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Metabolic data for curium
LIMITS FOR INTAKES OF RADIONUCLIDES
BY WORKERS
111
METABOLIC DATA FOR CURIUM 1. Metabolism No data are given in Reference Man (ICRP, 1975) for curium.
Reliance must, therefore, be placed on animal data, which have been reviewed by an ICRP task group (ICRP, 1972) and, more recently, by Durbin (1973). 2. Metabolic Model (a) Uptake to blood The fractional absorption of curium compounds from the gastrointestinal tract has been studied only in the rat (Semenov, 1971, 1972; Semenov et al., 1973; Sullivan and Crosby, 1975), with reported values ranging from 3 x lo- 5 to 7 x 10m4. By analogy with the chemically similar and more extensively studied americium, fr is taken to be 5 x 10m4. It should be noted that greater gastrointestinal absorption might be expected for complexed forms of curium and that enhanced absorption has been reported in very young rats (Semenov et al., 1973; Sullivan and Crosby, 1975). (b) Inhalation classes As with americium, curium compounds, including the oxide (McClellan et al., 1972; Craig et al., 1975; Sanders, 1975), are more quickly lost from the lung than are the corresponding compounds of plutonium (Durbin, 1973). The limited data suggest that all compounds of curium should be assigned to inhalation class W.
Inhalation class D W Y
fi 5 x 1o-4 -
(c) Distribution and retention
The data available on the metabolic behaviour of curium in animals are generally in accord with the task group (ICRP, 1972) recommendation that the metabolic model used for plutonium shotild also be used for the other actinides. Experimental evidence (Richmond and Thomas, 1975) indicates that the fractions of curium and plutonium translocated to the gonads are rather similar. In this report it has been assumed that, of curium entering the transfer compartment, 0.45 is translocated to bone and 0.45 to the liver. The fraction of curium translocated to the gonads is assumed to be 3.5 x 10s4 for the testes and 1.1 x 10m4 for the ovaries, these values corresponding to a fractional translocation to the gonads of lo- 5 per g of gonadal tissue. The remainder of curium entering the transfer compartment is assumed to go directly to excretion. Curium translocated to mineral bone is assumed to be retained in that tissue with a biological half-life of 100 years, while curium translocated to the liver is assumed to be retained in that tissue with a biological half-life of 40 years. Curium translocated to the gonads is assumed to be retained indefinitely in that tissue (Richmond and Thomas, 1975).
112
REPORT OF COMMlTTJiE 2
(d) Chelated compounds Chelated forms of curium are not considered in this report. It is known that they have greater biological mobility than do other compounds of curium (Durbin, 1973). 3. Classification of Isotopes for Bone Dosimetry The distribution of curium in the skeleton of the rat is indistinguishable from that of americium (Durbin, 1973). The element is deposited mainly on the endosteal surfaces of mineral bone and only slowly redistributed throughout its volume by processes such as resorption and burial. For this reason all isotopes of curium considered in this report are, for the purposes of dosimetry, assumed to be uniformly distributed over bone surfaces at all times following their deposition in the skeleton.
References Craig, D. K., Cannon, W. C.. Catt. D. L., Herring, J. P., Olson, R. J., Powers, G. J. and Watson, C. R. Distribution of “‘Am and “*Cm in dogs after inhalation of the oxides. In: Pacific Northwest Laboratory Annual Report for 1974 to the USAEC Division of Biomedical and Environmental Research. Part I Biomedical Sciences, pp. 17-18 (BNWL-1950 Pt. 1), 1975. Durbin, P. W. Metabolism and biological effects of the transplutonium elements. In: Uranium, Plutonium, Transplufonium Elements, Eds. Hodge, H. C., Stannard, J. N. and Hursh, J. B., pp. 739-896. Springer-Verlag, Berlin, 1973. ICRP Publication 19, The Metabolism of Compounds of Pluronium and Other Actinides, Pergamon Press, Oxford, 1972. ICRP Publication 23, Report of the Task Group on Reference Man. Pergamon Press, Oxford, 1975. McClellan, R. O., Boyd, H. A., Gallegos, A. F. and Thomas, R. G. (1972). Retention and distribution of ‘“Cm following inhalation of ‘**CmCls and s44Cm01.rs by beagle dogs. Health Phys. 22, 877-885. Richmond, C. R. and Thomas, R. L. (1975). Plutonium and other actinide elements in gonadal tissue of man and animals. Health Phys. 29, 241-250. Sanders, C. L. Toxicology of inhaled 24*CmOa in rats. In: Pacific Northwest Laboratory Annual Report for 1974 to the USAEC Division of Biomedical and Environmental Research. Part I Biomedical Sciences, pp..35-37 (BNWL-1950 Pt. 1), 1975. Semenov, A. I. (1971). Kinetics of the exchange of s4*Cm. Radiobiologiya 11, 155. Semenov, A. I. Distribution of curium 244 in the rat organism. In: Biological Effects of Radiafion from External and Internal Sources, Eds. Moskalev, Yu. I. and Kalistratova, V. S., pp. 302-305. Meditsina, Moscow, 1972. fjemenov. A. I., Moskalev, Yu. I. and Zalikin, G. A. (1973). Influence of age on the absorption of ‘**Cm from the rat gastrointestinal tract. Radiobiologiya 13, 155. Sullivan, M. F. and Crosby, A. L. Absorption of uranium-233, neptunium-237, plutonium-238, americium-241, curium-244 and einsteinium-253 from the gastrointestinal tract of newborn and adult rats. In: Pacific Northwest Laboratory Annual Report for 1974 to the USAEC Division of Biomedical and EitvironmenIal Research. Part I Biomedical Sciences, pp. 105-108 (BNWL-1950 Pt. I), 1975.
LIMITS FOR INTAKES OF RADlONUCLIDES BY WORKERS
Annual limits on intake, ALI
and derived air concentrations, of curium
DAC(Bq/m’)
(40 h/wk) for isotopes
Inhalation
Radionuclide ALI DAC ALI
DAC ALI
Oral
Class W
f, = .5 x 1o-4
f, = 5 x 10-4
6 x lo* 4 x lo6 (5 x 106) Bone surf. 5 x 10’
DAC AL1
2 x 10” (3 x 106) Bone surf. I x 10’ (1 x 10’) Bone surf. 9 x 104 (2 x 105) Bone surf. 5 x IO’ (8 x 10.) Bone surf. 5 x lo4 (8 x 104) Bone surf. 5 x 104 (9 x 104) Bone surf. 1 x IO4 (2 x 104) Bone surf. 2 x 109
DAC
-
DAC ALI DAC AL1 DAC AL1
DAC AL1 DAC AL1 DAC AL1 DAC AL1
4 x 2 x 2 x (2 x Bone
10’ 10. lo4 104) surf.
8 9 x 10s (1 x 106) Bone surf. 4 x 102 1 x lo4 (1 x 104) Bone surf. 4 3 x 102 (5 x 10’) Bone surf. 1 x 10-l 4 x 102 (7 x 102) Bone surf. 2 x 10-l 2 x 10’ (3 s 102) Bone surf. 8 x 1O-3 2 x 102 (3 x 102) Bone surf. 8 x lo-’ 2 x 102 (4 x 10’) Bone surf. 9 x 10-1 5 x 10’ (9 x 10’) Bone surf. 2 x 10-a 5 x 108 (8 x 10’) Bone surf. 2 x 10s
113
BY WORKERS
111
METABOLIC DATA FOR CURIUM 1. Metabolism No data are given in Reference Man (ICRP, 1975) for curium.
Reliance must, therefore, be placed on animal data, which have been reviewed by an ICRP task group (ICRP, 1972) and, more recently, by Durbin (1973). 2. Metabolic Model (a) Uptake to blood The fractional absorption of curium compounds from the gastrointestinal tract has been studied only in the rat (Semenov, 1971, 1972; Semenov et al., 1973; Sullivan and Crosby, 1975), with reported values ranging from 3 x lo- 5 to 7 x 10m4. By analogy with the chemically similar and more extensively studied americium, fr is taken to be 5 x 10m4. It should be noted that greater gastrointestinal absorption might be expected for complexed forms of curium and that enhanced absorption has been reported in very young rats (Semenov et al., 1973; Sullivan and Crosby, 1975). (b) Inhalation classes As with americium, curium compounds, including the oxide (McClellan et al., 1972; Craig et al., 1975; Sanders, 1975), are more quickly lost from the lung than are the corresponding compounds of plutonium (Durbin, 1973). The limited data suggest that all compounds of curium should be assigned to inhalation class W.
Inhalation class D W Y
fi 5 x 1o-4 -
(c) Distribution and retention
The data available on the metabolic behaviour of curium in animals are generally in accord with the task group (ICRP, 1972) recommendation that the metabolic model used for plutonium shotild also be used for the other actinides. Experimental evidence (Richmond and Thomas, 1975) indicates that the fractions of curium and plutonium translocated to the gonads are rather similar. In this report it has been assumed that, of curium entering the transfer compartment, 0.45 is translocated to bone and 0.45 to the liver. The fraction of curium translocated to the gonads is assumed to be 3.5 x 10s4 for the testes and 1.1 x 10m4 for the ovaries, these values corresponding to a fractional translocation to the gonads of lo- 5 per g of gonadal tissue. The remainder of curium entering the transfer compartment is assumed to go directly to excretion. Curium translocated to mineral bone is assumed to be retained in that tissue with a biological half-life of 100 years, while curium translocated to the liver is assumed to be retained in that tissue with a biological half-life of 40 years. Curium translocated to the gonads is assumed to be retained indefinitely in that tissue (Richmond and Thomas, 1975).
112
REPORT OF COMMlTTJiE 2
(d) Chelated compounds Chelated forms of curium are not considered in this report. It is known that they have greater biological mobility than do other compounds of curium (Durbin, 1973). 3. Classification of Isotopes for Bone Dosimetry The distribution of curium in the skeleton of the rat is indistinguishable from that of americium (Durbin, 1973). The element is deposited mainly on the endosteal surfaces of mineral bone and only slowly redistributed throughout its volume by processes such as resorption and burial. For this reason all isotopes of curium considered in this report are, for the purposes of dosimetry, assumed to be uniformly distributed over bone surfaces at all times following their deposition in the skeleton.
References Craig, D. K., Cannon, W. C.. Catt. D. L., Herring, J. P., Olson, R. J., Powers, G. J. and Watson, C. R. Distribution of “‘Am and “*Cm in dogs after inhalation of the oxides. In: Pacific Northwest Laboratory Annual Report for 1974 to the USAEC Division of Biomedical and Environmental Research. Part I Biomedical Sciences, pp. 17-18 (BNWL-1950 Pt. 1), 1975. Durbin, P. W. Metabolism and biological effects of the transplutonium elements. In: Uranium, Plutonium, Transplufonium Elements, Eds. Hodge, H. C., Stannard, J. N. and Hursh, J. B., pp. 739-896. Springer-Verlag, Berlin, 1973. ICRP Publication 19, The Metabolism of Compounds of Pluronium and Other Actinides, Pergamon Press, Oxford, 1972. ICRP Publication 23, Report of the Task Group on Reference Man. Pergamon Press, Oxford, 1975. McClellan, R. O., Boyd, H. A., Gallegos, A. F. and Thomas, R. G. (1972). Retention and distribution of ‘“Cm following inhalation of ‘**CmCls and s44Cm01.rs by beagle dogs. Health Phys. 22, 877-885. Richmond, C. R. and Thomas, R. L. (1975). Plutonium and other actinide elements in gonadal tissue of man and animals. Health Phys. 29, 241-250. Sanders, C. L. Toxicology of inhaled 24*CmOa in rats. In: Pacific Northwest Laboratory Annual Report for 1974 to the USAEC Division of Biomedical and Environmental Research. Part I Biomedical Sciences, pp..35-37 (BNWL-1950 Pt. 1), 1975. Semenov, A. I. (1971). Kinetics of the exchange of s4*Cm. Radiobiologiya 11, 155. Semenov, A. I. Distribution of curium 244 in the rat organism. In: Biological Effects of Radiafion from External and Internal Sources, Eds. Moskalev, Yu. I. and Kalistratova, V. S., pp. 302-305. Meditsina, Moscow, 1972. fjemenov. A. I., Moskalev, Yu. I. and Zalikin, G. A. (1973). Influence of age on the absorption of ‘**Cm from the rat gastrointestinal tract. Radiobiologiya 13, 155. Sullivan, M. F. and Crosby, A. L. Absorption of uranium-233, neptunium-237, plutonium-238, americium-241, curium-244 and einsteinium-253 from the gastrointestinal tract of newborn and adult rats. In: Pacific Northwest Laboratory Annual Report for 1974 to the USAEC Division of Biomedical and EitvironmenIal Research. Part I Biomedical Sciences, pp. 105-108 (BNWL-1950 Pt. I), 1975.
LIMITS FOR INTAKES OF RADlONUCLIDES BY WORKERS
Annual limits on intake, ALI
and derived air concentrations, of curium
DAC(Bq/m’)
(40 h/wk) for isotopes
Inhalation
Radionuclide ALI DAC ALI
DAC ALI
Oral
Class W
f, = .5 x 1o-4
f, = 5 x 10-4
6 x lo* 4 x lo6 (5 x 106) Bone surf. 5 x 10’
DAC AL1
2 x 10” (3 x 106) Bone surf. I x 10’ (1 x 10’) Bone surf. 9 x 104 (2 x 105) Bone surf. 5 x IO’ (8 x 10.) Bone surf. 5 x lo4 (8 x 104) Bone surf. 5 x 104 (9 x 104) Bone surf. 1 x IO4 (2 x 104) Bone surf. 2 x 109
DAC
-
DAC ALI DAC AL1 DAC AL1
DAC AL1 DAC AL1 DAC AL1 DAC AL1
4 x 2 x 2 x (2 x Bone
10’ 10. lo4 104) surf.
8 9 x 10s (1 x 106) Bone surf. 4 x 102 1 x lo4 (1 x 104) Bone surf. 4 3 x 102 (5 x 10’) Bone surf. 1 x 10-l 4 x 102 (7 x 102) Bone surf. 2 x 10-l 2 x 10’ (3 s 102) Bone surf. 8 x 1O-3 2 x 102 (3 x 102) Bone surf. 8 x lo-’ 2 x 102 (4 x 10’) Bone surf. 9 x 10-1 5 x 10’ (9 x 10’) Bone surf. 2 x 10-a 5 x 108 (8 x 10’) Bone surf. 2 x 10s
113