Morphological properties, chemical composition, cancer risks and toxicological potential of airborne particles from traffic and urban background sites

From a sampling campaign from December 2018 to June 2019, at a traffic and an urban background site in Coimbra, Portugal, two particulate matter (PM10) samples from each month were selected to characterise the morphology by scanning electron microscopy, to determine the organic and inorganic chemical composition by multiple analytical techniques and to assess the ecotoxicity by the Vibrio fischeri bioluminescence inhibition assay. PM10 concentrations in winter were approximately twice as high as those recorded in the spring. Biomass burning was the greatest contributor to air pollution in winter at both sites. The contribution of vehicle emissions to the PM10 at the roadside was, on average, 7 times higher than at the background location. Distinct particle morphologies were observed. Higher abundances of aggregates enriched in Fe, Ti, Ba, Cr, Co, Cu, Zr, Mn and soot particles were registered in samples from the roadside. Bivariate plots suggested common sources of PAHs, mostly traffic and biomass burning, across the city. Benzo[a]pyrene equivalent concentrations were within the values documented for other European cities. Cancer risks resulting from exposure to PAHs by inhalation were estimated to be low (10−6 ≤ to <10−4) for both sites. The noncarcinogenic risks from particulate trace elements were always higher than the target value of 1. Cancer risks for Cr were found to be higher than the acceptable level (10−6). The calculation of toxic units indicated that 64% of the samples from the roadside location were toxic and 14% very toxic, while the corresponding shares for the urban background site were 50% and 7%, respectively. Many PM10-bound constituents, especially markers of biomass burning (e.g. anhydrosugars) and traffic emissions (e.g. Fe, Cu, Zn), showed significant statistical correlations with toxicity.