IRSST Management of Occupational Manganism: Consensus of an Experts’ Panel

IRSST Management of Occupational Manganism:

Consensus of an Experts’ Panel

Occupational manganism


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"Few scientific data are available on the reversibility of the neurotoxic effects associated with  chronic Mn overexposure. The researchers believe that the effects are rather irreversible (Ellenhorn  and Barceloux 1988). However, there is some evidence that recovery may occur when the exposure stops (Smyth et al. 1973). Antiparkinson drugs such as levodopa may be able to reverse some of the neuromuscular signs of manganism (Ejima et al. 1992; Rosenstock et al. 1971), but these drugs have several side effects, and reports indicate that they do not improve the patients’ neurotoxic symptoms (Calne et al. 1994; Chu et al. 1995; Cook et al. 1974; Ellenhorn and Barceloux 1988; Haddad and Winchester 1990; Huang et al. 1989). The ATSDR review (2000) reports that symptoms of manganism can be improved by certain medical treatments, but the improvement is generally temporary and damage to the brain permanent.

Huang et al. (1993, 1998) documented the progression of manganism in five workers chronically exposed to Mn in the ferroalloy sector. Their results show that the disease continues to progress even 10 years after leaving the workplace. Roels et al. (1999) carried out an eight-year longitudinal study on the same cohort as that published in 1992 in order to determine the reversibility of three early neurotoxic effects: hand-eye coordination (HEC), hand steadiness (HS), and simple visual reaction time (SVRT). They concluded that the tests used were reproducible and reliable throughout the study. They also demonstrated that past severity of Mn exposure determined the relative significance of the loss in precision in hand and forearm movement (HEC) in exposed workers as compared to the control group as well as their recovery potential. However, for the two other tests, HS and SVRT, no recovery was noted, suggesting that these conditions are irreversible.

However, when neurological damage is measured, it could be reversible but could also worsen over time, even in the absence of occupational exposure. As a result, it is important to intervene as rapidly as possible, in a phase that is possibly still reversible. Then, any significant additional exposure to manganese or to any other neurotoxic agent could contribute to the acceleration in the progression of the disease."

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"...concentration at which no effect (NOAEL) should occur on the CNS or pulmonary system of healthy workers. This level is 0.07 mg Mn/m3 in respirable dust and represents an average exposure level for a healthy worker.

Based on the level of scientific knowledge and for practical reasons, the experts agreed on the  following recommendations for keeping workers with manganism at work or for returning them to work when medical conditions permit: the occupational exposure to manganese should be kept as low as possible and should be accompanied by a ceiling value, a value never to be exceeded of 0.03 mg/m3, measured in respirable dusts. This value is based on the ATSDR established NOAEL. The ATSDR value of 0.07 is divided by 2 and, rather than being an average value for the work shift, it is converted to a ceiling value. Since the ATSDR level has been established for healthy workers, the experts concluded that half this value, 0.03 mg/m3, evaluated in respirable dusts and never to be exceeded should not be detrimental to the health of the confirmed (definite and probable) or suspected (possible) diseased worker and should be applied to all those cases where medical diagnosis is such that the worker is judged capable of returning to or staying at work."