Toxicological Review of Barium and Compounds

2.  CHEMICAL AND PHYSICAL INFORMATION 

Barium is a dense alkaline earth metal in Group IIA of the periodic table.  Naturally 

occurring barium is a mix of seven stable isotopes.  There are more than 20 known isotopes, but 

most of them are highly radioactive and have half-lives ranging from several milliseconds to 

several minutes.  The free element is a silver-white soft metal that oxidizes readily in moist air 

and reacts with water.  Barium does not exist in nature in the elemental form but occurs as the 

divalent cation in combination with other elements (Agency for Toxic Substances and Disease 

Registry [ATSDR], 1992).  The physical and chemical properties of barium and selected barium 

compounds are presented in Table 1–1.  The barium compounds with the following counter ions 

are relatively soluble in water: acetate, nitrate, and halides (except fluoride), whereas compounds 

with carbonate, chromate, fluoride, oxalate, phosphate, and sulfate counter-ions are quite 

insoluble in water (World Health Organization [WHO], 2001).  

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Barium makes up 0.05% of the earth’s crust, and the two most prevalent naturally 

occurring barium compounds are barite (barium sulfate) and witherite (barium carbonate) ores. 

Barium enters the environment through the weathering of rocks and minerals and through 

anthropogenic releases.  The primary source of barium in the atmosphere is industrial emissions 

(ATSDR, 1992).  Barium concentrations ranging from 2 × 10

-4

 to 2.8 × 10

-2 

:

g/m

3

 (mean of 1.2 × 

-2 

:

g/m

3

) have been detected in urban areas of North America (ATSDR, 1992).  Barium is 

naturally occurring in most surface waters and in public drinking water supplies.  Barium content 

in U.S. drinking water supplies ranges from 1 to 20 

:

g/L; in some areas barium concentrations as 

high as 10,000 

:

g/L have been detected (WHO, 1990).  Barium is ubiquitous in soils, with 

concentrations ranging from 15 to 3000 ppm (ATSDR, 1992). 

The primary route of exposure to barium appears to be ingestion from food and drinking 

water.  Barium is found in many food groups.  In most foods, the barium content is relatively low 

(<3 mg/100 g) except in Brazil nuts, which have a very high barium content (150-300 mg/100 g) 

(WHO, 1990).  Bread is considered the largest source of dietary barium, contributing an 

estimated 20% of total intake (Ysart et al., 1999).  The WHO (1990) reported several published 

estimates of dietary intake of barium by humans; daily dietary intake ranged from 300 to 1770 

:

g Ba/day, with wide variations; this is equivalent to 4-25 

:

g Ba/kg-day, assuming a 70 kg adult 

body weight.  A daily intake of 0.03-0.60 

:

g Ba/kg-day from drinking water can be estimated by 

using the drinking water concentration of 1-20 

:

g/L, a reference consumption rate of 2 L/day, 

and body weight of 70 kg.  The range from these two sources combined is 0.004-0.026 mg 

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Ba/kg-day.  The chemical and physical properties of barium and selected barium compounds are 

shown in Table 1–1. 

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Table 1–1.  Physical and chemical properties of barium and selected barium compounds 

Barium 

Barium acetate 

Barium 

carbonate 

Barium 

chloride 

Barium 

hydroxide 

Barium oxide 

Barium sulfate 

CAS Registry 

number

a 

7440-39-3 

543-80-6 

513-77-9 

10361-37-2 

17194-00-2 

1304-28-5 

7727-43-7 

Molecular 

formula 

Ba 

Ba(C

2

H

3

O

2

)

2 

BaCO

3 

BaCl

2 

Ba(OH)

2

@8H

2

O

 BaO

 

BaSO

4 

Molecular 

weight 

137.34 

255.43 

197.35 

208.25 

315.48 

153.34 

233.4 

Melting point, 

°C 

725 

41

a 

1740 (

" form, 

at 90 atm)

a 

963 78 1923 

1580 

(decomposes) 

Boiling point, °C 

1640 

no data 

decomposes 

1560 

550

a 

2000 

1149 (monoclinal 

transition point)

a 

Vapor pressure, 

mm Hg 

10 at 1049 °C 

no data 

essentially zero

a 

essentially zero

a 

no data

a 

essentially zero

a 

no data

a 

Water solubility, 

forms barium 

588 at 0 °C, 

0.02 at 20 °C, 

375 at 20 °C

a 

56 at 15 °C, 

38 at 20 °C, 

0.00222 at 0 °C, 

g/L 

hydroxide 

750 at 100 °C 

0.06 at 100 °C 

947 at 78 °C 

908 at 100 °C 

0.00413 at 100 °C 

Specific gravity 

3.5 at 20 °C 

2.468 

4.43 

3.856 at 24 °C 

2.18 at 16 °C 

5.72 

4.50 at 15 °C 

a

 ATSDR, 1992. 

Source: Weast and Astle, 1981, unless otherwise noted.

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