Professor Harry A. Roels,   PhD, MSc
Louvain Centre for Toxicology and Applied Pharmacology
Université catholique de Louvain, Brussels, Belgium

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Manganese (Mn) is a naturally occurring metal that is available to the human body through different sources, including food. It is essential to Mn-dependent enzymes and of importance for many biological processes including metabolic pathways, bone growth, reproduction, immune function, blood clotting, and energy production at the cellular level.  Mn homeostasis is maintained through a tight balance between its absorption and secretion.  Inhalational exposure to elevated levels of Mn may occur in certain occupations, including mining, steel works, dry battery plants, and welding, and it may lead to excessive deposition of manganese in the lung, absorption in the blood stream and distribution to different body tissues, including the brain, via systemic circulation.  Mn can also travel upwards along the olfactory nerve and deposit in neural tissues, although this pathway is not of great importance in terms of neurotoxic insult in workers. The deposition of Mn in the brain via the systemic blood circulation and its transport across the blood-brain-barrier is the most important route of Mn deposition in the brain, particularly in the basal ganglia, which can lead to a parkinsonian condition, called manganism.