Title  : SKIN CANCER INCIDENCE, ULTRAVIOLET RADIATION BENCHMARKS SET
Type   : Press Release
NSF Org: OD / LPA
Date   : November 18, 1993
File   : pr9386



Cheryl Dybas  December 18, 1993
(202) 357-9498       NSF PR 93-86


SKIN CANCER INCIDENCE,
ULTRAVIOLET RADIATION BENCHMARKS SET

Significant increases in ultraviolet (UV) radiation and skin cancer
incidence are expected from the depletion of stratospheric ozone between
1979 and 1992, according to new estimates published in the November 4
issue of the British journal, Nature.  The report is authored by Sasha
Madronich, a scientist with the National Center for Atmospheric Research
(NCAR) in Boulder, Colorado, and F.R. de Gruijl, a dermatologist with
Utrecht University in the Netherlands.  The National Science Foundation
supported the research. "UV radiation has been implicated in the
induction of skin cancers in fair-skinned people," explains Madronich.
"Reductions in stratospheric ozone are expected to allow more solar
ultraviolet to reach the earth's surface." The figures are based on an
analysis of the 14-year record of atmospheric ozone from the Total Ozone
Mapping Spectrometer (TOMS) aboard the Nimbus 7 satellite.  They update
an earlier calculation published by Madronich, and based on the 1979-89
TOMS data.  By combining ozone data with a computer model of the UV
propagation through the atmosphere, Madronich estimated the long-term
increase for several UV wavelengths known to cause erythema (sunburn) in
humans, damage to in vitro DNA molecules and skin cancer in laboratory
mice. The UV increases were then combined with data on skin cancer
induction to calculate the percentage of increases in non-melanoma skin
cancer incidence for different latitudes.  The results are shown in the
attached table.

Madronich and de Gruijl found statistically significant increases at
middle and high latitudes of both hemispheres.  They found no
significant changes for the tropics.  Although the highest percentage
increases are found in the polar region, skin cancer is relatively
uncommon there because of the low natural levels of UV radiation and the
relatively sparse population.  Thus, these large-percentage increases
translate to relatively few new cases of skin cancer.  More important,
according to the authors, are the increases in mid-latitudes, because
much of the fair-skinned population is concentrated here.  (See attached
sheet for a few major midlatitude cities in the Northern Hemisphere with
their 1990 census population figures.)

"Increases in annually integrated ultraviolet doses, shown in the table,
are within one standard deviation of zero only within about 10o latitude
of the Equator and become significant at the two standard deviation
level polewards of 35o in both hemispheres," reports Madronich.
"Relative to the 1979-89 changes, trends at middle and high latitudes
are generally persisting but now carry substantially greater certainty."

Madronich and de Gruijl note several important assumptions in their
study:

1.        The calculations considered ozone change only and do not
account for any long-term changes in cloud cover and local pollution,
both of which are known to block some of the UV light.  Cloudiness and
pollution may have increased at some locations but decreased at others,
so the actual net UV change may vary among places even at the same
latitude.

2.        The calculation is based only on ozone depletion that has
actually occurred between 1979 and 1992 and assumes that no additional
ozone depletion will occur.  Because skin cancer may take several
decades to develop, the effects of the 1979-1992 UV increase will not be
manifested immediately.  In the meantime, additional ozone depletion may
occur.

3.        The most critical unknown in this study is how human behavior
will change in the future decades.  According to Madronich, it is
perhaps optimistic but entirely possible that, with more awareness about
the connection between UV and skin cancer, people will increasingly
protect themselves from UV through the use of appropriate clothing,
sunglasses and sunscreens and by minimizing outdoor exposure two hours
before and after solar noon.

        NCAR is sponsored by the National Science Foundation.

-end-

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by competitively awarding grants to educational institutions for
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