Chromium - Toxicology of Metals - page 480

After parenteral administration to rats, Cr is excreted
predominantly in the urine. Hopkins (1965) found less
than 2% of the intravenous dose in the feces 8 hours
after injection. Visek et al . (1953) found less than 20%
after 4 days. Studies on the mechanism of Cr excretion
by the kidneys indicate glomerular fi ltration followed
by tubular reabsorption of up to 60% of the fi ltered
amount (Collins et al ., 1961).
The rate of excretion of Cr in the gastrointesti-
nal tract is not known. Biliary excretion of Cr has
been demonstrated in the rat (Cikrt and Bencho,
1979; Norseth et al ., 1982); less than 1% of an intra-
venously injected dose of the trivalent form was
excreted in 5 hours, 6-8% of corresponding doses of
the hexavalent form was found (Norseth et al ., 1982).
The fecal content of Cr may vary considerably and
is mainly a consequence of ingested unabsorbed Cr
compounds.
The elimination curve for Cr, as measured by
whole-body counting, has an exponential form. In rats,
three different compartments of the curve have been
identifi ed with half-times of 0.5, 5.9, and 83.4 days,
respectively (Mertz et al ., 1965).
In kinetic studies in humans to evaluate red cell
lifetime, a rapid excretion component related to non-
erythrocyte Cr has been identifi ed. Chromium used for
labeling of erythrocytes is almost exclusively excreted
in the urine. Kinetic studies of this rapid component
have not been reported, and half-time is only given for
Cr representing the red cell compartment (Shih et al .,
1972). Tossavainen et al . (1980) calculated a half-life of
15-41 hours for Cr in urine from four welders using a
linear one-compartment kinetic model. The kinetics of
excretion of Cr as the GTF or chromomodulin is not
known.

other parts of the world. Values up to approximately
300 µ g/kg for the lung and 40 µ g/kg for the liver and

approximately 15 g/kg for the kidneys were reported

from Japan (Hyodo et al ., 1980). All values are on a
wet-weight basis. Gerhardsson and Nordberg (1993)
reported on a median lung tissue concentration of
390

µ

g Cr/kg wet weight in smelter workers in North-
ern Sweden having attracted lung cancer compared
with 110

µ

g Cr/kg in deceased rural referents.
Previously reported normal levels of Cr in blood of
3-30

µ

g/L (Feldman et al ., 1968) and urinary excretion
of up to 10

µ

g/day (Cornelius et al ., 1975; Mertz, 1975)
were probably too high. Later the concentration of Cr
in plasma was reported to be 0.14

µ

g/L (Nomiyama
et al ., 1980; Veillon et al ., 1979). Paakka et al . (1989)
determined the lung tissue level of Cr in 45 deceased
subjects in Northern Finland using plasma emission
spectroscopy and found the average level at 1.3 and
4.8

µ

g/g in dry and wet tissue, respectively. For a
review, see Guthrie (1982).
The Cr concentration in all tissues decreases from
the moment of birth up to the age of approximately
10. After this time, there is a slight increase in lung
concentration, but a continuing fall in all other organs
(Schroeder et al ., 1962). This indicates that Cr in the
lungs is a result of deposition from inhaled air, whereas
Cr in food is the main source of Cr in other organs.

µ

7 DOSE AND OUTCOME EFFECTS

Trivalent Cr has been suggested to be essential for
the maintenance of normal glucose tolerance in ani-
mals and humans, and the factor of the group of fac-
tors containing Cr(III), called GTF (chromodulin) has
been suggested to be responsible for the favorable
action of Cr (Mertz, 1969; 1975). The Cr status in diabe-
tes subjects seems to be abnormal, and Cr is capable of
potentiating insulin, but so far the exact structure(s) of
the biological active Cr complex(es) has (have) not been
identifi ed (Mertz, 1982). Therefore, Cr supplementa-
tion still cannot be considered as a therapeutic agent in
established diabetes, however, it may delay or prevent
the appearance of diabetes in some cases (Guthrie,
1982). In reviewing the biochemistry of Cr, Vincent
(2000) indicated that recent studies had shed some
light on how Cr contributes to maintaining a proper
carbohydrate metabolism on a molecular level, where
it seems that the oligopeptide chromodulin seems to
play a role in binding chromic ions in response to a
chromic ion fl ux, resulting in stimulation of the recep-
tor's tyrosine kinase activity. In this, the chromodulin
may play a role in an autoamplifi cation mechanism in
insulin signaling.

6.5 Concentrations in Biological
Fluids and Tissues
The highest concentration of Cr in humans is found
in hair, values from 200-2,000

g/kg as reported (Mertz,
1969). Schroeder et al . (1962) reported on 700

µ

g/kg of
Cr in the lung for persons in the New York/Chicago
area; other organs had lower concentration: liver
270

µ

g/kg. There are geographi-
cal variations in Cr concentrations: the values from the
Denver area were 140

µ g/kg and kidney 90 µ

µ g/kg for the lung, 30 µ g/kg for

the liver, and 40 g/kg for the kidney. In a case-refer-

ent study on lung cancer in Finland, Antilla et al . (1989)
found that average lung tissue levels of Cr in smokers
was 6.4

µ

g/g in nonsmoking referents.
A high concentration of Cr in the lung and a lower con-
centration in other organs were confi rmed by Tipton
and Cook (1963, 1965) both in the United States and

µ g/g versus 2.2 µ