The United States Environmental Protection Agency (U.S. EPA) has just completed and published new toxicity criteria for benzo(a)pyrene – specifically an oral reference dose (RfD), an inhalation reference concentration (RfC), an oral slope factor (OSF), and an inhalation unit risk (IUR). Although toxicity criteria were considered for the dermal contact exposure pathway, the U.S. EPA concluded that the methods for dermal evaluation of benzo(a)pyrene required further development. 

The net effect of the new toxicity criteria, except for exposure to air under an industrial scenario, will be to reduce the estimated human health hazard that may be associated with benzo(a)pyrene on contaminated sites. The full benzo(a)pyrene report is available at this EPA website:

Toxicity criteria form the basis of human health risk assessments and the calculation of screening levels and remediation goals.  The U.S. EPA and state environmental regulatory agencies will use the new toxicity criteria to inform environmental risk management decisions on sites where benzo(a)pyrene is identified as a chemical of concern.

What is Benzo(a)pyrene?

Benzo(a)pyrene is often considered to be the most carcinogenic chemical within the polycyclic aromatic hydrocarbon (PAH) class of chemicals, and therefore often drives cleanup at PAH contaminated sites.  PAHs are ubiquitous in the environment from natural sources (e.g., coal tars, shale oils, and crude oils, and forest fires) and as a result of anthropogenic activities, including the combustion of fossil fuels in industrial processes and automobiles.  Workers may be exposed to benzo(a)pyrene in the production of aluminum, coke, graphite, and silicon carbide, and in the distillation of coal tar for consumer and medical products.  Cigarette smoke and smoked or barbecued foods are major non-occupational sources of benzo(a)pyrene.  Dermal exposure may occur through contact with materials containing soot, tar, or crude petroleum, including consumer and medical products containing coal tar, such as coal tar-based shampoos and treatments for skin conditions like eczema and psoriasis.  Environmental exposures that are high enough to be a health concern may occur on sites where PAHs have been produced or released.  There is no known commercial use for benzo(a)pyrene.

How Might Screening Levels Change?

Given the new toxicity criteria, the U.S. EPA’s Regional Screening Levels (RSLs) for benzo(a)pyrene will also change.

RSLs for benzo(a)pyrene were generated, using the U.S. EPA’s on-line RSL calculator, for residential and composite worker receptors for soil, tap water, and air (Table 1).


Based on this evaluation, all RSLs for benzo(a)pyrene will increase (i.e. become less stringent), except the composite worker screening level for air.  With increased screening levels, benzo(a)pyrene will be less likely to trigger further investigation, mitigation, or remediation.

Screening levels published by state regulatory agencies are also likely to change based on the new toxicity criteria for benzo(a)pyrene.


About the Author

Scott Dwyer is Practice Leader, Risk Analysis & Toxicology at Kleinfelder. Kleinfelder is a leading engineering, construction management, design and environmental professional services firm, providing solutions to meet our world’s most complex infrastructure challenges.  Leveraging its integrated, cross-disciplinary team of nearly 2,000 professionals in 70 offices across the U.S., Canada, and Australia, Kleinfelder partners with private and public sector clients to deliver leading-edge solutions on a variety of large-scale projects.  The firm’s reputation for expertise, innovation, and quality, earned since Kleinfelder’s inception in 1961, has solidified our position as a trusted consultant and industry leader.