Chemical speciation and sequential extraction of Mn in workroom aerosols: analytical methodology and results from a field study in Mn alloy plants

Workers in the Mn alloy producing industry are exposed to aerosols containing a variety of Mn compounds (MnO, MnO2, Mn2O3, Mn3O4, FeMn and SiMn). This paper reports a novel four-step chemical speciation/ fractionation procedure developed for characterisation of workroom aerosols collected in, Mn alloy producing plants. The following components of the aerosol have been quantified: "water soluble" Mn dissolved in 0.01 M ammonium acetate; Mn-o and Mn2+ dissolved in 25% acetic acid; Mn3+ and Mn4+ dissolved in 0.5% hydroxylamine hydrochloride in 25%, acetic acid; and "insoluble" Mn digested in aqua regia and hydrofluoric acid. Dissolution of pure Mn compounds with well-defined stoichiometries were essentially complete in the respective leaching steps with detectable amounts of < 1% in others. Recoveries of a mixed quality control sample were also acceptable in the range 92-97% for the different oxidation states. The levels measured in the inhalable and respirable fractions in three Mn alloy producing plants were approximately 300 and 35 <mu>g m(-3) of total Mn, respectively. The most obvious feature of the speciation results is that none of the-work areas is characterised by a single Mn contaminant. The predominant oxidation states in the inhalable aerosol fraction are Mn-o and Mn2+ independent of job functions/departments. The occurrence of insoluble Mn compounds in both the inhalable and respirable aerosol fractions is significantly higher during production of SiMn.