TOXICOLOGICAL PROFILE FOR BARIUM AND COMPOUNDS ...

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2. HEALTH EFFECTS
apparent positive tumorigenic response was due to barium hydroxide or some
other component of the barium hydroxide tobacco leaf extract.
2.3 TOXICOKINETICS
2.3.1 Absorption
2.3.1.1 Inhalation Exposure
No studies were located regarding absorption of barium in humans
following inhalation exposure: However, results of studies with experimental
animals suggest that the rate and extent of absorption of barium from the
respiratory tract depends on the exposure level, how much barium reaches the
alveolar spaces, the clearance rate from the upper respiratory tract, and the
solubility of the particular form of barium that was administered.
The results of a hamster study indicated that after inhalation of barium
chloride, 65% of the administered dose was deposited in the nasal region and
was eventually absorbed into the body (Cuddihy and Ozog 1973b). Radioactive
barium sulfate that is injected directly into the trachea of rats can be taken
up into the epithelium membranes, and remain in these membranes for at least a
few weeks (Gore and Patrick 1982; Takahashi and Patrick 1987). These studies
have also shown that barium in the trachea can be cleared to the lymphatic
system (Takahashi and Patrick 1987).
Results of experiments with dogs have indicated that, following
inhalation of barium chloride or barium sulfate, approximately half of the
barium chloride dose and three-fourths of the barium sulfate dose are
deposited in the pulmonary region (Cuddihy et al. 1974). About one-fourth of
the absorbed barium is transported to the skeleton, the remainder is excreted
in the urine and feces within 2 weeks. The biological half life of
radioactive barium sulfate in the pulmonary region has been calculated to be 8
days in the dog (Morrow et al. 1964) and 10 days in the rat (Cember et al.
1961). Total body deposition in dogs that inhaled radioactive barium chloride
was found to be 51% of the total inhaled activity, indicating that at least
this much was absorbed (Morrow et al. 1964). Experiments in rats exposed to
barium sulfate via intratracheal injection have shown that about 7% of the
initial lung burden was finally cleared to the blood (Spritzer and Watson
1964).
2.3.1.2 Oral Exposure
As with other metals, barium is probably very poorly absorbed from the
gastrointestinal tract. The International Commission for Radiation Protection
(ICRP) estimates that the gastrointestinal absorption of barium is less than
5% (ICRP 1973). This percentage is supported by studies of two men whose
daily input and fecal excretion were monitored for 50 weeks (Tipton et al.
1969).