Beyond Benzo[a]pyrene: Human Health Risks of Airborne Polycyclic Aromatic Hydrocarbon Mixtures

Abstract:

Polycyclic aromatic hydrocarbons (PAH) are potent human carcinogens that exist in the environment as complex mixtures of hundreds of different species. Scientific research and environmental guidelines commonly use a single representative compound, known as benzo[a]pyrene (BAP), rather than accounting for individual species explicitly. Previous studies have argued that this compound is the dominant contributor to the human health impacts of PAH mixtures. However, these studies do not consider some highly toxic species, which include other emitted PAHs, as well as PAH degradation products, such as the nitro-PAHs. Here, we reevaluate the suitability of BAP as an indicator of human cancer risk from airborne PAHs on a global scale. We develop and apply a global-scale atmospheric model (GEOS-Chem) and conduct a health impact analysis to estimate the human health impacts of 16 PAHs and their nitro-PAH. We use a novel method to quantify health impacts of PAHs that can account for compound-specific effects. We find that BAP is only a minor contributor to the human health risks of PAHs (12 %). The remaining human cancer risk is attributed to other directly emitted PAHs (63 %), and the nitro-PAHs (25 %) – species which are not regulated, and not monitored in the environment regularly. We conclude that the use of a single indicator compound to represent PAH mixtures is inadequate, and leads to inaccurate estimates for relative spatial and temporal differences in the health impacts of PAHs. We recommend that further scientific research, environmental guidelines and environmental monitoring extend beyond BAP to other PAHs and their degradation products.