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Manganese is an essential element of the diet and a known cofactor in many enzymatic processes. Most reported cases of manganese toxicity in humans have involved occupational exposure to inhaled manganese dusts and fumes. Toxicity has also occurred in patients receiving parenteral nutrition and recently in intravenous (IV) methcathinone users.

Manganese salts are brightly pigmented and were most likely first used to make paint. Manganese dioxide has been found in prehistoric paints and has been used as a decolorant in glass making since at least the Roman Empire. Manganese–iron alloys were found in Spartan weapons, but the combination was most likely fortuitous but unintentional. In the early 19th century, it was discovered that addition of manganese to iron produced a stronger metal alloy, and manganese became an important component of most steel. The largest industrial use of manganese today is in steelmaking, and more than 85% of manganese in production is used to make ferromanganese alloys.

Manganese, primarily in the form of oxides, is released during mining, and inhalational exposure to dusts from grinding manganese ore has been the most important source of manganese toxicity. Inhalation of inorganic manganese compounds may also occur during smelting, welding, or burning coal, oil, or fuel containing manganese compounds. Manganese was linked to the development of a characteristic neuropsychiatric syndrome since the 1800s when it was described in French pyrolusite mill workers.17 A neuropsychiatric syndrome in welders is also attributed to inhalation of manganese oxide fumes12,14,56; however, many of the studies used to support this claim are methodologically flawed.31,36

Other industrial uses of manganese include: manganese chloride in dry-cell battery manufacture and as a catalyst for chlorination of organic compounds; manganese dioxide in batteries and glass production; and manganese sulfate to make ceramics, fungicides, and pesticides. Manganese toxicity from these professional applications has not been reported.

Permanganates were first discovered to be strong oxidizing agents in the 18th century. Weak solutions of potassium permanganate 0.01% are still used in medicine as topical drying and antiseptic skin preparations. Potassium, sodium, and barium permanganate also have uses in the pharmaceutical, chemical, and photographic industries. The toxicity of permanganates is mostly related to their oxidizing effects and is not discussed further here.

Manganese chloride and manganese sulfate are used as nutritional supplements.10Manganese toxicity is well documented in patients receiving total parenteral nutrition (TPN),21,43,48 particularly infants and young children. An epidemic of manganese toxicity was recently reported from the use of IV methcathinone prepared using potassium permanganate as an oxidizing agent.66 Manganese contamination of freebase cocaine may occur if manganese–carbonate is used as a reagent. The addition of methylcyclopentadienyl manganese tricarbonyl (MMT), a lead alternative, to gasoline has been allowed in Canada since 1976 and in the United States since 1995, but more research is needed to understand the contribution of MMT ...

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