Registration Dossier
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EC number: 275-735-5 | CAS number: 71630-92-7 Substance obtained by burning the husk removed from the rice paddy. Contains silica as well as the elements aluminum, calcium, carbon, chromium, copper, indium, iron, lead, magnesium, manganese, molybdenum, phosphorus, silver, sodium, tin, and zinc.
Specific investigations: other studies
Administrative data
Link to relevant study record(s)
Description of key information
Rice husk ashes induce haemolysis in rat erythrocytes. This effect is enhanced by previous heat treatment of the rice husk ashes, through which the amount of cristobalite and tridymite is increased.
Additional information
A haemolytic toxicity test in rat erythrocytes and a cytotoxicity test in alveolar macrophages guinea pigs were performed with untreated rice husk dust, 350°C-carbonized rice husk, 650 °C-, 850 °C-, 1100 °C, 1300 °C incinerated rice husk and quartz, respectively. In the haemolytic toxicity test, the percentage haemolysis relative to a negative (saline) and a positive (saponine) control as well as the haemolytic index (% haemolysis of rice husk sample/% haemolysis of quartz sample) were determined after 1 h incubation. Additionally, chemical analysis of the rice husk ashes in the 1100°C group and the amount of free silica as well as the different silica polymorphs were determined. Percentage haemolysis induced by rice husk dust continuously increased with the treatment temperature from 13.9% (untreated) to 86.3% (1300 °C group). Quartz-induced haemolysis was 93.9% and the haemolytic index increased accordingly from 0.15 (untreated) to 0.92 (1300 °C). Rice husk ashes generated at 1100 °C consisted of 92.1% silicon dioxide. The free silica content as well as the relative amount of cristobalite and tridymite increased with the temperature at which the ashes had been treated (Liu et al. 1996).
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