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A reliable 90 day oral toxicity study is available (Wolfe 1992,). In this study rats were dosed with flux calcined diatomaceous earth at 1% (average of 698.3 mg/kg/day) and 5% (average of 3737.9 mg/kg/day).There were no treatment related effects in urine silica content. In a supporting 90 day oral study (Bertke 1963) silica analysis was performed on the liver, kidneys and spleen of rats fed diatomaceous earth at 5%. There was no significant increase in the percentage of residual silica in liver, kidneys and spleens of the test animals compared to control animals which received none of the test material. This data indicates that there is no accumulation of silica in body tissues.

 

The following conclusion is taken from the UNEP (2004) report for synthetic and amorphous silicas regarding absorption, disposition and elimination:

Analytical data on the kinetics of silica deposition in the lung of experimental animals during and after prolonged exposure to silica are largely consistent. The initial uptake phase is characterized by relatively high deposition followed by a phase of low increase. Synthetic amorphous silicas are rapidly eliminated from the lung tissue, whereas crystalline silica exhibits a marked tendency to accumulate. No disproportionate deposition of synthetic amorphous silica occurs in the lymph nodes.

 

After oral ingestion, there is no accumulation of synthetic amorphous silica in body tissues. Upon cessation of exposure rapid elimination occurs. Intestinal resorption appears to be insignificant in animals and humans the human test, the small apparent increases in the urine output of human volunteers were remarkably low as compared with the high dose of 2500 mg SiO2 applied subcutaneously are subjected to rapid dissolution and removal.

 

References:

UNEP (2004) Synthetic amorphous silica and silicates - SIDS Initial Assessment Report for SIAM 19.