The Importance of Acid Digestion of Urine Prior to Spontaneous Deposition of 210Po

Abstract

Historically, radiochemical analysis of 210Po in urine has used spontaneous deposition of the nuclide directly from raw urine onto a suitable metal disc. Consequently, the urinary excretion fraction for Po in some current metabolic and dosimetric models is based on studies which inherently assume that metabolized (i.e., filtered out of the blood by the kidneys) 210Po is plated with the same efficiency as tracer 210Po which has been added to urine samples. Urine samples collected after intravenous administration of 210Po citrate to two species of nonhuman primates were divided and simultaneously analyzed via two methods: the historical procedure of plating 210Po from raw urine for one sample and a method which includes the addition of 208Po tracer and sample digestion with concentrated HNO3 prior to 210Po deposition for the other sample. A more significant amount of 210Po was consistently recovered when the urine was wet ashed then when it was not wet ashed. A temporal relationship was found to describe the change in the ratio of the deposition recoveries for the two methods. Possible mechanisms for this phenomenon and its dosimetric implications are discussed.

ICRP Publication 137: Occupational Intakes of Radionuclides: Part 3

“…The selected value of 3 is a compromise, based on a fairly wide range of values determined for human subjects and non-human primates. The selected value is slightly lower than the value determined for tamarins (Cohen et al., 1989; Fellman et al., 1989) and higher than the value determined for baboons (Fellman et al., 1989). The true ratio seems likely to be lower than the value of 10 or more determined by Silberstein et al.…”

“…The true ratio seems likely to be lower than the value of 10 or more determined by Silberstein et al. (1950b) for human subjects, in view of findings of Fellman et al. (1989) that the measurement technique of Silberstein et al substantially underestimates the concentration of polonium in urine, at least in baboons and tamarins.…”

“…Urine and blood both showed a biological half-time of 43 d. Total urinary and faecal excretion determined for Days 47–52 post exposure indicated a ratio of faecal to urinary excretion of 6.5. The technique used to measure 210 Po in urine did not involve wet-ashing of samples, and thus could have underestimated urinary excretion of 210 Po (Fellman et al., 1989). (580) Scott and West (1975) measured excretion of 210 Po in urine and faeces of a worker following accidental inhalation of material thought to consist of small particles of 210 Po oxide.…”

“…Thus, it appears that at least 14.5% of the ingested amount was absorbed to blood. The estimate of 0.5% for urinary excretion may be an underestimate due to problems with the measurement technique (Fellman et al., 1989). (583) Subject 2 of Silberstein et al.…”

“…Urine and blood both showed a biological half-time of 43 d. Total urinary and faecal excretion determined for Days 47–52 post exposure indicated a ratio of faecal to urinary excretion of 6.5. The technique used to measure 210 Po in urine did not involve wet-ashing of samples, and thus could have underestimated urinary excretion of 210 Po (Fellman et al., 1989).…”