Journal of
Photochymistry
Photobiology
B:Biology
Journal of Photochemistry and Photobiology B: Biology 46 (1998) 20-39
Health risks
J. Longstreth a-*, F.R. de Gruijl b, M.L. Kripke ‘, S. Abseckd, F. Arnold’, H.I. Slaperf,
G. Velders g, Y. Takizawa h, J.C. van der Leun b
a The Institute for Global Risk Research. LLC, 9119 Kirkdale Road, Suite 200, Bethesda, MD 20817, USA
b Institute of Dermatology, University Hospital Utrecht. Heidelberglaan 100, NL-35X4 CX Utrecht, Netherlands
‘Department of Immunology, Box 178, The University of Texas, M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030-4095, USA
’ ICF Incorporated, 1850 K Street, NW, Suite 1000. Washington, DC 200062213, USA
e 4135 CrawfordAvenue, Miami, Fl33133, USA
‘National Institute of Public Health and the Environment (RIVM), Laboratory of Radiation Research, P.O. Box 1, 3720 BA Bilthoven, Netherlands
p Air Research Laboratory, RIVM, National Institute of Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, Netherlands
h National Institute for Minamata Disease, 4058 Hamn, Minamata City, Kumnmoto 867-0008, Japan
Abstract
The health risks associated with ozone depletion will principally be those due to increased ultraviolet B (UV-B) radiation in the environment,
i.e., increased damage to the eyes, the immune system, and the skin. Some new risks may also be introduced with the increased use of
alternatives to the ozone-depleting substances ( ODSs) . Quantitative risk estimates are available for some of the UV-B-associated effects,
e.g., cataract and skin cancer; however, the data are insufficient to develop similar estimates for effects such as immunosuppression and the
toxicity of alternatives. Ocular damage from UV exposures includes effects on the cornea, lens, iris, and associated epithelial and conjunctival
tissues. The most common acute ocular effect of environmental ultraviolet radiation (UVR) is photokeratitis. Also known as snowblindness
in skiers, this condition also occurs in other outdoor recreationists. Chronic eye conditions likely to increase with ozone depletion include
cataract, squamous cell carcinoma, ocular melanoma, and a variety of comeal/conjunctival effects, e.g., pterygium andpinguecula. Suppression
of local (at the site of UV exposure) and systemic (at a distant, unexposed site) immune responses to a variety of antigens has been
demonstrated in both humans and animals exposed to UV-B. In experiments with animals these effects have been shown to worsen the course/
outcome of some infectious diseases and cancers. There is reasonably good evidence that such immunosuppression plays a role in human
carcinogenesis; however, the implications of such immunosuppression for human infectious diseases are still unknown. In light-skinned
populations, exposure to solar UVR appears to be the most important environmental risk factor for basal and squamous cell carcinomas and
cutaneous melanoma. Originally it was believed that total accumulated exposure to UVR was the most important environmental factor in
determining risk for these tumors. Recent information now suggests that only squamous cell carcinoma risk is related to total exposure. In the
cases of both basal cell carcinoma and melanoma, new information suggests that increases in risk are tied to early exposures (before about
age 15), particularly those leading to severe sunburns. Testing of a number of the chlorofluorocarbon (CFC) alternatives indicates that most
of these chemicals have low acute toxicity, and low to moderate chronic toxicity. Some chemicals that were originally proposed as alternatives
have been dropped from consideration because these tests raised concerns about toxicity and/or manufacturing difficulties. In one instance,
high accidental occupational exposure was associated with liver damage, underlining the need for care in the use of these substitutes. Recent
quantitative risk estimates have been developed for cataract, melanoma, and all skin cancers combined. These estimates indicate that under
the Montreal Adjustments, cataract and skin-cancer incidence will peak mid-century at additional incidences of just under 3 per 100 000 and
about 7 per 100 000, respectively. 0 1998 UNEP. Published by Elsevier Science S.A. All rights reserved.
Keywords: Chlorofluorocarbons: Health risks: Ozone-depleting substances; Ultraviolet-B radiation; Skin cancer: Cataract; Photoaging
1. Introduction
Nearly everyone and indeed every living thing is likely to
be exposed to sunlight and the UV-B it contains for various
periods during their life. In humans and animals, exposure is
principally via the eyes and skin, with effects occurring as a
result of the absorption of solar energy by molecules (termed
chromophores) present in the tissues/cells of these organs.
As displayed in Fig. 1, the absorption of light energy leads
* Corresponding author. Tel.: + l-301-530-1527; Fax: +301-530-1646;
E-mail: tigerr@cpcug.org
to changes in these molecules that eventually can result in a
biological effect.
loll-1344/98/$ - see front matter 0 1998 UNEP. Published by Elsevier Science S.A. AU rights reserved.
PII SlOl l-1344(98)00183-3

Chromophore
\i;JI~rod”cts
Fig. 1. Events in light-induced effects
Chromophores absorb light energy from the various wave-
lengths with differing efficiencies. This pattern of absorption
is called an absorption spectrum and is characteristic of the
type of molecule involved. Fig. 2 shows absorption spectra
for five of the chromophores present in skin and eye tissues
that are thought to be important to the biological effects of
UV-B in humans and animals. These are DNA, tyrosine and
tryptophan (two amino acids that are largely responsible for
the UV absorbance of proteins), rruns-urocanic acid (a mol-
ecule present in large amounts in the outermost layer of skin),
and melanin (the principal pigment of the skin). The gray
area in Fig. 2 marks that part of the UV spectrum, wavelengths
under 290 nm, which is not present in terrestrial energy. Thus
only those portions of these absorption spectra appearing in
the white area (above 290 nm) are likely to be of any rele-
vance to the effects associated with environmental exposures.
As Fig. 2 indicates, for all of the molecules except melanin,
absorption efficiency drops rapidly within the terrestrial UV-
B spectral region with little or no absorbance in the UVA
spectral region (above 320 nm). Thus the increase in UV-B
that accompanies ozone depletion will increase the amount
of biologically active radiation present in ambient sunlight.
While it is difficult to predict quantitatively exactly how these
1.8
DOPA-MELANIN
TRYPTOPHAN
260 280 300 320 340
WAVELENGTH (nm)
Fig. 2. UVR absorption spectra of molecules important to UV-induced health
effects.
increases will be distributed globally, such increases have
been observed in a variety of sites across the world. Because
of the biological activity of UV-B. such increases are likely
to have marked consequences for humans as well as other
living creatures. Some of these consequences could be ben-
eficial, e.g.. a greater production of vitamin D in the skin of
humans, but far more are likely to be detrimental.
This paper presents an overview of the consequences likely
to accompany increases in UV-B. It will focus on the possible
health risks and only briefly mention possible beneficial
effects when these might offset adverse effects or when con-
cerns about them might modify adaptive strategies. The
paper’s design is adapted from a four-step risk-assessment
approach. It first identifies the hazards. Secondly, it discusses
a variety of factors that can modify exposure or susceptibility.
Thirdly. it presents quantitative and qualitative estimates of
risk with their attendant uncertainties, and fourthly, it ends
with a brief discussion of potential risks associated with
several of the strategies being adopted to manage or mitigate
risk.
2. Hazards for humans
Humans have three major organ systems whose cells and
tissues are commonly exposed to sunlight: the eye, the
immune system. and the skin, and it is in these three systems
that the effects of sunlight on health have been documented.
The cells/tissues exposed in the eye are principally those
associated with the cornea, the iris, and the lens; those of the
skin,include the outermost layer of the skin, the stratum cor-
neum, and the epidermis; and those of the immune system
are the Langerhans (or antigen-presenting) cells that reside
in, or migrate through, the epidermis.
Each of the different types of UV-exposed tissues contains
a collection of chemical substances the light-absorbing prop-
erties of which can contribute to the process shown in Fig. 1.
Furthermore, the organ systems are structured such that some
tissues/cells will absorb part of the UV energy before it
reaches others. Thus the spectrum of light that first hits the
surface of an organ such as the skin is not the same as that
reaching tissues/cells located deeper, e.g.. in the basal layer
of the epidermis. As a result. the wavelength dependence, or
action spectrum. of a particular end-point of concern rarely
looks exactly like the absorption spectrum of a particular
chromophore. Fig. 3 shows action spectra for several of the
more important effects, sunburn, DNA damage (dimers), and
carcinogenesis, that will be discussed in detail below. Note
again that only absorbance above 290 is relevant to environ-
mental exposures.
2.1. Effects on the eye
As indicated above. the eyes are a principal route of expo-
sure to ultraviolet radiation (UVR). As illustrated in Fig. 4,
when sunlight (and the UVR it contains) impinges on the