Studies of strontium biokinetics in humans. Part 1: optimisation of intrinsic labelling of foodstuffs with stable isotopes of strontium.

The radioactive isotopes of strontium, mainly (90)Sr, which are common fission products, may significantly contribute to the internal exposure of the population in case of their accidental release into the environment and transfer to the food chain. For (90)Sr, the internal radiation dose is significantly dependent on the fractional absorption of the ingested activity (f(1)-value). Human data on the absorption of dietary strontium and of soluble forms of the element give values ranging from about 0.15 to 0.45 (up to 1.0) for adults. The International Commission on Radiological Protection (ICRP) has adopted f(1)-values of 0.6 for children of less than 1 year of age, 0.4 for children between 1 and 15 years and 0.3 for adolescents above 15 years of age. This study was aimed at investigating how far these values correspond to the actual uptake of strontium from contaminated foodstuffs. A methodology is presented that has been developed for preparing foodstuffs intrinsically labelled with stable isotopes and that will be used in tracer kinetic investigations. The results show that cress and salad can be adequately labelled, i.e. a strontium concentration of 1.36+/-0.47 g per kg of cress (wet weight) and of 0.29+/-0.04 g per kg of salad (wet weight) may be obtained within 15 days and 24 days, respectively. For the biokinetic investigations on humans, applying stable isotopes of Sr as tracers, about 0.1-1 mg strontium is required per volunteer, i.e. a few grams of the edible parts of the labelled material are sufficient.