Mother-to-Fetus Transfer

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

Table 5 -14. Uranium Balance for Reference Man(a)

Intake:

Food and fluids:

1.9

g/day

Inhalation:

7.0 E-3

g/day

Losses:

Feces:

1.4 - 1.8

g/day

Urine:

0.05 - 0.5

g/day

Other (hair)

0.02

g/day

(a)

(ICRP 1992).

The range of intake and losses has been observed to vary over several orders of magnitude,

depending upon the uranium concentration in foods and in the water supply.

5.6.6 Mother-to-Fetus Transfer

The embryo/fetus is included as part of the 10% of the systemic uptake that is uniformly distributed in

all "other" soft tissues except the liver and gonads. Methods for evaluating embryo/fetal uptake and dose

have been described in NUREG/CR-5631 (Sikov et al. 1992) and its 1993 addendum (Sikov and Hui

1993). For uptakes occurring during the first two months of pregnancy, the activity in the embryo/fetus is

assumed to have the same concentration as in the mother's "other soft tissue." For later uptakes, the

embryo/fetal concentration gradually increases relative to the maternal concentration, but is assumed to

remain uniformly distributed in the embryo/fetus. At three months, the embryo/fetal concentration is one-

and-a-half times the mother's "other" soft tissue concentration. At six months, it is twice the mother's, and

at eight months, it is three times the maternal "other" concentration. Following transfer to the

embryo/fetus, uranium activity is assumed to remain uniformly distributed, without clearance, until birth.

The Nuclear Regulatory Commission has developed simplified methods for assessing the gestation

period dose to an embryo/fetus in Regulatory Guide 8.36. Application of these methods shows that very

large maternal intakes of uranium are required to produce uptakes that would deliver 500 mrem, or even

50 mrem to the embryo/fetus. The NUREG/CR-5631 Addendum notes that maternal inhala tion intakes of

nominally 100 times the annual limit on intake (ALI) are required to give a 50-mrem embryo/fetal

dose. For ingestion intakes, a 1000 ALI maternal intake of uranium is required to give a 50-mrem dose to

the embryo/fetus. Thus, providing adequate radiation protection to limit maternal intake of uranium to the

occupational limits will adequately provide for the protection of the embryo/fetus.

5.7 INTERPRETATION OF BIOASSAY RESULTS

Bioassay measurements detecting uranium in workers can be init ially interpreted as indicating that

occupational intakes may have occurred. Standard bioassay procedures are not sufficiently sensitive to

detect differentiate occupational intakes from the range of environmental background levels in vivo or in

excreta. For example, there may be significantly elevated uranium bioassay results in certain populations

who obtain their drinking water from wells. Since most uranium bioassay measurement

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