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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
0.01
--
TLV-TWA = Threshold Limit Value, Time-Weighted Average
TLV-STEL = Threshold Limit Value, Short-term Exposure Limit
2-25


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