Kinetics of inhaled 54MnCl2 aerosols: influence of inhaled concentration

Lung clearance, tissue distribution and elimination of manganese was studied in male Long-Evans rats. Animals were exposed for 1 hr by nose only to 54MnCl2 in concentrations of 54MnCl2: 129 mg Mn/m3 and 2.93 micrograms Mn/m3. Activity of 54Mn in lung, brain, liver, kidney, stomach, large and small intestine, blood, urine and feces was determined on days 0, 1, 2, 7, 14, 28, 60 and 121. Inhaled 54MnCl2 was cleared from the lung of rates biexponentially; at the high concentration, the fast and the slow phases had half-times, of 0.2 and 10.5 days, respectively. At the low concentration, the rapid and the slow phases had half times of 1.8 and 12.7 days, respectively. Relative uptake into the brain was independent of inhaled concentration and did not exceed 1 percent of lung deposition on day 0. After the high concentration, liver and kidney Mn levels peaked immediately at the end of exposure and decreased rapidly during the first two days. After the low exposure, liver and kidney accumulation was maximal on day 2 and then organ levels decreased like those of the high exposure group. Relative Mn content in the GI tract was similar after high and low exposure, except for the large intestine where much higher levels were measured in the early phase after inhalation of the high concentration. These data show that concentration of inhaled Mn has a significant influence on its organ distribution and elimination rates.