visible light mutagenesis

["Karam, Andrew" <Andrew_Karam@URMC.Rochester.edu>]

I just got my hands on the paper by Setlow recommended by a few of you.
According to this paper, up to 90% of melanomas may be caused by exposure to
UVA and visible light.  He suggests, based on this, that ozone depletion
will not cause a significant increase in skin cancers, but that use of UVA
tanning beds will.  He also states as one of his conclusions that "The
existence of photoreactivation suggests that, in sunlight, a high ratio of
visible to UVB radiation could result in the amelioration of the biologic
affects ascribable to pyrimidine dimers, and that the biologic effect of the
UVB in sunlight would be less than estimates based on experiments with
isolated wavelength bands."

In another view of the effects of visible light, Bill Bernhard, a
biophysicist here, told me that a high flux of non-ionizing photons can lead
to ionization if the flux is sufficiently intense that two photons interact
with an electron simultaneously AND the combined energy is sufficient to
cause an ionization.  He said this is most typically seen with lasers
because sunlight does not have sufficient intensity (i.e. photon flux) to
make the two-photon interaction plausible.

As always, many thanks to all of you who responded to my query.

Andy

Andrew Karam, CHP              (716) 275-1473 (voice)
Radiation Safety Officer          (716) 275-3781 (office)
University of Rochester           (716) 256-0365 (fax)
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