The following guidance was developed by the Minnesota Department of Health (MDH) in 2001 and updated in 2013 at the request of the Minnesota Pollution Control Agency (MPCA). For the supporting information used to derive this guidance, please contact the Health Risk Assessment Unit or refer to the document "Guidance for Evaluating the Cancer Potency of Polycyclic Aromatic Hydrocarbon (PAH) Mixtures in Environmental Samples", dated August 15, 2013 (PDF: 247KB/13 pages).
Polycyclic Aromatic Hydrocarbons: Methods for Estimating Health Risks from Carcinogenic PAHs
The Minnesota Department of Health (MDH) prepared this guidance to identify a consistent approach for agencies and programs to assess health risks from exposures to carcinogenic polycyclic aromatic hydrocarbons (cPAHs) in air, water, soil, and other media. Because of uncertainties associated with the toxicities of PAH mixtures, MDH uses conservative assumptions to evaluate potential risks. As more data become available, MDH re-evaluates and revises its risk assessment methods and procedures, as appropriate.
PAHs include hundreds of different chemicals that commonly occur as mixtures in the environment. Limited toxicological data are available on PAH mixtures; therefore, individual PAHs are typically evaluated as separate chemicals for risk assessment. The combined or cumulative risks for more than one PAH may be estimated using the assumptions that follow. Because of the limited data regarding PAH toxicities and exposures, risk estimates should be presented in the context of their limitations and uncertainties.
MDH recommends using benzo[a]pryene (B[a]P) as the index chemical for other cPAHs, and provides guidance for an evaluation of the potency of other cPAHs relative to benzo(a)pyrene.
1. B[a]P Carcinogenicity Evaluation
B[a]P is commonly used as the index chemical to estimate the health risks from exposure to cPAHs when no other appropriate toxicity value (oral or inhalation) has been identified for an individual cPAH.
- For evaluating risks from ingestion of B[a]P-contaminated water, MDH recommends a Health Based Value (HBV) of 0.06 ug/L (http://www.health.state.mn.us/divs/eh/risk/guidance/gw/bap,pdf). The HBV was developed in 2012 and is based on age-specific ingestion over a lifetime and age-dependent sensitivity to carcinogens. This HBV is based on the 2010 California EPA B[a]P adult-based oral slope factor of 1.7 (mg/kg-day)-1.
- For evaluating risks from inhalation exposure, MDH recommends a Health Risk Value (HRV) of 0.001 ug/m for B[a]P (http://www.health.state.mn.us/divs/eh/risk/guidance/air/table.html), which is based on a slope factor of 7.3 (mg/kg-day)-1. This slope factor is the geometric mean of the B[a]P slope factor range used by the U.S. Environmental Protection Agency (U.S. EPA, 2001).
- For evaluating risks from cPAH exposure from other oral exposures (e.g., soil ingestion) and dermal exposures, MDH recommends the use of the 2010 CA EPA B[a]P oral slope factor of 1.7 (mg/kg-day)-1. Because early life exposures to B[a]P are a concern and B[a]P is a linear carcinogen, it is appropriate to apply MDH’s methodology for addressing age-dependent sensitivity. The resulting age-adjusted slope factor for the oral exposure route is 2.8 (mg/kg-day)-1 for a 70 year exposure period, including early life exposure.
2. Guidance for the relative potency method
MDH finds that the most accurate assessment of cancer risk from a mixture, one based on site-specific toxicity information, will not likely be possible. Therefore, other approaches will be needed. Information about a similar mixture (“whole mixture potency”) is preferred, but is rarely available. Summing the individual potencies of constituents of the mixture (“relative potency method”; see Table 1, below, for a list of priority cPAHs and relative potencies) is a reasonable alternative. However, it is likely to be the least accurate site-specific method for evaluating mixture cancer potency.
As a default alternative for the most common types of cPAH mixtures, MDH recommends estimating the cancer potency of an environment sample by multiplying the B[a]P concentration in a mixture by a factor of seven (7) and comparing the result to media-specific criteria for B[a]P . MDH makes specific recommendations on cancer risk evaluation of PAH mixtures, relative potencies of individual cPAHs, important cPAH analytes, and determining appropriate analytical detection limits in the MDH “Guidance for Evaluating the Cancer Potency of Polycyclic Aromatic Hydrocarbon (PAH) Mixtures in Environmental Samples”, dated August 15, 2013 (PDF: 247KB/13 pages).
MDH recommends that all cPAH cancer risk evaluations include the use of age-dependent exposure estimates in combination with age-dependent adjustments to potency (as described in http://www.health.state.mn.us/divs/eh/risk/guidance/adafrecmd.pdf).
Finally, it is important to maintain a state-wide database of site and source-type specific cPAH concentrations so that different source-type default multipliers can be developed. This could significantly decrease analytical and cleanup costs in the future for sites with significant cPAH contamination.
Relative Potency Factors
64 (air only) 150 (oral/dermal)
5.6 (air only) 13 (oral/dermal)
Agency for Toxic Substances and Disease Registry, Minimal Risk Levels for Hazardous Substances, (Accessed January 22, 2001)*
California Environmental Protection Agency, (April 1999a; June 1999b) Air Toxics Hot Spots Program Risk Assessment Guidelines, (Accessed: January 2001).*
CA OEHHA (2010). Public Health Goals for Chemicals in Drinking Water: Benzo(a)pyrene. Technical Support Document, California Office of Environmental Health Hazard Assessment, Sacramento, CA. September 2010. http://oehha.ca.gov/water/phg/pdf/091610Benzopyrene.pdf
Collins, J.F., Brown, J.P., Alexeeff, G.V., Salmon, A.G. (1998) Potency Equivalency Factors for Some Polycyclic Aromatic Hydrocarbons and Polycyclic Aromatic Hydrocarbon Derivatives, Regulatory Toxicology and Pharmacology, 28, 45-54.
International Agency for Research on Cancer, Overall Evaluations of Carcinogenicity to Humans, (Accessed: February 14, 2001).
Minnesota Pollution Control Agency, Air Emissions Risk Analysis, (Accessed: July 2, 2004).
National Toxicology Program, 12th Report on Carcinogens, (Accessed: July 29, 2013).
National Toxicology Program, Toxicology and Carcinogenesis Studies of Naphthalene (CAS No 91-20-3) in F344/N Rats (Inhalation Studies), (Accessed: July 2, 2004).
US Environmental Protection Agency (August 1997) Exposure Factors Handbook, Volumes 1-3, EPA/600/P-95/002Fa.
US Environmental Protection Agency, Integrated Risk Information System, Benzo[a]pyrene, (Accessed: January 2001).*
US Environmental Protection Agency (1993) Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons, EPA/600/R-93/089.
*References that are sources of PAH toxicity values. This is not a comprehensive list of all possible sources. Additional values may be found by searching the primary literature, agency web sites, and other references. If a toxicity value is used for purposes other than screening and there is evidence that the chemical is a risk driver, MDH conducts further review of the supporting toxicological data. For consultation regarding a specific toxicity value, contact the Health Risk Assessment Unit.