Excretion of 241Am and 244Cm Following Two Cases of Accidental Inhalation

Abstract

Two incidents in which americium and curium aerosols were accidentally inhaled at the Savannah River Laboratory have provided some information on human metabolism of these elements. One occurred when a worker inhaled airborne particles containing relatively soluble 244Cm. A total of 202 nCi was excreted in the feces during the first 7 days. Chest counting revealed only 14 nCi after 4.5 hr; the amount in the chest rapidly dropped to 5 nCi in 4 days. Curium having a 10-day biological half life in the body dominated the excretion rate in both urine and feces for over 90 days. After 90 days, the biological half life increased to 78 days. A chelating agent, trisodium diethylenetriaminepentaacetate (DTPA), did not significantly increase the excretion rate of the relatively fixed curium. A second incident involved the inhalation of oxides of both curium and americium at a radiation ratio of 75% 244Cm and 25% 241Am. Over 1200 nCi were taken into the body. After 2.5 hr, 456 nCi remained in the chest. During the first 7 days, 1172 nCi was excreted in the feces, and all but 37 nCi was removed from the chest. About 4 nCi of the oxide appears to have been rapidly dissolved, either by gastric juices or as a result of an initial treatment with DTPA, and excreted with two biological half lives, i.e. 5.7 days for 244Cm and 35 days for 241Am. The ratio of americium to curium in the blood and fecal samples was 1:3, about the same as that in the inhaled oxide. The mixed oxides in the lungs after the first 7 days were removed by the circulatory system and by ciliary-mucus transport with a 28-day biological half life. Upon leaving the lungs, the americium and curium appeared to be fixed in the body and were excreted with a relatively long half life. Treatment with DTPA removed 1.5 nCi of the fixed material between days 50 and 118. Data obtained from analyses of urine and feces were plotted and regression lines were fitted by the least-squares method. By integrating the regression equation between various time sequences, the biological half lives of the residual radioisotopes were determined, permitting a temporal interpretation of the movement of the isotopes in the subjects.