Concise International Chemical Assessment Document 33
22
Table 2: Toxicity of barium to selected aquatic organisms.
a
Organism
Static/
flow
b
Temperature
(°C)
pH
Hardness
(mg/litre)
Duration
LC
50
/EC
50
(mg/litre)
Reference
Water flea
(Daphnia magna)
(fresh water)
static
21–23
7.4–9.4
173
24 h
LC
50
>530
LeBlanc (1980)
static
21–23
7.4–9.4
173
48 h
LC
50
410
(320–530)
7.4–8.2
44–53
48 h
LC
50
14.5
Biesinger &
Christensen (1972)
7.4–8.2
44–53
21 days
LC
50
13.5
c
(12.2–15.0)
static
11.5–14.5
7.2–7.8
235–260
24 h
EC
50
52.8
d
Khangarot & Ray
(1989)
static
11.5–14.5
7.2–7.8
235–260
48 h
EC
50
32.0
d
Crayfish (Orco-
nectes limosus)
(fresh water)
flow
15–17
7.0
96 h
LC
50
78
Boutet & Chaisemartin
(1973)
flow
15–17
7.0
30 days
LC
50
59
flow
15–17
7.0
30 days
LC
50
61
c
Crayfish (Austro-
potamobius
pallipes pallipes)
(fresh water)
flow
15–17
7.0
96 h
LC
50
46
flow
15–17
7.0
30 days
LC
50
39
flow
15–17
7
30 days
LC
50
43
c
Sheepshead
minnow (Cyprino-
don variegatus)
(marine water)
static
25–31
10–31
e
96 h
LC
50
>500
Heitmuller et al. (1981)
a
Adapted from IPCS (1990).
b
static = static conditions (water unchanged for the duration of the test); flow = intermittent flow-through conditions.
c
Test conducted with a food source.
d
EC
50
= concentration resulting in 50% immobilization.
e
Salinity (
0
/
00
).
weight was the most sensitive parameter measured and
showed a 50% reduction, relative to controls, at a barium
concentration of 41.2 mg/litre.
Barium sulfate is the principal constituent of
drilling muds used in oil drilling operations. These
muds also contain metals other than barium. No deaths
occurred in a number of unspecified marine fish,
crustaceans, and molluscs exposed to various levels (as
high as 7500 mg/kg) of drilling mud for an unspecified
period of time (Daugherty, 1951). Other studies reported
reduced populations of molluscs and/or annelids
exposed to barite in estuarine water, but it could not be
determined whether the results were due to larval
avoidance of barite or to barite toxicity (Tagatz & Tobia,
1978; Cantelmo et al., 1979).
10.2
Terrestrial environment
In general, barium has been shown to inhibit the
growth of bacteria, fungi, mosses, and algae (IPCS,
1990). Other relevant information was not identified.
11. EFFECTS EVALUATION
11.1
Evaluation of health effects
11.1.1
Hazard identification and dose–response
assessment
Barium enters the body primarily through the
inhalation and ingestion processes. The degree of
absorption of barium from the lungs and gastrointestinal
tract varies according to animal species, solubility of the
compound, and age of the animal. Studies in rats using a
soluble salt (barium chloride) have indicated that the
absorbed barium ions are distributed 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.
Barium and barium compounds
23
In humans, ingestion (accidental or intentional)
of barium compounds may cause gastroenteritis (vomit-
ing, diarrhoea, abdominal pain), hypopotassaemia,
hypertension, cardiac arrhythmias, and skeletal muscle
paralysis (IPCS, 1990; US EPA, 1990, 1998; ATSDR,
1992). The toxicity is dependent on the water solubility
of the barium compound; the lack of case reports of
systemic toxicity despite the routine oral administration
for many years of approximately 450 g barium sulfate as a
radiocontrast medium indicates that this practically
insoluble barium compound is not toxic by the oral route.
Due to its limited absorption by the dermal route,
systemic toxicity is not anticipated.
Medium- and long-term oral exposure animal
studies (McCauley et al., 1985; NTP, 1994) provide
evidence that the kidney is a sensitive target of barium
toxicity in rats and mice fed a nutritionally adequate diet.
Hypertension has been observed in studies in which rats
were fed a marginally adequate diet, particularly one with
inadequate calcium levels (Perry et al., 1983, 1985, 1989).
Although limited due to the small population size
(2000) and lack of individual measurements of exposure,
longer-term human studies (Brenniman & Levy, 1984;
Wones et al., 1990) have not found adverse effects
following oral exposure to relatively low concentrations
of barium in drinking-water.
Inhalation of barium carbonate powder was
associated with hypopotassaemic paralysis in a male
worker (Shankle & Keane, 1988).
Several case reports (Pendergrass & Greening,
1953; Seaton et al., 1986) and a cross-sectional exami-
nation of workers at a barite grinding facility reported by
Doig (1976) indicated reversible baritosis in workers
exposed to airborne barite ore or barium sulfate. Upon
exposure termination, there was an apparent decrease in
barium levels in the lung (Doig, 1976); the barium-related
lesions were also potentially reversible (ACGIH, 1992). A
NIOSH (1982) survey indicated prevalence of
hypertension in workers exposed to an unspecified
concentration of barium; these results should be
interpreted cautiously, because it is likely that the
workers were also exposed to other metals, including
lead, which has a known hypertensive effect.
Data on the toxicity of inhaled barium to animals
are limited; studies have deficiencies that preclude their
usefulness for hazard identification or dose–response
assessment.
A reproductive/developmental toxicity study did
not find any significant alterations in reproductive end-
points or in gestation length, pup survival, or occurrence
of external abnormalities in rats and mice exposed to
barium chloride in drinking-water (Dietz et al., 1992). The
low pregnancy rates in all groups, including controls,
limit the usefulness of this study.
Oral exposure studies in rats and mice (Schroeder
& Mitchener, 1975a,b; McCauley et al., 1985; NTP, 1994)
did not find significant increases in tumour incidence
following long-term exposure. The design of the
McCauley et al. (1985) and Schroeder & Mitchener
(1975a,b) studies was inadequate for carcinogenicity
evaluation. In the McCauley et al. (1985) study, small
numbers of animals of one sex were exposed to relatively
low concentrations of barium chloride for less than a
lifetime. The absence of adverse effects suggests that
the maximum tolerated dose (MTD) may not have been
achieved in this study. In the Schroeder & Mitchener
(1975a) rat study, only the incidence of total gross
tumours was reported; the lack of adverse effects
suggests that the only dose used was lower than the
MTD. The decrease in longevity in the mouse study by
Schroeder & Mitchener (1975b) suggests that the MTD
may have been achieved in this study. However, it
appears that only two types of cancer were examined
(leukaemia and lung tumours).
The design of the rat and mouse NTP (1994) oral
studies was adequate to assess carcinogenicity. These
studies used an adequate number of animals per group,
exposed animals for 2 years, tested several dosage
levels, and examined an extensive number of tissues. The
decreased survival and histological alterations in the
kidneys of the mice and the increased kidney weights in
the rats suggest that the MTD was achieved in both of
these studies. No carcinogenic effects were observed in
either species. In fact, significant negative trends in the
incidence of leukaemia, adrenal tumours, and mammary
gland tumours were observed in the rats.
Available data indicate that barium salts would not
be expected to have genotoxic potential, and the weight
of evidence from in vitro studies is negative.
Topical and ocular applications of barium nitrate
caused skin and eye irritation in rabbits. Barium
hydroxide and barium oxide irritate the eye, skin, and
respiratory tract. Physicochemical properties of barium
sulfate and the lack of reports of skin or eye irritation in
humans despite its widespread use, particularly for X-ray
purposes, suggest that barium sulfate is not irritating or
corrosive to either skin or eyes. Similarly, there is a lack
of reports of either skin or respiratory tract sensitization,
suggesting that barium sulfate is not a sensitizer.