Manganese neurotoxicity, a continuum of dysfunction: Results from a community based study

Excessive manganese (Mn) has been associated with neurobehavioral deficits and neurological and/or neuropsychiatric illness, but the level at which th is metal can cause adverse neurotoxic effects, particularly with long-term exposure, is still unknown. The objective of the present study was to asses s nervous system functions in residents exposed to manganese from a variety of environmental sources. A random stratified sampling procedure was used to select participants; persons with a history of workplace exposure to Mn and other neurotoxic substances were excluded. A self-administered question naire provided data on socio-demographic variables. Blood samples were anal yzed for total manganese (MnB) lead, mercury and serum iron. Nervous system assessment included computer and hand-administered neurobehavioral tests, computerized neuromotor tests, sensory evaluation and a neurological examin ation. The present analyses include 273 persons (151 women and 122 men); Mn B range: 2.5 mu g/L - 15.9 mu g/L (median: 7.3 mu g/L). Multivariate analys es were used and neuro-outcomes were examined with respect to MnB, laking i nto account potential confounders and covariables. Results were grouped acc ording to neurofunctional areas and MANOVA analyses revealed that higher Mn B ( 7.5 mu g/L) was significantly associated with changes in coordinated up per limb movements (Wilks' lambda = 0.92; p = 0.04) and poorer learning and recall (men: Wilks' lambda = 0.77; p = 0.002; women: Wilks' lambda = 0.86; p = 0.04). Further analyses revealed that with increasing log MnB (Simple regression : p<0.05) performance on a pointing task was poorer, frequency d ispersion of hand-arm tremor decreased, while harmonic index increased, and the velocity of a pronation/supination arm movement was slower. An Mn-age interaction was observed for certain motor tasks, with the poorest performa nce observed among chose _50 y and in the higher MnB category. Differences between genders suggest that men may be at greater risk than women, althoug h effects were also observed in women. These findings are consistent with t he hypothesis that Mn neurotoxicity can be viewed on a continuum of dysfunc tion, with early, subtle changes at lower exposure levels. (C) 1999 Inter P ress, Inc.