Concise International Chemical Assessment Document 33
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S E L E C T I O N O F H I G H Q U A L I T Y
N A T I O N A L / R E G I O N A L
A S S E S S M E N T D O C U M E N T ( S )
CICAD PREPARATION FLOW CHART
F I R S T D R A F T
P R E P A R E D
R E V I E W B Y I P C S C O N T A C T P O I N T S /
S P E C I A L I Z E D E X P E R T S
F I N A L R E V I E W B O A R D
2
F I N A L D R A F T
3
E D I T I N G
A P P R O V A L B Y D I R E C T O R , I P C S
P U B L I C A T I O N
S E L E C T I O N O F P R I O R I T Y C H E M I C A L
1 Taking into account the comments from reviewers.
2 The second draft of documents is submitted to the Final Review Board together with the reviewers’ comments.
3 Includes any revisions requested by the Final Review Board.
R E V I E W O F C O M M E N T S ( P R O D U C E R / R E S P O N S I B L E O F F I C E R),
P R E P A R A T I O N
O F S E C O N D D R A F T
1
P R I M A R Y R E V I E W B Y I P C S
(
REVISIONS AS NECESSARY
)
Barium and barium compounds
3
A consultative group may be necessary to advise
on specific issues in the risk assessment document.
The CICAD Final Review Board has several
important functions:
–
to ensure that each CICAD has been subjected to
an appropriate and thorough peer review;
–
to verify that the peer reviewers’ comments have
been addressed appropriately;
–
to provide guidance to those responsible for the
preparation of CICADs on how to resolve any
remaining issues if, in the opinion of the Board, the
author has not adequately addressed all comments
of the reviewers; and
–
to approve CICADs as international assessments.
Board members serve in their personal capacity, not as
representatives of any organization, government, or
industry. They are selected because of their expertise in
human and environmental toxicology or because of their
experience in the regulation of chemicals. Boards are
chosen according to the range of expertise required for a
meeting and the need for balanced geographic
representation.
Board members, authors, reviewers, consultants,
and advisers who participate in the preparation of a
CICAD are required to declare any real or potential
conflict of interest in relation to the subjects under
discussion at any stage of the process. Representatives
of nongovernmental organizations may be invited to
observe the proceedings of the Final Review Board.
Observers may participate in Board discussions only at
the invitation of the Chairperson, and they may not
participate in the final decision-making process.
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1. EXECUTIVE SUMMARY
This CICAD on barium and barium compounds
was prepared by the US Environmental Protection
Agency (EPA) and the United Kingdom’s Health and
Safety Executive (HSE) to update the WHO Environ-
mental Health Criteria monograph on barium (IPCS,
1990). The source documents were the US EPA’s
Toxicological review of barium and compounds (US
EPA, 1998), the Agency for Toxic Substances and
Disease Registry’s Toxicological profile for barium
(ATSDR, 1992), and the HSE’s Barium sulphate risk
assessment document, which concentrates on occupa-
tional exposure (Ball et al., 1997). Current (1998) literature
searches for toxicological data were used in the
preparation of the US EPA (1998) review. Updated
literature searches of on-line databases were conducted
in January 1999 to identify any references containing
toxicological or ecological information on barium that
were published subsequent to those incorporated in the
above-listed source documents. Data on barium sulfate
identified as of September 1997 were covered in the HSE
document. A further literature search was performed up
to April 1999 to identify any extra information published
since this review was completed. Information on the
nature of the peer review and the availability of the
source documents is presented in Appendix 1.
Information on the peer review of this CICAD is
presented in Appendix 2. This CICAD was approved as
an international assessment at a meeting of the Final
Review Board, held in Helsinki, Finland, on 26–29 June
2000. Participants at the Final Review Board meeting are
listed in Appendix 3. The International Chemical Safety
Cards for barium (ICSC 1052), barium chlorate (ICSC
0613), barium chloride (ICSC 0614), barium chloride
dihydrate (ICSC 0615), barium oxide (ICSC 0778), barium
peroxide (ICSC 0381), and barium sulfate (ICSC 0827),
produced by the International Programme on Chemical
Safety (IPCS, 1993, 1999a–f), have been reproduced in
this document.
Barium is a dense alkaline earth metal that occurs
in nature as a divalent cation in combination with other
elements. In addition to its natural presence in the
Earth’s crust, and therefore its natural occurrence in
most surface waters, barium is also released to the
environment via industrial emissions. The residence time
of barium in the atmosphere may be up to several days.
Barium sulfate exists as a white orthorhombic
powder or crystals. Barite, the mineral from which barium
sulfate is produced, is a moderately soft crystalline white
opaque to transparent mineral. The most important
impurities are iron(III) oxide, aluminium oxide, silica, and
strontium sulfate.
Barite is used primarily as a constituent in drilling
muds in the oil industry. It is also used as a filler in a
range of industrial coatings, as a dense filler in some
plastics and rubber products, in brake linings, and in
some sealants and adhesives. The use dictates the
particle size to which barite is milled. For example, drilling
muds are ground to an average particle diameter of 44
µm, with a maximum of 30% of particles less than 6 µm in
diameter.
There is no evidence that barium undergoes
biotransformation other than as a divalent cation. The
toxicokinetics of barium ions would be expected to be
the same as the toxicokinetics of soluble barium salts.
Studies in rats using a soluble salt (barium chloride)
have indicated that the absorbed barium ions are dis-
tributed via the blood and deposited primarily in the
skeleton. The principal route of elimination for barium
following oral, inhalation, or intratracheal administration
is in the faeces. Following introduction into the respira-
tory tract, the appearance of barium sulfate in the faeces
represents mucociliary clearance from the lungs and
subsequent ingestion.
In humans, ingestion of high levels of soluble
barium compounds may cause gastroenteritis (vomiting,
diarrhoea, abdominal pain), hypopotassaemia, hyper-
tension, cardiac arrhythmias, and skeletal muscle
paralysis. Insoluble barium sulfate has been extensively
used at large doses (450 g) as an oral radiocontrast
medium, and no adverse systemic effects have been
reported. No experimental data are available on barium
sulfate; however, due to the limited absorption of barium
sulfate from the gastrointestinal tract or skin, it is
unlikely that any significant systemic effects would
occur.
The acute oral toxicity of barium compounds in
experimental animals is slight to moderate. Intravenous
infusion of barium chloride results in increased blood
pressure and cardiac arrhythmias.
Barium hydroxide is strongly alkaline and therefore
corrosive. Barium nitrate caused mild skin irritation and
severe eye irritation in rabbits. The lack of reports of skin
or eye irritation in humans, despite its widespread use,
suggests that barium sulfate, often used as a contrast
medium, is not a strong irritant. Useful information on
the sensitization potential of barium compounds was not
identified.