Results from eleven years of neurological health surveillance at a manganese oxide and salt producing plant.

ABSTRACT

In 1983, Roels et al. (1987a, b) collected blood and urine samples and conducted neurological testing of workers at a manganese oxide and salt producing plant in Belgium, and at a nearby chemical plant. Workers from the manganese plant performed significantly worse than workers from the chemical plant on tests of short-term memory capacity, eye-hand coordination, hand steadiness, and visual reaction time. Between 1985 and 1996, workers at the manganese plant were tested routinely using the same battery of neurological tests and biological sampling that were employed by Roels et al. Blood and urine Mn levels remained comparable throughout the eleven years of testing to those measured in 1983 by Roels et al. On a gross basis, neurological test results during this period were comparable or superior to results obtained by Roels et al., despite the fact that workers were older and had been exposed longer. Large year-to-year differences were observed in some neurological test outcomes that could not be explained by age or Mn exposure. Older age was significantly associated with poorer performance on tests of short-term memory and eye-hand coordination. After controlling for age and year of testing, reduced hand steadiness was significantly associated with blood Mn and (Marginally) urine Mn, and both reaction time and one measure of hand steadiness were significantly associated with years of Mn exposure. No significant associations were found between any measure of Mn exposure and results from either short-term memory or eye-hand coordination tests. Investigations regarding whether neurological scores of individual workers studied by Roels et al. continued to worsen with continued occupational Mn exposure were hampered by lack of a suitable comparison group. However, there was no evidence that neurological effects seen earlier in these workers by Roels et al. were progressing towards clinical detectable signs.