Barium - Toxicology of Metals - page 399

4.1.2 Plants, Animals, and Dietary Intake

5 KINETICS

Increased barium concentrations have been detected
in plants near waste disposal sites and in urban areas.
Barium is present in gasoline. Monaci and Bargagli
(1997) found a highly signifi cant relationship between
lead and barium in leaves from the evergreen oak, Quer-
cus ilex, and suggested barium to be a valuable tracer
for vehicle emissions. Llugany et al . (2000) studied
barium toxicity in bush beans ( Phaseolus vulgaris) and
found that the presence of barium, even at concentra-
tions that do not affect plant growth, had a depressing
effect on the potassium concentrations in the leaves. In
addition, barium interfered with the sulfate and calcium
nutrition of the plant.
Despite relatively high concentrations in soils, only
a limited amount of barium is taken up in plants, and
there is a low transfer to animals. Thus, in most food
the barium concentration is relatively low, <0.1 mg/kg
and somewhat higher in cereal products with concen-
trations around 1 mg/kg. However, Brazil nut trees
are known to accumulate soil barium and extremely
high levels are found in Brazil nuts, 1500-3000 mg/kg
(WHO, 1990). High levels are also found in pecan nuts
and dry cocoa, with 6.7 and 12 mg/kg, respectively.
The daily dietary intake of barium has been esti-
mated in several studies, ranging from 0.3-1.8 mg
(WHO, 1990). In an American hospital diet, the aver-
age daily intake of barium was estimated as 0.4 mg,
whereas in the diet of the general population it may
be as high as 1.33 mg (Schroeder et al ., 1972). Grummitt
(1961) estimated that typical dietary barium intake
originated 25% from milk, 25% from fl our, 25% from
potatoes, and 25% from miscellaneous high-barium
foods consumed in minor quantities, especially nuts.

5.1 Absorption

5.1.1 Inhalation

Soluble forms of barium are readily absorbed from
all segments of the respiratory tract. Nasal absorption
of 133 BaCl 2 in hamsters was estimated at 60-80% of the
dose at 4 hours after dosing (Cuddihy and Ozog, 1973),
and alveolar absorption may be of similar magnitude.
According to measurements at tracer levels, even
131 BaSO 4 was found to be cleared from the lungs, with
a biological half-time of 8-9 days, through absorption
into the general circulation with subsequent urinary
clearance (Morrow et al ., 1964). This indicated some
solubility of BaSO 4 in body fl uids, possibly in colloidal
form.
Clearance of various forms of barium after expo-
sure was studied by Einbrodt et al . (1972) and by Cud-
dihy et al . (1974). Different compounds of barium were
cleared from the lungs in proportion to their solubili-
ties: in the case of BaSO 4 , the clearance rate depended
on the specifi c surface area of the inhaled particles and
was lower for heat-treated than for untreated particles.
Barium in fused montmorillonite clay had the lowest
clearance rate.

5.1.2 Ingestion

The absorption of ingested barium depends on such
factors as solubility of the salt, starvation, and age
of the animal and presence of sulfate in the diet. The
absorption of soluble barium chloride has been stud-
ied. In hamsters receiving 133 BaCl 2 by intragastric intu-
bation, absorption was 11-32% of the dose (Cuddihy
and Ozog, 1973). Taylor et al . (1962) reported absorp-
tion effi ciencies of barium chloride in rats varying from
7-85%, with the highest absorptions in fasted (20%)
and in young (85% at 14-18 days of age) rats. Sutton
et al . (1972) and Sutton and Shepherd (1973) found that
addition of sodium alginate to the diet reduced intes-
tinal absorption of barium in rat and man to 42-75%
(average 64%) of control.
Barium sulfate can be used as X-ray contrast mate-
rial for gastrointestinal examinations, because during
the relatively brief period of passage through the ali-
mentary canal, BaSO 4 remains essentially unabsorbed.
However, McCauley and Washington (1983) reported
similar absorption rates with barium sulfate as with
barium chloride after administration to rats by way of
gastric intubation of a low dose of barium, 10

4.2 Working Environment
The industrial uses of soluble barium are such that
hazardous conditions from atmospheric contami-
nations are uncommon. However, arc welding with
barium-containing stick electrodes and fl ux-cored
wires involves occupational exposure to soluble bar-
ium. Without appropriate preventive measures, the
median barium concentration in the breathing zone
was 2-4 mg/m 3 compared with 0.3 when preventive
measures were taken (Zschiesche et al ., 1992).
The OSHA Permissible Exposure Limit (PEL)
for soluble barium salts is 0.5 mg/m 3 TWA (time
weighted average). The fi gure has an “A4” notation
(not classifi able as a human carcinogen). For barium
sulfate dust, the PEL is 10 mg/m 3 as inhalable (total)
particulate matter and 5 mg/m 3 for the respirable
fraction.

g/kg
body weight. The peak in blood concentration after
administration of the sulfate was 85% of the peak after
administration of the chloride. Evidently, hydrochloric

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