Settled bus dust as a proxy of traffic-related emissions and health implications of exposures to potentially harmful elements

Limited information on potentially harmful elements (PHEs) contents of settled bus dusts and associated health risks for commuters is available in the literature. Here, magnetic measurements were combined with geochemical analysis to provide insight into the origin and occurrence of PHEs (Cr, Cu, Fe, Hg, Ni, Pb, and Zn) in settled bus dust samples from the urban area of Athens, Greece. Microscopic observations showed the abundance of angular and spherical Fe-rich particles, carbonaceous spherules, and a variety of Ba, Cu, Pb, and Zn-containing particles, typically deriving from vehicular emissions. Settled bus dust was magnetically enhanced in relation to the road-verge Athens soil, and exhibited a ten-fold (Hg), eight-fold (Zn, Cu), and four-fold (Pb) enrichment. The oral bioaccessibility of PHEs followed the order Zn > Pb > Cu > Cr > Ni > Fe > Hg. Potential adverse health risk effects through ingestion, inhalation of particles and Hg vapors, and dermal contact were assessed using the U.S. EPA risk assessment model. Potential cancer risk for drivers and children (1–6 years old), commuting four days per week for 120 min per day, were above the regulatory levels of 1 × 10−4. Non-cancer risks may also arise, mainly because of inhalation of Hg vapors. Despite the intrinsic uncertainty related mainly to toxicity data and exposure parameters, the risk assessment helped to prioritize Cr and Hg as the elements of major concern.