URINARY CHROMIUM CONCENTRATIONS IN HUMANS FOLLOWING INGESTION OF SAFEDOSES OF HEXAVALENT AND TRIVALENT CHROMIUM - IMPLICATIONS FOR BIOMONITORING

In this study, we evaluate the significance of increased urinary chrom ium concentrations as a marker of chromium exposure and potential heal th risk. Six human volunteers ingested trivalent chromium [Cr(III)] an d hexavalent chromium [Cr(VI)] at doses that are known to be sale but are much higher than typical dietary levels. The following dosing regi men was used: d 1-7, 200 mu g/d chromium picolinate (a dietary supplem ent); d 8-10, Cr(VI) inges tion at the U.S. Environmental Protection A gency (EPA) reference dose (RfD) of 0.005 mg/kg/d; d 11-13, no dose; d 14-16, Cr(III) ingestion at the U.S. EPA RfD of 1.0 mg/ kg/d; and d 1 7-18, postdose. Urine voids were collected throughout the dosing perio ds and analyzed for chromium. Our findings are as follows: (1) ingesti on of 200 mu g/d of chromium picolinate yielded significantly elevated urine concentrations such that each participant routinely exceeded ba ckground, (2) ingestion of the Cr(VI) RfD (0.005 mg/kg/d) yielded indi vidual mean urinary chromium levels (1.2-23 mu g/L) and a pooled mean urinary chromium level (2.4 mu g/L) that significantly exceeded backgr ound, and (3) ingestion of the Cr(III) RfD yielded no significant incr ease in urinary chromium concentrations, indicating that little, if an y, absorption occurred. Our work identified three critical issues that need to be accounted for in any future studies that will use urinary chromium as a marker of exposure. First, a minimum urinary chromium co ncentration of approximately 2 mu g/L. should be used as a screening l evel to critically identify individuals who may have experienced eleva ted exposures to chromium. Second, if Cr(III) levels in soils are know n to be less than 80,000 ppm and the Cr(III) is insoluble, urinary chr omium concentrations are nor an appropriate marker of exposure. Third, newer forms of chromium supplements that contain organic forms of Cr( III) must be considered potential confounders and their contribution t o residential chromium uptake must be carefully evaluated.