Barium and barium compounds
9
during a single summer sampling event, and the authors
advise caution in extrapolating the results to terrestrial
systems in general.
There is no evidence that barium undergoes envi-
ronmental biotransformation other than as a divalent
cation (IPCS, 1990).
6. ENVIRONMENTAL LEVELS AND
HUMAN EXPOSURE
6.1
Environmental levels
The levels of barium in air are not well docu-
mented, and in some cases the results are contradictory.
Tabor & Warren (1958) detected barium concentrations
ranging from <0.005 to 1.5 mg/m
3
in the air in 18 cities
and 4 suburban areas in the USA. No distinct pattern
between ambient levels of barium in the air and the
extent of industrialization was observed. In general,
however, higher concentrations were observed in areas
where metal smelting occurred (Tabor & Warren, 1958;
Schroeder, 1970). In a more recent survey in the USA,
ambient barium concentrations ranged from 0.0015 to
0.95 mg/m
3
(US EPA, 1984). In three communities in New
York City, USA, barium was measured in dust fall and
household dust (Creason et al., 1975). With standard
methods (US EPA, 1974), the dust fall was found to
contain an average of 137 mg barium/g, while the house
dust contained 20 mg barium/g.
Barium is found in almost all surface waters that
have been examined (NAS, 1977). The concentrations are
extremely variable and depend on local geology, water
treatment, and water hardness (NAS, 1977). Barium
concentrations of 7–15 mg/litre and 6 mg/litre have been
measured in fresh water and seawater, respectively
(Schroeder et al., 1972). The mean barium content of
various US surface waters ranges from 43 to 57 mg/litre
(Durum, 1960; Kopp, 1969; Kopp & Kroner, 1970;
Schroeder, 1970; Bradford, 1971). The concentrations of
barium in sediments of the Iowa River, USA, were
measured to be 450–3000 mg/kg (Tsai et al., 1978),
suggesting that barium in the water is removed by
precipitation and silting.
Studies of drinking-water quality in cities in the
USA have revealed levels of barium ranging from trace
to 10 mg/litre (Durfor & Becker, 1964; Barnett et al., 1969;
McCabe et al., 1970; McCabe, 1974; Calabrese, 1977;
AWWA, 1985). Drinking-water levels of at least 1000 mg
barium/litre have been reported when the barium is
present mainly in the form of insoluble salts (Kojola et
al., 1978). Levels of barium in Canadian water supplies
have been reported to range from 5 to 600 mg/litre
(Subramanian & Meranger, 1984), and barium
concentrations ranging from 1 to 20 mg/litre have been
measured in municipal water in Sweden (Reeves, 1986).
The concentration of barium in seawater varies
greatly among different oceans and varies with factors
such as latitude and depth within a given ocean. Several
studies have shown that the barium content in the open
ocean increases with the depth of water (Chow & Gold-
berg, 1960; Bolter et al., 1964; Turekian, 1965; Chow &
Patterson, 1966; Anderson & Hume, 1968). A Geosecs III
study of the south-west Pacific by Bacon & Edmond
(1972) found a barium profile of 4.9 mg/litre in surface
waters to 19.5 mg/litre in deep waters. Later studies by
Chow (1976) and Chow et al. (1978) corroborated these
values. Measured barium concentrations in the north-
east Pacific ranged from 8.5 to 32 mg/litre (Wolgemuth &
Broecker, 1970). Bernat et al. (1972) found that barium
concentration profiles for the eastern Pacific Ocean and
the Mediterranean Sea ranged from 5.2 to 25.2 mg/litre
and from 10.6 to 12.7 mg/litre, respectively. Anderson &
Hume (1968) reported concentrations in the Atlantic
Ocean ranging from 0.8 to 37.0 mg/litre in the equatorial
region and from 0.04 to 22.8 mg/litre in the North
Atlantic, with mean values of 6.5 and 7.6 mg/litre,
respectively. In Atlantic Ocean waters off Bermuda,
barium concentrations of 15.9–19.1 mg/litre have been
measured (Chow & Patterson, 1966).
The background level of barium in soils is consid-
ered to range from 100 to 3000 mg/kg, with an average of
500 mg/kg (Brooks, 1978).
Various studies document concentrations of bar-
ium in Brazil nuts ranging from 1500 to 3000 mg/kg
(Robinson et al., 1950; Smith, 1971a). Barium is also
present in wheat, although most is concentrated in the
stalks and leaves rather than in the grain (Smith, 1971b).
Tomatoes and soybeans also concentrate soil barium;
the BCF ranges from 2 to 20 (Robinson et al., 1950).
Levels of barium found in other food items range from
<0.2 mg/kg in meats to 27 mg/kg in dry tea bags
(Gormican, 1970). McHargue (1913) reported that the
barium content of dry tobacco leaves was in the range of
88–293 mg/kg. Later measurements yielded 24–170 mg/
kg, with an average value of 105 mg/kg (Voss & Nicol,
1960). Most of this barium is likely to remain in the ash
during burning. The concentrations of barium in tobacco
smoke have not been reported.
Concise International Chemical Assessment Document 33
10
6.2
Human exposure
The most important route of exposure to barium
appears to be ingestion of barium through drinking-
water and food. Particles containing barium may be
inhaled into the lung, but little is known regarding the
absorption of barium by this route.
Schroeder et al. (1972) estimated that the mean
daily intake of barium is 1.24 mg in food. Hamilton &
Minski (1972) estimated the total intake of barium from
the diet to be 603 µg/day. The ICRP (1974) estimated
barium intake from dietary sources to be approximately
0.67 mg/day. WHO (1996) reported daily dietary intake of
barium for adults for the period 1970–1991 as 0.18
(minimum), 0.30 (median), and 0.72 (maximum) mg/person.
In a number of dietary studies, the average intake of
barium ranged from 0.3 to 1.77 mg/day (Tipton et al.,
1966, 1969; Gormican, 1970; ICRP, 1974). This is
equivalent to 0.004–0.025 mg barium/kg body weight per
day, assuming a 70-kg adult body weight. The barium
content in school lunches from 300 schools in 19 states
in the USA ranged from 0.09 to 0.43 mg/lunch, with a
mean of 0.17 mg/lunch (Murphy et al., 1971).
The barium content in drinking-water seems to
depend on regional geochemical conditions. In a study
of the water supplies of the 100 largest cities in the USA,
a median value of 0.43 mg/litre was reported; 94% of all
determinations were <0.100 mg/litre (Durfor & Becker,
1964). Assuming daily water consumption
of 2 litres/person, this represents an average intake of
<0.200 mg barium/day. More recent studies by Letkie-
wicz et al. (1984) indicated that approximately 214 million
people in the USA using public water supplies are
exposed to barium levels ranging from 0.001 to
0.020 mg/litre. In certain regions of the USA, however,
barium levels may reach 10 mg/litre, and the average
intake could be as high as 20 mg/day (Calabrese, 1977).
Levels of barium in municipal water in Sweden as high as
20 mg/litre have been reported (Reeves, 1986).
Due to the paucity of information on the levels of
barium in ambient air, it is difficult to estimate the intake
from this source. The levels of barium in air rarely exceed
0.05 mg/m
3
(Tabor & Warren, 1958). This value can be
used to estimate daily barium intake via the lungs.
Assuming that the average lung ventilation rates for
newborn babies, male adults undergoing light activity,
and male adults undergoing heavy activity are 0.5, 20,
and 43 litres/min, respectively (ICRP, 1974; IPCS, 1994),
the intake via inhalation would range from 0.04 to 3.1
mg/day. Other age groups and females are included in
this range. Earlier, the ICRP (1974) reported that intake of
barium through inhalation ranges from 0.09 to 26 mg/day.
Using 0.95 mg/m
3
(the upper-end estimate of ambient
barium
concentrations from US EPA, 1984) and the
ventilation rates of ICRP (1974) for babies and adult
males, a range of intakes via inhalation of 0.68–59
mg/day can be estimated.
The ICRP (1974) reported the total dietary intake of
barium to be 0.75 mg/day, including both food and
fluids. Schroeder et al. (1972) estimated a total of
1.33 mg/day, including food, water, and air (0.001 mg)
intake.
Available data from industry in the United King-
dom indicate that airborne exposure to barium sulfate
can range from 3.5 to 9.1 mg/m
3
(8-h time-weighted
average [TWA], total inhalable dust) during the manual
addition of barite to mixing hoppers in the oil drilling
industry, with short-term (10-min TWA, total inhalable
dust) exposures as high as 34.1 mg/m
3
. During the
processing of barite ore, in
industries that typically use
enclosed processes and local exhaust ventilation (LEV),
exposures usually ranged between 1.3 and 3.7 mg/m
3
(total inhalable dust), with highest values in one factory
reaching 55.4 mg/m
3
. Exposure levels in the formulation
of plastics and coatings, where the process is usually
enclosed and LEV is used, are in the region of 1–
3.5 mg/m
3
(Ball et al., 1997).
The wiring used in some speciality arc welding
processes has been shown to contain 20–40% soluble
barium compounds, and fumes produced during these
processes contain 25% barium (Dare et al., 1984).
Welders using such wire are exposed to estimated air-
borne concentrations of 2.2–6.2 mg soluble barium/m
3
(NIOSH, 1978).
Personal air sampling in the vicinity of oven-
charger and batch-mixer workers in art glass manufac-
turing plants revealed median ambient air concentrations
of 0.041 and 0.0365 mg barium/m
3
, respectively (Apostoli
et al., 1998). Mean concentrations of barium measured by
personal sampling methods in various locations within
ceramic factories in Spain ranged from 0.0012 to 0.0758
mg/m
3
(Roig-Navarro et al., 1997).
Data from industry in the United Kingdom and
predictions made using the Estimation and Assessment
of Substance Exposure (EASE)
1
model suggest that
1
EASE is a general-purpose predictive model for
workplace exposure assessments. It is an electronic,
knowledge-based, expert system that is used where
measured exposure data are limited or not available. The
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