Iridium

Iridium (Ir) belongs to the platinum group elements and is one of the rarest elements in the Earth’s crust. Since Ir is a hard metal with good resistance to corro- sion, it is widely used in the electronic, chemical, and automotive industries. In the latter sector, Ir is pres- ent as an impurity or is found in alloys together with platinum, palladium, and rhodium in automobile cata- lytic converters. These devices are continuously sub- jected to physical and chemical stress that leads to Ir release in airborne particulate matter and a consequent increase in metal levels in the general environment. Current data relating to environmental Ir concen- trations in air, soil, roadside dust, water, and foods indicate quite low levels that are not thought to pose a serious threat to human health. However, the increase in general exposure levels and the widespread indus- trial use of this metal have raised concern in the sci- entific community regarding potential adverse health effects for the general and occupationally exposed populations. Limited knowledge of the toxicological mechanisms of Ir in different physical and biological systems pre- vents researchers from making a correct evaluation of the risks derived from exposure to this metal and also from reaching definite conclusions regarding the potential adverse effects of low-“dose,” long-term exposures. Recently, the in vitro cytotoxic and genotoxic poten- tial 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, as indicated by increased levels in a series of urinary pro- teins and an immunological imbalance with a skew toward a T helper 2 (Th2) cytokine pattern. Hypersen- sitivity and allergic reactions were described in occu- pationally 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, little is known of the toxicological charac- teristics of Ir and further research is needed to define its potentially hazardous properties and their princi- pal toxicological mechanisms so that an appropriate evaluation and management of Ir risk can be made with regard to the general and occupationally exposed populations