ATTACHMENT 2
PREGNANT WORKER'S GUIDE

POSSIBLE HEALTH RISKS TO THE FETUS OF WOMEN WHO ARE
EXPOSED TO RADIATION DURING PREGNANCY

During pregnancy, you should be aware of things in your surroundings or in your style of life that could affect your unborn fetus. For those of you who work with radioactive materials and/or radiation producing devices or who have access to such areas, it is desirable that you understand the biological risks of radiation to your unborn fetus.

Everyone is exposed daily to various kinds of radiation: heat, light, ultraviolet, microwave, ionizing, and so on. For the purposes of this guide, only ionizing radiation (such as x-rays, gamma rays, neutrons, and other high-speed atomic particles) is considered. Actually, 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 the four following sources:

The first two of these sources expose the body from the outside, and the last two exposes it from the inside. The average person is thus exposed to a total dose of about 294 millirem per year from natural background radiation.

In addition to exposure from normal background radiation, radiation exposure can result from man-made materials and devices. Some consumer products such as smoke detectors, static eliminators and building materials contain radioactive material. The following lists the average annual dose from man-made radiation.

Medical procedures may also 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.

In summary, the average person is exposed to radiation daily, receiving a radiation dose of approximately 360 mrem/year (3.6 mSv/year). A dose of about 294 millirem/year (2.94 mSv/year) is from natural background radiation, while medical radiation exposure and consumer products contribute the rest (Refs 4, 19, 20).

NUCLEAR REGULATORY COMMISSION POSITION

NRC and State 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 fetus. This assumption is said to be conservative because there are no data showing ill effects from small doses; the National Academy of Sciences has expressed "uncertainty as to whether a dose of, say, 1 rad would have any effect at all." As it is known that the unborn fetus is more sensitive to radiation than adults, particularly during certain stages of development, the NRC and State has established a special dose limit for protection of the unborn fetus. However, such a limit could result in job discrimination for women of child-bearing potential. The NRC has taken the position that special protection of the unborn fetus 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 fetus 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 fetus during pregnancy. It is hoped this will help pregnant employees balance the risk to the unborn fetus 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 fetus As Low As Reasonably Achievable (ALARA).

RADIATION EXPOSURE LIMITS

Since 1906, it has been known that rapidly dividing, undifferentiated cells are more sensitive to radiation. The embryo/fetus³ is composed of cells that meet these criteria and are more sensitive to radiation. In addition, scientific studies have shown that the embryo/fetus is more sensitive to radiation than the adult (particularly during the first 2-3 months after conception when a woman may not be aware that she is pregnant). Because of the sensitivity of the unborn fetus, the exposure to the unborn fetus of a "declared pregnant worker" shall be limited to 500 millirem (5 mSv) for the entire pregnancy (Refs 20, 25, 26); the guidance also recommends that substantial variations in the rate of exposure be avoided and efforts should be made to avoid exceeding 50 mrem per month to the pregnant worker.

ADVICE FOR EMPLOYEE

Although the risks to the unborn fetus are small under normal working conditions, it is still advisable to limit the radiation dose from occupational exposure to be ALARA, not to exceed 500 millirem (5 mSv) for the total pregnancy. The employee, Principle Investigator and Radiation Control Office should work together to decide the best method for minimizing exposure and accomplishing this goal. Some methods include reducing the time spent in radiation areas, wearing some shielding over the abdominal area, and maximizing the distance from radiation sources. The medical/health physicist will be able to estimate the probable dose to the unborn fetus during the normal nine month pregnancy period and to inform the employee of the amount. If the predicted dose exceeds 50 millirem (0.5 mSv) per month, work schedules or procedures shall be modified to limit the dose to the 500 millirem recommended limit. It is important that the employee inform her Principal Investigator and the Radiation Control Officer of her condition as soon as she realizes she is pregnant, so that the exposure to the unborn fetus can be minimized.

INTERNAL HAZARDS

This guidance has been directed primarily toward a discussion of radiation doses received from external sources. Workers must also be aware of the risk of radioactive material entering the body in working places where unsealed radioactive material is used. Nuclear medicine clinics, research laboratories, and certain manufacturers use radioactive material in bulk form, often as a liquid or a gas. General precautions include the following:

1. Do not smoke, eat, drink or apply cosmetics around radioactive material.
2. Do not pipette solutions by mouth.
3. Use disposable gloves while handling radioactive material.
4. Wash hands after working around radioactive material.
5. Wear lab coats or other protective clothing whenever there is a possibility of spills.

Remember that the Principal Investigator is required to have demonstrated that he/she will have safe procedures and practices before the Radiation Control Office will authorize their approval to use radioactive material under one of the University's radioactive material licenses. Workers are urged to follow established procedures and consult the Radiation Control Office or medical/health physicist whenever problems or questions arise.

RADIONUCLIDE CHARACTERISTICS

Biological data has been collected for a set of radionuclides which are expected to be of greatest significance for prenatal exposure in the work environment. These materials are: tritium, as gas and water; tritium and carbon in three typical organic forms--glucose, amino acid, and thymidine; and iodine.

TRITIUM

Trace amounts of inorganic tritium in gaseous form or when incorporated into water are readily absorbed from the lung or gastrointestinal (GI) tract. In air most tritium will form water, as will some small amount of that which is absorbed, so that little tritium actually enters the body as a gas. Physiologic studies demonstrate that water crosses the placenta in both directions. The percentage water content of the embryo and fetal tissues generally is measurable greater than that of the corresponding tissues in adults, so that their relative tritium concentrations may be slightly greater. For practical purposes, it may be assumed that the concentration of tritium in the conceptus is the same as that of the pregnant woman, and that it would be readily excreted in parallel with its loss from her body.

Tritium in the form of tritiated water is assumed to be uniformly distributed throughout the maternal and embryo/fetal soft tissues. It is assumed that tritiated water has a biological half-life of 10 days (Ref. 23).

ORGANICALLY BOUND TRITIUM AND CARBON

1. Glucose
    
   Glucose is actively transported from maternal to fetal blood across the placental layers and uterine blood. Fetal brain, liver, kidney and skeletal muscle are the major organs that utilize glucose, and the overall glucose utilization rate is higher in the fetus than in the pregnant female.
    
   Glycolysis of tritium-labeled glucose produces tritiated water, which then can exchange and distribute throughout the intracellular and extracellular water pools in both maternal and fetal compartments. A limited fraction of the tritiated water may subsequently become incorporated into lipid via lipogenesis, but this is sufficiently small that it can be ignored for dosimetry purposes. Catabolism of 14C-labeled glucose results in 14CO2 production in the fetus, but this does not accumulate in the fetus, rather it is randomly excreted to the mother via the placenta, and then exhaled. There are essentially no available concentration data for 3H-glucose or 14C-glucose applicable to radiation dosimetry (Ref. 23).
2. Amino Acids
    
   In general, the concentrations of free amino acids in fetal tissues are similar to those in maternal tissues. Significant amounts of labeled amino acids are incorporated in protein during organogenesis or the growth phases of gestation. Concentration concurrently would be reduced through dilution by further incorporation of amino acids during progressive growth, so that consistently major deviations from maternal concentration would not be expected (Ref. 23).
3. Thymidine
    
   Biological behavior of radiolabeled thymidine under conditions of accidental or environmental exposure is not clear. There does not appear to be any major differences between the metabolic behavior of 3H- or 14C-labeled thymidine and both precursors are incorporated into the DNA of proliferating cells. Only a fraction (10%) of that which enters the adult is incorporated; most of the remainder is catabolized rapidly and excreted. There is long-term retention of incorporated thymidine; it remains in the DNA until the cell divides, where it is partitioned between the daughter cells, and some may be re-utilized when the cell dies. The processes by which thymidine crosses the placenta have not been established (Ref. 23).

IODINE

The fetal thyroid begins to concentrate iodine at about 90 days of age and continues to accumulate iodine throughout gestation. Inorganic iodine in the blood readily crosses the placenta and is accessible to the embryo or fetus. Depending on which iodine radionuclides are involved, their decay schemes and half-lives, and whether exposure is chronic or acute, the thyroid concentration in the last months of pregnancy has been estimated to be as much as three to ninefold greater in the human fetus than in the adult.

The thyroid begins to secrete iodine shortly after it starts to concentrate iodine, and this secretion continues throughout gestation resulting in an organic iodine concentration of about 75% that in maternal blood. The concentrations of individual species of organic iodine (in particular triiodothyronine (T3) and thyroxine (T4) in fetal and maternal blood are not well correlated, which suggests that there is little, if any, placental transfer of organic iodine. Concentrations of T3 and T4 change abruptly at birth, and within about a week, reach values comparable to adults (Refs. 23, 24).

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¹Radiation dose in this document is described in three different units. The rad is a measue of the amount of energy absorbed in a certain amount of material (100 ergs per gram). Equal amounts of energy absorbed from different types of radiation my lead to different biological effects. The rem is a unit that reflects the different biological effects done to the body by different types of radiation. The millirad and millirem refer to 1/1000 of a rad and rem, respectively. The Sievert (Sv) is the System Internationale unit that equivalent to 100 rem; the millisievert (mSv) refers to 1/1000 of a Sievert.

²Variations by a factor of 2 (above and below) are not unusual.

In conformity with 10CFR20 and 64E-5, the term embryo/fetus is used throughout this document to represent all stages of pregnancy. The definitions are taken from Stedman's Medical dictionary, 21st edition, The Williams and Wilkins Company, Baltimore, MD 1966 and read as follows:
Embryo: An organism in the early stages of development; in man, from conception until approximately the end of the second month. Developmental stages from this time are commonly designated as fetal.
Fetus: The unborn young of a viviparous animal after it has taken form in the uterus; in man, the product of conception from the end of the eighth week to the moment of birth.
Undifferentiated Cells: Those cells in early development which have not progressed to a mature and specialized state, such as muscle or nerve cells.