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Barium and barium compounds

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Barium and barium compounds

25

11.1.3

Sample risk characterization

There are a number of different approaches to

assessing the risks to human health posed by chemicals.

For example, barium sulfate is the most likely substance

of occupational concern and is of very low toxicity.

Since exposure estimates can vary widely, the risk

characterizations below are provided as examples for

illustrative purposes. 

11.1.3.1 Ingestion

Dog and rat pharmacokinetic studies (Taylor et al.,

1962; Cuddihy & Griffith, 1972) suggest that gastro-

intestinal absorption of barium may be higher in young

animals than in older ones. Brenniman & Levy (1984)

examined persons 18–75+ years of age living in the

community for more than 10 years. It is likely that this

study included adult residents who were exposed to

elevated barium levels as children, but it may not

account for all of the uncertainty. The barium database

consists of subchronic and chronic toxicity studies in

three species (humans, rats, and mice) and a marginally

adequate first-generation reproductive/developmental

toxicity study. The rat and mouse study (Dietz et al.,

1992) gave no indication that developmental or repro-

ductive end-points are more sensitive than other end-

points; interpretation of the study results is limited by

very low pregnancy rates in all groups, including con-

trols, and examination of a small number of develop-

mental end-points. No modifying factor is proposed for

this assessment.

The US EPA (1998) derived an RfD of 0.07 mg/kg

body weight per day for barium, based on the NOAEL of

0.21 mg/kg body weight per day for no adverse health

effects identified in the Wones et al. (1990) and

Brenniman & Levy (1984) human studies, with an

uncertainty factor of 3 to account for some database

deficiencies and potential differences between adults

and children. The primary route of exposure to barium

appears to be ingestion in drinking-water and food. A

daily intake of 0.03–0.60 mg barium/kg body weight per

day from drinking-water can be estimated using the

drinking-water concentration of 1–20 mg/litre, a reference

consumption rate of 2 litres/day, and a body weight of 70

kg. IPCS (1990) reported several published estimates of

dietary intake of barium by humans, ranging from 300 to

1770 mg barium/day, with wide variations; this is

equivalent to a range of 4–25 mg barium/kg body weight

per day, assuming a 70-kg adult body weight. Hence,

populations consuming high dietary barium levels may

have intakes approximating or exceeding the oral RfD

value of 0.07 mg/kg body weight per day and the

tolerable intake of 0.02 mg/kg body weight per day. 11.1.3.2 Occupational (barium sulfate )

Another sample risk characterization is based on

occupational exposure primarily to barium sulfate in the

United Kingdom. In general, the highest typical levels of

exposure appear to occur in offshore drilling activities.

The highest exposures for which measured data are

available apparently occur during addition of the barite

ore from the bulk hopper to the mud mixing tank. There

are no concerns for human health with typical exposures

that arise during drilling activities if the machinery is

enclosed and LEV used. However, where the machinery

is not enclosed and appropriate LEV is not available,

modelled data indicate that exposures could be much

higher, on the order of several tens of mg/m

3

 of total

inhalable dust. The consequences for human health of

long-term exposures at such high levels are not clear.

Because of the low exposures involved, there are

no concerns for human health during the processing of

barite ore where LEV is used. A similar conclusion can

be drawn regarding its use in the formulation of plastics

and coatings, although, from modelled data, exposures

could be much higher and the human health picture less

reassuring in these industries if LEV is not used. The

extremely high personal sampling values for total

inhalable dust (55 mg/m

3

 8-h TWA) measured at one

factory milling barite ore merit further consideration. At

present, workers wear powered respirators that should

substantially reduce the current level of personal

exposure to levels below those measured in the atmos-

phere. 

If occupational exposures are controlled to less

than 10 mg/m

3

 (total inhalable dust, which is primarily of

low toxicity) as an 8-h TWA, it would appear that there

are no significant risks to human health.

11.1.4

Uncertainties in the evaluation of health risk

An area of scientific uncertainty concerning the

non-cancer hazard assessment for barium is the identi-

fication of the most sensitive end-point of barium

toxicity in humans. The results of the NTP (1994)

medium-term rat study suggest that renal effects may be

a more sensitive end-point than hypertension. However,

it is not known if a similar relationship would exist

following long-term exposure or in humans. The

Brenniman & Levy (1984) human study examined the

effect of barium on blood pressure but did not inves-

tigate sensitive renal end-points (kidney disease was

assessed by a health questionnaire only). The long-term

rat study (NTP, 1994) did not measure blood pressure.

Another area of scientific uncertainty is whether any

toxicological or toxicokinetic differences exist between

children and adults. Animal data (Taylor et al., 1962;



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