Concise International Chemical Assessment Document 33

Barium and barium compounds

5

The kidney appears to be the most sensitive target

organ in rats and mice exposed repeatedly to barium

chloride in drinking-water. Long-term studies of barium

exposure in laboratory animals have not confirmed the

blood pressure, cardiac, and skeletal muscle effects seen

in humans and laboratory animals orally exposed to

acutely high levels.

Inhalation exposure of humans to insoluble forms

of barium results in radiological findings of baritosis,

without evidence of altered lung function and

pathology. Information on the toxicity of inhaled barium

in animals is limited. Repeated exposure to barium oxide

via inhalation may cause bronchitis to develop, with

cough, phlegm, and/or shortness of breath. In a limited

study, minor histopathological changes were seen in the

lungs of rats exposed to barium sulfate at 40 mg/m

3

 for

5 h/day, 5 days/week, but there was no evidence of

fibrogenic potential. Animal studies involving respira-

tory tract instillation of barium sulfate have shown

inflammatory responses and granuloma formation in the

lungs; this would be expected with exposure to substan-

tial amounts of any low-solubility dust, leading to a

change in lung clearance and subsequently to lung

effects.

Currently available data indicate that barium does

not appear to be a reproductive or developmental hazard,

although animal studies are limited. Barium was not

carcinogenic in standard National Toxicology Program

rodent bioassays. Although no in vivo data are

available, in vitro data indicate that barium compounds

have no mutagenic potential.

Oral intake from drinking-water and food is the

most prevalent route of exposure to barium compounds

for the general population. For the occupational environ-

ment, data from industry in the United Kingdom and

predictions made using the Estimation and Assessment

of Substance Exposure (EASE) model suggest that

exposures can be controlled to less than 10 mg/m

3

 8-h

time-weighted average (total inhalable dust). In some

situations, control will be to levels significantly below

this value. Short-term exposures may be higher than

10 mg/m

3

 for some tasks.

The critical end-points in humans for toxicity

resulting from exposure to barium and barium com-

pounds appear to be hypertension and renal function.

Using a no-observed-adverse-effect level (NOAEL) in

humans of 0.21 mg barium/kg body weight per day, a

tolerable intake value of 0.02 mg/kg body weight per day

for barium and barium compounds has been developed

in this document.

Dissolved barium in aquatic environments may

represent a risk to aquatic organisms such as daphnids,

but it is apparently of lesser risk to fish and aquatic

plants, although data are limited. No adverse effects

have been reported in ecological assessments of

terrestrial plants or wildlife, although some plants are

known to bioaccumulate barium from the soil.

2. IDENTITY AND PHYSICAL/CHEMICAL

PROPERTIES

Barium (Ba; CAS No. 7440-39-3) is a dense alkaline

earth metal in Group IIA of the periodic table (atomic

number 56; atomic mass 137.34). 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 (ATSDR, 1992).

Two commonly found forms of barium are barium

sulfate (CAS No. 7727-43-7) and barium carbonate (CAS

No. 513-77-9), often found as underground ore deposits.

These forms of barium are not very soluble in water:

0.020 g/litre (at 20 °C) for barium carbonate and 0.001 15

g/litre (at 0 °C) for barium sulfate. 

Barium sulfate exists as a white orthorhombic pow-

der or crystals. Barite, the mineral from which barium

sulfate is produced, is a moderately soft crystalline white

opaque to transparent mineral. The most important

impurities are iron(III) oxide, aluminium oxide, silica, and

strontium sulfate.

Some of the more commonly

used synonyms of barium sulfate include barite, barytes,

heavy spar, and blanc fixe.

The barium compound most commonly used in

toxicity studies is barium chloride (water solubility

375 g/litre at 20 °C). 

Additional physical/chemical properties of barium

and barium compounds are presented in the

International Chemical Safety Cards reproduced in this

document.

3. ANALYTICAL METHODS

Information on analytical methods for determining

barium levels in environmental samples is available in

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Concise International Chemical Assessment Document 33

6

 Table 1: Analytical methods for determining barium in environmental samples.

a,b

Sample matrix

Preparation method

Analytical

method

Detection limit

Percent recovery

Air

Collect sample on cellulose and extract

with hot acid; evaporate extract to

dryness and dissolve residue in acid

FAAS

No data

No data

Air (occupational

exposure)

XFS

15 µg

Water

Acidify sample and pass through ion-

exchange resin

FAAS

3 mg/litre

11.6% RSD

Pass sample through ion-exchange

resin

FAES

mg/litre levels

No data

Extract sample with buffered HFA

solution

FAAS

5 mg/litre

No data

No data

GFAAS

7 mg/litre

No data

Inject sample directly into graphite

furnace

GFAAS

0.6 mg/litre (seawater)

0.2 mg/litre (fresh water)

13% RSD

Water and

wastewater

Digest sample and evaporate to

dryness; dissolve residue in acid

FAAS, GFAAS,

ICP-AES

100 mg/litre (FAAS)

2 mg/litre (GFAAS)

94–113% (FAAS)

96–102% (GFAAS)

Industrial

wastewater

Digest sample; mix with cation-

exchange resin, dry, and analyse

XFS

290 mg/litre (on a 500-

ml sample)

5.1% RSD

Unused

lubricating oil

Dissolve sample in 2-methylpropan-2-

ol: toluene (3:2); add potassium

naphthenate solution

FAAS

No data

No data

a

From ATSDR (1992); Ball et al. (1997).

b

FAAS = flame atomic absorption spectroscopy; FAES = flame atomic emission spectroscopy; GFAAS = graphite furnace atomic

absorption spectroscopy; HFA = hexafluoroacetylacetone; ICP-AES = inductively coupled plasma–atomic emission spectrometry;

RSD = relative standard deviation; XFS = X-ray fluorescence spectroscopy.

Table 1. There are no published methods for the quan-

titative measurement of barium particles (e.g., barium

sulfate) in air. NIOSH (1987) suggested a flame atomic

absorption method to determine soluble barium particles

in air following collection on a cellulose ester membrane

filter and re-extraction with hot hydrochloric acid solu-

tion. Insoluble barium compounds require an ashing

procedure prior to measurement. The estimated limit of

detection by this method is 2 µg per sample, and its

precision is 2.5% at 43–180 µg per sample. Another

approach is to collect respirable dust samples and

assess them gravimetrically (US OSHA, 1990). Atomic

absorption spectroscopy is the most commonly used

analytical method for measuring low levels of barium and

its compounds in air, water, wastewater, geological

materials, and various other materials. Sample prepara-

tion typically involves digestion with nitric acid,

although dilution with other agents may also be

employed to solubilize barium. Flame atomic absorption

spectroscopy and graphite furnace atomic absorption

spectroscopy are analytical methods used to determine

levels of barium in water and wastewater in the ranges of

parts per billion and parts per trillion. Other analytical

techniques include the less sensitive methods of X-ray

fluorescence spectroscopy and neutron activation

analysis and the less commonly used methods of

scintillation spectroscopy and spectrography (ATSDR,

1992). In general, analytical procedures measure total

barium ion present and do not allow for speciation of

barium compounds.

Inductively coupled plasma–atomic emission

spectrometry is a relatively effective and sensitive

method for measuring low levels of barium in water,

blood, urine, and bones. Detection limits of 0.25 mg

barium/litre of urine, 0.6 mg barium/litre of blood, and

0.0005 mg barium/g of bone have been achieved.

However, in a given sample containing barium, there is

potential for interference from spectral bands of other

compounds (e.g., boric acid or sodium borate) that may

be present. Detection limits of 7 µg barium/litre of

erythrocytes and 66 µg barium/litre of plasma have been

obtained using neutron activation analysis (ATSDR,

1992).

4. SOURCES OF HUMAN AND

ENVIRONMENTAL EXPOSURE

Barium is the 16th most abundant non-gaseous

element of the Earth’s crust, constituting approximately

0.04% of it. The two most prevalent naturally occurring

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