In vitro reduction kinetics of hexavalent chromium in human blood.

This study examines time- and concentration-dependent changes in distribution of hexavalent chromium [Cr(VI)] and total chromium [Cr-(TOT)] in reconstituted human blood following addition of potassium dichromate. Fresh human blood stabilized with EDTA was obtained from human volunteers soon after meal ingestion and at 2.5 h after a light meal (herein defined as "2.5-h fasted" conditions). Cr(VI) spiked into plasma under 2.5-h fasting conditions at 3.0-12.5 micrograms/L was stable for several hours, indicating a lack of appreciable reductive capacity in isolated plasma. Spiked plasma following a recent meal exhibited immediate but variable reduction of Cr(VI) up to 300 micrograms/L. When the spiked plasma was recombined with the red blood cell (RBC) fraction, rapid reduction occurred in both the plasma and the RBC fractions based on measurement of Cr(VI) and Cr(TOT). The data indicate that plasma reduction capacity is enhanced by a recent meal, but may be overwhelmed at Cr(VI) concentrations between 2000 and 10,000 micrograms/L. These data also suggest that the RBC fraction apparently has the capacity to reduce Cr(VI) at concentrations in blood up to 15,000 micrograms/L, and that the rate of Cr(VI) uptake into RBCs may not exceed the rate of intracellular reduction at these concentrations.