ALL FEMALE USERS OF RADIOACTIVE MATERIALS AT WPI MUST READ AND UNDERSTAND THE INFORMATION BELOW.
The NRC sets radiation dose limits for both radiation workers and members of the public in restricted areas. Members of the public have very low dose limits in comparison with those assigned to radiation workers. When a female worker becomes pregnant, however, a difficult regulatory problem is created. Should the dose limits for the mother (a radiation worker) or the dose limits for the fetus (a member of the public) be used. The short answer is that the woman has the right to choose.
The reason for lower dose limits is that the cells of a fetus replicate at a very high rate and therefore the possibility of doing damage to the cells is increased dramatically. Remember, it is more harmful to have a drink of alcohol than it is to get an x-ray of the chest.
Radiation workers at WPI rarely accumulate any dose at all to their whole body, however, we do concern ourselves with this issue. At WPI, we give the worker the choice of not working with radioactive material at all. If a student or other user of radioisotopes should become pregnant and wish to make that known, she may ask for someone else to do all work with radioisotopes. This will not be held against her.
It has been known since 1906 that cells are dividing very rapidly and are undifferentiated in their structure and function are generally more sensitive to radiation. In the embryo stage, cells meet both these criteria and thus would be expected to be highly sensitive to radiation. Furthermore, there is direct evidence that the embryo/fetus is radiosensitive. There is also evidence that it is especially sensitive to certain radiation effects during the first 2 to 3 months after conception when a woman may not be aware that she is pregnant.
Section 20.1207 of 10 CFR Part 20 places different radiation dose limits on workers who are minors than on adult workers. Workers under the age of 18 are limited to one-tenth of the adult radiation dose limits. This carries over to the fetus of pregnant worker and is discussed in section 20.1208 of 10 CFR Part 20.
The NRC's present limit on the radiation dose that can be received on the job is 5,000 millirems per year. Working minors (those under 18) are limited to a dose equal to one-tenth that of adults, 500 millirems per quarter.
Because of the sensitivity of the unborn child, the NRC specifies an effective dose equivalent limit of 500 millirems to an unborn child if the pregnancy has been declared by the mother.
PART 1: Effects on the Embryo/Fetus of Exposure to Radiation and Other Environmental Hazards
In order to decide whether to continue working while exposed to ionizing radiation during her pregnancy, a woman should understand the potential effects on an embryo/fetus, including those that may be produced by various environmental risks such as smoking and drinking. This will allow her to compare these risks with those produced by exposure to ionizing radiation.
Table 1 provides information on the potential effects resulting from exposure of an embryo/fetus to radiation and nonradiation risks. The second column gives the rate at which the effect is produced by natural causes in terms of the number per thousand cases. The fourth column gives the number of additional effects per thousand cases believed to be produced by exposure to the specified amount of the risk factor.
The following section discusses the studies from which the information in Table 1 was derived. The results of exposure of the embryo/fetus to the risk factors and the dependence on the amount of the exposure and explained.
1. Radiation Risks
1.1 Childhood Cancer
Numerous studies of radiation-induced childhood cancer have been performed, but a number of them are controversial. The National Academy of Science (NAS) BEIR report reevaluated the data from these studies and even reanalyzed the results. Some of the strongest support for a causal relationship is provided by twin data from an Oxford survey. For maternal radiation doses of 1,000 millirems, the excess number of deaths (above those occurring from natural causes) was found to be 0.6 death per thousand children.
1.2 Mental Retardation and Abnormal Smallness of the Head (Microcephaly)
Studies of Japanese children who were exposed while in the womb to the atomic bomb radiation at Hiroshima and Nagasaki have shown evidence of both small head size and mental retardation. Most of the children were exposed to radiation doses in the range of 1 to 50 rads. The importance of the most recent study lies in the fact that investigators were able to show that the gestational age (age of the embryo/fetus after conception) at the time the children were exposed was a critical factor. The approximate risk of small head size as a function of gestational age is shown in Table 1. For a radiation dose of 1,000 millirems at 4 to 7 weeks after conception, the excess cases of small head size was 5 per thousand; at 8 to 11 weeks, it was 9 per thousand.
In another study, the highest risk of mental retardation occurred during the 8 to 15 week period after conception. A recent EPA study has calculated that excess cases of mental retardation per live birth lie between 0.5 and 4 per thousand per rad.
1.3 Genetic Effects
Radiation induced genetic effects have not been observed to date in humans. The largest source of material for genetic studies involves the survivors of Hiroshima and Nagasaki, but the 77,000 births that occurred among the survivors showed no evidence of genetic effects. For doses received by the pregnant worker in the course of employment considered in this guide, the dose received by the embryo/fetus apparently would have a negligible effect on descendants.
2. Nonradiation Risks
A recent study involving the birth records of 130,000 children in the State of Washington indicates that the risk of death to the unborn child is related to the occupation of the mother. Workers in the mental industry, the chemical industry, medical technology, the wood industry, the textile industry, and the farms exhibited stillbirths or spontaneous abortions at a rate of 90 per thousand above that of workers in the control group, which consisted of workers in several other industries.
It has been recognized since ancient times that alcohol consumption had an effect on the unborn child. Carthaginian law forbade the consumption of wine on the wedding night so that a defective child might not be conceived. Recent studies have indicated that small amounts of alcohol consumption have only the minor effect of reducing the birth weight slightly, but when consumption increases to 2 to 4 drinks per day, a pattern of abnormalities called the fetal alcohol syndrome (FAS) begins to appear. This syndrome consists of reduced growth in the unborn child, faulty brain function, and abnormal facial features. There is a syndrome that has the same symptoms as full-blown FAS that occurs in children born to mothers who have not consumed alcohol. This naturally occurring syndrome occurs in about 1 to 2 cases per thousand.
For mothers who consume 2 to 4 drinks per day, the excess occurrences number about 100 per thousand; and for those who consume more than 4 drinks per day, excess occurrences number 200 per thousand. The most sensitive period for this effect of alcohol appears to be the first few weeks after conception, before the mother-to-be realizes she is pregnant. Also, 17% or 170 per thousand of the embryo/fetuses of chronic alcoholics develop FAS and die before birth. FAS was first identified in 1973 in the United States where less than full-blown effects of the syndrome are now referred to as fetal alcohol effects (FAE).
Smoking during pregnancy causes reduced birth weights in babies amounting to 5 to 9 ounces on the average. In addition, there is an increased risk of 5 infant deaths per thousand for mothers who smoke less than one pack per day and 10 infant deaths per thousand for mothers who smoke one or more packs per day.
Numerous other risks affect the embryo/fetus, only a few of which are touched upon here. Most people are familiar with the drug thalidomide (a sedative given to some pregnant women), which causes children to be born with missing limbs, and the more recent use of the drug diethylstilbestrol (DES), a synthetic estrogen given to some women to treat menstrual disorders, which produced vaginal cancers in the daughters born to women who took the drug. Living at high altitudes also gives rise to an increase in the number of low-birth-weight children born, while an increase in Down's Syndrome (mongolism) occurs in children born to mothers who are over 35 years of age. The rapid growth in the use of ultrasound in recent years has sparked an ongoing investigation into the risks of using ultrasound for diagnostic procedures.
PART 2: Pregnant Worker's Guide Possible Health Risks to Children of Women Who Are Exposed to Radiation During Pregnancy
During pregnancy, you should be aware of things in your surrounding or in your style of life that could affect your unborn child. For those of you who work in or visit areas designated as Restricted Areas (where access is controlled to protect individuals from being exposed to radiation and radioactive materials), it is desirable that you understand the biological risks of radiation to your unborn child.
Everyone is exposed daily to various kinds of radiation: heat, light, ultraviolet, microwave, ionizing, and so on. For the purpose of this guide, only ionizing radiation (such as x-rays, gamma rays, neutrons, and other high-speed atomic particles) is considered. Actually, everything is radioactive and all human activities involve exposure to radiation. People are exposed to different amounts of natural "background" ionizing radiation depending on where they live. Radon gas in homes is a problem of growing concern. Background radiation comes from three sources:
|Effect||Number Occurring from Natural Causes||Risk Factor||Excess Occurrences from Risk Factor|
|Cancer death in children||1.4 per thousand||Radiation dose of 1000 millirems
received before birth
|0.6 per thousand|
|Effect||Number Occurring from Natural Causes||Radiation dose of 1000 millirads
received during specific periods
|Excess Occurrences from Risk Factor|
|Small head size||40 per thousand||4-7 weeks after conception||5 per thousand|
|Small head size||40 per thousand||8-11 weeks after conception||9 per thousand|
|Mental retardation||4 per thousand||Radiation dose of 1000 millirads
received 8 to 15 weeks after
|4 per thousand|
|Effect||Number Occurring from Natural Causes||Occupation||Excess Occurrences from Risk Factor|
|Stillbirth or spontaneous
|200 per thousand||Work in high risk occupations||90 per thousand|
|Effect||Number Occurring from Natural Causes||Alcohol Consumption||Excess Occurrences from Risk Factor|
|Fetal alcohol syndrome||1 to 2 per thousand||2-4 drinks per day||100 per thousand|
|Fetal alcohol syndrome||1 to 2 per thousand||More than 4 drinks per day||200 per thousand|
|Fetal alcohol syndrome||1 to 2 per thousand||Chronic alcohol (more than 10 drinks per day)||350 per thousand|
|Perinatal infant death
(around the time of birth)
|23 per thousand||Chronic alcoholic (more than
10 drinks per day
|170 per thousand|
|Effect||Number Occurring from Natural Causes||Smoking||Excess Occurrences from Risk Factor|
|Perinatal infant death||23 per thousand||Less than 1 pack per day||5 per thousand|
|Perinatal infant death||23 per thousand||One pack or more per day||10 per thousand|
|Average Annual Dose|
|Terrestrial - radiation from soil
|Cosmic - radiation from outer
|Radioactivity normally found
within the human body
|Dosage range (geographic and
|75 to 5,000 millirem|
The first two of these sources expose the body from the outside, and the last one exposes it from the inside. the average person is thus exposed to a total dose of about 125 millirems per year from natural background radiation.
In addition to exposure from normal background radiation, medical procedures may contribute to the dose people receive. The following table lists the average doses received by the bone marrow (the blood-forming cells) from different medical applications.
|X-Ray Procedure||Average Dose|
|Normal chest examination||10 millirem|
|Normal dental examination||10 millirem|
|Rib cage examination||140 millirem|
|Gall bladder examination||170 millirem|
|Barium enema examination||500 millirem|
|Pelvic examination||600 millirem|
NRC regulations and guidance are based on the conservative assumption that any amount of radiation, no matter how small, can have a harmful effect on an adult, child, or unborn child. This assumption is said to be conservative because there are no data showing ill effects from small doses; The National Academy of Sciences recently expressed "uncertainty as to whether a dose of say, 1 rad would have any effect at all." Since it is known that the unborn child is more sensitive to radiation than adults, particularly during certain stages of development, the NRC has established a special dose limit for unborn children. Also, since this dose limit could result in job discrimination for women of childbearing age and perhaps in the invasion of privacy (if pregnancy tests were required), the NRC has taken the position that the special protection of the unborn child should be voluntary and should be based on decisions made by workers and employers who are well informed about the risks involved.
For the NRC position to be effective, it is important that both the employee and the employer understand the risk to the unborn child from radiation received as a result of the occupational exposure of the mother. This document tries to explain the risk as clearly as possible and to compare it with other risks to the unborn child during pregnancy. It is hoped this will help pregnant employees balance the risk to the unborn child against the benefits of employment to decide if the risk is worth taking. This document also discusses methods of keeping the dose, and therefore the risk, to the unborn child as low as is reasonably achievable.
Radiation Dose Limits
The NRC's present limit on the radiation dose that can be received on the job is 5,000 millirems per year. Working minors (those under 18) are limited to a dose equal to one-tenth that of adults, 500 millirems per year. For women who choose to declare their pregnancy a dose limit of 500 millirem for the entire period of pregnancy is used.
Advice for Employee and Employer
Although the risks to the unborn child are small under normal working conditions, it is still advisable to limit the radiation dose from occupational exposure to no more than 500 millirems for the total pregnancy. Employee and employer should work together decide the best method for accomplishing this goal. Some methods that might be used include reducing the time spent in radiation areas, wearing some shielding over the abdominal area, and keeping an extra distance from radiation sources when possible. The employer or health physicist will be able to estimate the probable dose to the unborn child during the normal nine-month pregnancy period and to inform the employee of the amount. If the predicted dose exceeds 500 millirems, the employee and employer should work out schedules or procedures to limit the dose t the 500-millirem recommended limit.
It is important that the employee inform the employer of her condition as soon as she realizes she is pregnant if the dose to the unborn child is to be minimized.
This document has been directed primarily toward a discussion of radiation doses received from sources outside the body. Workers should also be aware that there is a risk of radioactive material entering the body in workplaces where unsealed radioactive material is used. Nuclear medicine clinics, laboratories, and certain manufacturers use radioactive material in bulk form, often as a liquid or a gas. A list of the commonly used materials and safety precautions for each is beyond the scope of this document, but certain general precautions might include the following:
- Do not smoke, eat, drink, or apply cosmetics around radioactive material.
- Do not pipette solutions by mouth.
- Use disposable gloves while handling radioactive material when feasible.
- Wash hands after working around radioactive material.
- Wear lab coats or other protective clothing whenever there is a possibility of spills.
Remember that the employer is required to have demonstrated that it will have safe procedures and practices before the NRC issues it a license to use radioactive material. Workers are urged to follow established procedures and consult the employer's radiation safety officer or health physicist whenever problems or questions arise.