Manganese and Rhenium

Abstract Manganese (Mn) and rhenium (Re) are group 7 (VIIB) transition elements. They both can exist in multiple valence states ranging from −3 to +7. While manganese is one of the most abundant elements in the earth's crust, rhenium is one of the rarest elements. The main use of manganese is in steel production. Organic manganese compound methylcyclopentadienyl manganese tricarbonyl (MMT) is used as an additive to gasoline. Rhenium is one of the densest metals known. It is used in high‐temperature superalloys and, for example, in platinum–rhenium catalysts. Manganese is an essential nutrient and readily available from a wide variety of foods. The main target organ of manganese toxicity is the brain. Clinical adverse effects have been described in occupational settings due to inhalation of Mn fumes and dusts, but excessive manganese intake may also result from dietary, environmental, or from its dysfunctional excretion. High exposure to manganese in miners and smelters has led to manganism, that is, a severe movement disorder, cognitive dysfunction, behavioral disturbances, and loss of libido. This is due to manganese accumulation and adverse effects in the brain basal ganglia. Recognition of subtle neurobehavioral effects in workers exposed to lower levels of manganese has led to progressive actions to limit occupational exposure. Manganese exposure has shown also effects in the respiratory system, which, however, may rather be due to particulate matter than to manganese ion. High doses of manganese have affected the sperm parameters and fertility of males in animal studies. Developmental neurotoxicity studies in animals suggest that early Mn exposure may impair learning, memory, and attention of the offspring. Very few information exists on the toxicity of rhenium. Limited evidence suggests low acute toxicity of perrhenates. Perrhenates accumulate in the thyroid. Repeated exposure to ammonium perrhenate has resulted in thyroid enlargement and follicular cell hypertrophy in animals at high doses.