Vehicle exhaust catalysts (VECs) using platinum, palladium, and rhodium are fitted to vehicles to convert noxious exhaust emissions into less harmful gases. Platinum group elements (PGEs) are continuously released from VECs and the concentrations of these metals in the environment have increased significantly in the last two decades. The VEC-emitted PGEs can interact with different kinds of compounds present in the environment and be transformed into soluble species able to enter the food chain. This study of the speciation and bioavailability of PGEs examines the behavior of these metals in the environment and their potential to affect human health. The speciation of platinum, palladium and rhodium in the presence of inorganic ligands commonly found in the environment and also acetic and oxalic acids (analogues of the most commonly postulated binding sites on humic substances) was investigated through thermodynamic modelling and solubility experiments combined with mathematical modelling, respectively. All of the ligands studied were capable of mobilizing the PGEs as soluble complexes that can be transported easily in environmental and biological systems. In order to evaluate the potential pathways of PGEs from VECs into humans, physiologically-based tests were used to study the uptake of platinum, palladium and rhodium from road dust, powdered exhaust catalyst and metal hydroxide samples by the human respiratory and digestive tracts. PGEs in road dust samples were found to be highly bioavailable (up to 87%). The greatest PGE bioavailabilities were observed in lung solutions analogous to the fluid with which inhaled particles would come into contact after phagocytosis by cells. From the toxicological perspective, it is important to consider the possible formation of PGE-chloride complexes due to the presence of Cl ions in the stomach and lung environments, perhaps with increased health risks because of the known toxic and allergenic effects of these compounds on animals and human beings.