Chromium bioavailability

Free, ionic species of metals are at their highest concentrations at lower pH, so metals tend to be more bioavailable under these conditions.121128 At acidic pH, more protons are available to saturate metal-binding sites.99 For example, metals are less likely to form insoluble precipitates with phosphates when the pH of the system is lowered because much of the phosphate has been protonated. Under basic conditions, metal ions can replace protons to form other species, such as hydroxo-metal complexes. Some of the hydroxo-metal complexes are soluble, such as those formed with cadmium, nickel, and zinc, whereas those formed with chromium and iron are insoluble. 

Han F.X., Su Y., Monts D.L., Sridhar B.B.M. Distribution, transformation and bioavailability of trivalent and hexavalent chromium in contaminated soil. Plant Soil 2004b 265 243-252. 

L. Landner and R. Reuther (eds.) Metals in Society and in the Environment. A Critical Review of Current Knowledge on Fluxes, Speciation, Bioavailability and Risk for Adverse Effects of Copper, Chromium, Nickel and Zinc. 2004... 

It is emphasized that Cr+3, probably because of its very low solubility in seawater, appears to have a much lower bioavailability to most groups of marine animals than Ct 6, which is more water soluble (Carr et al. 1982). The clam Rangia cuneata appears to be an exception it accumulated up to 19 mg Cr/kg in soft parts, on a dry weight basis, during exposure for 16 days to chromium-contaminated muds, and retained most of it for an extended period the estimated biological half-time was 11 days (Carr et al. 1982). In general, benthic invertebrates rarely accumulate chromium from contaminated sediments (82 to 188 mg Cr+Vkg) only a few examples have been recorded (Neff etal. 1978). 

Bioavailability of chromium compounds from environmental media... 

Bartlett, R.J. and B.R. James. 1988. Mobility and bioavailability of chromium in soils. Pages 267-304 in J.O. Nriagu and E. Nieboer (eds.) Chromium in the Natural and Human Environments. John Wiley, NY. 

Figure 10.1. Four measurement results corresponding to measurands. 1, the amount concentration of chromium in the test sample 2, the amount concentration of chromium(VI) in the test sample 3, the amount concentration of chromium(VI) in the lake sampled and 4, the amount concentration of bioavailable chromium(VI) in the lake sampled.

Ghode, R., Muley, R. and Sarin, R. (1995) Operationally determined chemical speciation of barium and chromium in drilling fluid wastes by sequential extraction. Chem. Spec. Bioavail., 7, 133—137. 

The bioavailability of chromium(III) was determined in 8 healthy adults who were administered 400 pg chromium(III)/day as chromium picolinate for 3 consecutive days by Gargas et al. (1994). The mean absorption of chromium was 2.8% 1.4 % (standard deviation). 

Uptake of potassium dichromate was determined in a man who was given 0.8 mg of chromium(VI) in drinking water 5 times each day for 17 days (Paustenbach et al. 1996). Steady-state concentrations of chromium in blood were attained after 7 days. Red blood cell and plasma levels returned to background levels 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. 

Risk assessment. The model accounts for most of the major features of chromium(VI) and chromium(III) absorption and kinetics in the rat, and reduction from the chromium(VI) to the chromium(III) valence state, but the bioavailability/absorbability of chromium from environmental sources is mostly unknown, except for bioavailability/absorbability of a few chemically defined salts. Furthermore, the mechanisms by which chromium reserves from bone tissue are released into plasma as well as age, physiological conditions and species variations are important considerations in the refinement of any PBPK model for risk assessment purposes. 

Gargas et al. (1994) employed a three compartment model describing the urinary excretion of chromium (Aitio et al. 1988) to estimate the bioavailability of chromium(III) from chromium(in) picolinate in volunteers ingesting capsules containing 400 pg. The model contained 3 compartments, a fast-exchange compartment receiving 40% of absorbed chromium with a half-life of 7 hours, a medium-exchange... 

Using these models for estimating bioavailability, distribution, and excretion, Steams et al. (1995a) predicted that chromium(III) may accumulate in the body of humans ingesting large doses of chromium picolinate dietary supplements. 

A maximum of 47% of the total chromium in ferrochrome smelter dust may be bioavailable as indicated by acid/base extraction. About 40% of the bioavailable chromium may exist as chromium(VI), mostly in the form of Cr207"2 or Cr04"2 (Cox et al. 1985). There are no data in the reviewed literature indicating that chromium particles are transported from the troposphere to the stratosphere (Pacyna and Ottar 1985). By analogy with the residence time of general particles with mass median diameters similar to that of chromium, the residence time of atmospheric chromium is expected to be <10 days (Nriagu 1979). 

The bioconcentration factor (BCF) for chromium(VI) in rainbow trout (Salmo gairdneri) is 1. In bottom-feeder bivalves, such as the oyster (Crassostrea virginica), blue mussel (Mytilus edulis), and soft shell clam (Mya arenaria), the BCF values for chromium(III) and chromium(VI) may range from 86 to 192 (EPA 1980, 1984a Fishbein 1981 Schmidt and Andren 1984). The bioavailability of chromium(ni) to freshwater invertebrates (Daphnia pulex) decreased with the addition of humic acid (Ramelow et al. 

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