Rhodium

Rhodium (Rh), a rare metal belonging to the platinum group elements, occurs naturally at low concentrations in the Earth's crust. It is widely used in the glass, chemical, and electronic industries, but its principal application is as an active catalyst material in automobile converters. However, while these devices have improved general air quality, they have also become a primary anthropogenic source of Rh in the environment. Several studies have demonstrated that Rh is emitted in small quantities as a result of chemical, physical, and thermal stresses on the converters due to mechanical abrasion and high temperatures. Rh contamination, which begins in airborne particulate matter, roadside dust, soil, sludge, and water, subsequently leads through diverse pathways to the bioaccumulation of this element in living organisms. In exposed subjects, Rh salts have been associated with immunological disorders such as asthma and contact dermatitis.The limited data regarding Rh toxicity and its effects, the general belief that environmental Rh levels are too low to pose a serious threat to human health, and the idea that Rh is only released in its metallic, relatively inert form in biological reactions have prevented an adequate assessment of the risks related to the environmental exposure to this metal. Recently, however, reported increases in environmental levels and more information on Rh concentrations in the finest fractions of particulate matter have stimulated considerable interest and debate concerning the potential impact of this metal on human health. Moreover, the findings of a number of innovative studies that demonstrated the cytotoxic and genotoxic effects of Rh on cellular systems and the induction of immunological alterations in animal models have provided the impetus for further investigation into the effects of Rh on human health and for a reassessment of the risk derived from exposure to the metal.