The use of toxic equivalency factors in assessing occupational and environmental health risk associated with exposure to airborne mixtures of polycyclic aromatic hydrocarbons (PAHs)

The health risk associated with inhalatory exposure to PAHs either in the occupational atmosphere or in outdoor air is commonly assessed on the basis of benzo(a)pyrene (BaP) concentrations in air. The PAH-related health risk is calculated with the help of epidemiological data from coke oven workers. The proportion of individual carcinogenic PAHs to BaP has been shown to vary in different environments by one to two orders of magnitude. Despite this, the unit risk value for BaP derived from epidemiological studies of coke oven workers is used for risk estimation of these environments. Toxic equivalency factors (TEFs) for individual PAHs were used to estimate human health risk associated with inhalatory exposure to PAHs. Given the uncertainties involved in risk assessment in general, a variability of risk estimation for PAH mixtures based on the toxic equivalency factor concept by a factor 2.6 is low and rather unreasonably precise. This underlines the importance of BaP as a surrogate compound of a PAH mixture.