Toxicological Review of Barium and Compounds

identified, while in others the thymus was not discernable.  The splenic atrophy was 

characterized by diminution of the hematopoietic elements of red pulp and depletion of 

lymphocyctes in the periarteriolar lymphoid sheath.  

A statistically significant decrease in forelimb grip strength was observed at day 90 in 

female mice in the 4000 ppm treatment group.  According to the authors, this finding may have 

been due to debilitation of the animals.  No significant changes were observed in other 

neurobehavioral endpoints (undifferentiated motor activity, thermal sensitivity judged by a tail 

flick latency test, startle response to acoustic and air-puff stimuli, or hindlimb grip strength or 

hindlimb foot splay).  A LOAEL of 450 mg/kg-day can be identified for decreased survival, 

increased incidences of nephropathy, and splenic and thymic lesions.  A NOAEL of 200 mg/kg-

day can be identified for the absence of these effects. 

4.2.1.2.  NTP (1994) Chronic Mouse Study 

In the chronic mouse study, male and female B6C3F1 mice (60 animals/group/sex) 

received BaCl

2

×2H

2

O in their drinking water at concentrations of 0, 500, 1250, or 2500 ppm for 

103 weeks (males) and 104 weeks (females).  Using weekly water consumption and body weight 

data, the authors estimated the doses of barium were 30, 75, and 160 mg/kg-day for males and 

40, 90, and 200 mg/kg-day for females, respectively.  The animals were fed an NIH-07 mash 

diet.  Barium concentration of the diet was not reported.  At the 15-month interim evaluation, a 

limited number of mice (9, 10, 10, and 10 males and 10, 7, 10, and 6 females from the 0, 500, 

1250, and 2500 ppm treatment groups, respectively) were sacrificed.  Venous blood was 

collected for hematology and clinical chemistry, which included analysis of plasma barium 

concentrations.  A complete necropsy and detailed histopathologic examination was performed 

on all animals.  Organ weights and clinical chemistry data were reported for animals sacrificed at 

15-month interim but not the terminal or moribund sacrifices. 

In the 2500 ppm treatment group the percent survival, 65% for males and 26% for 

females, was significantly reduced when compared to controls.  The effect on survival became 

apparent in females at week 15 and in males at week 65.  Reduced survival rates were attributed 

to chemical-related renal lesions.  Survival was not affected in any other exposure groups.  The 

final mean body weights of males and females in the 2500 ppm treatment group were 8% and 

12% lower, respectively, than those of the corresponding control groups.  Water consumption 

was not affected. 

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At the 15-month interim evaluation, the absolute and relative spleen weights of the 

female mice in the 2500 ppm treatment group were 14% lower than those of the controls.  The 

mean absolute and relative thymus weights of male mice in the 2500 ppm treatment group were 

42% and 38% lower than the control group.  Liver and kidney weights were not affected. 

Hematology data were unremarkable.  Several male mice in the 2500 ppm treatment group had 

elevated levels of BUN, alanine aminotransferase, and creatine kinase.  A number of females in 

all of the exposure groups had elevated levels of BUN.  Barium serum concentrations were 

significantly elevated in all three dose groups of both sexes when compared to controls.  Barium 

serum concentrations increased in a dose-dependent manner with a 140% and 160% increase 

observed in males and females from the 2500 ppm treatment group, respectively. 

Chemical-related nephropathy was observed in 19/60 male and 37/60 female mice in the 

2500 ppm treatment group.  These lesions were predominately qualified as moderate to marked 

corresponding to severity grades of 3 or 4 (see Table 4–1).  Nephropathy was observed in 2/58 

male and 1/60 female mice in the 1250 ppm treatment group.  Two female mice in the 500 ppm 

treatment group and one untreated male also exhibited signs of nephropathy.  The pathology data 

for individual animals were obtained by EPA from NTP (NTP, 2004).  These reports indicate 

that the signs of nephropathy were minimal in the control male and the low dose females 

(severity score = 1).  The lesions found in animals from the intermediate dose group were 

qualified as mild or moderate (severity scores = 2 or 3), and in the high dose group they were 

reported to be mild to severe (severity scores = 2–4).  EPA considered mild to marked lesions to 

be related to barium exposure.  Note that the technical report (NTP, 1994) states the number of 

animals that were microscopically examined for the renal lesions study was approximately 50 for 

the 2-year study and approximately 10 at the 15-month interim sacrifice.  The 2-year data set 

included numerous animals that died or were sacrificed early (some earlier than 15 months); 

therefore, the two data sets were combined for this assessment. 

The cases of chemical-related nephropathy were generally accompanied by aggregates of 

irregularly shaped brown crystals in the renal tubules and interstitium.  The chemical 

composition of the crystals was not determined, but may have contained precipitated barium or 

barium salts (NTP, 1994).  

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Table 4–1.  Incidence and mean severity scores for nephropathic lesions in 

B6C3F1 mice exposed to barium chloride dihydrate in drinking water 

Control

a 

500 ppm

a

 1250 ppm

a 

2500 ppm

a 

Female Mice 

0/60 (0) 

2/60 (1) 

1/60 (2) 

37/60 (3.6 ) 

Male Mice 

1/59 (1) 

0/60 (0) 

2/58 (2.5) 

19/60 (3.6) 

a

 Incidence is expressed as the number of cases in the entire test population (2-year and 15-month 

evaluations); mean severity scores are shown in parentheses (severity data were obtained by EPA 

from NTP). 

Source: NTP, 2004. 

Lymphoid depletion was observed in the spleen, thymus, and lymph nodes of mice from 

the 2500 ppm treatment group, particularly those that died early.  These changes may have been 

secondary effects related to reduced body weight and stress. 

No increase in the incidences of neoplasms was observed in barium-exposed mice.  In 

female mice from the 2500 ppm treatment group, the incidences  of several neoplasms were 

significantly lower (p<0.05) than the controls.  The investigators attributed this finding to the 

marked reduction in survival of the barium-exposed animals.  A LOAEL of 160 mg/kg-day can 

be identified for a statistically significantly increased incidence of chemical-related renal lesions. 

The next lower dose is not identified as the NOAEL because a low level of chemical-related 

nephropathy was also observed in this treatment group.  For this reason, a NOAEL of 30 mg/kg-

day was identified for the absence of chemical-related renal lesions. 

4.2.1.3.  NTP (1994) Subchronic Rat Study 

In the subchronic rat study, male and female F-344/N rats (10 animals/group/sex) 

received drinking water containing 0, 125, 500, 1000, 2000, and 4000 ppm BaCl

2

×2H

2

O for 13 

weeks.  Using weekly water consumption and body weight data, the authors estimated the doses 

of barium were 10, 30, 65, 110, and 200 mg/kg-day for males and 10, 35, 65, 115, and 180 

mg/kg-day for females, respectively.  The animals were fed NIH-07 pellets.  Barium 

concentration of the diet was not reported.  Complete histopathologic examinations were 

performed on all rats in the control group and 4000 ppm treatment group.  Histopathologic 

examinations were also performed on the kidney, liver, spleen, and thymus of all rats in the 2000 

ppm treatment group and on the adrenal gland, heart, and salivary gland of female rats in the 

2000 ppm treatment group.  Organ weights were recorded.  Complete blood counts (CBCs) and 

select clinical chemistry parameters, including barium, sodium, potassium, calcium, and 

phosphorous, were evaluated. 

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