Synthetic amorphous magnesium silicate, with molar ratio (SiO2:MgO) range of 1.4-4

Endpoint summary

Additional information

Pharmacokinetics of silica deposition were investigated in a 13 week inhalation study in rats. Silica  could be detected in the lungs of all exposed rats at the end of the exposure period: In all males, residual amounts were still present after half a year post-exposure, while only one female rat showed silica in the lung at that time. After exposure (one week post-exposure), in 3/10 males and 5/10 females silica was found in the lymph nodes, which slowly declined during recovery. In a 90 day inhalation study the silica burden in the lungs was investigated for amorphous and crystalline forms of silica.

Amorphous silica increased quickly during the first 6.5 weeks of exposure (some 0.76 mg SiO2/lung), but only slowly after the second half of the exposure period (plateau phase, steady state at about 0.88 mg SiO₂/lung), while the level of crystalline silica increased steadily from about 0.34 mg SiO2/lung (after 6.5 weeks) and even disproportionately to approx. 0.82 mg/lung (after 13 weeks). During recovery, amorphous silica lung burden disappeared rapidly from lung tissue down to about 15% (after 12 weeks post-exposure) and to about 6 % of the final level after exposure (at 32 weeks post-exposure). On the other hand, crystalline silica persisted in the lung with no substantial decrease post-exposure.

Read-across/surrogate data

For the toxicokinetic investigations the use of data derived for silicon dioxide are justified for read-across to magnesium silicate. Justification for read-across is warranted given the similarities in toxicity profile and physico-chemical properties for silicon dioxide and magnesium silicate.