Answer to Question #829 Submitted to "Ask the Experts"

Category: Alpha Emitters — Uranium

The following question was answered by an expert in the appropriate field:

What are the US daily and annual limits for inhalation of depleted uranium in milligrams?

This well-put, seemingly simple specific question is anything but,
having many nuances that should be addressed. Appendix C to Title 10,
Code of Federal Regulations Part 20, specifies Annual Limits on Intake
in units of activity for the various uranium isotopes and natural
uranium, but not for depleted uranium although there is a value for
specific activity for depleted uranium given in the footnotes to the
table. Using this information, an Annual Limit on Intake (ALI) can be
calculated in terms of grams for depleted uranium and is as follows:

Oral Intake: 27. 78 g

Inhalation: Class D Compounds: 2.78 g Class W Compounds:
2.22 g Class Y Compounds: 0.11 g The above values are slightly less
than twofold greater than the comparable values for natural uranium.
Note that the above values are given in grams, not milligrams, and that
the letters D, W, and Y refer to the solubility characteristics of the
uranium, which in turn determines how quickly it is cleared from the
body. The most restrictive value is for inhalation of Class Y
compounds, which are cleared very slowly from the body. Note also that
there is no daily limit on intake specified; in theory at least, the
entire ALI can be taken into the body in a single day provided there is
no further intake during the year.

Ronald L. Kathren, CHP

Professor Emeritus Washington State University

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