Transfer to the Fetus - doe-std-1136-20040039

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

2.4.2 Transfer to the Fetus

Little information exists on the placental transfer or developmental toxicity of uranium isotopes

(Sikov et al 1992). The data available with pregnant rats suggest that the effects produced from exposure to

uranium may be due to chemical toxicity to the pregnant animals and their embryos/fetuses. Fetoplacental

concentrations of uranium peak one day following intravenous injection of a pregnant rat. Although

concentrations in the placenta decrease thereafter, the concentration in the fetal membranes remains

relatively constant. Selective deposition in some fetal organs will occur when exposure is during the fetal

developmental stages (NRC 1992b).

Data from animal experiments suggest that the distribution pattern of uranium is fairly uniform,

especially at the early stage of gestation. Concentrations of uranium in the embryo/fetus are taken to be

the same as those in the maternal soft tissues (excluding the kidney) during the first two months, and they

progressively increase thereafter. Following transfer into the embryo-fetus, uranium activity is assumed to

be distributed uniformly and to remain without excretion.

2.5 CHEMICAL VERSUS RADIOLOGICAL HAZARDS

Both the chemical and radiological hazards of uranium are moderate compared to those of other

industrial materials and radionuclides. Table 2-6 provides 10 CFR 835 derived air concentration values

for selected radionuclides. Table 2-10 compares Threshold Limit Values (TLV) published by ACGIH for

uranium and selected other metals. The comparison of TLVs is presented to provide perspective on the

need for uranium workplace controls, as compared to other hazardous materials. Since these materials

affect the body in different ways, this should not be considered a comparison of relative hazards.

The predominant hazard associated with uranium exposure depends upon its degree of enrichment,

its chemical form, and its physical form. The degree of enrichment determines the gamma radiation

intensity and the overall specific activity. The effect that enrichment has on specific activity is illustrated

in Figure 2-2. That figure (adapted from NRC Regulatory Guide 8.11) also gives 3.6 x 10-7 Ci/g as the

specific activity of depleted uranium and lists the formula used in Section 2.1.1 for calculating specific

activity of enriched uranium.

Table 2 -10. 1999 ACGIH Threshold Limit Values (TLVs) for Selected Metals

Soluble and Insoluble TLV

TLV-TWA, mg/m3

TLV-STEL, mg/m3

Metal

Uranium

0.2

0.6

Beryllium

0.002

Lead

0.05

0.45

0.05

Mercury vapor, all forms

except alkyl

Arsenic

0.01

TLV-TWA = Threshold Limit Value, Time-Weighted Average

TLV-STEL = Threshold Limit Value, Short-term Exposure Limit

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