Long term exposure to "low levels" of manganese oxides and neurofunctionalchanges in ferroalloy workers

Occupational exposure to manganese can cause early neurobehavioral effects in low- or a-symptomatic workers. A battery of neuropsychological tests was administered to a group of 61 ferroalloy male workers and 87 controls. The average (geometric mean) manganese concentrations in fetal dust at the pla nt have changed from 1981 to 1997 respectively from 1597.03 mu g/m(3) to 23 9 mu g/m(3) at the furnace area; from 151.53 to 255.76 mu g/m(3) at the cas ting area; from 167 to 54.7 mu g/m(3) at the maintenance (welding operation s), yielding a current overall value of 54.25 mu g/m(3). A cumulative expos ure index was calculated for each alloy worker and the average value (geome tric mean) resulted to be 1204.87 mu g/m(3) x years, which divided by the a verage length of exposure (15.77 years), showed the concentration of 70.83 mu g/m(3) of manganese in total dust. Blood and urinary manganese geometric means resulted significantly higher in the exposed workers (9.18 mu g/l an d 1.53 mu g/g creatinine, respectively) than in controls (5.74 mu g/l and 0 .40 mu g/g creatinine, respectively). A positive correlation was observed b etween the airborne manganese concentrations in total dust and blood mangan ese (n = 55; R = 0.36; R2 = 0.13; p = 0.0068), whereas no association resul ted between cumulative exposure index and both blood manganese and urinary manganese. Higher prevalence of symptoms reporting was observed in the allo y workers concerning irritability, loss of equilibrium and rigidity. Tremor parameters including the central frequency and its dispersion, resulted to be statistically different in the exposed workers compared to the controls . Motor functions exploring the coordination of rapid and alternating movem ents and memory functions resulted to be impaired in the manganese workers. Dose-effect relationships were observed between the cumulative exposure in dex and some of the test results, whereas no relationship was found with th e airborne manganese concentrations and the biological indicators of exposu re. These findings are consistent with the existing knowledge of a cumulati ve mechanism of action of manganese, which must be carefully considered whe n setting safe exposure levels. In order to be protective for the entire wo rking life, the average annual exposure level should be lower than 100 mu g /m(3). (C) 1999 Inter Press, Inc.