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
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