Economic implications of manganese neurotoxicity.

Manganese neurotoxicity is linked primarily to inhalation exposure, and its clinical features are almost totally based on high doses, such as those experienced by miners. Manifestations of lower level exposures can take two forms. One is the appearance of neurobehavioral deficits. A second, equally subtle, form is as a promoter, borrowing the term used in carcinogenesis, of neurodegenerative disease. Such low-level environmental exposures may be more potent than expected if they occur as ultrafine particles able to penetrate directly into the brain. The neurological disorder linked most closely to manganese is Parkinson's disease (PD). Although most observers recognize that the features of manganese-induced parkinsonism differ from those of idiopathic PD, they overlap considerably. The overlaps should be expected because the underlying lesions, although distinguishable, are closely linked because they belong to structures with complex interdependent circuitry. Such interdependence makes it feasible to undertake an analysis of how manganese neurotoxicity might elevate the risks of PD. A relatively small increment in risk, expressed as a leftward shift in the age prevalence of PD, incurs significant economic costs.