Manganese cumulative exposure and symptoms: a follow-up study of alloy workers

Long-term exposure to manganese (Mn) particulates through inhalation can be neurotoxic, with deficits in neuromotor and cognitive domains. Mn-exposed individuals also report symptoms, including fatigue, mood changes, irritability, concentration difficulties, and sweating in the absence of physical effort. The long-term course of Mn-related symptoms after cessation of exposure has never been examined. Male workers from a Mn-alloy production plant participated in a study on nervous system functions (initial examination), and were followed-up 14 years after plant closure. The relation between self-reported symptoms and Mn cumulative exposure index (CEI) was examined among 71 Mn-alloy workers and 71 referents. Symptoms from the questionnaire were grouped into categories, and the reported frequency was compared between referents and Mn-alloy workers in each Mn CEI tertile using General Linear Models, controlling for age, education, and alcohol consumption. A gradual increase in symptoms frequency was observed for complaints related to hearing and movement control both at initial and follow-up examination, and fatigue and autonomic nervous system only at initial examination. In addition, an exposure-effect relation was apparent for symptoms related to memory, concentration and balance reported at both examinations, with Mn-workers in the highest CEI tertile reporting the highest level of symptomatology. Sleeping complaints were not associated with exposure to Mn, while musculoskeletal pain and muscular weakness were reported more often by Mn-workers than referents but were not clearly related to CEI. The findings suggest that former Mn-alloy workers continue to perceive symptoms many years after cessation of exposure. Despite the limitations of self-reported symptoms, subjective complaints are an important part of a health assessment since they relate directly to perceived health status and day-to-day functioning.