Radiation is all around us as part of our natural environment. By completing this chart, you will obtain a realistic value of the amount of radiation you are exposed to annually. On average we are exposed to about 300 mrem per year. How much are you exposed to?
same. A change in attitude, if it is to occur, may have little to do with studies and proof of safety. There is good reason to believe that studies of radiation effects, no matter the number and how well done, are not the issue. Other, unrelated issues are at work. We shall tackle this problem after visiting a nuclear power plant.
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