Chemistry Reference
In-Depth Information
increases, uptake of molybdenum increases. For exam-
ple, a Scottish study demonstrated that grasses grown
in soil with pH 5.5 have a molybdenum content of
1.1 mg/kg dry weight and the molybdenum content
increases progressively reaching 5.2 mg/kg when the
pH is 7.5 (Mills and Davis, 1987).
demonstrated that hexavalent molybdenum is readily
absorbed from the gastrointestinal tract. Absorption
is between 40 and 85% in guinea pigs, rats, and goats
(Anke
et al
., 1971; Fairhall
et al
., 1945; Neilands
et al
.,
1948; Van Campen and Mitchell, 1965).
Molybdenum is very well absorbed by humans over
a broad range of intakes. Absorption, determined by
use of stable isotopes as tracers, ranged from 88-93%
with dietary intakes of 22-1400
4.2 Water, Soil, and Ambient Air
The concentration of molybdenum in the ocean is
approximately 0.01 mg/L (Kuroda and Tarni, 1974;
Muzzarelli and Rocchetti, 1973; Sugawara
et al
., 1962).
Levels in American rivers range from 5-30 mg/L (Ture-
kian and Scott, 1967). Molybdenum in drinking water
ranges from 0.11-6.21
g/day (Turnlund
et al
.
1995a). An absorption study with intrinsically labeled
foods suggested that the effi ciency of absorption may
be less from some foods, as absorption was 57% from
soy compared with 87% from kale (Turnlund
et al
.,
1999).
µ
g/L (Bostrom and Wester,
1967; Chappell
et al
., 1979; Hrabovska and Groch,
1978; Osmolovskaya, 1967; Valcuk and Copik, 1974).
In mineral water, molybdenum levels are between 2.3
and 3.3
µ
5.2 Distribution
Studies of the distribution of molybdenum in
guinea pigs and rats after a single oral administra-
tion of molybdenum trioxide show that there was an
immediate accumulation in the kidneys, liver, and
bone. Similar distribution is seen in rats, cows, and
goats after prolonged exposure. The highest concen-
trations are found in the kidneys (Anke
et al
., 1971;
Fairhall
et al
., 1945; Huber
et al
., 1971; Robinson
et al
.,
1964).
In mice, after a single intravenous injection, the
highest concentrations were found in the kidneys,
liver, and pancreas, 1-24 hours after exposure.
A decrease with time took place in the kidneys and
pancreas, whereas the concentrations of molybdenum
in the liver remained constant during the observation
period (Rosoff and Spencer, 1973).
Fourteen days after intragastric and subcutane-
ous application of 25-40
g/L (Nevoral, 1975). In areas where molyb-
denum ore is mined, considerable contamination may
occur, which can cause high concentrations in drink-
ing water, leading to daily intakes of more than 1000
µ
µ
g
(Chappell, 1974).
Molybdenum in normal soil varies between 0.1 and
10 mg/kg (Brogan
et al
., 1973; Reddy, 1964). In mining
areas and near molybdenum-emitting industries, con-
siderably higher values have been reported (Chappell,
1974). Molybdenum in sewage sludge was found to
vary between 2 and 30 mg/kg dry weight (Berrow and
Webber, 1972).
In ambient air in urban areas, molybdenum ranged
from 0.01-0.03
g/m
3
, and in nonurban areas it varied
between 0.001 and 0.0032
µ
µ
g/m
3
(Schroeder, 1970).
g/kg body weight to rats,
most of the molybdenum was present in the kidneys,
liver, hard tissues, and skin. Concentrations of the ele-
ment in tissues were dose dependent (Lener and Bibr,
1973).
Molybdenum reacts with skin collagen and alters
the mechanochemical properties of collagen fi bers
(Bibr
et al
., 1977; Lener
et al
., 1976). It accumulates in
long bone, in growth cartilage, and in diaphysis spon-
giosis (Lener
et al
., 1974). The maximum concentration
in teeth occurs in dentin, cement, and to a lesser extent
in enamel (Lener, 1978).
In the blood, molybdenum is bound in the form of
molybdate, specifi cally to
µ
5 METABOLISM
5.1 Absorption
5.1.1 Inhalation
Little data are available on absorption of molybde-
num after inhalation. Guinea pigs showed no notice-
able absorption after exposure through inhalation to
285 mg Mo/m
3
as molybdenum disulfi de. Hexava-
lent molybdenum compounds were absorbed to an
appreciable extent, even though it was not possible to
measure the absorption (Fairhall
et al
., 1945). There are
no human data on absorption of molybdenum after
inhalation.
α
2
-macroglobulin, and in
erythrocytes to proteins of the erythrocyte membrane,
especially spectrin (Bibr
et al
., 1983; Kselikova
et al
.,
1980). Molybdenum concentrations in the blood of
humans increase as dietary intake increases. In con-
trolled human studies, concentrations increased
from 4-44 nmol/L in plasma when intake increased
5.1.2 Ingestion
Gastrointestinal absorption is high in animals and
humans. Animal data from single exposure studies
