• Manganese
• manganism
• miners
• occupational health

Couper's 1837 case series description of a neurological syndrome with features of parkinsonism—tremor in the extremities, gait disturbance, whispering speech—in five manganese (Mn) ore crushers is widely regarded as the first report of severe neurotoxicity in humans resulting from Mn over-exposure.1 More than a century had passed when Rodier2 published his widely quoted survey of nervous system impairment among Moroccan manganese miners in the British Journal of Industrial Medicine. According to Rodier, in the intervening years between Couper's and his 1955 publication, manganese was recognised as a “poison affecting the nervous system… (but was) less well known than other metallic poisons”.

Rodier's publication summarises findings from a prevalence survey of neurological signs and symptoms conducted among 3849 workers employed at three mines. He acknowledged some limitations of his study, including difficulties establishing accurate denominator data due to transient components of the workforce that included “basic” and “day” labourers, frequent absenteeism “especially at festivals and harvest times”, and job changes that occurred when ore seams were exhausted. Contemporary occupational epidemiologists will appreciate the challenges encountered in efforts to estimate person-time with proper attribution to exposure category. The survey revealed 151 cases of nervous system effects in the workforce, 132 of whom held jobs drilling blast holes, which entailed the most intense Mn exposures, …