ABSORPTION AND ELIMINATION OF TRIVALENT AND HEXAVALENT CHROMIUM IN HUMANS FOLLOWING INGESTION OF A BOLUS DOSE IN DRINKING-WATER

These studies investigate the magnitude and valence state of chromium absorbed following plausible drinking water exposures to chromium(VI). Four adult male volunteers ingested a single dose of 5 mg Cr (in 0.5 liters deionized water) in three chromium mixtures: (1) Cr(III) chlori de (CrCl3), (2) potassium dichromate reduced with orange juice (Cr(III )-OJ); and (3) potassium dichromate [Cr(VI)], Blood and urine chromium levels were followed for 1-3 days prior to and up to 12 days after in gestion, The three mixtures showed quite different pharmacokinetic pat terns. CrCl3 was poorly absorbed (estimated 0.13% bioavailability) and rapidly eliminated in urine (excretion half-life, similar to 10 hr), whereas Cr(III)-OJ was absorbed more efficiently (0.60% bioavailabilit y) but more slowly (half-life, similar to 17 hr), and Cr(VI) had the h ighest bioavailability (6.9%) and the longest half-life (similar to 39 hr). All three chromium mixtures caused temporary elevations in red b lood cell (RBC) and plasma chromium concentrations, but the magnitude and duration of elevation showed a clear trend (Cr(VI) > Cr(III)-OJ > CrCl3), The data suggest that nearly all the ingested Cr(VI) was reduc ed to Cr(III) before entering the bloodstream based on comparison to R BC and plasma chromium patterns in animals exposed to high doses of Cr (VI), These findings support our prior work which suggests that water- soluble organic complexes of Cr(III) formed during the reduction of Cr (VI) in vivo explain the patterns of blood uptake and urinary excretio n in humans at drinking water concentrations of 10 mg/liter or less. ( C) 1996 Academic Press, Inc.