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E.12
E.5 SPECIFIC CONSIDERATION OF HEALTH EFFECTS FROM KRYPTON-85
The radiological significance of 8 5 Kr was reviewed in a recent report of the National
Council on Radiation Protection and Measurements (NCRP 1975). Most of the discussion in
this appendix derives from that report, which should be consulted for details or for more
extensive citation of the literature.
Because krypton is virtually inert chemically, it is not metabolized. Exposure of
humans results from 85Kr in the atmosphere external to the body, from 8 5 Kr inhaled into
the lung, and to a much smaller degree from 8 5 Kr dissolved in body fluids and tissues.
Over 99% of the decay energy of 85Kr is in the form of a relatively weak beta ray (mean
energy, 0.25 MEV) which limits the hazard from external exposure. There is general agree-
ment that the dose to the sensitive cells of the skin from external exposure is about
100 times larger than the dose to the lung or any other internal organ (NCRP 1975, Kirk
1972, Soldat et al. 1975, Snyder et al. 1975).
The NCRP Report (1975) considers four categories of delayed effects from long-term
exposure to low-level environmental concentrations of 8 5 Kr. These are: 1) genetic
effects, 2) overall carcinogenic effects, 3) carcinogenic effects on skin, and 4) possible
interaction of ionizing and ultraviolet radiation.
Estimation of genetic and overall carcinogenic effects of 8 5 Kr exposure involves no
unusual features. Doses to gonads and to total body have been considered essentially iden-
tical by all who have considered the problem (NCRP 1975, Kirk 1972, Soldat et al. 1975).
Genetic and carcinogenic risk factors chosen for general applicaion in this Statement
(Table E.1.2) should be appropriate to 85Kr.
Carcinogenic effects on skin do constitute a unique problem, however, since the human
exposure dose from 85 Kr is 100 times higher to the skin than to any other tissue. Dose-
response data on radiation-induced skin cancer are limited, but suggest a threshold-type
response; certainly the skin is less susceptible to radiation carcinogenesis than are many
other tissues. The BEIR Report (Weston 1973), after review of the available data, concludes
that "numerical estimates of risk at low dose levels would not seem to be warranted."
As a consequence, neither dose to skin nor estimated health effects that might result
from low-level skin irradiation are presented in this Statement. (Skin cancer is perhaps
the most easily controlled of all malignancies and is rarely fatal.)
The possibility of interaction between the radiation from 85Kr and solar ultraviolet
radiation, the latter of which is considered to be responsible for most human skin cancer,
was raised in the NCRP Report (NCRP 1975). There is no direct evidence for such interaction,
but the possibility was thought to justify further epidemiological and laboratory
studies.