Abstract

Cryolite occurs in the nature as monoclinic crystals or in synthetic form as an amorphous powder. The natural form may be coloured reddish or brown or even black. Cryolite has a melting point >1 000 degrees C and its main use is in the production of aluminum where it forms the electrolytic bath. It has also found industrial use in the production of insecticides, metals and alloys, glass and enamels, welding rods, resins, explosives and fireworks, and polishes. The toxic effects of cryolite are largely due to its content of aluminum and fluoride. Thus, its toxic effects, if not known, have to be based on known adverse effects of aluminum and fluoride. Fluoride appears to be easily absorbed from the gastrointestinal tract and the lungs following exposure to cryolite. Data in the literature do indicate that aluminum can be absorbed from the lung by alveolar macrophages. However, this absorption has not been quantitated. Only small amounts of aluminum is absorbed from the gastrointestinal tract, and the absorption appear to be even less in the presence of fluorides. Neither fluorides nor aluminum seems to be absorbed through the skin in amounts that might cause adverse effects. Fluoride resulting from the absorption of cryolite is retained in bones and high concentrations have been detected in the kidney, which is the organ primarily involved in fluoride excretion. In general, high concentrations of aluminum have been detected in the skeleton and in the lungs, and prolonged exposure to aluminum may result in increased levels of aluminum in liver, kidneys, and brain tissue. It seems likely that the Al3+ from exposure to cryolite will show a similar distribution in the body as observed with other aluminum compounds. With a reported oral LD50 > 5 000 mg/kg in rats and the lowest lethal oral dose in rabbits being 9 000 mg/kg, it appears that cryolite has a low acute toxicity in experimental animals. No estimated lethal dose of cryolite in humans was located in the literature, but symptoms of acute intoxication include nausea, loss of appetite, vomiting, drowsiness, excessive salivation, pressure on the heart and chest, and obstipation have been reported. There are no data available in the literature allowing the assessment of acute toxicity of cryolite following dermal or inhalation exposure. Due to its low oral acute toxicity in rats, one might suspect cryolite also to have low acute toxicity when administered by the inhalation or dermal route. There are no relevant data either from humans or animals to assess irritating or corrosive effects of cryolite. The are limited data to assess toxic effects of cryolite when given orally over a prolonged time-period. The only study located in the literature indicates minor toxic effects when given to rats in doses of approximately 125 – 500 mg cryolite/kg/day for 4 weeks. However, repeated oral exposure to fluorides in general may cause fluorosis in rats at a dose of ~ 50 mg/kg/day. In humans, prolonged oral exposure to aluminum could lead to fibrosis, fracturing bone disease and encephalopathy (“dialysis dementia”). Aluminum has also been suggested to be involved in Alzheimer’s disease. Thus, it is possible that prolonged oral exposure to cryolite could lead to fluorosis, fibrosis, softening of bone. Neurological effects, however, are less likely to occur. The main route of exposure to cryolite is by inhalation. Several epidemiological studies describing adverse effects following inhalation to cryolite and other fluorides in humans were located in the literature. Prolonged (i.e. several years) occupational inhalation exposure to cryolite may cause skeletal fluorosis. An intake of 20 – 80 mg fluoride appears to be sufficient to cause fluorosis in humans. Impairment of lung function was not correlated with exposure to cryolite and no association was found between chronic bronchitis and exposure to cryolite dust. However, cases of cryolite-induced pneumoconiosis have been described in the literature. It has been reported that people that inhale 2.4 to 6.0 mg fluorides/m3 for many years suffer from serious bone damage. Furthermore, several studies indicate that aluminum compounds, especially stamped aluminum powder, causes lung fibrosis in exposed humans. In several of the cases, lung fibrosis was accompanied by atrophy and secondary emphysema. The relative contribution of cryolite to the observed health effects in aluminum production workers is difficult to estimate, since exposure to other fluorides occur as well. However, it appears that cryolite is one important factor and is able to cause severe damage to the human body. No data regarding repeated dermal exposure to cryolite, fluorides (except hydrofluoric acid), or aluminum compounds in humans or experimental animals were located in the literature. There are limited data either from humans or animals that indicate a carcinogenic risk from exposure to cryolite. In a Danish cohort study of male cryolite workers an increased risk of 2.37 of respiratory cancer was identified. However, the excess cancer risk identified in workers exposed to fluorides, including fluoride-spar and aluminum production workers (cryolite exposure) may be due to other factors than fluoride exposure. There are no data on genotoxic effects of cryolite in humans or in experimental systems. There are data, however, that indicate that aluminum is a DNA-protein cross-linking agent and has a clastogenic effects (e.i. causing chromosome aberrations). Clastogenic effects have also been described with fluorides, but could be due to cytotoxic effects. There are no information available on teratogenic or reproductive effects of cryolite. No data exists on the reproductive toxicity of fluorides in humans or developmental toxicity in humans or experimental animals. One study in rats, however, indicate that the testis of rats is a target for fluorides. Furthermore, there are indications that aluminum may cause delays in skeletal and neurobehavioural development in pups, whereas other studies were negative. At present it is not possible to assess teratogenic effects of cryolite. The data could indicate that cryolite has a low reproductive toxicity potential. In conclusion, it appears that the critical adverse effects of cryolite are related primarily to prolonged inhalation exposure, but similar effects may also occur following oral exposure. Such effects include skeletal fluorosis, lung fibrosis, pneumoconiosis. Neurotoxic effects related to its content of aluminum can not excluded.

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