Airborne Particulate Matter, Platinum Group Elements and Human Health

Abstract

The platinum group elements (PGE), platinum (Pt), palladium (Pd) and rhodium (Rh), are emitted in small amounts in the exhaust of automobiles equipped with catalytic converters, which employ these metals as catalysts to convert nitrous oxide (NOx), carbon monoxide (CO) and hydrocarbons (HCs) into more benign forms prior to their release. While catalytic converters have reduced these noxious emissions, the environmental concentrations of PGE concentrations have significantly increased over time due to their use. More recent studies on PGE in biologically relevant media such as airborne fine and ultrafine particulate matter (PM) indicate that exposures to these metals are indeed a human health concern. First, emitted PGE may be easily mobilised and solubilised by various compounds commonly present in the environment, thereby enhancing their bioavailability. Second, PGE may be transformed into more toxic species upon uptake by organisms. Third, PGE are also present in the fine fraction of aerosols that have been associated with increases in morbidity and mortality, especially in vulnerable populations such as children and the elderly. All these factors highlight the need to monitor environmental levels of PGE and continue research on their bioavailability, behaviour, and speciation and associated toxicity to enable us to better assess the risks they may pose to human health.