U.S. Nuclear Regulatory Commission
Question 71: The "Class" column of 10 CFR 20 Appendix B
covers inhalation, but does not refer to ingestion. When
there are two ALIs for ingestion, how do these relate to
the "Class," since they really were based upon the f1 value
for gut absorption? (Note: The f1 value is the fractional
uptake from the small intestine to blood).
Answer: The ALIs for ingestion do not relate to the
"Class," which refers to the retention time in the
pulmonary region of the lung. There are two situations for
which there are two ALIs for ingestion. One is when the
ALI is determined by the non-stochastic dose to an organ.
In this case, the organ or tissue to which the limit
applies is shown, and the ALI for the stochastic limit is
shown in parentheses (for example, see ingestion ALI for
beryllium-10). The other case (and the case presumably in
question) is when different f1 values were used to
calculate the ingestion ALIs. For example, see the entry
for cobalt-60, for which the ingestion ALIs are 500 (on the
first line) and 200 (on the second line). These ingestion
ALI values have no relationship to the corresponding
"Class" on the same line (W on the first line and Y on the
second line). Rather, as explained in Federal Guidance
Report No. 11, these different ingestion ALIs are based on
two different f1 values: f1 = 0.05 for ALI = 500, and f1 =
0.3 for ALI = 200. As shown in Federal Guidance Report No.
11, Table 3, f1 = 0.05 for "oxides, hydroxides and trace
inorganic," and f1 = 0.3 for "organic complexed and other
inorganics." For inhalation of cobalt-60, f1 = 0.05 for
both "oxides, hydroxides, halides and nitrates" (class Y),
and "all others" (class W).
The following information on Federal Guidance Report No. 11
is provided for those not familiar with this document: The
title of this report is "Limiting Values of Radionuclide
Intake and Air Concentration and Dose Conversion Factors of
Inhalation, Submersion and Ingestion." The report is
subtitled "Derived Guides for Control of Occupational
Exposure and Exposure-to-Dose Conversion Factors for
General Application, Based on 1987 Federal Radiation
Protection Guidance." The report was published by the U.S.
Environmental Protection Agency (EPA) as report number
EPA-520 / 1-88-020 on September 1, 1988. The ALI and DAC
values in this report are used in Appendix B of the revised
Part 20. (References: 10 CFR 20 Appendix B, Federal
Guidance Report No. 11).