Transfer of Aged Pu to Cattle Grazing on a Contaminated Environment

Abstract

Estimates are obtained of the fraction of ingested or inhaled 239+240Pu transferred to blood and tissues of a reproducing herd of beef cattle, individuals of which grazed within fenced enclosures for up to 1064 d under natural conditions with no supplemental feeding at an arid site contaminated 16 y previously with Pu oxide. The estimated (geometric mean [GM]) fraction of Pu transferred from the gastrointestinal tract to blood serum was about 5 x 10(-6) (geometric standard error [GSE] = 1.4) with an approximate upper bound of about 2 x 10(-5). These results are in reasonable agreement with the value of 1 x 10(-5) recommended for human radiation protection purposes by the International Commission on Radiological Protection (ICRP) for insoluble Pu oxides that are free of very small particles. Also, results from a laboratory study by Stanley (St75), in which large doses of 238Pu were orally administered daily to dairy cattle for 19 consecutive days, suggest that aged 239+240Pu at this arid grazing site may not be more biologically available to blood serum than fresh 239+240Pu oxide. The estimated fractions of 239+240Pu transferred from blood serum to tissues of adult grazing cattle were: femur (3.2 X 10(-2), 1.8; GM, GSE), vertebra (1.4 X 10(-1), 1.6), liver (2.3 X 10(-1), 2.0), muscle (1.3 X 10(-1), 1.9), female gonads (7.9 X 10(-5), 1.5), and kidney (1.4 X 10(-3), 1.7). The blood-to-tissue fractional transfers for cattle initially exposed in utero were greater than those exposed only as adults by a factor of about 4 for femur (statistically significant) and of about 2 for other tissues (not significant). The estimated (GM) fraction of inhaled Pu initially deposited in the pulmonary lung was 0.34 (GSE = 1.3) for adults and 0.15 (GSE = 1.3) for cattle initially exposed in utero (a statistically significant difference), which may be compared with the expected fraction of 0.11 at the study site using the ICRP lung model for humans.

Gastrointestinal fractional absorption of radionuclides in adult domestic ruminants

“…Coughtrey, 1990;Harrison et al, 1994;Gilbert et al, 1989;Ham et al, 1989). Whilst for some radionuclides this approach may provide an estimate of absorption, it is insensitive and negative values of absorption can be derived.…”

“…These are similar to the values of fractional absorption of 1.4 Â 10 À4 estimated by Sutton et al (1978). Gilbert et al (1989) report an absorption fraction of 1 Â10 À5 for 241 Am for cattle grazing in an enclosure on a nuclear weapons test site. This value was based on transfer from the gastrointestinal tract to blood serum using a model and has not been incorporated into the summary information presented in Table 1 as intake rates of vegetation and soil were assumed.…”

The transfer of 239/240Pu to cow milk

“…Based on Stanley et al (1974Stanley et al ( , 1976) data Review 1.5 Â 10 À6 Sirotkin (1987) Origin not specified Review 2.0 Â 10 À6 Korniejev et al (1987) Denotes maximum value; refers to three Russian references and one American reference Review 1.0 Â 10 À7 Sirotkin (1991) Value given in % daily intake of 1.0 Â 10 À5 . Origin not specified Review 1.1 Â 10 À6 IAEA (1994) Based on Coughtrey, 1990.100 days prediction Review 1.1 Â 10 À6 Jackson and Stone (2003) Derived from data in Smith et al (1979) and Gilbert et al (1988) but not specified how Model 2.8 Â 10 À7 Coughtrey et al (1984) For 100 days. Retention function, milk concentration assumed to be in equilibrium with that of soft tissues other than liver.…”

“…However, for ruminants fed environmental sources of 239/240 Pu, Beresford et al (2000b) estimated true absorption values in the range from 7 Â 10 À5 to 1.2 Â 10 À4 . Gilbert et al (1988Gilbert et al ( , 1989) estimated absorption factors for cattle grazing in an enclosure on a nuclear weapons test site of 5 Â 10 À6 for 239/240 Pu and 1 Â 10 À4 for 238 Pu, based on transfer from the gut to blood serum using a model incorporating activity concentrations, ingestion rates and biological half-lives. Therefore, on the basis of the available ruminant data relating to environmental relevant sources, the gastrointestinal absorption factor used in the commonly quoted model of Coughtrey (1990) is too high by at least an order of magnitude.…”

Use of the true absorption coefficient as a measure of bioavailability of radiocaesium in ruminants

“…A general problem associated with existing f 1 values is that they do not always represent an estimation of the same measurement [9,24]; for example, the degree of absorption may be represented by A a [9], tissue retention [41][42][43] or A t [23]. This inconsistency needs to be addressed if any confidence is to be placed in outputs of predictive models which utilise f 1 values.…”