Concise International Chemical Assessment Document 33

Barium and barium compounds

7

barium ores are barite (barium sulfate) and witherite

(barium carbonate). Barite occurs largely in sedimentary

formations, as residual nodules resulting from weather-

ing of barite-containing sediments, and in beds along

with fluorspar, metallic sulfides, and other minerals.

Witherite is found in veins and is often associated with

lead sulfide. Barium is found in coal at concentrations up

to 3000 mg/kg, as well as in fuel oils (IPCS, 1990;

ATSDR, 1992). Estimates of terrestrial and marine

concentrations of barium are 250 and 0.006 g/tonne,

respectively (Considine, 1976).

Barite ore is the raw material from which nearly all

other barium compounds are derived. Barite is mined in

Morocco, China, India, and the United Kingdom. Crude

barite ore is washed free of clay and other impurities,

dried, and then ground before use. Barite is usually

imported as crude ore or crushed ore for milling or as

ready-milled ore. Barite can be 90–98% barium sulfate.

World production of barite in 1985 was estimated to be

5.7 million tonnes. 

Because of its high specific gravity, low abrasive-

ness, chemical stability, and lack of magnetic effects,

barite is used as a weighting agent for oil and gas well

drilling muds, which counteracts high pressures encoun-

tered in the substrata (IPCS, 1990). It is also used as a

filler in a range of industrial coatings, as a dense filler in

some plastics and rubber products, in brake linings, and

in some sealants and adhesives. The use dictates the

source of barite used. Some sources produce very pure

white barite, which is used in coatings, while barite from

other sources is off-white and is used in applications

where the colour is unimportant. The use will also dictate

the particle size to which barite is milled. For example,

drilling muds are ground to an average particle diameter

of 44 µm, with a maximum of 30% of particles less than 6

µm in diameter. Barium and its compounds are used in

diverse industrial products ranging from ceramics to

lubricants. Barium is used in the manufacture of alloys,

soap, rubber, and linoleum; in the manufacture of valves;

as a loader for paper; and as an extinguisher for radium,

uranium, and plutonium fires. Barium compounds are

used in cement, specialty arc welding, glass industries,

electronics, roentgenography, cosmetics,

pharmaceuticals, inks, and paints. They have also been

used as insecticides and rodenticides (e.g., barium meta-

borate, barium polysulfide, and barium fluorosilicate).

Anthropogenic sources of barium are primarily

industrial. Emissions may result from mining, refining, or

processing of barium minerals and manufacture of

barium products. Barium is released to the atmosphere

during the burning of coal, fossil fuels, and waste. 

Barium is also discharged in wastewater from metallur-

gical and industrial processes. Deposition on soil may

result from human activities, including the disposal of fly

ash and primary and secondary sludge in landfills (IPCS,

1990). Estimated releases of barium and barium

compounds to the air, water, and soil from manufacturing

and processing facilities in the USA during 1998 were

900, 45, and 9300 tonnes, respectively.

1

5. ENVIRONMENTAL TRANSPORT,

DISTRIBUTION, AND TRANSFORMATION

Both specific and non-specific adsorption of bar-

ium onto oxides and soils have been observed. Specific

sorption occurs onto metal oxides and hydroxides.

Adsorption onto metal oxides probably acts as a control

over the concentration of barium in natural waters.

Electrostatic forces account for a large fraction of the

non-specific sorption of barium on soil and subsoil. The

retention of barium, like that of other alkaline earth

cations, is largely controlled by the cation-exchange

capacity of the sorbent. Complexation by soil organic

material occurs to a limited extent. The K

d

 (soil sorption)

value, the dissociation constant between sediment and

barium in sediments, is 5.3 × 10

5

 ml/g (McComish & Ong,

1988).

Examination of dust falls and suspended particu-

lates indicates that most contain barium. The presence of

barium is mainly attributable to industrial emissions,

especially the combustion of coal and diesel oil and

waste incineration, and may also result from dusts blown

from soils and mining processes. Barium sulfate and

carbonate are the forms of barium most likely to occur in

particulate matter in the air, although the presence of

other insoluble compounds cannot be excluded. The

residence time of barium in the atmosphere may be

several days, depending on the particle size. Most of

these particles, however, are much larger than 10 µm in

size and rapidly settle back to earth. Particles can be

removed from the atmosphere by rainout or washout wet

deposition.

Soluble barium and suspended particulates can be

transported great distances in rivers, depending on the

rates of flow and sedimentation. Cartwright et al. (1978)

studied the chemical control of barium solubility and 

1

 Toxic Chemical Release Inventory (TRI) database,

Office of Toxic Substances, US Environmental Protection

Agency, Washington, DC, 1998.

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Concise International Chemical Assessment Document 33

8

showed that, for most water samples, barium ion con-

centration is controlled by the amount of sulfate ion in

the water.

While some barium in water is removed by preci-

pitation, exchange with soil, or other processes, most

barium in surface waters ultimately reaches the ocean.

Once freshwater sources discharge into seawater, barium

and the sulfate ions present in salt water form barium

sulfate. Due to the relatively higher concentration of

sulfate present in the oceans, only an estimated 0.006%

of the total barium brought by freshwater sources

remains in solution (Chow et al., 1978). This estimate is

supported by evidence that outer-shelf sediments have

lower barium concentrations than those closer to the

mainland.

Marine concentrations of barium generally

increase with depth, suggesting that barium may be

incorporated into organisms in the euphotic zone and

subsequently sedimented and released in deeper waters

(IPCS, 1990). In laboratory testing, the uptake of barium

by algae in culture media was 30–60% after 15 days of

exposure to barium concentrations of 0.04, 0.46, and

4.0 mg/litre of medium, the relative accumulation being

inversely related to the barium concentration in the

medium and directly related to the exposure duration

(Havlik et al., 1980). Barium was not incorporated into

organic components but was bound primarily to the cell

membrane or other non-extractable components.

Accumulation of barium ions (

133

Ba) in the cells of the

alga Scenedesmus obliquus has been shown to increase

with increasing pH between pH 4 and 7, then remain

constant over the pH range 7–9 at a barium concentra-

tion of 10

–6

 mol/litre, with a calculated affinity constant

(K

m

) of 4.8 (Stary et al., 1984). In a marine environment

contaminated with heavy metals (including barium),

Guthrie et al. (1979) measured barium concentrations of

7.7 mg/litre in water and 131.0 mg/kg wet weight in

sediment. Among barnacles, crabs, oysters, clams, and

polychaete worms tested for barium content in this

marine environment, only barnacles showed higher

concentrations of barium (40.5 mg/kg wet weight) than

that of the water.

Barium sulfate is present in soil through the natural

process of soil formation; barium concentrations are

high in soils formed from limestone, feldspar, and biotite

micas of the schists and shales (Clark & Washington,

1924). When soluble barium-containing minerals weather

and come into contact with solutions containing

sulfates, barium sulfate is deposited in available geologi-

cal faults. If there is insufficient sulfate to combine with

barium, the soil material formed is partially saturated with

barium. In soil, barium replaces other sorbed alkaline 

earth metals from manganese dioxide, silicon dioxide, and

titanium dioxide under typical environmental conditions,

by ion exchange (Bradfield, 1932; McComish & Ong,

1988). However, other alkaline earth metals displace

barium from aluminium oxide (McComish & Ong, 1988).

Barium sulfate in soils is not expected to be very

mobile because of the formation of water-insoluble salts

and its inability to form soluble complexes with humic

and fulvic materials. Under acid conditions, however,

some of the water-insoluble barium compounds (e.g.,

barium sulfate) may become soluble and move into

groundwater (US EPA, 1984).

Despite relatively high concentrations in soils,

only a limited amount of barium accumulates in plants.

Barium is actively taken up by legumes, grain stalks,

forage plants, red ash (Fraxinus pennsylvanica) leaves,

and black walnut (Juglans nigra), hickory (Carya sp.),

and brazil nut (Bertholletia excelsa) trees; Douglas-fir

(Pseudotsuga menziesii) trees and plants of the genus

Astragallu also accumulate barium (IPCS, 1990). Barium

has also been shown to accumulate in mushrooms

(Aruguete et al., 1998). No studies of barium particle

uptake from the air have been reported, although

vegetation is capable of removing significant amounts of

contaminants from the atmosphere. Plant leaves act only

as deposition sites for particulate matter. Although

levels of barium in wildlife have not been documented,

barium has been found in dairy products and eggs

(Gormican, 1970; IPCS, 1990), indicating that barium

uptake occurs in animals.

A bioconcentration factor (BCF) for soil to plants

was estimated as 0.4 (0.02 standard error of the mean

[SEM]), based on samples of a variety of plant species

(mean barium concentration of 29.8 mg/kg [13.7 SEM])

that were taken from a site in which the mean concentra-

tion of barium in the soil was 104.2 mg/kg (9.5 SEM)

(Hope et al., 1996). Based on the ratio of barium concen-

tration in the soil to whole-body barium concentration,

the same authors computed bioaccumulation factors of

0.2 (0.002 SEM) for terrestrial insects, 0.02 (0.0004 SEM)

for white-footed mice (Peromyscus leucopus), and 0.02

(0.0005 SEM) for hispid cotton rats (Sigmodon hispidus).

Based on dissolved barium concentrations in surface

water of 0.07 mg/litre (0.02 SEM) and whole-body barium

concentrations of 2.1 mg/kg (0.5 SEM) in fish, measured

at the same study site, a BCF of 129.0 litres/kg (13.5

SEM) was estimated. The authors also estimated mean

depuration rates in white-footed mice and hispid cotton

rats to be 0.4/day (0.01 SEM) and 0.2/day (0.01 SEM),

respectively, indicating that barium is “lost from these

receptors at a fairly rapid rate.” Field data were collected 

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