Abstract
Manganese (Mn) is a required trace element for growth and reproduction with Mn
deficient diets resulting in growth retardation, skeletal and joint cartilage abnormalities,
fetotoxicity, testicular degeneration, diabetes and vestibular dysfunction. Mn
requirements range from 30-100 ppm in the diet for various species. Man ingests 2.3-7 mg
Mn/day. Calculated absorbed doses of Mn for man range from 80-450 μg/day from
dietary sources.
Excessive body burden of Mn can occur from excessive exposures from intravenous
supplementation or from occupational exposures or from decreased Mn excretion seen
with chronic liver disease. Exposures during welding have ranged from 0.024-0.22 mg/m3
in the last decade with higher exposures when there was GMAW welding, no ventilation
or welding on manganese alloy steel. Exposures associated with manganism have been
above 3 mg Mn/m3
fabrication industries. Manganism is an illness that includes extrapyramidal symptoms and
findings (parkinsonism), psychiatric symptoms, intentional tremor, dystonia, and
incoordination. In non-human primates, no clinical or pathological changes occur when
exposures are limited to 3 mg Mn/m3
readily to treatment with chelating agents (EDTA or PAS), even when treatment is first
started years after exposure ceases.
Manganism differs both clinically and pathophysiologically from Parkinson’s Disease
(PD). The latter involves damage to dopaminergic neurons in the substantia nigra while
with manganism there is damage downstream from this dopaminergic pathway. In PD,
where there are decreased levels of dopamine, treatment with L-dopa can result in clinical
improvement while in manganism, where dopamine levels are generally normal, L-dopa is
usually ineffective. Studies by Racette and his colleagues have been used to hypothesize
that welders may develop classical PD at an earlier age than the general population. The
age distribution in these populations was, however, similar to other PD populations seen
and have occurred primarily in the mining and manganese alloy
or less. Clinical findings of manganism respond
in physician offices. Further, studies of PD patients have not identified an increased
prevalence of either welders or exposure to Mn in these populations.
Exposures to Mn at levels below those associated with a risk of manganism can result in
changes found on sensitive neurophysiological studies including tests of eye-hand
coordination, hand steadiness (tremor), and simple reaction time. When exposure to Mn
is discontinued, neurophysiological abnormalities improve or disappear. These
neurophysiological studies are used for worker monitoring as a supplement to industrial
hygiene monitoring studies. Further these studies have been used to define acceptable
exposure levels to Mn. Various agencies have set acceptable continuous (environmental)
exposures to Mn at levels ranging from 0.05-31.5 μg/m3
assuming 100% absorption of inhaled Mn, would result in daily absorbed doses of Mn
ranging from 0.05-470 μg/d, similar (at least at the upper range) to those seen from dietary
sources. The current workplace threshold limit value for Mn is 200 μg/m3
. In adults, such exposures,
.