Renal excretion of tellurium after peroral administration of tellurium in different forms to healthy human volunteers.

As tellurium ranks among the rare non-essential trace elements there is only little known of its intestinal absorption and its metabolic behaviour in humans. Data for risk evaluations needed for occupational medicine are based on animal experiments only. In order to investigate the metabolic behaviour of tellurium in man, tellurium in different forms was administered perorally to healthy male human volunteers. It was given as sodium tellurate, sodium tellurite, metallic colloid and intrinsically bound in cress. For the latter, cress was cultivated with tellurium-containing water in order to provide tellurium for ingestion in a form which is more equivalent to foodstuffs. After the administration the urinary excretion of tellurium was determined. Tellurium concentrations were measured in urine samples by means of graphite furnace atomic absorption spectroscopy (GFAAS) after wet ashing and a preconcentration of tellurium by solvent extraction with isobutyl methyl ketone (IBMK). From the cumulative tellurium excretion in the first four days after the administration, a percentage intestinal absorption of 25% +/- 10% for soluble tellurium salts can be calculated. The renal tellurium excretion is faster after administration of hexavalent tellurium than after ingestion of the tetravalent form. This can explain the higher toxicity of the tetravalent tellurium compounds found in animal experiments. The introduction of tellurium to cress lowered the intestinal absorption to approximately 15%. For metallic tellurium the fractional intestinal absorption was found to be about 10%.