Relationship between external and internal parameters of exposure to manganese in workers from a manganese oxide and salt producing plant

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Abstract
In a plant producing manganese (Mn) oxides and salts, 11 different workplaces were identified. The current exposure to airborne Mn (total dust, personal sampling, n = 80) varied from 0.07 to 8.61 mg/m. The geometric mean and median values amounted approximately to 1 mg/m3 and the 95th percentile was 3.30 mg/m3. The concentration of Mn in blood (Mn‐B) in a group of 141 Mn‐exposed male workers ranged from 0.10–3.59 μg/100 ml compared to 0.04–1.31 μg/100 ml in a group of 104 control subjects. The ranges of the concentrations of Mn in urine (Mn‐U) were 0.06–140.6 and 0.01–5.04 μg/g creatinine for the exposed and control groups, respectively. The average level of Mn‐B in the Mn group was more than twice as high as in the control group (arithmetic mean, 1.36 vs 0.57 μg/100 ml) and that of Mn‐U was ten times higher in the Mn group (geometric mean, 1.56 vs 0.15 μg/g creatinine). The Mn‐B level did not change significantly after 8 h of Mn exposure, whereas the Mn‐U level dropped rapidly when exposure ceased (half‐life less than 30 h).On an individual basis, neither Mn‐B nor Mn‐U correlated with the current levels of Mn‐air or duration of Mn exposure. There was also no relationship between Mn‐B and Mn‐U. On a group basis, there was no correlation between the mean Mn‐B levels and the current levels of Mn‐air at each workplace; however, a slight but significant correlation (r = 0.62, p < 0.05) was found between the geometric mean of Mn‐U of each subgroup (n = 11) and the current level of Mn‐air at their corresponding workplaces. On a group basis (n = 6), Mn‐U did not correlate with the estimation of past integrated exposure of the workers, while group means of Mn‐B significantly correlated with past integrated exposure. These results indicate that the individual evaluation of the Mn exposure intensity remains difficult on the basis of Mn‐B and Mn‐U. On a group basis however, Mn‐U appears to reflect very recent exposure, while Mn‐B is to some extent a reflection of the body burden of Mn.