No Safe Dose for Low Level Radiation
John William Gofman was a legend in the health aspects of radiation. They guy actually discovered three elements while an undergraduate, a bona fide radiation physics genius. He also graduated medical school, and established the Biomedical Research Division at the Lawrence Livermore National Laboratory, for the purpose of evaluating the health effects of all types of nuclear activities. This guy was working for the Atomic Energy Commission. He held three patents in nuclear work, published over 100 studies in journals, and authored four books on the health risks of radiation.
John died a few years back, but his work includes this effort to show the risks of low level radiation to the public. It will answer many questions on the subject.
Beir VII, the Cliff Notes Version
Beir VII stands for Biological Effects of Ionizing Radiation VII which is an update of the BEIR V report (NRC 1990) back in 1990. A large group of experts were commissioned to look into the health effects of low level radiation or low-dose, low linear energy transfer (LET). Since much of what we know about radiation is from the Hiroshima and Nagasaki survivors, more info becomes available as these survivors live out their years and sucumb to disease.
They took another look at the dosimetry at Hiroshima and Nagasaki and increased the certainty to the dose estimates and providing more confidence in the relationship between radiation exposure and the health effects observed in the survivors. New information available from radiation worker studies, medical radiation exposures, and groups with environmental exposures.
The cancer risk estimates have not changed much since the 1990 report, but they trust data more because of the increase in epidemiologic and biological info nowavailable.
The estimation of genetic (hereditary) effects of radiation has advanced. Human molecular biology has been incorporated into genetic risk estimation, and it’s now possible to project risks for genetic diseases .
Cellular and molecular biology have also added information on the process that cells respond to radiation-induced damage and to associations between DNA damage response and cancer.
The NRC found scientists and educators with expertise in ionizing radiation, while others were experienced in other fields. All members were chosen by looking at any conflict of interest.
The committee held 11 meetings over a period of 4.5 years. An array of experts in Cancer, NASA, University Professors, and doctors then wrote the report after much public commentry from the public, government experts, and experts in many fields.
TABLE 1 Units of Dose
Unita
Symbol
Conversion Factors
Becquerel (SI)= Bq= 1 disintegration/s = 2.7 × 10−11 Ci
Curie= Ci= 3.7 × 1010 disintegrations/s = 3.7 × 1010 Bq
Gray (SI)= Gy= 1 J/kg = 100 rads
Rad= rad= 0.01 Gy = 100 erg/g
Sievert (SI)= Sv= 1 J/kg = 100 rem
Rem= rem= 0.01 Sv
Ionizing radiation like X-rays or gamma rays is radiation that has enough energy to knock off electrons from molecules. Free electrons can then cause damage to cells. Nothing that makes the effects of man-made radiation different from the effects of naturally occurring radiation. Cancers that are caused by radiation exposure aren’t much different than cancers that occur from other causes.
Evidence suggests that exposure to high levels of ionizing radiation can cause illness or death. In addition to cancer, ionizing radiation at high doses caused mental retardation in the children of mothers exposed to radiation during pregnancy. Data from atomic bomb survivors suggest that high doses are also connected to heart disease and stroke.
Low-LET radiation deposits less energy in the cell along the radiation path and is considered less destructive per radiation track than high-LET radiation. Examples of low-LET radiation include X-rays and Gamma rays. Cancer, hereditary diseases, heart disease,and other effects are possible.
Clarence Dally became the first known radiation cancer victim in 1904. His boss, Thomas Edision, said “The x rays had affected poisonously my assistant, Mr. Dally”. These days, radiation is the most studied hazards to humans. Standards have become stricter over the years in an attempt to protect humans.
Low dose radiation are those doses in the range of zero up to 100 mSv (0.1 Sv) of low-LET radiation. The annual background exposure from natural sources of low-LET radiation is close to 1 mSv.
I will add to this blog as often as possible until the entire report has been covered. Please mark your spot as this article will grow.
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Sunday, July 13th, 2008 Page 3 of BEIR VII
We get some radiation from the ground, building materials, air, food, the universe, and even elements in our bodies. In the United States, the majority of exposure to background ionizing radiation comes from exposure to radon gas and its decay products. The National Research Council 1999 report, Health Effects of Exposure to Radon (BEIR VI), reported on the health effects of radon.
Annual exposures worldwide to natural radiation sources is between 1 and 10 mSv. Average is around 2.4 mSv, about one-half (1.2 mSv per year) comes from radon and its decay products. Average annual background exposures in the United States is (3.0 mSv) due to higher radon levels. Number two source of natural ionizing radiation exposure comes from cosmic rays, followed by terrestrial sources, and “internal” emissions.
“Internal” emissions come from radioactive isotopes in food and water . Exposures from eating and drinking are due in part to the uranium and thorium series of radioisotopes present in food and drinking water.
People worldwide are exposed to low-LET radiation in the range of 0.2–1.0 mSv, with the average being around .9 mSv. 82% of this radiation is from natual sources, 18% from manmade sources. Of the manmade sources, 79% comes from medical uses. Only 5% comes from work, fallout, and the nuclear fuel production and use. Traveling by aircraft adds 0.01 mSv for each 1000 miles traveled, being near a coal-fired power plant adds 0.0003 mSv), being close to X-ray luggage scanners adds 0.00002 mSv, and living within 50 miles of a nuclear power plant adds 0.00009 mSv.
Computed tomography (CT) as a way of screening for early signs of disease among asymptomatic adults. Estimated radiation dose and risks from such procedures, a single full-body scan results in a dose of 12 mSv. A typical mammogram has an dose of 0.13 mSv, almost 100 times less.
People who work at medical facilities, in mining or milling, or with nuclear weapons take steps to lower exposures to radiation. The maximum amount of radiation that workers are allowed to receive are 50 mSv per year . The exposure limits for a pregnant worker,are much lower.
About 210,000 military and civilian personnel were exposed to about 200 atmospheric weapons tests. Soldiers recived doses as low as 0.4 mSv and as high as 31 mSv. That would be from five chest X-rays to approximately 390 chest X-rays, one chest X-ray to be about 0.08 mSv.
Ionizing radiation can change the structure of molecules, including DNA. these changes are complex enough that the body’s repair mechanisms might not work perfectly. A very small fraction of imperfect repairs might result in cancer. Mutations could occur in the sperm and eggs, causing heritable disease. This has not been yet been detected in the survivors of Hiroshima and Nagasaki.
Sixty five percent of the surviors recieved less than 100 mSv, low dose ranges. That is about 40 times the average yearly background radiation exposure. But doses from 40 to 1600 times the average yearly background exposurewer thought to produce excess cancers ,above the levels expected in the population. In pregnant women,excess cancers can be detected at doses as low as 10 mSv. A linear relationship was found, more exposure resulted in more cancers.
Estimating Cancer Risk
BEIR VII developed risk models for estimating the relationship ionizing radiation and health effects. The linear no-threshold model (LNT) provided the best description of the relation between low-dose exposure to ionizing radiation and the incidence of cancers. At doses less than 40 times yearly background exposure (100 mSv), it is difficult to evaluate cancer risk. After looking over the data, the committee concluded that the risk would continue in a linear fashion at lower doses without a threshold, that the smallest dose has the potential to cause a small increase in risk to humans.
Approximately 42 people out of a 100 will develope cancer in their lifetime anyway, then add one more cancer per 100 exposed to a single exposure of LET 0.1 Sv radiation. Age at exposure and sex affects the risk, with females having more risk ,and kids exposed at young ages the most risk.
Approximately one individual per thousand would develop cancer from an exposure to 0.01 Sv. And one individual per hundred would be expected to develop cancer from a lifetime of exposure to natural background radiation not counting radon and other high-LET radiation. Risk estimates are uncertain, there could be a factor of two or three times smaller or larger might be possible.
Estimating Risks to Children of Parents Exposed to Ionizing Radiation
Hereditary diseases from mutations contribute to illness and death . Mutations occur in the DNA of the sperm and ova and can be transmitted to offspring and following generations. Studies on the children of A-bomb survivors looked for stillbirths, early neonatal deaths, congenital abnormalities, deaths among live-born infants over a period of about 26 years. Growth and development of the children, chromosomal abnormalities, and specific types of mutations were followed.
If three mutations occur spontaneously in 1 million people in one generation, six mutations will occur if the same people are exposed to 1 Sv of ionizing radiation, and three of these six mutations would be due to the radiation exposure. The studies showed that at the 400 mSv or less dose recieved, the genetic risks were very low. Other studies of the children of those exposed to high doses of radiation for radiotherapy of cancers have also shown little increase in genetic diseases. BEIR VII estimates that one would not expect to see an excess of adverse effects in a sample of about 30,000 children evaluated in Hiroshima and Nagasaki. One reason is that those infants that were still born or died early on could not pass on any defects.
BEIR VII looked at claims that low doses of radiation are more harmful than a LNT model of effects would suggest, then concluded that radiation health effects research as a whole does not support this view. In essence, the committee concludes that the higher the dose, the greater is the risk; the lower the dose, the lower is the likelihood of harm to human health. Any single track of ionizing radiation may cause cellular damage. However, if only one ionizing particle passes through a cell’s DNA, the chances of damage to the cell’s DNA are proportionately lower than if there are 10, 100, or 1000 such ionizing particles passing through it.
One theory is that cells do not necessarily have to be hit directly by a radiation track for the cell to be affected. Some say that hit cells communicate with nonhit cells by chemical signals or other means. “Bystander” cells may be affected, resulting in a greater effect at low doses than would be predicted by extrapolating the response at high doses. Others believe that the bystander cells just die.
Others claimed that radiation was actually good for humans, the so called Hormesis theory. BEIR VII rejected those claims saying that the preponderance of information shows some risk, even at low doses. Before coming to this conclusion, the committee looked at reports that advocated Hormesis, but the reports were found either to be based on ecologic studies or to cite findings not representative of the data.
Ecologic studies looked at regions, and have suggested that the incidence of cancer is much higher or lower than the numbers observed. But a closer look says that the risks of ionizing radiation at low doses, are a function of dose.
The main studies establishing the health effects Hiroshima and Nagasaki showed less than 100 mSv). The arguments for thresholds or beneficial health effects were not supported by the data. And studies of cancer in children following exposure in utero or in early life indicate that radiation-induced cancers can occur at low doses. The Oxford Survey of Childhood Cancer found that at a rate of 10 to 20 mSv, a 40 percent increase in the cancer rate among children up to 15 years old.
There is also support for the LNT view of how cancers form. Studies show that a single radiation track traversing the nucleus of an appropriate target cell has some small chance of damaging the DNA. Other findings, such as ionization spurs can cause multiple damage in a short length of DNA, making it difficult for the cell to repair or causing incorrect repair.
BEIR VII concluded that there is no evidence to indicate a dose threshold below which the risk of cancer is zero, but that the occurrence of radiation-induced cancers at low doses will be small. The committee maintains that other health effects like heart disease and stroke can occur at high radiation doses, but that more studies were needed to show any connection between low doses of radiation and noncancer health effects. Additionally, although health effects in children of exposed parents may not have been found, there is some proof that radiation-induced mutations in mice and other organisms have been found, so humans could be harmed.
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Page 10 of BEIR VII
Dr. Harley on Long Term and Low Level Ionizing Radiation
Some in the epidemiology field doubt that long term, low level ionizing radiation are harmful to humans. Some believe in “Hormesis”, a theory that radaition is good for you. In the following white paper, Professers Rudi H. Nussbaum and Wolfgang Köhnlein address the inconsistincies and open questions in the Hormesis theory.
It is a very readable paper, for its length.
Open questions and inconsistencies on health effects of low dose radiation
Another view on this subject is Dr. Walden’s article on Long term and low level effects of ionizing radiation.
Very readable and covers just about everything you would want to know about low level radiation.
