Toxicological Review of Barium and Compounds

ACRONYM LIST

ACGIH 

AIC 

AMAD 

ATSDR 

BMD

BMDL 

BMDS 

BMR 

BUN 

CASRN 

CDC 

CMD 

EKG 

EPA 

ETIC 

FEP 

HDL 

HSDB 

IARC 

IRIS 

LDL 

LOAEL 

NCEA 

NE 

NIH 

NIOSH 

NOAEL 

NRC 

NTIS 

NTP 

PBPK 

RfC 

RfD 

TWA 

UF 

American Conference of Governmental Industrial Hygienists 

Akaike Information Criterion 

Activity median aerodynamic diameter 

Agency for Toxic Substances and Disease Registry 

 Benchmark 

Dose 

Benchmark dose lower 95% bound 

Benchmark dose software 

Benchmark response 

Blood urea nitrogen 

Chemical Abstracts Service Registry Number 

Centers for Disease Control 

Count median diameter 

Electrocardiogram 

U.S. Environmental Protection Agency 

Environmental Teratology Information Center 

Free erythrocyte porphyrin 

High density lipoprotein 

Hazardous Substances Data Bank 

International Agency for Research on Cancer 

Integrated Risk Information System 

Low density lipoprotein 

Lowest-Observed-Adverse-Effect Level 

National Center for Environmental Assessment 

Norepinephrine 

National Institutes of Health 

National Institute for Occupational Safety and Health 

No-Observed-Adverse-Effect Level 

National Research Council 

National Technical Information Service 

National Toxicology Program 

Physiologically Based Pharmacokinetic 

Reference Concentration 

Reference Dose 

Time-weighted average 

Uncertainty/Variability Factor 

x 

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1.  INTRODUCTION

This document presents background information and justification for the Integrated Risk 

Information System (IRIS) Summary of the hazard and dose-response assessment of barium. 

IRIS Summaries may include an oral reference dose (RfD), inhalation reference concentration 

(RfC) and a carcinogenicity assessment

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. 

The RfD and RfC provide quantitative information for noncancer dose-response 

assessments.  The RfD is an estimate of an exposure, designated by duration and route, to the 

human population (including susceptible subgroups) that is likely to be without an appreciable 

risk of adverse health effects over a lifetime.  It is derived from a statistical lower confidence 

limit on the benchmark dose (BMDL), a no-observed-adverse effect level (NOAEL), a lowest-

observed-adverse-effect level (LOAEL), or another suitable point of departure, with 

uncertainty/variability factors applied to reflect limitations of the data used.  The RfD is 

expressed in units of mg/kg-day.  The inhalation RfC is analogous to the oral RfD, but provides a 

continuous inhalation exposure estimate.  The inhalation RfC considers toxic effects for both the 

respiratory system (portal-of-entry) and for effects peripheral to the respiratory system 

(extrarespiratory or systemic effects).  It is generally expressed in units of mg/m

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. 

The carcinogenicity assessment provides information on the carcinogenic hazard 

potential of the substance in question and quantitative estimates of risk from oral and inhalation 

exposures.  The information includes a weight-of-evidence judgment of the likelihood that the 

agent is a human carcinogen and the conditions under which the carcinogenic effects may be 

expressed.  Quantitative risk estimates are presented in three ways to better facilitate their use: 

(1) generally, the slope factor is the result of application of a low-dose extrapolation procedure 

and is presented as the risk per mg/kg-day of oral exposure, (2) the unit risk is the quantitative 

estimate in terms of either risk per µg/L drinking water or risk per µg/m

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 air breathed, and (3) the 

95% lower bound and central estimates on the concentration of the chemical substance in 

drinking water or air that represent cancer risks of 1 in 10,000, 1 in 100,000, or 1 in 1,000,000. 

Development of these hazard identification and dose-response assessments has followed 

the general guidelines for risk assessment as set forth by the National Research Council (1983). 

U.S. Environmental Protection Agency (EPA) guidelines that were used in the development of 

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An IRIS summary for barium and compounds was prepared in 1998 with minor 

revisions in 1999.  The RfD was revised in 2005. 

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this assessment may include the following:  A Review of the Reference Dose and Reference 

Concentration Processes (U.S. EPA, 2002), Science Policy Council Handbook: Peer Review 

(U.S. EPA, 2000a), Science Policy Council Handbook: Risk Characterization (U.S. EPA, 

2000b), Benchmark Dose Technical Guidance Document (U.S. EPA, 2000c), Supplementary 

Guidance for Conducting Health Risk Assessment of Chemical Mixtures (U.S. EPA, 2000d), 

Draft Revised Guidelines for Carcinogen Assessment (U.S. EPA, 1999), Guidelines for 

Neurotoxicity Risk Assessment (U.S. EPA, 1998a), Science Policy Council Handbook: Peer 

Review (U.S. EPA, 1998b), Guidelines for Reproductive Toxicity Risk Assessment (U.S. EPA, 

1996a),  Proposed guidelines for carcinogen risk assessment (U.S. EPA, 1996b), Use of the 

Benchmark Dose Approach in Health Risk Assessment (U.S. EPA, 1995), Interim Policy for 

Particle Size and Limit Concentration Issues in Inhalation Toxicity (U.S. EPA, 1994a),  Methods 

for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry 

(U.S. EPA, 1994b), Guidelines for Developmental Toxicity Risk Assessment (U.S. EPA, 1991), 

Recommendations for and Documentation of Biological Values for Use in Risk Assessment (U.S. 

EPA, 1988), Guidelines for the Health Risk Assessment of Chemical Mixtures (U.S. EPA, 

1986a), and Guidelines for Mutagenicity Risk Assessment (U.S. EPA, 1986b). 

The literature search strategies employed for this compound were based on the Chemical 

Abstracts Service Registry Number (CASRN) and at least one common name.  As a minimum, 

the following data bases were searched:  RTECS, HSDB, TSCATS, CCRIS, GENETOX, EMIC, 

EMICBACK, ETICBACK, TOXLINE, CANCERLINE, MEDLINE, and MEDLINE back files. 

Any pertinent scientific information submitted by the public to the IRIS Submission Desk also 

was considered in the development of this document. 

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