HUMAN INGESTION OF CHROMIUM(VI) IN DRINKING-WATER - PHARMACOKINETICS FOLLOWING REPEATED EXPOSURE

Regulatory agencies have established safe drinking water concentration s for hexavalent chromium [Cr(VI)] based in part on the presumed capab ility of human gastric juices to rapidly reduce Cr(VI) to nontoxic tri valent chromium [Cr(III)] prior to systemic absorption. This study exa mines dose-related pharmacokinetics in humans following repeated oral exposure to Cr(VI) in drinking water. In particular, we sought to exam ine whether plausible drinking water exposures to Cr(VI) caused a sust ained increase in red blood cell chromium levels, a specific marker fo r systemic uptake of Cr(VI). Adult male volunteers ingested a liter (i n three volumes of 333 mi, at approximate 6-hr intervals) of deionized water containing Cr(VI) concentrations ranging from 0.1 to 10.0 mg/li ter. Samples of urine, plasma, and red blood cells were collected and analyzed for chromium. A dose-related increase in urinary chromium exc retion was observed in all volunteers. Red blood cell and plasma chrom ium concentrations became elevated in certain individuals at the highe st doses. The RBC chromium profiles suggest that the ingested Cr(VI) w as reduced to Cr(III) before entering the bloodstream, since the chrom ium concentration in the RBCs dropped rapidly postexposure. These find ings suggest that the human gastrointestinal tract has the capacity to reduce ingested Cr(VI) following ingestion of up to 1 liter of water containing 10.0 mg/liter of Cr(VI), which is consistent with USEPA's p osition that the Cr(VI) drinking water standard of 0.10 mg Cr(VI)/lite r is below the reductive capacity of the stomach. (C) 1997 Academic Pr ess