1 26Al and 67Ga were given as citrates to a healthy male volunteer by intravenous injection. The retention of both tracers was studied by body radioactivity measurement. Levels in blood and excreta were determined by y-ray spectrometry and/or accelerator mass spectrometry. 2 More than half of the 26Al had left the blood after 15 min and the decline continued, leaving <1% in blood after 2 d; the losses occurred both to renal excretion and through uptake by other compartments. Estimated excre tion up to 13 d was 83% (urine) and 1.8% (faeces). Whole-body retention of 15% at 13 d declined to ∼4% at 1178 d, when the daily reduction corresponded to a bio logical half-life of 7 y, suggesting that sustained intake of dietary aluminium may lead to a progressively increas ing internal deposit. 3 The metabolism of 67Ga differed markedly from that of 26Al in all aspects studied.

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A study was undertaken to determine the fraction of ingested aluminium taken up by two male volunteers, following their ingestion of either aluminium citrate or aluminium hydroxide. In addition, the effects of simultaneous citrate ingestion on the gastrointestinal absorption of aluminium from its hydroxide was studied. Volunteers received three oral doses of 26Al-labelled aluminium compound in water. The doses were administered directly into the stomach using a paediatric feeding tube. Blood samples were collected from the volunteers at 1, 4 and 24 h after administration, and their daily output of urine and faeces was collected for 6 days. These samples were analysed for their 26Al content using either coincidence gamma-counting or accelerator mass spectrometry. The uptake of aluminium was greatest following its administration in the citrate form and was least following intake as the aluminium hydroxide suspension. The co-administration of citrate, with the aluminium hydroxide suspension, was found to enhance the levels of 26Al uptake in both volunteers. Using a urinary excretion factor based on the results of previous studies, the fractional aluminium uptake from each of the species was calculated: aluminium citrate, 5.23 x 10(-3); aluminium hydroxide, 1.04 x 10(-4); aluminium hydroxide with citrate, 1.36 x 10(-3).

1 Six healthy male volunteers received intravenous injec tions of 26Al as citrate. Accelerator mass spectrometry and γ-ray spectrometry were used to determine levels of the tracer in blood and excreta at times up to 5-6 d. 2 There was a rapid clearance from blood (mean 2% of injection remaining after 1 d) and major loss in urine (59% up to 1 d), but 27 ± 7 (s.d.)% was retained in the body at 5 d. Faecal excretion was negligible (1% up to 5 d). 3 The mean results accord with the early metabolic pat tern in the single subject of a previous, more extensive study, who had retained 4% of the injection after 3 y. Together, the two studies point to the likelihood of large inter-subject differences in the long-term accumulation of dietary aluminium by populations receiving a given level of daily intake.

1 After overnight fasting, two young male adults each received a single oral dose of 100 Bq 26Al in tap water. Coincidence gamma-ray spectrometry and accelerator mass spectrometry were used to determine the 26Al content of excretion collections and of blood samples. 2 Close to 100% of the intake was recovered in faeces during the first 7 days. Gastro-intestinal uptake, determined by comparing urinary excretion with patterns previously established following intravenous administration of 26Al, averaged 0.22% in the two subjects. 3 Uptake fractions based on comparisons of blood concentration following ingestion and injection were much lower, but were judged to be unreliable. It is concluded that aluminium present in most water supplies is unlikely to contribute as much as 1% of a typical daily uptake of 10 mg from food.