Toxicological profile for barium and barium compounds

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3.  HEALTH EFFECTS 

sites) based on the results of studies where doses were higher or were administered in different species.  

Figure 3-2 shows a conceptualized representation of a PBPK model. 

If PBPK models for barium exist, the overall results and individual models are discussed in this section in 

terms of their use in risk assessment, tissue dosimetry, and dose, route, and species extrapolations. 

No information on available PBPK models for barium has been identified. 

3.5 

MECHANISMS OF ACTION  

3.5.1 

Pharmacokinetic Mechanisms 

No studies were located for animals or humans that describe observed mechanisms for barium absorption 

across the skin, lung, or gut or barium distribution, metabolism, or excretion. 

3.5.2 

Mechanisms of Toxicity 

The mechanism of barium toxicity has not been fully elucidated.  Presumably, high-dose exposure to 

barium consistently results in a number of effects including ventricular tachycardia, hypertension and/or 

hypotension, and muscle weakness and paralysis (Deng et al. 1991; Diengott et al. 1964; Downs et al. 

1995; Gould et al. 1973; Jha et al. 1993; Koch et al. 2003; Talwar and Sharma 1979; Wetherill et al. 

1981).  There is strong evidence that many of these effects result from increases in intracellular potassium 

levels.  Barium is a competitive potassium channel antagonist that blocks the passive efflux of 

intracellular potassium, resulting in a shift of potassium from extracellular to intracellular compartments 

(Roza and Berman 1971).  The intracellular translocation of potassium results in a decreased resting 

membrane potential, making the muscle fibers electrically unexcitable and causing paralysis (Koch et al. 

2003).  Hypokalemia (serum potassium levels below 3.5 mEq/L) has been reported in a number of 

individuals exposed to high doses of barium (Deng et al. 1991; Diengott et al. 1964; Downs et al. 1995; 

Gould et al. 1973; Jha et al. 1993; Koch et al. 2003; Lewi and Bar-Khayim 1964; Phelan et al. 1984; 

Talwar and Sharma 1979; Wetherill et al. 1981).  Intravenous infusion of potassium often relieves many 

of the symptoms of barium toxicity (Dreisbach and Robertson 1987; Haddad and Winchester 1990; 

Proctor et al. 1988).  However, there is also evidence that some of these effects may be due to barium-

induced neuromuscular blockade and membrane depolarization (Phelan et al. 1984; Thomas et al. 1998). 

Two investigators (Phelan et al. 1984; Thomas et al. 1998) have shown an apparent direct relationship  

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3.  HEALTH EFFECTS 

67 

BARIUM AND BARIUM COMPOUNDS 

Figure 3-2.  Conceptual Representation of a Physiologically Based 

Pharmacokinetic (PBPK) Model for a  

Hypothetical Chemical Substance 

I n h a le d   c h e m  ic  a l  

E  x  h a le d   c h e m  ic  a l  

L u n g s  

L iv e r  

F a  t  

S lo  w  ly  

p e rf u  s e d  

t is s u e s  

R ic  h  ly  

p e rf u  s e d  

t is s u e s  

K  id n e y  

S k  in  

V 

E 

N 

O 

U 

S 

B 

L 

O 

O 

D 

A 

R 

T 

E 

R 

I 

A 

L 

B 

L 

O 

O 

D 

V 

m a  x  

K 

m 

I n g e s t io n  

G I  

T ra  c  t  

F e  c  e  s  

U rin  e

  C  h e m  ic  a ls  

c o n ta c tin g   s k in  

Note:  This is a conceptual representation of a physiologically based pharmacokinetic (PBPK) model for a 

hypothetical chemical substance.  The chemical substance is shown to be absorbed via the skin, by inhalation, or by 

ingestion, metabolized in the liver, and excreted in the urine or by exhalation. 

Source:  adapted from Krishnan and Andersen 1994 

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68 

BARIUM AND BARIUM COMPOUNDS 

3.  HEALTH EFFECTS 

between serum barium levels and the degree of paralysis or muscle weakness in two individuals orally 

exposed to barium. 

3.5.3 

Animal-to-Human Extrapolations 

Most of the available data in humans comes from case reports involving acute oral exposure to 

presumably high doses of barium; the primary effects noted were gastrointestinal distress and effects 

associated with hypokalemia (e.g., ventricular tachycardia, hypo or hypertension, paralysis).  Only one 

human exposure study (Wones et al. 1990) provided reliable information on exposure level; this study did 

not find any significant alterations in blood pressure in subjects exposed to relatively low doses of 

barium.  The available data in laboratory animals suggest that toxicity of ingested barium is similar across 

species.  Studies conducted by the NTP (1994) in rats and mice found similar targets of toxicity; although 

some differences in sensitivity were found between the species.  Following intermediate-duration 

exposure, renal effects were observed at lower doses in rats (115 mg barium/kg/day) than in mice 

(450 mg barium/kg/day).  However, NTP (1994) concluded that rats and mice were equally sensitive to 

the barium-induced renal effects because adverse effect levels when estimated on a per unit surface area 

basis were similar for the two species.  In the absence of contrary data, it is assumed that humans and 

animals would have similar targets of toxicity and equal sensitivity.   

3.6 

TOXICITIES MEDIATED THROUGH THE NEUROENDOCRINE AXIS  

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine 

system because of the ability of these chemicals to mimic or block endogenous hormones.  Chemicals 

with this type of activity are most commonly referred to as endocrine disruptors.  However, appropriate 

terminology to describe such effects remains controversial.  The terminology endocrine disruptors, 

initially used by Thomas and Colborn (1992), was also used in 1996 when Congress mandated the EPA to 

develop a screening program for “...certain substances [which] may have an effect produced by a 

naturally occurring estrogen, or other such endocrine effect[s]...”.  To meet this mandate, EPA convened a 

panel called the Endocrine Disruptors Screening and Testing Advisory Committee (EDSTAC), and in 

1998, the EDSTAC completed its deliberations and made recommendations to EPA concerning endocrine 

disruptors.  In 1999, the National Academy of Sciences released a report that referred to these same types 

of chemicals as hormonally active agents.  The terminology endocrine modulators has also been used to 

convey the fact that effects caused by such chemicals may not necessarily be adverse.  Many scientists 

agree that chemicals with the ability to disrupt or modulate the endocrine system are a potential threat to 

the health of humans, aquatic animals, and wildlife.  However, others think that endocrine-active 

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