Silicate(2-), hexafluoro-, disodium, reaction products with lithium magnesium sodium silicate

Endpoint summary

Description of key information

Repeat dose studies for this substance have not been carried out on test animals for oral, dermal or inhalation routes of exposure and waivers have been justified for non-testing.
For oral exposure an estimate of the NOAEL has been made based on results from a 90 day study for Laponite type 2, a read-across material of similar structure.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

50 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Additional information

Of relevance is a 90 day study carried out in 1973 on Laponite type 2, which is a similar structure to Laponite type 1 and consequently a “read-across” material. The main difference between the two materials being that type 1 contains fluoride in the clay lattice. Fluoride is known to be orally toxic above specified levels and so some assumptions must be made. 

The 90 day chronic test was designed to evaluate the repeat dose oral toxicity of Laponite on rats over a period of 3 months. The material was dispersed in deionised water and the rats were fed by intubation. The rats were split into four groups, even numbers of male/female. Group 1 was the control group, (just water), group 2 was low dose (5mg/kg bw), group 3 was medium dose (50mg/kg bw) and group 4 was high dose (500mg/kg bw). The high dose group saw some premature deaths and these were found to be due to the fact that the Laponite forms a gel at high dose and this had accumulated in the animal’s digestive system and had not been digested. This level of dosing would not be permitted under today's controls. For surviving rats at necropsy, there were no signs of abnormalities relating to the oral dosing of the Laponite. The high dosage group resulted in half of the rats failing to survive to completion of the test but all rats in the other two groups (with the exception of 1 in the low dose group whose death was not attributed to the treatment) all survived. No systemic toxic effect as ascertained by blood analysis and histopathological examination were observed, even in the high dose rats.

If the test were to be repeated with Laponite type 1, it is known that under the low pH conditions of a rat’s stomach that the material reverts back to the individual lattice components, including fluoride as F^-.

For NaF, the LOAEL (lowest-observed-adverse-effect-level) on rats in a repeat dose 28 day study done to OECD Guideline 407 (as reported in the REACH dossier for sodium fluoride) is 10 mg/kg bw/day as NaF, which equates to 4.5 mg/kg bw/day as F. This would be the equivalent of ~50 mg/kg bw/day for Laponite type 1 if all the fluoride in the material were to be absorbed through the stomach.

Therefore an estimate can be made that the NOAEL for Laponite type 1 in the worst case scenario that all fluoride became accessible for absorption under repeat dose testing could be ~ 50 mg/kg bw/day