RE: visible light mutagenesis

["Eric Cowdrey" <ericc@cancercare.mb.ca>]

There appears to be little doubt that, by itself, ultraviolet radiation
(UVR) is a known human carcinogen. This is true for both UVR from sunlight
or from artificial sources such as tanning bed lamps. See, for example, the
National Toxicology Program's statement at:

http://www.pslgroup.com/dg/41c12.htm

The evidence is good that UVR causes basal cell and squamous cell carcinomas
of the skin. See for example, the NRPB's "Board Statement on Effects of
Ultraviolet Radiation on Human Health," available on the NRPB website
(http://www.nrpb.org.uk/).  Using a UVR action spectrum that is similar to
that producing erythema, models to predict the incidence of these two forms
of cancer are reported in this document.

The evidence that UVR can cause melanoma is somewhat less firm, but is
there. See, for example:

Swerdlow, Anthony J. and Martin A. Weinstock. "Do tanning lamps cause
melanoma? An epidemiologic assessment", Journal of the American Academy of
Dermatology, Vol. 38, No. 1, p. 89 (January, 1998).

This review found six worldwide studies, including some done in Canada and
Sweden, that showed a positive correlation of melanoma with tanning bed use.
Not all the studies showed this, however, and the authors concluded that
there was some urgency to better define the situation in view of the
widespread use of artificial tanning equipment in Europe and North America,
paticularly by young people. The action spectrum for melanoma in humans is
not known at this time - if this can be elucidated, even if it extends into
the visible light range, it would be very useful!

Note also that the term "UVA tanning bed" is a bit misleading - all tanning
bed lamps produce both UVB and UVA radiation. The UVA content can be
engineered to higher levels, if desired, but in my experience with
measurements there is always some UVB present, too. Usually, too, the output
of both types of UVR exceeds that from the sun on the brightest summer day.

**************************************************************

Eric Cowdrey, M.Sc. (Physics)
Radiation Protection Officer
Department of Medical Physics
CancerCare Manitoba
100 Olivia Street
Winnipeg, Manitoba    R3E 0V9
CANADA

Tel (204) 787-2166
Fax (204) 775-1684
mailto:ericc@cancercare.mb.ca

Industrial hygiene in Manitoba: http://aiha.cancercare.mb.ca


-----Original Message-----
From: radsafe@romulus.ehs.uiuc.edu
[mailto:radsafe@romulus.ehs.uiuc.edu]On Behalf Of Karam, Andrew
Sent: Friday, August 11, 2000 3:28 PM
To: Multiple recipients of list
Subject: visible light mutagenesis


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)
601 Elmwood Ave. Box HPH   Rochester, NY  14642

Andrew_Karam@URMC.Rochester.edu
http://Intranet.urmc.rochester.edu/RadiationSafety

The brain is a wonderful organ.  It starts working the moment you get up in
the morning and does not stop until you get into the office.
Robert Frost

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