AERMOD modeling of ambient manganese for residents living near a ferromanganese refinery in Marietta, OH, USA

Elevated exposure to ambient manganese (Mn) is associated with adverse health outcomes. In Marietta, Ohio, the primary source of ambient Mn exposure is from the longest operating ferromanganese refinery in North America. In this study, the US EPA air dispersion model, AERMOD, was used to estimate ambient air Mn levels near the refinery for the years 2008–2013. Modeled air Mn concentrations for 2009–2010 were compared to concentrations obtained from a stationary air sampler. Census block population data were used to estimate population sizes exposed to an annual average air Mn > 50 ng/m³, the US EPA guideline for chronic exposure, for each year. Associations between modeled air Mn, measured soil Mn, and measured indoor dust Mn in the modeled area were also examined. Median modeled air Mn concentrations ranged from 6.3 to 43 ng/m³ across the years. From 12,000–56,000 individuals, including over 2000 children aged 0–14 years, were exposed to respirable annual average ambient air Mn levels exceeding 50 ng/m³ in five of the six years. For 2009–2010, the median modeled air Mn concentration at the stationary site was 20 ng/m³, compared to 18 ng/m³ measured with the stationary air sampler. All model performance measures for monthly modeled concentrations compared to measured concentrations were within acceptable limits. The study shows that AERMOD modeling of ambient air Mn is a viable method for estimating exposure from refinery emissions and that the Marietta area population was at times exposed to Mn levels that exceeded US EPA guidelines.