Carcinogenic potential, levels and sources of polycyclic aromatic hydrocarbon mixtures in indoor and outdoor environments and their implications for air quality standards

Both the World Health Organization and the UK Expert Panel on Air Quality Standards (EPAQS) have considered benzo(a)pyrene (BaP) as a marker of the carcinogenic potency of the polycyclic aromatic hydrocarbons (PAH) mixture, when recommending their respective guidelines for PAHs in outdoor air. The aim of this research is to compare the concentrations and relative abundance of individual PAH and their contribution to the overall carcinogenic potential of the PAH mixture in indoor and outdoor environments to assess the suitability of the UK air quality standard derived for outdoor air for use as a guideline for indoor environments. Samples were collected onto filters using active sampling in different indoor and outdoor microenvironments. The ratio of individual compounds to BaP, the BaP equivalent concentrations and the percentage contribution of each individual compound to the total carcinogenic potential of the PAH mixture were calculated. Mean concentrations were generally lower indoors (BaP = 0.10 ng/m3) than outdoors (BaP = 0.19 ng/m3), with the exception of indoor environments with wood burners (BaP = 2.4 ng/m3) or ETS (BaP = 0.6 ng/m3). The ratio of individual PAHs to BaP showed no significant differences between indoors (e.g. DahA/BaP = 0.27) and outdoors (DahA/BaP = 0.31). The relative contribution of BaP to the PAH overall carcinogenic potency is similar indoors (49%), outdoors (54%) and in the smelter environment (48%) used by EPAQS to derive the UK Air Quality Standard for ambient air. These results suggest the suitability of BaP as a marker for the carcinogenic potential of the PAH mixture irrespective of the environment. Despite small differences in PAH mixture composition indoors and outdoors, the level of protection afforded by the present EPAQS standard is likely to be similar whether it is applied to indoor or outdoor air.

Research Highlights
► ETS and wood burning were linked with high exposures to PAH indoors
► BaP contribution to PAH carcinogenicity is similar indoors and outdoors.
► BaP contribution to PAH carcinogenicity was not affected by PAH sources.
► BaP is good marker of the PAH carcinogenic potential irrespective of the environment.
► Outdoor PAH guidelines will provide similar level of protection indoors.