The influence of site, bulk metal composition and individual particle structure on bioaccessibility of road dust

Brown, Andrew David (2018) The influence of site, bulk metal composition and individual particle structure on bioaccessibility of road dust. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The impact of urban air quality on human health is of worldwide concern and responsible for 40,000 early deaths in the U.K. alone. Industry’s relocation to suburban areas, caused vehicle tailpipe emissions to become the largest air pollution contributor. Although new fuels, engine modifications, legislation and improved urban planning, resulted in pollutant reductions, air quality remains a concern. To that end, resuspended road dust (RD) has been identified as one of the largest contributors to urban airborne particulate matter (PM). This study focused on potentially harmful elements (PHEs) in RD (specifically Cr, Cu, Fe and Pb) to investigate their health hazards associated with chronic exposure to urban RD. The study required seasonal collections of RD from an urban site in Manchester, U.K. over a two-year period. Total Cr, Cu, Fe and Pb concentrations in the fine fractions (<125 μm) were determined for each sample and indicated enrichment of PHEs in the smaller particles. In addition, this study reports for the first time on the seasonal and size fraction variations of the structural and chemical nature of individual RD particles, as determined by sequential analysis using computer controlled scanning electron microscopy with energy dispersive x-ray detection (CC-SEM-EDX) and micro Raman spectroscopy. Furthermore, investigation of the similarities of the <38 μm fraction with the <10 μm fraction, indicated that it could be used as a proxy, thereby contributing to new knowledge. To assess human risk on exposure, in vitro data were used to inform the seasonal and particle size variance of the bioaccessibility via the respiratory and gastrointestinal routes. Finally, the study featured a risk assessment of the metal exposure using a version of the EPA risk assessment protocol adapted in this for use with RD, which features as a timely contribution to the field. The study highlighted the enrichment of PHEs in finer fractions of RD, seasonal speciation of metals in different size fractions and individual particles, and behaviour of RD in simulated biological fluids. However, the hypothesis and overarching theme concerning the effect particle chemical structure has on potential human health effects proved harder to elucidate, illustrating the incredibly complex nature of this field of study. Accordingly, a final chapter featuring a comparative case study of Hg enrichment and bioaccessibility in RD from three international sites showed the relevance of this hypothesis.