Environmental exposure to manganese in Mexico: Comparison of exposure determinants and effects between children and adult population

Introduction: The Molango Mining District in the State of Hidalgo, central region of Mexico, has one of the largest manganese (Mn) deposits in the world (considered as the second largest deposit in Latin America and fifth worldwide). The exploitation, extraction, and transformation of the mineral began in 1960.  

Methods: A series of investigations have been conducted in the Mining District using an ecosystem approach to human health, evaluating Mn exposure of the residents in this area and the association with neuropsychological outcomes.  Results: Soil Mn levels were mostly within the ranges considered as adequate and Mn in drinking water samples were below maximum permissible limits (0.15 mg/L). Results of the health and the environmental components of this investigation showed air Mn concentrations above international recommendations for non occupational exposure (0.05 µg/m3), blood Mn (MnB) levels for an adult population sample in the range of 5.0–31.0 µg/L, and the association of air Mn with motor and cognitive impairments in adults residing in exposed communities. Recent research showed adverse cognitive effects due to Mn exposure (measured as hair and blood Mn), affecting the intellectual function in school-aged children, the most vulnerable of whom were younger girls. No consistent associations were found for the motor function evaluated in environmentally exposed children. The MnB levels for children were very similar to previous studies in adults from the same area. Mn exposure has shown to have an inverse association with serum prolactin levels for both adults and children.  Discussion: The resident of the Mining District are exposed to Mn by inhalation. In adults, the main effect of environmental Mn exposure has been associated with motor skills and attention, but the effect on children seems to include other functions. Our results indicate that the verbal processing functions are mainly affected in children.