The main water soluble salts are : the
acetate, chloride, hydroxide, oxide, nitrate.
The main insoluble salts are : the
arsenate, carbonate, chromate, fluoride, oxalate, sulphate.
Uses :
-Rodenticide, insecticide,
fungicide
-Manufacture of glass
-Manufacture of ceramics
-Vulcanization of synthetic
rubber
-Production of pigments
-Manufacture of electronic
components
-Manufacture of detergents for
lubricating oils
-Purification of industrial
waters
-Industry of painting
-Industry of paper
-In pottery
-Coating of welding electrodes
-Surface treatment in the metallurgical
industry
-Barium sulphide is used in the
production of certain types of fluorescent tubes
-Barium sulphate is used in medical
radiology and in the manufacture of white pigments (litophone)
-Etc.
Exposure
:
1-Environmental :
Barium naturally occurs at low
concentrations in ambient air, usually < 0.05 µg/m3, but
is found at relatively high concentrations in soils , nearly 500
mg/kg. In fresh surface water, concentrations may vary from < 5
to 15,000 µg/L. and it contributes to water hardness.
Foodstuffs provide also barium and the daily human intake has been
estimated to be in the order of 1 mg.
2-Industrial :
The pulmonary route of entry is the most
significant in the industrial setting (see exposure limit
recommendations).
Routes of entry
:
Soluble barium salts are well absorbed
by pulmonary and oral routes of entry.
Insoluble salts inhaled and deposited
are eliminated only slowly and can accumulate in the lungs as a
result of long-term exposure. Barium compounds are not reputed to
penetrate by skin unless the cutaneous barrier is broken as in
chemical burns; a case has been described in the relevant medical
literature which had been caused by barium chloride in fusion.
Toxicity
:
1 - Solubility :
The toxicity of barium salts is related
largely to their solubility, which conditions their digestive
absorption and bioavailability. Water and acid soluble salts are
very toxic when ingested.
The carbonate BaCO3 is insoluble in
water at neutral pH, it becomes soluble in acid environments,
which is not without consequence in vivo because of the gastric
pH. There would be under this condition, production of barium
chloride BaCl2 from the solubilized carbonate; barium chloride is
one the most toxic of soluble barium salts.
2 - Metabolism :
The biological half-life of barium
varies between 2 and 20 hours. Absorbed barium is mainly deposited
in bones, which accounts for 93% of the body burden in man. It is
mainly excreted in feces and a small part (1 to 10%) in urine.
3 - Exprimental toxicity :
In the case of barium carbonate, the
Lethal Dose Fifty (LD50) is :
-mouse (ingestion): 200 mg/kg,
-rat (ingestion): 418 mg/kg,
which makes it a very toxic chemical by
ingestion.
Barium stimulates the striated and
cardiac muscles. This hyperstimulation causes arrhythmias,
myoclonus, digestive disorders and arterial hypertension by direct
effect on the smooth muscles of the arterial wall independently of
the renin-angiotensin system and catecolamines.
4 - Acute intoxication by ingestion
:
The lethal dose in man varies, according
to barium compounds involved, between 1 and 15 g. by ingestion.
Acute intoxications are rare and generally due to suicidal
attempts with the chloride or the carbonate.
Some cases of collective food
intoxications were reported, related to food contamination, and to
confusion between carbonate and barium sulphate at the time of
radiological examinations. Barium carbonate having been
substituted accidentally for potato flour during the preparation
of sausages, 144 people were poisoned in Israel in 1963. Two
patients died.
A - Clinical findings :
At the beginning, there are digestive
disorders :
-diarrhoea, sometimes
hemorrhagic,
-severe abdominal pain,
-nausea and vomiting.
Initially there is intense asthenia,
sometimes accompanied by :
-muscle cramps,
-myoclonus,
-muscular contractures.
Later there is :
-gradually increasing flaccid paralysis
involving the 4 limbs, the diaphragm, and the pharyngolaryngeal
junction, which often requires to resort to artificial
ventilation.
-the clinical picture may mimick a
rapidly evolving Guillain-Barré's syndrome
-respiratory disorders and
rhabdomyolysis were reported.
Cardiac symptoms and clinical signs
dominate the prognosis :
-Initially there can be arterial
hypertension sometimes followed by hypotension due to digestive
liquid losses (diarrhoea, vomiting).
-Disorders of excitability and
conduction,
-Ventricular tachycardia,
-Torsades de pointes (" twisting of the
points ") leading sometimes to an unexpected ventricular
fibrillation responsible for the fatal types of the
intoxication.
Renal complications were reported in an
exceptional manner :
-Acute kidney failure with preserved
diuresis,
-Opacification of kidneys due to barium
precipitation.
Death occurs by respiratory failure or
ventricular fibrillation.
B - Laboratory findings :
- Biological examinations highlight
disorders related to water loss caused by diarrhoea.
- Hypokaliemia (low levels of blood
potassium) sometimes very significant with acidosis, is
characteristic of the intoxication. However, initially it can be
masked by respiratory acidosis.
-When the blood concentration of barium
was measured in the course of acute intoxications, values greater
than 100 µg/L were observed. However, blood concentrations
fall quickly during the first 48 hours to become again lower than
10µg/L.
- As renal clearance of barium is rapid,
the duration of the intoxication lasts 2 to 4 days.
C - Treatment :
It comprises usual symptomatic measures
:
-Gastric lavage, rehydration and
correction of hydroelectrolytic imbalance.
-Oral magnesium sulphate (Epsom salt) or
sodium sulphate makes it possible to precipitate soluble barium
salts present in the digestive tract as barium sulphate
(insoluble).
Perfusion of the same salts by
intravenous route could cause renal complications, by intratubular
precipitation of barium.
-Perfusion of important amounts of
potassium is often necessary to correct hypokaliemia mainly due to
disorders of potassium membrane transfer, which are corrected only
by the elimination of circulating barium.
- Treatment of cardiac disorders is
symptomatic.
5 - Pulmonary effects :
Handling of pulverulent barium sulphate
was accompanied, at the time of already old observations, by
benign pneumonias generally resulting in pulmonary radiological
images consisting of nodules disseminated in both lung fields
without clinical symptoms, nor anomalies of respiratory functional
tests, it is barytosis.
It also occurs during significant
exposures to lithophone and barium oxide.
On the other hand, serious fibrosis was
reported among workers of barium mines because of the presence of
crystaline silica in the ore.
Aqueous solutions of barium hydroxide
and oxide are strongly alkaline and can cause significant ocular
burns and skin irritation. The carbonate and the sulphate of
barium are irritating to the mucous membranes of the upper
airways, the carbonate can also be irritating to the skin and the
eyes.
6 - Local effects :
Aqueous solutions of barium hydroxide
and oxide are strongly alkaline and can cause significant ocular
burns and skin irritation. The carbonate and the sulphate of
barium are irritating to the mucous membranes of the upper
airways, the carbonate can also be irritating to the skin and the
eyes.
Carcinogenesis
:
Barium chromate(VI) is the only compound
recognized as carcinogenic in man.
Mutagenesis
:
Barium chloride dihydrate was not
mutagenic in Salmonella typhimurium, nor did it induce sister
chromatid exchanges or chromosomal aberrations in cultured Chinese
hamster ovary cells.
Developmental effects
:
In a mating trial, no adverse anatomical
effects were observed in the offspring of rats or mice receiving
up to 4000 ppm barium chloride dihydrate in the drinking water,
although rat pup weight was reduced.
Reproduction
:
In rats and mice receiving up to 4000
ppm barium chloride dihydrate in the drinking water, reproductive
indices were unaffected.
Exposure limit
recommendations :
The TLV-TWA (ACGIH) for soluble barium
salts is 0.5 mg/m3. The TLV for barium sulphate dust (insoluble)
is 10 mg/m3.
Prevention
:
Good housekeeping of your studio is
important as for any other chemical.
Avoidance of processes generating
unnecessary dust is also important.
Depending on the severity of exposure,
local ventilation should be used and the aspired air should be
vented outside to avoid producing dust from work tables and the
floor.
Very effective filter masks should be
worn if the severity of exposure justifies it during preparation
of glazes and clays.
It should be forbidden to drink, eat or
smoke in the workshop.
Especially, one should not confuse
barium carbonate with table sugar when preparing coffee.
Medical surveillance
:
An electrocardiogram is recommended as
part of the periodical examination of workers exposed to soluble
salts. Periodical urinary and blood mesurements could also be
carried out; in subjects not professionally exposed blood
concentrations are lower than 10 µg/L, and lower than
20µg/L in the urine.