SOME EFFECTS OF THE ADMINISTRATION OF THORIUM NITRATE TO MICE

Abstract

A method for the determination of microgram amounts of thorium in tissues by the use of the thorium isotope UX1 was developed.When an aqueous solution of thorium nitrate was administered orally to mice, the LD50 was found to be between 1.76 and 2.0 gm. of thorium per kgm. body weight. Mice supplied with a 0.1% solution of thorium nitrate as their only source of water exhibited a greater mortality than was found in a control group. The subcutaneous injection of 50 mgm. of thorium as a thorium nitrate solution into mice produced an acute, necrotizing, inflammatory reaction at the site of injection, but no other effects. The exposure of a group of mice to an aerosol of thorium nitrate solution on each of 90 days for 40 min. each day had no effect on their mortality. The average initial concentration of thorium for each exposure to the aerosol of thorium nitrate was 330 mgm. thorium per cu. m. of air and the average final concentration was 114 mgm. of thorium per cu. m. of air.Evidence was obtained that all the thorium administered orally as thorium nitrate solution to mice is excreted by way of the feces and that no absorption from the gastrointestinal tract takes place. It is suggested that thorium nitrate owes its oral toxicity to its local action on the mucosa of the gastrointestinal tract.No evidence was obtained that thorium was transported to the viscera and very little thorium was excreted after the subcutaneous injection of 0.5 mgm. of thorium as thorium nitrate solution into mice. Most of the thorium remained at the site of injection for at least seven days. The cutaneous application of 0.3 ml. of BAL (2,3-dimercaptopropanol) appeared to cause a slight increase in the excretion of thorium, but the distribution of thorium in the mouse was not affected by this treatment.A group of mice was exposed for 180 min. to an aerosol of thorium nitrate that gave a maximum concentration of 107 mgm. of thorium per cu. m. of air and a final concentration of 3 mgm. of thorium per cu. m. of air. After this treatment the average amount of thorium found in and on one mouse was 256 μgm. Most of this was on the skin and most was excreted by way of the feces within a few days. Less than 0.2 μgm. of thorium was found in the liver, kidneys, spleen, blood, or femurs, immediately after the exposure or one day later. The average amount of thorium found in the lungs of one mouse immediately after the exposure was 3.12 μgm. and this amount decreased slowly over a period of 35 days.