TOXICOLOGICAL PROFILE FOR CHROMIUM - Davidborowski.com

CHROMIUM 1292. HEALTH EFFECTSat approximately 6 hour intervals over a 5–15 minute period. After at least 2 days without dosing, the3-day exposure regimen was repeated at 10 mg chromium/day. Estimated doses based on body weightwere 0.05 and 0.1 mg/kg/day, respectively. Bioavailability based on 4-day urinary excretion was 1.7%(range 0.5–2.7%) at 0.05 mg chromium(VI)/kg/day and 3.4% (range 0.8–8.0%) at 0.1 mgchromium(VI)/kg/day. Absorption of 0.05 mg chromium(VI)/kg appeared to be somewhat lower whengiven as three divided doses rather than when given as a single bolus dose (1.7 vs. 5.7%).Uptake of potassium dichromate was determined in a man who was given 0.8 mg of chromium(VI) indrinking water 5 times each day for 17 days (Paustenbach et al. 1996). Steady-state concentrations ofchromium in blood were attained after 7 days. Red blood cell and plasma levels returned to backgroundlevels within a few days after exposure was stopped. The data are consistent with a bioavailability of 2%and a plasma elimination half-life of 36 hours.Studies with 51 chromium in animals indicate that chromium and its compounds are also poorly absorbedfrom the gastrointestinal tract after oral exposure. When radioactive sodium chromate (chromium(VI))was given orally to rats, the amount of chromium in the feces was greater than that found when sodiumchromate was injected directly into the jejunum. Since chromium(III) is absorbed less readily thanchromium(VI) by the gastrointestinal tract, these results are consistent with evidence that the gastricenvironment has a capacity to reduce chromium(VI) to chromium(III). Furthermore, the administration ofradioactive chromium(III) or chromium(VI) compounds directly into the jejunum decreased the amountof chromium recovery in the feces indicating that the jejunum is the absorption site for chromium(Donaldson and Barreras 1966). Absorption of either valence state was #1.4% of the administered oraldose in rats (Sayato et al. 1980) and hamsters (Henderson et al. 1979). Based on distribution (seeSection 2.3.2.2) and excretion (see Section 2.3.4.2) studies in rats administered chromium by gavage for2–14 days from various sources, that is, from sodium chromate (chromium(VI)), from calcium chromate(chromium(VI)), or from soil contaminated with chromium (30% chromium(VI) and 70%chromium(III)), the low gastrointestinal absorption of chromium from any source was confirmed.Chromium appeared to be better absorbed from the soil than from chromate salts, but less than 50% of theadministered chromium could be accounted for in these studies, partly because not all tissues wereexamined for chromium content and excretion was not followed to completion (Witmer et al. 1989,1991). Adult and immature rats given chromium(III) chloride absorbed 0.1 and 1.2% of the oral dose,respectively (Sullivan et al. 1984). This suggests that immature rats may be more susceptible to potentialtoxic effects of chromium(III) compounds.