Increase in the platinum group elements content in road dust from São Paulo city, Brazil, due to exhaust emissions from vehicle catalytic converter, over a 10-year period

Abstract

Platinum Group Elements (PGEs) are widely used as catalysts in vehicle emission reduction, and road dust is a primary receptor for PGE releases. However, the determination of PGEs in these samples by ICP-MS is affected by matrix interferences, and measurement and sampling uncertainties are often overlooked. This study presents the first PGEs measurements in road dust samples from São Paulo city avenues, including matrix separation and estimation of measurement uncertainty includes analytical and sampling uncertainties. Measurement uncertainties for PGEs ranged from 12.3% to 19.5%, and analytical uncertainty ranged from 2.25% to 5.64%. PGEs concentrations: Pt (2.6 - 227 ng g-1), Pd (16.3 - 1875 ng g-1), Rh (2.02 - 257 ng g-1). Three methodologies were applied to evaluate the PGEs and other metals contamination in 54 road dust samples (< 100 µm fraction) collected in 2008, 2016 and 2018 at 18 sites with high (17 sites) and low (1 site) volumes of traffic. Metal pollution index (MPI), enrichment factor (EF) and statistical analyses. These evaluations suggested that PGEs and Mo contamination were originated from automobile exhaust emissions. Cu and Zn contamination seemed to have been caused by tires and brakes vehicular sources (non-exhaust emissions), but Ni and Pb contamination seemed from non-vehicular sources. Only rare earth elements are mostly associated with crustal source. The changes in PGE ratios stemmed from decreased Pt and increased Pd concentrations. A considerable portion of these metals in road dust is bioaccessible and poses health risks to the population near high-traffic density avenues, through ingestion, dermal contact, and inhalation pathways.