Silicic acid, lithium magnesium sodium salt

Endpoint summary

Description of key information

Two studies carried out at different times for skin irritation on rabbits gave Primary Irritation Index scores of 0.18 and 0.5 respectively. According to the scoring system these results imply only mild irritation in rabbits and no requirement for human classification. 
Similarly two in vivo studies have been reported for eye irritation with slightly conflicting results. As a result of the conflict an in vitro test was commissioned based on the effect of the substance on a dead cow's eye. Based on the in vitro test results for the effect of this substance on bovine corneal opacity and permeability, the score result was of the same order as the -ve control used (saline solution) and thus deemed to be not irritating to eyes.  The in vivo studies showed the substance not to be an eye irritant when administered in aqueous medium but showed some moderate irritation when administered as a powder. The powder results have been discounted as detailed in the discussion.

Key value for chemical safety assessment

Skin irritation / corrosion

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Additional information

One of the in vivo tests reported for eye irritation was carried out on the test material as received i.e. as a fine crystalline powder. The powder was introduced directly into the rabbit's eye and the eyelid held shut. Irritation mainly of the conjunctivae was observed in all rabbits on the first day, which is not unsurprising since any gritty powder with a slightly alkaline pH introduced and left in the eye would produce the same effect. After wash out the irritancy reduced and returned to normal in most animals after the 2nd or 3rd day. The fact that the test material had been used as received and not dispersed in liquid medium is not typical of how this product would enter the eye in consumer product formulations and is not the way this test would be done today. So the "moderately irritating" reported result, whilst factual for the way this test was carried out, is found to be lacking in application and has been disregarded for irritancy classification. This decision has been vindicated by the BCOP in vitro test, which showed that the substance had no effect on the corneal opacity and permeablity of a dead cow's eye. By using the eye of a dead animal the effect of irritancy caused by abrasion has been removed and the test is designed to show the chemical effect of the substance on the cornea, in this case negative.

Justification for classification or non-classification

Results of in vitro and in vivo studies undertaken and evidence from human exposure to this substance both at the manufacturing site and in the consumer market indicates that this material is not an irritant to either skin nor eyes.