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At least 19 recordsLinked to original sources
PubMed2002

Chromium isotopes and the fate of hexavalent chromium in the environment.

Measurements of chromium (Cr) stable-isotope fractionation in laboratory experiments and natural waters show that lighter isotopes reacted preferentially during Cr(VI) reduction by magnetite and sediments. The 53Cr/52Cr ratio of the product was 3.4 +/- 0.1 per mil less than that of the reactant. 53Cr/52Cr shifts in water samples indicate the extent of reduction, a critical process that renders toxic Cr(VI) in the environment immobile and less toxic.

California↗
PubMed1994

Measurement of blood volume with an enriched stable isotope of chromium (53Cr) and isotope dilution by combined gas chromatography-mass spectrometry.

We used an established isotope dilution gas chromatography-mass spectrometry method to measure blood volumes with an enriched stable isotope of chromium. The results were compared with those of the conventional method, which involves radioactive 51Cr. The two methods were compared simultaneously in two male subjects of different sizes, and essentially identical volumes were obtained. The isotope dilution method is insensitive to contamination with natural (unenriched) chromium and can be used to measure all of the stable isotopes of chromium. The method has potential applications in simultaneous erythrocyte survival studies. The absence of radioactivity makes possible an accurate means of studying blood volume changes in children and during pregnancy.

Blood Volume Determination↗
PubMed1998

Distribution of a stable isotope of chromium (53Cr) in serum, urine, and breast milk in lactating women.

To determine the fate and distribution of chromium during lactation, six lactating women (25-38 y old) were given three doses of the tracer 53Cr (7.55 micromol/d, or 400 microg/d) on days 1, 2, and 3 of the study. Diet records, blood samples taken while subjects were fasting, and 24-h composite milk and urine samples were collected from day 0 to day 6. Fasting blood samples, morning milk samples, and 24-h urine samples were also collected on days 8, 10, 15, 30, 60, and 90. 53Cr and natural and total chromium concentrations in biological fluids were measured with gas chromatography-mass spectrometry and total urinary chromium was measured with atomic-absorption spectrometry. 53Cr was detectable in serum 2 h after dosing and continued to be detected from day 30 to day 60. Changes in total serum chromium concentration in response to the oral dose suggested that chromium concentrations in blood were not tightly regulated. 53Cr was not detected in breast milk and no significant changes in natural chromium concentration in milk were observed in response to the oral doses, suggesting that breast-milk chromium concentrations are independent of intake. The estimated chromium intake of exclusively breast-fed infants was 2.5 nmol/d (0.13 microg/d), below the lower end of the range of estimated safe and adequate daily dietary intakes (10-40 microg/d) for infants 0-6 mo of age. The baseline chromium concentration in urine and the minimum 53Cr absorption in lactating women were comparable with values for nonpregnant, nonlactating subjects. Chromium losses in breast milk do not appear to be compensated for via increased absorption or decreased excretion.

Administration, Oral↗
PubMed1998

Acute and chronic resistive exercise increase urinary chromium excretion in men as measured with an enriched chromium stable isotope.

Both exercise and chromium exert beneficial effects on insulin function. The mechanism by which exercise improves insulin response may involve an alteration in Cr metabolism. To determine the effects of acute and chronic resistive exercise on urinary Cr losses, we measured the effects of acute resistive exercise and 16 wk of resistive exercise training on urinary Cr losses of 10 men 53-63 y of age. Subjects consumed diets in compliance with the American Heart Association Phase I diet with a Cr content of 30 +/- 4 microg/d. Sixteen weeks of resistive exercise training led to approximately 40% increases in upper and lower body strength, increases in fat-free mass and decreases in the percentage of body fat. An enriched stable isotope of Cr, 53Cr, was employed to differentiate the exogenously administered Cr from the native endogenous Cr. Both acute and chronic resistive exercise increased 53Cr losses. These data demonstrate that the improvements in body composition due to resistive exercise are associated with increased urinary Cr losses that are consistent with increased absorption.

Adipose Tissue↗
PubMedDate not supplied

Red cell volume determination using a stable isotope of chromium.

OBJECTIVE: To validate and improve a method of red cell volume determination by use of a stable isotope of chromium. METHODS: Twelve subjects were sequentially injected with red blood cells labeled with a stable isotope of chromium (53Cr) and red blood cells labeled with radioisotopic chromium (51Cr). Measurement of 53Cr dilution was by gas chromatography/mass spectrometry. Measurement of 51Cr dilution was by gamma counter. RESULTS: Comparison of the two methods led to results that differed on average by 34.5 +/- 45.0 mL (1.8 +/- 2.2%), 0.3 to 3.2%, 95% confidence interval. CONCLUSION: Measurement of red cell volume by use of a stable isotope of chromium is accurate, with potential applications including measurement in pregnant women and children or other groups in whom exposure to radioisotopes is undesirable.

Blood Volume↗
PubMed2004

Using chromium stable isotope ratios to quantify Cr(VI) reduction: lack of sorption effects.

Chromium stable isotope values can be effectively used to monitor reduction of Cr(VI) in natural waters. We investigate effects of sorption during transport of Cr(VI) which may also shift Cr isotopes values, complicating efforts to quantify reduction. This study shows that Cr stable isotope fractionation caused by sorption is negligible. Equilibrium fractionation of Cr stable isotopes between dissolved Cr(VI) and Cr(VI) adsorbed onto gamma-Al2O3 and goethite is less than 0.04 per thousand (53Cr/52Cr) under environmentally relevant pH conditions. Batch experiments at pH 4.0 and pH 6.0 were conducted in series to sequentially magnify small isotope fractionations. A simple transport model suggests that adsorption may cause amplification of a small isotope fractionation along extreme fringes of a plume, leading to shifts in 53Cr/52Cr values. We therefore suggest that isotope values at extreme fringes of Cr plumes be critically evaluated for sorption effects. A kinetic effect was observed in experiments with goethite at pH 4 where apparently lighter isotopes diffuse into goethite clumps at a faster rate before eventually reaching equilibrium. This observed kinetic effect may be important in a natural system that has not attained equilibrium and is in need of further study. Cr isotope fractionation caused by speciation of Cr(VI) between HCrO4- and CrO4(2-) was also examined, and we conclude that it is not measurable. In the absence of isotope fractionation caused by equilibrium speciation and sorption, most of the variation in delta53Cr values may be attributed to reduction, and reliable estimates of Cr reduction can be made.

Absorption↗