2
Introduction
Cancer potency evaluations of environmental mixtures are a necessary component of cancer risk
assessments. MDH has reviewed and relied on a large number of authoritative scientific analyses to
determine appropriately protective cancer risk assessments for polycyclic aromatic hydrocarbons (PAHs).
Extensive reviews of potential exposures and health effects of PAHs and PAH mixtures are available
from the U.S. Agency for Toxic Substances and Disease Registry (ATSDR, 1995
), the International
Agency for Research on Cancer (IARC, 2013, 1973) and the U.S. Environmental Protection Agency
(EPA, 1986, 2009). In addition, the European Food Safety Authority (EFSA)
(http://www.efsa.europa.eu/) is actively conducting research on PAH laboratory analyses and food
exposures to PAHs.
Environmental exposures to PAHs are always to mixtures of PAHs. Individual PAHs are not found
isolated in the environment. PAHs originate from three sources:
• diagenic - natural PAHs generated by biological processes (retene and perylene are examples of
PAHs that may be from diagenic or petrogenic sources)
• petrogenic - typically, petroleum and fossil fuels (these typically include many alkylated PAHs)
• pyrogenic - products of incomplete combustion (typically the biggest component of most urban
and industrial samples)
Mixtures of diagenic PAHs are generally not considered to have health impacts on people at
environmental exposures levels. Short-term environmental exposures to petrogenic and pyrogenic PAHs
can lead to tissue irritation (e.g., skin, respiratory, eyes, gastrointestinal). Dermal irritation can be
enhanced by exposure to sunlight, sometimes causing severe irritation and rash. MDH recommends
avoiding exposure of the skin and eyes, as well as short-term inhalation of large amounts of PAHs.
In addition to irritation, decreased fertility, developmental neurological effects and renal toxicity have
been demonstrated in laboratory animals exposed to relatively high levels of PAHs. MDH recommends
evaluating the non-carcinogenic health effects from exposure to PAHs using criteria developed for
individual PAHs or mixtures (e.g., total petroleum hydrocarbons). These criteria and guidance on
evaluating the potency of non-carcinogenic mixtures are not discussed in this guidance.
The most studied endpoint for long term PAH exposure, and the endpoint exclusively addressed in this
guidance, is cancer. Long term occupational exposures to PAH mixtures (often confounded by exposure
to other materials as well) have been associated with increased incidence of lung, skin, gastrointestinal
tract, bladder, and scrotal cancer. Individual carcinogenic PAHs (cPAHs) have been shown to have
different cancer potencies and may induce different types of cancer in laboratory animals (e.g., oral
exposure to benzo[a]pyrene or dibenzo[a,l]pyrene predominantly result in gastrointestinal tract cancers or
lung cancer, respectively).
Early life exposures to a number of cPAHs (e.g., benzo[a]pyrene, dibenzo[a,h]anthracene, 7,12-
dimethylbenz[a]anthracene) have demonstrated that younger animals are more sensitive than older
animals, and cPAHs are generally assumed to be more potent when exposure occurs early in life (
US
EPA, 2005). The amount of exposure to environmental contaminants will also change over a lifetime.
Therefore, MDH recommends applying age-dependent potency adjustment factors (ADAFs) in
conjunction with age-specific exposure parameters when conducting cancer risk assessments. MDH offers
guidance on the incorporation of ADAFs (
MDH, 2010).
While there may be hundreds of different PAHs and analogues in a mixture, only a few compounds are
typically analyzed when evaluating an environmental mixture. Table 1 is a list of many of the PAHs that
are recommended for analysis by different environmental and health agencies. The lists were compiled