A number of circumstances of environmental exposure
to carcinogens has definitely been linked with an
increased risk of cancer in humans. For all of them, it
is not possible to quantify with precision the burden of
human cancer they cause. It is likely however that in
most populations, environmental cancer is responsible
for a relatively small proportion of total cancers, in the order of 0.5–1% (Doll and Peto, 1981; Peto, 2001).
However, this proportion is likely to be higher in
populations with special exposure circumstances, such
as arsenic contamination of drinking water or proximity
to an important source of asbestos exposure. Furthermore,
the involuntary nature of the exposure makes its
elimination a particularly important target in terms of
health equity.
Knowledge on occupational causes of cancer is more
advanced than in the case of other groups of carcinogens.
However, current understanding of the relationship
between occupational exposures and cancer risk is
far from complete: for many experimental carcinogens
that occur in the workplace, little or no human cancer
data are available. Examples of such agents are ceramic
fibres, acrylamide, dichloromethane and acetaldehyde:
they all cause tumours in experimental animals and no
adequate data in exposed humans are available. One
should also consider that the relatively low burden of
occupational cancer in industrialized countries is the
successful result of strict regulations on recognized
carcinogens. As in the case of environmental cancer, the
facts that exposure is involuntary and can be eliminated
give to prevention of occupational cancer a special
status among interventions towards cancer control