Environmental Engineering Reference
In-Depth Information
postulated mode of carcinogenic action. Use of the Framework should increase the
transparency of the analysis by ensuring that the facts and reasoning have been doc-
umented clearly, including any inconsistencies and uncertainties in the available
data.
The Conceptual Framework has been developed to assist in the assessment of car-
cinogenic end-points, but the principles upon which it is based are broad, and enable
its use in analysing modes of action of non-neoplastic effects of contaminants.
12.3.7 Methods for the Hazard Identification of Carcinogens
A variety of Risk Assessment methods has been used elsewhere, for example by
the United States Environmental Protection Agency (US EPA
1986
,
2005
), and the
World Health Organization (WHO
1993
).
Advances in biological knowledge are enabling mechanistic data, pharmacoki-
netic data and other relevant data to be increasingly taken into account in classifying
and assessing the risks of carcinogens.
Existing methodologies have difficulties in conveying the broad range of health
implications of exposure to contaminants. This, combined with a high “dread factor”
for cancer, has resulted in many cases in a disproportionate regulatory, political and
public focus on cancer as compared to other-than-cancer health effects.
Australia, for example, uses a variety of methods for classifying carcinogens
including the International Agency for Research on Cancer's method for the classi-
fication of carcinogens (IARC
1978
) which was the first system for qualitatively
categorising carcinogenic contaminants Initially, the approach was to adopt a
strength-of-evidence scheme to decide whether, for humans and experimental ani-
mals separately, there was sufficient or limited evidence of carcinogenicity for
a contaminant, mixture, or exposure circumstance, or whether data were inad-
equate for classification (prior IARC monographs essentially only summarised
existing tumourigenicity studies). Since then, the scheme has evolved whereby now
all data, including human, animal and in vitro studies are assessed for an over-
all weight-of-evidence evaluation of human carcinogenicity (Vainio and Wilbourn
1992
).
A major contributor to this evolution was the decision that “in the absence of
adequate data on humans, it is reasonable, for practical purposes [it is biologically
plausible and prudent (IARC
1987
)], to regard contaminants for which there is suffi-
cient evidence of carcinogenicity in animals as if they presented a carcinogenic risk
to humans” (IARC
1983
,
1987
). Thus considerable weight is given to the animal
cancer bioassays, though some researchers are not convinced of the validity of this
philosophy.
A further decision by IARC was to incorporate information on the mechanism
of action of contaminants in the evaluation process (Vainio et al.
1992
). For exam-
ple, in practical terms, this means that category Group 1 (sufficient evidence for
carcinogenicity in humans) “could be extended to include agents for which the
evidence of carcinogenicity in humans is less than sufficient, but for which there is
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