INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 107
BARIUM
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experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.
Published under the joint sponsorship of
the United Nations Environment Programme,
the International Labour Organisation,
and the World Health Organization
World Health Orgnization
Geneva, 1990
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chemicals.
WHO Library Cataloguing in Publication Data
Barium.
(Environmental health criteria ; 107)
1.Barium
I.Series
ISBN 92 4 157107 1 (NLM Classification: QV 618)
ISSN 0250-863X
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CONTENTS
1. SUMMARY AND CONCLUSIONS
1.1. Summary
1.1.1. Identity, natural occurrence, and analytical methods
1.1.2. Production, uses, and sources of exposure
1.1.3. Kinetics and biological monitoring
1.1.4. Effects on experimental animals
1.1.5. Effects on human beings
1.1.6. Effects on organisms in the environment
1.2. Conclusions and recommendations
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Identity
2.2. Physical and chemical properties of barium
2.3. Physical and chemical properties of barium compounds
2.4. Analytical sampling
2.4.1. Water
2.4.2. Soils and sediments
2.4.3. Air
2.4.4. Biological materials
2.5. Analytical procedures
2.5.1. Commonly used analytical methods
2.5.1.1 AAS - direct aspiration method
2.5.1.2 AAS - furnace technique
2.5.1.3 AAS - ICP
2.5.2. Analytical methods used for special applications
2.5.2.1 Mass spectrometry
2.5.2.2 X-ray fluorescence spectrometry
2.5.2.3 Neutron activation analysis
3. SOURCES IN THE ENVIRONMENT
3.1. Natural occurrence
3.2. Man-made sources
3.2.1. Production levels, processes, and uses
4. ENVIRONMENTAL TRANSPORT AND DISTRIBUTION
4.1. Transport and distribution between media
4.1.1. Air
4.1.2. Water
4.1.3. Soil
4.1.4. Vegetation and wildlife
4.1.5. Entry into the food chain
4.2. Biotransformation
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels
5.1.1. Air
5.1.2. Water
5.1.2.1 Surface waters
5.1.2.2 Drinking-water
5.1.2.3 Ocean waters
5.1.3. Soil and sediment
5.1.4. Food
5.1.5. Feed
5.1.6. Other products
5.1.7. Nuclear fallout
5.2. General population exposure
5.2.1. Environmental sources, food, drinking-water, and air
5.2.2. Other sources
5.2.3. Subpopulations at special risk
5.3. Occupational exposure during manufacture, formulation, or use
6. KINETICS AND METABOLISM
6.1. Absorption
6.1.1. Inhalation route
6.1.1.1 Laboratory animals
6.1.1.2 Humans
6.1.2. Oral route
6.1.2.1 Laboratory animals
6.1.2.2 Humans
6.1.3. Parenteral administration
6.2. Distribution
6.2.1. Levels in tissues of experimental animals
6.2.2. Levels in human tissue
6.3. Elimination and excretion
6.3.1. Laboratory animals
6.3.2. Humans
6.4. Metabolism
6.4.1. Laboratory animals
7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT
7.1. Microorganisms
7.1.1. Viruses
7.1.2. Bacteria
7.1.3. Inhibition of growth
7.1.4. Specific effects
7.2. Aquatic organisms
7.2.1. Aquatic plants
7.2.2. Aquatic animals
7.2.3. Effects of marine drilling muds
7.3. Bioconcentration
8. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO SYSTEMS
8.1. Acute exposure
8.1.1. Oral route
8.1.2. Inhalation route
8.1.3. Parenteral administration
8.1.4. Topical route
8.2. Short-term exposures
8.2.1. Inhalation route
8.2.2. Oral route
8.3. Long-term exposure
8.3.1. Inhalation route
8.3.2. Oral route
8.4. Reproduction, embryotoxicity, and teratogenicity
8.4.1. Reproduction
8.4.2. Embryotoxicity and teratogenicity
8.5. Mutagenicity and related end-points
8.6. Tumorigenicity and carcinogenicity
8.7. Special studies
8.7.1. Effects on the heart
8.7.2. Vascular effects
8.7.3. Electrophysiological effects
8.7.4. Effects on synaptic transmission and catecholamine release
8.7.5. Effects on the immune system
8.7.6. Ocular system
9. EFFECTS ON MAN
9.1. General population exposure
9.1.1. Acute toxicity - poisoning incidents
9.1.2. Short-term controlled human studies
9.1.3. Epidemiological studies
9.1.3.1 Cardiovascular disease
9.1.3.2 Other effects
9.2. Occupational exposure
9.2.1. Effects of short- and long-term exposure
9.3. Carcinogenicity of barium chromate
10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT
10.1. Evaluation of human health risks
10.1.1. Exposure levels
10.1.1.1 General population
10.1.1.2 Occupational - air exposures
10.1.1.3 Acute exposures
10.1.2. Toxic effects; dose-effect and dose-response relationships
10.1.3. Risk evaluation
10.2. Evaluation of effects on the environment
11. RECOMMENDATIONS FOR FURTHER STUDIES
12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCES
RESUME ET CONCLUSIONS
EVALUATION DES RISQUES POUR LA SANTE HUMAINE ET EFFETS SUR L'ENVIRONNEMENT
RECOMMANDATIONS EN VUE D'ETUDES COMPLEMENTAIRES
RESUMEN Y CONCLUSIONES
EVALUACION DE LOS RIESGOS PARA LA SALUD HUMANA Y DE LOS EFECTOS SOBRE EL
MEDIO AMBIENTE
RECOMENDACIONES PARA ULTERIORES ESTUDIOS
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR BARIUM
Members
Dr V. Bencko, Department of Hygiene, Institute of Tropical
Health, Postgraduate School of Medicine and Pharmacy,
Prague, Czechoslovakia
Dr X.C. Ding, Department of Toxicology, Institute of Occu-
pational Health, Shanghai, People's Republic of Chinaa
Dr T. Eikmann, Institute for Hygiene and Occupational
Medicine, Medical Faculty, Technical University of
Rhineland-Westphalia, Aachen, Federal Republic of
Germany
Dr J.P. Flesch, Division of Standards Development and
Technology Transfer, National Institute for Occu-
pational Safety and Health, Robert A. Taft Labora-
tories, Cincinnati, Ohio, USA
Ms K. Hughes, Environmental Health Directorate, Department
of National Health and Welfare, Tunney's Pasture,
Ottawa, Ontario, Canada
Dr F. Izumi, Department of Pharmacology, University of
Occupational and Environmental Health, School of Medi-
cine, Fukuoka, Japan
Dr M.L. Tosato, Istituto Superiore di Sanità, Rome, Italy
(Chairperson)
Secretariat
Dr B.H. Chen, International Programme on Chemical Safety,
World Health Organization, Geneva, Switzerland
(Secretary)
Dr P.G. Jenkins, International Programme on Chemical
Safety, World Health Organization, Geneva, Switzerland
Dr T. Ng, Office of Occupational Health, World Health
Organization, Geneva, Switzerland
Dr L. Papa, Environmental Criteria and Assessment Office,
US Environmental Protection Agency, Cincinnati, Ohio,
USA (Rapporteur)
a Invited but unable to attend.
NOTE TO READERS OF THE CRITERIA MONOGRAPHS
Every effort has been made to present information in
the criteria monographs as accurately as possible without
unduly delaying their publication. In the interest of all
users of the environmental health criteria monographs,
readers are kindly requested to communicate any errors
that may have occurred to the Manager of the International
Programme on Chemical Safety, World Health Organization,
Geneva, Switzerland, in order that they may be included in
corrigenda, which will appear in subsequent volumes.
* * *
A detailed data profile and a legal file can be
obtained from the International Register of Potentially
Toxic Chemicals, Palais des Nations, 1211 Geneva 10,
Switzerland (Telephone No. 7988400 or 7985850).
ENVIRONMENTAL HEALTH CRITERIA FOR BARIUM
A WHO Task Group on Environmental Health Criteria for
Barium met in Geneva from 20 to 24 November 1989. Dr M.
Mercier, Manager, IPCS, opened the meeting and welcomed
the participants on behalf of the heads of the three IPCS
cooperating organizations (UNEP/ILO/WHO). The Task Group
reviewed and revised the draft criteria monograph and made
an evaluation of the risks for human health and the en-
vironment from exposure to barium.
The first draft of this monograph was prepared by
Dr L. PAPA of the US Environmental Protection Agency.
The second draft was also prepared by Dr L. Papa, incor-
porating comments received following the circulation of
the first draft to the IPCS Contact Points for Environ-
mental Health Criteria documents. Dr B.H. Chen and Dr
P.G. Jenkins, both members of the IPCS Central Unit, were
responsible for the overall scientific content and
editing, respectively.
The efforts of all who helped in the preparation and
finalization of the document are gratefully acknowledged.
ABBREVIATIONS
AAS Atomic absorption spectrophotometry
BUN Blood urea nitrogen
CNS Central nervous system
ECG Electrocardiogram
IARC International Agency for Research on Cancer
ip Intraperitoneal
iv Intravenous
LLD Lowest lethal dose
PNS Peripheral nervous system
sc Subcutaneous
1. SUMMARY AND CONCLUSIONS
1.1. Summary
1.1.1. Identity, natural occurrence, and analytical methods
Barium is one of the alkaline earth metals, having a
relative atomic mass of 137.34 and an atomic number of 56.
It has seven naturally occurring stable isotopes, of which
138Ba is the most abundant. Barium is a yellowish-white
soft metal that is strongly electropositive. It combines
with ammonia, water, oxygen, hydrogen, halogens, and sul-
fur, energy being released by these reactions. It also re-
acts strongly with metals to form metal alloys. In nature
barium occurs only in a combined state, the principal
mineral forms being barite (barium sulfate) and witherite
(barium carbonate). Barium is also present in small quan-
tities in igneous rocks and in feldspar and micas. It may
be found as a natural component of fossil fuel and is
present in air, water, and soil.
Certain barium compounds, such as acetate, nitrate,
and chloride are relatively water soluble, whereas the
fluoride, carbonate, oxalate, chromate, phosphate, and
sulfate salts have very low solubility. With the exception
of barium sulfate, the water solubility of the barium
salts increases with decreasing pH.
Sampling of barium in aqueous and gaseous media is
conducted in the same way as it is for any other material.
Sediments, sludge, and soil samples are oven-dried or
sintered. The samples are then extracted in 1% HCl for
analysis of trace elements, including barium. Biological
samples are frozen or lyophilized and are prepared for
barium analysis using dry-washing procedures.
Atomic absorption and flame and plasma emission
spectrometry are the most commonly employed analytical
methods. Neutron activation, isotope dilution mass spec-
trometry, and X-ray fluorescence are also used.
1.1.2. Production, uses, and sources of exposure
Barite ore is the raw material from which nearly all
other barium compounds are derived. World production of
barite in 1985 was estimated to be 5.7 million tonnes.
Barium and its compounds are used in diverse industrial
products ranging from ceramics to lubricants. It is used
in the manufacture of alloys, as a loader for paper, soap,
rubber, and linoleum, in the manufacture of valves, and as
an extinguisher for radium, uranium, and plutonium fires.
Anthropogenic sources of barium are primarily indus-
trial. Emissions may result from mining, refining, or
processing of barium minerals and manufacture of barium
products. Barium is also discharged in waste water from
metallurgical and industrial processes. Deposition on soil
may result from man's activities, including the disposal
of fly ash and primary and secondary sludge in landfill.
It was estimated that in 1976, mining and processing of
barite ore in the USA released approximately 3200 tonnes
of particulates into the air, and fugitive dusts from the
use of barite in oil drilling and oil-related industries
accounted for approximately 100 tonnes of particulates. In
1972, the barium chemical industry in the USA released an
estimated 1200 tonnes of particulates into the atmos-
phere.
Environmental transport of barium occurs through the
air, water, and soil. Atmospheric barium consists of par-
ticulates whose transport is regulated by normal atmos-
pheric and meteorological circumstances. Transport of
barium in water is subject to interaction with other ions,
including sulfate, which regulates and limits barium con-
centration. Little information is available regarding the
aqueous transformations and transport of barium.
Exposure to barium can occur through air, water, or
food. The levels of barium in the air are not well docu-
mented. In the USA, the usual concentration is estimated
to be 0.05 µg/m3 or less. No distinct correlation has
been observed between ambient levels of barium in the air
and the extent of industrialization, although higher con-
centrations occur around smelters.
The presence of barium in sea water, river water, and
well-water has been documented, and it is also found in
sediments and natural waters in contact with sedimentary
rocks. Barium is present in almost all surface waters at
concentrations up to 15 000 µg/litre and contributes to
the hardness of the water. The barium concentration in
wells depends on the content of leachable barium in rocks.
Drinking-water contains 10-1000 µg/litre, although water
in certain regions of the USA has been shown to have con-
centrations in excess of 10 000 µg/litre. Municipal water
supplies depend upon the quality of surface and ground
water and, depending on the hardness, contain a wide range
of barium concentration. Studies from USA show levels in
drinking-water ranging from 1-20 µg/litre. Based on this
information and assuming a consumption rate of 2 litres
per day, the daily intake would be 2-40 µg barium.
Several studies have estimated a daily dietary intake
range of 300-1770 µg with large variations. Humans seldom
eat plants in which barium is present in significant
amounts or the part of the plant in which the barium ac-
cumulates. The Brazil nut tree is an exception, reported
concentrations being 1500-3000 µg/g. Tomatoes and soy
bean are also known to concentrate soil barium, the bio-
concentration factor ranging from 2 to 20.
In general, barium does not accumulate in common
plants in sufficient quantities to be toxic to animals.
However, it has been suggested that the large quantities
of barium (as high as 1260 mg/kg) accumulated in legumes,
alfalfa, and soybeans could cause problems in domestic
cattle.
The barium content of dry tobacco leaves averages 105
mg/kg, most of which is likely to remain in the ash during
burning. No values for barium concentrations in tobacco
smoke have been reported.
Another source of barium exposure is nuclear fallout.
However, with the establishment of atmospheric test ban
treaties, the quantity of radioactive barium in the en-
vironment has decreased.
1.1.3. Kinetics and biological monitoring
The average person (70 kg) contains approximately
22 mg of barium, most of which (91%) is localized in the
bone. Trace quantities are found in various tissues such
as the aorta, brain, heart, kidney, spleen, pancreas, and
lung. Total barium in human beings tends to increase with
age. The levels in the body depend on the geographical
location of the individual. Barium has also been found in
all samples of stillborn babies, suggesting that it can
cross the placenta.
It is difficult to assess the uptake of ingested
barium because a number of factors affect absorption. For
instance, the presence of sulfate in food results in the
precipitation of barium sulfate. Studies on experimental
animals and limited human data indicate that soluble
barium is absorbed through the intestine to the extent of
< 10% in adults but more in the young. Uptake occurs rap-
idly in the salivary and adrenal glands, heart, kidney,
mucosal tissue and blood vessels, and finally in the
skeleton. Like calcium, barium accumulates in bone. It is
deposited preferentially in the most active areas of bone
growth, primarily at the periosteal surfaces. Other fac-
tors important in absorption and deposition include age
and dietary restriction. Older rats exhibit decreased
absorption and bone concentrations of barium. Fasting
elicits an increase in barium absorption.
Inhaled barium can be absorbed through the lung or
directly from the nasal membrane into the bloodstream. In
rats, exposure results in deposition in the bones, but
continued exposure results in decreased deposition both in
the bones and the lungs. Insoluble compounds, such as
barium sulfate, accumulate in the lungs and are cleared
slowly by ciliary action.
Barium is eliminated in the urine and in the faeces,
the rates varying with the route of administration. Within
24 h, approximately 20% of a barium dose, injected into
humans, was eliminated in the faeces and approximately 5%
in the urine. Plasma barium is almost entirely cleared
from the bloodstream within 24 h. The elimination of
ingested barium in both human beings and animals occurs
principally in the faeces rather than in the urine. Fol-
lowing inhalation exposure, there is a slow elimination of
barium from bone and, thus, from the whole body. An esti-
mate of the biological half-life for barium in the rat is
90-120 days. For adequate biological monitoring of human
exposure, the elimination of barium in urine as well as in
faeces should be monitored.
1.1.4. Effects on experimental animals
In the rat, oral LD50 values of 118, 250, and 355
were measured for barium chloride, fluoride, and nitrate,
respectively. The acute effects of barium ingestion
include salivation, nausea, diarrhoea, tachycardia, hypo-
kalaemia, twitching, flaccid paralysis of skeletal muscle,
respiratory muscle paralysis, and ventricular fibril-
lation. Respiratory muscle paralysis and ventricular fib-
rillation may lead to death. Various studies have demon-
strated the detrimental effect of barium upon ventricular
automaticity and pacemaker current in the heart. Intra-
venous barium injections to anaesthetized dogs indicated
that these acute effects were due to prompt and substan-
tial hypokalaemia and could be prevented or reversed by
potassium administration.
Barium causes mild skin and severe eye irritation in
rabbits.
When rats ingested tap water containing up to 250 mg
barium/litre for 13 weeks, no signs of toxicity were
observed, although some groups showed a decrease in the
relative weight of the adrenals.
Rats given 10 or 100 mg barium/litre in their
drinking-water for 16 months experienced hypertension, but
a level of 1 mg/litre did not induce any blood pressure
changes. Analysis of myocardial function at 16 months
(100 mg barium/litre) revealed significantly altered car-
diac contractility and excitability, myocardial metabolic
disturbances, and hypersensitivity of the cardiovascular
system to sodium pentobarbital.
Oral or inhalation administration of barium carbonate
in rats resulted in adverse reproductive effects. In
addition, the death rate was higher for the newborn off-
spring of barium-treated dams. There is limited evidence
of teratogenicity of barium, but no conclusive evidence of
carcinogenicity is available.
Barium possesses chemical and physiological properties
that allow it to compete with and replace calcium in pro-
cesses mediated normally by calcium, particularly those
relating to the release of adrenal catecholamines and
neurotransmitters, such as acetylcholine and noradrena-
line.
Limited information is available regarding the immuno-
logical effects of barium in animals.
1.1.5. Effects on human beings
Several cases of poisoning due to the ingestion of
barium compounds have been reported. Barium doses as low
as 0.2-0.5 mg/kg body weight, generally resulting from the
ingestion of barium chloride or carbonate, have been found
to lead to toxic effects in adult humans. Clinical fea-
tures of barium poisoning include acute gastroenteritis,
loss of deep reflexes with onset of muscular paralysis,
and progressive muscular paralysis. The muscular paralysis
appears to be related to severe hypokalaemia. In most
reported cases, rapid and uneventful recovery occurred
after treatment with infused potassium salts (carbonate or
lactate) and/or oral administration of sodium sulfate.
Limited epidemiological studies have been conducted to
investigate the possible relationship between barium con-
centrations in drinking-water and cardiovascular mor-
tality, but the results have been inconsistent and incon-
clusive.
No increase in the incidence of elevated blood press-
ure, stroke, or heart and kidney disease was observed in a
population exposed to high concentrations of barium in
drinking-water when compared to a similar group exposed to
lower levels. In a short-term human volunteer study, no
effects on blood pressure were induced by the consumption
of barium in drinking-water.
An increase in the incidence of hypertension was
reported among workers exposed to barium, compared with
non-exposed workers. Baritosis has been observed in indi-
viduals occupationally exposed to barium compounds. A
study group consisting of barium-exposed workers and
people residing near a landfill site containing barium was
found to have an increased prevalence of musculoskeletal
symptoms, gastrointestinal surgery, skin problems, and
respiratory symptoms.
No conclusive association was found between the level
of barium in drinking-water and the incidence of congeni-
tal malformations. There is no evidence that barium is
carcinogenic.
1.1.6. Effects on organisms in the environment
Barium directly affects the physico-chemical proper-
ties as well as the infectivity of several viruses and
their ability to multiply. It also affects the development
of germinating bacterial spores and has a variety of
specific effects on different microorganisms, including
the inhibition of cellular processes.
Little information is available on the effects of
barium on aquatic organisms. There were no effects on sur-
vival in fish following exposure for 30 days. However, in
a 21-day study, impairment of reproduction and reduction
in growth were observed in daphnids at a dose of 5.8 mg
barium/litre. No evidence has been found to indicate that
barite is toxic to marine animals. However, exposure to
barite in large amounts could adversely affect coloniz-
ation by benthic animals.
Marine plants, as well as invertebrates, may actively
accumulate barium from sea water.
1.2. Conclusions and recommendations
Barium, at concentrations normally found in our en-
vironment, does not pose any significant risk for the gen-
eral population. However, for specific subpopulations and
under conditions of high barium exposure, the potential
for adverse health effects should be taken into account.
Few data are available for evaluating the risk to the
environment posed by barium. However, based on the avail-
able information on the toxic effects of barium in
daphnids, it appears that barium may represent a risk to
populations of some aquatic organisms.
There is a need for epidemiological studies, for
research on bioavailability and cardiovascular and immuno-
logical toxicity, and for additional information on
chronic aquatic toxicity. In order to establish better
protection measures, more data on exposures in the work-
place and the use of biomarkers are necessary.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Identity
Barium is a member of the alkaline earth metals in
Group IIA of the periodic table, along with beryllium,
magnesium, calcium, strontium, and radium. The symbol for
the element is Ba. Barium has an atomic number of 56 and a
relative atomic mass of 137.34. The CAS registry and RTECS
registry numbers for barium are 7440-39-3 and CQ8370000,
respectively. Metallic barium is obtained by reducing
barium oxide with aluminum or silicon in a vacuum at high
temperature.
Twenty-five barium isotopes have been identified
(CRC, 1988). There are seven naturally occurring stable
isotopes with mass numbers of 130, 132, 134, 135, 136,
137, and 138, 138Ba being the most abundant (Lederer et
al., 1967). The others are unstable isotopes with half-
lives ranging from 12.8 days for 140Ba to 12 seconds for
143Ba (CRC, 1988). Two of these isotopes, 131Ba and
139Ba, are used in research as radioactive tracers. A
list of common barium compounds with their formulae and
CAS registry numbers is presented in Table 1.
2.2. Physical and chemical properties of barium
Important physical and chemical properties of barium
relevant to exposure assessment and effects are shown in
Table 2. It is a silver-white, soft metal, relatively
volatile and readily distilled (Goodenough & Stenger,
1973). Powdered barium is pyrophoric and very dangerous
to handle in the presence of air or other oxidizing gases
(Quagliano, 1959). As might be expected from its high
electrode potential (-2.912 V), barium is extremely reac-
tive and the free energy of formation of its compounds is
very high. Therefore it does not exist in nature in the
elemental state but occurs as the divalent cation, Ba2+,
in combination with other elements. Barium reacts readily
with halogens, oxygen, and sulfur to form halides, oxide,
and sulfide. It also reacts with nitrogen and hydrogen at
higher temperatures to form the nitride and hydride, and
it reacts vigorously with water displacing hydrogen to
form the hydroxide. Treatment of barium hydroxide with
hydrogen peroxide at low temperatures forms barium per-
oxide, which can also be formed by direct combination of
oxygen with barium oxide or the metal. Barium exhibits
little tendency to form complexes; the amines formed with
NH3 are unstable and the beta -diketons and alcoholates
are not well characterized.
Table 1. Common barium compoundsa
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Substance Formula CAS No. RTECS No.
-----------------------------------------------------------------------------------
Aluminium barium titanium oxide Not given 52869-91-7 BD 0345400
Barium acetate Ba(C2H3O2)2.H2O 543-80-6 AF 4550000
Barium azide Ba(N3)2 18810-58-7 CQ 8500000
Barium bromate Ba(BrO3)2.H2O 13967-90-3 EF 8715000
Barium cadmium laurate (C12H24O2)4.Ba.Cd Not given OE 9805000
Barium cadmium stearate (C18H36O2)4.Ba,Cd 1191-79-3 WI 2830000
Barium calcium titanium oxide Not given 52869-93-9 CQ 8580000
Barium carbonate BaCO3 513-77-9 CQ 8600000
Barium chlorate Ba(ClO3)2.H2O 13477-00-4 FN 9770000
Barium chloride BaCl2 10361-37-2 CQ 8950000
Barium chloride, dihydrate BaCl2.2H2O 10326-27-9 CQ 8751000
Barium chromate (VI) BaCrO4 10294-40-3 CQ 8760000
Barium cyanide Ba(CN)2 542-62-1 CQ 8785000
Barium fluoborate Ba(BF4)2 13862-62-9 CQ 8925000
Barium fluoride BaF2 7787-32-8 CQ 9100000
Barium hypochlorite Ba(ClO2)2 13477-10-6 NH 3480000
Barium iron oxide BaFe12O19 12047-11-9 CQ 9520800
Barium nitrate Ba(NO3)2 10022-31-8 CQ 9625000
Barium oxide BaO 1304-28-5 CQ 9800000
Barium perchlorate Ba(ClO4)2.4H2O 13465-95-7 SC 7550000
Barium permanganate Ba(MnO4)2 7787-36-2 SD 6405000
Barium peroxide BaO2 1304-29-6 CR 0175000
Barium silicofluoride BaSiF6 17125-80-3 CR 0525000
Barium sulfate BaSO4 7727-43-7 CR 0600000
Barium sulfide BaS 50864-67-0 CR 0270000
Barium sulfide, mixture with sulfur Not given 8077-30-3 CR 0660000
Barium sulfonates Not given Not given CR 0700000
Barium zirconium (IV) oxide BaZr4O4 12009-21-1 CR 0875000
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a Source: RTECS (1985).
Table 2. Physical and chemical properties of bariuma
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Atomic number 56
Relative atomic mass 137.34
Physical state solid metal
Colour yellowish-white
Melting point 725 °C
Boiling point 1640 °C
Solubility in water reacts with release of H2
Solubility in alcohol soluble (decomposes)
Solubility in benzene insoluble
Relative density (at 20 °C) 3.51
Extremely reactive with water, ammonia, halogens, oxygen
most acids
Electrode potential (Eo(aq)Ba2+/Ba)
(at 25 °C, 1 atm.) -2.912 volts
Electronegativity 1.02
Flame coloration test green
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a Source: Weast (1983), Windholz (1983).
Barium attacks most metals with the formation of
alloys; iron is the most resistant to alloy formation.
Barium forms alloys and intermetallic compounds with lead,
potassium, platinum, magnesium, silicon, zinc, aluminium,
and mercury (Hansen, 1958). Metallic barium reduces the
oxides, halides, and sulfides of most of the less reactive
metals, thereby producing the corresponding metal.
2.3. Physical and chemical properties of barium compounds
Barium compounds exhibit close relationships with the
compounds of calcium and strontium, which are also alka-
line earth metals. The physical and chemical properties
of various barium compounds are listed in Table 3. Barium
acetate, nitrate, and chloride are quite soluble, whereas
the arsenate, carbonate, oxalate, chromate, fluoride, sul-
fate, and phosphate salts are very poorly soluble. All
barium salts, except for barium sulfate, become increas-
ingly soluble as the pH decreases. These salts dissolve
partially in carbonic acid and completely in hydrochloric
or nitric acids. Strong sulfuric acid is required to dis-
solve barium sulfate.
Table 3. Physical and chemical properties of various barium compoundsa
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Relative Relative Solubility Melting Boiling
Compound molecular density in waterb pointc point
mass (°C) (°C)
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Barium acetate 255.45 2.468 58.80 - -
Barium arsenate 689.83 5.10 0.55 1605 -
Barium carbonate 197.37 4.43 0.02 1790 (90) -
Barium chloride 208.25 3.856 375 (26) 962 1560
Barium chromate 253.32 4.498 0.0034 (16) - -
Barium fluoride 175.34 4.89 1.2 (25) 1375 2137
Barium hydroxide x 8H20 315.47 2.18 56 (15) 78 78 (-8H20)
Barium nitrate 261.38 3.24 87 592 d
Barium oxalate 225.35 2.658 0.093 (18) 400d -
Barium oxide 153.36 5.72 34.8 1918 ca.2000
Barium phosphate, dibasic 233.5 4.165 0.1-0.2 410 (710)d -
Barium triphosphate 601.93 4.10 insoluble - -
Barium sulfate 233.4 4.5 0.002 1580 -
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a CRC (1988).
b in g/litre at 20 °C; where the solubility was not measured at 20 °C, the temperature
used is shown in parentheses.
c at 760 mmHg; where the pressure was otherwise, it is given in parentheses.
d decomposes.
In aqueous solution, the barium ion can combine with
organic chelating agents. Owing to its similarity to cal-
cium in its chemical properties and because it lies below
calcium in the periodic table, barium is thought to inter-
act with biochemical pathways involving calcium ion-bind-
ing by competing for binding sites of chelation (Sillen &
Martell, 1964). Barium may also bind with organic ligands
to form biological complexes.
2.4. Analytical sampling
Barium does not require sampling or handling pro-
cedures different from those used in general analytical
practice. The greatest sources of sampling error in
environmental studies are the variations in the material
being sampled. Sampling procedures must not only take
into account the physical and chemical properties of the
specific barium compound but must also accurately reflect
variations in the media (water, air, and soil).
2.4.1. Water
The US EPA (1979a) recommended the following procedure
for sampling and preserving metals in aqueous solution. A
minimum of 200 ml is collected in an analytically clean
container, preferably made of polyethylene, with a poly-
propylene cap (no liner). For the determination of dis-
solved constituents (i.e. barium), the sample must be fil-
tered through a membrane filter (0.45 µm) preferably on-
site. The suspended constituents retained by the membrane
filter are saved if total barium analysis is required. The
filtered sample may be initially preserved by icing. How-
ever, as soon as possible, the sample must be acidified to
a pH <2 with nitric acid (normally 3 ml 1:1 nitric acid
per litre is sufficient). A maximum holding time of 6
months is recommended, although the length of time will
also depend on the type of sample used.
2.4.2. Soils and sediments
Samples of soils, sediments, and sludge are oven-dried
and stored in polyethylene containers. The samples are ex-
tracted in 1% hydrochloric acid for analysis of trace el-
ements including barium (Fortescue et al., 1976). Samples
of benthic intertidal sediments from sandy beaches can be
stored in clean polyethylene bottles and frozen (-15 °C)
(Chow et al., 1978). Benthic sediments are collected with
a non-contaminating box-core device, with only the top
1 cm of the core being saved.
2.4.3. Air
Barium is sampled in the same way as other compounds
in air. A known volume of air is drawn through a cellulose
filter to collect the compound in the particulate fraction
(NIOSH, 1977). Samples collected on the filters are
leached into hot water, filtered, and dried.
2.4.4. Biological materials
Biological tissues such as hair, blood, and placenta
are kept frozen or lyophilized before analysing for barium
(Creason et al., 1976). Dry-washing procedures are used
to prepare the samples for barium analysis. Research at
the National Bureau of Standards, Washington, DC, indi-
cated that bovine liver samples, lyophilized and ground,
showed no change in composition after prolonged storage at
room temperature (Becker, 1976). Similar procedures were
used for orchard plant leaves. Samples carefully dried and
lyophilized can be adequately stored at room temperature
for several years with no significant changes in trace
metal composition (Becker, 1976).
2.5. Analytical procedures
In general, analytical procedures measure total barium
ion present rather than specific barium compounds.
Analysis for soluble barium in aqueous solutions re-
quires consideration of contaminating substances that may
interfere with the assay. Certain contaminants can affect
absorption as well as emission spectra. Maruta et al.
(1972) observed that the presence of aluminum depressed
the barium signal and that the addition of alkali com-
pounds (except caesium) suppressed barium ionization.
Magill & Svehla (1974) also noted that several anions and
cations interfered with the analysis of barium.
Separation of barium from interfering components is
achieved by ion-exchange chromatography. Akiyama & Tomita
(1973) employed a chromium phosphate ion exchanger. Other
workers have used Dowex 50 ion-exchange resin, with vari-
ous degrees of cross linking (Dybczynski, 1972; Wolgemuth
& Broecker, 1970; Bacon & Edmond, 1972; Pierce & Brown,
1977). Elution is carried out with hydrochloric acid.
Pierce & Brown (1977) used a chelating agent, ethylenedi-
amine tetraacetic acid (EDTA), to elute barium from the
Dowex 50 column in a semi-automated procedure. Quantifi-
cation of low concentrations of barium using chemical
methods (wet, gravimetric) is at present seldom attempted.
Owing to the high ionization properties of barium and
spectral interference from calcium emissions, the use of
instrumental methods for analysing barium is often diffi-
cult.
2.5.1. Commonly used analytical methods
Atomic absorption spectrophotometry (AAS) is a readily
available and widely used analytical technique for deter-
mining several metals in solution from a variety of
samples. The US EPA (1974, 1979a) recommends two AAS
methods for barium, the direct aspiration method and the
furnace technique.
2.5.1.1 AAS - Direct aspiration method
The optimal concentration range for determining barium
by the AAS direct aspiration method, using a wavelength of
553.6 nm, is 1-20 mg/litre, with a sensitivity of 0.4
mg/litre and a detection limit of 0.03 mg/litre (US EPA,
1979a). An AAS direct aspiration method for the determi-
nation of water-soluble barium components in air has been
described by NIOSH (1977). The air sample is drawn through
a cellulose membrane filter on which the analyte is col-
lected. The working range of the method was estimated to
be 0.15-1.3 mg/m3, with a sensitivity of 0.0004 mg/m3.
2.5.1.2 AAS - Furnace technique
For concentrations of barium <0.2 mg/litre, the fur-
nace technique is recommended. The optimal concentration
range for barium determination by the furnace technique is
10-200 µg/litre, the detection limit being 2 µg/litre. A
detection limit of 0.5 ng/ml using a 20 µl sample was
also reported for this method (Slavin, 1984). The Associ-
ation of Official Analytical Chemists (AOAC, 1984) used
emission spectrography for measuring barium concentrations
in plant tissue. The coefficient of variation for barium
analysis was between 7 and 15%, depending on the type of
plant tissue analysed. The analysis of barium in drinking-
water was performed by Pierce & Brown (1977) using this
method; they reported a detection limit and sensitivity
for barium of 3.0 and 10.0 µg/litre, respectively.
2.5.1.3 AAS - ICP
In recent years, emission spectrometry employing an
inductively coupled plasma (ICP) source has been used
routinely (Garbarino & Taylor, 1979). Detection limits of
<0.1 ng/ml have been reported (Fassel & Kniseley, 1974),
with less of the chemical or ionization interference typi-
cally seen with other emission spectroscopic systems.
Optical emission methods, however, are expensive when used
for a single element analysis, but this problem is largely
offset when several elements are analysed simultaneously.
2.5.2. Analytical methods used for special applications
2.5.2.1 Mass spectrometry
Because of expense and low sample throughput, mass
spectrometry is not a commonly used procedure for the
analysis of barium or other elements. However, aqueous
barium samples, purified by ion exchange, are particularly
amenable to this procedure (Bacon & Edmond, 1972). Peaks
for 135Ba and 138Ba can be scanned and replicate analy-
ses can be performed with a coefficient of variation of
0.17%. Isotope dilution mass spectrometry is an extremely
valuable reference method. Several investigators have
indicated that the isotope dilution mass spectrometric
method circumvents the need for large samples and tedious
purification procedures. Internal standardization provides
a high degree of precision, element selectivity, and sen-
sitivity (Chow & Patterson, 1966; Wolgemuth & Broecker,
1970; Bernat et al., 1972).
2.5.2.2 X-ray fluorescence spectrometry
This technique has been used to measure barium concen-
trations in human tissue (Forssen & Erametsa, 1974) and in
river sediments (Tsai et al., 1978). The coefficient of
variation of this method was 5.6% when river sediments
were analysed (Tsai et al., 1978).
2.5.2.3 Neutron activation analysis
Neutron activation can be used for multi-element
analysis. This technique has been used to determine barium
in sludge (Nadkarni & Morrison, 1974), in marine sediments
(Chow et al., 1978), and biological tissues (Heffron et
al., 1977). The correlation coefficient of the data when
compared with isotope dilution methods is 0.923, and the
limit of detection is 1 µg (Reeves, 1986).
3. SOURCES IN THE ENVIRONMENT
3.1. Natural occurrence
Barium is a relatively abundant element found combined
with other elements in soils, rocks, and minerals. It
ranks seventh in abundance among the minor elements and
sixteenth among the non-gaseous elements in the earth's
crust (Schroeder, 1970), and constitutes about 0.04% of
the earth's crust (Reeves, 1979). Barium also occurs as
gangue in lead and zinc ore deposits. The terrestrial
abundance of barium has been estimated at 250 g/tonne, and
its occurrence in sea water is 0.006 g/tonne (Considine,
1976).
The two most prevalent naturally occurring compounds
of barium are barite (barium sulfate) and witherite
(barium carbonate). Barite crystallizes in the orthorhom-
bic system. It occurs in beds or masses in limestone,
dolomite, shales, and other sedimentary formations; as
residual nodules resulting from the weathering of barite-
bearing dolomite or limestone; and as gangue in beds
together with fluorspar, metallic sulfides, and other
minerals.
Witherite crystallizes in the orthorhombic system. It
is found in veins and is often associated with galena
(lead sulfide), as at Alston Moor, Cumberland, England. It
is also found associated with barite at Freiberg, Saxony,
German Democratic Republic, and at Lexington, Kentucky,
USA.
Barium occurs in coal at concentrations up to 3000
mg/kg (Bowen, 1966). It also occurs in fuel oils, the
barium content varying with the petroleum source.
Barium is ubiquitous in soils, being found at concen-
trations ranging from 100-3000 µg/g (Schroeder, 1970;
Robinson et al., 1950). Brooks (1978) estimated an average
soil concentration of 500 mg/kg. Due to its abundance in
soils, barium may be present in the air in areas with high
natural dust levels.
Barium can be transported into ground-water aquifers
through the leaching and eroding of barium from sedimen-
tary rocks. The level of barium present in the ground
water is related to the hardness of the water, since
barium is always present with calcium (Kopp & Kroner,
1968). Cartwright et al. (1978) reported that the high
barium levels in ground water in Illinois, USA, were
derived from the sandstone formation of the Cambrian-
Ordovician aquifer. The highest concentrations occurred
in fine-grained and older sediments. Barium was found in
94% of the surface waters examined, the concentrations
range being 2-340 µg/litre (Kopp & Kroner, 1967).
Barium in surface waters is ultimately transported
into the oceans where it combines with the sulfate ion
present in salt water to form barium sulfate. Barium in
the ocean is in a steady state; the amount entering from
rivers is balanced by the amount falling to the bottom as
particles to form a permanent part of the sediment on the
ocean floor (Wolgemuth & Brocker, 1970). Barium concen-
trations in sea water of 6 µg/litre and in fresh water of
7-15 000 µg/litre (an average of 50 µg/litre) have been
reported (Reeves, 1986).
3.2. Man-made sources
3.2.1. Production levels, processes, and uses
Barite ore is the raw material from which nearly all
other barium compounds are derived. World production of
barite in 1985 was estimated to be approximately 5.7
million tonnes. The major world producers of barite are
China, the United States, USSR, India, Mexico, Morocco,
Ireland, Federal Republic of Germany, and Thailand. Other
producers are Canada, France, Spain, Czechoslovakia, and
England (Vagt, 1985).
China, as the world's leading producer, accounted for
about 1.0 million tonnes or 17% of world output in 1984.
The USA, the second largest producer, accounted for 0.70
million tonnes in 1984 and also imported 1.6 million
tonnes. Canada produced approximately 64 000 tonnes and
consumed around 78 000 tonnes in 1984 (Vagt, 1985).
Emissions of barium into the air from mining, re-
fining, and processing barium ore can occur during loading
and unloading, stock-piling, materials handling, and
grinding and refining of the ore. According to emission
factors determined by Davis (1972), mining and processing
of barite ore released an estimated 3200 tonnes of par-
ticulates into the air in 1976 in the USA (US Bureau of
Mines, 1976). Emission into water may occur during the
purification of barite ore and subsequent discharge of the
industrial water to the environment.
Fossil fuel combustion may also release barium into
the air. Pierson et al. (1981) found that >90% of the
barium additive in diesel fuels is emitted in vehicle
exhaust, where it is totally in the form of barium sul-
fate.
Coal-fired power plants emit barium into the atmos-
phere via ash. Some barium escapes into the atmosphere as
fly ash (Cuffe & Gerstle, 1967), while the rest is gener-
ally disposed of in landfill. Barium in coal ash ranges
from 100-5000 mg/kg (Miner, 1969). Hildebrand et al.
(1976) reported the presence of barium at a concentration
of 0.02 mg/litre in the effluent from a coal conversion
plant.
In the USA, the barium chemical industries released an
estimated 1200 tonnes of particulates into the atmosphere
in 1972 (Davis, 1972; Rezink & Toy, 1978). Waste water
from barium chemical production processes is another
potential source of barium emission.
Although most fugitive dust emissions and process
effluents are reduced by control technologies, an area of
concern is the emission of soluble barium to the atmos-
phere from dryers and calciners. Baghouses can reduce the
uncontrolled emission factor (up to 10 g/kg final product)
to 0.25 g/kg (Rezink & Toy, 1978). The release of soluble
barium into the atmosphere around these plants was esti-
mated at 56 tonnes for 1972 (Rezink & Toy, 1978), but it
has decreased as barium chemical production has declined.
The plastics industry is a relatively important source of
barium emission to the atmosphere. It utilizes barium as
a stabilizer to prevent discoloration during processing.
Another source of barium emission is the manufacture
of glass. Emissions of barium-containing particulates with
an average size of 1 µm have been reported by various
authors (Stockham, 1971; Davis, 1972). Davis (1972)
estimated an emission of 1 kg/1000 kg of barium used in
the glass industry. In a study of glass furnace emissions,
Stockham (1971) found negligible emissions of barium in
the formation of flint glass but a 1-10% emission level of
the particulates in the effluent of amber glass manufac-
turing.
The detonation of nuclear devices in the atmosphere is
a source of atmospheric radioactive barium. The radioac-
tive isotopes 140Ba and 143Ba are products of the decay
chains from thermal-neutron fission of 235U. Among the
isotopes of barium, 140Ba has the longest half-life (12.8
days) and contributes 10% of the total fission products at
10 days after nuclear fission. At 60 days, however, its
contribution falls to 2% of total activity (French, 1963).
The concentration of barium particles in the atmosphere
due to this source, in terms of actual weight, is im-
measurably small. Due to the short half-life and low con-
centrations of barium radionuclides, this source is not
considered a significant source of barium in the environ-
ment.
Barium is used extensively by man and is an essential
component of a vast number of manufacturing processes,
some of which are identified in Table 4. It is used in the
manufacture of alloys, as a loader for paper, soap, rub-
ber, and linoleum, in the manufacture of valves, and in
the production of lights and green flares. Barium is also
used in cement where concrete is exposed to salt water, in
the radio industry to capture the last traces of gases in
vacuum tubes, in the ceramic and glass industries, as an
insecticide and rodenticide, and as an extinguisher for
radium, uranium, and plutonium fires (Browning, 1969).
Table 4. Main uses of some barium compoundsa
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Barium compound Uses
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Acetate Catalyst for organic reactions; textile mordant; oil and grease
lubricator; paint and varnish driers
Aluminate In ceramics; in water treatment
Azide In high explosives
Bromate Analytical reagent; oxidizing agent; corrosion inhibitor in low
carbon steel; in the preparation of rare earth bromates
Bromide In the manufacture of other bromides; in photographic compounds;
in the preparation of phosphors
Carbonate In the treatment of brines in chlorinealkali cells to remove
sulfates; as a rodenticide; in ceramic flux, optical glass, case-
hardening baths, ferrites, radiation-resistant glass for colour
television tubes; in manufacturing paper
Chlorate In pyrotechnics (green fire); as textile mordant; in the manufac-
ture of other chlorates and of explosives and matches
Chloride In the manufacture of pigments, colour lakes, glass; as a mordant
for acid dyes; in pesticides, lube oil additives, boiler compounds,
and aluminum refining; as a flux in the manufacture of magnesium
metal; in leather tanner and finisher, in photographic paper and
textiles
Chromate In safety matches; as a pigment in paints; in ceramics; in fuses;
in pyrotechnics; in metal primers; in ignition control devices
Citrate As a stabilizer for latex paints
Cyanide In metallurgy and electroplating
Cyanoplatinite In X-ray screens
Diphenylamine sulfonate As an indicator in oxidation-reduction titrations
Ethylsulfate In organic preparations
Fluoride In ceramics; in the manufacture of other fluorides; in crystals
for spectroscopy; in electronics; in dry-film lubricants; in
embalming; in glass manufacture; manufacture of carbon brushes for
DC motors and generators
Fluorosilicate In ceramics; in insecticidal compositions; in the preparation of
silicon tetrafluoride
Table 4. (cont.)
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Barium compound Uses
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Hydroxide, monohydrate In the manufacture of oil and grease additives; in barium soaps
and chemicals; in the refinishing of beet sugar and animal and
vegetable oils; as an alkalizing agent in water softening; as a
sulfate removal agent in the treatment of water and brine; in
boiler scale removal; as a depilatory agent; as a catalyst in the
manufacture of phenol-formaldehyde resins; as insecticide and
fungicide; as a sulfate-controlling agent in ceramics; as a
purifying agent for caustic soda; as a steel carbonizing agent; in
glass; synthetic rubber vulcanization; as a corrosion inhibitor;
in drilling fluids, lubricants
Hydroxide, octahydrate In organic preparations; in barium salts; in analytical chemistry
and pentahydrate (and uses described for the monohydrate)
Hypophosphite In medicine and nickel plating
Iodide In the preparation of other iodides
Manganate (VI) As a paint pigment
Metaphosphate In glasses, porcelain, and enamels
Molybdate In electronic and optical equipment, as a pigment in paints and
protective coatings
Nitrate In pyrotechnics (green light); in incendiaries; chemicals (barium
peroxide); ceramic glazes; as a rodenticide; in vacuum-tube
industry
Nitrite In diazotization reactions; for the prevention of corrosion of
steel bars; in explosives
Oxalate As an analytical reagent; in pyrotechnics
Oxide As a dehydrating agent; in the manufacture of lubricating oil
detergents
Perchlorate In explosives; in rocket fuels (experimentally); in the determi-
nation of ribonuclease; as an absorbent of water in C and H analy-
sis
Permanganate As a strong disinfectant; in the manufacture of permanganates; as
a dry cell depolarizer
Peroxide In bleach; decolorizing glass; thermal welding of aluminum; in the
manufacture of hydrogen peroxide and oxygen in cathodes; in dyeing
and printing textiles; as an oxidizing agent in organic synthesis
Phosphate, secondary In fireproofing compositions; in the preparation of phosphors
Potassium chromate As a component of anticorrosive paints for use on iron, steel, and
light metal alloys
Table 4. (cont.)
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Barium compound Uses
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Selenide In photocells; in semiconductors
Silicate In refining sugar from molasses
Sodium niobate In lasers, electro-optical modulators, and optical parametric
oscillators
Stearate As a waterproofing agent; as a lubricant in metalworking, plastics,
and rubber; in wax compounding; in the preparation of greases; as
a heat and light stabilizer in plastics
Sulfate As weighting mud in oil-drilling; in paper coatings; in paints; as
filler and delustrant for textiles, rubber, linoleum, oilcloth,
plastics, and lithograph inks; as base for lake colours; as X-ray
contrast medium; as opaque medium for gastrointestinal radiography;
in battery plate expanders, radiation shields, photographic paper,
artificial ivory, cellophane; in heavy concrete for radiation
shields
Sulfide In luminous paint; as a depilatory; as a fireproofing agent; in
barium salts; in vulcanizing rubber; in the manufacture of litho-
pone; in generating pure hydrogen sulfide for analytical purposes;
as the main starting material for the production of most barium
compounds
Sulfite In analysis; in the manufacture of paper
Tartrate In pyrotechnics
Thiocyanate To make aluminum or potassium thiocyanates; in dyeing; in photo-
graphy; as a dispersing agent for cellulose
Thiosulfate In explosives, luminous paints, matches, varnishes; as an iodometry
standard; in photographic diffusion-transfer processes.
Titanate (IV) In ferroelectric ceramic; pure or combined with iron, used in
electronic storage devices, dielectric amplifiers, digital calcu-
lators, memory devices, and magnetic amplifiers
Tungstate As a pigment; in X-ray photography for the manufacture of inten-
sifying and phosphorescent screens
Zirconate In the manufacture of silicone rubber compounds stable up to
246 °C; in electronics
Zirconium silicate In the production of electrical resistor ceramics and glaze
opacifiers; as a stabilizer for coloured ground coat enamels
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a Source: Hawley (1977), Windholz (1983), Shreve (1967).
Barite is a valuable industrial mineral because of its
high specific gravity, low abrasiveness, chemical stab-
ility, and lack of magnetic effects. Its main use is as a
weighting agent for oil- and gas-well drilling muds
required to counteract high pressures confined by the
substrata. The oil- and gas-well drilling industries used
90% of the 2.24 million tonnes of barite consumed in the
USA in 1976 (US Bureau of Mines, 1976). In the same year,
unloading and handling this material released an estimated
112 tonnes of particulates into the atmosphere (Davis,
1972; US Bureau of Mines, 1976).
Complexes of barium with other compounds are used as
additives, which act as dispersants, stabilizers, and
inhibitors in several kinds of oils. A barium-based
organometallic compound is used to reduce stack smoke
emissions from diesel engines. Miner (1969) estimated the
amount of barium emitted in diesel exhaust to be a maximum
of 12 mg/m3 (<25% soluble barium at full load). This
estimate was based on the presence of an additive concen-
tration in diesel fuel of 0.075% barium by weight.
Barium compounds are used in the electronics and com-
puter industries, as contrast media in roentgenography, in
sugar processing, and as an ingredient in various products
such as cosmetics, cloth, leather, linoleum, oil cloth,
plastics, pharmaceuticals, printer's ink, photographic
paper, depilatories, pyrotechnics, detergents, high-tem-
perature greases, and water softeners (US Bureau of Mines,
1976).
The manufacture of paint also uses barium compounds,
including the sulfate, carbonate, and lithopone (a white
pigment consisting of a mixture of zinc sulfide, barium
sulfate, and zinc oxide). These compounds are relatively
unreactive, and their most important pigment properties
are high specific gravity, relatively low oil absorption,
and easy wettability by oils and grinding agents. The
amount of barium that these products add to the environ-
ment has not been determined, but most atmospheric
emissions are related to material handling (US Bureau of
Mines, 1976).
One of the routinely used technologies for treating
radium-containing water is to precipitate the radium as
barium-radium sulfate or adsorb it on materials containing
natural or activated barium sulfate (Havlik et al.,
1980).
4. ENVIRONMENTAL TRANSPORT AND DISTRIBUTION
4.1. Transport and distribution between media
4.1.1. Air
Examination of dust falls and suspended particulates
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 inciner-
ation, 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 com-
pounds 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 rain-
out or wash-out wet deposition. These two forms of depo-
sition efficiently clear the atmosphere of pollutants, but
they are not well understood. Without knowing the amount
of barium in the atmosphere, it is difficult to evaluate
the processes of deposition, transport, and distribution.
4.1.2. Water
Soluble barium and suspended particulates can be
transported great distances in rivers, depending on the
rates of flow and sedimentation. In the absence of any
possible removal mechanisms, the residence time of barium
in aquatic systems could be several hundred years.
Cartwright et al. (1978) studied the chemical control of
barium solubility and showed that for most water samples,
barium ion concentration is controlled by the amount of
sulfate ion in the water.
Unless it is removed by precipitation, exchange with
soil, or other processes, barium in surface waters ulti-
mately reaches the ocean. Once freshwater sources dis-
charge into sea water, 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.
Upon entering the ocean, barium is transported down-
ward by the physical processes of mixing. It is depleted
in the upper layers of the ocean by incorporation into
biological matter, which settles toward the ocean floor
(Goldberg & Arrhenius, 1958). The higher concentration of
barium in deep water relative to surface water probably
reflects the deposition of barium onto suspended particles
forming at the ocean surface and the subsequent release of
barium to the deep water as the particles are destroyed in
transit to the ocean floor. In the ocean, barium is in
steady state; the amount entering the ocean through rivers
is balanced by the amount falling to the bottom as par-
ticles forming a permanent part of the sediment (Wolgemuth
& Brocker, 1970).
4.1.3. Soil
Barium is present in the soil through the natural pro-
cess of soil formation, which includes the breakdown of
parent rocks by weathering. Barium levels 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 geological faults. If there is
insufficient sulfate to combine with barium, the soil
material formed is partially saturated with barium. Barium
replaces other cations in the soil particles by ion
exchange.
Barium salts are preferentially absorbed by argil-
laceous elements. Colloidal clays have been found to
decompose insoluble barium sulfate by binding barium.
Bradfield (1932) found that, in the reaction between
purified sodium clay and barium sulfate, the sulfate ion
became much more soluble, thus releasing the barium into
the clay.
Barium in soils would not be 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 may become soluble
and move into ground water (US EPA, 1984).
4.1.4. Vegetation and wildlife
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 leaves, and the black walnut, hickory, and
brazil nut trees. The Douglas fir tree and plants of the
genus Astragallu also accumulate barium. 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. There
is no evidence that barium is an essential element in
plants (Reeves, 1979).
No information is available on barium levels in wild-
life.
4.1.5. Entry into the food chain
Certain plants used by humans as food sources actively
accumulate barium. It is also found in dairy products and
eggs (Gormican, 1970).
4.2. Biotransformation
There is no evidence that barium undergoes biotrans-
formation other than as a divalent cation.
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels
Environmental levels are generally reported as total
barium ion rather than as specific barium compounds.
5.1.1. Air
The levels of barium in the air are not well docu-
mented, and in some cases the results are contradictory.
Tabor & Warren (1958) detected barium concentrations from
<0.005 to 1.5 µg/m3 in the air in 18 cities and 4 sub-
urban areas in the USA (Table 5). Of 754 samples analysed,
most of the observations made were at concentrations up to
0.05 µg/m3. No distinct pattern between ambient levels
of barium in the air and the extent of industrialization
was observed. In general, however, a higher concentration
was observed in areas where metal smelting occurred (Tabor
& Warren, 1958; Schroeder, 1970). In a more recent survey
in the USA, barium concentration ranged from 0.0015 to
0.95 µg/m3 (US EPA, 1984).
In three communities in New York City, barium was
measured in dustfall and household dust (Creason et al.,
1975). With standard methods (US EPA, 1974), the dustfall
was found to contain an average of 137 µg barium/g dust,
while the house dust contained 20 µg barium/g.
5.1.2. Water
The presence of barium in sea water, river water, and
well water has been well documented. It occurs in almost
all surface waters that have been examined (NAS, 1977).
The concentration present is extremely variable and de-
pends on factors (e.g., local geology) that affect
aquifers and any water treatment that has occurred. The
concentration of barium in water is related to the hard-
ness of the water, which is defined as the sum of the
polyvalent cations present, including the ions of calcium,
magnesium, iron, manganese, copper, barium, and zinc (NAS,
1977). Barium concentrations of 7 to 15 000 µg/litre have
been measured in fresh water and 6 µg/litre in sea water
(Schroeder et al., 1972).
Table 5. Barium in the ambient air of various cities in the USAa
-----------------------------------------------------------------------------------------
Percentage of samples at various concentrations (ug/m3)
City --------------------------------------------------------
< 0.005 > 0.005-0.05 > 0.05-0.5 > 0.5-1.5
-----------------------------------------------------------------------------------------
Houston (urban, suburban) 24 60 10 6
Boston (urban), Chicago, Denver, 32 52 16 0
E. St. Louis, Louisville,
Minneapolis, New Orleans,
Portland, Salt Lake City, Tampa
Boston (suburban), Chattanooga, 36 64 0 0
E. Chicago, Washington, DC
Fort Worth, Jersey City, New York, 66 34 0 0
Philadelphia,
Lakehurst (NJ), Paulsboro (NJ) 100 0 0 0
(suburban)
-----------------------------------------------------------------------------------------
a Source: Tabor & Warren (1958)
5.1.2.1 Surface waters
In the USA, levels of barium in water vary greatly
depending on local geochemical influences. Levels reported
in various studies are shown in Table 6.
Table 6. Barium content in USA surface waters
------------------------------------------------------------------------
Barium Concentration (µg/litre)
Source Range Mean Reference
------------------------------------------------------------------------
Fresh water 7-15 000 50 Schroeder (1970)
River water 9-150 57 (54 median) Durum (1960)
Surface water 2-340 43 Kopp (1969);
Kopp & Kroner (1970)
Surface water 10-12 000 50 Bradford (1971)
------------------------------------------------------------------------
5.1.2.2 Drinking-water
Municipal water supplies depend upon the quality of
surface waters and ground waters, and these, in turn,
depend upon local geochemical influences. Studies of the
water quality in cities in the USA have revealed levels of
barium ranging from a trace to 10 000 µg/litre (Durfor &
Becker, 1964; Barnett et al., 1969; McCabe et al., 1970;
McCabe, 1974; Calabrese, 1977; AWWA, 1985). Drinking-water
levels of at least 1000 µg barium/litre have been
reported when the barium is present mainly in the form of
insoluble salts (Kojola et al., 1978). Levels of barium in
Canadian water supplies have been reported to range from
5 to 600 µg/litre (Subramanian & Meranger, 1984), and
municipal water levels in Sweden ranging from 1 to
20 µg/litre have been measured (Reeves, 1986).
5.1.2.3 Ocean waters
The concentration of barium in sea water varies
greatly with factors such as latitude, depth, and the
ocean in question. Several studies have shown that the
barium content in the open ocean increases with the depth
of water (Chow & Goldberg, 1960; Bolter et al., 1964;
Turekian, 1965; Chow & Patterson, 1966; Anderson & Hume,
1968). A Geosecs III study of the southwest Pacific by
Bacon & Edmond (1972) found a barium profile of
4.9 µg/litre in surface waters to 19.5 µg/litre in deep
waters. Later studies by Chow (1976) and Chow et al.
(1978) corroborated these values. The barium concen-
tration in the northeast Pacific ranges from 8.5 to
32 µg/litre (Wolgemuth & Brocker, 1970). Bernat et al.
(1972) found that barium concentration profiles for the
eastern Pacific Ocean and the Mediterranean Sea ranged
from 5.2 to 25.2 µg/litre and from 10.6 to 12.7 µg/litre,
respectively.
Anderson & Hume (1968) reported concentrations in the
Atlantic Ocean ranging from 0.8 to 37.0 µg/litre in the
equatorial region and from 0.04 to 22.8 µg/litre in the
North Atlantic, with mean values of 6.5 and 7.6 µg/litre,
respectively. In Atlantic Ocean waters off Bermuda, barium
concentrations of 15.9-19.1 µg/litre have been measured
(Chow & Patterson, 1966).
5.1.3. Soil and sediment
The presence of barium in soils has received attention
since it was first documented in the muds of the River
Nile (Knop, 1874) and the soils of the USA (Crawford,
1908). In the earth's crust the barium concentration is
400 to 500 mg/kg (Wells, 1937; Schroeder, 1970; Davis,
1972). Later works have verified the levels found in the
early studies. The background level of barium in soils is
considered to range from 100 to 3000 mg/kg, the average
abundance being 500 mg/kg (Brooks, 1978).
The concentrations of barium in sediments of the Iowa
river are 450 to 3000 mg/kg (Tsai et al., 1978), sugges-
ting that barium in the water is removed by precipitation
and silting and may possibly affect the ecology of benthic
organisms.
5.1.4. Food
A review of the early literature summarizes the quan-
tity of barium present in many plants (Robinson et al.,
1950). Barium has been found in grain stalks, forage
plants, red ash leaves, and in the black walnut, hickory,
and Brazil nut trees. With the exception of the Brazil nut
tree, those parts of the plants that accumulate barium are
seldom eaten by man. Various studies document the concen-
trations of barium in Brazil nuts ranging from 1500-3000
mg/kg (Robinson et al., 1950; Smith, 1971a). Barium is
also present in wheat, although most is concentrated in
the stalks and leaves rather than in the grain (Smith,
1971b). Tomatoes and soybeans also concentrate soil
barium, the bioconcentration factor ranging from 2 to 20
(Robinson et al., 1950). Gormican (1970) determined the
barium content of a large number of food items, including
dairy products, cereals, fruits and vegetables, and meats
(Table 7). In the beverages group, tea and cocoa had the
highest barium content (2.7 and 1.2 mg/100 g, respect-
ively) on a dry-weight basis. Among breads, cereal prod-
ucts, and cracker products, bran flakes (0.39 mg/100 g)
and enriched instant cream of wheat (0.2 mg/100 g) had the
highest levels. Eggs were found to have 0.76 mg/100 g, and
swiss cheese 0.22 mg/100 g. Fruits and fruit juice had low
barium levels, the highest values being in raw, unpeeled
apples (0.075 mg/100 g). These levels are similar to those
found in grapes (<0.05 mg/100 g) and cooked prunes (0.064
mg/100 g). All meats showed concentrations of 0.04 mg per
100 g or less. Vegetables had relatively low barium
levels, with the exception of beets (0.26 mg/100 g) and
sweet potatoes (0.22 mg/100 g). Among nuts, pecans had the
highest barium content (0.67 mg/100 g).
5.1.5. Feed
Barium generally does not accumulate in common plants
in sufficient quantities to be toxic to animals. However,
Robinson et al. (1950) suggested that the large quantities
of barium (as high as 1260 mg/kg) accumulating in legumes,
alfalfa, and soybeans grown in soils containing high
exchangeable barium content may cause problems in domestic
cattle.
Table 7. Barium contents of some common foodsa
------------------------------------------------------------------
Food Barium content
(mg/100 g)
------------------------------------------------------------------
Beverages and dietary concentrates
Chocolate syrup 0.17
Coffee
Instant, dry 0.36
Ground, dry 0.32
Beverage, brewed <0.008
Cocoa, dry 1.2
Meritene, plain flavour, dry 0.11
Sustagen, imitation vanilla flavour 0.056
Tea, orange pekoe
Bag, dry 2.7
Beverage, steeped <0.004
Breads, cereal products, crackers, and pastas
Bread
Rye 0.062
White 0.051
Whole wheat 0.11
Bran flakes, 40% 0.39
Cheerios (cereal) 0.13
Corn flakes (cereal) 0.04
Crackers
Graham 0.11
Saltines 0.04
Egg noodles, uncooked 0.16
Macaroni, uncooked 0.11
Oatmeal, rolled oats (quick), uncooked 0.11
Puffed Rice <0.04
Quick Cream of Wheat (cereal)
Enriched, uncooked 0.2
Regular, uncooked 0.15
Rice Krispies <0.04
Rice, white uncooked <0.04
Shredded Wheat 0.22
Wheaties (cereal) 0.14
Spaghetti, uncooked 0.11
Cheese
American 0.12
Cottage, creamed <0.04
Swiss 0.22
Eggs
Whole 0.76
White <0.01
Yolk 0.058
Milk
Nonfat solids <0.08
Fluid
Whole <0.01
Skim <0.01
Buttermilk <0.01
Ice cream, vanilla <0.01
Sherbet, orange <0.01
Fruits and fruit juices
Apple
Raw, unpeeled 0.075
Juice, canned <0.002
Sauce, canned, drained <0.01
Apricots, canned, drained <0.01
Banana, ripe <0.01
Blueberries, waterpack, drained 0.014
Table 7. (cont.)
------------------------------------------------------------------
Food Barium content
(mg/100 g)
------------------------------------------------------------------
Cantaloupe <0.01
Cherries, Royal Anne, canned, drained 0.029
Grapes
Fresh, with peel <0.05
Juice, canned 0.023
Grapefruit
Juice, canned <0.008
Sections
Fresh, skinless <0.01
Canned, drained <0.01
Orange
Juice, frozen, reconstituted <0.008
Sections, skinless <0.008
Pineapple
Crushed, canned, drained 0.014
Juice, canned 0.008
Peach, cling, canned, drained <0.01
Pear, canned, drained 0.047
Prunes
Cooked 0.064
Juice 0.014
Watermelon 0.022
Meat, poultry, fish, and shellfish
Beef, fresh, uncooked
Flank, round, rump, sirloin, or tenderloin <0.02
Ground <0.02
Liver <0.04
Lamb, fresh, uncooked
Chop <0.02
Leg <0.02
Luncheon meat, big bologna <0.02
Pork, fresh, uncooked
Bacon <0.04
Ham <0.02
Liver <0.04
Loin <0.02
Veal, fresh, uncooked
Round or steak <0.02
Poultry, uncooked
Chicken, roaster
Dark meat <0.02
White meat <0.02
Turkey, roaster
Dark meat <0.02
White meat <0.02
Fish and shellfish
Crab, haddock, salmon, sockeye, sole, or tuna <0.02
Shrimp <0.02
Table 7. (cont.)
------------------------------------------------------------------
Food Barium content
(mg/100 g)
------------------------------------------------------------------
Nuts
Peanuts
Butter <0.04
Salted, blanched 0.21
Pecans 0.67
Walnuts 0.072
Sugars and flours
Sugar
Brown <0.04
Powdered <0.04
White <0.04
Flour, bleached, enriched 0.072
Vegetables
Asparagus spears, frozen, uncooked <0.02
Beans
Baked with pork <0.02
Green, frozen, uncooked 0.16
Lima, baby, frozen, uncooked 0.031
Wax, canned, salt-free, drained 0.11
Beets, canned, salt-free, drained 0.26
Broccoli, frozen, uncooked <0.02
Brussels sprouts, frozen, uncooked <0.02
Cabbage, uncooked <0.02
Carrots, uncooked 0.052
Cauliflower, frozen, uncooked <0.02
Celery, fresh <0.02
Corn, whole kernel, canned, salt-free, drained <0.02
Cucumber <0.02
Lettuce <0.02
Mushrooms, stems and pieces, canned <0.02
Onions, fresh, mature 0.053
Peas, canned, salt-free, drained <0.02
Potato
Fresh, uncooked <0.02
Instant, uncooked 0.056
Pumpkin, canned 0.053
Spinach, frozen, uncooked 0.04
Squash, frozen, cooked 0.083
Sweet potatoes, canned 0.22
Tomato
Fresh <0.02
Juice, canned, salt-free <0.008
------------------------------------------------------------------
a Source: Gormican (1970)
5.1.6. Other products
McHargue (1913) reported that the barium content of
dry tobacco leaves was in the range 88-293 mg/kg. Later
measurements yielded 24-170 mg/kg, with an average value
of 105 mg/kg (Voss & Nicol, 1960). Most of this barium is
likely to remain in the ash during burning. The concen-
trations of barium in tobacco smoke have not been
reported.
Bowen (1956) reported the following levels of barium
in plants: 15 mg/kg dry weight in plankton; 31 mg/kg dry
weight in brown algae; 18 mg/kg dry weight in ferns; and
14 mg/kg dry weight in angiosperms.
5.1.7. Nuclear fallout
The principal potential source of radioactive isotopes
of barium is nuclear weapons testing. Atmospheric testing
suspends radioactive dusts in the upper troposphere where,
depending on atmospheric conditions, dusts are carried
around the world several times.
The lightest dust particles reach the stratosphere.
Several years are required for the bulk of this radioac-
tive material to be deposited on the ground. Since 1952,
when tests began on nuclear weapons with high explosive
yields, fall-out from the stratosphere has been more or
less continuous. Most of this nuclear fall-out occurs in
the temperate and polar regions of the earth. The total
radiation from nuclear testing has added 10-15% to the
naturally occurring radiation throughout the world.
Because 140Ba and 143Ba are radioactive by-products
of the thermal nuclear fission of 235U, their concen-
tration in the environment increases after the detonation
of a nuclear device in the atmosphere. After a single
atmospheric nuclear detonation in China, Gudiksen et al.
(1965) detected 140Ba at an altitude of 10 670 m at
levels of 177-530 x 106 atoms/m3 over north-western USA.
This far exceeds the levels normally present in the atmos-
phere.
Radioactive particles are normally cleared from the
atmosphere by rain and snow. Cooper et al. (1970) moni-
tored 140Ba concentrations in rain and snow in 772
samples collected between 1958 and 1969 and found that
debris containing 140Ba was deposited after the atmos-
pheric testing of nuclear weapons in China. Evans et al.
(1973) reported the atmospheric level of barium, 4 days
after a test in China, to be 4.5 pCi/m3, which is ap-
proximately 30 times higher than the normal background
level (0.14 pCi/m3).
5.2. General population exposure
5.2.1. Environmental sources, food, drinking-water, and air
The most important route of exposure to barium appears
to be ingestion of barium through drinking-water and food.
Particles containing barium may be inhaled into the lung,
but little is known regarding the absorption of barium by
this route.
In studies of dietary intake in two hospitals, 300
schools, and individual subjects in the USA, Underwood
(1977) determined that the average intake of barium ranged
from 300 to 1700 µg/day. An earlier study had found that
the barium intake from diets served to adults in American
hospitals in the summer was not more than 303 µg/day and
in winter not more than 592 µg/day (Gormican, 1970).
Tipton et al. (1966, 1969) studied five adult subjects
whose self-selected diets were examined for varying
lengths of time. Barium concentrations were measured in
all foods consumed for 30 days by two subjects, 70 days by
one other, and 347 days by the remaining two subjects. In-
takes of barium showed large variations and ranged from
650 to 1770 µg/day.
In the United Kingdom, the total intake of barium from
the diet was estimated by Hamilton & Minski (1972) to be
approximately 603 µg/day and by the ICRP (1959) to be
900 µg/day. Schroeder et al. (1972) estimated that the
mean daily intake of barium in food is 1.24 mg, in water
0.086 mg, and in air 0.001 mg, giving a total of 1.33
mg/day. The ICRP (1974) reported the dietary intake of
barium to be 0.75 mg/day, including both food and fluids.
The contribution from drinking-water was estimated to be
about 0.08 mg/day, which leaves 0.67 mg/day from other
dietary sources. When Murphy et al. (1971) analysed school
lunches from 300 schools in 19 states in the USA, the
barium content ranged from 0.09 to 0.43 mg/lunch, with a
mean of 0.17 mg. Milk, potatoes, and flour have been
suggested to be the major sources of barium in diets in
the USA (Calabrese et al., 1985).
The barium content in drinking-water seems to depend
on regional geochemical conditions. In a study of the
water supplies of the 100 largest cities in the USA, a
median value of 43 µg/litre was reported; 94% of all de-
terminations were <100 µg/litre (Durfor & Becker, 1964).
This represents an average intake of <200 µg/day.
More recent studies by Letkiewicz et al. (1984) indi-
cated that approximately 214 million people in the USA
using public water supplies are exposed to barium levels
ranging from 1 to 20 µg/litre. In certain regions of the
USA, however, barium may reach 10 000 µg/litre. In these
areas, the average intake could be as high as 20 000 µg/day
(Calabrese, 1977).
Drinking-water appears to be an important source of
human exposure to barium. The digestive system is
extremely permeable to soluble barium, allowing rapid
absorption into (and removal from) the bloodstream
(Castagnou et al., 1957). This is important when consider-
ing uptake of barium from drinking-water, since a large
percentage of barium in water is in the soluble form.
Due to the paucity of information on the ambient
levels of barium in the air, it is difficult to estimate
the intake from this source. As described earlier
(section 5.1.3), the levels of barium in air rarely exceed
0.05 µg/m3 (Tabor & Warren, 1958). This value can be
used to estimate daily barium intake via the lungs.
Assuming that the average lung ventilation (LV) rate for
newborn babies, male adults undergoing light activity, and
male adults undergoing heavy activity is 0.5, 20, and 43
litres/min, respectively (ICRP, 1975), the intake via
inhalation would range from 0.04 to 3.1 µg/day. Other age
groups and females are included in this range. Earlier,
the ICRP (1974) reported that intake of barium through
inhalation ranges from 0.09 to 26 µg/day.
Because the chemical properties of the barium entering
the lung are not known, it is difficult to ascertain the
amount retained. Retention in adult animals is approxi-
mately 20% (Cuddihy & Ozog, 1973), which suggests that
insoluble barium accumulates and is slowly removed.
Another source of exposure is radioactive isotopes of
barium from nuclear fall-out after the explosion of nu-
clear weapons. 140Ba and 143Ba are the main radioactive
products of the thermal-nuclear fission of 235U, and
their half-lives are 12.8 days and 12 seconds, respect-
ively (CRC, 1988). Therefore, the potential for exposure
depends on its presence at ground level (air, soil, water
contamination), as well as on the time elapsed since
explosion. In terms of biochemical and pharmacological
effects, the exposure to barium from this source is not
significant. However, because exposure to radioactive
isotopes results in bone deposition, retention may be a
concern.
5.2.2. Other sources
Barium sulfate is the major barium compound used med-
icinally. This very poorly soluble compound is employed
as an opaque contrast medium for roentgenographic studies
of the gastrointestinal tract. There is limited evidence
that the ingestion of the compound may cause deleterious
biological effects. However, one study suggested that
radiation-induced gastrointestinal effects may be reduced
by the ingestion of barium sulfate (Conard & Scott,
1961).
5.2.3. Subpopulations at special risk
Patients receiving drugs such as acetazolamide (glau-
coma treatment; diuretic agent) or thiazide diuretics have
increased urinary potassium excretion (¾60% and 400%,
respectively) and would be at higher risk of potassium
deficiency due to barium toxicity. Patients subject to X-
ray studies of the gastrointestinal tract have shown
occasional increases in serum protein-bound iodine (PBI)
(Wallach, 1978).
5.3. Occupational exposure during manufacture, formulation, or use
The US National Institute for Occupational Safety and
Health (NIOSH) has investigated occupational exposures to
barium in a variety of industrial operations in response
to requests submitted by employers and workers for health
hazard evaluations and technical assistance. Table 8
summarizes the exposures and adverse health effects found
in these investigations.
Occupational exposure to soluble barium compounds has
been reported for workers exposed to welding fumes (Dare
et al., 1984). The wiring used in arc welding processes
was shown to contain 20-40% soluble barium compounds, and
fumes produced during these processes contained 25%
barium. Urine analysis of workers revealed barium concen-
trations ranging from 31 to 234 µg/litre after 3 h of
exposure. Follow-up samples taken approximately 12 h
after exposure contained levels ranging from 20 to
110 µg/litre. The level in the urine of controls ranged
from 1.8 to 4.7 µg/litre. No air samples were collected,
but NIOSH (1978) reported that welders using the same wire
were exposed to 2200 to 6200 µg soluble barium per m3.
Table 8. Occupational exposure to barium in various industries
---------------------------------------------------------------------------------------------------------
Concentration Number of
Industry Compound range, mg/m3 samplesa Health effects Comments Reference
---------------------------------------------------------------------------------------------------------
Magnetic plastic BaFe12O19 < 0.08-2.2 22 none reported NIOSH
Ba (soluble) < 0.01-0.27 (1976)
Steel, arc welding Ba (soluble) 2.2-6.1 5 none reported see Dare NIOSH
et al. (1984) (1978)
Vinyl floor Ba (soluble) < 0.4 9 none reported NIOSH
(1979)
Metal alloys Ba (soluble) 0.02-1.7 12 musculoskeletal, exposures to NIOSH
gastrointestinal, lead, zirconim, (1980)
skin, respiratory UV, visible,
and IR radiation
Mineral ores Ba (soluble) 0.01-1.92 27 hypertension exposure to NIOSH
lead, zinc (1982)
Petroleum refinery, Ba (soluble) 0.03-0.05 (mean) NR none NIOSH
TCCU turn-around 0.015-2.50 (max) (1984)
Auto parts Ba (soluble) 0.002-0.68 68 none reported NIOSH
(1985)
Aluminium foundry Ba (soluble) 0.001-0.037 13 eye, nasal exposures to NIOSH
irritation silica, (1987a,
formaldehyde b,c)
Fire extinguisher BaO 0.08-1.7 4 none reported ZnO fumes NIOSH
(1987a,
b,c)
---------------------------------------------------------------------------------------------------------
a NR = not reported.
6. KINETICS AND METABOLISM
6.1. Absorption
Barium enters the body primarily through the inha-
lation and ingestion processes. The degree of absorption
of barium from the lungs and gastrointestinal tract varies
according to the animal species, the solubility of the
compound, gastrointestinal tract content, and age. Studies
with soluble barium salts have shown that these compounds
are readily absorbed (Cuddihy & Griffith, 1972; Cuddihy &
Ozog, 1973; Cuddihy et al., 1974; McCauley & Washington,
1983). Recent studies have indicated that poorly soluble
barium compounds may also be absorbed (McCauley &
Washington, 1983; Clavel et al., 1987).
6.1.1. Inhalation route
6.1.1.1 Laboratory animals
Cuddihy & Ozog (1973) studied the absorption of
labelled barium chloride (133BaCl2) solutions in
1-year-old Syrian hamsters. Absorption into the general
circulation of solutions deposited on nasal membranes was
compared with gastrointestinal tract absorption. During
the first 4 h after administration, barium absorption from
the nasal passages was approximately 61%, compared with
11% gastric absorption. The authors concluded that the
nasopharynx is a major absorption site for inhaled aero-
sols of soluble barium, especially for readily soluble
aerosols having mass median aerodynamic diameters >5 µm.
Gutwein et al. (1974) observed that on day 24 after
the exposure of male Sprague-Dawley rats (275 g) by nasal
intubation to combustion products from diesel fuel con-
taining a barium-based additive in solution (vehicle not
specified), more than 85% of the administered dose was
found in the bone, indicating significant absorption in
the respiratory tract.
The principle mechanism for removing insoluble par-
ticles from the lung is transport by the ciliated epi-
thelium and its associated mucosal lining, followed by
swallowing. Spritzer & Watson (1964) evaluated the ciliary
clearance of poorly soluble barium sulfate and found that
52% of the compound introduced into rat lung was removed
by ciliary action. The other 48% was removed by ``lung-to-
blood transfer mechanisms'' (probably macrophage ac-
tivity), which led to disposal of the sulfate particles.
These mechanisms suggest that solubilization of the barium
sulfate occurs in vivo.
Clearance from the lungs of various forms of barium
after inhalation exposure of rats and beagle dogs was
studied by Einbrodt et al. (1972) and Cuddihy et al.
(1974). Einbrodt et al. (1972) exposed rats to barium sul-
fate (40 mg/m3) for 2 months, and this was followed by a
4-week observation interval. Animals were killed at 2-week
intervals. After 2 weeks of exposure, the barium content
in the lungs was high but decreased rapidly over the next
4 weeks of exposure and then increased again during the
observation period. Barium accumulation in bone tissue in-
creased initially, but with continued exposure decreased.
There was no absorption into lymph tissue.
In beagle dogs exposed to various barium compounds
(chloride, sulfate, heat-treated sulfate, or barium in
fused montmorillonite clay), barium was cleared from the
lungs at a rate of proportional to its solubility (Cuddihy
et al., 1974). The longest retention time in the lungs
was for barium adsorbed to clay; more than 500 days after
exposure, 10% of the initial body burden was still in the
lungs and skeleton (Cuddihy et al., 1974). For barium sul-
fate, there was a long-term slow clearance, with virtually
no change in lung tissue levels of barium from 8 to 16
days after exposure. The clearance rate depended on the
specific surface area of the inhaled particles. In Syrian
hamsters, barium sulfate was found to be cleared from the
lungs with a biological half-life of 8-9 days (Morrow et
al., 1964). This indicated some dispersion of barium sul-
fate in body fluids, possibly in a colloidal form.
6.1.1.2 Humans
There are no quantitative data on the deposition and
absorption of barium compounds through inhalation in
humans.
6.1.2. Oral route
6.1.2.1 Laboratory animals
The absorption of ingested barium depends on factors
such as the presence of food in the intestine, the sulfate
content in the food, the age of the animal, and the
location of the barium in the gastrointestinal tract.
Absorption of barium from the gastrointestinal tract has
been studied in rats (Taylor et al., 1962). Labelled
barium chloride was administered by intragastric intu-
bation to groups of 5-10 brown-hooded female rats (14 days
to 70 weeks old). Absorption was estimated as the radio-
activity 7 h after exposure in the carcass plus urine
minus gastrointestinal tract in relation to the dose. The
absorption decreased with age, from approximately 85% of
the administered dose at 14-18 days of age, to 63% at 22
days, to approximately 7% after 6-8 or 60-70 weeks of age.
Deprivation of food before administration (18 h) markedly
increased the absorption of barium, from approximately 7%
in fed animals to 20% in fasted animals 6-8 or 60-70 weeks
old. Administration of the compound in cow's milk did not
affect absorption.
In studies by Cuddihy & Ozog (1973), groups of 5-10
Syrian hamsters (1 year old) were administered labelled
barium chloride by intragastric intubation. The absorption
estimate was based on carcass radioactivity 4 h after
exposure in relation to carcass radioactivity immediately
after intravenous administration (100%). Results show that
following a 12 h fasting, a combination of gastric (32%)
and intestinal (11%) absorption was found during the first
4 h after administration. McCauley & Washington (1983)
examined the absorption of specific barium salt anions in
male Sprague-Dawley rats, administering radiolabelled
barium chloride, sulfate, or carbonate to fasted (24 h)
and non-fasted rats by gastric intubation. Animals were
sacrificed from 2 to 480 min after administration and
blood concentrations were measured. In general, barium
blood concentrations were higher in fasted animals and
reached a peak 15 min after dosing, whereas non-fasted
animals had lower barium blood concentrations and peaked
60 min after dosing. The peak blood concentrations of the
carbonate and sulfate salts were 45% and 85%, respect-
ively, of that of the chloride.
Orally administered barium chloride (133BaCl2) was
found to be rapidly absorbed from the gastrointestinal
tract of male weanling rats, the peak concentration in the
bloodstream and soft tissues occurring 30 min after
dosing. Total uptake of barium increased with increasing
dosage, but, there appeared to be a saturation point for
oral absorption (Clary & Tardiff, 1974).
6.1.2.2 Humans
There are few data on the absorption of barium from
the human gastrointestinal tract. Tipton et al. (1969)
reported that two males fed controlled diets for 80 weeks
absorbed between 2 and 6% of the barium content in their
diet, based on urinary elimination. Elimination via the
gastrointestinal tract was not given. Recent studies by
Clavel et al. (1987) have shown that insoluble barium
salts commonly used during radiological investigations are
absorbed by the intestine and are excreted in the urine.
6.1.3. Parenteral administration
The in vivo solubility of four barium compounds (the
chloride, sulfate, and carbonate salts and fused clay
forms of previously aerosolized material resuspended in
distilled water) was studied in rats after intramuscular
injection (Thomas et al., 1973). The chloride and carbon-
ate salts were found to be equally soluble in the soft
tissues and were absorbed from the injection site very
rapidly.
6.2. Distribution
6.2.1. Levels in tissues of experimental animals
Studies in rats and mice have shown that barium is
incorporated into the bone matrix in much the same way as
calcium (Bauer et al., 1956; Taylor et al., 1962; Bligh &
Taylor, 1963; Domanski et al., 1969; Dencker et al.,
1976). This means that the major part of the body burden
will be in the skeleton. Soft tissues generally have low
concentrations of barium, an exception being pig-mented
areas of the eye (Sowden & Pirie, 1958). Barium is
incorporated into the bone, especially in young animals
that are still growing. In mature animals, 60-80% of the
barium initially deposited is removed from the femur
during the first 14 days after exposure (Bligh & Taylor,
1963). The uptake of barium into bone decreases with the
age of the animal. No detrimental effects on the
integrity of the bone have been seen.
Dencker et al. (1976) injected labelled barium chlor-
ide (133BaCl2) intravenously in pigmented and albino
mice (63 µg barium/kg body weight). Autoradiography
revealed that uptake was rapid and retention times were
longest in calcified tissues, cartilage, and melanin-con-
taining tissues. In other tissues, the radioactivity
rapidly disappeared. In the mouse fetus, the authors found
that barium is mainly taken up by the skeleton, especially
in the growth zones. Except for the eye, soft tissues had
a low uptake.
Barium deposition appears to occur preferentially in
the most active areas of bone growth (Bligh & Taylor,
1963), although research indicates that the preferential
uptake of barium is localized primarily in the periosteal,
endosteal, and trabular surfaces of the bone (Ellsasser et
al., 1969).
McCauley & Washington (1983) found that 24 h after an
intragastric dose of labelled barium chloride to rats, the
highest concentration was in the heart, followed by the
eye, kidney, liver, and blood. Clary & Tardiff (1974)
found that labelled barium chloride (133BaCl2) admin-
istered orally to weanling male rats entered the blood-
stream and soft tissues, peak concentrations occurring 30
min after administration. Uptake was observed in the sub-
maxillary salivary gland, adrenal gland, kidney, gastric
mucosa, and blood vessels. The deposition of barium in
hard tissues was detected after 2 h. In a more recent
study, Tardiff et al. (1980) administered barium chloride
(10, 50, or 250 mg barium/litre of drinking-water) to
young adult rats of both sexes for 4, 8, or 13 weeks.
Barium deposition in liver, skeletal muscle, heart, and
bone was dose-dependent but not related to the length of
exposure. The highest concentration of barium was observed
in the bones. In the soft tissues, concentrations were <1
mg/kg even after 13 weeks of exposure to 250 mg barium per
litre. In the bone, the average concentration was 226
mg/kg.
In dogs, inhalation of radioactive barium (the chlor-
ide or sulfate salts) resulted in significant (when com-
pared to other tissues) radioactive deposition in the bone
(chloride) and in the lung (sulfate) (Cuddihy & Griffith,
1972). Rats that inhaled 40 mg barium sulfate over a 2-
month period initially accumulated barium in their bones
(jaw and femur). However, the rate of deposition decreased
with continued exposure (Einbrodt et al., 1972). Simi-
larly, 2 weeks after the initiation of exposure, lung
barium content was high, whereas it decreased over the
next 4 weeks but increased again during 4 weeks in the
post-inhalation period. No evidence for the transport of
barium in lymph was noted by these authors.
6.2.2. Levels in human tissue
It has been estimated that the ``Standard Man'' (a
term borrowed from radiation dosimetry) of 70 kg contains
approximately 22 mg of barium (Tipton et al., 1963). A
major part of the element is concentrated in the bone
(nearly 91%), the remainder being in soft tissues such as
the aorta, brain, heart, kidney, spleen, pancreas, and
lung (Schroeder, 1970). In human beings there is no
increase of total barium with age, except in the aorta and
lung (Venugopal & Luckey, 1978). Sowden & Stitch (1957)
reported that uptake of barium into bone did not increase
with age (Table 9). Bligh & Taylor (1963) and Ellsasser et
al. (1969) found that barium deposition in the bone oc-
curred preferentially in the active sites of bone growth.
Table 9. Concentration of barium in human bone (µg/g) according to agea
-------------------------------------------------------------------------
0-3 months 1-13 years 19-33 years 33-74 years
-------------------------------------------------------------------------
No. of subjects 7 9 9 10
Concentration range 1.9-13.0 2.1-21.0 4.3-7.9 3.7-17.3
Mean 7.0 7.7 5.1 8.5
Standard deviation ± 4.0 ± 7.0 ± 0.12 ± 4.0
-------------------------------------------------------------------------
a Source: Bligh & Taylor (1963).
In the USA, the highest concentration in soft tissues
was found in the large intestine, muscle, and lung. The
median values were approximately 0.15 mg/kg wet weight
(Tipton & Cook, 1963; Tipton et al., 1965; Schroeder e