world cancer report - iarc

ENVIRONMENTAL POLLUTION
SUMMARY
> Pollution of air, water and soil is estimated
to account for 1-4% of all cancers.
> A small proportion of lung cancer ( Carcinogenic indoor air pollutants
include tobacco smoke, and cooking
fumes in particular regions, including
parts of Asia.
> Chlorofluorocarbons cause destruction
of the ozone layer and enhance the risk
of skin cancer through increased ultraviolet
radiation.
> Contamination of drinking water is not a
general carcinogenic hazard, but high
levels of arsenic and chlorination byproducts
in some communities carry a
risk.
In a broad sense, “environmental factors”
are implicated in the causation of the
majority of human cancers [1]. In respect
of many such environmental factors, such
as active smoking, alcohol intake, sun
exposure and dietary make-up, individuals
exercise a degree of control over their
level of exposure. However in the present
context, “environmental pollution” refers
to a specific subset of cancer-causing
environmental factors; namely, contaminants
of air, water and soil. One characteristic
of environmental pollutants is that
individuals lack control over their level of
exposure. The carcinogenic pollutants for
which most information is available
include asbestos (referring here to nonoccupational
exposure), toxic agents in
urban air, indoor air pollutants and chlorination
by-products and other contaminants
of drinking water. Relevant risk fac-
tors include place of residence: whether
rural or urban, and the relationship to
major industrial emission sources. Various
determinations suggest that environmental
pollution accounts for 1-4% of the total
burden of cancer in developed countries
[2,3].
Asbestos
Asbestos is one of the best characterized
causes of human cancer in an occupational
context (Occupational exposures, p33);
the carcinogenic hazard associated with
inhalation of asbestos dust has been
recognized since the 1950s [1]. Non-occupational
exposure to asbestos may occur
domestically and as a consequence of
localized pollution. Cohabitants of
asbestos workers may be exposed to dust
brought home on clothes. The installation,
degradation, removal and repair of
asbestos-containing products in the context
of household maintenance represents
another mode of domestic exposure.
Further afield, whole neighbourhoods may
be subject to outdoor pollution as a result
of local asbestos mining or manufacture.
The erosion of asbestos or asbestiform
rocks may constitute a natural source of
asbestos exposure in some parts of the
world.
In common with occupational exposure,
exposure to asbestos under domestic circumstances
results in an increased risk of
mesothelioma, a rare tumour derived from
the cells lining the peritoneum, pericardium
or pleura. Likewise, non-occupational
exposure to asbestos may cause lung cancer,
particularly among smokers [4]. A
consequence of neighbourhood exposure,
namely a very high incidence of mesothelioma,
is evident among inhabitants of villages
in Turkey where houses are built
from erionite (a zeolite mineral).
Outdoor air pollution
Ambient air pollution has been implicated
as a cause of various health problems,
including cancer, and in particular as a
cause of lung cancer. Air may be polluted
by a complex mixture of different gaseous
and particulate components. The concentrations
of specific components vary
greatly with locality and time. A critical
exposure scenario is therefore hard to
define, particularly as relevant biological
mechanisms are largely unknown. It is,
however, possible to attribute at least
some carcinogenic risk to particular
atmospheric pollutants, including
benzo[a]pyrene, benzene, some metals,
particulate matter (especially fine particles)
in general, and possibly ozone.
Over recent decades, emission levels have
been tending to decrease in developed
countries, so that concentrations of traditional
industrial air pollutants such as sulfur
dioxide and particulate matter have
fallen. However, vehicular exhaust
remains a continuing or even increasing
Fig. 2.22 Fuel used for heating and cooking, and
high levels of cooking oil vapours are responsible
for the high incidence of lung cancer among
women in some parts of Asia.
Fig. 2.23 Air pollution is common to many large
cities throughout the world.
Environmental pollution 39