Toxicological Review of Barium and Compounds

3.  TOXICOKINETICS 

3.1.  ABSORPTION 

3.1.1.  Gastrointestinal Absorption 

Barium sulfate  is commonly administered to humans as a radiopaque contrast compound 

to visualize the digestive tract.  Despite its common use as a contrast material, human data on the 

gastrointestinal absorption of barium sulfate and other barium compounds are limited.  In a mass 

balance study conducted by Lisk et al. (1988), one man consumed a single dose of 179 mg Ba 

from 92 g of Brazil nuts and it was estimated that at least 91% of the dose was absorbed.  In an 

unpublished doctoral dissertation (Bligh, 1960), the absorption of orally administered 

140

barium 

and 

45

calcium was reported for five female cancer patients.  Mean and standard deviation of the 

calculated absorption for barium was 9 ± 6%.  

Reported absorption of barium in animal studies ranges from less than 1% to greater than 

80%.  Taylor et al. (1962) reported gastrointestinal absorption for a single gavage dose of 

133

BaCl

2

 in older (6-70 weeks of age) nonfasted rats to be 7%-8%, compared to 20% in older 

fasted animals, and 63%-84% in younger (14-22 days) nonfasted rats.  These data suggest that 

both age and feeding status affect the absorption of barium.  In 30-day retention studies 

conducted by Della Rosa et al. (1967) and Cuddihy and Griffith (1972), the reported 

gastrointestinal absorption in adult dogs was 0.7%-1.5% and 

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7% in younger dogs (43-250 days 

of age). 

McCauley and Washington (1983) and Stoewsand et al. (1988) compared absorption 

efficiencies of several barium compounds.  

131

Ba-labeled barium sulfate and barium chloride 

were absorbed at “nearly equivalent rates” (based on blood and tissue levels) in rats following 

single gavage doses of the compounds each equaling 10mg barium  (McCauley and Washington, 

1983).  Similar concentrations of barium were found in the bones of rats fed diets with 

equivalent doses of barium chloride or barium from Brazil nuts.  McCauley and Washington 

(1983) suggested that the similarity in absorption efficiency between barium sulfate and barium 

chloride may have been due to the ability of hydrochloric acid in the stomach to solubilize small 

quantities of barium sulfate.  This is supported by the finding that barium carbonate in a vehicle 

containing sodium bicarbonate was poorly absorbed.  The buffering capacity of sodium 

bicarbonate may have impaired the hydrochloric acid-mediated conversion to barium chloride. 

The results of these studies suggest that soluble barium compounds or barium compounds that 

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yield a dissociated barium ion in the acid environment of the upper gastrointestinal tract have 

similar absorption efficiencies. 

Barium sulfate is often considered to be very poorly absorbed.  The results of the 

McCauley and Washington (1983) study provide evidence that at low  concentrations the 

absorption of barium sulfate is similar to barium chloride.  High concentrations of barium sulfate 

are likely to exceed the ability of the gastric hydrochloric acid to liberate significant amounts of 

barium ions from  barium sulfate.  However, some of the barium sulfate will still be absorbed. 

Statistically significant increases in the levels of barium in the blood and urine have been 

reported in humans ingesting 58 to 400 g barium sulfate in radiopaque contrast materials (Claval 

et al., 1987; Mauras et al., 1983). 

3.1.2.  Respiratory Tract Absorption 

No data are available on respiratory tract absorption of barium in humans.  Animal 

studies provide evidence that barium compounds, including poorly water-soluble compounds 

such as barium sulfate, are absorbed from the respiratory tract.  Morrow et al. (1964) estimated 

that the biological half-time of 

131

BaSO

4

 in the lower respiratory tract was 8 days in dogs 

inhaling 1.1 

:

g/L barium sulfate (count median diameter [CMD] of 0.10 

:

m, 

F

g

 of 1.68) for 30­

90 min.  Twenty-four hours after an intratracheal injection of 

133

BaSO

4

, 15.3% of the 

radioactivity was cleared from the lungs.  The barium sulfate was cleared via mucociliary 

clearance mechanisms (7.9% of initial radioactive burden) and via lung-to-blood transfer (7.4% 

of radioactivity) (Spritzer and Watson, 1964).  Clearance half-times of 66 and 88 days were 

calculated for the cranial and caudal regions of the trachea in rats intratracheally administered 2 

:

g 

133

BaSO

4

 (CMD of 0.34 

:

m, 

F

g

 of 1.7) (Takahashi and Patrick, 1987). 

Differences in water solubility appear to account for observed differences in respiratory 

tract clearance rates for barium compounds.  The clearance half-times of several barium 

compounds were proportional to solubility in dogs exposed to aerosols of barium chloride 

(activity median aerodynamic diameter [AMAD] of 2.3 

:

m, 

F

g

 of 1.5), barium sulfate (AMAD 

of 1.0 

:

m, 

F

g

 of 1.6), heat-treated barium sulfate (AMAD of 0.9 

:

m, 

F

g

 of 1.4), or barium 

incorporated in fused montmorillonite clay particles (AMAD of 2.2 

:

m, 

F

g

 of 1.7) (Cuddihy et 

al., 1974). 

3.1.3.  Dermal Absorption 

No data are available on dermal absorption of barium compounds. 

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