The influence of complexing agents on the solubility and absorption of aluminium in rats exposed to aluminium in water

The influence of citrate (0-31 mm), fluoride (0 or 2.6 mM) and silicate (0 or 2.6 mM) on the absorption of Al (0-18 mM) was studied in rats. We tested the hypothesis that the solubility and absorption of Al increases in the g astrointestinal (GI) tract in the presence of the complexing agents. Male r ats were exposed for 6 or 7 weeks to soluble Al in acidic drinking water (p H 2.5-3.0) with or without the complexing agents. At the end of exposure Al was fractionated in the stomach content, in order to study if the solubili ty of Al was changed after ingestion. Al absorption was estimated by Al ana lysis of the right femur bone. Speciation calculations indicated that citra te and fluoride caused formation of soluble Al-citrate (97%) and -fluoride (>60%) complexes in the water. Silicate did not affect the theoretical spec iation. In all cases, a large fraction of soluble Al became insoluble in th e stomach after ingestion. The concentration of soluble Al increased only i n the presence of citrate or a mixture of fluoride and silicate, but citrat e was the only complexing agent that influenced the absorption of Al in the rat. This indicates that the form of Al may be changed in the GI tract whe n soluble drinking-water Al is ingested, and that the solubility of Al in d rinking water and GI tract may not be good predictors of the bioavailabilit y of Al even when chelating agents are present.