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Description of key information

There is no requirement to generate experimental toxicokinetic data under REACH. No toxicokinetic data are identified; however a theoretical assessment of the toxicokinetic properties of the substance is made, based on existing toxicity data, and taking into account the physico-chemical properties of the substance.

Key value for chemical safety assessment

Absorption rate - oral (%):
5
Absorption rate - dermal (%):
5
Absorption rate - inhalation (%):
100

Additional information

The following information is taken into account for any hazard / risk assessment:

 

General Notes

Micromica is a synthetic mica, a silicate mineral. Compositional analysis shows that Micromica is predominantly silicon dioxide (SiO2) and magnesium oxide (MgO), with smaller proportions of potassium oxide (K2O) and fluoride (F).

 

Oral Absorption

Under standard conditions, Micromica is a white crystalline powder, essentially insoluble in water. On this basis, it would be expected that Micromica would be poorly absorbed after oral administration. This prediction is supported by acute oral toxicity data on micromica, which reported an oral LD50 >5000 mg/kg bw, and on synthetic mica, in which “no adverse clinical signs or physical findings” were reported, with a reported oral LD50 >9000 mg/kg bw. Repeated-dose oral toxicity studies on the chemically and structurally similar material (synthetic mica) also found a lack of effects, even at doses as high as 5000 mg/kg bw/day (for 90 days), indicating a lack of absorption. A health-precautionary value of 5% has been taken forward for chemical safety assessment.

 

Dermal Absorption

Considering the structure, composition and very low aqueous solubility, dermal absorption is not expected. No systemic toxicity data using dermal administration are available, but there is no indication from local irritation studies that Micromica can penetrate the skin. A health-precautionary value of 5% has been taken forward for chemical safety assessment.

Inhalation Absorption

The mean particle size (D50) of Micromica is 8.376 μm, with a D10 of 3.65 μm and a D90 of 16.49 μm. Particle sizes below 10 μm are generally considered inhalable (i.e. able to reach the thoracic and alveolar regions of the lungs), and thus have the potential to cause adverse health effects after inhalation exposure. An acute inhalation toxicity study on a related substance did not find any effects even at the limit concentration (LC50 > 5.1 mg/L), indicating that even if Micromica were to reach the thoracic and alveolar regions of the lungs, it would not be absorbed. Nevertheless, a highly health-precautionary value of 100% has been taken forward for chemical safety assessment.

 

Distribution, Metabolism and Excretion

As it is essentially insoluble, if a small portion of Micromica was systemically absorbed, it would not be expected to be widely distributed to the tissues. As a crystalline, inorganic material, normal enzymatic metabolism would not be expected to effect any biotransformation on Micromica. The most likely outcome is excretion through the bile and faeces, with the substance essentially unchanged.