|Monthly Tech-Tip |
The main water soluble salts are: the acetate, chloride, hydroxide, oxide, nitrate.
The main insoluble salts are : the arsenate, carbonate, chromate, fluoride, oxalate, sulphate.
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 also source barium and the daily human intake has been estimated to be in the order of 1 mg.
The pulmonary route of entry is the most significant in the industrial setting (see exposure limit recommendations).
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 the 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).
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 (one the most toxic of soluble barium salts).
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.
In the case of barium carbonate, the Lethal Dose Fifty (LD50) is :
This 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.
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
At the beginning, there are digestive disorders :
Initially there is intense asthenia, sometimes accompanied by:
Later there is :
Cardiac symptoms and clinical signs dominate the prognosis :
Renal complications were reported in an exceptional cases:
Death occurs by respiratory failure or ventricular fibrillation.
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.
Barium chromate(VI) is the only compound recognized as carcinogenic in man.
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.
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.
In rats and mice receiving up to 4000 ppm barium chloride dihydrate in the drinking water, reproductive indices were unaffected.
The TLV-TWA (ACGIH) for soluble barium salts is 0.5 mg/m3. The TLV for barium sulphate dust (insoluble) is 10 mg/m3.
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.
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.
By Edouard Bastarache
Article by Edouard Bastarache
Edouard Bastarache is a well known doctor that has written many articles on the subject of toxicity of ceramic materials and books on technical aspects of ceramics. He writes in both English and French.
A pure source of BaO for ceramic glazes. This is 77% BaO and has an LOI of 23% (lost at CO2 on firing).
The Use of Barium in Clay Bodies
Considerations regarding the use of barium carbonate in pottery and structural clay bodies for precipitation of soluble salts.