2.6. Carcinogenic risk
The carcinogenic risk due to exposure to the PAHs was estimated
and expressed per unit amount of BaP equivalents (BaPeq). Thisrequires the analytical determination of the concentration of the PAHs
in the mixture and a quantitative estimate of the carcinogenic
potencies of relevant PAHs in animals relative to the potency of BaP.
Several authors have proposed different potency equivalency factors
(PEF, see Table S1 Supplemental Material) and we have selected three
different approaches to assess the PAH carcinogenic potential. These
approaches are a modified version of Nisbet and Lagoy (1992) as
explained hereafter, the approach proposed by the WHO International
Programme on Chemical Safety (1999) and the approach followed by
the EPAQS (1999). The modified version of Nisbet and Lagoy (1992)
uses all the PEFs proposed by the authors except for DahA. In this case
the DahA PEF used is 1, as suggested by Malcolm and Dobson (1994),
which is more consistent with the PEF proposed by other authors for
this particular compound (see Table S1, Supplemental Material). This
modified approach has been followed by other authors previously
(Chen and Liao, 2006).
The BaP dose equivalent for each PAH compound is calculated by
multiplication of the measured concentration of the mixture component
(PAH) by the respective PEF. These dose equivalents are summed
to express the carcinogenicity of the mixture in terms of an equivalent
exposure to the index compound (i.e. BaP).