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Re: Inflight radiation exposure
I agree that we are discussing a non-problem here. Doses
are very small. However, I cannot let one comment pass
without issuing a rebuttal. The timing of radiation risk
to an unborn embryo depends on the end point:
1. Exposure preimplantation (days 1-10 post coitus) leads
to prenatal death in studies of rodents. These data are
presumed to apply to humans. No other effects have been
observed from exposure in this period. This is a
deterministic effect with a threshold generally accepted as
about 10 rem. A few studies suggest 5 rem. The NCRP
states no statistically significant effect below 15 rem.
2. Exposure during major organogenesis (about days 10-50
p.c.) leads to congenital anomalies and neonatal death in
rodents, again a deterministic effect with a threshold
about 10 rem. Growth and mental retardation may also follow
exposure during this period.
3. Exposure during the fetal period (after day 50 p.c.)
leads to growth and mental retardation. The period of
maximum sensitivity to mental retardation in the Japanese
survivors irradiated in utero was 8-15 weeks p.c.
Note that most of these effects occur from exposure in the
first trimester with only growth and mental retardation
carrying over into early second trimester.
***********************************************************
S. Julian Gibbs, DDS, PhD Voice: 615-322-3190
Professor of Radiology FAX: 615-322-3764
Dept. of Radiology & Radiological Sciences
Vanderbilt University Medical Center
Nashville TN 37232-2670 Email:j.gibbs@vanderbilt.edu
***********************************************************
Tell me and I forget; teach me and I remember; involve me
and I learn.
--Chinese proverb
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