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
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
2
.
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
3
.
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
3
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
2
An IRIS summary for barium and compounds was prepared in 1998 with minor
revisions in 1999. The RfD was revised in 2005.
1
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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