Manganese neurotoxicity in industrial exposures: proof of effects, critical exposure level, and sensitive tests

Manganese neurotoxicity has been known for more than 150 years, since Couper (1837) described a syndrome, similar to Parkinson's disease, in Scottish workers exposed to high levels of dust while grinding "black oxide of manganese" at a chemical industry. Since then, the syndrome has been described in several groups of highly exposed miners and other workers. A thorough review of manganese neurotoxicity was provided by the WHO (1981) and a recent update was written by Mergler and Baldwin (1997). From these reviews it is evident that the critical effect from manganese exposure is damage to the central nervous system, and that the effects, once established, are generally irreversible. Therefore, the early detection of symptoms of manganese neurotoxicity in populations at risk is of the utmost importance. In spite of this fact, only about a dozen studies of manganese exposed groups of workers have been performed using psychological test methods. These studies are briefly presented, the preponderance of proof for Mn neurotoxicity even in present industrial settings is demonstrated, the critical exposure level is briefly discussed, the test methods are evaluated, and recommendations for a test battery useful for studies of manganese neurotoxicity, are presented.