Concise International Chemical Assessment Document 33

Concise International Chemical Assessment Document 33

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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.

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REVISIONS AS NECESSARY

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Barium and barium compounds

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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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Concise International Chemical Assessment Document 33

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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.

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