Toxic equivalency factors (TEFs) for polycyclic aromatic hydrocarbons (PAHs)

The polycyclic aromatic hydrocarbons (PAHs; also referred to as the polynuclear aromatic hydrocarbons or PNAs) are commonly encountered at hazardous waste sites and are often the focus of site remediation activities. However, toxicity criteria are not available for all the PAHs. In the past, EPA has assessed risks posed by mixtures of PAHs by assuming that all carcinogenic PAHs are as potent as benzo[a]pyrene (B[a]P), one of the most potent PAHs. The available information on the toxicity of the PAHs suggests that most are considerably less potent than B[a]P and therefore, the EPA approach is likely to overestimate risks. Several approaches have been developed to allow the relative potency of the different PAHs to be considered in a site-specific risk assessment. This paper evaluates these approaches and presents a modified version that we feel more accurately reflects the state of knowledge on the relative potency of these compounds.