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

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.