Registration Dossier
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.
Endpoint summary
Administrative data
Key value for chemical safety assessment
Additional information
No information on genotoxic effects specific for rice husk ashes are available. Crystalline silica is the major component of toxicological concern. Therefore, data on crystalline silica is most likely to apply to rice husk ashes.
Silica (form not specified) has not tested positive in standard bacterial mutagenesis assays (IARC, 1997). By using the alkaline single cell gel/comet assay, crystalline silica (Min-U-Sil 5) induced DNA damage (i.e., DNA migration) in cultured Chinese hamster lung fibroblasts (V79 cells) and human embryonic lung fibroblasts (Hel 299 cells) at concentrations ranging from 17.2 to 103.4μg/cm² (Zhong et al., 1997). The ability of heated and flux-calcined diatomaceous earth (with a high percentage of crystalline silica) to induce dose-dependent morphological transformation of cells in vitro has been demonstrated in experiments with Syrian hamster embryo cells (Elias et al., 2006).
The ability of crystalline silica to induce micronuclei in mammalian cells in culture has also been demonstrated (Oshimura et al., 1984). However, other in vitro studies did not observe chromosomal aberration (Oshimura et al., 1984), hprt (hypoxanthine-guanine phosphoribosyl transferase) gene mutation (Driscoll et al., 1997), or aneuploid or tetraploid cells (Oshimura et al., 1984).
Min-U-Sil 5 particles were tested for their ability to induce a significant number of sister chromatid exchanges in cultures of human lymphocytes plus monocytes or of human purified lymphocytes. The results were not “clear cut” for any of the three doses tested (0.5, 5.0, and 50μg/cm²) (Pairon et al., 1990).
An in vivo treatment of rats with crystalline silica (quartz and cristobalite) induced mutation in rat alveolar epithelial cells (Driscoll et al., 1997; Johnston et al. 2000).
These and a number of other studies have been reviewed by the International Agency for Research on Cancer (IARC, 1997), the International Programme on Chemical Safety (IPCS, 2000) and the US National Institute for Occupational Safety and Health (NIOSH, 2002). In summary, results of genotoxicity studies of crystalline silica are ambiguous, and a direct genotoxic effect for quartz has neither been confirmed nor ruled out.
Short description of key information:
There are no data available on in vitro or in vivo genotoxicity of rice husk ashes. The results of genotoxicity studies of crystalline silica are not conclusive, and a direct genotoxic effect has not been confirmed or ruled out.
Endpoint Conclusion:
Justification for classification or non-classification
No conclusive data available
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