Iridium

Iridium (Ir) belongs to the platinum group elements and is one of the rarest metals in the Earth's crust. Due to its good resistance to corrosion, Ir is widely used in the electronic, chemical, and automotive industries. In this latter sector, Ir is present as an impurity or in platinum, palladium, and rhodium alloys in automobile catalytic converters. These devices are subjected to physical and chemical stress that leads to Ir release in airborne particulate matter, therefore, increasing its levels in the general environment. Available data on Ir concentrations in air, soil, roadside dust, water, and foods indicate quite low levels. However, the increase in the exposure levels and the widespread industrial use of this metal raised scientific concerns regarding potential adverse health effects for the general and occupationally exposed populations. Limited knowledge on the toxicological mechanisms of Ir in different physical and biological systems hinders the evaluation of the risks and conclusions on the potential adverse effects of low-"dose", long-term exposures. Recently, the in vitro cytotoxic and genotoxic potential of Ir, mediated by oxidative stress reactions and the induction of direct DNA damage, was demonstrated in rat fibroblasts. Interestingly, in vivo results showed that oral Ir exposure in rats induced nephrotoxic effects and an immunological imbalance with a skew toward a T helper 2 cytokine pattern. Hypersensitivity and allergic reactions were described in occupationally and nonoccupationally exposed subjects with symptoms including rhinorrhea, asthma, contact dermatitis, and urticaria, indicating the sensitizing potential of Ir, albeit at a relatively low level. Overall, further research is needed to define Ir potentially hazardous properties and their principal toxicological mechanisms so that an appropriate evaluation and management of Ir risk can be made with regard to the general and occupationally exposed populations.