Objectives The goal of this study was to assess long-term neurobehavioral effects associated with low airborne concentrations of manganese in a ferroalloy plant.

Methods During a period of forced cessation of work (1 to 42 d) neurobehavioral performance on tests of simple reaction time, finger tapping, digit span, additions, symbol digit, and shapes comparison was evaluated for 58 workers exposed from 1 to 28 years to manganese.

Airborne manganese concentrations in total dust had been reduced in the last 10 years from 70-1590 mug. m-3 to 27-270 mug. m-3.

For each worker, manganese concentrations in blood and urine were measured, and a cumulative exposure index was also calculated.

Significant relationships were found between the blood manganese and urinary manganese levels and between these biological measures and the cumulative exposure index.

Correlations were also found between the blood manganese level, the urinary manganese level, and the cumulative exposure index and the following tests : finger tapping, symbol digit, digit span, and additions.

The correlation coefficients increased as the latency time after the cessation of exposure and work seniority increased.

Conclusions :

The results support the hypothesis that the neurobehavioral effects observed at exposure levels well below current occupational standards are related to manganese body burden, which is better reflected by the blood manganese level after the cessation of exposure.